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Extreme floods in the Pacific coastal region Melone, Anthony Michael 1986

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EXTREME FLOODS IN THE P A C I F I C COASTAL REGION  by ANTHONY MICHAEL MELONE A T H E S I S SUBMITTED I N P A R T I A L FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in THE FACULTY OF GRADUATE STUDIES Department of C i v i l  We a c c e p t  this  Engineering  t h e s i s as  to the r e q u i r e d  standard  THE UNIVERSITY OF B R I T I S H August ©  conforming  COLUMBIA  1986  A n t h o n y M i c h a e l M e l o n e , 1986  In  presenting  this  requirements  f o r an  British  Columbia,  freely  available  that  permission  scholarly  advanced  I agree for  purposes or  understood  that gain  in  by  degree the  reference  may his  copying  shall  partial  that  for extensive  Department  financial  thesis  not  be or  of  Civil  Date:  August  1986  Library and  study.  I  this  granted  by  the  her  be  allowed  Columbia  of  further  Head  of It  thesis my  of i t  agree  thesis  this  without  the  make  representatives.  or p u b l i c a t i o n  of  University  shall  of  Engineering  The U n i v e r s i t y o f B r i t i s h 2075 W e s b r o o k Place Vancouver, Canada V6T 1W5  the The  copying-  permission.  Department  at  fulfilment  for my is for  written  - i i -  ABSTRACT  The  research  extreme  hydrograph  A multi-disciplinary  components  coastal to  a  region;  hydrograph  extreme  Based  include  was  for estimation  an  assessment  of f l o o d  of r e g i o n a l  rainfall  model;  examination  of  examination  of h i s t o r i c a l  i s shown t h a t a  floods  of  atmospheric flood  the  region  with s i m i l a r  i n the c o a s t a l r e g i o n  encompassing  characteristics role  of  a  analysis  flood  f o r input  snowpack  during  model.  the area bounded by the c r e s t s  hydrologic  coastal  hydrologic modelling.  processes which  d a t a , and  of  p r o d u c i n g mechanisms i n the  analysis  assessment  undertaken  snow h y d r o l o g y and  events; and a p p l i c a t i o n of a hydrograph  on  forms  procedures  investigation  areas of hydrometeorology,  Study  it  developed  rain-on-snow f l o o d s on ungauged watersheds i n the P a c i f i c  region. the  program  of  affect flood  climate,  frequency,  of the c o a s t a l  mountains  characteristics.  are r a i n f a l l - i n d u c e d ,  either  Extreme  as r u n o f f  from  r a i n f a l l - o n l y or as a combination of r a i n and snowmelt.  Recorded  storm r a i n f a l l  regional though  characteristics  the magnitude  intensity  of  data a v a i l a b l e  fall  intensities  part  of  this  duration  i n the  data,  and  could  be  rainfall from  occurring  varies  Atmospheric  within  coastal  single  this  range  to the 24-hour region  examined  identified  s t u d y were a n a l y z e d .  intensities  range  along the c o a s t was  between  be c o n s i d e r e d as i n p u t r a i n f a l l  on  available  stations.  Environment storms  Results rainfall  f o r both m u l t i  set l i m i t s  from  to determine  data  Multi-storm  Service  and  ratios  of  are i n a r e l a t i v e l y  the h o u r l y  even  rain-  t h a t were i d e n t i f i e d  show t h a t  and  whether  single  storm  intensities  data to a hydrograph  model.  as  shorter narrow  intenstity  that  need  to  - i i i -  With regard  to b a s i n  response to extreme rain-on-snow, a v a i l a b l e  litera-  t u r e suggests t h a t f o r a r i p e snowpack, development of an i n t e r n a l age  network  liquid are  within  water.  the  snowpack  Consequences  i s the  of t h i s  dominant  conclusion  t h a t a watershed undergoes a t r a n s i t i o n  terrain-controlled approach  water  conditions  movement  which  would  and  mechanism f o r  on hydrograph procedures  from s n o w - c o n t r o l l e d  basin  occur  routing  on  drain-  storage  the  same  to more  characteristics basin  without  a  snowcover.  Lag  and  route  hydrograph techniques  t h i s method can be a p p l i e d of the the  two  rain-on-snow  floods  be  and o v e r l a n d  flow considerations;  to  groundwater.  which  of snowmelt  for estimating for  extreme  region.  estimate  travel  s i m u l a t e s b a s i n response; 3) and 4)  and r a i n f a l l ;  combination of r e s u l t s  coastal  procedure can  from c h a n n e l i z e d  the sum  analysis  this 1)  as  dology  suggest  from  each  input r a i n f a l l rain-on-snow  whether  R e s u l t s from a n a l y s i s  i s adopted:  storage c o e f f i c i e n t  The  to rain-on-snow f l o o d s .  to assess  methodology  following basin  were i n v e s t i g a t e d  consider  applied time 2)  when  through select a  take water  inputs  there are no  losses  study component p r o v i d e s  a metho-  data and f o r u n d e r t a k i n g hydrograph floods  in  the  mountainous  Pacific  - iv-  TABLE OF CONTENTS  PAGE ABSTRACT  i i  LIST OF TABLES  v i i  LIST OF FIGURES  X  ACKNOWLEDGEMENTS  xiv  1.  INTRODUCTION  2.  FLOOD CHARACTERISTICS IN THE COASTAL REGION  13  2.1 CLIMATE  13  2.2 HISTORICAL STREAMFLOW RECORDS  21  2.3 CASE STUDIES  32  2.4 SUMMARY  43  3.  1  CHARACTERISTICS OF STORM RAINFALL IN THE COASTAL REGION  ... 45  3.1 INTRODUCTION  45  3.2 OVERVIEW  47  OF PRECIPITATION SYSTEMS  3.3 SOURCE OF B.C. RAINFALL INTENSITY DATA  51  3.4 INTENSITY-DURATION-FREQUENCY CURVES  56  3.4.1 3.4.2  Development and Use of IDF Curves Depth-Duration R e l a t i o n s h i p s  56 60  3.4.2.1  A n a l y s i s of B.C. Data  60  3.4.2.2  Formulas f o r B.C. Data  64  3.4.3  Depth-Frequency R e l a t i o n s h i p s  73 73 76  3.4.4  3.4.3.1 A n a l y s i s of B.C. Data 3.4.3.2 Formulas f o r B.C. Data Comparison With Other P a c i f i c Northwest Data  78  3.5 TIME DISTRIBUTION OF SINGLE STORM RAINFALL 3.5.1 3.5.2  A n a l y s i s o f B.C. Data Comparison With Other Northwest Data  82 Pacific  3.6 ELEVATION EFFECTS ON STORM RAINFALL 3.6.1 3.6.2 3.6.3 3.7 SUMMARY  82  Background A n a l y s i s of S e l e c t e d Storm Data R e l a t i o n s h i p to Annual P r e c i p i t a t i o n  93 97 97 100 109 115  - V -  TABLE OF CONTENTS (continued)  PAGE 4.  5.  PHYSICAL ASPECTS OF WATER FLOW THROUGH SNOW  118  4.1  INTRODUCTION  118  4.2  FLOW PATHS AND SNOW METAMORPHISM  120  4.3  WATER INPUTS DURING RAIN-ON-SNOW  126  4.4  SUMMARY  131  DEVELOPMENT OF RAIN-ON-SNOW HYDROGRAPH MODEL  133  5.1  PERSPECTIVE ON HYDROLOGIC MODELS  133  5.2  CONTINUOUS FLOW VS EVENT MODELS  138  5.3  SELECTION OF MODELLING PROCEDURE  140  5.4  SOURCES OF RAIN-ON-SNOW DATA  144  5.5  APPROACH TO MODEL DEVELOPMENT  148  5.6  LAG AND ROUTE HYDROLOGIC MODEL  150  5.6.1 5.6.2  Procedures f o r Computation T r a v e l Time  150 152  5.6.3  Storage C o e f f i c i e n t  160  5.7  ANALYSIS OF FLOOD HYDROGRAPHS ON MANN CREEK  165  5.7.1 5.7.2  165  Basin Location R a i n f a l l Flood of October to November 2, 1950 5.7.2.1 5.7.2.2 5.7.2.3  28, 1950  H y d r o m e t e o r o l o g i c a l Data T r a v e l Time and Storage C o e f f i c i e n t A p p l i c a t i o n of Lag and Route Hydrograph Model  165 165 168 172  - vi -  TABLE OF CONTENTS (continued)  PAGE 5.7.3  Rain-On-Snow F l o o d of February 1951 5.7.3.1 5.7.3.2 5.7.3.3  3-8, 175  H y d r o m e t e o r o l o g i c a l Data T r a v e l Time and Storage Coefficient A p p l i c a t i o n of Lag and Route Hydrograph Model  175 179 181  5.8 ANALYSIS OF FLOOD HYDROGRAPH ON LOOKOUT CREEK 5.8.1 5.8.2  184  Basin Location Rain-On-Snow F l o o d of December 21-24, 1964  184  5.8.2.1 5.8.2.2  184  5.8.2.3  184  H y d r o m e t e o r o l o g i c a l Data T r a v e l Time and Storage Coefficient A p p l i c a t i o n of Lag and Route Hydrograph Model  191 194  5.9 DISCUSSION OF RESULTS  201  REFERENCES APPENDIX APPENDIX  208 I II  APPENDIX I I I APPENDIX  IV  MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA AND SOUTHEAST ALASKA .  217  DEPTH-DURATION—FREQUENCY DATA FOR THE. BRITISH COLUMBIA COASTAL REGION  ...  224  MAXIMUM 24-HOUR RAINFALL ON RECORD AT BRITISH COLUMBIA COASTAL STATIONS ..  283  WATER PERCOLATION THROUGH SNOW  341  - vii  -  LIST OF TABLES PAGE TABLE 2.1 TABLE 2.2 TABLE 2.3 TABLE 2.4 TABLE 2.5 TABLE 3.1  MEAN MONTHLY PRECIPITATION FOR REPRESENTATIVE COASTAL STATIONS  16  MONTHLY DISTRIBUTION OF MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA  26  MONTHLY DISTRIBUTION OF MAXIMUM FLOODS ON RECORD IN SOUTHEAST ALASKA  27  SUMMARY OF FLOOD REGIMES AT COASTAL BRITISH COLUMBIA STATIONS  28  MONTHLY ADJUSTMENT FACTORS FOR PROBABLE MAXIMUM PRECIPITATION  39  COASTAL B.C. STATIONS WITH RAINFALL INTENSITY DATA  52  TABLE 3.2  DENSITY OF RAIN GAUGE NETWORKS  54  TABLE 3.3  DEPTH-DURATION DATA FOR PITT POLDER  61  TABLE 3.4  DEPTH-DURATION RATIOS FOR IDF CURVES  62  TABLE 3.5  COMPARISON OF DEPTH-DURATION RATIOS  64  TABLE 3.6  FORMULAS RELATING RAINFALL DEPTH TO DURATION ....  65  TABLE 3.7  DEPTH-DURATION FORMULAS FOR COASTAL B.C  68  TABLE 3.8  COMPARISON OF RAINFALL DEPTH RATIOS  72  TABLE 3.9  DEPTH-FREQUENCY DATA FOR PITT POLDER  74  TABLE 3.10  DEPTH-FREQUENCY RATIOS FOR IDF CURVES  75  TABLE 3.11  DEPTH-DURATION RATIOS IN THE PACIFIC NORTHWEST ..  79  TABLE 3.12  DEPTH-FREQUENCY RATIOS IN THE PACIFIC NORTHWEST  80  TIME OF OCCURRENCE OF MAXIMUM HOURLY INTENSITIES  91  TABLE 3.13  - viii  -  LIST OF TABLES (continued)  PAGE TABLE 3.14  TABLE 3.15  SINGLE STORM PRECIPITATION DATA IN THE PACIFIC NORTHWEST  94  STORM DATA NEAR MOUNT SEYMOUR (FITZHARRIS, 1975)  105  RELATIONSHIP BETWEEN 24-HOUR AND ANNUAL PRECIPITATION  113  DISTRIBUTION OF SHORT AND LONG DURATION PRECIPITATION  114  TABLE 4.1  HOURLY RAINFALL INTENSITIES  126  TABLE 4.2  REPRESENTATIVE SNOWMELT RATES  129  TABLE 4.3  REPRESENTATIVE  130  TABLE 5.1  SOURCES OF RAIN-ON-SNOW FLOOD DATA  TABLE 5.2  STORAGE COEFFICIENTS FOR RAIN-ON-SNOW EVENTS  TABLE 5.3  MANN CREEK RAINFALL DATA: OCTOBER 28 NOVEMBER 2, 1950  167  TABLE 5.4  MANN CREEK CLIMATOLOGICAL  175  TABLE 5.5  MANN CREEK RAINFALL DATA: FEBRUARY 3-8, 1951  TABLE 5.6  MANN CREEK AIR TEMPERATURE DATA:  TABLE 3.16  TABLE 3.17  RAINFALL AND  SNOWMELT INPUTS  146 ....  STATIONS ....  163  176  FEBRUARY 3-8, 1951  176  TABLE 5.7  MANN CREEK SNOWCOURSE DATA: FEBRUARY, 1951  177  TABLE 5.8  SNOWMELT AND RAINFALL ESTIMATES  177  TABLE 5.9  RAINFALL AT MCKENZIE BRIDGE:  TABLE 5.10 TABLE 5.11  DECEMBER 21-24, 1964  186  RAINFALL NEAR LOOKOUT CREEK BASIN AIR TEMPERATURE (°C) NEAR LOOKOUT CREEK BASIN ...  187 189  - ix -  LIST OF TABLES (continued)  PAGE TABLE 5.12  SNOWMELT ESTIMATED FOR LOOKOUT CREEK  190  TABLE 5.13  SNOW DEPTHS IN CASCADE RANGE: DECEMBER 1964  190  TABLE 5.14  SNOW DEPTHS AT SANTIAM PASS ( E l e v . 1448 m)  199  - X  -  LIST OF FIGURES F i g u r e 2.1  Physiographic  F i g u r e 2.2  Mean Monthly Temperatures  F i g u r e 2.3  Mean Monthly Sea L e v e l P r e s s u r e December, A f t e r Thomas (1977)  (kPa) f o r  Mean Monthly Sea L e v e l Pressure  (kPa) f o r  F i g u r e 2.4  Regions of B r i t i s h Columbia  14  for Coastal Stations  ..  17  19  J u l y , A f t e r Thomas (1977)  20  F i g u r e 2.5  Maximum Floods  24  F i g u r e 2.6  Flood Frequency Curves f o r Cheakamus R i v e r Near Mons (1924-47)  29  R a t i o s of Maximum Instantaneous t o Maximum D a i l y Floods  31  F i g u r e 2.7  F i g u r e 2.8  F i g u r e 2.9  F i g u r e 2.10  F i g u r e 2.11  On Record  P r e c i p i t a t i o n at Terrace Nov. 1 , 1975  A i r p o r t f o r O c t . 31  Intensity-Duration-Frequency Terrace A i r p o r t P r e c i p i t a t i o n i n Vancouver December 25, 1972  33  Curves f o r 34 Area on 36  I n t e n s i t y - D u r a t i o n - F r e q u e n c y Curves f o r Vancouver I n t e r n a t i o n a l A i r p o r t  37  F i g u r e 2.12  Rain-On-Snow Flood Hydrographs  42  F i g u r e 3.1  Twenty-Four Columbia  Hour P r e c i p i t a t i o n i n B r i t i s h  ( A f t e r Hogg and C a r r , 1985) Stations  46  F i g u r e 3.2  Lengths of Record a t C o a s t a l B.C.  F i g u r e 3.3  IDF Curves f o r Vancouver K i t s i l a n o  57  F i g u r e 3.4  Depth-Duration R a t i o s  62  F i g u r e 3.5  Depth-Frequency R a t i o s  f o r IDF Curves f o r IDF Curves  55  75  - xi-  LIST OF FIGURES (continued)  PAGE F i g u r e 3.6  Maximum 24-Hour R a i n f a l l on Record  F i g u r e 3.7  Time D i s t r i b u t i o n (after  of 12-Hour R a i n f a l l  Hogg, 1980)  87  F i g u r e 3.8  Depth-Duration R a t i o s  F i g u r e 3.9  Monthly D i s t r i b u t i o n o f Maximum R a i n f a l l s on Record S o i l C o n s e r v a t i o n S e r v i c e Type 1A Storm Distribution  F i g u r e 3.10  F i g u r e 3.11  Annual P r e c i p i t a t i o n  f o r 24-Hour R a i n f a l l  Station Locations  F i g u r e 3.13 F i g u r e 3.14  F i g u r e 3.17  F i g u r e 4.1  90 96  99  F i g u r e 3.12  F i g u r e 3.16  88  i n the North Cascade  Mountains  F i g u r e 3.15  84  i n North Vancouver  103  Transect  A: E l e v a t i o n vs 24-Hour P r e c i p i t a t i o n  104  Transect December Transect December  B: R a i n f a l l D i s t r i b u t i o n f o r 6-7, 1970 B: R a i n f a l l D i s t r i b u t i o n f o r 9-11 , 1970  106 107  T r a n s e c t B: R a i n f a l l D i s t r i b u t i o n f o r February 13-15, 1971  108  R e l a t i o n s h i p Between 24-Hour and Annual p r e c i p i t a t i o n  111  Snowpack Response to Rain-On-Snow ( a f t e r Colbeck, 1976) on H y d r o l o g i c  122  F i g u r e 5.1  Perspective  Models  133  F i g u r e 5.2  L o c a t i o n Map f o r Oregon Watersheds  147  F i g u r e 5.3  Comparison o f Wide Channelized Flow V e l o c i t i e s  154  and Overland  - xii -  LIST OF FIGURES (continued)  PAGE F i g u r e 5.4  Overland Flow V e l o c i t i e s ( a f t e r C o n s e r v a t i o n S e r v i c e , 1974)  Soil 157  F i g u r e 5.5  Rain-On-Snow F l o o d Hydrograph on Lookout Creek  F i g u r e 5.6  Mann Creek Topography  F i g u r e 5.7  Recorded Hydrograph on Mann Creek: O c t . 27-  ... 161 166  Nov. 6, 1950  167  F i g u r e 5.8  Mann Creek Time-Area Graph  170  F i g u r e 5.9  Semi-Log P l o t o f Mann Creek Hydrograph  171  F i g u r e 5.10  Simulated R a i n f a l l Hydrograph on Mann Creek  174  F i g u r e 5.11  Recorded Hydrograph on Mann Creek: February 3-8, 1951 Semi-Log P l o t o f Rain-on-Snow Hydrograph on Mann Creek  F i g u r e 5.12  F i g u r e 5.13  178 180  Simulated Rain-on-Snow Hydrograph on Mann Creek  183  F i g u r e 5.14  Lookout Creek Topography  185  F i g u r e 5.15  December 1964 P r e c i p i t a t i o n  187  F i g u r e 5.16  Time D i s t r i b u t i o n of R a i n f a l l  188  F i g u r e 5.17  Rain-on-Snow Flood Hydrograph on Lookout Creek: December 19-27, 1964  192  F i g u r e 5.18  Lookout Creek Time-Area Graph  193  F i g u r e 5.19  Semi-Log P l o t of Rain-on-Snow F l o o d on Lookout Creek  Hydrograph 195  - xiii  -  LIST OF FIGURES (continued)  PAGE F i g u r e 5.20  Figure  IV.1  F i g u r e IV.2  F i g u r e IV.3  F i g u r e IV.4  F i g u r e IV.5  Simulated Rain-on-Snow F l o o d Hydrograph on Lookout Creek  197  Wave Speed vs I n f l u x Rate ( a f t e r Colbeck and Davidson, 1973)  IV-2  Water P e r c o l a t i o n Through Snow ( a f t e r Tucker and Colbeck, 1977)  IV-4  P e r c o l a t i o n Rates f o r V e r t i c a l U n s a t u r a t e d Flow  IV-7  Comparison of P r e d i c t e d and Observed Outflow Hydrographs ( a f t e r Dunne e t a l . , 1976)  IV-9  T r a v e l Times f o r B a s a l S a t u r a t e d Flow  IV-12  - xiv -  AC KNOWLEDGEMENTS  I am a p p r e c i a t i v e of the a d v i c e , supervisor Russell,  D r . Michael  P.Eng.;  Quick,  Dr. B i l l  cooperation  P.Eng.;  Caselton,  and f r i e n d s h i p of my t h e s i s  and committee  P.Eng.;  members  Dr. A l Freeze,  D r . Denis  p.Eng.; and  Dr. o l e v Slaymaker. m  Special  thanks  to  my  wife,  Jolanta,  f o r her p a t i e n c e  and  support  throughout the Ph.D. program.  I am indebted ians  t o the l a t e D r . "Chick"  Evans, one of the g r e a t humanitar-  and amateur g o l f e r s o f our time,  f o r the honor of p a r t i c i p a t i n g i n  the  Evans  and  p r o f e s s i o n a l success  the  Scholars  opportunities  program  that  which  which were  he e s t a b l i s h e d .  I have  Much of the academic  experienced  provided  to me  can be a t t r i b u t e d to  by  the Evans  Scholars  Foundation.  The  generosity  services critical  Financial Peterson and  of  Klohn  Leonoff  and the c o r r e s p o n d i n g  diligence  to the p r e p a r a t i o n of t h i s  assitance  for this  L t d . i n providing  word  of Mrs. L i n d a  processing  Davidson  were  manuscript.  research  Memorial S c h o l a r s h i p i n C i v i l  was  provided  Engineering  by  the E a r l  and a N a t u r a l  E n g i n e e r i n g Research C o u n c i l of Canada Postgraduate  R.  Sciences  Scholarship.  INTRODUCTION  1.  Most development p r o j e c t s such as dams, r a i l r o a d mine  sites,  that due of  flood  pipeline analysis  installations  be undertaken  t o the r e l a t i v e l y the P a c i f i c  sparse  Northwest  and new  townsite  most  flood flow  flows data  process ques  common  methods  h y d r o l o g i c data  coastal  collection  region, flood  the a p p l i c a t i o n  for a basin.  i n coastal  typical  The a p p l i c a t i o n  British  problems  of a  Columbia  commonly  model  which  of these  f o r estimating  simulates  by  of streamthe r u n o f f  estimation  i s especially d i f f i c u l t .  encountered  i n much  must be under-  analysis  flood  However,  data.  practice  statistical  require  network  analysis  specific  i n current engineering  can be c a t e g o r i z e d as e i t h e r or  planning  f o r p r o j e c t d e s i g n purposes.  taken i n many i n s t a n c e s without adequate s i t e  The  and highway e x t e n s i o n s ,  techni-  For example,  the p r a c t i c i n g  engineer  in  B r i t i s h Columbia i n c l u d e :  i)  the streamflow the  gauge network operated  precipitation  gauge  network  by Water Survey  which  reports  o f Canada and  to the  Atmospheric  Environment S e r v i c e are r e l a t i v e l y sparse i n remote r e g i o n s ;  ii)  available  streamflow  transposed  with  and  confidence  precipitation over  t e r r a i n with i t s c o r r e s p o n d i n g  iii)  many  streamflow  and  long  data  cannot  be  readily  d i s t a n c e s due to mountainous  l o c a l variations i n climate;  precipitation  stations  currently  in  opera-  -  tion  do  not  have  long  s t a t i s t i c a l analysis  iv)  available  though  term  often  streamflow  estimates,  2 -  overall  data  described  extreme are  data  study  used  extreme  greater  While  when flood  with  generally  of  daily  flow  flood  dis-  instantaneous  i s to overcome  a  a  rational  sufficient  the shortcomings i n basis  site  for  estimating  s p e c i f i c design  i s a subjective  classification  s p e c i f i c design  objective.  refers  t o any f l o o d  the focus  of t h i s  region  these  generally  which i n c l u d e s  and Oregon. other  investigation  with  applicable  data  and i s  For t h i s  a return  of  some data  the c o a s t a l  multi-disciplinary investigation hydrometeorology,  i s presented i n four  to the e n t i r e  British  period  snow h y d r o l o g y  and r e s u l t s  region  Columbia,  northern  s o u t h e a s t Alaska and the c o a s t a l  Accordingly,  segments  i s on c o a s t a l  i n v e s t i g a t i o n of c o a s t a l B r i t i s h Columbia  A  to mean  than about 20 y e a r s .  Washington in  flood  meaningful  for design.  establishing  Extreme  i n context  r e s u l t s are a l s o  coastal  by  limited  o f maximum  research  i n instances  not a v a i l a b l e .  are o f t e n  an e s t i m a t e  of t h i s  above  floods  commonly  the  goal  and, t h e r e f o r e ,  cannot be undertaken;  charge i s u s u a l l y r e q u i r e d  The  records  r e g i o n of  from  are i n c l u d e d  pacific  studies i n this  floods.  i s undertaken  encompassing  and h y d r o l o g i c  modelling.  the areas Research  components whose primary obj e c t i v e s are as f o l l o w s :  -  3 -  CHAPTER 2: t o develop an understanding  o f the f l o o d producing  for  flood  the r e g i o n  common  t o extreme  CHAPTER  floods,  of engineering  3: t o provide  rainfall  f o r input  those  hydrologic  i s on i d e n t i f y i n g  instances  on  identifying  to the c o a s t a l  component lead  by  region.  those  as  planning  a basis  c h a r a c t e r i s t i c s which a r e The emphasis  c l i m a t i c and r u n o f f  these  are the flows  data  f o r estimating  t o a hydrograph model.  are a v a i l a b l e f o r a b a s i n  identified  4:  extreme  floods.  regard  flood  to assess  basin  conditions  In p a r t i c u l a r ,  commonly  which  interest  i n many  the time  d i s t r i b u t i o n of  T h i s assessment i s undertaken  which  the r o l e  to i t s c o n t r i b u t i o n  5:  t o develop  estimates  coastal  conditions  t h a t when supplemental  of i n t e r e s t the more g e n e r a l  of  f o r conditions  mountains applied  application  a hydrograph  of  the  trends  which  events  runoff  leading  to  of a snowpack i s i n v e s t i g a t e d to t o t a l  runoff  and i t s  r u n o f f through the snow.  model  Pacific  for rainfall  affect  snowmelt  e f f e c t on the amount and r a t e of r a i n f a l l  CHAPTER  study  f o r the c o a s t a l r e g i o n may be improved.  CHAPTER  with  of  of t h i s  and d e s i g n .  a r e g i o n wide s c a l e , a l t h o u g h i t i s r e c o g n i z e d  site  mechanisms  that  lead  i s capable  t o extreme  Northwest.  events.  producing  floods  Hydrograph  are examined  to extreme rain-on-snow f l o o d  of  for their  i n the  procedures potential  -  Even  though  Chapter,  each  4  -  study component i s presented s e p a r a t e l y  i t i s the combination of r e s u l t s  understanding  of f l o o d  initial  ing  mechanism  coastal and  task f o r any f l o o d which  region,  summer  snowmelt basins  result  experience  examination undertaken in  floods  runoff.  assessment  must  be  The both  i n this  either  analysis.  during  p r o c e s s e s which flood  data  affect  and  further  required  capable  of  f o r the mountainous c o a s t a l  which a r e  because  the y e a r . climate  analysis  study, i t i s shown t h a t extreme  procedures  Based  simulating  of storm  rainfall  of f l o o d  frequency  rain-on-snow  Therefore, floods  of rain-on-snow  analysis,  distribu-  T h e r e f o r e , the hydrograph p r o -  f o r i n p u t to a model.  task of hydrograph  s e p a r a t e l y from assessment  are  region.  n a t u r a l s t a r t i n g p o i n t i n the development  ment i s an e s s e n t i a l  on an  f l o o d s on most b a s i n s  onto the b a s i n must be e s t i m a t e d .  cedures i s a n a l y s i s of storm r a i n f a l l  some  i n the r e g i o n ,  A requirement common t o a l l hydrograph models i s t h a t the time tion  In the  i n spring  Floods  the c o a s t a l r e g i o n are generated from rai-n-on-snow e v e n t s .  hydrograph  produc-  or a combination of r a i n and  i s complicated  of f l o o d s  methods.  snowmeIt-induced  and w i n t e r .  rainfall-only  types  of h i s t o r i c a l  f l o o d hydrograph  in fall  situation  of atmospheric  r e g i o n and the develop-  s i m u l a t e d by hydrograph  are g e n e r a l l y  from  leads to an  a n a l y s i s i s t o e s t a b l i s h the f l o o d  or r a i n f a l l - i n d u c e d  rainfall-induced  ultimately  mechanisms i n the c o a s t a l  ment of a n a l y t i c a l procedures f o r extreme  The  which  i n a different  This assess-  and can be undertaken  of b a s i n response and r u n o f f  characteristics.  - 5 -  At  an ungauged  hyetograph  watershed  f o r input  characteristics intensity project sity  compared  that  density  gauge  vary over s h o r t d i s t a n c e s  of the d i f f i c u l t y  from  between region is  rainfall  station  where  rainfall  these data  of o n l y  58  (World  stations.  records  stations  to the  rainfall  inten-  and i s r e l a t i v e l y  Meteorological terrain.  Organization,  Therefore,  near a p r o j e c t data  i tis site.  to a p r o j e c t  because r a i n f a l l can  both i n plan and e l e v a t i o n .  i n estimating coastal  even  Assessment  as e x t e n s i v e  undertaken  data  are transposed  i n mountainous regions  storm  region,  i s to examine whether r e g i o n a l available  a  storm  i s a v a i l a b l e , transposing  i n the mountainous  fied  regional  t o produce  First,  a p r e c i p i t a t i o n gauge i s not l o c a t e d  i s especially d i f f i c u l t  study  required  model.  i n mountainous  site  this  a  to recommendations  when a r e g i o n a l  analysis  at  consists  Even  Because  hydrograph  estimated  B.C.  f o r network  common  are u s u a l l y  The e x i s t i n g gauge network which  i n coastal  1970)  steps  are a v a i l a b l e , and then  site.  sparse  to a  are  data  two  when  as an e x p l o r a t o r y  one g o a l  the magnitude rainfall  as the c o a s t a l exercise  f o r hydrograph established for  c h a r a c t e r i s t i c s can be i d e n t i -  of r e g i o n a l  and d i v e r s e  rainfall  of r a i n f a l l  characteristics in a  region  without  varies  i s uncommon, and  previous  knowledge as  to whether the a n a l y s i s w i l l produce usable r e s u l t s .  Two  types  of r a i n f a l l  hyetographs analysis from  f o r input  of r a i n f a l l  analysis  i n t e n s i t y data to a  can be used  hydrograph  model.  to produce  One  type  synthetic  results  from  i n t e n s t i e s from many d i f f e r e n t storms and the other  of i n t e n s i t i e s o c c u r r i n g  within  a single  storm.  Atmos-  - 6 -  pheric of  Environment S e r v i c e summarizes m u l t i - s t o r m  their  IDF  s t a t i o n s by p r o d u c i n g I n t e n s i t y - D u r a t i o n - F r e q u e n c y  curves  period,  provide  but  do  intensities based  on  only  not  intensity  methods  intensities  provide  information regarding v a r i a t i o n s  data  single  employed  occurring  average  within a single  because  This  storm.  from  storm  using  data  IDF  within single  IDF  in  the  coastal  programs w r i t t e n to  for a given  are  i s an  seldom  curves,  scan  the  data  is  procedure to  examine  storm  data  ratios each  adopted  tape,  of 1, 2, 6 and  station  tions .  for analysis  multi-storm  identified  and  then  T h i s method  of  recorded  obtained  on  identify  in  of  intensity this  study  To  in  rainfall  hyetographs  a t each  magnetic  of  tape,  the and  extreme r a i n f a l l  available ratio  upon  intensities  as p a r t of t h i s  for further  in a  return  improve  rainfall  study. 58  sta-  computer  events  and  analysis.  regional r a i n f a l l  data  Curves.  d u r a t i o n and  available.  analysis  e x t r a c t h o u r l y i n t e n s i t i e s w i t h i n the storm  The  (IDF)  approach commonly a p p l i e d  storms i s a l s o undertaken  r e g i o n be  data a t each  Development of s y n t h e t i c  curves  exercise requires a l l hourly  tions  intensity  from  format.  characteristics AES  and  For  single  example,  12-hour to 24-hour p r e c i p i t a t i o n  are c a l c u l a t e d  compared  a t a l l other  i s one  to c o r r e s p o n d i n g  ratios  approach t o i d e n t i f y i n g  at  sta-  regional characteris-  tics  even when the amount of r a i n f a l l  both  s e t s of i n t e n s i t y d a t a , computer programs are w r i t t e n to e x t r a c t the  n e c e s s a r y data from magnetic tape and  i s d i f f e r e n t between s t a t i o n s .  undertake  For  the r e q u i r e d c a l c u l a t i o n s .  - 7 -  Results and  of the a n a l y s i s  single  these  storm  data  that  need  site  data.  no h i g h  elevation  region.  To  provide  B.C. d a t a ,  of  results  rainfall from  i n B.C.  teristics  s i m i l a r t o those c a l c u l a t e d  The  next  step  rain-on-snow its  Results  at higher  available  contribution  i n t e n s i t y data further  identified  elevations  from the  Oregon regional  i n B.C.  than  f o r lower e l e v a t i o n s  hydrograph  i s to assess  of snowmelt  procedures  the r o l e  to t o t a l  runoff  rain-on-snow  water  percolation  charac-  i n B.C.  capable  of  and i t s e f f e c t  A fundamental q u e s t i o n  and to  are c u r r e n t l y  of a snowpack w i t h  response from the b a s i n . i s whether  there are  of a n a l y s i s of U.S. data show r e g i o n a l  i n developing floods  i n the absence of  i n t e n s i t y i n the c o a s t a l  illustrate  characteristics  stations  engineer  rainfall  to  In p r a c t i c e ,  of B.C. data i s t h a t  rainfall  obtained  B.C.  on the range o f h o u r l y i n t e n s i -  by a d e s i g n  s t a t i o n s which r e c o r d  are a l s o  c h a r a c t e r i s t i c s f o r both IDF  i n coastal  r e s u l t s of a n a l y s i s  supplement  Washington  applicability  to s e t l i m i t s  to be c o n s i d e r e d  One concern regarding  regional  can be i d e n t i f i e d  r e s u l t s can be used  ties  and  show t h a t  simulating regard on  to  runoff  which a r i s e s f o r extreme  through  the snow medium or  development of i n t e r n a l drainage channels i s the dominant r o u t i n g mechanism.  Quantitative  colation 1972) is  through  and a b a s a l  also  available  formulations snow  in a  saturated  vertical layer  to suggest  water p e r c o l a t i o n , c o n t r o l s  have been proposed d e s c r i b i n g  (Colbeck,  that  runoff  unsaturated  an  during  zone  1974a).  internal  water  (Colbeck,  per1971,  However, evidence  drainage  network,  not  extreme rain-on-snow f l o o d s .  - 8 -  The  approach  (i)  to review  and  snow  taken  i n this  available  hydrology;  study  t o assess  literature  (ii)  to a s s e s s  to the flow of l i q u i d water  results  with  for to  to t h e i r  rain-on-snow f l o o d s .  results  through  impact  Once  of a snowpack i s :  i n the g e n e r a l areas  pertain  regard  the r o l e  on  the r o l e  of  of snow p h y s i c s  research  snow; and ( i i i )  hydrograph  studies  to i n t e r p r e t  procedures  required  of a snowpack on b a s i n  rain-on-snow i s a s s e s s e d , then requirements  which  of a hydrograph  response model can  be e s t a b l i s h e d .  Perhaps that  the most  snowpack  properties be  coastal  (Smith,  response  r e g i o n , much  near  Warm  0°C as  Some l i q u i d  water  but  once  cesses  "wet"  ripe  results  of the snowpack  most  when  are  of  liquid  i s achieved  by g r a v i t y  snowpack i s commonly  Research  i n snow h y d r o l o g y i s  the  can be  those  whose  snow  water  and  referred  water  (Colbeck  observations  snowpacks to i n p u t s of l i q u i d  must  considered.  interior Also,  i s present  in  temperatures snow  can  be  (Colbeck,  1982a).  or c a p i l l a r y  water,  are t r a n s m i t t e d by  and Davidson,  to as a r i p e  physical  c a t e g o r i z e d as "warm"  season.  inputs  with  of snowpack response  i s h e l d i n a snowpack as absorbed  saturation  dominated  recognize  of snow p r o p e r t i e s being  snowpacks  during  categorized  to  Therefore, discussion  by a d e s c r i p t i o n  1973).  remain  concept  i s not c o n s t a n t , b u t r a t h e r v a r i e s  of the snow.  qualified  the  important  1973).  pro-  A warm, wet  snowpack.  of snow h y d r o l o g i s t s f o r response water show:  of  ( i ) snowpack response i s  -  usually  less  apparent  than p r e d i c t e d  explanation  preferential and  and  watershed trolled of  the  (iii)  development  initiated,  snowpack  a  becomes of  transition The  f o r water  of d i s t i n c t  are  from  to undergo  flow from  snowcovered  of  the  in a  above  melt  channels causes snow-controlled  conclusions  response  occur  without a  the b a s i s  hydrograph  watershed  basin  a  to  suggest t h a t  channels  snowcovered terrain-condevelopment  r o u t i n g mechanism d u r i n g  on  hydrograph  model,  becomes  terrain  characteristics snowcover.  and  might  This  ( i i ) as  procedures  for  approach  assessment  of  to  and  assess  by  l a g and  whether  each method rain-on-snow  Northwest.  This  without knowing internal  movement  in a  i t i s possible  that  conditions snowpack  f o r hydrograph procedures developed i n t h i s  Unit-hydrograph  to  water  controlled,  t i o n to extreme rain-on-snow f l o o d s i n the c o a s t a l  tion  as  rain-on-snow a r e : ( i ) water p e r c o l a t i o n p r o c e s s e s do not need t o  simulated  ployed  self-perpetuating  rapid  i s the dominant  the  channels; ( i i ) once  they are  more  and  rain-on-snow.  extreme  study  percolation,  flow  above o b s e r v a t i o n s  an i n t e r n a l d r a i n a g e network  Consequences  be  theories  i s formation  water movement.  extreme  -  by  d r a i n a g e routes  drainage  develop;  9  route  empirical  floods  are  mountainuous  can  response  and  in  this  coefficients  em-  be m o d i f i e d regions  of  for applicathe  i s undertaken as an e x p l o r a t o r y  be  simulated  forms  study f o r a p p l i c a -  investigated  snowpack response, even with  d r a i n a g e network,  graph p r o c e d u r e s .  in  could  would  region.  relationships  for r a i n f a l l - o n l y  investigation whether  techniques  which  using  Pacific exercise  the f o r m a t i o n of an conventional  hydro-  -  initial  screening  lag  and  route  in  this  study  lag  and  can  be  sents  of  for  conditions  basins  methods  procedure  i s that  across  leads  rainfall  and  the b a s i n .  can  than  having  rely  This  One  that  the  investigation  attraction inputs  to  of  the  the  model  T h i s o p t i o n more a c c u r a t e l y r e p r e -  watershed  regions.  conclusion  more d e t a i l e d  snowmelt  terrain.  to  the  rain-on-snow.  each  rather  to  warrants  to  i n mountainous  through  and  -  application  distributed  principles  two  hydrograph  route method  particle  the  10  Also,  be on  procedure  is  travel  time  estimated  based  equations  developed  of a  on  water  hydraulic for  other  particularly  attractive  for  requires estimates  for travel  time  ungauged watersheds.  The  l a g and  through of ing  route  hydrograph  the b a s i n and a storage c o e f f i c i e n t which s i m u l a t e s  the watershed. travel  mates,  time  without  Procedures based  any  the  extreme  rain-on-snow  estimates  suitable  snowpack.  of  time  Storage flood  for  the  and  Alternatively,  added  coefficients  hydrographs  rain-on-snow  overland  increment  route  are  drainage  s u i t a b l e watersheds are i d e n t i f i e d  velocity  f o r water  calculated  as  esti-  movement  from  tabulated  are i d e n t i f i e d  hydrograph  coastal hydrologic  flow  recorded  preliminary  procedures.  watersheds i n c o a s t a l B.C.  research.  segments  channelized  f o r use w i t h l a g and  requirements for  on  characterists  are demonstrated i n t h i s study f o r e s t i m a t -  additional  through  No  method  which s a t i s f y  a n a l y s i s to a basins  region  of  are  the  standard  examined  Pacific  in  data  needed other  Northwest  i n the Cascade Mountains i n Oregon.  and  - 1 1 -  Two  drainage basins,  the  potential  late (i)  Mann  f o r applying  rain-on-snow f l o o d s . analysis  fast  runoff  using  event  Mann  rain-on-snow, same b a s i n  Development  contribution  Creeks, a r e s e l e c t e d  l a g and route  of a r a i n f a l l - o n l y  simulated on  and Lookout  of hydrograph procedures i n c l u d e s :  peaks  t o examine  and to compare  for rainfall-only;  on Lookout Creek  to c o n f i r m  i n mountainous  one storage c o e f f i c i e n t ; Creek  hydrograph procedures to simu-  event on Mann Creek  to f l o o d  to examine  t h a t the  regions  can be  ( i i ) a n a l y s i s of a rain-on-snow  whether  the model  the storage  can be  coefficient  adapted f o r  with  that  on the  and ( i i i ) a n a l y s i s of a rain-on-snow event  t o undertake a second a p p l i c a t i o n  of the,model,  and t o  a s s e s s s t o r a g e c o e f f i c i e n t s d u r i n g more extreme f l o o d e v e n t s .  Results  from Mann and Lookout Creeks show l a g and route hydrograph p r o -  cedures  can be a p p l i e d  the  following  the  basin  the  appropriate  basin  to s i m u l a t e  methodology  i s adopted:  from c h a n n e l i z e d storage  rain-on-snow  hydrographs  ( i ) estimate t r a v e l  and o v e r l a n d  coefficient;  flood  time through  flow c o n s i d e r a t i o n s ;  ( i i i ) specify  as the sum of snowmelt and r a i n f a l l ;  water  when  (ii)  inputs  and ( i v ) c o n s i d e r  select to the  there are  no l o s s e s t o groundwater.  Selection an One  of a s t o r a g e  coefficient  important consideration question  rain-on-snow floods.  which floods  f o r the f a s t  i n application  arises  i s how  compare  on the same  Storage c o e f f i c i e n t s  on-snow hydrograph d i f f e r  does  component  of r u n o f f i s  of l a g and route p r o c e d u r e s . the basin  on Mann Creek  storage with  coefficient for  that  for a rainfall  by a f a c t o r of two.  for rainfall and a  rain-  However, the rain-on-snow  -  flood  on Mann Creek  still  partly  Mann Creek  nal  drainage  i s not a very  floods network  coincidence ponse  a  floods.  event and perhaps  to t e s t  the concept t h a t an i n t e r -  causes  basin  response  this  rain-on-snow event on Lookout Creek i s s i m i l a r  demonstrate  on Mann Creek.  This  r e s u l t may be  a more t e r r a i n - c o n t r o l l e d  rain-on-snow f l o o d s .  study from  t o be  I t i s worth n o t i n g t h a t the storage  Until  further  recorded  extreme  rain-on-snow  basin  res-  r e s e a r c h i s under-  taken, i t i s recommended t h a t p r e l i m i n a r y storage c o e f f i c i e n t s in  runoff i s  i s the case, then data from the  snowpack  for rainfall-only  or i t may  f o r extreme  If this  within  to that f o r r a i n f a l l  the c o e f f i c i e n t  extreme  cannot be used  c o e f f i c i e n t f o r an extreme to  -  snow-con t r o l l e d .  two  similar  12  floods  calculated  be adopted f o r  use with l a g and route hydrograph p r o c e d u r e s .  Available tively than  high  tions,  suggests  that  extreme  rainfall  combined  by  for this  the Corps region.  of  Engineers  It i s likely  t o ungauged  mountainous  that  for alternative  snowmelt  occurring  highlighted  as  an  watersheds  temperature  because  melt equations are seldom  during  the s p e c i a l  important  topic  case  rela-  snowmelt  temperature-index e q u a t i o n  such as developed by the Corps of E n g i n e e r s , w i l l  applied  with  temperatures on Lookout Creek produces much g r e a t e r  predicted  developed  needed  evidence  requiring  development of p r o c e d u r e s f o r e s t i m a t i n g extreme  climatic  available.  further  equa-  c o n t i n u e to be  other  of extreme  index  data  Therefore,  rain-on-snow i s analysis  rain-on-snow  i n the  floods.  - 13 -  2.  FLOOD CHARACTERISTICS IH THE COASTAL REGION  2.1  CLIMATE  The  c l i m a t e of the n o r t h e r n  has  been d e s c r i b e d by v a r i o u s  Thomas  (1974), Schaefer  Pacific  c o a s t a l r e g i o n along  authors  i n c l u d i n g Chapman  (1978), and C h i l t o n (1981).  r e g i o n extends the e n t i r e l e n g t h of the p r o v i n c e by  the c r e s t  climatic the  The  region  Cascade  adjacent  serve  distinct facing  within  mountain  small  annual  local  than  lowlands  eastern of  interaction  tend faces  Vancouver  and the F r a s e r of Vancouver  River  This  and Oregon bounded by immediately  include  months o c c u r r i n g  exist between  in fall  can be  the mountains.  Island,  along  the  islands  comprise  and the Olympic  and  circulathe c o a s t  For example,  identified  to have more c l o u d s  and  W i t h i n the  atmospheric  of a i r masses.  region  of  relatively  in precipitation  features d i s t r i b u t e d  estuary  Island  region  range of temperature.  t o the movement  which  i n F i g u r e 2.1.  t  variations  the c o a s t a l  slopes  The c o a s t a l c l i m a t i c  southeast A l a s k a  the w e t t e s t  and major topographic  zones  rainshadow  i n t o Washington includes  (1952), Hare and  and i s g e n e r a l l y bounded  shown  of the c o a s t a l  with  however,  as  Columbia  Columbia.  features  as b a r r i e r s  precipitation eastern  and  due t o the complex  patterns  Georgia  British  precipitation  region,  temperature  which  Range,  climatic  Mountains  southward  and a r e l a t i v e l y  coastal  tion  extends  t o northern  annual  winter,  the C o a s t a l  Mountain  primary  high  of  British  along  west-  and r e c e i v e more Also, of  the  a zone which Mountains  the  south-  Strait  lies  of  i n the  i n Washington  - 14 -  FORT  NELSON  GREAT PLAINS  \ MOUNTAINS A N D \ S O U T H E R N ROCKY • MOUNTAINS ) CRANBROOK  Figure  2.1  Physiographic  Regions o f B r i t i s h  Columbia  s  - 15 -  State. also  This  the  zone  warmest  i s the with  driest  segment  more hours  of  of  the  bright  coastal  sunshine  region  during  and  the  is  summer  months.  Monthly  precipitation  coastal  stations  to  Sitka,  the  along  i n c l u d e d i n Table 2.1  stations  for representative  from Vancouver, B r i t i s h Columbia These data  the c o a s t y e t a l s o  distribution  example, annual tive  extending  are  Alaska i n the n o r t h .  precipitation basis  data  ranges  i n c l u d e d i n Table  from  2.1.  i s similar 1259  f o r the  to 4388 mm  However, on  south  the v a r i a b i l i t y  show t h a t on a monthly  of p r e c i p i t a t i o n  precipitation  illustrate  i n the  in  percentage  region.  For  for representa-  a percentage  basis at  each s t a t i o n , a summer month r e c e i v e s i n the order of o n l y 3 to 6 p e r c e n t of  the  annual  precipitation  while  r e c e i v e about 10 t o 15 p e r c e n t . p e r i o d of h i g h p r e c i p i t a t i o n  the  southern  southward for  of  the  progression  in  the  of  the  wettest  winter  months  Comparison of these data a l s o shows t h a t  the  segments  each  starts  coastal  earlier region.  occurrence  of  i n the  northern  Williams  (1948)  maximum d a i l y  the year of about one degree of l a t i t u d e f o r each 4.5  than i n noted  a  precipitation  days.  TABLE 2 . 1 MEAN MONTHLY PRECIPITATION FOR REPRESENTATIVE COASTAL STATIONS*  Vancouver  U.B.C. % of annual  mm  p r e c i p.  To f1 no A1r p o r t P o r t 1Hardy A i r p o r t % of % of annual annual mm mm preclp. p r e c l p.  Ocean Fal Is % of mm  Cape S t . James P r i n c e 1Rupert A i r p o r t % of % of annual annual annual pr ec 1 p. mm p r e c l p. mm p r e c l p.  Sitka % o1 mm  annu< prec  Jan  173  14  404  12  211  12  459  10  162  11  228  9  197  8  Feb  133  11  366  11  159  9  392  9  137  9  222  9  162  7  Mar  116  9  372  11  142  8  346  8  130  8  201  8  177  7  Apr  69  5  234  7  108  6  302  7  107  7  190  8  136  6  May  60  5  143  4  69  4  217  5  85  ' 6  140  6  1 18  5  June  43  3  102  3  71  4  192  4  74  5  130  5  88  4  July  37  3  86  3  52  3  151  3  58  4  103  4  132  5  Aug  53  4  114  3  69  4  227  5  79  5  158  6  200  8  Sept  72  6  163  5  136  7  376  9  125  8  233  9  292  12  Oct  133  11  392  12  245  14  625  14  198  13  367  15  388  16  Nov  162  13  432  13  245  14  514  12  187  12  268  11  305  12  Dec  208  16  479  15  277  15  587  13  191  12  284  11  258  11  Annual  1259  * Station  3287  1784  l o c a t i o n s shown on F i g u r e 2.1  4388  1533  2524  24 53  - 17 -  Temperature along  data  p l o t t e d on F i g u r e 2.2 f o r three  the c o a s t a l r e g i o n  illustrate  representative stations  the r e l a t i v e l y  a given  s t a t i o n and the s i m i l a r annual  tions.  Chapman (1952) noted an average r e d u c t i o n i n mean annual tempera-  ture  (corrected  to sea l e v e l ) along  trend  s m a l l annual range a t  i n temperature between  the c o a s t  from  60° to 24°20'  sta-  north  l a t i t u d e of about 0.6°C per degree of l a t i t u d e .  18  _2 I  J  I  F  I  M  '  '  A  M  J  '  J  •  1  A  S  '  O  '  N  '  D  MONTH F i g u r e 2.2 Mean Monthly Temperatures f o r C o a s t a l  The  climate  macro-scale  of the c o a s t a l r e g i o n atmospheric  processes.  lation  i s produced by a s t r o n g  polar  latitudes.  Alaska  and  high  During pressures  this  Stations  i s c o n t r o l l e d on a seasonal During  winter  b a s i s by  months v i g o r o u s  circu-  temperature g r a d i e n t between t r o p i c a l and season  inland  low p r e s s u r e s  combine  over  to produce  the G u l f  strong  of  pressure  - 18  gradients  over  southerly  surface  patterns  The  western  winter  Oregon,  winds  f o r December  -  prevail.  atmospheric  scale, upon air  to  the  frontal  the  coast,  aloft  of  break  often  bringing  British  level  shown on  pattern  where  causes  away  from  strong  responsible  they the  where  pressure  2.3.  numerous  storms  to  move i n a n o r t h e a s t e r l y  dissipate. storm  On  centers  southwesterly  f o r the  Columbia  atmospheric  Figure  P a c i f i c Ocean and  Alaska  systems  and  sea  are  circulation  Gulf  which are  Mean  (Thomas, 1977)  d e v e l o p r a p i d l y i n the n o r t h e r n direction  Washington  flows  coastal region's  a  smaller  and  impinge  of warm moist heaviest  rain-  falls.  During 1977).  summer months a weaker atmospheric The  summer  large high pressure of J u l y on  c o a s t a l climate  The  F i g u r e 2.4.  For  the frequency  summary  annual coastal  of  trends  this  and  for  effect  of  more  local  aspect  on  circulation  winds p r e v a i l  i n t e n s i t y of P a c i f i c  circulation  temperature  Variations within  diverse coastline.  the  (Thomas,  dominance  summer c o n d i t i o n p r e s s u r e  northwesterly  atmospheric  develop  region.  i s c o n t r o l l e d by  develops  of  a  c e n t r e which expands northward as shown f o r the month  weaker than i n the w i n t e r , c o a s t , and  circulation  topographic patterns  the  much of  suggests  precipitation  frontal  such  as  systems  are the  diminished.  for  how  similar  the  r e g i o n , however, r e s u l t  features as  along  storms i s  patterns  and  gradients  entire  from  the  e l e v a t i o n , slope  and  impinge  of  the  very  F i g u r e 2.3  Mean Monthly Sea L e v e l P r e s s u r e s (kPa) f o r December, a f t e r Thomas (1977)  - 20 -  F i g u r e 2.4  Mean Monthly Sea L e v e l P r e s s u r e (kPa) f o r J u l y , a f t e r Thomas (1977)  - 21 -  HISTORICAL  2.2  Historical southeast floods  flood  STREAMFLOW  data  RECORDS  f o r the c o a s t a l  A l a s k a were reviewed  to e s t a b l i s h  t h a t have been recorded  larities  among the d a t a .  examining  unit  instantaneous  (discharge  to maximum d a i l y  of B r i t i s h  the t y p i c a l  and t o i d e n t i f y  These f l o o d  discharge  region  general  Columbia and  range of extreme trends  and s i m i -  c h a r a c t e r i s t i c s were documented by per u n i t  area),  discharge, flood  ratios  producing  of maximum  mechanisms and  p e r i o d o f year when extreme f l o o d s have o c c u r r e d .  Identification of  British  of streamflow  Columbia  gauging  and s o u t h e a s t  f o r review i n t h i s study proceeded  i)  stations fied in  stations  Alaska  and the s e l e c t i o n  located within  coastal  i n a r e f e r e n c e index  G e o l o g i c a l Survey  British  (Environment  Columbia  while  Alaska  flood  data  stations  which  were  designated  such  as  were  from a r e p o r t prepared  (Lamke, 1979).  updated t o 1982 by the USGS o f f i c e  ii)  of s t a t i o n s  identi-  Canada, 1983b) and those  Flood  were r e a d i l y a v a i l a b l e f o r B r i t i s h Columbia 1983a),  region  as f o l l o w s :  s o u t h e a s t A l a s k a were o b t a i n e d  U.S.  w i t h i n the c o a s t a l  from  data  by the  through 1982  (Environment  the 1979  Canada,  report  were  flows  were  and  Taku  i n Anchorage.  as having  regulated  omitted.  iii)  major  rivers,  R i v e r s which f l o w b a s i n s extend  the F r a s e r ,  through  the c o a s t a l  Skeena,  Stikine  r e g i o n b u t whose  i n l a n d beyond the c o a s t were o m i t t e d .  drainage  -  iv)  o n l y data were  The al  from  -  those  stations  Columbia  resulted and  47  stations  more than  rivers  by  included  Before  region  to of  flood  recognize  the  in  one  66  of 66  southeast  station  stations.  data> a v a i l a b l e sources  these d a t a .  c l i m a t e and  stations  Alaska.  i n coastIn  so t h a t o n l y 58 The  list  As  one  of  for  scatter  the  of  coastal  i n any  British  different  stations  would i n t u i t i v e l y  basin runoff c h a r a c t e r i s t i c s  area.  themselves  which  In  addition  there  i n h e r e n t l y lead  are  expect,  is  a n a l y s i s of the a v a i l a b l e f l o o d d a t a .  i n any  i t is  derived  from  variability  across the e n t i r e  limitations  to s c a t t e r  region,  results  produce a range i n the magnitude of f l o o d s on  drainage  i)  of r e c o r d  i n Appendix I .  important  local  represented  analyzing  analysis  ten or more years  i n the s e l e c t i o n  Columbia some r i v e r s had were  with  reviewed.  s c r e e n i n g process British  22  in  coastal  record f o r a given  in  the  results  data  records  derived  from  These data l i m i t a t i o n s i n c l u d e :  p e r i o d s of r e c o r d are not c o n c u r r e n t f o r a l l s t a t i o n s ,  although  i n g e n e r a l most f l o o d data are f o r more r e c e n t y e a r s .  ii)  l e n g t h of record  record varies  is likely  to  among s t a t i o n s .  have  experienced  than a s t a t i o n with a s h o r t e r r e c o r d .  a  A station more  rare  with event  a long flood  - 23 -  iii)  flows a  are p u b l i s h e d based  short  duration  corresponding  mean  on a f i x e d  storm  24-hour time p e r i o d ,  hydrograph  daily  flow  spans  two  when  days,  the  may be d e c e p t i v e l y low compared  to the recorded peak f o r each day.  iv)  the magnitude  of an extreme  flood  the p o r t i o n of the s t a g e - d i s c h a r g e that in  i s relatively  this  ill-defined  plotted  r a t i n g curve  due to absence  on F i g u r e 2.5 as u n i t  British  d i s c h a r g e versus  l e s s d e f i n e d when viewed a g a i n s t other r e g i o n s .  are flood the  on r e c o r d  also data  range  a t each  from  station  of gauged  Columbia and Alaska  though the data p o i n t s are s c a t t e r e d , a s i n g l e  floods  estimated  flows  range.  Maximum f l o o d s on r e c o r d a t c o a s t a l are  i s normally  from  included  on  reinforces of data  a c r o s s the r e g i o n .  the a d j a c e n t F i g u r e 2.5 the concept  illustrates  interior  band of data  area.  i s neverthe-  p l a t e a u of B r i t i s h  of a s i n g l e  Even  F o r example, the l a r g e s t  f o r comparison.  the e f f e c t s  drainage  stations  The  single  Columbia band  of  h y d r o l o g i c r e g i o n , while  of l o c a l  climatic  variations  10.0  10  100  1000  5.0  x  V  CVl  E (A  X  x  xx  e  UJ CD  100 0 0 0  •  Coastal British Columbia  x  Southeast  o  Interior Plateau of British Columbia  Alaska  x  1.0  ro —  10 0 0 0  ••I 0.5  or < o  CO Q  0.1  CP  z ZD  o Q 0 5  0.0M  too  10  DRAINAGE AREA Figure 2.5  1000  (sq km )  Maximum Floods on Record  10000  100000  - 25 -  Additional obtained The  insight  by  monthly  British  to  examining  the  the p e r i o d  of year  d i s t r i b u t i o n of the maximum  Columbia  and s o u t h e a s t  respectively.  The t a b l e s  coastal  have occurred  region  90 p e r c e n t  c h a r a c t e r i s t i c s of  have been  Alaska  illustrate during  recorded.  when floods  coastal these on  floods floods  record  can be occurred.  for coastal  are shown i n T a b l e s 2.2 and 2.3,  that  the most extreme f l o o d s  the f a l l  i n the  and w i n t e r p e r i o d when over  - 26 -  TABLE 2.2 MONTHLY DISTRIBUTION OF MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA*  Number of Floods  Percent  March  0  0  April  1  2  May  0  0  June  3  5  July  0  0  August  0  0  4  7%  3  5  October  13  22  November  10  17  December  16  28  January  10  17  2  4  Spring/Summer  Fall/Winter September  February  54 1. 2.  93%  L i s t of c o a s t a l B r i t i s h Columbia s t a t i o n s i n Appendix I . Only one s t a t i o n c o n s i d e r e d f o r main stem of each r i v e r .  TABLE 2.3 MONTHLY DISTRIBUTION OF MAXIMUM FLOODS ON RECORD IN SOUTHEAST ALASKA* Number of F l o o d s  Percent  March  0  0  April  0  0  May  0  0  June  0  0  July  0  0  August  4  9  4  9%  Spring/Summer  Fa11/Winter September  14  32  13  30  November  8  18  December  3  7  January  1  2  February  1  2  October  ~  40  List  of s o u t h e a s t Alaska s t a t i o n s  i n Appendix I .  91%  - 28 -  As  part  Canada, the  of a 1982),  Yukon.  frequency  flood  analysis  discharge  of alone  frequency  B.C.  coast  fall  and w i n t e r  each  the f l o o d  data  resulted  from  with  I t was  floods  types  such  to ensure a similar  determined  considered i n this  that  however,  criterion  were  or snowmeIt-induced  flood  flood  flood  data  producing  by Water Survey  that  i n spring  (Environment i n B.C. and  to conduct  that  some  a  flood  of record. annual  for selecting  maximum  flows f o r on the  rainfall-induced  i n the  and summer, while  others  flood  regimes  regimes  were  identi-  had t o be i d e n t i f i e d a t  selected  f o r frequency  mechanism.  analysis  A summary of f l o o d  of Canada f o r the 58 d i f f e r e n t  study i s i n c l u d e d i n Table 2.4.  TABLE 2.4 SUMMARY OF FLOOD REGIMES AT COASTAL BRITISH COLUMBIA STATIONS  F l o o d Regime Predominantly r a i n f a l l - i n d u c e d f l o o d s i n f a l l and w i n t e r  Number o f S t a t i o n s 43  Predominantly snowmelt-induced f l o o d s i n s p r i n g and summer Both r a i n f a l l - i n d u c e d f l o o d s i n f a l l and w i n t e r and snowmelt-induced f l o o d s i n s p r i n g and summer  An  stations  either  t h a t two d i s t i n c t These  was  basins  9 or more years  observed  that  of Canada  on drainage  revealed,  not an adequate  analysis.  Survey  of the study  station  on the same b a s i n .  station  regimes  objective  a t each  was  by Water  data were examined  experienced  e x p e r i e n c e d both fiable  undertaken  The primary  examination  flood  study  14 58  basins  - 29 -  For  the  flood rate  flood  separate  greater  same b a s i n  separately typical  as  having  frequency a n a l y s i s with each  of these  were  classified  both  on the same b a s i n , Water Survey  the 14 s t a t i o n s  mates the  stations  regimes  results of  14  flood  s e t of data.  frequency  for rainfall-induced  for rainfall  floods.  analyses  and snowmelt-induced  snowmelt  showed t h a t  than  those  frequency floods  a sepa-  Examination  return period  floods  Flood  and  of Canada conducted  the 50, 100 and 200-year  f o r snowmelt  rainfall  o f the  f o r each  flood  esti-  derived f o r  curves  are shown  on F i g u r e 2.6 f o r a  c o a s t a l B.C. s t a t i o n .  20  1.05  2  1.25  RETURN  F i g u r e 2.6 F l o o d Frequency  Curves  5  10  20  50  200  PERIOD ( years )  f o r Cheakamus R i v e r Near Mons  (1924-47)  -  Ratios ium  floods  Alaska These  of maximum on  stations data  illustrate  instantaneous  record  that  greater  the f l a s h y  to maximum d a i l y d i s c h a r g e  f o r a l l coastal  reviewed  indicate  significantly  30 -  for this the range  than  many basins i n the c o a s t a l  study of f l o o d  f o r larger  nature  British  region.  are p l o t t e d ratios  basins.  of f l o o d s  Columbia  which  f o r the maxand  on  F i g u r e 2.7.  f o r small  The l a r g e r  southeast  basins i s  flood  ratios  are r a i n f a l l - i n d u c e d  on  10  100  1000  10000  100 000  • x  l»  X  •  Coastal British Columbia  x  Southeast  Alaska  I  • X X X  X X  i  X  »  X  •  X «  •  X  X  •  X  X  •  X  I  •  X  •  )  X X <  (  X  *  10  X <  •  •  11 Xx  •  I  ••*  * X  X  1i  • 1 • •  <  •• •  •  •  t  X  100 DRAINAGE  Figure 2.7  X  •  •  )  •  I  *  ••  1000 AREA  10000  (sq km )  R a t i o s o f Maximum Instantaneous  to Maximum D a i l y F l o o d s  100000  -  CASE  2.3  Four  case  These  STUDIES  studies  i n preceding  are s e l e c t e d  either  to i l l u s t r a t e  characteristics  described  s e c t i o n s which l e a d to extreme f l o o d s i n the c o a s t a l r e g i o n .  characteristics  pressure  32 -  systems  generally  in fall  as r a i n f a l l - o n l y  include  and w i n t e r ;  storms  floods  which  which  result  from  low  are r a i n f a l l - i n d u c e d  o r as rain-on-snow; and f l o o d  hydrographs  which  are very f l a s h y i n the mountainous c o a s t a l r e g i o n .  November, 1978 F l o o d near T e r r a c e , B r i t i s h Columbia ( S c h a e f e r , A multi-day resulted  rainfall  the  Both  south  the Zymoetz R i v e r  winds  the  Charlotte  Queen  which  their  r e s u l t e d from  west with  5000 m  i n the area  surrounding  near Terrace  largest flood  Terrace,  British  and the K i t i m a t  on r e c o r d  during  River to  this  storm,  t o be about the 100-year r e t u r n p e r i o d f l o o d .  storm  storm's  flooding  experienced  estimated  The  event, h e a v i e s t on October 31 and November 1, 1978,  i n serious  Columbia.  1979)  heavy with  wave which approached  of about 85 knots Islands.  considerable 1500 m  close  moisture  which  area  o f November  time  the  storm  distribution period  of p r e c i p i t a t i o n  i s shown  on  south-  north o f of the  the s u r f a c e Freezing  to the storm  to  levels  increased  f r o n t impinged  on the  and d r i e d out markedly.  recorded  F i g u r e 2.8.  the  the source  levels.  1 a cold  mainland c o a s t , a f t e r which the airmass cooled  The  was  prior  from  the c o a s t  to s a t u r a t i o n from  at higher  i n the T e r r a c e  By the a f t e r n o o n  and reached  The airmass  p r e c i p i t a i o n was  averaged  to 3000 m.  aloft  a frontal  a t Terrace  The g r e a t e s t  Airport for  rates  of  accu-  - 33 -  mulation morning fell  For  greater  of the storm  than  on October  one  hour  occurred  31 , although  durations  range  of l e s s  than  which  effectively  of storm  durations  storm  was  ended  4 days estimated  less  peak  than  The  Airport  f o r durations two y e a r s ;  the  first  return  are shown  less  also  of November 1.  intensities  the storm.  a t Terrace^  unremarkable  mated r e t u r n p e r i o d s  one hour,  during  r e l a t i v e l y heavy r a i n  near the end of the storm d u r i n g the a f t e r n o o n  showers  The  f o r periods  than  occurred periods on  during for a  F i g u r e 2.9.  one hour with  f o r longer d u r a t i o n s  esti-  from 2 t o  r e t u r n p e r i o d s ranged from 85 t o 95 y e a r s .  250  1200 OCT. 30  0000  I200 OCT. 31  DATE  F i g u r e 2.8.  Precipitation  0000  AND TIME  a t Terrace  1200 NOV. I  0000  (HOURS )  Airport  f o r O c t . 31 - Nov. 1, 1975  OONMEES SUR L ' 1 N T E N S I T E . L P  SMORt D U R R T I O N R P I N F P L L 1 N T E N S I T Y - D U R R T I O N FREOUENCY DPTP F O R PUREE E l L n FREQUENCE 0 E 9 CHUTES DE P L U I E DE COURTE DUREE P DPSED OH RECORDING R P 1 N CPUCE D P T P FOR THE P E R I O D BOSEE3 SUR L E 9 D0NNEE9 DU P L U V I O 0 R P P H E 9 POUR L P P E R I O D S  is  so  3a  eo  a  MINUTES  F i g u r e 2.9  DURRTI ON  DUREE  Intensity-Duration-Frequency  1869 - 1993  BC  16 YEPRS/PNS  is  e HOURS  TERRACE R  HEURE9  Curves f o r T e r r a c e  Airport  - 35  December, 1972 A storm 23  to  storm  Rainstorm a t Vancouver, B r i t i s h Columbia (Eddy,  began i n the  26  hours  produced  e a r l y morning hours on  at climatological the  largest  I n t e r n a t i o n a l A i r p o r t (92.9 while  other  -  stations in  December 25  s t a t i o n s i n the  and  Vancouver  24-hour  precipitation  mm)  i n Vancouver's c i t y c e n t r e  the  and  area  experienced  on  near  record  record  storm caused e x t e n s i v e f l o o d i n g i n the g r e a t e r Vancouver  During  the morning of December 25th, a deep low  northward  over  the  aloft  with  winds  Queen  Charlotte  the  Alaska  air  continued  from  of  the  Islands.  coast,  Precipitation  Gulf  the  Ah  southwest  was  While  frontal  eastward ended  Alaska.  across  quite  the  deep  time d i s t r i b u t i o n s  of  Vancouver  abruptly  storm tion  rainfall  low,  longer  esting 951  m  1972.  to  duration  note  p l o t t e d on  for durations  amount exceeding  an that  overlooking  this  over  the  recorded  on  were  snow changed  moving  across  mainland  passed  and  the  towards of  warm  coast. a  weak  The  show t h a t while  with  higher  to r a i n  relatively  the  24-hour  It i s inter-  elevation station e a r l y on  The  precipita-  hours were  extreme  in  return periods for  f o r Vancouver A i r p o r t .  more  a  The  area.  about two  Ridge,  mm)  warm a i r  tongue  50-year r e t u r n p e r i o d event.  Hollyburn  Vancouver,  than  of  to move  the  system  (141.5  amounts.  lying  the  and  This  area was  continued  F i g u r e 2.10.  F i g u r e 2.11  less  intensities  estimated  time  area.  at Vancouver A i r p o r t and  are shown on F i g u r e 2.11  characteristics intensities  low  Island  when  Vancouver's c i t y c e n t r e are shown on a range of d u r a t i o n s  this  from  a t Vancouver  tongue  wave a s s o c i a t e d with  r i d g e of h i g h p r e s s u r e began to b u i l d  The  at  lasted  area.  pressure  associated  1979)  December  at 25,  F i g u r e 2.10.  Precipitation  i n Vancouver Area on December 25,  1972.  - LZ -  - 38 -  Probable Maximum P r e c i p i t a t i o n - C o q u i t l a m Lake watershed  (Schaefer,1981)  An  analysis  the g e n e r a t i o n  of  a probable maximum f l o o d  shed  of meteorological conditions associated  located  tions  was undertaken  with  f o r the Coquitlam Lake  water-  a p p r o x i m a t e l y 30 km n o r t h e a s t of downtown Vancouver.  i n the 181 s q km b a s i n range  r e a c h i n g 1400 m around  from  Eleva-  153 t o 2000 m with s e v e r a l  peaks  the drainage b a s i n boundary.  As p a r t o f the study, the most extreme p r e c i p i t a t i o n events on r e c o r d f o r d u r a t i o n s o f one to four days were analyzed a t Coquitlam Lake and Vancouver  International  Airport.  At Coquitlam  were a n a l y z e d f o r the p e r i o d ver  International  to  1981.  occurred seven  The  Although events  eight  during  events  Airport  most  differed frontal  s o u t h w e s t e r l y a i r flows  considered Weather  contributing  extreme from  from  study  aloft.  through  to case.,  surface  instability  which  concluded  five  lyzed  largest  one day storms  f o r the two s t a t i o n s  f o r each  severe  in  all  and s t r o n g  was r u l e d  i s consistent that  January.  features areas  Lake  while the  through  common  low p r e s s u r e  finding  from 1937  February,  t o the t o t a l p r e c i p i t a t i o n This  events  a t Coquitlam  o c c u r r e d from October  were not a f a c t o r i n the r e g i o n west o f the Cascade  The  multi-day  1924 t o 1981, and a t Vancou-  analyzed  November  Vertical  factor  (1966)  events  case  waves,  i n the a n a l y s i s .  Bureau  eight  seven m u l t i - d a y events were analyzed  a t Vancouver A i r p o r t  included  significant  of r e c o r d from  the p e r i o d  details  Lake  out as a  i n a l l storms with  a U.S.  thunderstorms  Mountains.  c a l e n d e r month were a l s o  i n c o n j u n c t i o n with recorded  ana-  temperature and  - 39 -  moisture each  data  storm.  maximum  to estimate Based  on t h i s  precipitation  developed  the maximum analysis  (PMP) would  f o r the r e l a t i v e  amount  precipitable  water  i t was concluded occur  that  i n December,  of p r e c i p i t a t i o n  available  that  in  the probable  and r a t i o s could  were  occur i n  other months of the y e a r , Table 2.5.  TABLE 2 . 5 MONTHLY ADJUSTMENT FACTORS FOR PROBABLE MAXIMUM P R E C I P I T A T I O N  JAN  FEB  MAR  APR  MAY  JUN  JUL  AUG  SEP  OCT  NOV  DEC  0.91  0.76  0.68  0.62  0.59  0.58  0.59  0.65  0.78  0.91  0.99  1.00  0.85  0.69  0.59  0.54  0.48  0.46  0.49  0.56  0.69  0.83  0.96  1.00  Coqu I t l am Lake Vancouver International Airport  - 40 -  F l o o d of December 1964 During along  the  period  coastal  between ienced  the  Coastal  which  occurred  have  agricultural more flood  Prior  to  Pacific  in  land  than  was  $65  the  record  River  valley  ranges.  during  Many  this  low  region.  the  and ocean  coast.  c o a s t caused  The  second In  the  largest  flood  Willamette  inundated, three l i v e s  million.  Initial  Along  coastal  exper-  and  i t is  on  record  Pacific  storm  storms  a  85,000 ha  were l o s t  flood  Oregon  high  and  six lives  pressure  consisted  with  at s u c c e s s i v e l y lower  the storm systems  of  losses  were  airmass  area between Hawaii  located  M i x i n g of warm moist  that  River v a l l e y  precipitation  and  high  behind  lost  million.  storm  temperatures  allowed  rivers  lies  r e g u l a t i o n , the peak f l o w on the W i l l a m e t t e  December 19-23  by  occurred  which  period  airmass spread over Oregon from December 14-18  December 20  west  Mountain  on  extensive flooding  Willamette  l o s s e s were more than $60  accompanied  across  the  1861.  much of the ground.  the  Cascade  floods  been  the  1964  Ocean occupied most of the ocean  An a r c t i c  of  and  in  that without f l o o d  would  and  December 19-23, and  largest  River  were  from  Oregon  their  estimated  i n C o a s t a l Oregon (Waananen e t a l , 1971)  and p a r t l y  latitudes  a i r with  to i n t e n s i f y .  cold  froze  from December 18-20  largely  moist  the  and A l a s k a .  tropical as  was  of snow over much  n o r t h e a s t of Hawaii  warm  over  eroded  a i r to  they approached  Arctic  on  move the  a i r west of the  - 41  From to  December  3000 m  21-23  causing  temperatures almost  River  the  d u r i n g December  in 150 550  the  Cascade Range.  to mm  basin  280 mm in  for  the  the  storm 19-23  same  Range.  The  flows  rainfall  river  r u n o f f was  increased  the  twenty-fold  region  from  showed  combined  stations.  resents  flood  50  a  years.  the  two-fold The  with  sentative  to  mm  with  this  of r a i n along  discharge  with  rain.  380 mm  of  to higher  rates  rose  In  the  rain  to  altitudes  the c o a s t ranged  i n excess  was  snowmelt.  start  of  the  extremely  as  of  from  high  as  200 mm  in  as  heavy  i n some i n s t a n c e s ,  flows  storm  on  rapid  December  19  to  a  of f l o o d hydrographs f o r many s t a t i o n s  increases  in  discharge  f l a s h y nature of streamflow  flood  as  much as  snowmelt i s i l l u s t r a t e d  Each  occur  levels  p o i n t measurements  storm  by  Examination  s h o r t as f o u r h o u r s . rainfall  460  freezing  s t a t i o n s i n Oregon.  supplemented  peak on December 22. in  and  to  as  Precipitation  a t a few  of  brought  period  24-hours were recorded  response  s h a r p l y and  Average p r e c i p i t a t i o n  the  Coast  rose  a l l precipitation  Willamette valley  -  hydrograph an  estimated  on  over  periods  as  response  to extreme  F i g u r e 2.12  f o r repre-  plotted  on  F i g u r e 2.12  return period  of  at  repleast  - 42 -  F i g u r e 2.12.  Rain-On-Snow Flood  Hydrographs  - 43 -  2.4 1)  SUMMARY A single entire  hydrologic region exists  along  the c o a s t which extends the  l e n g t h of the p r o v i n c e and i n c l u d e s s o u t h e a s t  A l a s k a , and i s  bounded t o the e a s t by the c r e s t of the C o a s t a l Mountain range.  2)  C l i m a t i c features trends and  i n precipitation  winter.  Within  with  A relatively  the w e t t e s t  small  annual  the c o a s t a l r e g i o n , however, l o c a l  cipitation  and temperature  atmospheric  circulation  distributed  3)  i n the c o a s t a l r e g i o n  include months  and  occurs.  variations  exist  i n pre-  interaction  between  major  topographic  form  over  Gulf. and  features  along the c o a s t .  macro-scale  pressure  in fall  range  The c l i m a t e of the c o a s t a l r e g i o n i s c o n t r o l l e d by  occurring  annual  temperature  due to the complex  patterns  consistent  atmospheric  areas  over  the G u l f  the P a c i f i c  During  of Alaska  Ocean and move from  summer months  the i n t e n s i t y  processes.  and  a high  frequency  on a seasonal  During cause  winter  basis  months  numerous  low  storms to  the southwest towards the  pressure  of P a c i f i c  centre  forms o f f - s h o r e  storms  i s diminished  compared t o w i n t e r .  4)  Detailed' meteorologic storms and  i n the c o a s t a l r e g i o n  will  areas  analyses  result  from  storm  conclude  will  occur  that during  systems which develop  the  most  the w i n t e r from  extreme months  low p r e s s u r e  o f f s h o r e and g e n e r a l l y approach the c o a s t from the southwest.  - 44 -  5)  Extreme f l o o d s o c c u r i n the f a l l in  the c o a s t a l  fall-induced  region.  floods  These  result  and w i n t e r on most d r a i n a g e b a s i n s floods  from  are r a i n f a l l - i n d u c e d .  rainfall  runoff  only  or  Rainfrom  a  combination of r a i n and snowmelt r u n o f f .  6)  For those both  a  flood  stations  i n coastal  fall/winter regime,  rainfall  extreme  British and a  Columbia  determined  spring/summer  rainfall-induced  floods  to have  snowmelt-induced are  greater  than  those e s t i m a t e d on the same b a s i n f o r snowmelt f l o o d s .  7)  Any h y d r o l o g i c a n a l y s i s to  predict  fall and  extreme  undertaken  floods  must be capable  r u n o f f and r u n o f f r e s u l t i n g snow.  tions  to model c o a s t a l b a s i n s i n order  from  of s i m u l a t i n g  the i n t e r a c t i o n  both  between  A model of these r u n o f f processes must undertake  w i t h a time  s t e p much  less  the f l a s h y nature of most c o a s t a l  than  rainrain  calcula-  one day i n order to s i m u l a t e  floods.  - 45  -  3.  CHARACTER!STICS OF STORM RAINFALL IN THE COASTAL REGION  3.1  INTRODUCTION  An assessment of storm B.C.  s i n c e extreme  during  fall  engineer  rent  are  as  do  and  situations  not  Major  in  long  the  stations  intensities  i n data  shown on F i g u r e 3.1  report  are not  described  of  primary  used  to  able. coastal  goal  identifying  estimate  The  premise  region  following:  of  rainfall  extending  24-hour  above  are  pre-  regions;  most  data  data  in cur-  cannot  be  to mountainous  so  that  not  easily  shorter  overcome.  a rainfall  frequency  g e n e r a l trends i n the  rainfall  distribution  One atlas  distribu-  E n g i n e e r i n g d e s i g n i n the  i n this  coastal  data  at a  chapter  was  undertaken  with  regional characteristics  i n i n s t a n c e s where  the  the  available.  presented  t h a t such  remote  long d i s t a n c e due  only  i n B.C.  data  practicing  include:  records; a v a i l a b l e  (1985) produced  rainfall  in  the  e l e v a t i o n s ; many s t a t i o n s  however, r e q u i r e s more d e t a i l e d  Analysis  rainfall-induced  facing  region  sparse  which i l l u s t r a t e s  o f 24-hour p r e c i p i t a t i o n  are  in coastal  available.  much l a r g e r s c a l e than i s c u r r e n t l y  the  coastal  low  term  basins  obstacles  c o n f i d e n c e over  study by Hogg and C a r r  region,  drainage  is relatively  have  with  many  shortcomings  tion  most  located at r e l a t i v e l y  d u r a t i o n storm  recent  i s required for flood analysis  months.  network  transposed  terrain;  The  winter  gauge  operation  readily  f l o o d s on  i n design  cipitation stations  and  rainfall  local  data  c h a r a c t e r i s t i c s might e x i s t length  of  the  province  which are  not  can  be  avail-  f o r the d i v e r s e  was  based  on  the  F i g u r e 3.1  Twenty-Four Hour P r e c i p i t a t i o n  i n B r i t i s h Columbia ( a f t e r Hogg and C a r r ,  1985)  - 47 -  i ) atmospheric Chapter 2  pressure suggest  maps  similar  presented macro-scale  c l i m a t e along the e n t i r e c o a s t a l  i i ) monthly  precipitation  Table 2.1  on  data  F i g u r e s 2.3  circulation  and  patterns  for coastal  i n Chapter 2 i l l u s t r a t e  B.C.  t h a t even  stations though  t i o n on a percentage b a s i s i s s i m i l a r among the  two  storm in  o b s e r v a t i o n s noted  rainfall  the monthly  then  perhaps  Ratios  of  duration  presented  trends  rainfall are used  The  depth  prompted  i n the f o l l o w i n g  also  be  for a  the  the magnitude of distribu-  stations.  region-wide  sections.  approach  identified  for  given duration  i n the a n a l y s i s  amount of r a i n f a l l  3.2  can  affect  presented i n  analysis  rather  storm  to  that  than r a i n f a l l  to i d e n t i f y i n g  of  That i s , i f t r e n d s  d i s t r i b u t i o n of p r e c i p i t a t i o n e x i s t i n the c o a s t a l  T h i s method i s one the  above  in  region.  p r e c i p i t a t i o n v a r i e s c o n s i d e r a b l y along the c o a s t , monthly  The  2.4  region,  precipitation. of  a reference  magnitude a l o n e .  r e g i o n a l c h a r a c t e r i s t i c s when  i s q u i t e d i f f e r e n t between  stations.  OVERVIEW OF PRECIPITATION SYSTEMS following  section,  prior  coastal  B.C.,  storms.  Oke  classification  discussion  of  precipitation  to p r e s e n t i n g a n a l y s i s to  provide  (1978) system  used for  an a  systems  undertaken  i s included with  rainfall  overview  of  the  nature  consensus  of  the  literature  atmospheric  phenomena  and  based  in  this  data i n  structure to on  develop  of a  horizontal  - 48 -  scales. scale  Braun  in  and  their  Slaymaker  discussion  (1981)  of  incorporated  atmospheric  and  hydrologic  g e n e r a l , atmospheric phenomena can be c l a s s i f i e d  i ) Macroscale  (or s y n o p t i c  scale)  z o n t a l s c a l e s o f 100-10 000 km Examples  of  this  scale  basis  map  analysis  which  low  of  systems.  In  follows:  include  those  and  with  hori-  h i g h - p r e s s u r e systems  regions f o r a period  prediction  reduces  concepts  and l i f e t i m e s from one day to a week.  include  f o r weather  as  processes  o f t e n a f f e c t weather over l a r g e The  similar  a t the s y n o p t i c  vast  amounts  of  of a few  scale  data  which  is  into  days.  weather-  meaningful  p a t t e r n s t h a t can be i n t e r p r e t e d by a m e t e o r o l o g i s t .  i i ) Microscale processes order of 1 cm several form  include  to 1 km  minutes.  from d i f f e r e n t i a l  phenomena  caused  an  of m i c r o s c a l e motion  such  as  rapid  horizontal  a i r flowing  growth,  varying  include  scales  over  rough  and possess  v i g o r o u s u p d r a f t s and  in  the  from a second  convection  cells  h e a t i n g of a d j a c e n t airmasses and  turbulence example  with  and with time s c a l e s  These  by  those  terrain. typical  to  which  mechanical  Tornados  are  characteristics  downdrafts,  and  random  movement.  i i i ) Local and  and  mesoscale  macroscale  processes include  phenomena  100 m  to 500 km  with a  scale  processes  include  squall  and  time  have scale  land-sea  l i n e s of thunderstorm  those which  horizontal up and  activity.  l i e between micro  scales  to a day.  ranging  Examples  mountain-valley  from  of meso-  breezes,  and  - 49 -  In a d d i t i o n , p r e c i p i t a t i o n according 1982).  to the primary  i s usually divided into  mode causing  uplift  These c a t e g o r i e s of p r e c i p i t a t i o n  i ) Convective  precipitation  results  precipitation  horizontal In  convergence  some i n s t a n c e s  along an airmass  i i i ) Orographic passes  for  motion For  this  precipitation  i s caused  topography  also  trigger  convective  tain  slopes,  increase  and cause  airstreams.  of  m  i n an area  a i r through  of low p r e s s u r e . of warm moist a i r  of an airmass  cyclonic  a convenient  as i t  for analytical are a f f e c t e d  study. by  framework  In r e a l i t y ,  many  scales  and which c o n t i n u o u s l y change with may  instability  uplift  by u p l i f t i n g  above p r o v i d e  observations  occurring simultaneously  movement,  the ascent  rises.  feature.  phenomena d e s c r i b e d  rising  column  i s gener-  boundary.  meteorological  example,  instability  i s r e i n f o r c e d by u p l i f t  c a t e g o r i z i n g p h y s i c a l processes  however,  by  of airstreams  over a t o p o g r a p h i c  Meteorological  are d e s c r i b e d below:  and the airmass  i s caused  types  of a i r (Barry and C h o r l e y ,  when a l o c a l  ated as a p o r t i o n of a i r i s heated  i i ) Cyclonic  three p r i n c i p a l  induce  orographic  from  differential  precipitation  through  of -  time.  p r e c i p i t a t i o n but heating  of moun-  by r e t a r d i n g the r a t e of  funnelling  effects  of v a l l e y s  on  - 50 -  The  structure  couver  and  region  in coastal  radar-derived was  limited  patterns typical range  evolution  of  B.C.  precipitation to  the  observed by Bonser  of s c a l e s  i i ) Mesoscale.  as they impinge  was  i i i ) Microscale. fall  the r a i n f a l l  Radar  data  provide decay  a  of c e l l s  was  approached  though  characteristics  (1982) based the of  study  on  area  precipitation  i n a q u a l i t a t i v e manner as  on c o a s t a l  B.C.  mountains.  The storm  from a low p r e s s u r e system pass-  identified  as  a  band  moving  patches ahead  the mountains  north  i n the  of the  front.  of Vancouver i t  to other p o r t i o n s of the system behind i t .  appeared  convective to remain  cells  formed  within  i n the same p o s i t i o n  broad  rain-  relative  to  band.  t o g e t h e r with means  Even  and as i r r e g u l a r  Individual  areas and  Bonser  area.  of the f r o n t  retarded r e l a t i v e  by  the Van-  phenomena observed f o r a s i n g l e  resulted  Precipitation  band  they approached  below:  Precipitation  rainfall  as  can be c o n s i d e r e d  i n g over the Vancouver  a  examined  region,  i s described  i ) Macroscale.  As  were  of m e t e o r o l o g i c a l  i n December 1980  direction  storms  measurements.  Vancouver  f o r many storms  five  of  data  examining  within  the  processing  movement of  system.  and storm  visual  display  systems  Unfortunately,  and  software  growth  and  the radar s t a t i o n i n  - 51 -  Abbotsford,  B.C. used by Bonser i n h i s study ceased o p e r a t i o n i n 1982 and  t h e r e i s c u r r e n t l y no s t a t i o n o p e r a t i n g anywhere i n B r i t i s h  The  interaction  cult  of d i f f e r e n t  s c a l e s o f motion i s one o f the most  problems o f q u a n t i t a t i v e meteorology,  treat  of k i l o m e t r e s  (Anthes  e t a l . , 1978).  models,  data  source  recorded  i n size Lacking  at rain  of information a v a i l a b l e  and  from  adequate  gauge  range  from  seconds  radar  networks  f o r storm  diffi-  as i t i s not y e t p o s s i b l e to  n u m e r i c a l l y a l l r e l e v a n t s c a l e s which  thousands  Columbia.  a c e n t i m e t r e to  to months  techniques  remain  in  time  and p h y s i c a l  the most  important  a n a l y s i s by e n g i n e e r i n g  hydro-  logists .  3.3  SOURCE OF B.C. RAINFALL INTENSITY DATA  Rainfall  data  for  stations  58 s t a t i o n s Data  throughout (Table  analyzed  computer and  are a v a i l a b l e  to undertake  Canada.  3.1) a t which  i n this  programs  from  study  were  Atmospheric  Environment  S e r v i c e (AES)  In c o a s t a l  B.C. there  are c u r r e n t l y  rainfall  intensity  data  provided  by AES on magnetic  were w r i t t e n t o e x t r a c t p e r t i n e n t data  are r e c o r d e d .  from  tape and the tape  c a l c u l a t i o n s with these data as d e s c r i b e d i n the f o l l o w -  ing s e c t i o n s .  Of  the 58 c o a s t a l  Mainland  area,  tributed  across  the  coastal  pared zation  B.C. s t a t i o n s ,  27 a r e l o c a t e d i n the Vancouver/Lower  6 i n the V i c t o r i a / S a a n i c h P e n i n s u l a the remainder  of the r e g i o n .  r e g i o n o u t s i d e o f the Vancouver  area  and 25 are d i s -  The network  and V i c t o r i a  density for  areas  i s com-  i n Table 3.2 t o recommendations by the World M e t e o r o l o g i c a l O r g a n i (WMO,  1970).  - 52 -  TABLE 3.1 COASTAL B.C. STATIONS WITH RAINFALL INTENSITY DATA  Location North West Latitude Longitude  Elev. (m)  Abbotsford A A g a s s i z CDA A l o u e t t e Lake A l t a Lake Bear Creek  49 49 49 50 48  02 15 17 09 30  122 121 122 122 124  22 46 29 57 00  58 15 117 668 351  7 26 13 13 7  B e l l a Coola Hydro Buntzen Lake Bur nab y Mtn BCHPA Campbell R i v e r BCFS Campbell R i v e r BCHPA  52 49 49 50 50  22 23 17 04 . 03  126 122 122 125 125  49 52 55 19 19  14 17 465 128 30  14 15 9 10 11  C a r n a t i o n Creek C h i l l i w a c k Microwave Clowhom F a l l s Com ox A Coquitlam Lake  48 49 49 49 49  54 07 43 43 22  125 121 1 23 124 1 22  00 54 32 54 48  61 229 23 24 1 61  7 17 15 14 13  Courtney Puntledge D a i s y Lake Dam Estevan P o i n t Haney Microwave Haney UBC  49 49 49 49 49  41 59 23 12 16  125 123 126 1 22 122  02 08 33 31 34  24 381 7 320 143  20 15 10 20 20  Jordan R i v e r D i v e r s i o n Jordan R i v e r G e n e r a t i n g Kitimat Ladner BCHPA Langley L o c h i e l  48 48 54 49 49  30 25 00 05 03  124 124 128 123 1 22  00 03 42 03 35  393 5 17 2 1 01  10 11 10 13 12  M i s s i o n West Abbey Nanaimo Departure Bay North Vane. Lynn Creek P i t t Meadows STP P i t t Polder  49 49 49 49 49  09 13 22 13 18  122 1 23 123 1 22 122  16 57 02 42 38  221 8 191 5 2  21 1 3 19 9 19  Station  No. of Years of Record  - 53 -  TABLE 3.1 (continued) COASTAL B.C.  STATIONS WITH RAINFALL INTENSITY DATA  Station Port Port Port Port Port  Alberni A C o q u i t l a m C i t y Yard Hardy Mellon Moody G u l f O i l Ref.  Location North West Latitude Longitude  Elev. (m)  No. of Years of Record  49 49 50 49 49  15 16 41 31 17  124 122 127 123 1 22  50 46 22 29 53  2 7 22 8 1 30  15 13 10 11 13  P o r t Renfrew BCFS P r i n c e Rupert A Saanich Densmore Sandspit A Spring Island  48 54 48 53 50  35 18 30 15 00  124 1 30 123 131 127  24 26 25 49 25  6 34 38 5 11  11 14 10 12 8  Stave F a l l s S t r a t h c o n a Dam Surrey Kwantlen Park. Surrey M u n i c i p a l H a l l Terrace A  49 50 49 49 54  14 00 12 06 28  1 22 125 122 122 128  21 35 52 50 35  55 201 93 76 217  8 15 22 20 15  T e r r a c e PCC Tofino A Vancouver A Vancouver Harbour Vancouver K i t s i l a n o  54 49 49 49 49  30 05 11 18 16  128 125 .123 1 23 123  37 46 10 07 11  58 20 3 0 23  15 V3 31 8 30  Vancouver PMO Vancouver UBC V i c t o r i a Gonzales H e i g h t s Victoria Int. A V i c t o r i a Marine Radio  49 49 48 48 48  17 15 25 39 22  1 23 123 123 123 1 23  07 15 19 26 45  59 87 69 19 32  10 6 51 19 17  V i c t o r i a Shelbourne V i c t o r i a U. of V i c t . Whi te Rock STP  48 48 49  28 28 01  123 1 23 122  20 20 46  38 46 15  9 19 18  Canada  (1981b)  Note:  Station descriptions  from Environment  54  TABLE  3.2  DENSITY OF RAIN GAUGE NETWORKS  Recommendations by Flat  WMO:  regions  600-900 k m / s t a t i o n 2  Mountainous r e g i o n s  100-250 k m / s t a t i o n 2  Small mountainous i s l a n d s irregular precipitation British  with 25  Information presented fall  intensity  also  emphasizes rainfall  data  i n T a b l e 3.2  in coastal  that  analysis  B.C.  Even i n i n s t a n c e s when r a i n f a l l  the shortcomings  regard  less  This than  intensity  summary  15  30 years of r e c o r d .  years  rain-  to network d e n s i t y .  undertaken  without  data  It  requirfrom  the  surrounding area.  i n t e n s i t y data are a v a i l a b l e from a  Lengths  of r e c o r d f o r the 58  local  undertake stations  i n the c o a s t a l r e g i o n are i l l u s t r a t e d  shows of  of  region, engineering design  to be  a n a l y s i s of the d a t a .  record r a i n f a l l  F i g u r e 3.2. have  2  the p e r i o d of r e c o r d i s o f t e n too s h o r t to c o n f i d e n t l y  statistical which  2  with  f o r much of the o f t e n has  225 000 km /25 s t a t i o n s = 9 000 k m / s t a t i o n  illustrates  p r o j e c t s i t e or from the immediately  station  2  Columbia:  Coastal region excluding Vancouver and V i c t o r i a a r e a s :  ing  km /station  data  that and  over only  half two  of  the  stations  coastal have  on  stations more  than  - 55 -  0  ' 0  1  1  10  1  20  30  NUMBER OF STATIONS EQUAL  F i g u r e 3.2  In  a d d i t i o n to  are data  the  (Environment  24-hour  OR  40  WITH  GREATER  250  58  s t a t i o n s which  characteristics stations  record  s t a t i o n s i n c o a s t a l B.C.  Canada,  could  1981a). of  then  c u r r e n t l y a v a i l a b l e f o r design  A  VALUE  used  purposes.  60  RECORD SHOWN  rainfall  intensity,  there  which r e c o r d o n l y 24-hour  intensity to  1  Stations  particular  rainfall be  50  L E N G T H OF  THAN  Lengths of Record a t C o a s t a l B.C.  approximately  regional  TO  L-  1  b e n e f i t of would  g r e a t l y expand  be the  identifying that data  these base  - 56 -  3.4  INTENSITY-DLTRATION-FREOLTENCY CORVES  3.4.1  Development and Dse of IDF Curves  Intensity-duration-frequency Environment  Service  record  rainfall  curves  a t each  maximum  series  minutes each  curves  A  f o r each  intensity. station of  to 24 hours,  annual  (IDF) curves  maximum  of  The  the  procedure  IDF curve  y s i s and i l l u s t r a t e f i t lines  rainfall  intensities  conducting series,  i s important  used  B.C.  by  AES  from  a  which  data  IDF  annual  ranging  frequency  generating  Atmospheric  to develop  recorded  f o r durations  finally  by  AES  i s shown  from  5  a n a l y s i s with  s e t of b e s t f i t  with  p o i n t s with  the same r e t u r n p e r i o d  relationship for a particular  intensities within  return  f o r durations  from  the same storm  return period.  curves  provide  average  period,  b u t do not p r o v i d e  period.  i n t e n s i t i e s within a single  intensity  f o r another  i s , the s e t o f  to 24 hours  given  rainfall  do not g e n e r a l l y  the 24-hour r a i n f a l l  for a  information storm.  t o the i n t e n s i t y  That  5 minutes  intensities  that since  f o r each d u r a t i o n , r a i n f a l l  t o produce  anal-  illustrate  t o r e c o g n i z e i n the development of IDF curves  the same  Plotted  r e l a t i o n s h i p f o r that d u r a t i o n .  one d u r a t i o n i s not n e c e s s a r i l y r e l a t e d  duration  on F i g u r e 3.3.  of the extreme value frequency  the "depth-frequency"  annual maximum s e r i e s are generated  occur  stations  an extreme v a l u e  and  produced  connecting  the " d e p t h - d u r a t i o n "  for  coastal  c o n s i s t s of producing  p o i n t s f o r each d u r a t i o n are r e s u l t s  It  by  f o r s e l e c t e d r e t u r n p e r i o d s and f o r the range of d u r a t i o n s .  typical  Best  58  are prepared  duration  regarding v a r i a t i o n s  depth. and  IDF  return  in rainfall  - Z.S -  - 58 -  Use  of  IDF  analysis  has  1982). was  relationships  One  been  widely  procedure  originally  to  develop  synthetic  incorporated  i n Canadian  i s commonly r e f e r r e d  proposed  by  Keifer  i s generated  such  and  (1957).  throughout the storm d u r a t i o n of i n c r e m e n t a l r a i n f a l l  sent  sequence  a  from  of  the  Chicago  a variety  the  of storms in a  and  single  generally  storm.  time  sequence  of r a i n f a l l  relative  of peak i n t e n s i t y w i t h i n  for a synthetic  oped  method  intensities appears  An  alternative  symmetrically with  quite  recommended  arbitrary,  by  the  U.S.  time.  i t has Bureau  been of  Even  not  storm  storms on r e c o r d  a guide f o r c h o o s i n g the time sequence curves.  do  intensities  The  IDF  intensities  applied  records.  hyetograph  this  second  extensively  Reclamation  within  i s used  i s to d i s t r i b u t e  though  repre-  for design.  d e s i g n storm i s determined from a n a l y s i s of h i s t o r i c a l  from  i s com-  Nevertheless, this  the  timing  a  As noted above, however, IDF curves are de-  intensities  method  and  method  hyetograph  procedure i s used p a r t l y because of l i m i t e d a l t e r n a t i v e s  In  (McKelvie,  this  prised  w i t h data  resulting  In  storm  veloped  flood  to as the Chicago method  Chu  the  for  practice  design  with the same r e t u r n p e r i o d .  that  hyetographs  (USBR,  and  1977)  as  devel-  rainfall approach is  still  for  flood  studies.  Regional  characteristics  analyzing The  d e p t h - d u r a t i o n and  initital  extreme  of IDF curves are i n v e s t i g a t e d  data base  depth-frequency  consisted  v a l u e frequency a n a l y s i s ,  of r a i n f a l l prior  i n this  relationships depths produced  to e s t i m a t e s by  AES  study by  separately. by AES  from  of b e s t f i t  - 59 -  curves  included  acteristics fall given  to  the  are  on  IDF  assessed  24-hour  d u r a t i o n are  graphs. by  depth,  assessed  For  each  calculating and by  station  ratios  of  depth-frequency calculating  ratios  depth-duration  char-  short duration  rain-  characteristics to a  reference  for  a  depth  taken as the 10 y e a r p e r i o d .  Rainfall  depth-duration-frequency  data  are i n c l u d e d Ln Appendix I I f o r each  analyzed  in  of the 58 c o a s t a l  this B.C.  investigation stations.  - 60 -  3.4.2  Depth-Duration Relationships  3.4.2.1  Analysis of B.C. Data  Rainfall  intensity  relationship period  between  and to assess  coastal basis  region.  calculating  and  duration  of t h i s  "depth-duration"  relationships  ratios  depths  stations  included These  each  for  depth  the v a r i a b i l i t y  Regional  Rainfall  hours.  from AES are analyzed  to determine the  for a  relationship  given  return  throughout  characteristics  the  provide  a  f o r a range o f d u r a t i o n s i n i n s t a n c e s when  i s known o n l y f o r one d u r a t i o n .  Depth-duration  Depth  rainfall  f o r estimating r a i n f a l l  rainfall  for  data a v a i l a b l e  of  were o b t a i n e d  coastal  duration  rainfall  a t each  i n Appendix  rainfall  duration  ratios  short  f o r the  to  calculated  depths were used  by t h i s  to  are  the  procedure  with  of depth  return  are t a b u l a t e d  depth.  12 and 24  the r a t i o  the same  by  c o a s t a l B.C.  o f 1, 2, 6,  to c a l c u l a t e  depth  assessed  24-hour  of the 58 a v a i l a b l e  II f o r durations  the 24-hour  region  period.  i n Appendix I I  each i n d i v i d u a l c o a s t a l s t a t i o n .  Rainfall  data  and  depth-duration  ratios  calculated  for Pitt  southwestern  B.C. are i n c l u d e d i n T a b l e 3.3 t o i l l u s t r a t e  of  undertaken  analysis  show  that  the r a t i o  i n this  of r a i n f a l l  study.  These  on IDF curves  results  Polder i n  typical  results  for Pitt  Polder  f o r a given  the 24-hour depth i s r e l a t i v e l y c o n s t a n t with r e t u r n p e r i o d .  d u r a t i o n to  - 61 -  TABLE 3.3 DEPTH-DURATION DATA FOR PITT POLDER  R a i n f a l l Data (mm) From AES Duration 1 2 6 12 24  hr hr hr hr hr  2 1 2.4 18.9 42.7 67.3 98.9  5 1 4.7 22.9 51 .7 80.3 119.0  Return P e r i o d (Years) 25 10 16.2 25.4 57.7 88.9 1 32.2  18.1 28.7 65.3 99.8 149.0  50  19.1 31 .2 70.9 107.9 1 61 .5  100 20.9 33.6 76.4 115.9 1 73.8  Depth-Duration R e l a t i o n s h i p s Duration 1 2 6 12 24  hr hr hr hr hr  2  5  10  25  50  100  0.13 0.19 0.43 0.68 1 .00  0.12 0.19 0.43 0.67 1 .00  0.12 0.19 0.44 0.67 1 .00  0.12 0.19 0.44 0.67 1 .00  0.12 0.19 0.44 0.67 1 .00  0.12 0.19 0.44 0.67 1 .00  - 62 -  Examination of r e s u l t s of a n a l y s i s o f r a i n f a l l the r e g i o n period  i n t e n s i t y data from  across  shows d e p t h - d u r a t i o n r a t i o s have minimal v a r i a t i o n with  return  a t each of the a v a i l a b l e c o a s t a l  magnitude  o f these  relatively duration  depth  narrow range ratios  ratios  from  B.C. s t a t i o n s . a l l available  f o r the c o a s t a l  f o r 58 c o a s t a l  stations  region.  Furthermore, the stations  are i n a  Mean values  o f depth-  are l i s t e d  i n Table  3.4 and  shown g r a p h i c a l l y on Figure 3.4.  TABLE 3.4 DEPTH-DURATION RATIOS FOR IDF CURVES  Duration (Hours) 1 2 6 12 24  2 0.16 0.24 0.48 0.72 1 .00  Depth R a t i o s f o r C o a s t a l Return P e r i o d (Years) 5 10 25 50 100 0.16 0.23 0.46 0.69 1.00  0. 16 0. 23 0.45 0.68 1 .00  0. 16 0. 23 0.44 0.67 1 .00  0. 17 0. 23 0.43 0. 67 1 .00  0.17 0.23 0.42 0.66 1 .00  DURATION (HOURS)  Figure  3.4  Depth-Duration R a t i o s f o r IDF Curves  Region Mean Std. Dev. ( a l l values) 0.16 0.23 0.45 0.68 1 .00  0.06 0.06 0.06 0.05  - 63 -  These  results  are p a r t i c u l a r l y i n t e r e s t i n g  tude o f r a i n f a l l For  example,  ranges  varies  considerably  the 24-hour  from  75  storm  t o 380 mm  considering  between s t a t i o n s  rainfall  with  f o r the a v a i l a b l e  that  across  a 100-year 58 c o a s t a l  the magnithe r e g i o n .  return  period  stations;  mean  annual p r e c i p i t a t i o n a t these s t a t i o n s ranges from about 650 t o 3500  The  regional  ratios coastal site to  c h a r a c t e r i s t i c of IDF curves  i s especially B.C.  stations  useful  identified  for application  which  record  only  f o r depth-duration  to the a p p r o x i m a t e l y  24-hour  mm.  data.  When a  250  project  i s near one o f these s t a t i o n s , frequency a n a l y s i s can be undertaken provide  period. depths  an  estimate  of a  Then, d e p t h - d u r a t i o n f o r any  shorter  24-hour  rainfall  with  r a t i o s can be a p p l i e d  durations  which  may  be  a  desired  to estimate required  return rainfall  f o r design  purposes.  Depth-duration cluded range  ratios  from  other  regions  i n T a b l e 3.5 f o r comparison. of  ratios  within  this  range  regions  of B r i t i s h  has  been  Columbia.  These data  calculated  are d i s t i n c t  from  of B r i t i s h  Columbia  show t h a t  f o r the c o a s t a l those  ratios  are i n -  even though a region,  calculated  values  i n other  - 64  TABLE  -  3.5  COMPARISON OF DEPTH-DURATION RATIOS  Physiographic Region  Location Mean o f 58 S t a t i o n s C a s t e l g a r , B.C. Kamloops, B.C. F o r t S t . John, B.C.  B.C. Coast Southeast Mountains Interior Plateau Great P l a i n s  3.4.2.2  Formulas f o r B.C.  Data  Results  of  coastal  F i g u r e 3.4  analysis  provide a graphical  with  duration.  tion  which  are  users of the  Various  at  Chen  34  0.16 0.44 0.35 0.42  British  of how  p r o v i d e s formulas  i n a more c o n v e n i e n t  0.45 0.79 0.62 0.74  Columbia  description  format  12 hours  data  rainfall  relating  0.68 0.87 0.77 0.87  presented depth  depth  f o r programming  on  varies  and  dura-  purposes  by  results.  commonly a p p l i e d sities  This section  formulas  proposed.  of  Duration 6 hours  1 hour  which (1976)  relate  summarized  to r a i n f a l l  cities  depth  the main  data as p a r t  a c r o s s the  c u r r e n t l y a p p l i e d by AES  rainfall  duration  types of  formulas  have  These  formulas  data are i n c l u d e d i n Table  been  which  of a study of r a i n f a l l  United States.  to Canadian  to  are  inten-  and 3.6.  that  65  TABLE 3.6 FORMULAS RELATING RAINFALL DEPTH TO DURATION  No.  Equation  3.1  I =  3.2  Reference  t + b  Meyer  I =  Bernard (1932) concluded a f t e r a n a l y z i n g f u r t h e r much of the data initially reviewed by Meyer t h a t Eq. 3.1 i s only suitable for s h o r t d u r a t i o n s of about 5 to 120 minutes.  a  I =  a) Bernard  b)  3.3  (1921, 1928)  Comment  :t +  c  tP + c  I = rainfall  (1932)  Environment Canada (1983c)  Sherman  (1931)  a) Because of the apparent limitation of Eq. 3.1, Bernard proposed Eq. 3.2 f o r longer d u r a t i o n s o f 2 t o 24 hours.  b) AES a p p l i e s Eq. 3.2 to stations a c r o s s Canada f o r durations of 5 minutes to 24 hours, except where inspection of IDF curves shows the e q u a t i o n t o be inappropriate.  Sherman found Eq. 3.3 t o be a p p l i c a b l e f o r the complete range of d u r a t i o n s from 5 minutes t o 24 hours. Chen (1976) used Eq. 3.3 i n h i s study of r a i n f a l l intensities i n 34 c i t i e s i n the U.S.  K e i f e r and Chu (1957) Used by K e i f e r and Chu i n t h e i r development of a p r o c e dure f o r g e n e r a t i n g s y n t h e t i c hyetographs, commonly r e f e r red to as the Chicago Method.  intensity;  t = d u r a t i o n ; a, b and c = s t a t i o n  coefficients  - 66 -  Formulas form"  presented  types  reasonable based in  of r e l a t i o n s . to suppose  mostly  3.6 a r e g e n e r a l l y These  that  fitting  generally techniques  formulas  their  on precedent.  an e r a which  curve  i n Table  acceptance  predates  computer  likely  as " s t a n d a r d -  are a l l e m p i r i c a l  Considering that  were  considered  as standard  and i t  equations i s  the formulas were analysis,  very  simple  is  proposed  commonly  compared  applied  to  those  c u r r e n t l y i n u s e . Review o f Eq. 3.2 shows t h a t t h i s r e l a t i o n s h i p r e p r e sents a s t r a i g h t  line  developed  extension  as an  o f t e n do not p l o t 5 minutes are  on a l o g - l o g  commonly  of Eq. 3.2  as a s t r a i g h t  to 24 h o u r s . concave  plot.  line  Rainfall  Perhaps  because  over  intensity  data  an e n t i r e d u r a t i o n range  from  intensities  up or down over  Eqs. 3.3 and 3.4 were  rainfall  plotted  the 5-60 minute  on l o g - l o g range  scales  compared to  longer d u r a t i o n i n t e n s i t i e s .  Eq. 3.2 i s c u r r e n t l y a p p l i e d tions data the  a c r o s s Canada.  Fitting  by AES t o r a i n f a l l  rainfall  sta-  a curve i n the form of Eq. 3.2 to Canadian  f o r d u r a t i o n s ranging from following:  i n t e n s i t y d a t a from  5 minutes  intensity  data  t o 24 hours  results  f i t the curve w e l l  i n one of  over  the en-  t i r e d u r a t i o n range; the curve does not f i t the d a t a w e l l over the e n t i r e range  b u t i s n e v e r t h e l e s s c o n s i d e r e d by AES to be an a c c e p t a b l e a p p r o x i -  mation; AES  o r Eq. 3.2 does not f i t the data w e l l enough t o be recommended by  i n which case no a l t e r n a t i v e  intensity-duration  formula i s p r o v i d e d .  The c r i t e r i a d e s c r i b e d above are g e n e r a l l y a p p l i e d i n a s u b j e c t i v e manner by  AES based  1985).  on i n s p e c t i o n  of p l o t t e d  I n s p e c t i o n of IDF curves  c o a s t a l B.C. s t a t i o n s  rainfall  developed  intensity  data  (Hogg,  by AES f o r the 58 a v a i l a b l e  shows many s t a t i o n s are i n the second  category.  - 67  Based  on  assessment  empirical  equations  of  on  curves  B.C.,  in  in  this  tively, only  Eq.  3.2  1 to  available  was 24  of  hours  of  regional to  and  b  provided  intensity  in  Eq.  by  duration  r e s u l t s of  a nonlinear  and  applied  rainfall  Computing Centre  coefficients a  to  the  equations  applied  from the UBC  the  the  currently  intensity  inspection  investigation  from  late  coastal  procedures  relating  24-hour range and  -  for  a  these  by  5  develop  minute  methods on  are  to IDF  included  characteristics.  Alterna-  data  AES  to  not  curve  with  durations  fitting  (Moore, 1984) 3.2  AES  which  routine,  was  best  ranging  used  f i t the  NL2S0L,  to  calcu-  available  data.  A  summary  in  of  Table 3.7.  because  rain  Coefficient  i t reflects  coefficient of  c o e f f i c i e n t s derived  and  will at  vary the  Coefficient b  istic  i t shows the  for  quite  of  rainfall.  between same  each  is  magnitude  period. as  a  for  stations  station  i s more  coastal  variable For  which  because  in  the  a given  receive  intensity  representative  station is  of  a  included  coastal duration,  region this  d i f f e r e n t amounts varies  regional  with  return  character-  i n t e r r e l a t i o n s h i p between i n t e n s i t i e s a t a s t a t i o n  a range of d u r a t i o n s  with the  same r e t u r n  period.  TABLE 3.7 DEPTH-DURATION FORMULAS FOR COASTAL B.C.*  Station  2-years a b  5-years a b  Return P e r i o d 10-years 25-years a b a b  50-years a b  100-years a b  Abbotsford A A g a s s i z CDA A l o u e t t e Lake A l t a Lake Bear Creek  85 53 45 40 150  0.46 0.39 0.31 0.42 0.45  183 69 55 43 289  0.58 0.41 0.32 0.40 0.51  265 80 61 45 393  0.60 0.42 0.33 0.39 0.54  384 94 69 47 534  0.64 0.43 0.33 0.38 0.56  483 104 75 49 644  .0.67 0.44 0.33 0.38 0.57  588 115 82 51 757  0.69 0.45 0.33 0. 37 0.59  B e l l a Coola Hydro Buntzen Lake Burnaby Mtn BCHPA Campbell R i v e r BCFS Campbell R i v e r BCHPA  40 58 49 69 106  0.32 0.34 0.36 0.45 0.51  45 72 61 102 223  0.30 0.33 0.37 0.49 0.61  49 81 69 125 325  0.29 0.33 0.38 0.51 0.66  55 93 80 156 478  0.28 0.33 0.39 0.52 0.71  59 102 87 180 606  0.28 0.33 0.39 0.53 0.74  63 110 95 204 746  0.27 0.33 0.40 0.54 0.76  C a r n a t i o n Creek C h i l l i w a c k Microwave Clowhom F a l l s Comox A Coquitlam Lake  45 63 45 56 42  0.32 0.45 0.36 0.43 0.26  53 92 63 80 43  0.31 0.49 0.39 0.46 0.24  59 114 76 96 45  0.30 0.51 0.40 0.47 0.23  66 141 93 119 46  0.30 0.52 0.42 0.49 0.22  71 163 106 135 48  0.30 0.54 0.43 0.50 0.21  77 185 118 152 49  0.29 0.55 0.43 0.50 0.21  Courtney puntledge Daisy Lake Dam Estevan P o i n t Haney Microwave Haney UBC  44 46 79 67 51  0.37 0.37 0.36 0.41 0.35  57 85 99 87 61  0.38 0.44 0.36 0.42 0.36  65 115 112 101 69  0.39 0.47 0.36 0.43 0.36  77 155 128 119 78  0.39 0.50 0.36 0.44 0.36  85 187 140 1 32 85  0.40 0.52 0.36 0.44 0.36  93 220 152 145 91  0.40 0.53 0. 36 0.45 0.36  112 44 45 52 71  0.39 0.34 0.32 0.45 0.45  174 46 51 65 101  0.42 0.32 0.30 0.46 0.48  218 47 55 74 1 23  0.43 0.30 0.29 0.47 0.49  275 49 60 85 152  0.44 0.29 0.29 0.48 0.51  318 50 64 94 174  0.45 0.28 0.28 0.48 0.52  361 52 69 102 198  0.45 0.27 0.28 0.49 0.53  Jordan R i v e r D i v e r s i o n Jordan R i v e r G e n e r a t i n g Kitimat Ladner BCHPA Langley L o c h i e l  TABLE 3.7 DEPTH-DURATION FORMULAS FOR COASTAL (continued)  B.C.*  r Station  2-years a b  5-years a b  Return P e r i o d 10-years 25-years a b a b  50-years a b  100-years a b  M i s s i o n West Abbey Nanaimo Departure Bay North Vancouver Lynn Creek P i t t Meadows STP P i t t Polder  95 72 52 71 47  0.47 0.50 0.31 0.43 0.33  151 201 58 125 54  0.52 0.63 0.29 0.48 0.32  194 313 62 165 59  0.55 0.68 0.28 0.50 0.32  251 474 67 217 66  0.57 0.72 0.27 0.53 0.32  296 603 71 258 71  0.59 0.75 0.27 0.54 0.31  342 740 75 299 75  0.60 0.77 0.26 0.55 0.31  Port port Port Port Port  45 46 33 73 39  0.34 0.35 0.29 0.33 0.32  74 58 32 75 51  0.39 0.36 0.25 0.31 0.33  96 66 32 76 58  0.42 0.37 0.23 0.30 0.34  128 76 32 78 68  0.45 0.38 0.22 0.29 0.35  153 84 33 80 75  0.47 0.39 0.21 0.28 0.35  180 91 33 82 83  0.48 0.39 0.20 0.27 0.35  P o r t Renfrew BCFS P r i n c e Rupert A Saanich Densmore Sandspit A Spring I s l a n d  73 55 34 66 61  0.30 0.37 0.36 0.45 0.34  1 25 55 35 79 68  0.36 0.33 0.33 0.45 0.32  165 56 36 88 73  0.39 0.31 0.32 0.45 0.31  220 57 38 99 79  0.42 0.30 0.31 0.45 0.30  263 58 39 107 83  0.43 0.28 0.30 0.46 0.30  308 60 40 114 88  0.45 0.28 0.29 0.46 0.30  Stave F a l l s S t r a t h c o n a Dam Surrey Kwantlen Park Surrey M u n i c i p a l H a l l Terrace A  50 84 59 50 68  0.35 0.48 0.41 0.41 0.47  49 146 85 78 91  0.31 0.52 0.43 0.45 0.47  48 191 103 97 106  0.29 0.55 0.45 0.47 0.48  49 254 126 123 125  0.27 0.57 0.46 0.49 0.48  50 302 143 143 139  0.26 0.58 0.46 0.50 0.48  50 352 160 163 1 54  0. 25 0.60 0.47 0.51 0.48  T e r r a c e PCC Tofino A Vancouver A Vancouver Harbour Vancouver K i t s i l a n o  45 78 68 95 47  0.42 0.36 0.47 0.49 0.39  85 88 92 182 58  0.47 0.35 0.49 0.57 0.39  114 95 108 252 65  0.49 0.35 0.50 0.61 0.39  151 103 129 353 74  0.51 0.35 0.50 0.65 0.39  179 110 145 436 80  0.51 0.35 0.51 0.68 0.39  207 116 160 522 86  0.52 0.35 0.51 0.69 0.39  Alberni Coquitlam C i t y Yard Hardy Mellon Moody Gulf O i l R e f i n .  TABLE 3.7 DEPTH-DURATION FORMULAS FOR COASTAL B.C.* (continued)  Station M i s s i o n West Abbey Vancouver PMO Vancouver UBC V i c t o r i a Gonzales Heights Victoria Int. A V i c t o r i a Marine Radio V i c t o r i a Shelbourne V i c t o r i a U. of V i c t o r i a White Rock STP  Mean S t d . Dev  * i n t e n s i t y - d u r a t i o n equation  2-years a b  5-years a b  Return P e r i o d 10-years 25-years a b a b  50-years a b  100-years a b  95 43 60 36 42 43  0.47 0.36 0.44 0.39 0.40 0.37  151 44 87 41 47 55  0.52 0.33 0.47 0.36 0.38 0.37  194 45 106 44 50 63  0.55 0.31 0.49 0.35 0.37 0.38  251 47 131 49 54 73  0.57 0.30 0.50 0.34 0.37 0.38  296 49 150 52 57 80  0.59 0.29 0.51 0.33 0.36 0.38  342 50 169 56 59 87  0.60 0.28 0.52 0.33 0.36 0.38  46 37 105  0.43 0.37 0.53  51 38 291  0.41 0.34 0.66  55 38 453  0.40 0.32 0.71  60 40 685  0.40 0.31 0.75  63 41 874  0.39 0.30 0.78  67 43 1070  0.39 0.29 0.80  0.39 0.06  j _  a  0.41 0.09  0.41 0.11  0.42 0.12  0.43 0.13  0.43 0.14  - 71 -  The r e l a t i o n s h i p  between two i n t e n s i t i e s  C o n v e r t i n g to r a i n f a l l  and I  depth, R, Eq. 3.5  2  can be shown as f o l l o w s  becomes:  «3.6)  T -r {rJ 2  Setting  2  R  1  = R and t  1  = t to r e p r e s e n t r a i n f a l l  than 24 hours, and s e t t i n g represent r a i n f a l l  R  2i  1440  V  inserting  Table 3.7  yields:  R2,  calculated  "d t  2  = t 4 hours 2  (1440 minutes) to  ( 3  the  1440 V t I of  a  2  less  depth i n 24 hours, Eq. 3.6 s i m p l i f i e s t o :  - i - ( i ! £ y - "  Comparison  = R4  2  t )  Finally,  *  R  depth f o r any time  rainfall  mean  =  0  0  1  3  7  value  (  0 .  of  b  f o r the  coastal  region  '  7 )  from  ,3.8)  M  UU137!  depth  ratios  presented  with Eq. 3.8 i s i n c l u d e d below.  i n T a b l e 3.4  with  those  - 72  -  TABLE  3.8  COMPARISON OF RAINFALL DEPTH RATIOS  Duration (Hours)  Mean Depth R a t i o s f o r C o a s t a l Region T a b l e 3.4/Figure 3.4 Eq.  3.8  1  0.16  0.15  2  0.23  0.23  6  0.45  0.44  12  0.68  0.66  24  1 .00  1 .00  Depth-duration F i g u r e 3.4  equations  are d e r i v e d by  below f o r lower  R  t  which r e p r e s e n t 80 p e r c e n t inserting  and upper l i m i t s ,  /1440\°"  confidence  the a p p r o p r i a t e v a l u e  limits  on  f o r b as shown  respectively:  ... .(3.9)  5%; l4To(— j =  (3.10)  A closer tions  examination  shows some i n t e r e s t i n g  of T e r r a c e A w i t h stations West the  of c o e f f i c i e n t b l i s t e d  T e r r a c e PCC  i n close proximity.  Abbey, Fraser  Lake i s one  two  variations.  For  Comparison  of  b  Coquitlam  lower  values  comparison  can  vary  between  Lake  and  Mission  the mountains immediately  near Vancouver, shows t h a t c o e f f i c i e n t  the  coastal sta-  example,  shows t h a t c o e f f i c i e n t  stations located i n  River of  local  for individual  calculated  f o r the  b  for  north  of  Coquitlam  coastal region  while  - 73  the  corresponding  values  in  alone  the  i s not  calculated  value  for  region.  The  adequate  at  one  to  -  Mission above  to  reliably  another  range of depth r a t i o s observed  site  Depth-Frequency Relationships  3.4.3.1  Analysis of B.C.  Rainfall  intensity  tics  the  to assess  coastal region.  provide  a  basis  duration depth. B.C. 50  of  rainfall  i s assessed  for  100  years.  period.  in this  are analyzed  with study  to determine  "depth-frequency"  rainfall  for  a  the  frequency by  of  rainfall  ratios  rang-  characterisof  return  return period.  occurrence  calculating  the  relationship  range  ratios  for  to a  a  given  reference  a t each of the 58 a v a i l a b l e c o a s t a l  i n Appendix I I f o r r e t u r n p e r i o d s  These  Depth  ratios  also considering  depths  were used  to  of  c a l c u l a t e d by  this  2,  10,  25,  calculate ratios  of depth f o r each r e t u r n p e r i o d to a r e f e r e n c e depth taken return  proximity  return period for durations  Regional  R a i n f a l l depths were obtained  and  higher  depth  the v a r i a b i l i t y of t h i s  estimating  depth  stations included  the  that  precipitation  p e r i o d s i n i n s t a n c e s when r a i n f a l l i s known o n l y f o r one  Variation  of  suggest  without  a v a i l a b l e from AES  from 1 to 24-hours and  throughout  one  Data  r e l a t i o n s h i p between r a i n f a l l depth and ing  is  f o r the c o a s t a l r e g i o n .  3.4.3  data  Abbey  observations  transpose  station  west  as the  procedure  are  10-year  tabulated  i n Appendix I I f o r each i n d i v i d u a l c o a s t a l s t a t i o n .  Rainfall  data  and  southwestern B.C.  depth-frequency are repeated  ratios  i n Table  3.9  calculated for P i t t to i l l u s t r a t e  Polder  typical  in  results  - 74 -  of  depth-frequency  analysis.  ratios  on IDF curves  period  depth  Results  f o r a given  i s relatively  for Pitt  return  constant  Polder  period  show  t h a t the  to the 10-year  f o r a range o f d u r a t i o n s  return  from  1 to  24-hours. TABLE 3.9 DEPTH-FREQUENCY DATA FOR PITT POLDER  Duration  2  1 hr . 2 hr 6 hr 12 h r 24 h r  0.77 0.74 0.74 0.76 0.75  Analysis  a t each  with d u r a t i o n . proximately data,  greatly  0.91 0.90 0.90 0.90 0.90  of r a i n f a l l  that  which  18.1 28.7 65.3 99.8 149.0  data  .00 .00 .00 .00 .00  station  depth-frequency  This r e s u l t  i s particularly  record  only  the data  be undertaken.  20.9 33.6 76.4 115.9 173.8  1 9.1 31 .2 70.9 107.9 1 61 .5  1.12 1.13 1.13 1.12 1.13  throughout  250 c o a s t a l B.C. s t a t i o n s ,  expand  hour data  1 1 1 1 1  intensity  ments o f depth-frequency can  16.2 25.4 57.7 88.9 1 32.2  100  Depth-Frequency R e l a t i o n s h i p s Return P e r i o d (Years) 5 10 25 50  2  1 hr 2 hr 6 hr 12 h r 24 h r  IDF  14.7 22.9 51 .7 80.3 119.0  12.4 18.9 42.7 67.3 98.9  Duration  shows  R a i n f a l l Data (mm) from AES Return P e r i o d (Years) 5 10 25 50  That  can be used  24-hour  base a c r o s s ratios  1 1 1 1 1  100 1 .29 1 .32 1 .32 1 .30 1 .31  .21 .22 .23 .21 .22  the B.C. c o a s t a l r e g i o n  ratios  do not v a r y g r e a t l y  u s e f u l because there are ap-  i n a d d i t i o n to 58 s t a t i o n s with  precipitation. the r e g i o n with  These which  250 s t a t i o n s local  f o r shorter duration r a i n f a l l  i s , depth-frequency  t o develop  a frequency  ratios curve  assess-  intensities  calculated  f o r 24-  f o r shorter duration  - 75 -  rainfall  which  may  depth-frequency and to  be  required  r a t i o s f o r 58 c o a s t a l  shown g r a p h i c a l l y on F i g u r e the 10-year  return  period,  cient  inference  3.5.  of v a r i a t i o n i n the c o a s t a l  80 p e r c e n t  confidence  region  values  i n Table  are shown with  arithmetic  A l s o , the s t a -  r e s u l t s i s t h a t the c o e f f i -  f o r the mean,  upper  and lower  TABLE 3.10  Duration (hours)  2  1 2 6 12 24 values) Mean S t d . Dev.  RATIOS f o r IDF CURVES  Return P e r i o d 10 25  5  (Years) 50  100  0.70 0.74 0.76 0.73 0.69  0.88 0.89 0.90 0.89 0.88  1.00 1 .00 1 .00 1 .00 1 .00  1.15 1 .13 1.12 1 .14 1.15  1.27 1 .23 1.22 1 .24 1 .27  1 .38 1 .33  0.72 0.05  0.89 0.02  1 .00  1 .14 0.02  1 .24 0.02  1 .35 0.03  1.31  1 .34 1 .38  (all  -  — r  II 1 1  1 —|—j™  / / /  1.4  -  CL O UJ  28 x  cr  a  o.  Q  -  /  >-  UJ  i  1 1 1 1  -  or < UJ  2  cr  CONFIC>ENCE .IMITS —  •  /  — r — /  -  / / /  1.2  //,'  -  -  i.o  a  0.8  CJ UJ or o.  0.6  -  '/  •  i  3  -1,1 11, 10  4 5  1  20  .1 ,IJ J i t.L 50  , I.  100  RETURN PERIOD (YEARS)  Figure  3.5:  Depth-Frequency Ratios  3.10  reference  l i m i t s are 0.28, 0.35 and 0.21, r e s p e c t i v e l y .  DEPTH-FREQUENCY  of  c a l c u l a t i o n s can con-  return period.  period  Mean  are l i s t e d  Results  any d e s i r e d  of the depth-return  purposes.  stations  although  v e r t these curves to r e f e r e n c e tistical  f o r design  f o r IDF Curves  200  - 76  Observations apply  to  region.  noted p r e v i o u s l y i n d i s c u s s i o n of d e p t h - d u r a t i o n r a t i o s  results  of  analysis  of  siderably  between  derived  the  r e g i o n and  depth-frequency  magnitude  Results  of  ranges  from about 650  3.4.3.2  ranges  from  Formulas f o r B.C.  t r i b u t i o n was  75  to  t o 3500  An e x p r e s s i o n r e l a t i n g  380 mm  rainfall  depth-frequency  and  coastal  rainfall  mean  varies  con-  analysis  are  with a 100-year  annual  precipitation  mm.  Data  rainfall  depth  and  frequency  p r e s e n t e d by Chow (1951, 1959)  f o r the extremal  (3.11)  T  R  =  T  the  rainfall  depth  with  return period  establishes curve.  T;  data; o = s t a n d a r d d e v i a t i o n of r a i n f a l l  extreme the  value  distribution,  ratio  between  I f the r a t i o between two  r e t u r n p e r i o d s T-| and  rainfall expressed.  R  T  with  dis-  as f o l l o w s :  cy f a c t o r which v a r i e s w i t h r e t u r n p e r i o d and  tive  i n the  = R + Ka  T  rainfall  For  of  f o r c o a s t a l s t a t i o n s where 24-hour storm period  ratios  also  i s r e l a t i v e l y s m a l l c o n s i d e r i n g the  t h a t the  stations.  return  where  of  That i s , the range of r a t i o s  diversity  R  -  return  T  2  any  the two  other  period  T  and  a  d a t a , and K  between points  depths,  i s known, then  mean of T  recorded  = frequen-  record length.  ratio  rainfall  R =  R  1  any  on  two  the  and R , 2  points  frequency  with  respec-  the r a t i o between any  known  rainfall  depth  other  can  be  - 77 -  Consider: R  x  = R + K a  2  = R + K a  x  R  (3.12) (3.13)  2  S o l v i n g Eq. 3.12 and 3.13 s i m u l t a n e o u s l y  yields:  Ki R2 ~ K2 R:1  R  K\ — K R\ — R  C7  (3.14)  2  (3.15)  2  Ki - K  2  Substituting r a t i o RIJI/R-) RT  K  =  R  T  -K  x  K  2  — K  2  -K  X  K  x  (R£\  T  — K  2  3.16 shows how the r a t i o  for  the extreme v a l u e d i s t r i b u t i o n the frequency  numerical region,  curve  (3.16)  \Ri)  Eq.  on  Eq. 3.11 and 3.12 and t a k i n g the  yields:  K  x  Eq. 3.14 and 3.15 i n t o  between  i s known.  rainfall  when the r a t i o  the r e s u l t s  presented  t r a t i v e d e s c r i p t i o n o f how depth  can be determined  between any two depths  E q . 3.16 i s i n a convenient  p r e s e n t a t i o n of depth-frequency  while  depths  relationships  form f o r  i n the c o a s t a l  on F i g u r e 3.5 p r o v i d e a more  r a t i o s v a r y with r e t u r n p e r i o d .  illus-  - 78  3.4.4  Comparison with Other P a c i f i c Northwest Data  Rainfall and  intensity  data  available  Oregon  are  compared  These data  from  the U.S.  al In  applicability addition,  stations  Sources  1973)  U.S.  and  Cascade  results  stations  of  provide  obtained  data  Depth  ratios  format  that  were was  lated  at  these  values  T a b l e 3.11  for  quency r a t i o s .  to  this  study  further  higher  for  the  considered  analyses  Washington  calculated  those  with  to B.C.  stations  regionB.C.  elevations  than  i n t h i s study  undertaken  (Brunengo,  data  include  at  the  six stations  1985).  Data  from  a t l a s were o b t a i n e d  data.  from  calculated ratios  U.S.  stations  A summary of depth  i n Washington  depth-duration  B.C.  for coastal  where p r e c i p i t a t i o n gauges are known to be  applied  coastal  for  Washington  B.C.  maps i n the p r e c i p i t a t i o n - f r e q u e n c y  study o n l y a t p o i n t s  of  of the Western United S t a t e s ( M i l l e r e t a l ,  frequency of  in  region  to i l l u s t r a t e  i n coastal  Atlas  Mountains  coastal  c h a r a c t e r i s t i c s documented  p r e c i p i t a t i o n data  results  f o r the  were o b t a i n e d  currently available  of U.S.  pluvial  with  of r a i n f a l l  precipitation-Frequency  the  -  for and  and  Oregon  coastal i n Table  B.C. 3.12  iso-  for this located.  in  the  ratios  and  same  calcu-  comparison  is  included  for  in  of in  depth-fre-  - 79 -  TABLE 3.11 DEPTH-DURATION RATIOS IN THE PACIFIC NORTHWEST  Location Latitude Longitude  Station  -  C o a s t a l B.C.  -  Elev. (m)  Ratio 1-hr  to 24-Hr Depth 6-hr 12-hr  -  0.16  0.45  0.68  Washington Palmer  ( )  47  18  121  51  280  0.18  0.45  0.68  47  09  1.21  56  399  0.18  0.47  0.70  Cedar Lake (1)  47  25  121  44  476  0.19  0.40  0.64  Lester  47  12  121  29  497  0.18  0.47  0.68  47  08  1 21  38  527  0.14  0.47  0.70  R a i n i e r Longmire (2)  46  45  121  49  842  0.17  0.47  0.74  Snowqualmie Pass (2)  47  25  121  25  921  0.13  0.41  0.71  Stampede Pass  47  17  121  20  1207  0.11  0.39  0.63  47  44  121  05  1241  0.16  0.48  0.73  48  52  121  40  1265  0.13  0.41  0.71  45  19  123  21  256  0.17  0.46  0.73  43  43  122  26  380  0.16  0.41  0.71  44  10  122  10  419  0.13  0.38  0.69  42  37  123  22  1170  0.17  0.46  0.73  1  Mud Mtn Dam  ( ) 2  <) 1  Greenwater  ( ) 1  Stevens Pass Mt. Baker Lodge  ^) 2  Oregon Haskins Dam Hills  ^2)  Creek Dam (2)  McKenzie  Bridge  ( ) 2  Sexton Summit WB (2)  Data from Brunengo (2  >  (1985)  Data from M i l l e r e t a l (1973)  - 80 -  TABLE 3.12 DEPTH-FREQUENCY RATIOS IN THE PACIFIC NORTHWEST  Location Lat Long  Station  -  C o a s t a l B.C.  Elev. (m)  -  Ratio 2  to 10-Yr Return P e r i o d 25 50 100  -  0.72  1 .14  1 .24  1 .35  Washington Palmer  ( )  47  18  121  51  280  0.74  1 .13  1 .22  1 .32  47  09  121  56  399  0.71  1 .13  1 .24  1 .35  47  25  121  44  476  0.78  1 .10  1 .20  1 .27  47  12  121  29  497  0.74  1 .15  1 .23  1 .33  ^^ ^  47  08  121  38  527  0.67  1 .14  1 .29  1 .39  R a i n i e r Longmire  ^ ^ 46  45  121  49  842  0.60  1 .18  1 .31  1 .43  Snowqualmie Pass ^ ^ 47  25  121  25  921  0.64  1 .19  1 .31  1 .41  Stampede Pass ^ ^  47  17  121  20  1207  0.67  1 .15  1 .28  1 .40  47  44  121  05  1241  0.64  1 .18  1 .31  1 .40  48  52  121  40  1265  0.63  1 .15  1 .25  1 .42  45  19  123  21  256  0.69  1 .17  1 .31  1 .53  43  43  122  26  380  0.70  1 .14  1 .28  1 .40  44  10  122  10  419  0.75  1 .17  1 .29  1 .38  ^ ) 42  37  123  22  1170  0.70  1 .17  1 .31  1 .43  1  Mud Mtn Dam Cedar Lake Lester  ( ) 2  ( ) 1  I ) 1  Greenwater  2  2  2  Stevens Pass  ^ ) 2  Mt. Baker Lodge  ^) 2  Oregon Haskins Dam Hills  ( ) 2  Creek Dam  McKenzie  Creek  <^ 2  ( )  Sexton Summit WB  2  2  Data from Brunengo (2  >  (1985)  Data from M i l l e r e t a l (1973)  - 81 -  Results  of a n a l y s i s  of U.S. data  included  i n Tables 3.11 and 3.12 show  t h a t depth r a t i o s c a l c u l a t e d f o r s t a t i o n s i n the c o a s t a l r e g i o n ington  and Oregon  result  i s particularly  relatively of  high  are i n the same range  elevations  p r e c i p i t a t i o n data  variation  informative  Mountains.  for individual stations  quency r a t i o s w i t h d u r a t i o n  ratios  i n coastal  B.C.  as some of the U.S. s t a t i o n s  i n the Cascade  i n depth-duration  c o a s t a l B.C. s t a t i o n s .  as those  o f Wash-  with  i s relatively  Also,  i n Washington  return  period  and  This  are a t  examination shows the depth-fre-  s m a l l j u s t as was observed f o r  - 82 -  3.5  TIME DISTRIBUTION OF SINGLE STORM RAINFALL  3.5.1  A n a l y s i s o f B . C . Data  Analysis  of r a i n f a l l  this  study  single  t o assess  storm  development curves  intensities  data  whether  i n coastal  of s y n t h e t i c  B.C.  hyetographs  intensities  same 58 s t a t i o n s  A computer magnetic record, rence  hourly of peak  Analysis limited  was to a  rainfall  occurring  within  t o scan  At each  increments w i t h i n intensities undertaken calendar  i s usually  sections,  on i n t e n s i t y data  from IDF  applied  i n design  single  storms  recorded  situations  are i n v e s t i g a t e d a t  the 24-hour  day time  period.  within  of i n t e n s i t i e s  a storm within  Even  data  on  rainfall  on  were  periods though  of longer a 24-hour  provided  and time of o c c u r -  period  24-hour  IDF c u r v e s .  24-hour  the 24-hour r a i n f a l l  f o r continuous  sufficient  hourly  s t a t i o n , maximum  within  occurred  analysis  commonly  i n the p r e c e d i n g  i n c o a s t a l B.C. f o r which AES prepared  AES.  on r e c o r d  instances, rainfall  by  based  exist for  are seldom a v a i l a b l e .  program was w r i t t e n  tape  i s undertaken f o r  characteristics also  As noted  i s an a l t e r n a t i v e approach  Rainfall  s i n g l e storms  regional  o n l y because s i n g l e storm data  the  within  identified. and was not  maximum  24-hour  duration  i n many  period  of maximum  f o r hydrograph development i n the c o a s t a l  region.  Time  distribution  format could each  of maximum  s i m i l a r to t h a t  24-hour  applied  to IDF data  be more r e a d i l y u n d e r t a k e n . s t a t i o n was i d e n t i f i e d  rainfall  was  so t h a t  analyzed  in a  regional  Maximum 24-hour r a i n f a l l  ratio  assessment  on r e c o r d a t  and i t s time d i s t r i b u t i o n was analyzed  on an  - 83 -  hourly  basis  lated  i n Appendix I I I f o r each o f 58 c o a s t a l  different some  as a percentage of the 24-hour r a i n f a l l .  storm  instances  periods  are r e p r e s e n t e d  the same storm produced  by  Results  are tabu-  B.C. s t a t i o n s .  Twenty-one  the 58 s t a t i o n s  because i n  the maximum r a i n f a l l  on r e c o r d a t  more than one s t a t i o n .  Typical  24-hour  coastal  region  distributions are shown  on  f o r maximum Figure  3.6.  C o o l a and S t r a t h c o n a Dam are s e l e c t e d in  d i s t r i b u t i o n s of storm  B.C. of  the maximum 24-hour r a i n f a l l s  more  and S t r a t h c o n a  non-linear  rainfall  stages  from  to i l l u s t r a t e  calculated  record  Bear  i n the  Creek,  Bella  g r a p h i c a l l y the range  i n t h i s study  similar  on r e c o r d  at stations  are s e l e c t e d  for coastal  with  higher  region  t o those  distributions  intensity  rainfall  occurring  respectively.  shown on Figure  identified i n this  on F i g u r e  3.6 which shows the r e l a t i v e l y  data.  The magnitude o f 24-hour r a i n f a l l mm.  examples of  Each of  e x p e r i e n c e d maximum 24-hour r a i n -  trated  ranged from 65 t o 340  across the r e g i o n .  as i l l u s t r a t i v e  of the 24-hour p e r i o d ,  i n the c o a s t a l  distributions 58  Dam  distributions  and e a r l y  58 s t a t i o n s  fall the  Coola  late  the  Data  on  The somewhat l i n e a r d i s t r i b u t i o n f o r Bear Creek i s common f o r many  Bella  at  rainfall  rainfalls  3.6.  study  A summary of i s also  narrow band of  from s t a t i o n s  across  illusrainfall  the r e g i o n  - 84 -  o.  a> _1 o  _) <° (T  y  U. ^ o. —  rv  <ZL CC  o 1  ° in  CN L_  °  o *• I— z  u  s-  ce LJ o Q_ ™ o_  0  2  4  E  8  10  12  11  16  IB  20  22  21  HOUR  (a)  Maximum 24-Hour R a i n f a l l  a t Bear Creek (300.5 mm)  HOUR  (b)  Maximum 24-Hour R a i n f a l l  at Bella  F i g u r e 3.6. Maximum 24-Hour R a i n f a l l  Coola  (131.4 mm)  on Record  - 85 -  0  2  1  6  8  10  I2  HOUR  Maximum 24-Hour R a i n f a l l  M  IE  IS  20  22  a t S t r a t h c o n a Dam  21  (155.2 mm)  HOUR  Range of 24-Hour R a i n f a l l F i g u r e 3.5  Distributions  Maximum 24-Hour R a i n f a l l  on Record  - 86  A  study  storm in  of  12-hour r a i n f a l l  distributions  coastal  B.C.  Victoria  and  selected  at  Comox  event  f o r each  bined  to  also and  applied the  Results  across  Canada  (Hogg,  rainfall  data  coastal region. to  form  record.  a  Data  " c o a s t a l B.C." designated  as  from  from  found  that  of Canada  than  Agassiz,  duration  a l l four  base. the  regions  Twelve-hour  partial  data  1980)  Vancouver,  rainfalls series  were  with  s t a t i o n s were  S i m i l a r procedures  E a s t Coast,  Southern  one comwere  Ontario  Prairies.  of  analysis the  for  range  a wide  series.  Storm  single  undertaken  range of  of  This storms  by  12-hour  Hogg  data  result  for  shown  on  F i g u r e 3.7  distributions  represented  by  the  i n each partial  duration  f i t a much narrower  the  Southern  i n c o a s t a l B.C.  East that may  Coast,  Ontario  regional r a i n f a l l be  more r e a d i l y  which region  f o r c o a s t a l B.C.  suggests  f o r other r e g i o n s of Canada.  are  rainfall  return periods  distributions  corresponding  Prairies. of  on  regions  illustrates  than  the  station  a  to  analyzed  in  year  create  data  were more v a r i a b l e i n other  Hogg  each  -  and  range the  characteristics  identifiable  than  12 HOUR STORM R R I N B . C . CORST  87 -  DISTRIBUTION  NO. OF EVENTS »tl9 SELECTION CRITERIP, 6 HR [2 MR (MM • 10) 381 CURVES SNOW t Of €VENTS WITH X STORM RfltN J VQLUES PLOTTED  12 HOUR STORM R P I N CON EPST COPST  NO. OF EVENTS >8S SELECTION CRITERIA' S HR 12 HR (MM - 10] «39 CURVES SHOU X OF EVENTS WITH i 3T0RN RfltN } YPLUES PLOTTED  TIME (HOURS)  12 HOUR STORM R P I N PRRIRIES  TIME  DISTRIBUTION  NO. OF EVENTS »333 SELECTION CRtTEHIOi 6 HR 12 hP. (MM • 19) 30S CURVES SHOW X OF EVENTS WITH x STORM ROIN 1 VQLUES PLOTTED  DISTRIBUTION  (HOURS)  12 HOUR STORM R S I N D I STR I BUT Ci SOUTHERN ONTRRIO  NO. Or EVENTS »tflfl SELECTION CRIT£R[p. 6 HR \2 V.?. (MM • 13) 330 221 CURVES SHOW X OF 5v£f*TS -ITH * STORM RAIN S VQLUES PLOTTEt  / /y 1  30tf  j  /  1  \  /  /  /  /  /  /  S«/ 7  /  /  / 3  7  / /  9  *7  s TIME  TIME (HOURS)  Figure  3.7  Time D i s t r i b u t i o n  o f 12-Hour R a i n f a l l  (after  a i d (HOURS)  Hogg, 1980)  - 88 -  Regional this  rainfall  study by a n a l y z i n g  occurring within These data sis  characteristics for coastal  incremental  inter-storm rainfalls  data  within  the r e g i o n .  the l a r g e s t  similar  to t h a t used p r e v i o u s l y  illustrates  of h i g h e r  0  Results  storms  on r e c o r d  are shown on F i g u r e  f o r IDF d a t a .  those storms which tend  4  6  3.8 i n a format  The lower to be l i n e a r  3.8  limit  shown on  and the upper periods  the 24-hour p e r i o d .  8  10  12  14  16  18  DURATION (HOURS )  Figure  Analy-  do not v a r y  c h a r a c t e r i s t i c s o f 24-hour r a i n f a l l which have  i n t e n s i t y within  2  a t each s t a t i o n .  shows t h a t on a percentage b a s i s , maximum  across  F i g u r e 3.8 r e p r e s e n t s  rainfalls  f o r each c o a s t a l s t a t i o n i n Appendix I I I .  greatly  limit  1, 2, 3, 4, 6, 8 and 12-hour  the maximum 24-hour r a i n f a l l on r e c o r d  are l i s t e d  of these  maximum  B.C. are i n v e s t i g a t e d i n  Depth-Duration R a t i o s  f o r 24-Hour R a i n f a l l  20  22  24  - 89 -  Comparison curves about  rainfall  and i n F i g u r e 6-hour  durations, a  of h o u r l y  3.8 based  durations  rainfall  can be  intensities  to occur  For  each  durations are  from  shows  IDF curves  maximum  on  intensities  record  on r e c o r d  i n many  rainfall  intensities  ferred  to as " n e s t i n g " ,  ratios  obtained  data.  The p o t e n t i a l f o r n e s t i n g  from  of occurrence  This  i s c o n s i s t e n t with  separate  of these  occurred  instances.  For s h o r t e r would  produce  than have  within  data  i n t e n s i t i e s to data.  on r e c o r d f o r 24-hour  storms  shows maximum  the maximum 24-hour  occurrence,  sometimes r e -  the s i m i l a r r e s u l t s f o r depth  a n a l y s i s of IDF and s i n g l e storm i s apparent by examining  of maximum 1 , 6, 12 and 24-hour  i n c o a s t a l B.C. as shown on F i g u r e 3.9.  beyond  In p r a c t i c e the two curves  rainfall  Examination  on IDF  that  intensities  engineer i n the absence of s i t e  station,  based  similar.  maximum h o u r l y  s i n g l e storms.  i n Appendix I I I .  short duration  year  data  3.4  l e s s than 24-hours and maximum o c c u r r i n g w i t h i n  compared  rainfall  storm  on the range of h o u r l y  by the d e s i g n  coastal  i n Figure  are q u i t e  estimated  greater  within  be used to s e t l i m i t s considered  on s i n g l e  the two curves  s y n t h e t i c hyetograph with  been observed  intensities  rainfall  the p e r i o d o f  rainfalls  on r e c o r d  - 90  J  F M A M J  J  -  A S 0 N 0  MONTH OF OCCURRENCE OF M A X . I - HR RAINFALL  J F M A M J J A S O N D MONTH  OF OCCURRENCE  OF M A X . 1 2 - H R RAINFALL  Figure  3.9  Monthly D i s t r i b u t i o n  J F M A M J MONTH OF  J  J  A S O N O  OF OCCURRENCE  MAX. 6 - H R RAINFALL  F M A M J  J  A S O N O  MONTH OF O C C U R R E N C E OF  MAX. 24-HR  of Maximum R a i n f a l l s  RAINFALL  on Record  - 91 -  Results  presented  rainfall  on F i g u r e 3.8 p r o v i d e  increments  information  occurring  on the time sequence  a s y n t h e t i c hyetograph. intensities 58  stations  investigated 5-hour all  within  within was  a basis  single  storms,  within  f o r development  of  T h e r e f o r e , time o f o c c u r r e n c e o f maximum h o u r l y  examined.  intensities  hourly-  b u t do not p r o v i d e  of o c c u r r e n c e needed  the maximum 24-hour r a i n f a l l  to determine  f o r estimating  Maximum the time  24-hour  on r e c o r d rainfalls  of occurrence  the 24-hour p e r i o d .  a t each o f the on  record  of maximum  1,  were 3 and  A summary o f r e s u l t s f o r  s t a t i o n s i n the c o a s t a l B.C. r e g i o n i s i n c l u d e d  i n Table 3.13.  TABLE 3.13 TIME OF OCCURRENCE OF MAXIMUM INTENSITIES  Maximum 1-Hour Time o f No. of Occurrence Occurrences (Hours) 0-1 1-2 2-3 3-4 4-5 - 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-1 8 18-19 • 19-20 20-21 21-22 22-23 23-24  0 0 2 2 2 2 1 4 2 2 5 1 3 3 5 3 3 3 3 2 4 3 1 1  Maximum 3-Hour Time o f NO. o f Occurrence Occurrences (Hours) 0-3 1-4 2-5 3-6 4-7 5-8 6-9 7-10 8-11 9-1 2 10-13 11-14 12-15 13-16 14-17 15-18 16-19 17-20 18-21 19-22 20-23 21-24  0 0 1 3 3 1 5 2 3 2 1 2 5 2 5 4 3 5 2 5 1 2  Maximum 5-Hour No. o f Time o f Occurrence Occurrences (Hours) 0-5 1-6 2-7 3-8 4-9 5-1 0 6-11 7-1 2 8-13 9-1 4 10-15 11-16 12-17 1 3-18 14-19 15-20 16-21 17-22 18-23 19-23  1 1 3 1 2 2 5 3 2 3 2 2 2 5 5 4 4 4 1 5  - 92 -  Results there  this  First,  i n Table  i s no apparent  either of  presented  strong  e a r l y or l a t e observation hourly  3.13 suggest f o r the c o a s t a l B.C. r e g i o n bias  within  f o r periods  large  to the d e s i g n  rainfall  increments  24-hour engineer within  of high  i n t e n s i t y to occur  rainfalls. i n this  that  The consequences  region  are t w o - f o l d .  a s y n t h e t i c hyetograph  f o r the  c o a s t a l r e g i o n can be arranged i n many d i f f e r e n t time sequences and s t i l l produce 24-hour events with ly,  s e l e c t i o n by a d e s i g n  intensities  within  a  s i m i l a r p r o b a b i l i t i e s of o c c u r r e n c e . engineer  24-hour  o f a time  synthetic  sequence o f maximum  hyetograph  Secondhourly  can be governed  response c h a r a c t e r i s t i c s o f the b a s i n under c o n s i d e r a t i o n .  by  - 93 -  3.5.2  Comparison With Other P a c i f i c Northwest Data  Single  storm  ington  and Oregon  B.C.  These  regional mented  rainfall  data  data  available  are compared from  of  B.C.  single  atively  storm  precipitation  high  stations  tion  data  identified  Precipitation  data  f u r t h e r the  provide  docu-  data f o r  i n c o a s t a l B.C.  a t four  Mountains  stations  at r e l -  of Washington i n Oregon.  and a t  Precipita-  i n Washington r e p r e s e n t the l a r g e s t  a visual  f o r Oregon are from floods with  study f o r  i n s p e c t i o n of long the same storm  return periods  term  records.  p e r i o d i n December  ranging  from  about  50 to  years o c c u r r e d over most of the c o a s t a l r e g i o n .  Depth  ratios  calculated applied data is  extreme  from  i n this  stations  were o b t a i n e d  f o r each s t a t i o n  24-hour event  100  U.S.  of Wash-  characteristics  currently available  data  region  to i l l u s t r a t e  i n the c o a s t and Cascade Mountains  presented  when  obtained  rainfall  e l e v a t i o n s i n the Cascade  four  1964  storm  In a d d i t i o n ,  h i g h e r e l e v a t i o n s than s t a t i o n s  Single  to r e s u l t s  the U.S. were o b t a i n e d  applicability for coastal  f o r the c o a s t a l  f o r maximum  with  data  to B.C. d a t a .  from  hourly U.S.  increments stations  A summary  included i n Table  inter-storm  hourly  3.14.  Results  increments  ratios  to those  with  was U.S.  for coastal  B.C.  storm  c o a s t a l Washington and Oregon are i n the same range as those B.C.  that  are  with  of U.S. data single  events  format  calculated  calculated  of a n a l y s i s  calculated  24-hour  i n the same  of depth  and comparison of these values  within  show t h a t data  from  i n coastal  TABLE 3.14 SINGLE STORM PRECIPITATION DATA IN THE PACIFIC NORTHWEST  Location Latitude Longitude  Station  -  COASTAL B.C.  -  Elev (m)  -  24-Hour Precip (mm)  Max. O c c u r r i n g W i t h i n 24- Hours ( R a t i o to 24-Hour P r e c i p i t a t i o n ) 1-Hour 2-Hour 6-Hour 12-Hour  -  0.08  0.15  0.37  0.63  WASINGTON Snowqualmie P a s s ^ ^ Stampede P a s s ^ ) Stevens P a s s ( ) Mt. Baker L o d g e ( )  47 47 47 48  25 17 44 52  121 121 121 121  25 20 05 40  921 1207 1241 1265  178 202 130 127  0.10 0.08 0.08 0.06  0.16 0.15 0.14 0.12  0.38 0.38 0.33 0.32  0.72 0.64 0.53 0.58  Haskins Dam ^ ) 45 H i l l s Creek Dam ) 43 McKenzie Bridge RS ( ) 44 Sexton Summit WB ( ) 42  19 43 10 37  123 122 122 123  21 26 10 22  256 380 419 1170  138 92 103 113  0.09 0.07 0.08 0.10  0.18 0.14 0.11 0.19  0.42 0.36 0.29 0.37  0.72 0.62 0.55 0.57  -  0.15  0.25  0.47  0.69  1  1  1  1  OREGON 1  v 1  1  1  SCS TYPE 1A *  2 )  -  -  ( ) data from U.S. N a t i o n a l Weather S e r v i c e (2) a f t e r S o i l Conservation S e r v i c e (1982) 1  -  - 95 -  A r e g i o n a l 24-hour r a i n f a l l servation Sierra  Service  Nevada  California, 3.14  (SCS, 1973, 1982) f o r use on the c o a s t a l  and Cascade  dual  Data  of Oregon,  Washington  regions of Alaska i s also  presented  side  f o r the c o a s t a l  stations.  by examining  However,  procedures  this  used  apparent  by SCS  Con-  of the  and n o r t h e r n  compared storm  i n Table  distribution  by SCS are not i n the same range as those c a l c u l a t e d  coastal  solved  Mountains  and the c o a s t a l  to B.C. d a t a .  proposed  d i s t r i b u t i o n developed by the U.S. S o i l  at i n d i v i -  d i s c r e p a n c y can be r e -  t o develop  their  regional  curve.  Procedures  outlined  by SCS (1973) i n d i c a t e  their  single  t i o n i s d e r i v e d from IDF d a t a o b t a i n e d from r a i n f a l l of  h o u r l y increments  rainfall (Table the  depth  ratios  3.4) shows  SCS storm  proposed  by SCS f o r a s i n g l e  calculated  these  values  distribution  f o r coastal  are s i m i l a r .  i n the c o a s t a l  with g r e a t e r maximum h o u r l y i n t e n s i t i e s lysis  SCS a l s o  24-hour  Examination in  atlases. storm  distribuComparison  d i s t r i b u t i o n to  B.C. based  on  IDF d a t a  T h e r e f o r e , a p p l i c a t i o n of  region  produces  a  hyetograph  than have been observed from  ana-  of s i n g l e storm d a t a .  Finally, a  storm  proposes  rainfall.  The storm  of the curve  the storm  from  a time  hour  from hours 7 through 10.  sequence  distribution  f o r h o u r l y increments i s plotted  shows the maximum 1 -hour  on F i g u r e 3.10.  rainfall  7 t o 8 and the maximum 4-hour  within  occurs  increment  early occurs  SCS s t a t e s , however, s e l e c t i o n of the p e r i o d of  - 96  maximum i n t e n s i t y  i s based on d e s i g n  logical factors.  Therefore,  -  considerations  i t i s reasonable  d i s t r i b u t i o n was  proposed  to p r o v i d e  which  produces  conservative  generally  F i g u r e 3.10  S o i l Conservation  than meteoro-  to conclude t h a t t h i s  a standardized  t h a t h o u r l y increments are based on IDF  rather  results,  storm  s y n t h e t i c hyetograph  especially  considering  data.  S e r v i c e Type 1A Storm D i s t r i b u t i o n  - 97 -  3.6  ELEVATION EFFECTS ON STORM RAINFALL  3.6.1  Background  R e g i o n a l . c h a r a c t e r i s t i c s of storm sections  can be used  a drainage b a s i n . indicator  rainfall  In its  terrain  temporal  approach  to storm  engineering  facilities potential to  storm  radar  passes graph  analysis  within  usually  analysis i n  requires  storm  systems  i n t e r a c t with  moun-  i n two d i f f e r e n t one moves with  This  approach  frames of r e f e r e n c e .  the storm i s most  has not y e t r e c e i v e d  perhaps due i n p a r t  precipitation  radar  and observes  commonly  The L a g r a n g i a n  widespread  to a shortage  stations.  There  application of n e c e s s a r y is  the a p p l i c a t i o n of a L a g r a n g i a n  f o r engineering  studies  as there  adopted  little  approach  i s no p r e c i p i t a t i o n  station currently i n operation.  Engineering where  frame  i n B.C. f o r e x p l o r i n g analysis  Hydrograph  and i s a b a s i s f o r weather f o r e c a s t i n g .  as  preceding  elevation.  and decay.  studies,  such  basin.  e f f e c t s as storm  reference  growth  i n the  i s sometimes an adequate  B.C., however,  can be undertaken  a Lagrangian  for rainfall  an e n t i r e  of c o a s t a l  of e l e v a t i o n  by m e t e o r o l o g i s t s  in  across  t o be d i s t r i b u t e d with  Examination tainous  A p o i n t estimate  regions  presented  t o develop s y n t h e t i c hyetographs a t a p o i n t  of r a i n f a l l  mountainous  rainfall  studies  an observer  traditionally remains  through a r e g i o n . f o r one p o i n t  utilize  stationary This  approach  i n the b a s i n ,  a  Eulerian  and records leads  which  reference  rainfall  as a  frame storm  to development of a h y e t o -  i n turn  i s used  to  estimate  - 98 -  rainfall  over  difficulty basin For  increases  within  of  v a l l e y s on  ions  analyzed  point when  also  the  there are  trigger  may  can  large  be  under  uplift  in  orographic  convective i n s t a b i l i t y  cause  study.  transposed  variations  induce  increase cyclonic  and  basin  across  atmospheric  detailed  42 storms  precipitation  from  differential  funnelling  processes a f f e c t i n g  studies.  i n the c o a s t a l mountains  to a mountain  freezing  meteorologic  level  analysis  and  retarding  effects  interaction  of  "depends efficiency  barrier,  n o r t h of Vancouver,  i n a complex way with  which  the a i r mass s t a b i l i t y " .  the wind  (1980) concluded t h a t the p r i n c i p a l  form  airflow  humidity,  wind  instability,  strength,  by  rising  wet-bulb  of  mechanisms  direction  Browning  atmos-  physically-based  the c h a r a c t e r  Finally,  and  i n mountain-  of o r o g r a p h i c r a i n f a l l to  and  speed,  the  temperature,  the depth  existence  of of  of  review o f  factors  magnitude  and presence and nature of p r e - e x i s t i n g  cloud  r a i n conducted  influencing  topography,  terrain,  remove  a comprehensive  and mechanism of o r o g r a p h i c a l l y enhanced  induced  B.C.  p r i m a r i l y to wind  Another  microphysical  cloud,  structure  upon  storm  (1976)  moisture c o n t e n t of the lower  showed the r e l a t i o n  as" p r e c i p i t a t i o n ,  and  i s related  a i r mass s t a b i l i t y .  condensate  of  of  conclus-  Hetherington  of the d i s t r i b u t i o n of storm r a i n f a l l  r e g i o n s ( E l l i o t , 1977)  the  meteorological  the amount of o r o g r a p h i c r a i n f a l l  elevation  a  elevation.  p r e c i p i t a t i o n by  through  The  airstreams.  normal  phere,  the  drainage  measurement  terrain  slopes,  movement,  three  concluded  on  and  of  and mountainous t e r r a i n can be demonstrated by examining  of  speed  a  greatly  c o m p l e x i t y of  systems  ous  which  of mountain  rate  remainder  mountainous  storms  heating  The  with  example,  the  the  by  are the relative  potential  precipitation.  - 99 -  The  above d i s c u s s i o n  with e l e v a t i o n nomena. (1976)  a t 38  addition a  190 km These  of annual  stations  further  region  data  local  variations  i n storm  p r e c i p i t a t i o n by Rasmussen  i n the Northern  Cascade  Mountains  alone,  extending  s p e c i f i c pheand Tangborn of Washington  illustrate  p r e c i p i t a t i o n data are shown on F i g u r e  from  f o r stations  the Canadian  only  that  on  even  border  the western  within  southward  slope  a relatively  i s wide v a r i a t i o n i n p r e c i p i t a t i o n f o r a g i v e n  of local  the Cascades. region  elevation.  .8800  i z z  .7437 • 5443  g  .8718 .3384 .3909 ' .4295  ? 2500  4999  < Z  z < z <  9 •5840 > 1 9  .1233  .7781 .8009 .7379  2  .8089  .2157  .1479 80  .  • 8000  .527  .3141 .77/3  J4  *^48* 1484 J7507 . '5523 V 5 5 7  -324  r»2475 7478 .174  200  400  800 GAGE  Figure  3.11  1000  1200  1400  1400  1800  3.11  f o r about  • 8001 i 3500  rainfall  t h a t p r e c i p i t a t i o n amounts are a f f e c t e d by f a c t o r s i n  to e l e v a t i o n  and  that  are a f f e c t e d by the i n t e r a c t i o n of many s i t e  Examination  illustrates  for  illustrates  2000  ALTITUDE. I N METRES  Annual P r e c i p i t a t i o n i n the North Cascade Mountains  there  - 100  Detailed  meteorologic  rainfall, Elliott  similar (1977),  characteristics.  investigations  to  are  -  those  not  noted  those c h a r a c t e r i s t i c s which can available  in  available  for  effects  on  identified which  3.6.2  which as  can a  be  basis  base  region  is  for  of  regional  undertaken  and  to  investigation  immediately  more  some to  trends  establish currently  comprehensive  currently  of  elevation  can  engineering research  and  rainfall  network d e n s i t y  wide  storm  H e t h e r i n g t o n .(1976) study  Nevertheless,  applied  on  i d e n t i f i e d with l i m i t e d data  data  rainfall.  this  effects  still  be  studies,  and  of  elevation  i n t h i s study.  Analysis of Selected Storm Data  limited  of for  atmospheric tainous  elevation two  processes  terrain  local  variations  elevations  are  networks  First,  very  storm  as  rainfall  described  interaction  complex.  i s generally  in rainfall  from  i n the of  Secondly, not  low  in  coastal preceding  storm the  B.C.  systems  existing  of s u f f i c i e n t d e n s i t y  v a l l e y bottom e l e v a t i o n s  is  section, and  moun-  rain  gauge  to examine to  higher  near mountain c r e s t s .  investigations  recorded  on  affecting  B.C.  approach adopted  coastal  effects  reasons.  network i n c o a s t a l  cal  be  The  in  by  analysis  restricts  than i s p o s s i b l e  Analysis  The  B.C.  analysis  storm  serve  effects  coastal  elevation  above  undertaken  Alternatively,  of  region, rainfall along  f o r t h i s study i s to assess r e s u l t s of undertaken  and  then  by  compare  B.C. trends  data a t other s t a t i o n s mountain  slopes  Hydro  at  two  locations  identified in i n the  immediately  region. north  meteorologi-  of  their  in  the  reports  to  Data from gauge Vancouver  were  - 101  selected in  f o r comparison  to the m e t e o r o l o g i c  other segments of the B.C.  Two  meteorologic  include Lake  couver's  city  maximum  centre  and  1981) for  l o c a t e d a p p r o x i m a t e l y 100 km for  these  tion  s t u d i e s was  (WMO,  1973)  technique of  and  for  a  processes.  The  (PMP)  by  by  the  components  lifting  from  an  elevation  200  specific  -  are  ii)  storm  the  m.  of  Even  156  summed  - 1750  though  i n the b a s i n .  (B.C.  of  Van-  Hydro,  1983)  adopted  s e p a r a t i o n method.  resulting  to produce  PMP  m,  The  mountains  from  atmospheric  estimates  estimates  and  of  storm  f o r the range  i n the Coquitlam  of  basin  and  for  the  Cheakamus  of  the  PMP  studies  are  site  are apparent  and  were  results  t r e n d s i n the r e s u l t s  r a i n f a l l i n c r e a s e d l i n e a r l y with  relationship  northeast  a i r flow over  to m e r i t a d d i t i o n a l i n v e s t i g a t i o n .  linear  Coquitlam  The methodology  R e s u l t s were presented  f o r each b a s i n , two  considered  i)  1800  range  of  precipitation  s t u d i e s produced  for  Project  the  areas  e s t i m a t e s f o r an o r o g r a p h i c component  Each of the m e t e o r o l o g i c basin.  30 km  the o r o g r a p h i c  separate  i n mountainous  the World M e t e o r o l o g i c a l O r g a n i z a -  elevation.  i n each  about  densities  adequate.  studies for  Cheakamus  r a i n f a l l with i n c r e a s i n g  elevations  rainfall  n o r t h of Vancouver.  component of  two  the  i s known as  induced  convergence  storm  located  established  i n v o l v e s making  precipitation  of  precipitation  (Schaefer,  s t u d i e s as network  c o a s t a l r e g i o n are not  investigations  probable  Watershed  -  The  two  project  trends a r e :  elevation.  g e n e r a l l y extended  to the h i g h e s t e l e v a t i o n  - 102 -  Each of the above trends d e r i v e d tigated other  further  coastal  tained  i n this  study  B.C. s t a t i o n s  from m e t e o r o l o g i c a l  by examining  not used  recorded  Transect  A  of Vancouver as shown on F i g u r e  from  Burrard  Inlet  t o Grouse  d a t a f o r Atmospheric Environment S e r v i c e to Mount Seymour research  Elevation  are temporary  program ( F i t z h a r r i s ,  locations  data  from  Data were ob-  i n the mountains imme-  3.12.  Mountain  Stations record  and those i n c l u d e d established  shown along  precipitation on T r a n s e c t  as p a r t  B  o f a Ph.D.  1975).  e f f e c t s on p r e c i p i t a t i o n a l o n g T r a n s e c t  3.13 which p r e s e n t s  the average  each  elevation.  s t a t i o n versus  are i n v e s -  rainfall  i n the PMP s t u d i e s .  from s t a t i o n s along two d i f f e r e n t t r a n s e c t s  d i a t e l y north  analysis  A are shown  on F i g u r e  annual maximum 24-hour p r e c i p i t a t i o n a t This  r e l a t i o n s h i p appears l i n e a r j u s t as  was c a l c u l a t e d i n m e t e o r o l o g i c i n v e s t i g a t i o n s of s i n g l e storm PMP e v e n t s . In  addition,  within  the h i g h e s t  s t a t i o n i n the t r a n s e c t  about 200 m of c r e s t e l e v a t i o n s  at elevation  1128 m i s  along the top of the s l o p e .  Figure 3.12  Station Locations  i n North Vancouver  - 104 -  I400  200  /  j i  I000  ~  /  800  O r<  LU _i LU  6 00  400  200  40  60  / / / • / •• 1 •A » -/ 80  /  / /  /  /  /  100  120  140  STORM PRECIPITATION ( m m ) F i g u r e 3.13  T r a n s e c t A:  E l e v a t i o n vs 24-Hour  Precipitation  - 105  Storm  data  along  storms r a n g i n g  Transect  from  -  B were c o l l e c t e d  2 t o 81  hours  during  by  Fitzharris  the  (1975) f o r 73  1969-70 w i n t e r  and  storms r a n g i n g from 6 t o 91 hours d u r i n g the 1970-71 w i n t e r . precipitation  events  about 2 y e a r s . examination tion  rainfall  on  were  complexity  of atmospheric  storm  rainfall.  return periods less  processes  identified  as  However,  being  l e a d i n g to extreme f l o o d s .  relatively and  by F i t z h a r r i s had  Most of  74 the  than  i s apparent  from  of a l l 147 storms which showed no c o n s i s t e n t t r e n d s i n e l e v a -  effects  Table 3.15  The  examined  for  large  precipitation  c o n s i s t e d of  rain  over  of  three  interest  to  events this  listed  study  Each of the three events  amounts  most of  the  for  the  elevation  brief  of  on  storm  experienced  period  range .with  of  record  rain  mixed  with snow a t the top of the mountain.  Table  3.15  Storm Data Near Mount Seymour ( F i t z h a r r i s , Storm Duration  Date Dec 6-7, 1970 Dec 9-11 , 1970 Feb 13-15 , 1971  Precipitation 3.14  through  vation  3.16  range.  from  The  studies  with  f o r B.C.  each of  the  sampling  h i g h e s t sampling Linearity  elevation Hydro and  hour p r e c i p i t a t i o n recorded  along  three  storms are p l o t t e d  l o c a t i o n s over a 120 station  Transect  of the  profile  along Transect  on  t o 1260  Figures m  i s w i t h i n about 200 m of  of these  single B  storm  supports  of average A.  m  82 107 1 37  53 50 74  f o r twelve  peak of Mount Seymour. cipitation  P r e c i p i t a t i o n Amount (mm) E l e v a t i o n 120 m E l e v a t i o n 1260  (hrs)  26 31 43  data  1975)  profiles  results annual  of  elethe  of p r e two  maximum  PMP 24-  - 106 -  I400  «/ i  200  / /  ;  I000 /  r ~  /  800  o p<  LU  6 00  J  /  7  LU  /. / /  400  200  • 40  ./ / / 60  / *  80  100  120  STORM PRECIPITATION ( m m ) F i g u r e 3.14  T r a n s e c t B: R a i n f a l l D i s t r i b u t i o n f o r December 6-7, 1970  140  - 107 -  400  200  • I  •>  000  ~  1 1 1 1  m  1 !  800  / • /  o < >  U J 6 00  _i  LU  • /  /• "  / /  ,/ /  400  / •  ./ /.  200  /  40  60  80  STORM  F i g u r e 3.15  100  PRECIPITATION  120 (mm)  T r a n s e c t B: Rainfall Distribution for December 9-11, 1970  140  - 108 -  I400 -  / •  200  /  /•  I000  • / w  /  800  •/ /  h< LU _i  6 00  •/  • / •  400  /  /  •/  /. /.  2 00  /  4.0  60 STORM  F i g u r e 3.16  80  I00  PRECIPITATION  I20 (mm)  T r a n s e c t B: R a i n f a l l D i s t r i b u t i o n f o r February 13-15, 1971  I40  - 109  Precipitation yet  profile  sufficient  of  storm  currently  available  to support d e f i n i t i v e  theless , available tion  data  -  evidence  rainfall  for coastal  B.C.  are  c o n c l u s i o n s f o r the r e g i o n .  suggests  that  a  linear  d u r i n g extreme events  not  Never-  i n c r e a s e with e l e v a -  i s a reasonable  approxima-  t i o n f o r i n d i v i d u a l s l o p e s with a c o n s t a n t aspect i n the c o a s t a l r e g i o n .  Inasmuch as p r e c i p i t a t i o n p r o f i l e data analyzed i n t h i s from of  events  the  ies.  rate  with  a wide range  i n frequency  of i n c r e a s e w i t h e l e v a t i o n  Additional  r e s e a r c h of  elevation  and  supports  needed  for  studies method storm  results  engineering  of storm which  analytical use.  rainfall,  can  rainfall  3.6.3  of  serve  with  In  effects  the  a  with  absence  guideline  be on  the magnitude  compared between s t u d storm  rainfall  recorded of  data  regional  estimate  the  alternative  distribution  assessed  directly  methods must be a p p l i e d . assess  other  factors  study of r e g i o n a l ship  between  premise  that  based  which may  and  on  local-historical  data,  In these i n s t a n c e s the approach  rainfall  annual  of  Precipitation  For e n g i n e e r i n g d e s i g n s i t u a t i o n s when the d i s t r i b u t i o n of storm be  greatly  meteorologic  s e c t i o n p r e s e n t s an to  is  events  elevation.  R e l a t i o n s h i p t o Annual  cannot  i n the  processes d u r i n g extreme  study  the f o l l o w i n g  as  of o c c u r r e n c e ,  cannot  c o a s t a l r e g i o n which examines atmospheric  study are d e r i v e d  be  indices  characteristics  of  storm  i s g e n e r a l l y to  i n c o a s t a l B.C.  annual p r e c i p i t a t i o n d i s t r i b u t i o n may  be  alternative  rainfall.  short duration p r e c i p i t a t i o n  rainfall  the  For  this  relation-  i s examined.  The  an index f o r storm  - no -  rainfall during  is  the  based  fall  on  and  the  winter  fact  that  most  and  results  annual  from  the  precipitation  same type  of  sure system which produce the r e g i o n s l a r g e s t 24-hour r a i n f a l l  Annual  and  24-hour  precipitation  coastal  B.C.  stations  erence,  data  are  east  and  plotted  c o a s t o f Vancouver  are  data  plotted  separately  were on for  obtained  for  low  a l l available For  Vancouver  Fraser  Island inlcuding V i c t o r i a  west c o a s t of Vancouver I s l a n d , and other B.C.  and  coastal  pres-  events.  F i g u r e s 3.17. and  occurs  quick  ref-  Valley,  the G u l f I s l a n d s , stations.  - 111  -  I000 MEAN  (a)  0  ANNUAL  3000  PRECIPITATION  V A N C O U V E R AND F R A S E R  I000 MEAN  (b)  2000  2000 ANNUAL  4000 (mm)  VALLEY.  3000  PRECIPITATION  4000 (mm)  E A S T COAST OF V A N C O U V E R F i g u r e 3.17  R e l a t i o n s h i p Between 24-Hour Annual P r e c i p i t a t i o n  and  ISLAND  - 112 -  (c) cr x i  * x <  -J  3  WEST COAST OF VANCOUVER I S L A N D .  2 0 0  E E  —  I 5 0  —  ^-  '  o  o  t;  loo  ^ —  i t <  ^——  0  °  a.  o°  50  °o  °  o o  o  °  «  °°  o^—  °°  < cr tr Q. UJ  > <  i  0  i  1000 MEAN  (d)  1  1  2000 ANNUAL  1  3000  PRECIPITATION  OTHER B.C. COASTAL  F i g u r e 3.17  1  1  4000 (mm)  STATIONS  R e l a t i o n s h i p Between 24-Hour and Annual P r e c i p i t a t i o n  0  - 113  Envelope curves relationship tion  at  which  a  are  i n c l u d e d on  i n the  the  Figure  3.17  to i l l u s t r a t e  c o a s t a l r e g i o n between annual and  station.  lists  -  These  range  annual p r e c i p i t a t i o n  in  relationships percentages  represented  Table  are  of  1000 2000 3000 4000  in  3.3-7.1 3.3-5.5 3.3-5.5 -  Table  can be made based on annual p r e c i p i t a t i o n  precipitation  with  This  conclusion  bution  mean annual  to  that  B  annual the  of p r e c i p i t a t i o n t i o n 200  m are  a t 600  and  3.16 versus  Figure.  with  24-hour of  1200  m  to a  i n c l u d e d f o r s h o r t and  precipitation  at a l o c a t i o n .  the  of  further  For T r a n s e c t  There-  long  distribution  on  shown i n Table reference  long  3.17  value  durations.  storm  precipitaA,  record,  precipitation  term  of  e l e v a t i o n i s compared  precipitation  are  2.6-7.0 2.6-4.6 2.6-4.1 2.6-3.7  24-hour  examining  1970-71 winter  Results  (percent) Other C o a s t a l Stations  distribution  for  by  a  B on Figure 3.12.  precipitation  storms.  the  index  i s supported  maximum  that  that  i s an  A and  distribution  f o r three  indicate  suppose  elevation  from T r a n s e c t s  average  3.16  to  t i o n data  Transect  on each  3.6-5.3 3.6-4.7 3.6-4.5 3.6-4.4  estimate  reasonable  Table  Precipitation  included  for  in  precipitation  by envelope curves  Results  of  precipita-  3.16  2.7-4.9 3.2-4.8 3.4-4.7  rainfall.  24-hour  R a t i o of 24-Hour to Annual P r e c i p i t a t i o n West Coast of E a s t Coast of Vane and Vane, i s l a n d Vane. I s l a n d Fraser V a l l e y  Annual P r e c i p . (mm)  i t is  consistent  summarized  24-hour  R e l a t i o n s h i p Between 24-Hour and Annual  fore,  the  distrito and  that at  i s compared where  ratios  taken at  eleva-  - 114 -  Table 3.17 Distribution  o f s h o r t and Long D u r a t i o n  Precipitation  R a t i o of P r e c i p i t a t i o n Amounts 600 m:200 m 1200 m:200 m TRANSECT A Average Annual p r e c i p . Ave. Annual Max. 24-Hr P r e c i p . TRANSECT B Winter 1970-71 Dec 6-7, 1970 Dec 9-11, 1970 Feb 13-15, 1971  Even be  though  used  quired are  results  as an index  i s oftentimes  example, during  variations  a site  more . r e l i a b l e wetter  which  to assess purposes.  situations  more r e c o g n i z a b l e i n vegetation  1 1 1 1  .31 .12 .35 .32  annual  when  observations  procedures  of longer  than and  local  duration  cover  may  be  For  apparent  l o c a l r e s i d e n t s may be  as areas  above may p r o v i d e  of storm  precipita-  rainfall.  of deeper  of s u f f i c i e n t p r e c i p i t a t i o n  noted  the d i s t r i b u t i o n  such  i s s t i l l re-  recording stations  t h a t f o r storm forest  .79 .31 .88 .79  p r e c i p i t a t i o n can  judgement  or i n t e r v i e w s with  In the absence  investigative  1 1 1 1  3.17 suggest  However, d i s t r i b u t i o n  regarding  site,  design  design  reconnaissance,  fields.  1 .28 1 .31  f o r 24-hour p r e c i p i t a t i o n ,  f o r engineering  not a v a i l a b l e .  tion  shown i n Table  1 .13 1.13  snow or  records  on  the o n l y b a s i s on  precipitation  f o r engineering  - 115  3.7  SUMMARY  1.  Rainfall  i n t e n s i t y data  Service  (AES)  Columbia. that for  2.  for  Gauge  recommended mountainous  are  each  and  IDF  return  i n most  by  World  the  study period  by  period,  but  variation  of  region  Environment  region  of  i s much  British  less  Organization  than  (1970)  do  rainfall characteristics  Intensity-Duration-Frequency  average i n t e n s i t i e s not  provide  for a given  information  (IDF) duration  regarding  varia-  i n t e n s i t i e s w i t h i n a s i n g l e storm.  analyzing a  the  summarizes  producing  curves p r o v i d e  for  of  coastal  Meteorological  Service  c h a r a c t e r i s t i c s of  by  the  Atmospheric  terrain.  tions i n r a i n f a l l  Regional  in  density  station  Curves.  a v a i l a b l e from  stations  Atmospheric Environment at  3.  58  -  the  given  IDF  curves  variation  duration  depth w i t h  in  are  investigated  rainfall  (depth-frequency  duration  for a given  depth  in  with  this  return  relationships)  return period  and  (depth-  duration r e l a t i o n s h i p s ) .  4.  Ratios fall  of  rainfall  magnitude  regional  depth are  alone.  This  used  method  c h a r a c t e r i s t i c s when  between s t a t i o n s .  For  the 58  Columbia, 24-hour r a i n f a l l with 75 mm  to  t o 3500  380 mm.  mm,  and  i n the  the  analysis rather  i s one  approach  amount of  to  rainfall  than  identifying is  different  stations available in coastal a 100-year r e t u r n p e r i o d  mean annual  p r e c i p i t a t i o n ranges  rain-  British  ranges from from  650  mm  - 116 -  5.  Results  of  duration  regional  illustrates  regional  range  investigated  i n this  AES  prepared  seldom  f o r depth-  of depth of  and 3.5,  ratios  storm  on each  rainfall  IDF  study  curves.  intensity  data  i n design  of s i n g l e  storm  a t the same 58 s t a t i o n s  Development  from  IDF  situations  only  of  curves  synthetic  i s an  because  rainfall f o r which  hyetographs  approach  single  storm  commonly data a r e  available.  R e s u l t s o f a n a l y s i s of s i n g l e storm r a i n f a l l data i n c o a s t a l Columbia 24-hour  are  shown  rainfalls  illustrates  in  those which  B r i t i s h Columbia  F i g u r e 3.8.  which  time d i s t r i b u t i o n s  tend  of extreme  shorter  6-hour  durations,  produce  intenstities  a  curve  and  represents  the upper  limit Typical  recorded i n c o a s t a l  are shown on F i g u r e 3.6.  and i n F i g u r e 3.8 based  about  linear  24-hour r a i n f a l l s  IDF  beyond  lower  British  have p e r i o d s of h i g h e r i n t e n s i t y .  of h o u r l y  curves  The  t o be  Comparison  would  in  Columbia.  are  on  are shown  i n F i g u r e 3.4  characteristics  of the time d i s t r i b u t i o n  applied  8.  narrow  Regional analysis  based  7.  relationships  The r e l a t i v e l y  coastal British  6.  of IDF curves  and depth-frequency  respectively. figure  analysis  rainfall  durations  rainfall  synthetic  intensities  the  i n F i g u r e 3.4  on s i n g l e two  intenstities hyetograph  storm data shows  curves  are  similar.  e s t i m a t e d from  with  based  greater  on that For  IDF c u r v e s  maximum  than have been observed to occur w i t h i n s i n g l e  hourly  storms.  - 117  In p r a c t i c e of  9.  the  hourly  two  -  curves  rainfall  can  intensities  engineeer  i n the absence of s i t e  Analysis  of  produces  results  Columbia. 3.14,  rainfall  to  A n a l y s i s of U.S.  stations  further  at higher  coastal British  10.  to  be  considered  data  those  the  from  estimate  shorter  documented  e l e v a t i o n s than  now  Local variations f o r a l l storms. meteorologic  be  data,  the  Washington  of  British 3.12  and  rainfall  provides  s i n g l e storm  i n storm  intensities  rainfall  with  Rainfall distribution  250  Regional  a p p l i e d to 24-hour data  results  available  in  rainfall  are  at  and,  coastal  rainfall these  limited  available  mountain  rainfall  crests.  distribution  of  In  annual  the  to  greatly  purposes.  elevation  are  is controlled  data  charac-  therefore,  for design  B.C.  stations  not  constant  by s i t e  c o n d i t i o n s which e x i s t -during each storm.  t h a t d u r i n g extreme events, to  range design  coastal  are c u r r e n t l y  24-hour d a t a .  duration  assessment of  up  for  to a p p r o x i m a t e l y  expand the data base c u r r e n t l y a v a i l a b l e  tion  the  and  i n B r i t i s h Columbia, and  which r e c o r d o n l y can  nary  Oregon  regional applicability  for application  teristics  ic  by  the  Columbia.  especially useful  11.  on  data.  R e g i o n a l c h a r a c t e r i s t i c s of IDF curves and  stations  set l i m i t s  d a t a , i n c l u d e d i n Tables 3.11,  characteristics identified from  used to  intensity  similar  illustrates  be  in coastal  B.C.  specifPrelimisuggests  i n c r e a s e s l i n e a r l y with e l e v a absence  precipitation  i n d i c a t o r f o r the d i s t r i b u t i o n of extreme storm  of  historical  can  be  rainfall.  used  storm as  an  - 118 -  4.  PHYSICAL ASPECTS OF WATER FLOW THROUGH SNOW  4.1  INTRODUCTION  Development floods its  of hydrograph  requires  that  procedures  the r o l e  from  the b a s i n .  rain-on-snow development anism.  of i n t e r n a l  Quantitative  percolation  through  saturated  layer.  internal  drainage  water  drainage  in a  vertical  taken  (i)  to review a v a i l a b l e  and  snow  hydrology;  i n this  study  literature  on r u n o f f r e f o r extreme  the snow medium or  i s the dominant r o u t i n g  been  proposed  unsaturated  describing zone  i s also available  to a s s e s s  controls  mechwater  and a b a s a l  to suggest  t o the f l o w of l i q u i d  results  with  to t h e i r  floods.  the r o l e  that an  runoff during  of a snowpack i s :  i n the g e n e r a l areas  ( i i ) to a s s e s s  pertain  regard  regard to  floods.  approach  be  have  through  network, not water p e r c o l a t i o n ,  The  to rain-on-snow  channels  formulations snow  rain-on-snow  q u e s t i o n which a r i s e s  percolation  However, evidence  extreme rain-on-snow  rain-on-snow  r u n o f f and i t s e f f e c t  A fundamental  i s whether  of s i m u l a t i n g  o f a snowpack be assessed with  c o n t r i b u t i o n of snowmelt t o t o t a l  sponse  for  capable  results  water through impact  of r e s e a r c h snow; and ( i i i )  on hydrograph  Once the r o l e  of snow p h y s i c s studies  to i n t e r p r e t  procedures  of a snowpack on b a s i n  i s a s s e s s e d , then requirements  which  o f a hydrograph  required response model can  established.  O n l y those p h y s i c a l a s p e c t s of water f l o w through snow which a f f e c t on-snow f l o o d  hydrographs  i n the c o a s t a l  r e g i o n of the P a c i f i c  rain-  Northwest  - 119 -  are of  assessed liquid  aspects (1945, water  i n this  water  flow  provided  transmission  percolation f l o w along (1976)  Available  through snow some of  i s extensive;  describing For  quantitative  through  of water  and  heterogeneous  snow i n t e r a c t i o n  snow and  Gerdel  descriptions  of  for v e r t i c a l  homogeneous snow (1971, 1972),  of a snowpack (1974a), water  physical  example,  through snow; Colbeck developed t h e o r i e s  the base flow  snowpack response to i n p u t s  literature  the e a r l i e s t  through u n s a t u r a t e d  and  analyses  In p a r t i c u l a r ,  i s examined.  of water 1954)  study.  saturated  f l o w i n a d r y snowpack  (1979a);  more  microscopic  snow metamorphism have  been  undertaken by deQuervain (1973) and Colbeck (1982a, 1983); water p r e s s u r e and  capillary  and Wankiewicz Colbeck is  within  a snowpack were assessed by Colbeck  (1978a); and g r a i n  (1979b, 1982b).  available  water  effects  from  and geometry were analyzed  An overview of much of the r e s e a r c h  Colbeck  percolation  clusters  (1978)  processes  or Wankiewicz  through  (1974b)  (1978b).  homogeneous  snow  A  is  by  noted above summary of included  in  Appendix IV.  It  was  originally  envisioned  that  a contribution  of t h i s  study would  be  the i n c o r p o r a t i o n of water p e r c o l a t i o n p r o c e s s e s i n t o a hydrograph model. However, assessment lowing  inputs  drainage ism  network,  during  which  of  of snow metamorphism and  liquid  water  to a  snowpack  not water p e r c o l a t i o n ,  extreme  leads to t h i s  rain-on-snow.  f l o w path development suggests that  i s the dominant  Examination  of  an  fol-  internal  r o u t i n g mechan-  available  literature  c o n c l u s i o n and the consequences of the c o n c l u s i o n  hydrograph procedures are p r e s e n t e d i n t h i s C h a p t e r .  on  -120-  Development of hydrograph  procedures  considering  than an i n t e r n a l  drain-  age network i s the primary r o u t i n g mechanism through the snowpack i s p r e sented dures  i n Chapter 5.  Preliminary results  i n Chapter 5 c o n f i r m s  additional  runoff  delay  of a p p l i c a t i o n of these proce-  t h a t d u r i n g extreme rain-on-snow  needs  to  be  included  for  floods,  water  no  percolation  through the snow.  4.2  FLOW PATHS AND SNOW METAMORPHISM  A mountainous  snowpack  i s highly  variable  i n both  snowcover i s d e p o s i t e d by a sequence  of d i s c r e t e  layered  snow  medium.  drifting wind and  which  crust,  of  example,  the s u r f a c e may cycles  can  snow metamorphism  of p r e c e d i n g c l i m a t o l o g i c a l  Layering  within  fect  on  whether  be  lead a t any  the  given  be  time,  rearranged  the snow h o r i z o n would  radiation,  ice layers.  therefore,  i s the  the  season  and  The  result  impede, a c c e l e r a t e  affects  or have no e f -  For example, some l a y e r s impede downward a  redistribution  of flow, and horizons.  Columbia  dye  are  flow  l a y e r s depend-  can d e v e l o p where f l o w c o n c e n t r a t e s below impeding phenomena  by  a higher density  Wankiewicz (1978b) c a t e g o r i z e d  some r e g i o n s cause  these  A  i s usually a  a b s o r p t i o n of s o l a r f o r m a t i o n of  space.  conditions.  on f l o w through the pack.  percolation,  to  may  repacks them i n t o  g l a z e d by  and  storms and  surface  snowpacks occurs throughout  paths taken by melt water. ing  the  breaks down g r a i n s and  freeze-thaw  state  For  time  well  documented  by  in British  studies  f l o w through snow undertaken by Wankiewicz (1976) and Jordan  fingering  of  (1978).  water  - 121  perhaps that  the  most  snowpack  properties  qualified  of  the  as  (Colbeck, ripe  snow.  is  isothermal  rather  snow h y d r o l o g y  v a r i e s with  remain  a l s o be  1973).  near  A  warm,  wet  Warm  0°C  categorized  is  physical  d i s c u s s i o n of snowpack response must  snow p r o p e r t i e s being  (Smith,  presented  at  0°C,  in  and  "irreducible-water  measure  as  considered.  "wet"  most  of  are the  when l i q u i d is  commonly  Much  Northwest can  snowpacks  during  snowpack  of  water  held  the  following  f o r wet  those snow  water  be  whose  season.  is  referred  the  pore  saturation". i n place  volume.  Once  Colbeck ferent shows  of water content snowpacks have  (1976).  For  an  as  the  rainfall  and  and been  input  snow c o n d i t i o n s was input,  liquid  water  Irreducible-water absorbed  or  present to  as  a  of  examined as and  4.1b  content  exceeds  saturation water  and  to equal  saturation  is  is  a  has  about  7%  satisfied, processes  1973).  s i z e on  investigated rain,  1957)  snowpacks,  through the snowpack by  Davidson,  grain  warm  capillary  (Scheidegger,  transmitted  dominated by g r a v i t y (Colbeck  homogeneous  for  irreducible-water  a d d i t i o n a l water i n p u t s are  effects  sections  snow whose  been shown through e x p e r i m e n t a t i o n  The  but  in  snowpack.  Analysis  of  recognize  c o a s t a l mountains of the p a c i f i c  "warm"  1982a).  to  Therefore,  a d e s c r i p t i o n of  temperature  snow can  concept  i s not-constant,  snowpack i n the  interior  the  the by  categorized  This  response  of  be  important  -  water p e r c o l a t i o n in a  theoretical  water p e r c o l a t i o n f o r shown on  through 4.1d  F i g u r e 4.1. show the  through study  by  three  dif-  Figure  4.1a  corresponding  - 122 -  I» 10  la) Roin - on-snow  0.8 0.6 0.4 0.2 _l  0  '  '  4  •  '  i  I  8  i  L  12  16  12  16  -J. l  20  i  i  i  i_  24  28x10  24  28x10'  24  28xl0  24  28x10'  s  (b) Ripe Snow  I « 10 h 0.8-  o oj in  0.6-  £  •  0.4-  Z>  •  0.2_l_  4  tile) Refrozen  8  20  Snow  J  (d) Fresh Snow  I x 10'' 0.8u  a>_ i/>  £  0.6-  0.4 3  0.212  16  20  Time (sec)  F i g u r e 4.1  Snowpack Response  to Rain-On-Snow ( a f t e r Colbeck,  1976)  - 123 -  response  for:  ripe  snow whose absorbed and c a p i l l a r y water  are  satisfied;  but  whose r e s i d u a l water i s r e f r o z e n ;  grain  sizes.  relatively  refrozen  As  snow which has the same g r a i n  illustrated  fast, inflow  on  s i z e s as r i p e  and f r e s h snow comprised  Figure  and o u t f l o w  occurs as o u t f l o w ; r e f r o z e n  requirements  4.1, response  shapes  snow r e q u i r e s  snow  of s m a l l e r  of r i p e  snow i s  are s i m i l a r , and a l l  an i n i t i a l water i n p u t  inflow  to r a i s e  snow temperature to 0°C and then responds much as r i p e snow; and response time o f f r e s h snow i s longer because water i s needed to s a t i s f y the i r r e ducible  water  slower. from  These  content, three  and water  examples  a snowpack f o l l o w i n g  movement  illustrate  through  that  finer grain  sizes i s  i n some i n s t a n c e s  outflow  a rain-on-snow event may be r e l a t i v e l y  small,  w h i l e f o r a r i p e snowpack o u t f l o w can be f a i r l y r a p i d and equal i n volume to r a i n and snowmelt  Introduction to  inputs.  of l i q u i d  accelerate  water i n t o a snowpack causes metamorphic  rapidly.  processes  C h a r a c t e r i s t i c s o f t h i s aging p r o c e s s are summa-  r i z e d by Colbeck (1977) and i n c l u d e :  i) rapid 3 mm  ii)  grain  growth  occurs  until  uniform  grain  diameters  2 to  develop.  permeability  o f wind  crusts  and i c e - l a y e r s  increases  l i q u i d water moves through the snowpack.  iii)  of  snow g e n e r a l l y d e n s i f i e s d u r i n g  melt metamorphism.  r a p i d l y when  - 124 -  In  c o n j u n c t i o n with  snow,  Gerdel  integrate; flow  horizontal  approximately  i c e planes  and v e r t i c a l to  internal  small  equal  to the r a t e  vertical  unsaturated  "further  study  versus open channel  and  basal  ... t o determine  their  p e r m e a b i l i t y i n c r e a s e s due to g r a i n  frictional decreases  A  follows d i s t i n c t  runoff  causes  the response  develop;  the  internal  and r a i n  will  a t the snow  flow  be  surface.  t h e o r i e s f o r both through  the e x t e n t  snow  that  of s a t u r a t e d  flow  by  routes channels  homogeneous snow, w e t t i n g -  Once flow paths  growth and f r i c t i o n a l  f o r subsequent to  are e s t a b l i s h e d ,  enlarge  flow. and,  melting  Additional consequently,  time o f the snow c o v e r .  review  undertaken  routes.  preferential  melting  comprehensive  input  t h a t even i n r e l a t i v e l y  advance  become  when  dis-  f l o w beneath the snowpack".  (1977) noted  they  and  of snowmelt  saturated  front  and  channels  i n h i s paper which presented  flow  i s needed  drainage  o f water  through  i n wet snow r a p i d l y  streams,  i s established discharge  (1974a) admitted  Colbeck  that  are d i r e c t e d  network  Colbeck  s t u d i e s o f the t r a n s m i s s i o n o f water  (1954) observed  channels  drainage  field  of  snow  leading  accumulation,  researchers  distribution,  i n snow  hydrology  melt  and  (Colbeck  e t a l . , 1979) p r o v i d e s the f o l l o w i n g summary:  i ) d e l a y i n r u n o f f from by  theory  based  a snowpack i s u s u a l l y l e s s  on homogeneous snow.  the development of d i s t i n c t  flow  than  The apparent  channels.  that predicted explanation i s  - 125 -  ii)  initiation structure  of f l o w channels i s p r o b a b l y of  the  f l o w known as  iii)  once  snow  cover  rather  controlled  than  the  by the d e t a i l e d  inherently  unstable  fingering.  preferential  drainage  routes  are  initiated,  they  are  self-  perpetuating.  i v ) drainage  from  the  snowpack  becomes  more  rapid  as  melt  channels  develop.  v) development causes  a  above  work  is  dominant  Consequences  of  rain-on-snow  are:  covered  basis  watershed  this  routing  mechanism  conclusion  ( i ) water  watershed becomes characteristics a  snow metamorphism  to undergo  suggest development  on  a  effectively  transition  snowcover.  and  terrain might  This  of an i n t e r n a l during  hydrograph  percolation  i n a hydrograph model,  response without  channels d u r i n g  from  snow-  to t e r r a i n - c o n t r o l l e d water movement.  observations the  simulated  flow  snowcovered  controlled  The  of  (ii)  assessment  of  do  net-  rain-on-snow.  procedures f o r  processes  not  extreme  need  to  be  as water movement i n a snow-  controlled,  approach  extreme  drainage  i t i s possible  conditions snowpack  which  that would  response  basin occur  forms  the  f o r hydrograph procedures developed i n Chapter 5 f o r a p p l i c a t i o n  to extreme rain-on-snow f l o o d s i n the c o a s t a l  region.  - 126  WATER INPUTS DURING RAIN—ON—SHOW  4.3 Water  transmitted  contributed coastal  by  return 380 mm.  typically The  snowpack and  are  derived  in  determined  in  snowmelt. this  Chapter  in  3,  estimates  coastal  3  these  events  about  3 and  8 percent,  corresponding  range  for  British  During  events chosen  during  a  rain-on-snow  Typical  event  i n p u t r a t e s f o r the  section  based  and  snowmelt  estimates  rainfall  with  on  is  on  hourly  rainfall using  equations.  i n Chapter  period  a  rainfall  temperature-index  shown  through  both  region  intensities  As  -  24-hour  Columbia  minimum and  TABLE  from  about  of  the  24-hour  intensities  75 mm  are shown i n T a b l e  4.1.  4.1  Hourly I n t e n s i t i e s Minimum Average  to are  rainfall.  f o r three 24-hour  HOURLY RAINFALL INTENSITIES  24-Hour Rainfall (mm)  100-year  maximum h o u r l y i n t e n s i t i e s  respectively,  of h o u r l y r a i n f a l l  for i l l u s t r a t i o n  range  a  (mm/hr) Maximum  75  2  3  6  150  5  6  12  380  11  16  30  - 127  The  generation of  of' melt its  i s dependent on  environment.  transfer net  with  air,  snowpack  the  Detailed Corps  analysis  of  available  this  equations  and  and  processes  the ground, and  these  processes  (1956), of  and  is  site  temperature-index  rates to  during  estimate  equations  rain-on-snow snowmelt  are  events.  i s an  used Use  alternative  U.S.  Army  studies  are Snow  The U.S.  which  s i m u l a t e more complex  Temperature-index i n the  equations Pacific  of E n g i n e e r s , 1972)  equations  as an index f o r snowmelt by  been  applied  Northwest both and  available  rain-on-snow  have  events  to  detailed  Army Corps of Engineers  empirical  relationships  typical  temperature-index  approach  used  during  the  water.  ( e . g . Western  of  can be  Seven  heat  from  to e s t i m a t e  showed t h a t temperature  Corps  radiation,  the  specific  snow conferences  heat  convective  from  and  1985).  thermo-budget snowmelt a n a l y s i s .  modelling  influence  condensation  available  amount  snowpack  heat c o n t e n t of r a i n  various  annual  by  the  the  (solar)  radiation,  released  where  which  shortwave  atmosphere) heat  process  exchange between  i n c l u d e absorbed  from  i n proceedings  study,  snowmelt  of  Engineers  Conference,  n e t heat  a i r , latent  c o n d u c t i o n of heat  thermodynamic  sources  (terrestrial  from  is a  the  Various  a  longwave  transfer  In  snowmelt  -  physical  deriving  phenomena.  extensively for  i n the United S t a t e s  (1956)  snowmelt  (U.S.  Army  Canada (Quick and P i p e s , 1976).  in  the  have  literature  recently  for  been  estimating  evaluated  (1985) f o r i s o t h e r m a l snowpack a t 0°C  a t two  Mountains of C a l i f o r n i a .  measured and compared  Snowmelt was  sites  by  i n the  snowmelt Kattelmann  Sierra  Nevada  to estimates  - 128 -  from  each  of seven  over an 11-year The  snowmelt  error  snowmelt equations  f o r rain-on-snow  p e r i o d on one b a s i n and a 24-year  equation  that  had  the lowest  events  occurring  p e r i o d on the o t h e r .  computed  (RMSE) a t each o f the two b a s i n s was proposed  root  mean  square  by Dunne and L e o p o l d  (1978): = (0.142 + 0.051J7 + 0.0125.P)T + 0.25  M where  M = daily  rainfall  The  2  equation  except wind  The  proposed  developed  the Corps  2  = windspeed  at 2 m  (m/s);  P =  daily  by Dunne and Leopold by  the U.S.  of Engineers  Army  i s similar  Corps  to the w i d e l y  of Engineers  e q u a t i o n has a l a r g e r  coefficient  (1956), f o r the  term: M  where  (cm); U  (cm); and Ta = mean a i r temperature ( ° C ) .  relationship  used  snowmelt  (4.1)  a  U^  U.S.  = (0.133+ 0 . 0 8 6 l 7 j + 0 . 0 1 2 6 P ) T + 0 . 2 3 5  = windspeed a t 15 m  Army  Corps  of  e q u a t i o n f o r rain-on-snow,  (4.2)  a  (m/s).  Engineers  (1956)  developed  another  not i n c l u d e d i n the study by Kattleman  snowmelt (1985),  f o r f o r e s t e d areas: M =  (0.339 + 0M26P)T  a  + 0.13  (  4  -  3  )  - 129 -  Eqn  4.3  i s commonly a p p l i e d  to e s t i m a t e  seldom a v a i l a b l e f o r a p r o j e c t s i t e . mated are  using  Eqns. 4.1  included  conditions  and 4.3  f o r comparison  snowmelt  because  Representative  wind  snowmelt  rates  f o r rain-on-snow i n the c o a s t a l  i n T a b l e 4.2  f o r a range  of  data  are  esti-  mountains  climatological  shown f o r i l l u s t r a t i o n .  TABLE  4.2  REPRESENTATIVE SNOWMELT RATES  24-Hour Rainfall (mm)  Mean A i r Temperature  CO  4.3  75 75  2 8  7 21  17 62  10 36  1 50 150  2 8  9 29  19 70  12 44  380 380  2 8  15 52  25 93  18 67  Comparison snowmelt  of  Results  results  estimates  on ungauged  and  i n Table 4.2 illustrates  based  produce  shows  the  effect  the d i f f i c u l t y  of  wind  i n estimating  speed  on  snowmelt  watersheds where c l i m a t e d a t a are not a v a i l a b l e .  from T a b l e s 4.1  estimates to  D a i l y Snowmelt (mm) Eqn. 4.1 Eqn. 4.1 Eqn. u = 0 m/s u = 10 m/s  on  Eqn.  for typical 4.3  representative  rainfall  are combined water  inputs  rates  and 4.2  for i l l u s t r a t i o n to  a  snowpack  in  for  snowmelt  i n Table the  r e g i o n f o r a range of r a i n f a l l events and mean a i r temperatures.  4.3  coastal  - 1 30 -  TABLE 4.3 REPRESENTATIVE RAINFALL AND SNOWMELT INPUTS  Mean Temp. ( °C)  Daily (mm)  Rainfall Ave. H r l y (mm/h)  Snowmelt Daily Ave. H r l y (mm) (mm/h)  Total Ave. H r l y (mm/h)  2 8  75 75  3.1 3.1  10 36  0.4 1.5  3.5 4.6  2 8  150 150  6.3 6.3  12 44  0.5 1.8  6.8 8.1  2 8  380 380  15.8 15.8  18 67  0.8 2.8  16.6 18.6  - 131  -  4.4  SUMMARY  1.  Development  of hydrograph procedures capable of s i m u l a t i n g  snow f l o o d s  requires  regard  to  effect  on  which  that  the r o l e  i t s contribution runoff  arises  of  extreme  snowpack be  snowmelt  response from  for  of a  to  the b a s i n .  rainfall  on  total A  ripe  rain-on-  assessed  with  runoff  and i t s  fundamental  question  snowpacks  is  whether  water p e r c o l a t i o n through the snow medium or development o f i n t e r n a l drainage  channels  evidence  suggests  is  the  that  dominant  the  routing  drainage  mechanism.  channel  Available  routing  mechanism  c o n t r o l s r u n o f f d u r i n g extreme rain-on-snow e v e n t s .  2.  Temperature,  water  content  and  grain  size  affect  response of snow-  packs t o rain-on-snow as shown, f o r example, on F i g u r e 4.1. d u c t i o n of l i q u i d water i n t o a snowpack causes metamorphic to  accelerate  rapidly  such  that  rapid  grain  growth  Intro-  processes  occurs,  perme-  a b i l i t y of wind c r u s t s and i c e - l a y e r s i n c r e a s e s and snow d e n s i t i e s .  3.  A comprehensive response  time  report  by  i s usually  Colbeck e t . a l . , less  1979  than p r e d i c t e d  by  concludes snowpack water  percolation  t h e o r y , and the apparent e x p l a n a t i o n i s development of d i s t i n c t channels. effectively  Development  of  flow  channels d u r i n g  snow  flow  metamorphism  causes a snow covered watershed to undergo a  from s n o w - c o n t r o l l e d to t e r r a i n - c o n t r o l l e d water movement.  transition  - 132 -  If  the development  of an i n t e r n a l  d r a i n a g e network  i s the dominant  r o u t i n g mechanism d u r i n g extreme rain-on-snow, then the consequences on  hydrograph procedures f o r extreme  percolation model, and terrain  processes  not need  to be  istics  might  cover.  This  i t i s possible  approach c o n d i t i o n s assessment  procedures  of  which  snowpack  developed  that  in  are:  simulated  ( i i ) as water movement i n a snowcovered  controlled,  hydrograph  do  rain-on-snow  basin  would  i n a hydrograph watershed becomes  response  character-  occur w i t h o u t a snow-  response  forms  Chapter 5  for  extreme rain-on-snow f l o o d s i n the c o a s t a l  ( i ) water  region.  the  basis  application  for to  -133-  5.  DEVELOPMENT OF RAIN-ON— SNOW HYDROGRAPH MODEL  5.1  PERSPECTIVE ON HYDROLOGIC MODELS  Development a balance model  data to  be maintained  implementation.  runoff while  of a h y d r o l o g i c model f o r a p p l i c a t i o n  processes a  may  less  may  complex  between  F o r example, require model  not a d e q u a t e l y  ability  of a v a i l a b l e d a t a . presented  input  complexity  data  physical  which  which ' operates  therefore,  and data  a detailed  describe basin  s u c c e s s f u l modelling,  developer's  model  available for d e s c r i p t i o n of  are o f t e n u n a v a i l a b l e ,  with  response  i s often  purposes r e q u i r e s t h a t  more r e a d i l y  available  i n a l l cases.  The key  dependent  to s i m u l a t e a complex process  on  the model  w i t h i n the l i m i t a t i o n s  T h i s process of t r a d e - o f f s i s i l l u s t r a t e d  on sketches  on F i g u r e 5.1.  a) T r a d e - o f f Diagram ( a f t e r Overton and Meadows, 1976)  F i g u r e 5.1  b) M o d e l l i n g Complexity ( a f t e r Haan and B a r f i e l d , 1978)  P e r s p e c t i v e on H y d r o l o g i c Models  - 134 -  There  are s t i l l  adopted Project of  many  i n addition objectives  approaches t o those  into  developer.  General  categories  below  by  simply  which  can be  trade-offs  noted  above.  analytical  models  descriptions  requirements  procedures may be i n -  on the p e r s o n a l  of h y d r o l o g i c  and b r i e f  modelling  the approach and output  instances  a model based  (1973) are noted  necessitated  may d i c t a t e both  the model, w h i l e i n other  corporated  to h y d r o l o g i c  preference proposed  are p r o v i d e d  by  of the Clarke  to c o n t r a s t  d i f f e r e n c e s i n t h e i r approach.  Deterministic  vs S t o c h a s t i c :  When v a r i a b l e s of a model are s p e c i f i e d by p r o b a b i l i t y d i s t r i b u t i o n s , the model i s s t o c h a s t i c ; when each v a r i a b l e specified  condition,  i s assigned a s i n g l e v a l u e  the model i s d e t e r m i n i s t i c .  Physically-based  vs E m p i r i c a l :  Physically-based  models undertake a n a l y s i s by r i g o r o u s  matical porate  for a  formulas which d e s c r i b e c o e f f i c i e n t s and  runoff  s o l u t i o n of mathe-  p r o c e s s e s ; e m p i r i c a l models  relationships  derived  from  observation,  incorexpe-  r i e n c e and experiment.  Continuous vs Event: Continuous operate  through  implemented input  models  only  variables.  generate  hydrographs  low and h i g h  flow  over  seasons;  long event  to e s t i m a t e a s i n g l e hydrograph  periods models  of time and are u s u a l l y  f o r a s p e c i f i e d s e t of  - 135 -  Lumped vs D i s t r i b u t e d : Lumped models t r e a t a watershed as i f i t were homogeneous; i n a d i s t r i b uted  model,  across  The  input  of t h i s  simulating  study  commonly  used  c h a r a c t e r i s t i c s are v a r i e d  flood  procedure  mountains  of the P a c i f i c  with  i s a subjective  a  specific  refers  to extreme  classification  design  objective.  to any f l o o d with  and i s  For t h i s  a return  period  than about 20 y e a r s .  Specifying analogous  that  only  extreme  rain-on-snow  to s e l e c t i n g a s p e c i f i c  which  occur  from  a basin  of importance i n many i n s t a n c e s  case  floods  from  through  will  the y e a r s .  of engineering  procedures  taken  with  an  of  design  s i t u a t i o n s i n the c o a s t a l r e g i o n o f the P a c i f i c  are g e n e r a l l y  information  data  f o r rain-on-snow  commonly  l i m i t e d to the f o l l o w i n g  analyzed  Extreme  planning  o f hydrograph awareness  be  the wide spectrum  Development  data  capable of  the procedures be a p p l i c a b l e  flood  generally  a hydrograph  i n the c o a s t a l  that  Extreme  i n context  extreme  greater  floods  I t i s intended  conditions.  events  response  i s to develop  rain-on-snow  Northwest.  study  and b a s i n  the b a s i n .  goal  flood  data  available  (although  is  of r u n o f f floods are  and d e s i g n .  floods for  i s underengineering  Northwest. supplemental  These site  may a l s o be a v a i l a b l e i n some i n s t a n c e s ) :  i ) topographic  mapping  a t approximate  scale  1:50 000.  Even  at  this  - 136  relatively 12 by  ii)  large scale  20 cm on a topo  estimate  data  f o r the  recorded  at  over  basin a  this  of  the b a s i n . of  interest  These d e s i g n data based  on  Even  analysis  without  to  the  is especially  basin.  difficult  In  estimate  of  snowmelt  i n c l u d e an  ture-index budget  snowmelt  energy  equations.  approach  mountainous  over  to  the  basin.  balance  because  about  Sufficient snowmelt  locations  and,  are  and  climatological  of  site  rainfall data  the  for  appliregions can  elevation.  for  estimating  e m p i r i c a l temperadata  f o r an  generally unavailable  therefore,  usually  precipitation  Procedures  approach  are  mountainous  v a r y over r e l a t i v e l y s h o r t d i s t a n c e s both i n p l a n and  iii)  i s only  engineer must n e v e r t h e l e s s assess  r e g i o n a l data  assessment  b a s i n , f o r example,  2  regional station.  confirmation, a design cability  60 km  map.  of r a i n f a l l  estimated  a  -  at  temperature-index  energy remote  equations  are u s u a l l y a p p l i e d .  i v ) s i t e photos and/or s i t e obtained ment  of  for specific such  development.  items  as  reconnaissance. design land  Site information i s usually  p r o j e c t s to a l l o w q u a l i t a t i v e use,  forest  cover  and  drainage  assessnetwork  - 137  Based on flood  the o b j e c t i v e of t h i s  conditions  following  and  on  guidelines  -  study to analyze  l i m i t a t i o n s of  are  established  data for  o n l y extreme rain-on-snow generally  development  available,  the  of  hydrograph  a s i n g l e event  i n response  procedures:  i ) rain-on-snow to s p e c i f i e d  floods  will  be  input r a i n f a l l  analyzed and  snowmelt.  i i ) a d e t e r m i n i s t i c approach w i l l be  iii)  runoff  c h a r a c t e r i s t i c s of  the  as  adopted.  basin  will  be  represented  by  empiri-  cal relationships.  iv)  provision w i l l be  for  distributing  incorporated  rainfall  i n the model.  and  snowmelt  across  the  basin  - 138 -  5.2 The  CONTINUOUS FLOW VS EVENT MODELS effect  floods  on m o d e l l i n g  approach "of  can be i l l u s t r a t e d  analyzing  by examining  only  extreme  rain-on-snow  a fundamental d i f f e r e n c e between  continuous flow and event models.  Continous and  flow models a r e developed  for a  wide  their  simulation  which  operates  conditions. include  in  climatic  f o r a short  and  runoff  are d i f f e r e n t  period  i n response  (Streamflow  Synthesis  by U.S. Army Corps and P i p e s ,  the Columbia  River  1976). Basin  to f l o o d p r o t e c t i o n ,  navigation  Therefore,  to a s i n g l e s e t of i n p u t i n the P a c i f i c  i s applied  reservoir  Northwest  Regulation)  (1972) and the UBC  The SSARR Model to guide  of time  those of an event model  and R e s e r v o i r  of Engineers  periods  conditions.  from  Continuous f l o w models i n o p e r a t i o n  (Quick  related  of  capabilities  the SSARR  developed Model  range  to operate over long  Watershed  extensively  regulation  and hydro power.  Model  decisions  The UBC Model  is  used by the B.C. M i n i s t r y of Environment f o r annual f l o o d f o r e c a s t i n g  on  the F r a s e r  River  and by B.C. Hydro  on the Columbia  and Peace  River  systems.  One  primary  requirement  water balance over and  snow and o u t f l o w  separating the  long  continuous  periods  from  flow  model  between water inputs  the b a s i n .  This  i s to maintain  surface  runoff  runoff,  components  therefore  occurs  example,  routing  has  downstream  stormflow a  i s g e n e r a l l y accomplished by  as  and  different river  c h a r a c t e r i s t i c s of  a  i n the form of r a i n  p r e c i p i t a t i o n i n p u t s i n t o one of three modes of t r a v e l  basin:  these  of a  groundwater response  flow surface  flow.  Each of  characteristic  at d i f f e r e n t runoff  through  times.  and For  i s important f o r  - 139  simulating while  peak  routing  flows  of  -  following  groundwater  periods  flow  is  which occur long a f t e r storm  periods.  Event  models  to  basin  response  are  only  for  fast  response  their  to  that  groundwater  developed a  period  of  times  are  runoff  which  treated  contribution  to  of  flood  input  dominated  contribute  as  high  necessary  simulate  s p e c i f i e d set  of  intensity  to  estimate  flows  data. by  which  processes flood  "losses" during  the  computation  at  a  from  operate  relatively  peak.  later  flows  result  with  the  occurs  low  These models  to  streamflow  rainfall,  Inputs period  period  to  since  than  the  generated f l o o d hydrograph.  In  summary, a  over  long  model  continuous  periods  focuses  hydrograph.  by  only Project  streamflow model must account  routing  on  those  objectives  which, i n t u r n , e s t a b l i s h e s goal flood  of  this  peaks  centrated tribute  on  to  f a s t runoff  study  is  to  resulting  from  examining  the  the  runoff  components processes  d i c t a t e the  a modelling  develope  the  type of  hydrograph  proportion  generate  information  to be  and  inputs  An  event  a  flood  required  implemented.  procedures  Emphasis,  of r a i n  routing  separately.  which  approach  rain-on-snow.  f l o o d peak and  components.  runoff  f o r water  for  The  estimating  therefore,  is  con-  melt i n p u t s  which con-  c h a r a c t e r i s t i c s of  relatively  - 140  5.3  -  SELECTION OF MODELLING PROCEDURE  Two  procedures  fall  i n common use  were examined  rences. ploys  One  for possible  method  a l a g and  for generating flood  applies  application  concept  1970).  Examples  practice Haan,  using  1973),  (Wisner  and  the HEC-1  of  SCS-TR20 PNG,  (Soil  1982).  The  Conservation l a g and  and  lag  and  route  include  in  (Williams  1973)  and  each  method  rain-on-snow view and to  for  i n mountainous  initial  assess  rainfall-only  i t s potential  concepts shape.  the  r e g i o n s of  s c r e e n i n g of each  m e r i t s f o r more d e t a i l e d  Each o f  However,  a even  be the  method  for application  investigated  modified Pacific  OTTHYMO  1973).  in  this  employed  for application Northwest.  An  to  over-  i s undertaken  in this  section  to rain-on-snow  floods  and i t s  examination.  h y d r o l o g i c models  utilizes  could  and  i s incorporated i n  Army Corps of E n g i n e e r s ,  are  (Gray,  engineering  study to assess whether e m p i r i c a l r e l a t i o n s h i p s and c o e f f i c i e n t s by  em-  develop-  Canada  HYMO  Service,  techniques  occur-  the o t h e r  and  applied  route procedure  F l o o d Hydrograph Package (U.S.  Unit-hydrograph  1982)  commonly  procedures  rain-  i s a v a i l a b l e i n standard  (Linsley et a l . ,  h y d r o l o g i c models  unit-hydrograph  and  D i s c u s s i o n of the c o n c e p t u a l  ment and a p p l i c a t i o n of each of these procedures h y d r o l o g y t e x t s both i n the U.S.  from  to rain-on-snow f l o o d  a unit-hydrograph  route t e c h n i q u e .  hydrographs  different with  noted  above  procedure  these  which to  differences  employ  estimate each  unit-hydrograph unit-hydrograph  procedure  requires  - 141 that  basin  l a g and  determined. this  When  assessment  recession  recorded  constant(s)  flood  f o r a watershed,  o f t e n be estimated  of  hydrographs basin  the u n i t - h y d r o g r a p h are u n a v a i l a b l e  and  i s based  from e m p i r i c a l r e l a t i o n s h i p s .  on data  southern  British  available  Ontario  Columbia.  rainfall  events  modifications  t o make  l a g and r e c e s s i o n c o n s t a n t can  A g e n e r a l e x p r e s s i o n f o r b a s i n l a g i s presented It  be  from  throughout  by Watt and Chow  (1985).  the U.S. and from  Quebec  i n Canada, but does not i n c l u d e data Because  of  this  absence  i n the c o a s t a l mountain  of u n i t - h y d r o g r a p h  from c o a s t a l  of v e r i f i c a t i o n  even f o r  r e g i o n s , i t was concluded  procedures  would  that  not be attempted f o r  t h i s i n v e s t i g a t i o n o f rain-on-snow f l o o d s .  A  second  consideration  techniques in  i s their  rainfall  averaged variation  for discarding  inability  and snowmelt a c r o s s a b a s i n .  conditions  to be i n p u t  in rainfall  b a s i n , unit-hydrograph  procedures  l a g and route  procedure  must  Unit-hydrographs  be  f o r hydrograph  is  modified  travel  c h a r a c t e r i s t i c s o f the watershed. b a s i n , although  In i n s t a n c e s  accounted  when the  f o r across the b a s i n be sub-  elements.  C l a r k (1945) and i s based on the p r i n c i p l e  the  variations  require basin  r e q u i r e t h a t the d r a i n a g e  by  by two f a c t o r s :  unit-hydrograph  readily for spatial  to the model.  and snowmelt  d i v i d e d i n t o s m a l l e r watershed  The  to p r o v i d e  conventional  time  Storage  i n the l a g and route  a n a l y s i s was f i r s t that r a i n f a l l  through  the b a s i n  proposed  onto a b a s i n and storage  i s actually distributed procedure  across  i t i s c o n s i d e r e d to  occur a t the b a s i n o u t l e t and i s s i m u l a t e d by a s i n g l e  linear  reservoir.  - 142 -  Travel on  time  o f a water p a r t i c l e  hydraulic  ungauged are  principles.  mountainous  available.  to assess the  variation  outlet.  chrones,  Lines  from  This  basins  In t h i s  feature  when  only  instance,  i n travel  can be estimated  i s particularly  topographic  from  points  segments  a basin  topography  time  connecting  various  through  attractive for and s i t e  can serve  different  o f equal  of the b a s i n  maps  based  as an  photos  indicator  p a r t s of the b a s i n to  travel  time,  called i s o -  to the o u t l e t  can then  be  established.  Lag a  and route  single  tion  storage  i s required  adequate and  procedures  portion istics (U.S.  coefficient. f o r long  to s i m u l a t e  Pipes,  simulate  1976).  procedures  hydrograph  of  is  whether  storage  lag  routing  simula-  coefficient  i s not  of Engineers,  Engineers,  coefficients  event,  that  response  character-  by a s i n g l e  routing  coefficient  1973).  by  flood  1972; Quick  fast  A p p l i c a t i o n of  l a g and  route  r e q u i r e s , t h e r e f o r e , i n v e s t i g a t i o n to can be d e r i v e d f o r snow covered  determined  A second  f o r rain-on-snow  basins  question  events  are  from r a i n f a l l - o n l y on the same b a s i n .  on p r e l i m i n a r y assessment d e s c r i b e d  and route  r e s e r v o i r and flow  manner as i s a p p l i e d f o r r a i n f a l l - o n l y .  d i f f e r e n t than those  Based  affected  represented  determine i f storage c o e f f i c i e n t s a similar  a single  (U.S. Army Corps  t o rain-on-snow events  in  one l i n e a r  However, f o r a n a l y s i s of a s i n g l e  can be more r e a d i l y Corps  with  In i n s t a n c e s when continuous  periods  runoff  o f the r u n o f f  Army  storage  procedures,  above of u n i t  the l a g and route  procedure  hydrographs and i s selected for  - 143 -  further floods.  investigation The  focus  of  i t s potential  of a n a l y s i s  will  be  for application on  examining  to rain-on-snow  methods  for e s t i -  mating  t r a v e l time and the storage c o e f f i c i e n t f o r a snow covered  shed.  The  and  l a g and route procedure  snowmelt  inputs  model complexity  and  basin  and a v a i l a b l e  allows  response, data.  for spatial variation and  achieves  a balance  waterin rain between  - 144 -  5.4  SOURCES O F RAIN-OH-SHOW DATA  Research  into  on-snow  the development  floods  requires  a  of hydrograph procedures f o r extreme  watershed  with  the f o l l o w i n g  rain-  f e a t u r e s and  a v a i l a b l e data f o r a n a l y s i s :  (i) (ii) (iii) (iv) (v) (vi) (vii) (viii)  h i g h e l e v a t i o n mountainous b a s i n u n r e g u l a t e d streamflow l o c a l gauge which r e c o r d s r a i n f a l l i n t e n s i t y c o n t i n u o u s l y r e c o r d i n g streamflow gauge snow over e n t i r e b a s i n r a i n f a l l o c c u r r i n g over e n t i r e snowpack l o c a l gauge which r e c o r d s a i r temperature b a s i n which has e x p e r i e n c e d and recorded extreme f l o o d event  Based  on  review  other  climatological  watershed  of  data,  i n coastal  requirements basins  of a v a i l a b l e  were examined  the P a c i f i c  Columbia  needed  i n other  Northwest  precipitation  i t was concluded t h a t  British  to a standard  streamflow,  which  satisfies  f o r research.  segments  there  i n t e n s i t y and i s no s u i t a b l e  a l l of the above  A l t e r n a t i v e l y , drainage  of the c o a s t a l h y d r o l o g i c  and s u i t a b l e watersheds were i d e n t i f i e d  region i n the  Cascade Mountains i n Oregon.  Two  basins  floods.  i n Oregon  for detailed  One i s the Mann Creek b a s i n which  Basin  Snow L a b o r a t o r y  neers  f o r research  tory  were s e l e c t e d  studies  are i n c o r p o r a t e d  Engineers,  1956);  (WBSL) e s t a b l i s h e d  a  of snowmelt.  i n the t e x t climatological  H y d r o m e t e o r o l o g i c a l Log 1949-51  analysis  of rain-on-snow  forms p a r t of the W i l l a m e t t e  by the U.S. Army Corps of E n g i Results  from t h i s  Snow Hydrology summary  snow  (U.S. Army  i s available  labora-  Corps of  i n the WBSL  (U.S. Army Corps of of E n g i n e e r s ,  1952);  - 145 -  and  a  special  available  research  note  (U.S.  Army  Corps  of  E n g i n e e r s , 1955)  is  which documented a rain-on-snow event on the b a s i n i n February  1951.  The  second b a s i n  snow  flood  flood  The  U.S.  during  region and  i n December  1964.  Geological  in a  special  in  to d e t a i l e d  addition  floods.  Drainage b a s i n s locations  the  hourly  gauges  the  i n Chap-  i n the  e t a l , 1971);  are a v a i l a b l e  of  streamflow coastal  precipitation  from  the U.S.  of Lookout Creek, hydrographs  i n Oregon d u r i n g  to assess s t o r a g e  on  extent  presented p r e v i o u s l y  (Waananen,  analysis  analyzed  Perspective  areal  rain-on-  Wea-  1965b).  on s i x other watersheds  and t h e i r  the  (USGS) documented  data f o r the r e g i o n  (1965a,  of  storm f o r r e c o r d i n g  publication  ther Bureau  data  overview  Survey  the December 1964  climatological  5.1  An  e x p e r i e n c e d an extreme  and damage to the c o a s t a l r e g i o n was  t e r 2.3 data  i s Lookout Creek which  the December 1964  characteristics  analyzed  i n this  during  relative  magnitude  can be gained by comparing  unit  of  storm are a l s o  extreme  rain-on-snow  study are d e s c r i b e d  i n Oregon are shown on F i g u r e  available  discharges  recorded  i n Table  5.2.  rain-on-snow  i n T a b l e 5.1  flood  w i t h those  f o r maximum f l o o d s on r e c o r d i n c o a s t a l B r i t i s h Columbia shown p r e v i o u s l y on  F i g u r e 2.5.  peaks  This  comparison  shows  some of  the  December 1964  flood  r a t e among the h i g h e s t on r e c o r d , while the rain-on-snow hydrograph  r e c o r d e d on Mann Creek i s not a very extreme e v e n t .  TABLE 5.1 SOURCES OF RAIN-ON-SNOW FLOOD DATA  Drainage Area (km )  Gauge E l e v (m)  Date of Flood  Maximum Discharge (m /s)  Maximum U n i t Discharge (m /s)/km  Latitude  Longitude  1. Nestucca R i v e r  45  19  123  25  16.0  552  22 Dec. 1964  2. Grave Creek  42  39  123  13  57.3  718  22 Dec. 1964  177  3.1  3. Lookout Creek  44  13  122  15  62.4  376  22 Dec. 1964  189  3.0  4. S. Fork C o q u i l l e R.  42  44  124  01  105  570  22 Dec. 1964  340  3.2  5. W. Fork I l l i n o i s R. i  42  03  123  45  110  462  22 Dec. 1964  456  4.1  6. H i l l s  43  41  122  22  137  497  22 Dec. 1964  303  2.2  42  53  122  55  141  390  22 Dec. 1964  251  1 .8  44  18  122  10  13.0  817  7 Feb. 1951  7.3  1 Nov. 1950  15.6  Station*  7. Elk  Creek  Creek  8. Mann Creek Mann Creek  * see F i g u r e 5.2 f o r s t a t i o n  2  ( r a i n only)  location  3  24.8  3  2  1.6  0.6 1 .2  - 147 -  F i g u r e 5.2.  L o c a t i o n Map  f o r Oregon Watersheds  - 148 -  5.5 The  APPROACH TO MODEL DEVELOPMENT primary o b j e c t i v e o f t h i s  investigation  i s to develop a rain-on-snow  hydrograph model which can be a p p l i e d i n a c o n s i s t e n t manner to mountainous  watersheds  f o r model method  where  recorded  calibration.  that  available.  historical  flood  data  are not a v a i l a b l e  A l a g and route procedure has been  i s compatible with  limited  site  data  An o u t l i n e o f procedures which w i l l  selected  which  are commonly  be implemented  whether a l a g and route hydrograph model can be a p p l i e d  as a  to assess  f o r extreme  rain-  on-snow f l o o d s i s as f o l l o w s :  (i)  examine  methods  f o r estimating  travel  time o f a water  particle  through the b a s i n .  (ii)  tabulate  storage c o e f f i c i e n t s  derived  from a n a l y s i s of recorded  extreme rain-on-snow f l o o d hydrographs.  (iii)  a p p l y l a g and route procedure f o r a r a i n f a l l - o n l y event on Mann Creek  to examine  peaks  i n mountainous  coefficient.  whether  the f a s t  runoff  contribution  r e g i o n s can be simulated  using  to f l o o d  one s t o r a g e  - 149 -  (iv)  apply  l a g and route  Creek  to examine whether  snow, and compare  procedure  f o r rain-on-snow  event  the model can be adopted  the s t o r a g e  coefficient  on  Mann  for rain-on-  to t h a t on the same  basin f o r r a i n f a l l - o n l y .  (v)  a p p l y l a g and route procedure Creek  t o undertake  a  second  f o r rain-on-snow event application  on Lookout  o f the model,  assess storage c o e f f i c i e n t s d u r i n g more extreme f l o o d  I t i s g e n e r a l l y r e c o g n i z e d (e.g. Loague and Freeze, procedures graph  can u l t i m a t e l y  through  a  However, while tion,  they  results  sequence  such  be m o d i f i e d  e x e r c i s e s are sometimes c l a s s i f i e d  cannot  fitting  hydrograph  any recorded  o f r e a s s i g n i n g parameter v a l u e s  are more an e x e r c i s e i n curve  events.  1985) t h a t  to reproduce  and t o  hydro-  i n the model.  as model  calibra-  f o r a s i n g l e event and  always be e x t r a p o l a t e d to other r u n o f f events  even on the  same b a s i n .  Acceptability will the  o f l a g and route procedures  be judged model.  on s i m u l a t i o n r e s u l t s  Even  though  events  c o u l d be achieved  event,  such  a process  a  better  through  t o extreme rain-on-snow  o f o n l y the i n i t i a l f i t between  recorded  events  a p p l i c a t i o n of and  simulated  a d d i t i o n a l model m o d i f i c a t i o n s f o r each  i s not p o s s i b l e i n f i e l d  application  t o ungauged  watersheds where recorded data are not a v a i l a b l e f o r c a l i b r a t i o n .  - 150 -  5.6  LAG AND ROUTE HYDROLOGIC MODEL  5.6.1  Procedures f o r Computation  Implementation area  o f l a g and route hydrograph  response  Calculations  characteristics proceed  area delineated on  water  across  area.  Second,  reservoir fast  estimating  travel  First,  water  travel  outlet  different  lagged  through  time  amounts  represent  i n this  and s t o r a g e  Water  each sub-  outlet  based  i n p u t s can be f o r each sub-  flows a r e " r o u t e d " through a  the b a s i n .  are described  the time-  f o r the b a s i n .  i n p u t s onto  the b a s i n .  characteristics  of r u n o f f  development  through  by s p e c i f y i n g  storage  p r e s e n t e d i n subsequent  Lagged  times  a t the b a s i n  whose  hydrograph  and the s t o r a g e c o e f f i c i e n t  i n two s t e p s .  the b a s i n  component  requires  by i s o c h r o n e s a r e "lagged" t o the watershed  particle  varied  procedures  those  Calculations  governing the required f o r  s e c t i o n , and procedures f o r  characteristics  o f the b a s i n are  sections.  flows a t the b a s i n o u t l e t are c a l c u l a t e d  as f o l l o w s :  B i = Ji iA  J  + R_A  R  x  where ments;  i ^ = lagged  i  l  Rj_ = water  area o f the sub-area example,  i  discharge  B = c o n s t a n t which  calculations;  + ••• + R _ A )  2  (inflow  varies  i n t o which  f o r a watershed  (5.8)  n  to reservoir)  with  input during  n+x  units;  after  t = time  i t h time increment;  i time  incre-  increment f o r ^  = drainage  the b a s i n i s d i v i d e d by i s o c h r o n e s . For  divided  into  three sub-areas  by i s o c h r o n e s a t  - 151 -  half-hour hour, as  intervals,  a time  and water i n p u t s i n mm and areas  for calculation  equal  to a h a l f -  i n km , Eqn. 5 . 8 would be w r i t t e n 2  follows:  I = 0.556(R A + R _ A i  Lagged duce  i  l  i  flows are routed  the s i m u l a t e d  tions  1  2  + R_A) i  through  flood  are undertaken  linear  by  2  <-> 5  3  a reservoir  a t the b a s i n o u t l e t  hydrograph  f o r the watershed.  combining  the c h a r a c t e r i s t i c  These  9  to p r o calcula-  equation  for a  reservoir:  S  and  increment  =  (5.10)  KQ  the c o n t i n u i t y  equation:  AS ~  Q  ^  (5.11)  where S = r e s e r v o i r  s t o r a g e ; K = storage c o e f f i c i e n t ; Q = r e s e r v o i r  flow; and I = r e s e r v o i r  out-  inflow.  Eqns. 5.10 and 5.11 can be combined and rearranged to y i e l d :  Q  = (/.• + Mutt  M  + Qi  {iKTAi)  where i and i+1 r e f e r  to s u c c e s s i v e time  increments.  Eqns.  a r e used  study  5.9  "routed" and  and 5.12  flows,  respectively,  i n this once  to produce  the time-area  runoff  storage c o e f f i c i e n t a r e e s t i m a t e d f o r the b a s i n .  "lagged"  and  characteristics  -  5.6.2  T r a v e l Time  Travel of  time  of a water p a r t i c l e  r u n o f f i s determined  tion  and those  channels.  feature  for  response.  success  plication  maps i n mountainous  they have s t i l l planning  of b a s i n  procedures  This  response,  assume  linear  been a p p l i e d s u c c e s s f u l l y  f o r a given  Accordingly,  and d e s i g n .  can be approximated  procedures  should  basins.  h y d r o l o g i c models i s t h e i r a p p l i c a t i o n  of l a g and route  investigation  shows  explanation  philosophy  floods.  regions  One  A similar  rain-on-snow  to form  f o r a l l runoff events.  and l a g and route  of e n g i n e e r i n g  of l i n e a r  range.  sufficiently  to as a n o n - l i n e a r c h a r a c t e r i s t i c  c o n d i t i o n where b a s i n response  limited  concentrates  component  to c h a n n e l i z a -  a l a r g e p o r t i o n of most drainage  Nevertheless,  instances  occurring prior  a b a s i n i s not c o n s t a n t  i s referred  many  design a  through  runoff  of t o p o g r a p h i c  contrast, unit-hydrograph  basin in  occurring after  are e v i d e n t through  T r a v e l time  which c o n t r i b u t e s to the f a s t  by flow v e l o c i t i e s  Examination  channels  in  152 -  i s adopted  i n this  to the s p e c i a l  methods  as l i n e a r  proposed  study  case  f o r ap-  of extreme  and t e s t e d  not be e x t r a p o l a t e d f o r a p p l i c a t i o n  over  i n this  to other  runoff  conditions.  Estimates  of v e l o c i t i e s  equation,  and non-channelized  theoretical  overland  f o r channelized  flow  velocities  velocities.  i n c h a n n e l i z e d flow can be estimated  flow w i l l will Travel  be based on Manning's  be based time  from Manning's  on e m p i r i c a l and  of a water equation:  particle  - 153  V  =  -  ± „0.67 ^0.5  (5.1)  n and  t = L/V  •••  where V = mean v e l o c i t y ; efficient;  t =  time;  shown, g r a p h i c a l l y on range of channel flow are  velocity  y = depth;  and  L  estimates  length.  f o r three  5.3.  S o l u t i o n of  typical  Manning's n v a l u e s .  proposed by  Figure  S = s l o p e ; n = Manning roughness  channel  F i g u r e 5.3  depths and  a l s o i n c l u d e d on  =  (5.2)  the S o i l  mountain  For  Eqn. slopes  comparison,  Conservation  5.1 and  cois a  overland  Service  (1974)  6  SLOPE = 3 ° =  5%  CHANNELIZED FLOW ( F r o m Manning e q u a t i o n ) OVERLAND  FLOW  ( A f t e r soil conservation s e r v i c e , 19 7 4 ) ~  u  4  CD W  o o  _j  LU >  'cm  SHORT  GRASS  PASTURE  F O R E S T WITH GROUND 0 0.04  0.05  DEPTH =  LITTER  0.06  0.07  0.08  0.09  0.10  MANNING " n " Figure  5.3(a)  Comparison o f Wide C h a n n e l i z e d and O v e r l a n d  Flow  Velocities  0.11  0.12  6 S L O P E =10°= 1 8 % CHANNELIZED FLOW ( F r o m Manning e q u a t i o n )  5  OVERLAND  FLOW  ( A f t e r soil conservation service , 1 9 7 4 )  e  >  2  C U f l D T tJ D A C O  F O R E S T WITH  "  0 0.04  1  0.05  D A C ri 1  1  IBF u n L  •• • •  >JH = 5 c m  GROW  1  D LITTER  0.06  0.07  0.08  0.09  0.10  MANNING " n " F i g u r e 5.3(b)  Comparison o f Wide and Overland  Flow  Channelized Velocities  0.11  0.12  Figure 5 . 3 ( c )  Comparison o f Wide C h a n n e l i z e d and Overland Flow V e l o c i t i e s  - 157  One the  method f o r e s t i m a t i n g o v e r l a n d flow v e l o c i t i e s Soil  Velocity ground Figure city  -  Conservation estimates  covers 5.4  for  a  a r e ' shown  shows  estimates  Service  do  with open channel  range  of  results  not  vary with  for  use  hillside  graphically  these  land flow v e l o c i t i e s  (1974)  on  been developed  i n hydrograph slopes  and  F i g u r e 5.4.  represent linear  e s t i m a t e d by  has  for  magnitude of the  analysis. different  Examination  b a s i n response rainfall  by  of  as v e l o -  event.  Over-  the S o i l C o n s e r v a t i o n are a l s o i n c l u d e d  f l o w curves on F i g u r e 5.3  for  comparison.  VELOCITY IN FEET PER SECOND  F i g u r e 5.4.  Overland 1974)  Flow v e l o c i t i e s  (after  S o i l Conservation Service,  - 158 -  Physically-based runoff for  have  representations  been  variations  which  in rainfall  conceptualization developed  proposed  demonstrate  intensity  of r u n o f f ,  f o r the i d e a l i z e d  of a n a l y s i s show v e l o c i t y  of the o v e r l a n d  non-linear  basin  response  (Henderson and Wooding, 1965).  termed case  flow component of b a s i n  kinematic-overland  of flow over  a plane  and depth i n c r e a s e s  flow,  The  has been  surface.  i n the downslope  Results direction  where f o r d i s t a n c e L:  where L = depth a t d i s t a n c e L; V V  water  particle  cient;  Based with  velocity  i = rainfall  over  rainfall  particle  velocities  12 mm/hr, coastal  intensity  estimated  region  for a  f o r an 18° s l o p e .  surface  calculated  are l e s s  water  length.  length  24-hour  0.15 m/s  =  roughness  hourly  rainfall  coeffi-  150 mm,  range  to r e s u l t s case  overland  intensity  from  =  i n the 0.04  -  and 0.08 t o  i n F i g u r e 5.3 shows  of o v e r l a n d  flow  varies  mean water  occurring  f o r a 10° s l o p e ,  f o r the i d e a l i z e d empirical  velocity  and r a i n f a l l  intensity  of  Comparison  particle  For i l l u s t r a t i o n ,  100 m  0.06 - 0.12 m/s  than  a t d i s t a n c e L; V = mean  L; n = Manning  mean  the maximum  f o r a 3° s l o p e ,  plane  flow,  and s l o p e  0.08 m/s  mean v e l o c i t i e s  velocity  and S = s l o p e .  f o r slope as  =  distance  intensity;  on k i n e m a t i c - o v e r l a n d  L  velocity  flow  on a  estimates  - 159  provided by  the  by  the  Soil  -  Conservation  S o i l Conservation  Service.  Empirical results  Service for overland  flow  are  presented  adopted  for  study because these r e s u l t s have r e c e i v e d widespread a p p l i c a t i o n neering  s t u d i e s and  kinematic  because Henderson  flow on a watershed s c a l e to r u r a l  Travel  time  for application  floods  will  be  ning's  equation  Conservation gauged  estimated and  on  Service.  watersheds  of  l a g and  r e l y on equations  basin  4,  this  considers  snowpack and  catchments.  route procedures  to  rain-on-snow on  Man-  e m p i r i c a l overland  flow v e l o c i t i e s  from  the  Soil  developed approach  the  is particularly  response  of  each  estimating  internal inputs  minimal.  travel  drainage at  the  attractive  basin  empirical results  f o r other b a s i n s and to  between  to the snowpack base i s  of  based  because  delay  the a p p l i c a t i o n  flow v e l o c i t i e s  T h i s procedure  t h a t an  i n engi-  from c h a n n e l i z e d  based on h y d r a u l i c p r i n c i p l e s and  Chapter  (1966) c a u t i o n s  this  can  be  for  estimated  r a t h e r than having  regions. time  snow s u r f a c e  to  As proposed i n  through  network has  un-  a  drainage  formed w i t h i n and  the  transmission  - 160  5.6.3 The  Storage l a g and  Coefficient  route procedure  shed by a s i n g l e age  coefficient  graphs  where  proximated  -  linear can  the  be  s i m u l a t e s s t o r a g e c h a r a c t e r i s t i c s of a water-  reservoir  l o c a t e d a t the b a s i n o u t l e t .  estimated  from  r e c e s s i o n p o r t i o n of  analysis the  of  fast  recorded  The  stor-  flood  hydro-  r u n o f f component  is  ap-  by: (5.6)  where Qt = d i s c h a r g e coefficient.  Taking  at  time  t; Qo  = discharge  l o g a r i t h m s of Eqn. 5.6  and  a t t=o;  and  K  =  storage  r e a r r a n g i n g terms y e i l d s : (5.7)  which from  shows  that  storage  coefficient  the slope on a graph p l o t t i n g  For i l l u s t r a t i o n on  the  F i g u r e 5.5  l n Q versus  a f l o o d hydrograph  on  graphs  plotted  relatively  l a r g e magnitude of t h i s the  graph  semi-log  on  storm.  scales  slope  be  estimated  time.  and  with  natural scales i l l u s t r a t e s  The  can  from Lookout Creek i n Oregon i s shown  natural  hydrograph  preceding  at  with  for a basin  extreme f l o o d  of  the  illustrates  semi-log  scales.  The  the  response  and  fast  compared  to w i n t e r  r e c e s s i o n p o r t i o n of storage  the  characteristics  flow  hydroof  the  basin.  Clark the  (1945) e n v i s i o n e d  r e c e s s i o n curve  While priate  this  that  the  storage  of a hydrograph  approximation  after  coefficient  be  estimated  c e s s a t i o n of a p u l s e of  i s r e l a t i v e l y s t r a i g h t f o r w a r d i n concept,  recorded hydrographs may  from  not be a v a i l a b l e .  rain. appro-  I t i s more l i k e l y  that  - 161 -  o a  CM  a  19  20  21  22 23 24 December, 1964  25  26  27  25  26  27  o  [ 7 /  19  20  F i g u r e 5.5.  21  V  ——  22 23 24 December, 1964  Rain-On-Snow Flood Hydrograph on Lookout  Creek  - 162 -  a f l o o d peak r e s u l t s from i n t e n s e r a i n f a l l w i t h i n a longer d u r a t i o n storm and  that  lower  recession. water  For  Similarly,  rain  may  still  f o r rain-on-snow  be o c c u r r i n g  instances  when  low i n t e n s i t y  hydrograph  recession,  recession  flows would  because  and a d d i t i o n a l  water  rain  inputs  hydrograph  has ceased.  or snowmelt  storage c o e f f i c i e n t s result  during  events snowmelt c o n t i n u e s to add  i n p u t s to the snowpack even a f t e r r a i n f a l l  during  age  intensity  may  from both water  to the b a s i n .  is still  Even  occurring  be o v e r e s t i m a t e d  release under  from  stor-  these c i r c u m -  stances, however, s t o r a g e c o e f f i c i e n t s measured from recorded hydrographs would  be more r e p r e s e n t a t i v e  larger  than  those o c c u r r i n g  cially  true  f o r extreme  much l a r g e r than snowmelt  Recession  curves  of a b a s i n when peak water during  rain-on-snow  from  f o r flood  extreme cients  Mann Creek  are much  This  i s espe-  recession.  when peak r a i n f a l l  i n t e n s i t i e s are  rates.  hydrographs  Oregon which e x p e r i e n c e d extreme one  hydrograph  inputs  from  rain-on-snow  i n the W i l l a m e t t e Basin  seven  drainage  basins i n  f l o o d s i n December 1964 and Snow L a b o r a t o r y f o r a  event i n F e b r u a r y 1951 were a n a l y z e d to e s t i m a t e s t o r a g e f o r use i n the l a g and route hydrograph  coefficient  f o r each  hydrograph  was  calculated  r e c e s s i o n curve p l o t t e d on semi-log graph paper. age b a s i n are summarized  i n T a b l e 5.2  procedure. from  less  coeffi-  The s t o r a g e  the s l o p e  of the  R e s u l t s f o r each d r a i n -  - 163 -  TABLE 5.2 STORAGE COEFFICIENTS FOR RAIN-ON-SNOW EVENTS  Drainage Area (km )  Station* 1. Nestucca  2  River  Storage Coefficient** (h)  Date of Flood  16.0  December 22,  1964  13  2. Grave Creek  57.3  December 22,  1964  6  3. Lookout Creek  62.4  December 22,  1964  20  4. S. Fork  C o q u i l l e R.  105  December 22,  1964  17  5. W. Fork  I l l i n o i s R.  110  December 22,  1964  10  1 37  December 22,  1964  15  7. E l k Creek  141  December 22,  1964  7  8.a Mann Creek  13.0  February  6. H i l l s  Creek  8.b Mann Creek  (rainfall  50  7, 1951  only) November 1 , 1950  19 S 25  * See Table 5.1 and F i g u r e 5.2 f o r s t a t i o n l o c a t i o n . * For s i n g l e l i n e a r r e s e r v o i r : s t o r a g e = storage c o e f f i c i e n t x discharge  Examination are  i n a relatively  during made  of r e s u l t s  an extreme  i n this  coefficients  study  i n Table 5.2 shows estimated narrow  range  rain-on-snow to develop  and b a s i n  f o r seven  event  drainage  i n December  functional  characteristics,  land  use when l a g and route procedures  coefficients  basins  1964.  relationships  i n Oregon  No attempt i s  between  use o r geometry.  c o e f f i c i e n t s i n c l u d e d i n T a b l e 5.2 are presented for  storage  storage Storage  as p r e l i m i n a r y e s t i m a t e s  a r e a p p l i e d to rain-on-snow f l o o d s  - 164 -  i n the P a c i f i c Northwest. gation snow  A recommended f o l l o w - u p study to t h i s  i s one which examines  hydrographs  storage c o e f f i c i e n t s  throughout  the c o a s t a l  region  investi-  from recorded  rain-on-  of Oregon,  Washington,  f o r the  rain-on-snow  B r i t i s h Columbia and A l a s k a .  Comparison flood  of  the  on Mann  storage  Creek w i t h  coefficient  those from Oregon  Mann Creek value i s much l a r g e r . ference snow. and,  therefore,  very  extensive  much  of  have  an  flood  an i n t e r n a l and water  the r u n o f f internal  provided  storage  Creek  d r a i n a g e network,  characteristics  not an extreme  of a  basin  mechanism. during  may approach t h a t f o r r a i n f a l l when no snowcover  events i n may  case, the  rain-on-snow  i s present.  been  control  i n Chapter 4.2,  In the l a t t e r  extreme  flood  not have  rain-on-snow  as d e s c r i b e d  dif-  flow through  through the snowpack c o u l d  F o r the extreme  routing  for this  aspects of water  snowmelt d r a i n a g e network may  process.  1964 shows the  explanation  of February 1951 was  percolation  the dominant  i n December  One p o s s i b l e  can be proposed based on p h y s i c a l The Mann  Oregon  estimated  events  - 165 -  5.7  ANALYSIS OF FLOOD HYDROGRAPHS ON MANN CREEK  5.7.1  Basin Location  The  Mann Creek b a s i n  i s l o c a t e d i n the Cascade  forms p a r t of the W i l l a m e t t e the C o o p e r a t i v e Weather Bureau. a  continuously  peaks  B a s i n Snow L a b o r a t o r y  The b a s i n has a drainage  represent  and extends from  2  gauge a t e l e v a t i o n 759 m to mountain  as e l e v a t i o n 1596 m.  F i g u r e 5.6  (WBSL) e s t a b l i s h e d by  area of 13 km  Basin  location  shown on F i g u r e 5.6 a t a s c a l e o f 1:48 000. on  i n Oregon and  Snow i n v e s t i g a t i o n s program of the Corps of Engineers and  r e c o r d i n g streamflow  as h i g h  Mountains  locations  and topography are  Reference  numbers i n c l u d e d  f o r hydrometeorological  instruments  t h a t were e s t a b l i s h e d f o r the WBSL r e s e a r c h program.  5.7.2  R a i n f a l l Flood of October 28, 1950 t o November 2, 1950  5.7.2.1  Hydrometeorological Data  A  summary  of h y d r o m e t e o r o l o g i c a l  m e t e o r o l o g i c a l Log 1949-51 periods rainfall  of i n t e n s e  rainfall  produced  the l a r g e s t  rainfall  are a v a i l a b l e  data  from  i s available  (U.S. Army Corps from  recorded  October  flood  two-year p e r i o d and o c c u r r e d p r i o r  Hourly  data  of E n g i n e e r s ,  28 - November  recorded  on Mann  t o snow accumulation  a t three  gauges  the WBSL H y d r o m e t e o r o l o g i c a l  data i s i n c l u d e d i n Table 5.3.  i n the WBSL  across Log.  Hydro-  1952) f o r 2, 1950.  Creek  two  This  d u r i n g the  i n the b a s i n .  the 13 km A summary  2  basin  of these  - 166 -  F i g u r e 5.6.  Mann Creek  Topography  - 167 -  TABLE 5.3 MANN CREEK RAINFALL DATA: OCTOBER 28 - NOVEMBER 2, 1950  Station Number*  Elevation (m)  General Location  28  D a i l y R a i n f a l l (mm) October November 29 30 31 1 2  21  817  Basin o u t l e t  107  48  13  9  78  15  8  994  Near Southeastern Boundary  102  48  18  13  99  4  Northwestern Boundary  100  39  19  23  93  11  1409  See F i g u r e 5.6 f o r gauge l o c a t i o n s .  Recorded the  streamflow  on Mann Creek  H y d r o m e t e o r o l o g i c a l Log  f o r the storm p e r i o d  i n two-hour  increments.  i s available i n  Flood  hydrographs  are shown on F i g u r e 5.7.  0  48  96  144  192  240  288  TIME (HRS) F i g u r e 5.7  Recorded Hydrograph  on Mann Creek: O c t . 27-Nov. 6, 1950  - 168  5.7.2.2 Travel on  Travel Time and Storage C o e f f i c i e n t time of a water p a r t i c l e  results  presented  velocities. velocities based  The  plied  procedure  i n watercourses  the b a s i n on  developing  these  through  i n Chapter  on Manning's e q u a t i o n  ments of in  -  5.6.2  adopted  the watershed i s e s t i m a t e d f o r channelized  for  identified  this  on a 1:50  f o r open channel  estimates  procedures  study 000  is  f o r overland i s to p r o v i d e  and  overland  flow  to  estimate  flow  scale  flow, and  topography  a c r o s s other  flow v e l o c i t i e s . ' a method  based  which  i s a v a i l a b l e to guide  Assessment of the time-area  the  goal  be  i n a c o n s i s t a n t manner on any ungauged watershed where o n l y a  g r a p h i c map  seg-  One  can  map  aptopo-  analysis.  r u n o f f c h a r a c t e r i s t i c s of the b a s i n  proceeded  as f o l l o w s :  (i)  transects  were  drawn  on  the  topographic  map  from  the  basin  o u t l e t to l o c a t i o n s along the watershed boundary.  (ii)  s e c t i o n s along  each  t r a n s e c t were designated  c h a n n e l i z e d or o v e r l a n d f l o w based  (iii)  (iv)  as  having  either  on the c r i t e r i o n noted  above.  s l o p e s were measured along each t r a n s e c t .  travel  times  s l o p e s and  for  overland  velocities  flow  proposed  (1974) f o r f o r e s t s with ground  were  by the litter.  estimated Soil  for  measured  Conservation Service  - 169 -  (v)  travel were 0.07.  times  f o r channelized  flow  estimated  f o r measured  slopes  Selection  watersheds  and Mannings  judgement  because  n  with  relative  study  "n" adopted  role  i n this  that s i t e  ments  and l i n e s  basin  outlet,  Creek  are shown  storage  photos  or a s i t e  along  connecting  called  visit  points  of equal  on F i g u r e 5.8 where  peak a t 19-hours.  travel  Creek  i s estimated  time  Results  isochrones  basin  during  increto the  f o r Mann  i l l u s t r a t e the  flood  the October  28 -  the s l o p e of r e c e s s i o n  hydrographs.  shown on F i g u r e 5.9 where the r e c e s s i o n c o n s t a n t peak  i n actual  f o r the b a s i n .  p l o t of the recorded  on the f i r s t  the impor-  can p l a y  i s o c h r o n e s , were drawn.  f o r Mann  provided  transect i n half-hour  November 2, 1950 r a i n f a l l event was estimated from on a semi-log  on v a l u e s  depth.  procedures.  each  runoff c h a r a c t e r i s t i c s  coefficient  i s based  This p a r t i c u l a r exercise h i g h l i g h t s  p o i n t s were i d e n t i f i e d  component  of mountainous  Mannings  time-are  is  "n" equal to  bed and banks and the flow  a p p l i c a t i o n of f l o o d hydrograph  curves  varies  stream  roughness between the channel  tant  The  mountainous  of Manning's n i n upper reaches  requires  by Chow (1959b).  (vi)  in this  This  f o r the f a s t  a t 25-hours  graph runoff  and on the second  - 170 -  F i g u r e 5.8.  Mann Creek Time-Area Graph  - 171  -  o  48  96  144  TIME  5.9.  192  240  (HRS)  Semi-Log P l o t of Mann Creek Hydrograph, October 27 - November 7, 1950  288  - 172  5.7.2.3 The to  Application of Lag and Route Hydrologic Model  primary a  purpose  hydrographs, in  1973),  logic 1950  application  study  for  the  2  shown  the  data  runoff  was  number  of  80  was  served r a i n f a l l  the  lag  and  of  the  of  still lag  as  28  flood  storage standard  Engineers,  undertaken  and  October  to  single  Army Corps of  b a s i n was  flood  a  flood  route -  in  hydro-  November  2,  from  rainfall  was  the  Hydrometeorological  fairly  uniform  over  the  event.  and  recorded  streamflow  t h a t about 73 p e r c e n t  (1974)  applied  using  are accepted  (U.S.  obtained  r u n o f f component.  Service  rain-on-snow  runoff contribution  Application  i n Table 5.3  peak i n d i c a t e d  vation  simulated  mountain  were  basin for this  fast  be  procedure  as f o l l o w s :  comparison of r a i n f a l l graph  fast  events  hydrograph  examining  the  rainfall-induced  rainfall As  13 km  iii)  coastal  on Mann Creek proceeded  i) hourly  ii)  to a  to  route  route procedures  for r a i n f a l l  for confirmation.  model  Log.  can  though l a g and  l a g and  prior  whether  regions  practice  the  event,  i s to assess  Even  engineering  applying  flood  mountainous  constant.  this  of  rainfall-only  peaks  -  to  To  curve  account  number  recorded  selected  approach  this  first  of r a i n f a l l  for losses,  rainfall  because  f o r the  for value  to  hydro-  occurred i n  the S o i l  Conser-  estimating  direct  the  basin;  represented  a  curve  the  ob-  and r u n o f f .  route  hydrograph  basin  using  estimated  graph  f o r r u n o f f response  model  effective  a storage c o e f f i c i e n t of 23  was  rainfall  characteristics hours.  a p p l i e d to as  the  input,  shown on  the  Mann  Creek  time-area  F i g u r e 5.8,  and  - 173 -  Results  of the i n i t i a l  examination simulated son  of  the f i r s t  of r a i n f a l l  indicated  provided  review  i s reasonable  of  Results show for  single  storage  estimated tion  from  l a g and  from  than  errors  procedure  the second.  Compari-  events  runoff  event  estimates  application  contributing regions  coefficient  and with  channelized  and o v e r l a n d  peaks can be estimated with l i m i t e d  for this  high  flow  recorded on  on e x t r a p o l a t i o n site.  of a l a g and route h y d r o l o g i c model  component  procedures  be based  the b a s i n  Alternatively,  was the l a r g e s t  would  peak  the b a s i n .  on or near  curve f o r the gauge  i n mountainous  of l a g and route  over  i n recorded d a t a .  s i n c e the f l o o d flow  hydrograph  rainfall  a l l gauges  Preliminary  route  f o r the second  i s greater  stage-discharge rating  the f a s t  rainfall  the  to suppose t h a t p u b l i s h e d streamflow  o f the i n i t i a l  that  runoff  to suggest  Therefore,  an e x i s t i n g  streamflow  of r a i n f a l l  p e r i o d may be i n e r r o r Mann Creek.  shows  r u n o f f peak but underestimated  and recorded  no evidence  are shown on F i g u r e 5.10.  hydrographs  t h a t recorded  More d e t a i l e d  it  flood  analysis  travel flow  to Mann  to f l o o d  can be time  hydrographs  simulated  using  a  f o r a water  particle  considerations.  Applica-  Creek  demonstrates  s i t e information.  how  flood  03  27  28  29  October, 1950 F i g u r e 5.10.  30  31  1  2  3  November,  4  1950  Simulated R a i n f a l l Hydrograph on Mann Creek  5  - 175 -  5.7.3  Rain-On-Snow Flood of February 3 - 8 , 1951  5.7.3.1  Hydroaetoerological Data  A  special  and  research  analyzes  note  (U.S. Army  Corps  snowmelt f o r a rain-on-snow  r u a r y 1951.  The WBSL H y d r o m e t e o r o l o g i c a l  recorded  climatological  by instruments  stations  referenced  across i n this  event,  i n Feb-  through-  data  flood  Creek  e x i s t e d over the e n t i r e b a s i n and p r e c i p i t a t i o n o c c u r r e d as r a i n  logical  3-8, 1951  on Mann  snowpack  the watershed.  the February  flood  1955) documents  a  out  During  of Engineers,  Log c o n t a i n s c l i m a t e -  the b a s i n . study  and  A  listing  their  of  general  l o c a t i o n i s i n c l u d e d i n Table 5.4.  TABLE 5.4 MANN CREEK CLIMATOLOGICAL STATIONS  Station Number* 21,22 11 8 20B 32 34 2,2B  Elevation (m) 817 902 994 997 1125 1213 1409  General Location basin outlet near s o u t h e a s t e r n boundary near s o u t h e a s t e r n boundary near s o u t h e a s t e r n boundary e a s t e r n boundary n o r t h e a s t e r n boundary northwestern boundary  * see F i g u r e 5.6 f o r gauge l o c a t i o n s  C l i m a t o l o g i c a l Data p r e c i p . , a i r temp., snow snowcourse p r e c i p . , a i r temp. snowcourse snowcourse snowcourse p r e c i p , a i r temp., snow  - 176 -  An  overview  of h y d r o l o g i c  Mann Creek i s p r o v i d e d  conditions  i n Tables  during  the rain-on-snow  5.5, 5.6 and 5.7 which  r a i n f a l l , a i r temperature and snowcourse d a t a ,  event on  summarize  daily  respectively.  TABLE 5.5 MANN CREEK RAINFALL DATA: FEBRUARY 3-8,  1951  Station Number  Elevation (m)  3  Daily Rainfall 4 5 6  (mm) 7  8  21  817  6  39  17  14  55  0  8  994  8  50  18  -  -  3  2  1409  9  43  14  —  —  0  TABLE 5.6 MANN CREEK AIR TEMPERATURE DATA: FEBRUARY 3-8,  1951  Station Number  Elevation (m)  21  817  0.6  0.6  2.2  1 .1  3.3  3.3  8  994  -0.6  -0.6  0.6  0.0,  2.2  1 .7  2  1409  0.0  0.6  2.2  2.2  3.3  MEAN = (max. + min.) /2  Mean D a i l y A i r Temperature (°C) 3 4 5 6 7 8  -1 .7  - 177 -  TABLE 5.7 MANN CREEK SNOWCOURSE DATA; FEBRUARY, 1951  Station Number  Elevation (m)  Date  Snow Depth (mm)  22  817  Feb. 2  762  267  1,1  902  Feb. 2  780  254  20B  997  Feb. 3  820  348  32  1125  Feb. 3  1288  503  34  1213  Feb. 2  2192  800  2B  1409  Feb. 1  2286  782  Estimates period Corps  f o r basin  are provided of Engineers  averaged  snowmelt  i n the r e s e a r c h (1955).  Water E q u i v a l e n t (mm)  and r a i n f a l l  note  during  published  A summary o f these  the storm  by the U.S. Army  estimates  i s included i n  T a b l e 5.8.  TABLE 5.8 SNOWMELT AND RAINFALL  From  To  ESTIMATES  Length (hrs)  Snowmelt (mm)  Rainfall (mm)  Feb.  3 (HR 17)  Feb. 5 (HR 18)  50  25  58  Feb.  5 (HR 19)  Feb. 6 (HR 18)  24  12  20  Feb. 6 (HR 19)  Feb. 7 (HR 24)  30  18  42  Feb. 8 (HR 1 )  Feb. 9 (HR 6)  30  22  0  - 178 -  Recorded the  streamflow  on Mann Creek  f o r the storm  H y d r o m e t e o r o l o g i c a l Log i n two-hour  period  increments.  i s available i n The  flood  hydro-  graph f o r February 3-8, 1951 i s . shown on F i g u r e 5.11.  0  24  48  72  96  120  TIME (HRS)  F i g u r e 5.11.  Recorded  Hydrograph on Mann Creek: February 3-8, 1951  144  - 179  5.7.3.2  Travel Time and Storage Coefficient:  A n a l y s i s of for  the  network at  the  minimal. basin  travel  time of a water p a r t i c l e  rain-on-snow  internal inputs  -  For  shown  has  formed  snow this  event  of  within  surface case  previously  and  the  on  February the  through the Mann Creek 3-8,  snowpack and  transmission  time-area  F i g u r e 5.8  1951  runoff for  to  considers delay  the  that  an  between water  snowpack  base  is  for  the  adopted  for  February  3-8,  characteristics  rainfall-only  basin  is  a n a l y s i s of the rain-on-snow e v e n t .  The  storage  1951  rain-on-snow  curve is  coefficient  on  a  shown on  for  event  semi-log  plot  F i g u r e 5.12  component i s estimated  is of  Mann  estimated the  where the a t 50  Creek  basin  from  recorded  the flood  during slope  of  the  hydrograph.  r e c e s s i o n constant  hours.  the  f o r the  recession This  fast  graph runoff  - 180 -  o  i  i  i  i  i  i  0  24  48  72  96  120  TIME  F i g u r e 5.12.  •  (HRS)  Semi-Log P l o t of Rain-on-Snow Hydrograph on Mann Creek  !  144  - 181  -  5.7.3.3  Application of Lag and Route Hydrograph Model  Lag  route  hydrograph  3-8,  1951  and  February adopted those tion  procedures  flood  event  f o r rain-on-snow and  for a r a i n f a l l - o n l y of  the  February  l a g and  3-8,  1951  i) hourly Log.  to  whether  the  for  the  can  be  model  on  the  same watershed.  to  Applica-  model to the rain-on-snow f l o o d  of  as f o l l o w s :  data  indicated  Mann Creek  t o compare b a s i n storage c h a r a c t e r i s t i c s  r u n o f f event  proceeded  a p p l i e d to  examine  route hydrograph  rainfall As  are  were  obtained  i n Table 5.5  from  the  rainfall  was  Hydrometeorological fairly  uniform  over  the b a s i n .  ii)  snowmelt (1955)  estimates  were  provided  added  to  by  hourly  the  U.S.  rainfall  Army  data  Corps  to  of  produce  Engineers the  total  i n p u t to the b a s i n .  iii)  detailed  water  balance  Corps of Engineers snowmelt of  water  runoff  losses  (1955) concluded  inputs  a  to groundwater  basin  to  contributing  i n p u t s to the l a g and  iv)  storage  calculations  the  to were  basin  the  undertaken  occurred  flood  route hydrograph  equal  r o u t i n g b a s i n r u n o f f through a s i n g l e  the  that approximately  extracted  coefficient  by  i n the  hydrograph. from  rain  50  linear  Army  a l l rain  fast  and  and  component  Accordingly, snowmelt  model.  to  U.S.  no  water —  hours  was  reservoir.  applied  for  - 182 -  v) the l a g and route hydrograph model was a p p l i e d conditions for  Results ary  time-area runoff  characteristics  similar  input  to those  rainfall-only.  of applying  the l a g and route  3-8, 1951 rain-on-snow f l o o d  Results  of hydrograph a n a l y s i s  simulated to  and  with the above  using  the b a s i n  conventional  taken  as  hydrological  model  to the Febru-  on Mann Creek are shown on F i g u r e 5.13. indicate  that  l a g and route  the sum  rain-on-snow f l o o d s procedures with  of r a i n f a l l  and  can be  water  snowmelt  and  input  with  no  l o s s e s t o groundwater.  Comparison rainfall  of s t o r a g e flood  and  coefficients differed in  Chapter  floods pack,  snow f l o o d not  the  approach  does  on Mann  F e b r u a r y 1951  response  conditions  not occur  which  Creek  f o r the October  rain-on-snow  by a f a c t o r of two.  4 suggests b a s i n  could this  coefficients  shows  the  Even though evidence presented  characteristics exist  on Mann Creek.  event  1950  f o r rain-on-snow  i n the absence  Perhaps  because  of a snow-  the r a i n - o n -  i s not a v e r y extreme event, an i n t e r n a l d r a i n a g e network d i d  form s u f f i c i e n t l y  to produce more t e r r a i n c o n t r o l l e d  runoff.  F i g u r e 5.13.  Simulated Rain-on-Snow Hydrograph  on Mann Creek,  February 3-8, 1951  - 184  -  5.8  ANALYSIS OF FLOOD HYDROGRAPH ON LOOKOUT CREEK  5.8.1  Basin Location  The  Lookout  Creek  approximately area  of  basin  10 km  62.4 km  gauge a t e l e v a t i o n  i n the Cascade  south of Mann Creek.  and  2  i s located  extends  420 m  from  a  to mountain  Lookout  peaks  as high  Rain-On-Snow Flood of December 21-24, 1964  5.8.2.1  Hydroaeteorological Data  throughout 24, over  1964.  rain-on-snow the C o a s t a l During  the e n t i r e  watershed. drainage  basin  as  was  event  occurred  and Cascade Mountains flood and  event on  data  the case  climatological  r e c o r d e d data a t r e g i o n a l  data  are  not  streamflow  as e l e v a t i o n  f o r Lookout  on  a  1631  m.  500.  Lookout  Creek  and  from December 21snowpack  as r a i n  measured  f o r research  stations.  recording  Creek  occurred  Oregon  a drainage  i n Oregon  Lookout  precipitation  Climatological  basin  Therefore,  the  flood  in  has  a t a s c a l e of 1:62  5.8.2  extreme  Creek  continuously  B a s i n topography i s shown on F i g u r e 5.14  An  Mountains  throughout the  directly  undertaken  Creek must be  existed  on  within Mann  the  Creek.  inferred  from  Figure 5.14.  Lookout Creek  Topography  - 186 -  Estimates  of  rainfall  from  rainfall  over  a  station  with  elevation.  from  a  south at  local  local  the  and  Hourly r a i n f a l l  station  at  o f the watershed  Lookout  Creek  basin  an assessment  of r a i n f a l l  data are a v a i l a b l e  McKenzie  Bridge  boundary.  require  located  recorded variation  f o r the storm  period  approximately  3.5 km  A summary of d a i l y  rainfall  recorded  McKenzie Bridge i s i n c l u d e d i n T a b l e 5.9.  TABLE 5.9 RAINFALL AT MCKENZIE BRIDGE: DECEMBER 21-24, 1964  Gauge L o c a t i o n Latitude Longitude 44  10  Hourly  122  fore,  stations  elevation  Alternatively, to  that  storm  December Pr e c i p i ta t i o n (mm) 24 21 22 23  419  data  effects  84  are not a v a i l a b l e  a t higher on  storm  precipitation  month varied  95  rainfall  McKenzie cannot  be  recorded  of December  a t lower  i n a similar  manner  and longer d u r a t i o n monthly d a t a .  32  70  f o r the storm  e l e v a t i o n s than  comparison of p r e c i p i t a t i o n  f o r the e n t i r e  indicates both  10  precipitation  regional  Elevation (m)  p e r i o d a t any  Bridge  and, t h e r e -  assessed  directly.  f o r the storm elevation  period  stations  between s t a t i o n s f o r  This r e s u l t  suggests  that  December monthly p r e c i p i t a t i o n data r e c o r d e d a t s t a t i o n s h i g h e r i n e l e v a tion  than  variation  McKenzie with  Bridge  elevation  could during  be the  used storm  as  an  indicator  period.  These  of  results  shown i n T a b l e 5.10 and a p l o t of December p r e c i p i t a t i o n versus is  shown on F i g u r e 5.15.  rainfall are  elevation  - 187 -  TABLE 5.10 RAINFALL NEAR LOOKOUT CREEK BASIN  Elev. (m)  Station  Location Latitude Longitude  P r e c i p i t a t i o n (mm) Dec. 21-26 Dec. Storm:Month  Marcola  44  10  122  51  162  255  535  Leaburg  44  06  122  41  206  -  512  C a s c a d i a S t a t e Park 44  24  122  29  259  233  519  0.45  McKenzie Bridge  44  10  122  10  419  323  684  0.47  Belnap S p r i n g s  44  18  122  02  656  -  762  -  Santiam Pass  44  25  121  52  1448  _  882  _  0.48  -  600  • / I200  //  /  800  / /  /  < > _j  UJ  400  /  •/  /  /•  • 200  400  600  P R E C I P I T A T I O N ( mm )  F i g u r e 5.15.  December 1964 P r e c i p i t a t i o n  800  I000  - 188  Examination region  of  of  Oregon  distribution Time  recorded  of  (U.S. storm  distributions  Cascadia  of  rainfall  intensity  Army Corps rainfall  of  had  a  precipitaiton  located approximately  are shown on F i g u r e  -  40 km  data  Engineers, similar  recorded  throughout 1966)  showed  p a t t e r n over a t McKenzie  to the northwest  — —  z:  Eo r /  CL.  21  December,  F i g u r e 5.16.  CC a s c a d i a — _  22  Time D i s t r i b u t i o n of  23 1964  Rainfall  coastal the  large Bridge  time  areas. and  a t e l e v a t i o n 259  5.16.  McKenzie Bra.dge  the  24  at m  - 189 -  A  summary of a i r temperature  Pass  located  included  approximately  i n Table 5.11  relatively  recorded a t McKenzie 10 km  northwest  f o r the storm p e r i o d .  h i g h temperatures  which  Bridge and a t Santiam  of Lookout These  Creek  basin i s  data i l l u s t r a t e the  o c c u r r e d d u r i n g days w i t h the l a r g e s t  rainfall.  TABLE 5.11 AIR TEMPERATURE (°C) NEAR LOOKOUT CREEK BASIN  Day  McKenzie Bridge ( E l e v . 419 m) Min. Mean Max.  Dec. 20  0  2  Dec. 21  0  Dec. 22  Santiam Pass ( E l e v . 1448 Mean Min. Max.  1 .1  -4  -3  10  5.0  -3  6  1 .1  4  12  8.3  3  8  5.6  Dec. 23  7  11  8.3  0  6  3.1  Dec. 24  7  9  7.8  1  4  2.2  Dec. 25  0  7  3.3  -2  2  0.0  -3.6  mean = (min + max)/2  Using a i r temperatures Pass, d a i l y  and p r e c i p i t a t i o n  snowmelt e s t i m a t e s based  e q u a t i o n f o r rain-on-snow  f o r McKenzie  Bridge and Santiam  on the U.S. Army Corps of E n g i n e e r s  (Eqn. 4.3) are p r e s e n t e d i n Table 5.12.  - 190  TABLE  -  5.12  SNOWMELT ESTIMATES FOR LOOKOUT CREEK  Day Dec.  McKenzie  D a i l y Snowmelt (mm) B r i d g e ( E l e v . 419 m) Santiam Pass  ( E l e v . 1448  21  24  7  Dec. 22  39  29  Dec.  23  37  15  Dec. 24  31  10  The  depletion  Cascade Corps data  of  snowpack  Range i s e v i d e n t  of  Engineers  are i n c l u d e d  during  from  (1966)  the  December  storm  period  snow depth data compiled by  and  i n T a b l e 5.13.  the  U.S.  Weather  Bureau  Corresponding water  along  the U.S.  (1965a).  equivalent  m)  the Army  These f o r the  snow depths are not a v a i l a b l e .  TABLE  5.13  SNOW DEPTHS IN CASCADE RANGE:  Elevation (m)  Station McKenzie  Bridge  Dec.  20  DECEMBER  1964  Snow Depth 21 22  (cm) 23  24  25  419  3  5  0  0  0  0  656  39  30  15  0  0  3  Government Camp  1189  140  114  51  15  10  25  Santiam Pass  1448  218  188  127  117  109  122  O d e l l Lake  1461  163  132  86  71  61  76  Crater  1974  208  229  213  173  168  188  Belnap S p r i n g s  Lake  - 191  Recorded cation  streamflow compiled  on  for  Lookout  the  (Waananen e t a l . , 1971) The  rain-on-snow  Figure  Creek  storm  Travel  period  to document hydrograph  rain-on-snow  that  the  U.S.  flood_flows  f o r December  an  particle  flood  internal  through  special  publi-  Geological  Survey  throughout 21-24,  mission  to the  d r a i n a g e network has  snowpack base  o b s e r v a t i o n s and  1964  the  region.  i s shown  on  time of a water  5.6.2.  Flow  velocities  f o r the  i s undertaken  consid-  within  the  This  assessment  snowpack. and  trans-  i s consistent  s t u d i e s by snow h y d r o l o g i s t s  f o r snowpack  water.  particle  f o r c h a n n e l i z e d and  basin  formed  Creek  i n p u t s a t the snow s u r f a c e  i s minimal.  research  response to i n p u t s of l i q u i d  Travel  the Lookout  of December 21-24, 1964  For t h i s c a s e , d e l a y between water  mates  by  in a  Travel Time and Storage C o e f f i c i e n t time o f a water  extreme  with  i s available  5.17.  5.8.2.2  ering  flood  -  through the watershed  overland flow v e l o c i t i e s  i n watercourses  identified  i s based  on  esti-  presented i n Chapter on  a  1:62  500  scale  topography map  are based on Manning's e q u a t i o n f o r open channel flow, and  across  other  segments  Travel  time  basin  outlet  whether  or  procedure Lookout  from was  not are  Creek  various  the points  determined  f l o w was outlined are  of  basin  on  i n the  based  on  estimates Lookout slope,  c o n s i d e r e d to be f o r Mann Creek  shown on  Figure  time-area runoff c h a r a c t e r i s t i c s  5.18  for  Creek  overland  watershed  estimated  channelized.  flow. to  roughness Details  the and  of  the  Results  for  where i s o c h r o n e s i l l u s t r a t e  the  i n Chapter 5.7.2.2.  f o r the b a s i n .  o  o-J 0  1  1  1  1  1  1  1  1  21  48  72  96  120  144  168  192  TIME  (HRS)  i  F i g u r e 5.17.  Rain-on-Snow Flood Hydrograph  on Lookout Creek: December 19-27, 1964  1 216  F i g u r e 5.18.  Lookout Creek Time-Area  Graph  - 194  The  storage c o e f f i c i e n t f o r Lookout Creek d u r i n g the December 21-24,  rain-on-snow semi-log  event  plot  F i g u r e 5.19 is  -  of  was  the  where  5.8.2.3 Lag  and  flood  the  recession  hydrograph.  recession constant  for  curve  slope  T h i s graph  the  fast  on  a  i s shown  runoff  on  component  Application of Lag and Route Hydrograph Model route hydrograph  procedures  flood  f o r rain-on-snow,  occurred model  from  hours.  December 21-24, 1964 model  recorded  the  estimated a t 20  estimated  1964  on  to  Mann  the  event  and  Creek.  are a p p l i e d t o Lookout Creek  to undertake  to analyze  Application  rain-on-snow  flood  of  a second  a p p l i c a t i o n of  a more extreme of  the  lag  December  and  21-24,  f o r the  flood  than  route 1964  the  which  hydrograph  proceeded  as  follows:  i ) hourly r a i n f a l l  a c r o s s the watershed was  data a t McKenzie B r i d g e and t i o n shown on F i g u r e  estimated based  on the v a r i a t i o n i n r a i n f a l l  on  recorded  with e l e v a -  5.15. »  ii)  daily  snowmelt was  equation  (Eqn. 4.3)  temperature was wind  data.  developed data  developed  are  from not  estimated  from  the U.S.  Army Corps of  Engineers  f o r rain-on-snow u s i n g recorded r a i n f a l l Eqn.  4.3  was  a p p l i e d to Lookout Creek because i t  snow r e s e a r c h s t u d i e s i n t h i s available  f o r snowmelt.  for  Hourly  and a i r  use  in  other  distribution  of  r e g i o n and empirical daily  because formulas  snowmelt  was  - 196  simulated during  by a s i n e curve  research  studies  -  as proposed by Colbeck and Davidson i n the  northern  Cascade Mountains  (1973)  i n Wash-  ington s t a t e .  iii)  hourly  rainfall  and  snowmelt were added to produce  water i n p u t to the  iv)  no  losses  Lookout  to  total  hourly  basin.  groundwater  Creek  the  basin.  were  This  considered  assessment  for was  water based  inputs on  to  the  results  of  a n a l y s i s of the rain-on-snow event on Mann Creek.  v)  the  l a g and  basin sponse  with  route hydrograph model was the  characteristics  c i e n t of 20  of i n i t i a l  ination  of  the  approximately  Further  shown on  the  time-area  F i g u r e 5.18,  graph f o r r u n o f f and  a  storage  re-  coeffi-  hours.  Results  is  above i n p u t d a t a ,  a p p l i e d to the Lookout Creek  a n a l y s i s are shown on F i g u r e 5.20a.  simulated 80  comparison  flood  percent of  hydrograph  greater  simulated  about 75 mm  more r u n o f f o c c u r r e d  on recorded  r a i n f a l l and  snowmelt  and  than  shows the that  flood  recorded  estimated  hydrographs  on December 22 estimates.  P r e l i m i n a r y exam-  than was  by  flood the  peak  model.  indicates  that  p r e d i c t e d based  - 197 -  - 198  Three p o s s i b l e e x p l a n a t i o n s lated  i)  -  f o r the d i f f e r e n c e between recorded  and  simu-  f l o o d hydrographs are as f o l l o w s :  since  the  December  21-24  flood  Lookout Creek, streamflow of  an  existing  coastal  Oregon  unit discharges during between  estimates  stage-discharge  r e g i o n of  recorded  and  event  was  the  curve.  storm  simulated  on  record  on  would be based on e x t r a p o l a t i o n However, other b a s i n s  a l s o experienced  this  largest  peak f l o o d s with  event.  flows  i n the  Therefore,  appears  too  similar  the d i f f e r e n c e  great  to  be  the  r e s u l t of measurement e r r o r a l o n e .  ii)  snow metamorphism causes an percolation  through  f i n e l y g r a i n e d new the  December  during  the  additional previous  iii)  field that site.  snow.  21-24  storm 75 mm  grained  flood,  snow  period. of  of  snow f e l l  on  air  on  metamorphism  However,  runoff  recorded  snow i s f a s t e r  s i n c e new  days would have had  Examination suggests  coarse  i n c r e a s e i n snow g r a i n s i z e s , and  for  December  to be  have  process  water  in transit  temperature  through  prior  to  melt r a t e s of the r e q u i r e d magnitude would not  measurements snow trapped Even  rainfall  by the  though  could  obtained  have  some been  by  forest  Beaudry  Golding  canopy a f f e c t s melt  snow which held  and  by  occurred  the  canopy,  t h i s p o t e n t i a l source of melt c o u l d account  prior  yield  an  snowmelt  the  to  occurred  to  from  through  data  more  the b a s i n p r i o r  would  this 22,  than  water  on  snowpack. the  storm  occur.  (1983)  showed  from a f o r e s t e d to  the  extreme  i t is unlikely  f o r an a d d i t i o n a l 75  that mm.  - 199 -  iv)  initial  snowmelt  estimates  case o f extreme r a i n f a l l Examination were  much  of snow greater  melt e q u a t i o n . very  are  data  those  than  shown  be  too low f o r the  i n T a b l e 5.13  temperatures.  suggests  p r e d i c t e d by the Corps  melt of  rates  Engineers  Even though water e q u i v a l e n t data are not a v a i l a b l e ,  c o n s e r v a t i v e assumptions  rates  Eqn. 4.3 may  combined with r e l a t i v e l y h i g h  depth  than  using  those  initially  i n Table 5.14  f o r snow d e n s i t y  estimated  yield  f o r the b a s i n .  f o r two reasonable  greater  melt  Calculations  estimates  of snowpack  density.  TABLE 5.14 SNOW DEPTHS AT SANTIAM PASS ( E l e v . 1448 m)  Dec. snow depth ( cm)  18 water equiv. (mm)  Dec. 18-20 new water snow equiv. ( cm) (mm)  Dec. 20 water equiv. (mm)  Dec. 22 Dec. 20-22 snow water snow depth equiv. melt ( cm) (mm) (mm)  137  453 (33%)  81  81 (10%)  534  127  419 (33%)  115  137  548 (40%)  81  162 (20%)  710  127  508 (40%)  202  A v a i l a b l e evidence  suggests  l y h i g h temperatures predicted in  this  t h a t extreme r a i n f a l l  on Lookout Creek produced  by the Corps of Engineers region.  Results  from  combined with  relative-  g r e a t e r snowmelt than t h a t  temperature-index  the l a g and route  equation  hydrograph  developed model are  shown a g a i n on F i g u r e 5.20b with water i n p u t on December 22 i n c r e a s e d by 75 mm  to correspond  Lookout  Creek  with r e c o r d e d  runoff.  Even though c l i m a t i c  are not as e x t e n s i v e as f o r a f u l l y  data f o r  instrumented  research  watershed, a v a i l a b l e r e g i o n a l data i n d i c a t e s an i n c r e a s e i n snowmelt more a c c u r a t e l y r e p r e s e n t s b a s i n c o n d i t i o n s d u r i n g the December f l o o d .  - 200  Results can  be  input  of hydrograph a n a l y s i s i n d i c a t e that extreme rain-on-snow f l o o d s simulated  to  results fall  -  and  ungauged  the  using  basin  conventional  taken  as  a l s o i n d i c a t e the snowmelt to watersheds  c o e f f i c i e n t and  the  sum  l a g and of  importance  rainfall  often  more  procedures with  and  snowmelt.  of c o r r e c t l y e s t i m a t i n g  the hydrograph model. is  route  difficult  t r a v e l times f o r b a s i n  Estimation than  response.  of  water  However,  input  rain-  i n p u t data  estimating  a  on  storage  - 201  5.9  DISCUSSION OF RESULTS  The  primary  estimation available  goal of  from  nents  include  region;  of  this  extreme  study i s to develop hydrograph  floods  on  assessment  analysis  application  of  of  an  initial  task r e q u i r e d  the  coastal  region  re-  of a  in  results  from t h i s  spring  and  bination  of r a i n  and  floods  snowmelt.  frequency a n a l y s e s , and region  from  to  a  extreme  Chapter 3,  the  floods;  the c o n t i n u i t y  snow f l o o d s  is initiated  summer  or  can r e s u l t  is in-  procedures i n  producing mechanism  region  are  generally  rainfall-induced  atmospheric processes which I t i s shown t h a t  analyzing  procedures  either  records,  affect  extreme  of storm  and  or a com-  flood  f o r extreme  characteristics  which  in fall  from r a i n f a l l - o n l y  In Chapter 2, h i s t o r i c a l  of hydrograph by  and  between  p r e v i o u s Chapters  of hydrograph  flood  coastal  are examined.  development  coastal  hydrograph  climate  floods  most b a s i n s i n the c o a s t a l r e g i o n are generated from rain-on-snow  In  compo-  Chapter.  i n the development  i n the  Rainfall-induced  snowpack d u r i n g  Study  i n the  f o r input  To i l l u s t r a t e  Floods  winter.  the c o a s t a l  of  thesis.  p r o d u c i n g mechanisms  i s to e s t a b l i s h  simulated.  snowmelt-induced  flood  T h i s g o a l i s achieved by combining  characteristics  overview  The  be  not  of a hydrograph model.  components,  procedures f o r  where data are  flood  rainfall  c l u d e d below with r e s u l t s  must  watersheds  each of the Chapters p r e s e n t e d i n t h i s  model; examination of the r o l e  study  ungauged  f o r model c a l i b r a t i o n .  sults  in  -  on  events.  rain-onrainfall  - 202  for  input  to a model.  -  E s t i m a t i o n of i n p u t data to a hydrograph  sometimes more d i f f i c u l t  on an ungauged watershed  response  of  coastal is  B.C.  i s especially  r e l a t i v e l y sparce and  tainous and  characteristics  terrain  the b a s i n . difficult  there i s d i f f i c u l t y  because  rainfall  can  than assessment  Assessment  because  model i s  of storm  the e x i s t i n g  rainfall  i n t r a n s p o s i n g data i n moun-  vary  over  short  distances in plan  of  the  difficulty  i n estimating  storm  rainfall  for  v e s t i g a t e whether r e g i o n a l c h a r a c t e r i s t i c s of storm r a i n f a l l tified  even when the magnitude of r a i n f a l l  l y s e s undertaken  hydrograph  identified  pheric  Environment  part  limits  of on  this  study.  the range  and  In  for single  practice,  to assess the r o l e from  establish  the r o u t i n g  Examination  in  study  This  storm  available  distributions  results  that  from  need  can be to be  Atmos-  developed  used  to s e t  c o n s i d e r e d by  regard to i t s e f f e c t  assessment  mechanism which  of a v a i l a b l e  suggests  data  characteristics  procedures f o r rain-on-snow  of a snowpack w i t h  the b a s i n .  model. this  Ana-  of s i t e d a t a .  next step i n d e v e l o p i n g hydrograph  response  v a r i e s between s t a t i o n s .  these  of h o u r l y i n t e n s i t i e s  a d e s i g n engineer i n the absence  is  iden-  f o r multi-storm i n t e n s i t y Service  to i n -  can be  i n Chapter 3 show t h a t r e g i o n a l r a i n f a l l  be  The  in  gauge network  a n a l y s i s i n the mountainous c o a s t a l r e g i o n , a n a l y s i s i s undertaken  as  the  elevation.  Because  can  of  i s undertaken  must be  literature  t h a t development  s i m u l a t e d by a  internal  runoff  i n Chapter 4 to  i n snow h y d r o l o g y  of an  on  floods  hydrograph conducted  drainage network  - 203 -  w i t h i n the snowpack, not water p e r c o l a t i o n , i s the dominant anism d u r i n g extreme  rain-on-snow  r o u t i n g mech-  floods.  Chapter 5 examines the a p p l i c a t i o n o f a hydrograph model to extreme  rain-  on-snow f l o o d s .  based  on  Procedures  the assessment  assessment once  are developed  o f snowpack r o u t i n g  of snowpack response  characteristics  to extreme  the r o u t i n g mechanism i s e s t a b l i s h e d  lating  the r u n o f f  t i o n s 5.1  study develops  l a g and r o u t e hydrograph model t o extreme  Preliminary  results  and  Lookout  Creeks  to  estimate  is  adopted:  (i)  extreme  from  application  suggest t h a t  i n Chapter 4. is critical  For reasons d i s c u s s e d  procedures  when  (ii)  of a  on Mann  procedure can be a p p l i e d the f o l l o w i n g  time through the b a s i n based  methodology  on c h a n n e l i z e d and  o v e r l a n d f l o w c o n s i d e r a t i o n s , w i t h o u t any a d d i t i o n a l ment f o r water  i n Sec-  floods.  of a l a g and route model  floods  The  because  for application  rain-on-snow  t h i s hydrograph  rain-on-snow  estimate t r a v e l  rainfall  analysis  then any model capable of simu-  process can be a p p l i e d .  and 5.3, t h i s  f o r hydrograph  time  incre-  t r a n s m i s s i o n through the snowpack.  s e l e c t the s t o r a g e c o e f f i c i e n t which s i m u l a t e s b a s i n response.  1  (iii)  specify  - 204 -  water  inputs  to  the b a s i n  as  the  sum  of r a i n f a l l  and  snowmelt.  (iv)  It  c o n s i d e r there are no water l o s s e s to groundwater.  can be  concluded from examination of the above methods  snow produces relatively  the  large  most  water  extreme inputs  flood  peaks  available  on  for runoff,  of changes i n b a s i n response c h a r a c t e r i s t i c s snowpack.  Once an i n t e r n a l  snowpack  i s to  rainfall  and snowmelt  runoff  that  contribute  produces  inputs the  peak  because  rather  of  Also,  during  because  the  than because  forms, the major  to the b a s i n occur  flood  rain-on-  t h a t can be a t t r i b u t e d  d r a i n a g e network snowmelt.  a basin  that  extreme  to a  role  of a  events most  i n the f a s t component o f  losses  to groundwater  are  r e l a t i v e l y s m a l l i n comparison.  One  topic  for additional  research  i n the development  of  hydrograph procedures i s to examine methods f o r e s t i m a t i n g ficients tion how  f o r use on ungauged  of a does  storage  cients be  with  based  rain-on-snow  f o r rain-on-snow f l o o d s  floods;  and  on t o p o g r a p h i c maps.  snowpack response to i n p u t s  from a p p l i c a t i o n i n t h i s  route  storage  coef-  questions a r i s e  secondly,  from p h y s i c a l c h a r a c t e r i s t i c s  identified on  Two  f o r extreme  coefficient  rainfall-only  be estimated  readily  below  coefficient  the storage  same b a s i n  watersheds.  l a g and  for selec-  floods.  First,  compare on the  can storage  of the b a s i n  coeffi-  which can  These concerns are d i s c u s s e d of l i q u i d  water  and  results  study o f the l a g and route model, and an o u t l i n e  f o r a f o l l o w - u p study to t h i s i n v e s t i g a t i o n i s p r e s e n t e d .  - 205 -  Snow h y d r o l o g i s t s of  have concluded (Colbeck e t a l . ,  flow channels during  This  approach r u n o f f  from s n o w - c o n t r o l l e d  conclusion  channel development,  that  development  snow metamorphism causes a snowcovered  to undergo a t r a n s i t i o n movement.  1979)  suggests  basin  that  response would  characteristics  to t e r r a i n - c o n t r o l l e d  during also  that exist  watershed  snow metamorphism  undergo a  were 23 and  respectively. very It  extreme  event and  i s worth  noting  rain-on-snow  perhaps  that  Lookout Creek d u r i n g Creek  the  the  runoff  basin  the December  for r a i n f a l l - o n l y .  flood  is still  storage  1964  In a d d i t i o n ,  on  partly  coefficient  flood  i s similar  storage  coefficent  of  may  i s not a  20 hours  to t h a t  s i x other mountainous  values  flood,  snow-controlled.  signify  on  on Mann  watersheds  had storage  2  c i e n t s o f 6 t o 20 hours d u r i n g the extreme rain-on-snow f l o o d These  coeffi-  rain-on-snow Mann Creek  i n Oregon r a n g i n g i n d r a i n a g e area from 16 to 141 km  1964.  and  i n the absence of a snowpack.  50 hours f o r a r a i n f a l l - o n l y and  However,  and  transition  T h i s o c c u r r e n c e i s not e v i d e n t f o r Mann Creek where b a s i n storage cients  water  coeffi-  i n December  that  sufficient  channel development had o c c u r r e d d u r i n g the extreme event such t h a t b a s i n response approached c o n d i t i o n s s i m i l a r  Further ining  assessment  of  the r e c e s s i o n  throughout Columbia  Alaska.  relationships hydrographs drainage  between  and  area.  coefficients  curves of r e c o r d e d  the c o a s t a l  and  storage  basin  hydrologic Analysis storage  can  be  can  be  undertaken by  exam-  extreme rain-on-snow f l o o d s  region  i n Oregon,  undertaken  coefficients  characteristics  A similar  to r a i n f a l l - o n l y .  such  approach has been  Washington,  to develop  calculated as  basin  from  length,  from  British  functional recorded slope  and  adopted f o r u n i t hydrograph  -  procedures been  combined  basin  (Watt  l a g and  taken, study lag  for r a i n f a l l  i t is from  and  of  Chow,  1985)  to  slope.  recommended  storage  recorded  that  extreme  Until  during  than  p r e d i c t e d by  the Corps  gion  for forested  areas.  such as developed ungauged  by  i n p u t data  calculated adopted  in  this  f o r use  with  P r e l i m i n a r y evidence  procedures  of Engineers  It is likely  to Lookout snowmelt  that  watersheds  to a hydrograph  Creek  was  because  continue  estimates  of  suggests  in this  to be  i n a l t e r n a t i v e melt  and  applied other  equations.  snowmelt  c u r r i n g d u r i n g the s p e c i a l case of extreme rain-on-snow i s h i g h l i g h t e d an  important  topic  for further  analysis  i n the development of  for  e s t i m a t i n g extreme rain-on-snow f l o o d s .  In  c o n c l u s i o n , study  characteristics  components  of extreme f l o o d s  presented  in  this  thesis  re-  equations,  wind  model are very important,  appli-  much g r e a t e r  temperature-index  of E n g i n e e r s , w i l l  study i s  from  e q u a t i o n developed  c l i m a t i c data are seldom a v a i l a b l e f o r use Since  be  between  r e s e a r c h i s under-  on the r e s u l t s of t h i s  rain-on-snow event,  the Corps  mountainous  relationship  further  rain-on-snow f l o o d s  route hydrograph extreme  a  coefficients  of snowmelt e q u a t i o n s .  this  v a r i o u s r e s e a r c h e r s have  produce  t o p i c f o r f u r t h e r r e s e a r c h based  l a g and  from  procedures.  that  to  where data  b a s i n l e n g t h and  a re-examination cation  and  route hydrograph  A second  floods  -  206  ocas  procedures  examine  the  i n the c o a s t a l h y d r o l o g i c r e g i o n ; p r o -  v i d e r e g i o n a l c h a r a c t e r i s t i c s of storm r a i n f a l l  f o r e s t i m a t i n g i n p u t data  - 207 -  to a hydrograph cedures  to extreme rain-on-snow f l o o d s .  on-snow events comes  model; and examine the a p p l i c a t i o n of l a g and route  will  available.  be analyzed  Recently  further  installed  I t i s hoped in British  Data  that  extreme  Columbia  prorain-  as data be-  C o l l e c t i o n Platforms  (DCP's)  by B.C. 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S c h a e f e r , D.G., (1978), "An Overview of America", Proceedings o f the IUFRO t i e s , Vancouver, 1978, p u b l i s h e d by f o r m a t i o n S e r v i c e s Branch, V i c t o r i a ,  the C l i m a t e s o f Western North J o i n t Meeting of Working parB.C. M i n i s t r y o f F o r e s t s , I n B r i t i s h Columbia.  S c h e a f e r , D.G., (1979), " M e t e o r o l o g i c a l Developments C o n t r i b u t i n g to the T e r r a c e Area Flood o f E a r l y November, 1978", prepared as i n p u t to a r e p o r t on the T e r r a c e area f l o o d by Inland Waters D i r e c t o r a t e of Environment Canada. S c h a e f e r , D.G., (1981), "A Study o f Probable Maximum P r e c i p i t a t i o n f o r the Coquitlam Lake Watershed", prepared f o r B.C. Hydro and Power A u t h o r i t y by Atmospheric Environment S e r v i c e . S c h e i d e g g e r , A.E., (1957), M a c M i l l a n , New York.  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"Climatological U.S. Department  Data, Oregon, December of Commerce, A s h e v i l l e ,  U.S. Weather Bureau, (1965b), " H o u r l y P r e c i p i t a t i o n Data, Oregon, December 1964", V o l . 14, No. 12, U.S. Department of Commerce, A s h e v i l l e , North C a r o l i n a .  - 216 -  REFERENCES (continued)  U.S.  Weather Bureau, (1966), "Probable Maximum P r e c i p i t a t i o n , Northwest States", H y d r o m e t e o r o l o g i c a l Report No. 43, U.S. Department of Commerce, Washington, D.C.  Waananen, A.O., H a r r i s , D.D. and W i l l i a m s , R.C., (1971), "Floods of December 1964 and January 1965 i n the Far Western S t a t e s , P a r t 1. D e s c r i p t i o n , P a r t 2. Streamflow and Sediment Data", U.S. G e o l o g i c a l Survey Water Supply Paper 1866-A, Washington. Wankiewicz, A., (1976), "Water P e r c o l a t i o n W i t h i n a Snowpack", Ph.D. T h e s i s , Geography Department, U n i v e r s i t y of B r i t i s h Columbia. 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W i l l i a m s , P., (1948), "The V a r i a t i o n of the Time of Maximum P r e c i p i t a t i o n along the West Coast of North America", B u l l e t i n of the American M e t e o r o l o g i c a l S o c i e t y , volume 29, Number 4, pages 143-145. Wisner, P. and PNG, C , (1982), "OTTHYMO, A P l a n n i n g Model f o r Master Drainage P l a n s " , Proceedings of the F i r s t I n t e r n a t i o n a l Symposium on Urban Drainage Systems, South Hampton. World  M e t e o r o l o g i c a l O r g a n i z a t i o n , (1970), "Guide t o H y d r o m e t e o r o l o g i c a l P r a c t i c e s " , T e c h n i c a l Paper No. 82, WMO-No. 168, Geneva.  World  M e t e o r o l o g i c a l O r g a n i z a t i o n , (1973), "Manual f o r E s t i m a t i o n o f Probable Maximum Precipitation", O p e r a t i o n a l Hydrology Report No. 1, WMO-No. 332, Geneva.  - 217 -  APPENDIX I MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA AND SOUTHEAST ALASKA  TABLE 1.1 MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA  Station Number  08MH104 08FB006 08DC006 08FB007 08FB002  Station  Drainage Area(A) (sq km)  Anderson Creek a t the mouth A t n a r k o River near t h e mouth Bear R i v e r above B i t t e r Creek B e l l a Coola R i v e r above Burnt Creek Bridge B e l l a Coola near Hagens&org  27.2 2430 350 3730 4040  Flood Regimes Spring/ F a l l / Summer Winter  X X  X  X  X  Maximum D a l l y Discharge on Record No. of Years Dlscharge(Q) Q/A of Record Date mVs (m /s)/km 3  Maximum I n s t a n t a n e o u s D i s c h a r g e on Record Peak Dally No. of Years DIscharge(Q ) Dlscharge(Q) o f Record Date m /s m^/s p  2  3  17 18 16  17 Dec 1971 24 Jan 1968 8 Oct 1974  17.2 289 225  0.63 0.12 0.64  NA 16 15  X  X  X  X  18 21  23 Jan 1968 24 Jan 1968  703 963  0.19 0.24  17 NA  Op Q  29 Jan 1968 8 Oct 1974  340 271  289 225  1.18 1.20  23 Jan 1968  828  703  1.18  08HA0I6 08HD00I  Blngs Creek near t h e mouth Campbell River a t o u t l e t o f Campbelt Lake  15.5  X  19  14 Jan 1968  14.8  0.95  NA  1400  X  38  0.61  NA  C a r n a t i o n Creek a t t h e mouth Chapman Creek above Sechelt Diversion Chapman Creek near Mil son  10.1  X  10  16 Nov 1939 26 Dec 1980  858  08HB048  21.6  2.14  10  23 Jan 1982  50.0  13.7  3.65  64.5  X  13  31 Oct 1981  78.8  1.22  13  31 Oct 1981  148  78.8  1.88  71.5  X  11  13 Oct 1962  193  2.70  NA  X  23  19 Oct 1940  197  0.69  21  19 Oct 1940  257  197  1.30  X  30  26 Dec 1980  457  1.29  NA  X  20  26 Dec 1980  262  0.41  20  26 Dec 1980  387  262  1.48  X  21  15 Oct 1974  572  1.55  20  1 Nov 1978  864  530  1.63  X  11  a Sep 1981  254  0.82  II  8 Sep 1981  262  254  1.03  95.6  X  4 Nov 1955 15 Oct 1974  0.68  1.44  1.63  29 Jan I960 15 Oct 1974  45.0  566  5 17  64.6  X  13 17  65.1  347  807  566  1.43  08GA060 08GA046  Creek 086A024 08HAOOI 08MH103 08EG012 08CG006  Cheakamus River near Mons Cheakamus River near Westholme C h l l l l w a c k R i v e r above SI esse Creek Exchamslks River near Terrace F o r r e s t Kerr Creek above 460 m contour  08HB003  Haslam Creek near Cassldy  08FF002  H i r s c h Creek Near the mouth  287  X  355 645  X  370 311  X  08CG00I  I s k u t R i v e r below Johnson 9350  X  X  24  !5 Oct 1961  6880  0.74  20  15 Oct 1961  7930  6880  1.15  08CG004  River I s k u t River above Snlppaker Creek Jacobs Creek above Jacobs  7230  X  X  16  9 Sep 1981  2080  0.29  16  9 Oct 1974  2520  2000  1.26  08MH108  Lake  12.2  X  14  19 Jan 1968  19.8  1.62  14  17 Sep 1968  24.6  5.4  4.52  TABLE  I.I  MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA  Station Number  Drainage Area(A) (sq km)  Station  Flood Regimes Spring/ F a l l / Summer Winter  Maximum D a l l y Discharge on Record No. of Years Olscharge(Q) Q/A o f Record Date m'/s (m^ )/kn|2 s  Maximum I n s t a n t a n e o u s D i s c h a r g e on Record Peak Dally No. of Years DIscharge(Q ) Dlscharge(Q) o f Record Date m^/s m'/s p  Q  08MH076  Kanaka Creek near Webster 47.7  X  23  14 Dec 1979  86.2  1.81  22  14 Dec 1979  146  86.2  1.69  08FE003  Corners Kemano R i v e r above Powerhouse T a l l race  583  X  10  15 Oct 1974  646  1.11  10  15 Oct 1974  889  646  1.38  1870  X  18  2 Nov 1978  595  0. 32  2  2 Nov 1978  702  595  1.18  X  19  1 Nov 1978  2410  1.21  19  1 Nov 1978  3000  2410  1.24  728  X  X  12  2 June1964  269  0.37  12  24 Oct 1966  603  229  2.63  08EG006  K l s p l o x R i v e r near Hazel t o n ' K l t l m a t River below H l r s c h Creek K l t s e g u e c l a R i v e r near Skeena Crossing Kltsumkalum R i v e r near Terrace Koklsh R i v e r a t Beaver Cove  2180 290  X  X X  22 14  3 June 1936 31 Jan 1935  883 334  0.41  883  883  1.00  1.15  18 NA  3 June 1936  08HF001  269  X  13  6 Feb 1963  134  0. 50  11  5 Oec 1962  164  128  1.28  209  X  26  14 Dec 1979  212  1.01  NA  Qua 1icum Beach L i t t l e QualIcum River a t o u t l e t o f Cameron Lake L i t t l e Wedeene R i v e r below  237  X  22  27 Dec 1980  166  0.70  21  27 Dec 1980  213  166  1.28  135  X  32  16 Jan 1961  189  1.40  NA  Bowbyes Creek  188  X  17  1 Nov 1978  274  1.46  16  1 Nov 1978  382  274  1.39  3.63 34.4 18.4  X X X  10 24 22  31 Oct 1981 19 Jan 1968 19 Jan 1968  9.25 28.3 25.0  2.55 0.82 1.36  10 NA NA  31 Oct 1981  16.2  9. 25  1.75  334 38.9  X X  15 10  26 Dec 1980 26 Dec 1980  270 53.5  0.81 1.38  15 10  26 Dec 1980 3 Nov 1975  369 121  270 44.2  1.37 2.74  12  1 Sep 1967  254  0.16  7  1 Sep 1967  311  254  1.22  08EB004 08FF001 08EF004  08HF003 08HA003 08HB029 08KB004 08FF003  086A06I 08MH020 08MH018 08GA054 08GA057 08GD007 08MHI29 08FC002  Koklsh R i v e r below Bonanza Creek K o k s l l a h River a t Cowichan Station L i t t l e QualIcum River  1990  near  Mackay Creek a t Montroyal Boulevard Mahood Creek near S u l l i v a n Mahood Creek near Newton Mamquam R i v e r above Mashlter Creek M a s h l t e r Creek near Squamlsh Most ay Creek near Dumbel1 Lake Murray Creek a t 216 S t r e e t Lang ley Nascal 1 R i v e r near Ocean Pal Is  X  •  1550  X  26.2  X  14  3 Dec 1982  19.7  1.33  12  23 Jan 1982  49.2  14.0  3.51  383  X  12  25 Oct 1947  886  2.31  5  25 Oct 1947  923  886  1.04  TABLE 1.1 MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA  Drainage Area(A) (sq km)  Station Number  08DB001 08MH105  Nass River above Shumal Creek Nlcomekl R i v e r below Murray Creek  08HF002  Nlmpklsh R i v e r near Eng1ewood  08GA052 08MH058 08MH006  Noons Creek near Port Moody N o r r l s h Creek near Dewdney North A l o u e t t e River a t 232nd S t r e e t Nusatsum R i v e r near Hagensborg  Flood Regimes Spring/ F a l l / Summer Winter  Maximum D a l l y Discharge on Record No. o f Years Discharged)) Q/A o f Record Date •Vs (m /s)/km 3  Maximum I n s t a n t a n e o u s D i s c h a r g e on Record Peak Dally No. of Years Discharge<Q ) Discharged)) p  2 Q  f  Record  Date  m3/s  Qp  m /s 3  X  45  15 Oct 1961  9460  0.49  16  9 Oct 1974  8920  7670  1.16  64.5  X  17  19 Jan 1968  28.3  0.44  12  26 Dec 1972  35.4  21.9  1.62  1760 6.99 117  X  11 15 21  31 Dec 1926 19 Nov 1962 26 Nov 1963  1270  X X  17.6 214  0.72 2.52 1.83  NA NA 21  26 Nov 1963  399  214  37.3  X  25  23 Dec 1963  76.2  2.04  14  26 Dec 1980  118  64.6  1.83  X  17  27 Sep 1973  190  0.71  15  7 Nov 1978  206  120  1.72  76.7 74.1  X X  11 11  93.4  1.22 0.65  11 NA  15 Oct 1974  126  69.4  1.82  48.1  19200  269  X  X  to to O V  1.86  080B002  P a l l a n t Creek near Queen Charlotte  08GA023 08FB004  Rubble Creek near G a r i b a l d i Salloamt R i v e r near Hagensborg  161  X  18  16 Dec 1980  141  0.88  17  16 Dec 1980  241  141  1.71  08HA010  San Juan R i v e r near Port Renfrew S a r l t a R i v e r near Bamfield  580 162  X X  23 31  26 Dec 1982 29 Jan I960  862 677  1.49 4.18  23 NA  26 Dec 1982  1160  862  1.35  08MH056  SI esse Creek near Vedder Crossing  162  X  24  29 Apr 1959  72.2  0.45  22  7 Nov 1978  212  49.6  4.27  08GA064  Stawamus R i v e r Below Ray Creek  40.4  X  11  26 Dec 1980  64.4  1.59  11  26 Dec 1980  113  64.4  1.75  X  30  15 Feb 1982  47.4  0.32  27  15 Feb 1982  49.2  47.4  1.04  08HB014  Sumas R i v e r Huntingdon  X  8 Oct 1974 4 June 1955  near 149  TABLE  1.1  MAXIMUM FLOODS ON RECORD IN COASTAL BRITISH COLUMBIA  Maximum Instantaneous D i s c h a r g e on Record Station Number  08MH033  Station  S . e l f z e r River a t Cuitus Lake  Drainage Area(A) (sq km)  Flood Reqlmes Spring/ Summer  65.0  Fall/ winter  X  Maximumi D a l l y D l s c h a r q e on Record No. of Years o f Record  Date  Q/A DI scharge(Q) m3/ (m /s)/km s  3  10  t2 Feb 1951  25.8  0.40 2.31 2.97  08HB024  Tsable R i v e r near Fanny Bay  113  X  23  15 Jan 1964  261  08HC002 08DD001 08MH098  Ucona R i v e r a t the Mouth  185  X  23 17  549 1000 12.8  0.68  20  19 Nov 1962 8 Oct 1974 23 Dec 1963  080A002  Yakoun R i v e r near Port Clements Yorkson Creek near Walnut Grove  22  28 Nov 1963  08MH097 08HE006 08EG0I1 08EF005  08EF00J  Unuk R i v e r near Stewart Mast Creek near Fort Lang ley  1480 11.4  X  477  X X  X  No. o f 2  of  Peak 0lseharge(Q )  Years  Record  Date  m /s J  SB. 0  NA  1.12  23 16 12  612  1.28  19 Nov 1962 9 Oct 1979  549 591  1.97 2.08  26 Dec 1980  1080 1230 24.1  16.2  1.49  15  27 Dec 1979  374  315  1.19  1 ISO 549  728 382  1.62 1.44  3140  1980  1.59  5.96  X  19  X  X X  22 23  30 Jan 1965 13 Nov 1975 15 Oct 1974  5.10 728 382  0.86 4.02 1.02  NA 18 23  13 Nov 1975 15 Oct 1974  X  X  20  1 Nov 1978  1980  0.66  20  1 Nov 1978  X  X  13  31 Oct 1961  1050  0.34  NA  3080  3  NA  Z e b a l l o s River near Z e b a l l o s 181 Zymagotltz River near Terrace 376 Zymoetz R i v e r above O.K. Creek 2980 Zymoetz R i v e r near Terrace  m /s  Oall y DI scharge(Q)  TABLE  I.2  MAXIMUM FLOODS ON RECORD IN SOUTHEAST ALASKA  .Station Number  Station  Drainage AraolA) (sq km)  Maximum D a l l y Olscharqe on Record Water Year No. o f Years DI scharge(Q) Record Of (Oct.-Sept.) m3/s  Q/A (m /s)/kro J  2  Maximum I n s t a n t a n e o u s O l s c h a r g e on Record 3 Peak Dall y No. o t Years Dlscharge(Qp) i Dlscharge(Q) o f Record Date m3/s  mVs  22. 0  15010000 15011500 15012000  Davis R i v e r near Hyder Red R i v e r near M e t l a k a t l a N i n s t a n l e y Creek near Ketchikan  207 117  10 15  1937 1977  295 240  1.43 2.05  10 15  12 Nov 1936 3 Nov 1976  552 351  295 240  1.87  40.1  28  1962  80.1  2.00  30  80.1  1.46  Harding R i v e r near WrangelI Cascade Creek near Petersburg  175 59.6  31 38  1962 1920  323 69.7  1.85 1.17  31 35  30 Jan 1962 14 Oct 1961 11 Sept 1947  117  15022000 15026000  425 92.7  323 56.6  1.32 1.64  1503100  21.5 84.2  10 32  1968 1957  42.5 128  1.98 1.52  10 NA  28 Sept 1968  too  42.5  2.35  15034000  Long R i v e r above Long Lake near Juneau Long R i v e r near Juneau  15036000 15040000 15044000  Speel River near Juneau Dorothy Creek near Juneau C a r l s o n Creek near Juneau  585 39.4 62.9  16 35 10  1961 1950 1454  898 47.9 98.8  1.54 1.22 1.57  17 37 10  27 Sept 1918 3 Nov 1949 12 Aug 1961  1008 50.4 144  566 47.9 82.1  1.81 1.05 1.75  15048000 15050000 15052000 15052500  11.8 25.3 31.3  29 38 20  1948 1961 1961  16.0 51.8 75.3  1.36 2.05 2.41  30 39 22  8 Sept 1948 6 Sept 1981 13 Aug 1961  23.8 76.5 95.4  16.0 27.8 75.3  1.49 2.75 1.27  15052800  Sheep Creek near Juneau Gold Creek a t Juneau Lemon Creek near Juneau Mendenhal1 R i v e r near Au ke Bay Montana Creek near Auke Bay  388 38.2  1.76 0.95  17 10  8 Sept 1981 23 Aug 1966  481 54.4  388 25.5  1.24 2.13  15053800 15054000  Lake Creek a t Auke Bay Auke Creek a t Auke Bay  23 Aug 1966  27.8  14.0  1.99  15056100 15056200 15059500  Skagway River a t Skagway West Creek near Skagway Whipple Creek near Ward Cove  15060000  Perseverance Creek near Wacker  15068000  Mahoney Creek near Ketchikan F a l l s Creek near Ketchikan Fish Creek near Ketchikan E l l a Creek near ketchlkan  83.1 51.0  15070000 15072000 15074000 15076000  Manzanlta Creek near Ketchikan  15078000 15080000  Grace Creek near Ketchikan Orchard Creek near Bel 1 Island  1.46  220  17  1981  40.1  10  1970  6.5 10.3 376  10 13 19  1966 1970 1967  14.0 5.9  2.15 0.57  10 NA  275  0.73  19  7 Sept 1981  464  237  1.96  112 13.7  15 12  1967  1.79 1.74  16 12  15 Sept 1967  278  1969  201 23.9  19 Nov 1968  80.1  201 23.9  3.35  7.3  30  1950  13.5  1923 1959  43.0 110  31 22  18 Oct 1964 2 Feb 1954  19.3 71.6  1.91  22 28  1.85 2.91  10. 1  14.8 94.5  30.9  2.32  1.16  28  1 Nov 1917  158  51.0  64 22  1920 1955  149 41.3  1.79 0.81  63 22  15 Oct 1961 7 Dec 1930  153 48.7  125 40.2  3.10 1.22 1.21  30 16  1962  110  1965  85.2  1.25 1.09  30 16  14 Oct 1961 4 Sept 1966  165  78.2  113  110 79.6  1.50 1.42  153  12  1920  164  1.07  11  1 Nov 1917  201  62.3  3.23  87.8  1.38  TABLE 1.2 MAXIMUM FLOODS ON RECORD IN SOUTHEAST ALASKA  Station Number  Drainage Area{A)  (sq km)  Station  13081500  S t a n l e y Creek near Cralg  15085100  Old Tom Creek near Kasaan  15085600 15085700 15085800 15086600 15088000  H a r r i s R i v e r near H o l l l s Maybeso Creek a t H o l l l s Big Creek near Point Baker Sawmill Creek near S i t k a  Indian Creek near  Hollls  Maximum D a l l y Discharge on Record No. o f Years Water Year DIscharge(Q) o f Record (Oct.-Sept.)  »Vs  134  17 32  1973 1952  19.0  1.78 1.24  239  32  18 Oct 1964 21 Nov 1979  442 31.4  143 15.4  3.09 2.04  13 5 14 3 14  170 250 107 41.1 181  46.7 144 61.4 38.5 141  3.64 1.74 1.74 1.07 1.28  1963  60.3  2.64  1962 1963 1966 1952  145 85.0 38.5 141  1.95 2.17 1.33 1.40  13 15 14 18 20  9.6  14  1977  36.8  3.83  14  2 Nov 1976  75.0  36.8  2.04  1.39 1.24  19.2  16  1963  26.7  Baranof River a t Baranof Takatz Creek near Baranof  82.9 45.3 146  29 18 17  1922 1968 1954  103 45.6 62.9  15106920  Kadashan R i v e r above Hook Creek near Tenakee  26.4  12  1973  15106 940  Hook Creek above Tr near Tenakee  11.6 20.7 37.6 97.6  13 13 14  62.9 35.2  Fish Creek near Auke Bay  9  15  15098000 15010000 15102000  P a v i o f River near Tenakee  SE.  14 14 18 26  Deer Lake O u t l e t near P o r t Alexander  15108000 15109000  17  3  22.8  15094000  Hook Creek near Tenakee T o n a l I t e Creek near Tenakee Kadashan R i v e r near Tenakee  3  74.3 39. 1 29.0 101  Sashln Creek near Big P o r t Walter  15106960 15106980 15107000  2  15.3  15093400  Hasselborg' Creek near Angoon  Q/A  (mVs)/km  Maximum I n s t a n t a n e o u s Discharge on Record Peak Dally No. o f Years DI scharge(Qp) Dlscharge(Q) o f Record n> /s m /s  Oct 1961 Dec 1959 Oct 1961 Sept 1966 Sept 1952  16  14 Dec 1962  31.7  1.01 0.43  25 18 17  6 Oct 1972 28 Sept 1968 23 Oct 1953  255 49.6 68.0  26.7 70.8 45.6 62.9  1.19 3.60 1.09 1.08  25.5  0.97  12  15 Sept 1976  52.4  16.1  3.25  20.2 25.6 64.3 127  1.74 1.24 1.71 1.30  13 13 14  15 Sept 1976 5 Oct 1979 9 Oct 1979  15  1979 1979 1979 1979  36.5 43.0 102  9.1 25.6 40.8  4.01 1.68 2.50  NA  24 20  1979 1960  95.4 33.1  1.52 0.94  24 20  30 Oct 1978 2 Oct 1961  131 60.0  95.4 18.1  1.37 3.31  - 224 -  APPENDIX I I DEPTH-DURATION-FREQUENCY DATA FOR THE BRITISH COLUMBIA COASTAL REGION  - 225 TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II. DATA  DATA  RETURN DURATION  2  5  1 FOR  FROM  PERIOD  1 0  ABBOTSFORD A  AES (YEARS) 25  50  100  1  HR  12.8  18.7  22.6  27.6  31 . 3  35.0  2  HR  18.5  24.8  29. 1  34.4  38.4  42.3  6  HR  35.6  40.3  43.5  47.5  50.5  53.4  12  HR  49.2  58.3  64.3  72.0  77.6  83.3  24  HR  61 . 7  77.8  88.3  101.8  111.6  121.4  DEPTH -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 o.  (YEARS) 25  50  100  1  HR  0.21  0.24  0.26  0.27  0.28  0.29  2  HR  0.30  0.32  0.33  0.34  0.34  0.35  6  HR  0.58  0.52  0.49  0.47  0.45  0.44  12  HR  0.80  0.75  0.73  0.71  0.70  0.69  24  HR  1 .00  1.00  1 .00  1 .00  1 .00  1 .00  DEPTH [-FREQUENCY R E L A T I O N S H I P S RETURN DURATION  2  5  PERIOD  (YEARS)  10  25  50  100  1  HR  0.56  0.83  1 .00  1 .22  1 .38  1 .54  2  HR  0.64  0.85  1 .00  1.18  1 .32  1 .45  6  HR  0.82  0.93  1 .00  1 .09  1.16  1 .23  12  HR  0.76  0.91  1 .00  1.12  1.21  1 .29  24  HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  - 226 -  TABLE I I .  2  DEPTH-DURATION-FREQUENCY DATA FOR AGASSIZ CDA RAINFALL DATA FROM AES RETURN PERIOD DURATION  2  5  (YEARS)  10  25  50  1 00  1 HR  10.8  13.1  14.6  16.5  17.9  19.3  2 HR  16.3  18.6  20.2  22. 1  23.5  25.0  6 HR  32.5  36.3  38.8  42.0  44.4  46.7  12 HR  50.0  57.2  62.0  68.2  72.7  77.2  24 HR  73.0  88.6  98.9  111.8  121.4  131.0  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD DURATION  2  5  (YEARS)  10  25  50  1 00  1 HR  0.15  0.15  0.15  0.15  0.15  0.15  2 HR  0.22  0.21  0.20  0.20  0.19  0.19  6 HR  0.45  0.41  0.39  0.38  0.37  0.36  HR  0.69  0.65  0.63  0.61  0.60  0.59  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  12  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD DURATION  2  5  (YEARS)  10  25  50  100  1 HR  0.74  0.90  1 .00  1.13  1 .23  1 .32  2 HR  0.81  0.92  1 .00  1.10  1.17  1 .24  6 HR  0.84  0.94  1 .00  1 .08  1.14  1 .20  12 HR  0.8.1  0.92  1 .00  1.10  1.17  1 .24  24 HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  - 227 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  I I . DATA  DATA  RETURN DURATION  2  5  3 FOR A L O U E T T E  FROM  PERIOD  LAKE  AES (YEARS)  10  25  50  100  1  HR  12.3  14.4  15.8  1 7.6  18.9  20.3  2  HR  20.2  24. 1  26.7  30.0  32.4  34.9  6  HR  44.9  49. 1  51 . 8  55.4  58.0  60.5  12  HR  70.0  81 . 7  89.6  99.5  106.8  114.1  24  HR  97.7  117.6  130.8  147.6  159.8  1  DEPTH-DURATION RETURN DURATION  2  5  72.  1  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1. HR  0.13  0.12  0.12  0.12  0.12  0.12  2  HR  0.21  0.20  0.20  0.20  0.20  0.20  6  HR  0.46  0.42  0.40  0.38  0.36  0.35  12  HR  0.72  0.69  0.69  0.67  0.67  0.66  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.77  0 . 9 1  1 .00  1.11  1 .20  1 .28  2  HR  0.76  0.90  1 .00  1.12  1.21  1.31  6  HR  0.87  0.95  1 .00  1 .07  1.12  1.17  12  HR  0.78  0.91  1 .00  1.11  1.19  1 .27  24  HR  0.75  0.90  1 .00  1.13  1 .22  1 .32  - 228 -  TABLE I I . 4 DEPTH--DURATION--FREQUENCY DATA FOR ALTA LAKE RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 HR  7.0  8.2  9.0  10.0  10.8  11.5  2 HR  11.0  12.6  13.6  14.9  15.9  16.8  6 HR  20.0 .  23.4  25.7  28.6  30.7  32.8  12 HR  29.5  36.5  41.0  46.9  51 .2  55.6  24 HR  43.0  56.2  64.8  75.8  84.0  92.2  DEPTH-DURATION  1 00  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.16  0.15  0.14  0.13  0.13  0. 13  2 HR  0.26  0.22  0.21  0.20  0.19  0.18  6 HR  0.47  0.42  0 .40  0.38  0.36  0.36  12 HR  0.69  0.65  0.63  0.62  0.61  0.60  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00 .  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  -  25  50  1 00  1 HR  0.78  0.91  1 .00  1.11  1.19  1 .28  2 HR  0.81  0.92  1 .00  1.10  1.17  1 .24  6 HR  0.78  0.91  1 .00  1.11  1.19  1 .28  12 HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  24 HR  0.66  0.87  1 .00  1.17  1 .30  1 .42  - 229 -  TABLE I I .  5  DEPTH-DURATION-FREQUENCY DATA FOR BEAR CREEK R A I N F A L L DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  23 .7  36.4  44.8  55.4  63.3  71.1  2 HR  35 .4  48 . 1  56.6  67.3  75.2  83. 1  6 HR  63 .8  82.0  94. 1  109.3  120.5  131.8  12 HR  88 .9  120.6  141.5  168.0  187.6  207.0  24 HR  141 .8  205.2  247.2  300.2  339.4  378.5  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  1 HR  0. 1 7  2 HR  5  10  25  50  0.18  0.18  0.18  0.19  0.19  0. 25  0.23  0.23  0.22  0.22  0.22  6 HR  0. 45  0.40  0.38  0.36  0.36  0.35  12 HR  0. 63  0.59  0.57  0.56  0.55  0.55  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  100  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0. 53  0.81  1 .00  1 .24  1 .41  1 .59  2 HR  0. 62  0.85  1 .00  1.19  1 .33  1 .47  6 HR  0. 68  0.87  1 .00  1.16  1 .28  1 .40  12 HR  0. 63  0.85  1 .0.0  1.19  1 .33  1 .46  24 HR  0. 57  0.83  1 .00  1.21  1 .37  1 .53  - 230 -  TABLE I I . 6 DEPTH-DURATION-FREQUENCY DATA FOR BELLA COOLA BC HYDRO RAINFALL DATA FROM AES RETURN PERIOD DURATION  2  5  (YEARS)  10  25  50  100  1 HR  10.6  13.0  14.6  16.6  18.1  19.6  2 HR  17.4  22.3  25.6  29.7  32.7  35.7  6 HR  36.7  47.7  55.0  64.2  71 .0  77.8  12 HR  59.6  76.8  88.2  102.6  1 13.3  123.8  24 HR  88.3  113.8  130.6  151.9  167.5  183.1  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD DURATION  2  5  (YEARS) 25  10  50  1 0 0  1  HR  0 . 1 2  0 . 1 1  0 . 1 1  0 . 1 1  0 . 1 1  0 . 1 1  2  HR  0 . 2 0  0 . 2 0  0 . 2 0  0 . 2 0  0 . 2 0  0 . 1 9  6  HR  0.42  0.42  0.42  0.42  0.42  0.42  12  HR  0 . 6 8  0 . 6 8  0 . 6 8  0 . 6 8  0 . 6 8  0 . 6 8  1 . 0 0  1 . 0 0  1 . 0 0  1 . 0 0  1 . 0 0  24 HR  *1 . 0 0  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD DURATION  2  5  (YEARS)  10  25  50  100  1 HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  2 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  6 HR  0.67  0.87  1 .00  1.17  1 .29  1.41  12 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  24 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  - 231 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.7 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  BUNTZEN  LAKE  AES (YEARS)  10  25  50  100  1 HR  14.5  18.6  21 .3  24.8  27.3  29.8  2  HR  23. 1  28.6  32.3  36.9  40.3  43.7  6  HR  50.0  61 .0  68.4  77.6  84.5  91 .3  12  HR  75.4  99. 1  115.0  1 34.8  1 49.5  164.3  24  HR  111.4  177.4  210.5  235.2  259.7  151.0  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  100  1  HR  0 .13  0.12  0.12  0.12  0.12  0. 1 1  2  HR  0 .21  0.19  0.18  0.18  0.17  0. 1 7  6  HR  0 .45  0.40  0.39  0.37  0.36  0 .35  12  HR  0 .68  0.66  0.65  0.64  0.64  0 .63  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH - F R E Q U E N C Y RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1 HR  0 .68  0.87  1 .00  1.16  1 .28  1 .40  2  HR  0 .72  0.89  1 .00  1.14  1 .25  1 .35  6  HR  0 .73  0.89  1 .00  1.14  1 .24  1 .34  1 2 HR  0 .66  0.86  1 .00  1.17  1 .30  1 .43  24  0 .63  0.85  . 1 .00  1.19  1 .33  1 .46  HR  -  232  -  TABLE I I . 8 DEPTH-DURATION-FREQUENCY DATA FOR BURNABY MTN BCHPA RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  11.0  13.3  14.8  16.7  18.1  19.5  2 HR  17.8  20. 1  21.5  23.4  24.8  26.2  6 HR  37.4  42.7  46.3  50.7  54.0  57.2  12 HR  54.4  63.8  70. 1  77.9  83.8  89.6  24 HR  75. 1  89.8  99.6  111.8  121.0  129.8  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.15  0.15  0.15  0.15  0.15  0.15  2 HR  0.24  0.22  0.22  0.21  0.21  0.20  6 HR  0.50  0.48  0.46  0.45  0.45  0.44  12 HR  0.72  0.71  0.70  0.70  0.69  0.69  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.75  0.90  1 .00  1.13  1 .22  1 .32  2 HR  0.83  0.93  1 .00  1 .09  1.15  1 .22  6 HR  0.81  0.92  1 .00  1.10  1.17  1 .24  12 HR  0.78  0.91  1 .00  1.11  1 .20  1 .28  24 HR  0.75  0.90  1 .00  1.12  1 .21  1 .30  - 233 -  TABLE I I . 9 DEPTH -DURATION -FREQUENCY DATA FOR CAMPBELL RIVER BCFS RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  10.7  13.9  15.9  18.6  20.6  22.5  2 HR  15.9  19.0  21.2  23.8  25.8  27.8  6 HR  30.8  37.0  41.2  46.3  50.2  54.0  12 HR  41.3  48.5  53.3  59.3  63.8  68.3  24 HR  54.0  65.3  73.0  82.6  89.8  96.7  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.20  0.21  0.22  0.23  0.23  0.23  2 HR  0.29  0.29  0.29  0.29  0.29  0.29  6 HR  0.57  0.57  0.56  0.56  0.56  0.56  12 HR  0.76  0.74  0.73  0.72  0.71  0.71  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.67  0.87  1 .00  1.17  1 .29  1.41  2 HR  0.75  0.90  1 .00  1.13  1 .22  1.31  6 HR  0.75  0.90  1 .00  1.13  1 .22  1.31  12 HR  0.77  0.91  1 .00  1.11  1 .20  1.28  24 HR  0.74  0\89  1 .00  1.13  1 .23  1.33  - 234 -  TABLE 11.10 DEPTH -DURATION--FREQUENCY DATA FOR CAMPBELL RIVER BCHPA RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1  00  1 HR  13.1  18.5  22.0  26.5  29.8  33. 1  2 HR  17.9  22.8  26. 1  30.3  33.4  36.4  6 HR  32.5  37.0  40.0  43.8  46.6  49.4  12 HR  43.9  48.8  52.2  56.4  59.5  62.6  24 HR  60.0  69.8  76.3  84.5  90.7  96.7  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.22  0.26  0.29  0.31  0.33  0.34  2 HR  0.30  0.33  0.34  0.36  0.37  0.38  6 HR  0.54  0.53  0.52  0.52  0.51  0.51  12 HR  0.73  0.70  0.68  0.67  0.66  0.65  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.60  0.84  1 .00  1 .20  1 .35  1 .50  2 HR  0.68  0.87  1 .00  1.16  1 .28  1 .39  6 HR  0.81  0.93  1 .00  1 .09  1.16  1 .24  12 HR  0.84  0.94  1 .00  1 .08  1.14  1 .20  24 HR  0.79  0.92  1 .00  1.11  1.19  1 .27  -  235  -  TABLE 11.11 DEPTH-DURATION-FREQUENCY DATA FOR CARNATION CREEK CDF RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  11.8  14.8  16.7  19.2  21 . 1  22.9  2 HR  19.8  24.5  27.6  31.5  34.4  37.3  6 HR  43.9  56.3  64.7  75.2  82.9  90.7  12 HR  64.7  83.2  95.4  110.8  1 22.3  1 33.7  24 HR  91 .9  119.0  1 37.3  1 59.8  176.9  193.7  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.13  0.12  0.12  0.12  0.12  0.12  2 HR  0.22  0.21  0.20  0.20  0.19  0. 1.9  6 HR  0.48  0.47  0.47  0.47  0.47  0.47  12 HR  0.70  0.70  0.69  0.69  0.69  0.69  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  2 HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  6 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  12 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  24 HR  0.67  0.87  1 .00  1.16  1 .29  1.41  -  2 3 6  -  TABLE 11.12 DEPTH-DURATION-FREQUENCY DATA FOR*CHILLIWACK MICROWAVE RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  10.0  12.8  14.6  17.0  18.7  20.4  2 HR  14.0  16.8  18.6  21 .0  22.7  24.4  6 HR  27. 1  31 .7  34.9  38.8  41 .7  44.6  1 2 HR  39.8  46.8  51.5  57.4  61 .7  66.0  2 4 HR  55.2  66.5  73.9  83.5  90.5  97.4  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.18  0.19  0.20  0.20  0.21  0.21  2 HR  0.25  0.25  0.25  0.25  0.25  0.25  6 HR  0.49  0.48  0.47  0.46  0.46  0.46  12 HR  0.72  0.70  0.70  0.69  0.68  0.68  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.68  0.87  1 .00  1.16  1 .28  1 .39  2 HR  0.75  0.90  1 .00  1.13  1 .22  1.31  6 HR  0.78  0.91  1 .00  1.11  1 .20  1 .28  12 HR  0.77  0.91  1 .00  1.11  1 .20  1 .28  24 HR  0.75  0.90  1 .00  1.13  1 .22  1 .32  - 237 -  TABLE 11.13 DEPTH-DURATION-FREQUENCY DATA FOR CLOWHOM FALLS RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  10.5  13.2  15.0  17.3  18.9  20.6  2 HR  15.9  18.9  21.0  23.5  25.4  27.3  6 HR  33.1  39.2  43.3  48.5  52.3  56.0  12 HR  52.3  60.2  65.5  72. 1  77.0  82.0  24 HR  78.0  92.9  1 02.7  124.3  133.4  DEPTH-DURATION  115.2  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.13  0.14  0.15  0.15  0.15  0.15  2 HR  0.20  0.20  0.20  0.20  0.20  0.20  6 HR  0.42  0.42  0.42  0.42  0.42  0.42  12 HR  0.67  0.65  0.64  0.63  0.62  0.61  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.70  0.88  1 .00  1.15  1 .26  1 .38  2 HR  0.76  0.90  1 .00  1.12  1 .21  1 .30  6 HR  0.76  0.91  1 .00  1.12  1 .21  1 .29  12 HR  0.80  0.92  1 .00  1.10  1.18  1 .25  24 HR  0.76  0.90  1 .00  1.12  1.21  1 .30  - 238 -  TABLE 11.14 DEPTH-DURATION-FREQUENCY DATA FOR COMOX A RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  1 HR  9.8  2 HR 6 HR  5  10  25  50  12.4  14.1  16.3  17.9  19.6  14.3  17.5  19.7  22.4  24.4  26.4  28. 1  33. 1  36.2  40.3  43.4  46.4  12 HR  41.2  48.2  52.9  58.8  63.2  67.6  24 HR  58. 1  69.4  77.0  86.4  93.6  100.6  100  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.17  0.18  0.18  0.19  0.19  0.19  2 HR  0.25  0.25  0.26  0.26  0.26  0.26  6 HR  0.48  0.48  0.47  0.47  0.46  0.46  12 HR  0.71  0.70  0.69  0.68  0.68  0.67  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1.00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.69  0.88  1 .00  1.15  1 .27  1 .38  2 HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  6 HR  0.78  0.91  1 .00  1.11  1 .20  1 .28  12 HR  0.78  0.91  1 .00  1.11  1 .20  1 .28  24 HR  0.75  0.90  1 .00  1.12  1.21  1.31  - 239 -  TABLE 11.15 DEPTH-DURATION-FREQUENCY DATA FOR COQUITLAM LAKE RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1  HR  14.5  16.6  17.9  19.6  20.9  22. 1  2  HR  22.7  25.3  ' 27. 1  29.3  30.9  32.5  6  HR  55.2  63.5  69. 1  76. 1  81.4  86.5  12  HR  92.9  110.8  122.6  137.5  1 48.6  1 59.6  24  HR  1 43.8  174.5  194.6  220.3  239.3  258.2  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1  HR  0.10  0.09  0.09  0.09  0.09  0.09  2  HR  0.16  0.15  0.14  0.13  0.13  0.13  6  HR  0.38  0.36  0.36  0.35  0.34  0.34  12  HR  0.65  0.63  0.63  0.62  0.62  0.62  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100 -  1  HR  0.81  0.93  1 .00  1 .09  1.16  1 .23  2  HR  0.84  0.94  1 .00  1 .08  1.14  1 .20  6  HR  0.80  0.92  1 .00  1.10  1.18  1 .25  12  HR  0.76  0.90  1 .00  1.12  1 .21  1 .30  24  HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  - 240 -  TABLE DEPTH-DURATION-FREQUENCY  R A I N F A L L  1 1 . 1 6 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  COURTENAY  PUNTLEDGE  AES (YEARS)  10  25  50  100  1  HR  9.6  12.1  13.7  15.9  17.4  19.0  2  HR  14.5  17.3  19.3  21.7  23.5  25.3  6  HR  30.6  36.6  40.6  45.6  49.3  53.0  12  HR  45.5  56.3  63.4  72.4  79. 1  85.7  24  HR  66.2  84.5  96.7  112.1  123.4  DEPTH-DURATION RETURN DURATION  2  5  1  34.6  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.14  0.14  0.14  0.14  0.14  0.14  2  HR  0.22  0.21  0.20  0.19  0.19  0.19  6  HR  0.46  0.43  0.42  0.41  0.40  0.39  12  HR  0.69  0.67  0.66  0.65  0.64  0.64  24-  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  R E L A T I O N S H I P S  PERIOD  (YEARS)  10  25  50  100  1  HR  0.70  0.88  1 .00  1.15  1 .27  1 .38  2  HR  0.75  0.90  1 .00  1.13  1 .22  1.31  6  HR  0.75  0.90  1 .00  1.12  1.21  1.31  12  HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  24  HR  0.68  0.87  1 .00  1.16  1 .28  1 .39  - 241 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.17 DATA  DATA  RETURN DURATION  2  1 HR  9.9  5  FOR  FROM  PERIOD  DAISY LAKE  DAM  AES (YEARS)  10  25  50  1 00  14.0  16.6  20. 1  22.6  25. 1  2  HR  15.5  20.6  23.9  28. 1  31.3  34.4  6  HR  32. 1  39.5  44.4  50.6  55.2  59.8  1 2 HR  47.5  55.3  60.6  67. 1  72.0  76.8  24  66.2  78.7  87. 1  97.7  1 05.4  HR  113.0  DEPTH-DURATION R E L A T I O N S H I P S RETURN DURATION  2  5  PERIOD  1 0  (YEARS) 25  50  1 00  1 HR  0.15  0.18  0.19  0.21  0.21  0.22  2  HR  0.23  0.26  0.27  0.29  0.30  0.30  6  HR  0.48  0.50  0.51  0.52  0.52  0.53  12 HR  0.72  0.70  0.70  0.69  0.68  0.68  24  1 .00  1 .00  1 .00  ' 1 .00  1 .00  1 .00  HR  DEPTH-FREQUENCY R E L A T I O N S H I P S RETURN DURATION  2  5  PERIOD  (YEARS)  10  25  50  100  1 HR  0.60  0.84  1 .00  1 .20  1 .36  1 .51  2  HR  0.65  0.86  1 .00  1 .18  1.31  1 .44  6  HR  0.72  0.89  1 .00  1.14  1 .24  1 .35  12  HR  0.78  0.91  1 .00  1.11  1.19  1 .27  24  HR  0.76  0.90  1 .00  1.12  1.21  1 .30  -  242  -  TABLE 11.18 DEPTH-DURATION-FREQUENCY DATA FOR ESTEVAN POINT RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  18.3  22.4  25. 1  28.5  31.0  33.5  2 HR  28.0  35.6  40.7  47.0  51.8  56.4  6 HR  61.6  73.9  82.0  92.3  99.9  107.5  90. 1  1 06.4  117.2  130.8  140.9  1 50.8  168.2  193.0  223.9  247.2  270.0  12 HR 24 HR  131.0  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  1 HR  0. 1 4  0.13  2 HR  0 .21  6 HR  10  25  50  100  0.13  0.13  0.13  0. 1 2  0.21  0.21  0.21  0.21  0 .21  0 .47  0.44  0.43  0.41  0.40  0 .40  12 HR  0 .69  0.63  0.61  0.58  0.57  0 .56  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1.00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0 .73  0.89  1 .00  1.14  1 .24  1.34  2 HR  0 .69  0.88  1 .00  1.16  1 .27  1.39  6 HR  0 .75  0.90  1 .00  1.13  1 .22  1.31  12 HR  0 .77  0.91  1 .00  1 .12  1 .20  1 .29  24 HR  0 .68  0.87  1 .00  1.16  1 .28  1 .40  - 243 -  TABLE 11.19 DEPTH-DURATION-FREQUENCY DATA FOR HANEY MICROWAVE RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  12.6  15.6  17.5  19.9  21 .8  23.6  2 HR  19.0  22.8  25.4  28.7  31.1  33.5  6 HR  37.2  42.6  46.2  50.7  54.0  57.4  1 2 HR  56.4  67.7  75. 1  84.5  91 .6  98.4  24 HR  78.7  97.0  124.3  1 35.6  1 46.9  109.0  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.16  0.16  0.16  0.16  0.16  0.16  2 HR  0.24  0.24  0.23  0.23  0.23  0.23  6 HR  0.47  0.44  0.42  0.41  0.40  0.39  12 HR  0.72  0.70  0.69  0.68  0.68  0.67  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.72  0.89  1 .00  1.14  1 .24  1 .35  2 HR  0.75  0.90  1 .00  1.13  1 .22  1 .32  6 HR  0.81  0.92  1 .00  1.10  1.17  1 .24  12 HR  0.75  0.90  1 .00  1.12  1 .22  1.31  24 HR  0.72  0.89  1 .00  1.14  1 .24  1 .35  - 244 -  TABLE 11.20 DEPTH-DURATION-FREQUENCY DATA FOR HANEY UBC RF ADMIN RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  11.8  14.3  16.0  18.1  19.6  21.2  2 HR  19.3  22.4  24.5  27. 1  29.0  30.9  6 HR  39.2  45. 1  49. 1  54. 1  57.8  61 .5  12 HR  59.5  71.0  78.6  88.3  95.4  1 02.6  24 HR  89.3  111.8  1 26.7  145.4  1 59.4  DEPTH-DURATION  173.3  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.13  0.13  0.13  0.12  0.12  0.12  2 HR  0.22  0.20  0.19  0.19  0.18  0.18  6 HR  0.44  0.40  0.39  0.37  0.36  0.35  12 HR  0.67  0.64  0.62  0.61  0.60  0.59  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.74  0.90  1 .00  1.13  1 .23  1 .32  2 HR  0.79  0.92  1 .00  1.11  1.19  1 .26  6 HR  0.80  0.92  1 .00  1.10  1.18  1 .25  12 HR  0.76  0.90  1 .00  1.12  1 .21  1.31  24 HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  - 245 -  TABLE 11.21 DEPTH-DURATION-FREQUENCY DATA FOR JORDAN RIVER DIVERSI RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  22.8  32.7  39.3  47.6  53.7  59.9  2 HR  35.0.  44.2  50.3  58.0  63.6  69.3  6 HR  71.5  92.9  107.2  125.2  1 38.4  151.7  12 HR  1 04.4  142.9  168.5  200.6  224.5  248.3  24 HR  1 50.0  205.2  241 .9  288.2  322.6  356.6  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.15  0.16  0.16  0.17  0.17  0.17  2 HR  0.23  0.22  0.21  0.20  0.20  0.19  6 HR  0.48  0.45  0.44  0.43  0.43  0.43  12 HR  0.70  0.70  0.70  0.70  0.70  0.70  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.58  0.83  1 .00  1 .21  1 .37  1 .52  2 HR  0.70  0.88  1 .00  1.15  1 .27  1 .38  6 HR  0.67  0.87  1 .00  1.17  1 .29  1 .41  12 HR  0.62  0.85  1 .00  1.19  1 .33  1 .47  24 HR  0.62  0.85  1 .00  1.19  1 .33  1 .47  - 246 -  TABLE II.22 DEPTH-DURATION-FREQUENCY DATA FOR JORDAN RIVER GEN STA RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  10.6  12.3  13.4  14.8  15.9  16.9  2 HR  17.6  20.3  22.2  24.4  26. 1  27.8  6 HR  37.4  44.6  49.3  55.4  59.8  64.3  12 HR  55.9  68.8  77.3  88. 1  96. 1  104.0  24 HR  75.4  99. 1  1 15.0  1 34.9  1 49.8  DEPTH-DURATION  1 64. 4  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.14  0.12  0.12  0.11  0.11  0.10  2 HR  0.23  0.21  0.19  0.18  0.17  0.17  6 HR  0.50  0.45  0.43  0.41  0.40  0.39  12 HR  0.74  0.69  0.67  0.65  0.64  0.63  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1  HR  0.79  0.92  1 .00  1.11  1.18  1.26  2  HR  0.80  0.92  1 .00  1.10  1 .18  1 .26  6  HR  0.76  0.90  1 .00  1.12  1.21  1 .30  12  HR  0.72  0.89  1 .00  1.14  1 .24  1 .35  24  HR  0.66  0.86  r o o  1.17  1 .30  1 .43  - 247 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.23 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  KITIMAT  2  AES (YEARS)  10  25  50  100  1  HR  11.9  14.5  16.2  18.4  20.0  21.6  2  HR  19.7  24. 1  27.0  30.7  33.4  36. 1  6  HR  44.5  57.5  66.2  77.2  85.3  93.4  12  HR  65.5  85.4  98.6  115.3  1 27.7  139.9  24  HR  88.8  109.7  123.6  141.1  1 54.3  167.0  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  100  1  HR  0.13  0.13  0.13  0.13  0.13  0.13  2  HR  0.22  0.22  0.22  0.22  0.22  0.22  6  HR  0.50  0.52  0.54  0.55  0.55  0.56  12  HR  0.74  0.78  0.80  0.82  0.83  0.84  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.73  0.89  1 .00  1.13  1 .23  1 .33  2  HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  6  HR  0.67  0.87  1 .00  1.16  1 .29  1.41  12  HR  0.66  0.87  1 .00  1.17  1 .29  1 .42  24  HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  - 248 -  TABLE  11.24  DEPTH--DURATION--FREQUENCY DATA  RAINFALL  DATA  RETURN DURATION  FOR LADNER  BCHPA  FROM A E S  PERIOD  (YEARS)  2  5  10  25  50  100  1  HR  8.1  9.8  10.9  12.4  13.5  14.5  2  HR  12.5  14.0  15.0  16.2  17.1  18.1  6  HR  22.3  24.5  26.0  27.8  29.2  30.5  12  HR  31.6  38.3  42.7  48.2  52.4  56.5  24  HR  43.2  56.2  64.6  75.6  83.5  91 .4  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.19  0.17  0.17  0.16  0.16  0 . 1 6  2  HR  0.29  0.25  0.23  0.21  0.21  0.20  6  HR  0.52  0.44  0.40  0.37  0.35  0.33  12  HR  0.73  0.68  0.66  0.64  0.63  0.62  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  2  HR  0.83  0.93  1 .00  1 .08  1.15  1.21  6  HR  0.86  0.94  1 .00  1 .07  1.12  1.18  12  HR  0.74  0.90  1 .00  1.13  1 .23  1 .32  24  HR  0.67  0.87  1 .00  1.17  1 .29  1 .42  - 249 -  TABLE 11.25 DEPTH-DURATION-FREQUENCY DATA FOR LANGLEY LOCHIEL RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  11.4  14.6  16.7  19.4  21 .4  23.4  2 HR  16.9  19.5  21.2  23.3  24.9  26.5  6 HR  31.4  37.3  41.2  46. 1  49.8  53.4  12 HR  46.4  55.2  61 .0  68.2  73.6  79.0  24 HR  61 .2  75.6  85.2  97.2  1 06.3  115.2  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.19  0.19  0.20  0.20  0.20  0.20  2 HR  0.28  0.26  0.25  0.24  0.23  0.23  6 HR  0.51  0.49  0.48  0.47  0.47  0.46  12 HR  0.76  0.73  0.72  0.70  0.69  0.69  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  2 HR  0.80  0.92  1 .00  1.10  1.18  1 .25  6 HR  0.76  0.91  1 .00  1.12  1 .21  1 .30  12 HR  0.76  0.91  1 .00  1.12  1.21  1 .30  24 HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  - 250 -  TABLE 11.26 DEPTH-DURATION-FREQUENCY  RAINFALL  DATA  DATA  RETURN DURATION  2  5  FOR M I S S I O N  WEST  ABBEY  FROM A E S  PERIOD  (YEARS)  10  25  50  100  1 HR  13.7  17.8  20.6  24. 1  26.6  2  HR  19.7  24.5  27.7  31.8  34.8  6  HR  35.3  40.6  44. 1  48.5  51 .7  55.0  12 HR  51.1  59.2  64.4  71.2  76. 1  81.1  24  72.5  85.4  94. 1  105. 1  HR  DEPTH-DURATION RETURN DURATION  2  5  113.0  29.2 ' 37.7  121.2  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1 HR  0 . 1 9  0.21  0.22  0.23  0.24  0.24  2  HR  0.27  0.29  0.29  0.30  0.31  0.31  6  HR  0.49  0.48  0.47  0.46  0.46  0.45  12 HR  0.71  0.69  0.68  0.68  0.67  0.67  24  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  HR  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1 HR  0.67  0.87  1 .00  1.17  1 .29  1 .42  2  HR  0.71  0.88  1 .00  1.15  1 .25  1 .36  6  HR  0.80  0.92  1 .00  1.10  1.17  1 .25  12 HR  0.79  0.92  1 .00  1.10  1 . 1 8  1 .26  24  0.77  0.91  1 .00  1.12  1 .20  1 .29  HR  -  251 -  TABLE  II.27  DEPTH--DURATION--FREQUENCY D A T A  RAINFALL  DATA  RETURN DURATION  2  1 HR  9.4  5  FOR  NANAIMO D E P A R T U R E  BA  FROM A E S  PERIOD  (YEARS)  10  25  50  15.4  19.5  24.5  28.3  32.0  100  2  HR  13.2  20.0  24.6  30.3  34.6  38.9  6  HR  23.9  29.6  33.3  38.0  41 .6  45. 1  12  HR  33.6  40. 1  44.4  49.8  53.9  57.8  24  HR  41 .3  50.4  56.4  64. 1  69.8  75.4  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  1 00  • 1 HR  0.23  0.31  0.35  0.38  0.41  0.43  2 HR  0.32  0.40  0.44  0.47  0.50  0.52  6  HR  0.58  0.59  0.59  0.59  0.60  0.60  12  HR  0.81  0.80  0.79  0.78  0.77  0.77  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  • 1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  10  (YEARS) 25  50  100  1 HR  0.48  0.79  1 .00  1 .26  1 .45  1 .65  2 HR  0.54  0.81  1 .00  1 .23  1 .41  1 .58  6  HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  12  HR  0.76  0.90  1 .00  1.12  1.21  1 .30  24  HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  - 252 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.28 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  N VANCOUVER  LYNN  CRE  AES (YEARS)  10  25  50  100  1 HR  14.4  17.5  19.6  22.2  24. 1  26.0  "• 2 HR  23.2  28.2  31.5  35.6  38.7  41.8  92.6  100.7  6  HR  51.7  64.9  73.5  84.5  12  HR  80.8  103.8  1 19.0  1 38.4  152.6  166.9  24  HR  1 20.2  1 56.5  180.5  211.0  233.5  255.8  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  1 00  1  HR  0.12  0.11  0.11  0.11  0.10  0.10  2  HR  0.19  0 . 1 8  0.17  0.17  0.17  0.16  6  HR  0.43  0.41  0.41  0.40  0.40  0.39  12  HR  0.67  0.66  0.66  0.66  0.65  0.65  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  10-  (YEARS) 25  50  100  1  HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  2  HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  6  HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  12  HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  24  HR  0.67  0.87  1 .00  1.17  1 .29  1 .42  - 253 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.29 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  PITT  MEADOWS S T P  AES (YEARS)  10  25  50  100  1  HR  12.5  17.5  20.9  25. 1  28.2  31.3  2  HR  18.0  24.9  29.5  35.3  39.6  43.9  6  HR  38.0  45.6  50.7  57. 1  61.8  66.5  12  HR  53.0  65.0  73. 1  83.2  90.7  98.2  24  HR  67.7  85.7  97.4  112.6  123.8  134.9  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.19  0.20  0.21  0.22  0.23  0.23  2  HR  0.27  0.29  0.30  0.31  0.32  0.33  6  HR  0.56  0.53  0.52  0.51  0.50  0.49  12  HR  0.78  0.76  0.75  0.74  0.73  0.73  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.60  0.84  1 .00  1 .20  1 .35  1 .50  2  HR  0.61  0.84  1 .00  1 .20  1 .34  1 .49  6  HR  0.75  0.90  1 .00  1.13  1 .22  1 .31  12  HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  24  HR  0.69  0.88  1 .00  1.16  1 .27  1 .38  - 254 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.30 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  1 0  PITT  POLDER  AES (YEARS) 25  50  1 00  1  HR  1 2.4  14.7  16.2  18.1  19.5  20.9  2  HR  18 .9  22.9  25.4  28.7  31.2  33.6  6  HR  42 .7  51 .7  57.7  65.3  70.9  76.4  12  HR  67 .3  80.3  88.9  99.8  107.9  115.9  24  HR  98 .9  1 19.0  1 32.2  1 49.0  161.5  173.8  D E P T H -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0. 1 3  0.12  0.12  0.12  0.12  0.12  2  HR  0. 1 9  0.19  0.19  0.19  0.19  0.19  6  HR  0. 43  0.43  0.44  0.44  0.44  0.44  12  HR  0. 68  0.67  0.67  0.67  0.67  0.67  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH - F R E Q U E N C Y RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0. 77  0.91  1 .00  1.12  1 .21  1 .29  2  HR  0. 74  0.90  1 .00  1.13  1 .22  1 .32  6  HR  0. 74  0.90  1 .00  1.13  1 .23  1 .32  12  HR  0. 76  0.90  1 .00  1.12  1.21  1 .30  24  HR  0. 7 5  0.90  1 .00  1.13  1 .22  1.31  - 255 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.31 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  PORT A L B E R N I  A  AES (YEARS)  10  25  50  1 00  1  HR  1 1.2  15.2  17.9  21.2  23.7  26.2  2  HR  18 .0  21.7  24. 1  27.2  29.5  31.8  6  HR  37 .9  42.4  45.3  49.0  51 .8  54.5  12  HR  59 .4  71.6  79.8  90.0  97.6  105.1  24  HR  87 . 1  108.5  122.9  154.3  167.5  D E P T H -DURATION RETURN DURATION  2  5  1 40.9  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0. 1 3  0.14  0.15  0.15  0.15  0.16  2  HR  0. 21  0.20  0.20  0.19  0.19  0.19  6  HR  0. 44  0.39  0.37  0.35  0.34  0.33  12  HR  0. 68  0.66  0.65  0.64  0.63  0.63  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0. 63  0.85  1 .00  1.19  1 .33  1 .47  2  HR  0. 75  0.90  1 .00  1.13  1 .22  1 .32  6  HR  0. 84  0.94  1 .00  1 .08  1.14  1 .20  12  HR  0. 74  0.90  1 .00  1.13  1 .22  1 .32  24  HR  0. 71  0.88  1 .00  1.15  1 .26  1 .36  - 256 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.32 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  1 0  PORT C O Q U I T L A M  CITY  AES (YEARS) 25  50  100  1  HR  11.0  13.4  15.0  17.0  18.4  19.9  2  HR  17.1  1.8.7  19.7  21.0  22.0  23.0  6  HR  36.9  42.4  46.0  50.6  54.0  57.4  12  HR  56.3  65.9  72.4  80.4  86.4  92.4  24  HR  81.1  96.7  107.0  1 20.0  129.6  139.2  DEPTH -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  100  1  HR  0.14  0.14  0.14  0.14  0.14  0.14  2  HR  0.21  0.19  0.18  0.18  0.17  0.17  6  HR  0.45  0.44  0.43  0.42  0.42  0.41  12  HR  0.69  0.68  0.68  0.67  0.67  0.66  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  2  HR  0.87  0.95  1 .00  1 .07  1.12  1.17  6  HR  0.80  0.92  1 .00  1.10  1.17  1 .25  12  HR  0.78  0.91  1 .00  1.11  1.19  1 .28  24  HR  0.76  0.90  1 .00  1.12  1.21  1 .30  - 257 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.33 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  PORT HARDY A  AES (YEARS)  10  25  50  100  1  HR  10.0  11.2  12.1  13.1  13.8  14.6  2  HR  16.3  19.1  20.9  23.3  25.0  26.7  6  HR  37.2  44.2  49.0  54.8  59.2  63.6  12  HR  61.0  73.3  81.4  91 .7  99.2  1 06.8  24  HR  89.5  116.6  134.6  157.4  174.2  D E P T H -DURATION RETURN DURATION  2  5  190.8  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.11  0.10  0.09  0.08  0.08  0.08  2  HR  0.18  0.16  0.16  0.15  0.14  0.14  6  HR  0.42  0.38  0.36  0.35  0.34  0.33  12  HR  0.68  0.63  0.60  0.58  0.57  0.56  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.83  0.93  1 .00  1 .09  1.15  1.21  2  HR  0.78  0.91  1 .00  1.11  1.19  1 .28  6  HR  0.76  0.90  1 .00  1 .12  1.21  1 .30  12  HR  0.75  0.90  1 .00  1.13  1 .22  1.31  24  HR  0.66  0.87  1 .00  1.17  1 .29  1 .42  - 258 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.34 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  1 0  PORT  MELLON  AES (YEARS) 25 '  50  100  1  HR  18.5  20.9  22.5  24.5  25.9  27.4  2  HR  30.4  33.9  36.1  39.0  41.1  43.2  6  HR  65.0  73.6  79.3  86.5  91 .8  97. 1  12  HR  98.9  119.2  1 32.6  149.5  1 62. 1  1 74.7  24  HR  1 42.6  176.6  199.4  228.0  249.4  270.2  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.13  0.12  0.11  0.11  0.10  0.10  2  HR  0.21  0.19  0.18  0.17  0.16  0.16  6  HR  0.46  0.42  0.40  0.38  0.37  0.36  12  HR  0.69  0.67  0.66  0.66  0.65  0.65  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  10  (YEARS) 25  50  100  1  HR  0.82  0.93  1 .00  1 .09  1.16  1 .22  2  HR  0.84  0.94  1 .00  1 .08  1.14  1 .20  6  HR  0.82  0.93  1 .00  1 .09  1.16  1 .22  12  HR  0.75  0.90  1 .00  1.13  1 .22  1 .32  24  HR  0.71  0.89  1 .00  1.14  1 .25  1 .35  - 259 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.35 DATA  DATA  RETURN DURATION  2  5  FOR  PORT MOODY G U L F O I L  FROM A E S  PERIOD  (YEARS)  10  25  50  1 00  1  HR  10.6  13.2  15.0  17.2  18.8  20.4  2  HR  17.0  19.6  21.4  23.6  25.2  26. 9  6  HR  38.3  44.3  48.4  53.5  57.2  61 . 0  12  HR  58.3  70.3  78.4  88.4  95.9  103.2  24  HR  84.5  1 05.4  119.0  1 36.3  1 49.0  161.8  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.13  0.13  0.13  0.13  0.13  0.13  2  HR  0.20  0.19  0.18  0.17  0.17  0.17  6  HR  0.45  0.42  0.41  0.39  0.38  0.38  12  HR  0.69  0.67  0.66  0.65  0.64  0.64  24  HR  1 .00  1.00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2.  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1  HR  0.71  0.88  1 .00  1.15  1 .26  1 .36  2  HR  0.79  0.92  1 .00  1.10  1.18  1 .26  6  HR  0.79  0.92  1 .00  1.11  1.18  1 .26  12  HR  0.74  0.90  1 .00  1.13  1 .22  1 .32  24  HR  0.71  0.89  1 .00  IT 1 5  1 .25  1 .36  -  260  -  TABLE 11.36 DEPTH-DURATION-FREQUENCY DATA FOR PORT RENFREW BCFP RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  20.6  28.5  33.7  40.4  45.3  50. 1  2 HR  36.5  45.2  50.9  58.2  63.5  68.9  6 HR  80.0  96.0  106.7  120. 1  130.0  139.9  12 HR  1 22.3  142.6  1 56.0  172.9  185.5  198.0  24 HR  168.0  197.3  217.0  241 .4  259.7  277.9  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  10  25  50  1 HR  0. 1 2  0.14  0. 16  0.17  0.17  0 .18  2 HR  0 .22  0.23  0.23  0.24  0.24  0 .25  6 HR  0 .48  0.49  0.49  0.50  0.50  0 .50  12 HR  0 .73  0.72  0.72  0.72  0.71  0 .71  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  5  100  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0 .61  0.84  1 .00  1 .20  1 .34  1 .49  2 HR  0 .72  0.89  1 .00  1.14  1 .25  1 .35  6 HR  0 .75  0.90  1 .00  1.13  1 .22  1 .31  12 HR  0 .78  0.91  1 .00  1.11  1.19  1 .27  24 HR  0 .77  0.91  1 .00  1.11  1 .20  1 .28  - 261 -  TABLE D E P T H -DURATION - F R E Q U E N C Y  RAINFALL  11.37 DATA FOR P R I N C E R U P E R T A  DATA  RETURN DURATION  2  5  FROM  PERIOD  AES (YEARS)  10  25  50  100  1  HR  12.3  14.3  15.7  17.4  18.6  19.8  2  HR  19.0  21 .8  23.7  26.1  27.8  29.6  6  HR  39. 1  49.3  56.0  64.6  70.9  77.2  12 HR  59.9  76.8  88. 1  1 02.2  1 12.8  123.2  24  89.5  112.3  1 46.6  161.0  175.0  HR  127.7  D E P T H -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  1 00  1  HR  0.14  0.13  0.12  0.12  0.12  0.11  2  HR  0.21  0.19  0.19  0.18  0.17  0.17  6  HR  0.44  0.44  0.44  0.44  0.44  0.44  12  HR  0.67  0.68  0.69  0.70  0.70  0.70  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY R E L A T I O N S H I P S RETURN DURATION  2  5  PERIOD  (YEARS)  10  25  50  100  1 HR  0.79  0.92  1 .00  1.11  1.19  1 .27  2  HR  0.80  0.92  1 .00  1.10  1.17  1 .25  6  HR  0.70  0.88  1 .00  1.15  1 .27  1 .38  12  HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  24  HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  - 262 -  TABLE I I . 3 8 DEPTH--DURATION--FREQUENCY DATA FOR SAANICH DENSMORE RAINFALL DATA FROM AES -  RETURN PERIOD (YEARS)  DURATION  2  5  10  25  50  1 HR  7.6  8.8  9.6  10.7  11.5  12.2  2 HR  12.5  14.3  15.5  17.0  18.2  19.3  6 HR  26.4  30.4  33.0  36.4  38.8  41 .2  12 HR  38.3  47.6  53.9  61 .8  67.6  73.4  24 HR  49.4  67.0  78.5  93. 1  1 03.9  115.0  100  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0 .15  0.13  0.12  0.11  0.11  0 . 11  2 HR  0 .25  0.21  0.20  0.18  0.17  0. 1 7  6 HR  0 .53  0.45  0.42  0.39  0.37  0 .36  12 HR  0 .77  0.71  0.69  0.66  0.65  0 .64  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  • 1 .00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0 .78  0.91  1 .00  1.11  1.19  1 .27  2 HR  0 .80  0.92  1 .00  1.10  1.17  1 .24  6 HR  0 .80  0.92  1 .00  1.10  1.18  1 .25  12 HR.  0 .71  0.88  1 .00  1.15  1 .25  1 .36  24 HR  0 .63  0.85  1 .00  1.19  1 .32  1 .46  - 263 -  TABLE II.39 DEPTH--DURATION -FREQUENCY DATA FOR SANDSPIT A RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  10.4  12.3  13.5  15.0  16.2  17.3  2 HR  16.2  19.0  20.9  23.2  25.0  26.8  6 HR  30.8  36.5  40.2  44.9  48.5  52.0  12 HR  40.0  46.4  50.8  56.2  60. 1  64.2  24 HR  52. 1  59.8  65.0  71.3  76. 1  80.9  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.20  0.21  0.21  0.21  0.21  0.21  2 HR  0.31  0.32  0.32  0.33  0.33  0.33  6 HR  0.59  0.61  0.62  0.63  0.64  0.64  12 HR  0.77  0.78  0.78  0.79  0.79  0.79  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 Of)  1 HR  0.77  0.91  1 .00  1.11  1 .20  1 .28  2 HR  0.77  0.91  1 .00  1.11  1 .20  1 .28  6 HR  0.77  0.91  1 .00  1.12  1.21  1 .29  12 HR  0.79  0.91  1 .00  1.11  1.18  1 .26  24 HR  0.80  0.92  1 .00  1.10  1.17  1 .24  - 264 -  TABLE II.40 DEPTH-DURATION-FREQUENCY DATA FOR SPRING ISLAND RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  15.4  18.7  20.9  23.7  25.7  27.8  2 HR  24. 1  27.8  30.3  33.4  35.7  38.0  6 HR  51 .5  61 .5  68.0  76.4  82.5  88.6  12 HR  81.4  1 04.8  120.4  140.0  1 54.6  1 69. 1  24 HR  121.7  156.7  179.8  209.0  230.9  252.5  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.13  0.12  0.12  0.11  0.11  0.11  2 HR  0.20  0.18  0.17  0.16  0.15  0.15  6 HR  0.42  0.39  0.38  0.37  0.36  0.35  12 HR  0.67  0.67  0.67  0.67  0.67  0.67  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.74  0.89  1 .00  1.13  1 .23  1 .33  2 HR  0.80  0.92  1 .00  1.10  1.18  1 .25  6 HR  0.76  0.90  1 .00  1.12  1.21  1 .30  12 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  24 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  - 265 -  TABLE 11.41 DEPTH-DURATION-FREQUENCY DATA FOR STAVE FALLS RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  12.0  13.6  14.7  16.0  17.0  18.0  2 HR  18.4  21.4  23.4  25.8  27.7  29.5  6 HR  40.4  49.6  55.7  63.5  69.2  74.9  12 HR  62.3  78.8  89.8  103.6  113.9  1 24. 1  24 HR  83.8  106.3  121.4  1 40.4  1 54.3  168.2  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.14  0.13  0.12  0.11  0.11  0.11  2 HR  0.22  0.20  0.19  0.18  0.18  0.18  6 HR  0.48  0.47  0.46  0.45  0.45  0.45  12 HR  0.74  0.74  0.74  0.74  0.74  0.74  2 4 HR  1 .00  1,00  1 .00 '  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.82  0.93  1 .00  1 .09  1.16  1 .23  2 HR  0.79  0.92  1 .00  1.11  1.18  1 .26  6 HR  0.72  0.89  1 .00  1.14  1 .24  1 .34  12 HR  0.69  0.88  1 .00  1.15  1 .27  1 .38  24 HR  0.69  0.88  1 .00  1.16  1 .27  1 .39  -  266 -  TABLE 11.42 DEPTH-DURATION-FREQUENCY DATA FOR STRATHCONA DAM RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  12.1  17.5  21 . 1  25.6  28.9  32.3  2 HR  17.1  21 .9  25.0  29.0  32.0  34.9  6 HR  31.4  38.6  43.5  49.6  54. 1  58.5  12 HR  45. 1  60.4  70.4  83.2  92.6  102.0  24 HR  61.7  88. 1  1 05.4  1 27.4  143.8  DEPTH-DURATION  1 60. 1  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0 .20  0.20  0.20  0.20  0.20  0 .20  2 HR  0 .28  0.25  0.24  0.23  0.22  0 .22  6 HR  0 .51  0.44  0.41  0.39  0.38  0 .37  12 HR  0 .73  0.69  0.67  0.65  0.64  0 .64  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1.00  DEPTH[-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0 .57  0.83  1 .00  1.21  1 .37  1 .53  2 HR  0 .68  0.87  1 .00  1.16  1 .28  1.39  6 HR  0 .72  0.89  1 .00  1.14  1 .24  1 .34  12 HR  0 .64  0.86  1 .00  1.18  1 .32  1.45  24 HR  0 .59  0.84  1 .00  1 .21  1 .36  1 .52  -  2 6 7  -  TABLE II.43 DEPTH-DURATION-FREQUENCY DATA FOR SURREY KWANTLEN PARK RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  11.1  14.5  16.8  19.7  21.8  24.0  2 HR  16.6  20.8  23.7  27.2  29.8  32.4  6 HR  32.6  39. 1  43.4  48.8  52.8  56.8  12 HR  48.7  60. 1  67.7  77.2  84.2  91.3  24 HR  67.9  89.3  1 03.4  121.4  1 34.9  148. 1  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.16  0.16  0.16  0.16  0.16  0.16  2 HR  0.24  0.23  0.23  0.22  0.22  0.22  6 HR  0.48  0.44  0.42  0.40  0.39  0.38  12 HR  0.72  0.67  0.65  0.64  0.62  0.62  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.66  0.86  1 .00  1.17  1 .30  1 .43  2 HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  6 HR  0.75  0.90  1 .00  1.12  1 .22  1.31  12 HR  0.72  0.89  1 .00  1.14  1 .24  1 .35  24 HR  0.66  0.86  1 .00  1.17  1 .30  1 .43  - 268 -  TABLE 11.44 DEPTH--DURATION -FREQUENCY DATA FOR SURREY MUNICIPAL HAL RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 HR  9.3  12.4  14.5  17.2  19.1  21.1  2 HR  13.6  17.2  19.6  22.6  24.8  27.0  6 HR  27.5  33.7  37.9  43.1  47.0  50.8  12 HR  40.3  49.6  55.7  63.4  69. 1  74.8  24 HR  55.4  68.4  77.0  87.8  96.0  103.9  1 00  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0 .17  0.18  0.19  0.20  0.20  0 .20  2 HR  0 .25  0.25  0.25  0.26  0.26  0 .26  6 HR  0 .50  0.49  0.49  0.49  0.49  0 .49  12 HR  0 .73  0.72  0.72  0.72  0.72  0 .72  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1.00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0 .64  0.86  1 .00  1.18  1 .32  1.45  2 HR  0 .70  0.88  1 .00  1.15  1 .27  1.38  6 HR  0 .73  0.89  1 .00  1.14  1 .24  1.34  12 HR  0 .72  0.89  1 .00  1.14  1 .24  1.34  24 HR  0 .72  0.89  1 .00  1.14  1 .25  1.35  - 269 -  TABLE 11.45 DEPTH-DURATION-FREQUENCY DATA FOR TERRACE A RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  10.1  13.6  15.8  18.7  20.8  22.9  2 HR  14.1  16.9  18.7  21.1  22.8  24.6  6 HR  25.8  32.6  37. 1  42.8  47.0  51.1  12 HR  38.8  52.3  61 .3  72.7  81.1  89.4  24 HR  55.7  79.4  95.3  115.2  129.8  144.5  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.18  0.17  0.17  0.16  0.16  0.16  2 HR  0.25  0.21  0.20  0.18  0.18  0.17  6 HR  0.46  0.41  0.39  0.37  0.36  0.35  12 HR  0.70  0.66  0.64  0.63  0.62  0.62  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.64  0.86  1 .00  1 .18  1 .31  1 .45  2 HR  0.75  0.90  1 .00  1.13  1 .22  1.31  6 HR  0.70  0.88  1 .00  1.15  1 .27  1 .38  12 HR  0.63  0.85  1 .00  1.19  1 .32  1 .46  24 HR  0.58  0.83  1 .00  1.21  1 .36  1 .52  - 270 -  TABLE II.46 DEPTH-•DURATION -FREQUENCY DATA FOR TERRACE PCC RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  1 HR  7.7  2 HR  5  10  25  50  100  12.0  14.9  18.5  21.2  23.9  12.1  18.7  23.2  28.8  32.9  37.0  6 HR  22.3  31.6  37.7  45.5  51 .4  57. 1  12 HR  33.4  45.2  53.0  62.9  70.2  77.5  24 HR  43.9  58.8  68.6  81.1  90.2  99.4  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.18  0.20  0.22  0.23  0.24  0.24  2 HR  0.28  0.32  0.34  0.35  0.36  0.37  6 HR  0.51  0.54  0.55  0.56  0.57  0.57  1 2 HR  0.76  0.77  0.77  0.78  0.78  0.78  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.52  0.81  1 .00  1 .24  1 .42  1 .60  2 HR  0.52  0.81  1 .00  1 .24  1 .42  1 .60  6 HR  0.59  0.84  1 .00  1.21  1 .36  1 .51  12 HR  0.63  0.85  1 .00  1.19  1 .32  1 .46  24 HR  0.64  0.86  1 .00  1.18  1.31  1 .45  - 271 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.47 DATA  DATA  RETURN DURATION  2  5  FOR  FROM  PERIOD  1 0  TOFINO A  AES (YEARS) 25  50  100  1 HR  17.8  20.7  22.7  25. 1  26.9  28.7  2  HR  28.0  31.5  33.8  36.8  38.9  41.1  6  HR  60.4  69.5  75.5  83.2  88.8  94.4  12  HR  87.0  99.7  1 08. 1  118.8  1 26.7  1 34.5  24  HR  128.2  176.4  200.6  218.6  236.6  1 57.0  DEPTH-DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  1 0  (YEARS) 25  50  1 00  1 HR  0.14  0.13  0.13  0.13  0.12  0.12  2  HR  0.22  0.20  0.19  0.18  0.18  0.17  6  HR  0.47  0.44  0.43  0.41  0.41  0.40  12  HR  0.68  0.64  0.61  0.59  0.58  0 .57  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  100  1 HR  0.79  0.91  1 .00  1.11  1.19  1 .27  2  HR  0.83  0.93  1 .00  1 .09  1.15  1 .22  6  HR  0.80  0.92  1 .00  1.10  1.18  1 .25  12  HR  0.80  0.92  1 .00  1.10  1.17  1 .24  24  HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  - 272 -  TABLE II.48 DEPTH-DURATION-FREQUENCY DATA FOR VANCOUVER HARBOUR RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  12.6  17.5  20.7  24.8  27.8  30.8  2 HR  17.5  22.7  26. 1  30. 5  33.7  36.9  6 HR  31.7  35.9  38.6  42. 1  44.6  47.2  12 HR  45.0  51 .6  56.0  61 .6  65.6  69.7  24 HR  62.2  75.8  85.0  96.2  104.6  113.3  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.20  0.23  0.24  0.26  0.27  0.27  2 HR  0.28  0.30  .0.31  0.32  0.32  0.33  6 HR  0.51  0.47  0.45  0.44  0.43  0.42  12 HR  0.72  0.68  0.66  0.64  0.63  0.62  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH[-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.61  0.84  1 .00  1 .20  1 .34  1 .49  2 HR  0.67  0.87  1 .00  1.17  1 .29  1.41  6 HR  0.82  0.93  1 .00  1 .09  1.16  1 .22  12 HR  0.80  0.92  1 .00  1.10  1.17  1 .24  24 HR  0.73  0.89  1 .00  1.13  1723  1 .33  -  273 -  TABLE 11.49 DEPTH -DURATION--FREQUENCY DATA FOR VANCOUVER INT'L A RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  10.1  12.7  14.4  16.6  18.3  19.9  2 HR  13.7  17.2  19.5  22.5  24.6  26.8  6 HR  25.7  30.4  33.5  37.4  40.3  43.3  12 HR  39.4  47.9  53.4  60.5  65.8  70.9  24 HR  52.8  66.5  75.4  86.6  95.0  103.4  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.19  0.19  0.19  0.19  0.19  0.19  2 HR  0.26  0.26  0.26  0.26  0.26  0.26  6 HR  0.49  0.46  0.45  0.43  0.42  0.42  12 HR  0.75  0.72  0.71  0.70  0.69  0.69  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.70  0.88  1 .00  1.15  1 .26  1 .38  2 HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  6 HR  0.77  0.91  1 .00  1.12  1 .20  1 .29  12 HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  24 HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  -  274  -  TABLE 11.50 DEPTH-DURATION-FREQUENCY DATA FOR VANCOUVER KITSILANO RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  1 HR  9.7  2 HR 6 HR  5  10  25  50  100  11.8  13.3  15.1  16.4  17.8  14.3  17.3  19.3  21.7  23.6  25.4  30. 1  36.2  40.4  45.6  49.4  53.3  12 HR  45.6  55.3  61 .7  69.7  75.7  81 .6  24 HR  60.2  76.3  86.9  1 00. 1  110.2  1 20.0  DEPTH -DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.16  0.16  0.15  0.15  0.15  0.15  2 HR  0.24  0.23  0.22  0.22  0.21  0.21  6 HR  0.50  0.47  0.46  0.46  0.45  0.44  1 2 HR  0.76  0.72  0.71  0.70  0.69  0.68  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.73  0.89  1 .00  1.14  1 .24  1 .34  2 HR  0.74  0.90  1 .00  1.13  1 .22  1 .32  6 HR  0.74  0.90  1 .00  1.13  1 .22  1 .32  12 HR  0.74  0.90  1 .00  1.13  1 .23  1 .32  24 HR  0.69  0.88  1 .00  1.15  1 .27  1 .38  -  275  -  TABLE 11.51 DEPTH-DURATION-FREQUENCY DATA FOR VANCOUVER PMO RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  1 HR  9.9  2 HR  5  10  25  50  11.6  12.8  14.2  15.3  16.4  15.6  18.1  19.7  21 .8  23.3  24.8  6 HR  33.2  39.4  43.6  48.8  52.6  56.5  12 HR  50.0  62.6  71 .0  81 .6  89.4  97.2  24 HR  68.6  94.3  1 49.0  164.9  111.6  DEPTH-DURATION  133.0  100  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.14  0.12  0.11  0.11  0.10  0. 10  2 HR  0.23  0.19  0.18  0.1 6  0.16  0.15  6 HR  0.48  0.42  0.39  0.37  0.35  0.34  12 HR  0.73  0.66  0.64  0.61  0.60  0.59  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.77  0.91  1 .00  1.11  1 .20  1 .28  2 HR  0.79  0.92  1 .00  1.11  1.18  1 .26  6 HR  0.76  0.90  1 .00  1.12  1 .21  1 .30  12 HR  0.70  0.88  1 .00  1.15  1 .26  1 .37  24 HR  0.62  0.85  1 .00  1.19  1 .34  1 .48  - 276 -  TABLE II.52 DEPTH-DURATION-FREQUENCY DATA FOR VANCOUVER UBC RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  10.0  13.1  15.1  17.6  19.5  21 .4  2 HR  14.0  16.8  18.7  21.1  22.8  24.6  6 HR  26.7  31.7  34.9  39. 1  42.2  45.2  12 HR  42. 1  52.0  58.4  66.7  72.8  79.0  24 HR  57.8  74.2  85.2  98.9  109.0  119.0  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.17  0.18  0.18  0.18  0.18  0.18  2 HR  0.24  0.23  0.22  0.21  0.21  0.21  6 HR  0.46  0.43  0.41  0.40  0.39  0.38  12 HR  0.73  0.70  0.69  0.67  0.67  0.66  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00 *  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  4-0  25  50  100  1 HR  0.66  0.87  1 .00  1.17  1 .29  1 .42  2 HR  0.75  0.90  1 .00  1.13  1 .22  1.31  6 HR  0.76  0.91  1 .00  1.12  1.21  1 .30  12 HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  24 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  - 277 -  TABLE 11.53 DEPTH-DURATION-FREQUENCY DATA FOR VICTORIA GONZALES HT RAINFALL DATA FROM AES RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 HR  7.2  9.1  10.4  12.0  13.2  14.4  2 HR  11.4  14.8  17.0  19.9  22.0  24. 1  6 HR  22.9  30.4  35.3  41 .6  46.2  50.8  1 2 HR  34.0  45.8  53.6  63.6  71 .0  78.4  24 HR  45. 1  63.8  76.3  91 .9  103.7  115.2  DEPTH-DURATION  100  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  1 00  1 HR  0.16  0.14  0.14  0.13  0.13  0.13  2 HR  0.25  0.23  0.22  0.22  0.21  0.21  6 HR  0.51  0.48  0.46  0.45  0.45  0.44  12 HR  0.75  0.72  0.70  0.69  0.69  0.68  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY  RELATIONSHIPS  RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.69  0.88  1 .00  1.15  1 .27  1 .38  2 HR  0.67  0.87  1 .00  1.17  1 .29  1 .42  6 HR  0.65  0.86  1 .00  1 .18  1.31  1 .44  12 HR  0.63  0.85  1 .00  1.19  1 .32  1 .46  24 HR  0.59  0.84  1 .00  1 .20  1 .36  1 .51  - 278 -  TABLE II.54 DEPTH--DURATION--FREQUENCY DATA FOR VICTORIA INT'L A RAINFALL DATA FROM AES RETURN PERIOD (YEARS) ' DURATION  2  5  10  25  50  1 HR  8.2  9.8  10.9  12.2  13.1  14.1  2 HR  12.6  14.7  16.1  17.9  19.2  20.5  6 HR  25.6  31.0  34.6  39.2  42.6  46.0  12 HR  38.0  47.0  53.0  60.6  66.2  71 .8  24 HR  49.4  63. 1  72.2  83.8  92.4  100  101.0  DEPTH-DURATION RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.17  0.16  0.15  0.15  0.14  0.14  2 HR  0.25  0.23  0.22  0.21  0.21  0.20  6 HR  0.52  0.49  0.48  0.47  0.46  0.46  12 HR  0.77  0.75  0.73  0.72  0.72  0.71  24 HR '  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD (YEARS) DURATION  2  5  10  25  50  100  1 HR  0.76  0.90  1 .00  1.12  1 .21  1 .30  2 HR  0.78  0.91  1 .00  1.11  1.19  1 .27  6 HR  0.74  0.90  1 .00  1.13  1 .23  1 .33  12 HR  0.72  0.89  1 .00  1.14  1 .25  1 .35  24 HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  - 279 -  TABLE  II.55  DEPTH-DURATION-FREQUENCY DATA FOR VICTORIA  MARINE  RAINFALL DATA FROM AES RETURN PERIOD DURATION  2  1 HR  9.4  2 HR  5  (YEARS)  10  25  50  11.8  13.4  15.4  16.9  18.4  15.4  18.8  21.1  24.0  26. 1  28.2  6 HR  31.0  37.6  41.9  47.5  51.5  55.6  12 HR  45.8  55.6  62.0  70.3  76.3  82.4  24 HR  64.8  84.5  97.4  114.0  1 26.2  1 38.5  DEPTH-DURATION  RELATIONSHIPS  RETURN PERIOD DURATION  2  1 HR  0. 1 4  2 HR  5  1 00  (YEARS)  10  25  50  100  0.14  0.14  0.14  0.13  0. 1 3  0 .24  0.22  0.22  0.21  0.21  0 .20  6 HR  0 .48  0.44  0.43  0.42  0.41  0 .40  12 HR  0 .71  0.66  0.64  0.62  0.60  0 .60  24 HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH-FREQUENCY RELATIONSHIPS RETURN PERIOD DURATION  2  5  (YEARS)  10  25  50  100  1 HR  0 .70  0.88  1 .00  1.15  1 .26  1 .37  2 HR  0 .73  0.89  1 .00  1.14  1 .24  1 .34  6 HR  0 .74  0.90  1 .00  1.13  1 .23  1 .33  12 HR  0 .74  0.90  1 .00  1.13  1 .23  1 .33  24 HR  0 .67  0.87  1 .00  1.17  1 .30  1 .42  - 280 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.56 DATA  DATA  RETURN DURATION  FOR  FROM  PERIOD  VICTORIA  SHELBOURNE  AES (YEARS)  2  5  10  25  50  9.6  10.8  12.2  13.2  14.2  1 00  1  HR  8.0  2  HR  1 1 .7  13.7  15.0  16.6  17.8  19.0  6  HR  23.8  27.3  29.6  32.6  34.8  37.0  12  HR  33.4  42.8  49. 1  57.0  62.9  68.8  24  HR  44.9  61.7  73.0  87. 1  97.4  108.0  D E P T H -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.18  0.16  0.15  0.14  0.14  0.13  2  HR  0.26  0.22  0.21  0.19  0.18  0.18  6  HR  0.53  0.44  0.41  0.37  0.36  0.34  12  HR  0.74  0.69  0.67  0.65  0.65  0.64  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.74  0.90  1 .00  1.13  1 .23  1 .32  2  HR  0.78  0.91  1 .00  1.11  1.19  1 .27  6  HR  0.80  0.92  1 .00  1.10  1.17  1 .25  12  HR  0.68  0.87  1 .00  1.16  1 .28  1 .40  24  HR  0.62  0.85  1 .00  1.19  1 .34  1 .48  - 281 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  11.57 DATA  DATA  RETURN  FOR V I C T O R I A  U VIC  FROM A E S  PERIOD  (YEARS)  DURATION  2  5  10  25  50  1 HR  8.0  9.4  10.3  11.5  12.4  13.3  1 00  2  HR  12.4  14.5  15.9  17.6  18.9  20. 1  6  HR  26.6  33.3  37.7  43.3  47.4  51 .5  12  HR  40.0  49.8  56.3  64.6  70.7  76.7  24  HR  49.9  67.7  79.7  94.6  1 05.6  116.6  DEPTH -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.16  0.14  0.13  0.12  0.12  0.11  2  HR  0.25  0.21  0.20  0.19  0.18  0.17  6  HR  0.53  0.49  0.47  0.46  0.45  0.44  12  HR  0.80  0.74  0.71  0.68  0.67  0.66  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH - F R E Q U E N C Y RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1 HR  0.77  0.91  1 .00  1.12  1 .20  1 .29  2  HR  0.78  0.91  1 .00  1.11  1.19  1 .27  6  HR  0.71  0.88  1 .00  1.15  1 .26  1 .37  12  HR  0.71  0.88  1 .00  1.15  1 .26  1 .36  24  HR  0.63  0.85  1 .00  1.19  1 .33  1 .46  - 282 -  TABLE DEPTH-DURATION-FREQUENCY  RAINFALL  II.58 DATA  DATA  RETURN DURATION  2  5  FOR WHITE  ROCK  STP  FROM A E S  PERIOD  (YEARS)  10  25  50  100  1  HR  11.7  19.6  24.9  31 .5  36.4  41.2  2  HR  16.0  24.0  29.3  36.0  41.0  45.9  6  HR  27.8  35.3  40.3  46.6  51 .2  55.9  12  HR  36.6  46.6  53.0  61.4  67.6  73.7  24  HR  50.4  64.8  74.4  86.6  95.5  104.6  DEPTH -DURATION RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  10  25  50  1 00  1  HR  0.23  0.30  0.33  0.36  0.38  0.39  2  HR  0.32  0.37  0.39  0.42  0.43  0.44  6  HR  0.55  0.55  0.54  0.54  0.54  0.53  12  HR  0.73  0.72  0.71  0.71  0.71  0.70  24  HR  1 .00  1 .00  1 .00  1 .00  1 .00  1 .00  DEPTH -FREQUENCY RETURN DURATION  2  5  RELATIONSHIPS  PERIOD  (YEARS)  1 0  25  50  100  1  HR  0.47  0.79  1 .00  1 .27  1 .46  1 .66  2  HR  0.55  0.82  1 .00  1 .23  1 .40  1 .57  6  HR  0.69  0.88  1 .00  1.15  1 .27  1 .39  12  HR  0.69  0.88  1 .00  1.16  1 .27  1 .39  24  HR  0.68  0.87  1 .00  1.16  1 .28  1 .41  -  283 -  APPENDIX I I I MAXIMUM 24-HOUR RAINFALL ON RECORD AT BRITISH COLUMBIA COASTAL STATIONS  -  284  -  TABLE I I I . 1 T I M E . D I S T R I B U T I O N OF  RAINFALL  ABBOTSFORD A MAXIMUM  DATE YR-M-D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  16 16 16 16 16 16 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17  1 2 3 4 6 8 12 24  R A I N F A L L ON  RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18  2.3 2.7 1 .7 1.1 1 .7 2.3 2.9 5.7 7.5 8.0 6.8 6.8 10.3 7.1 2.6 8.5 5.9 1 .4 3.3 1 .2 1 .6 2.4 3.1 1 .9  2.3 5.0 6.7 7.8 9.5 11.8 14.7 20.4 27.9 35.9 42.7 49.5 59.8 66.9 69.5 78.0 83.9 85.3 88.6 89.8 91.4 93.8 96.9 98.8  DURATION  (HOURS)  24-HOUR  FOR  10. 18. 24. 32. 47. 58. 75. 100.  2. 5. 7. 8. 10. 12. 15. 21 . 28. 36. 43. 50. 61 . 68. 70. 79. 85. 86. 90. 91 . 93. 95. 98. 1 00.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 2 4 - H R R A I N F A L L % OF (MM) 24-HR 10.3 17.4 24.2 31 . 9 46.5 57.6 74.4 98.8  PERCENT OF 2 4 - H O U R RAINFALL  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 18.1 34.5 35.7 36.2 46.5 57.6 74.4 98.8  79 79 79 79 79 79 79 79  8 8 8 8 12 12 12 12  17 17 17 17 17 17 16 16  - 285 -  TIME  TABLE I I I . 2 D I S T R I B U T I O N OF  RAINFALL  AGASSIZ CDA MAXIMUM  DATE YR-M- D 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75  12 1 1 12 1 12 1 12 12 2 12 2 12 2 12 2 12 2 12 2 2 12 1 2 ~2 12 2 12 2 12 2 12 2 12 2 12 2 12 2 12 2 12 2 12 2 12 2 12 2  1 2 3 4 6 8 12 24  RAINFALL  HOUR  HOURLY RAIN (MM)  21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 1 4 1 5 1 6 1 7 18 19 20  1 .8 2.3 6.4 4.3 3.6 9.1 6.6 5.3 4.8 3.6 4.6 4.3 5.1 4. 1 3.8 4.6 3.3 3.8 4.6 8.9 8.9 6.1 5.6 3.8  DURATION  (HOURS)  24-HOUR  ON  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 9.1 17.8 23.9 29.5 37.9 45.8 63. 1 1 19.3  8. 15. 20. 25. 32. 38. 53. 100.  RECORD CUM. RAIN (MM)  1 .8 4.1 10.5 14.8 18.4 27.5 34.1 39.4 44.2 47.8 52.4 56.7 61 .8 65.9 69.7 74.3 77.6 81.4 86.0 94.9 103.8 109.9 115.5 119.3  .  PERCENT OF 24-HOUR RAINFALL 2. 3. 9. 12. 15. 23. 29. 33. 37. 40. 44. 48. 52. 55. 58. 62. 65. 68. 72. 80. 87. 92. 97. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.6 20.2 24.4 32.0 39.6 49.8 63.8 119.3  79 79 62 83 79 79 80 75  10 10 2 6 12 12 12 12  27 27 3 10 9 9 25 1  - 286 -  TIME  TABLE I I I . 3 D I S T R I B U T I O N OF R A I N F A L L ALOUETTE LAKE  MAXIMUM  DATE YR-M-D 81 81 81 81 81 81 81 81 81  81  81 81 81 81 81 81 81 81  81 81 81 81 81 81  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  30 30 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31  HOUR  23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 14 1 5 16 1 7 18 19 20 21 22  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  4.8 10.8 2.0 0.2 0.2 0.4 10.0 15.2 9.6 3.6 2.6 4.0 2.8 3.2 8.8 7.2 10.8 7.2 5.2 6.0 5.6 6.8 6.4 6.0  4.8 15.6 17.6 17.8 18.0 18.4 28.4 43.6 53.2 56.8 59.4 63.4 66.2 69.4 78.2 85.4 96.2 1 03.4 1 08.6 114.6 1 20.2 127.0 1 33.4 139.4  3. 11 . 13. 13. 13. 13. 20. 31 . 38. 41 . 43. 45. 47. 50. 56. 61 . 69. 74. 78. 82. 86. 91 . 96. 100.  FOR  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 15.2 25.2 34.8 38.4 45.2 57.6 85.0 139.4  RECORD  11 . 18. 25. 28. 32. 41 . 61 . 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 18.4 27.3 34.8 38.8 54.3 67.2 96.6 139.4  79 79 81 82 80 80 80 81  9 9 10 12 12 12 12 10  4 3 31 3 25 25 25 30  - 287 -  TIME  TABLE I I I . 4 D I S T R I B U T I O N OF  RAINFALL  ALTA LAKE MAXIMUM  DATE YR-M- D 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  1 6 1 6 16 16 1 6 1 6 16 1 6 1 7 1 7 1 7 17 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7  HOUR  17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 16  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR  RAINFALL  ON  HOURLY RAIN (MM) 2.8 3.3 4.1 3.8 4.6 4.6 4.6 3.6 3.3 4.1 5.8 4.6 3.0 3.0 2.8 3.0 0.8 2.5 3.0 2.8 2.5 2.8 2.8 2.3  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 5.8 10.4 14.5 17.8 26.0 35.2 49.4 80.5  7. 13. 18. 22. 32. 44. 61 . 100.  RECORD CUM. RAIN (MM) 2.8 6.1 10.2 14.0 18.6 23.2 27.8 31 .4 34.7 38.8 44.6 49.2 52.2 55.2 58.0 61 .0 61 .8 64.3 67.3 70. 1 72.6 75.4 78.2 80.5  PERCENT O F 24-HOUR RAINFALL 3. 8. 13. 17. 23. 29. 35. 39. 43. 48. 55. 61 . 65. 69. 72. 76. 77. 80. 84. 87. 90. 94. 97. 1 00.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 9.7 15.7 18.6 24. 1 27.8 35.2 49.4 80.5  79 78 78 78 81 75 75 75  9 7 7 7 10 10 10 10  7 26 26 26 31 16 16 16  - 288 -  TIME  TABLE I I I . 5 D I S T R I B U T I O N OF  RAINFALL  BEAR CREEK MAXIMUM  DATE YR-M- D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  18 18 18 18 18 18 18  18 18 18 18 18 18 18 19 19 19 19 19 19 19 19 19 19  HOUR  1 1 1 2 1 3 1 4 1 5 1 6 1 7 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  RAINFALL  ON  HOURLY RAIN (MM)  CUM. RAIN (MM)  10.7 12.2 16.8 12.4 14.2 11.7 11.7 11.9 22.9 10.7 10.2 20.8 10.2 7.4 13.2 18.0 12.7 8.6 9.9 11.2 11.9 8.9 11.4 10.9  10.7 22.9 39.7 52. 1 66.3 78.0 89.7 101.6 124.5 135.2 145.4 166.2 176.4 183.8 197.0 215.0 227.7 236.3 246.2 257.4 269.3 278.2 289.6 300.5  FOR I N D I C A T E D MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 22.9 34.8 46.5 64.6 88.2 114.1 166.2 300.5  RECORD  8. 12. 15. 21 . 29. 38. 55. 1 00.  PERCENT OF 24-HOUR RAINFALL 4. 8. 13. 17. 22. 26. 30. 34. 41 . 45. 48. 55. 59. 61 . 66. 72. 76. 79. 82. 86. 90. 93. 96. 1 00.  DURATION: MAXIMUM ON RECORD  DATE .YR-M-D  (MM) 48.8 56.4 76.7 90.4 98.3 114.1 1 66.2 300.5  66 67 67 67 67 68 68 68  12 12 12 12 12 1 1 1  11 10 10 10 10 18 18 18  - 289 -  TABLE I I I . 6 TIME DISTRIBUTION OF RAINFALL BELLA COOLA HYDRO  MAXIMUM DATE YR-M-D 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  30 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31  1 2 3 4 6 8 12 24  RAINFALL ON RECORD  HOUR  HOURLY RAIN (MM)  24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 1 4 1 5 1 6 17 18 19 20 21 22 23  9.1 6.4 3w0 4. 1 2.5 1 .0 4.3 4.6 4.3 0.0 4. 1 4.1 2.8 3.8 3.6 4.6 5.6 5.8 5.8 10.2 13.2 14.0 7.6 6.9  DURATION  (HOURS)  24-HOUR  FOR  11 . 21 . 28. 34. 44. 53. 64. 1 00.  PERCENT OF 24-HOUR RAINFALL  9.1 15.5 18.5 22.6 25. 1 26. 1 30.4 35.0 39.3 39.3 43.4 47.5 50.3 54. 1 57.7 62.3 67.9 73.7 79.5 89.7 102.9 116.9 124.5 131.4  7. 12. 14. 17. 19. 20. 23. 27. 30. 30. 33. 36. 38. 41 . 44. 47. 52. 56. 61 . 68. 78. 89. 95. 1 00.  INDICATED DURATION:  MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 14.0 27.2 37.4 45.0 57.7 69. 1 83.9 131 .4  CUM. RAIN (MM)  MAXIMUM ON RECORD (MM) 15.0 27.2 37.4 45.0 57.7 69. 1 91 .3 131.4  DATE YR-M-D 76 75 75 75 75 75 71 75  10 27 10 31 10 31 10 31 10 31 10 31 11 18 10 30  - 290 -  TABLE I I I . 7 T I M E D I S T R I B U T I O N OF R A I N F A L L B U N T Z E N  MAXIMUM  DATE YR-M-D 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81  81 81 81 81 81 81 81  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  30 30 30 30 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31  1 2 3 4 6 8 12 24  R A I N F A L L ON  HOUR  HOURLY RAIN (MM)  21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 16 1 7 18 19 20  7.7 9.0 0.5 0.2 2.4 10.1 15.3 11.0 8.8 15.3 13.1 17.5 13.1 13.4 1 1 .7 13.9 13.0 15.2 11.7 11.7 11.9 8.3 15.8 8.5  DURATION  (HOURS)  24-HOUR  FOR  7. 12. 18. 23. 32. 43. 62. 100.  RECORD CUM. RAIN (MM)  7.7 16.7 17.2 17.4 19.8 29.9 45.2 56.2 65.0 80.3 93.4 110.9 124.0 137.4 149. 1 1 63.0 176.0 191.2 202.9 214.6 226.5 234.8 250.6 259. 1  PERCENT OF 24-HOUR RAINFALL 3. 6. 7. 7. 8. 12. 17. 22. 25. 31 . 36. 43. 48. 53. 58. 63. 68. 74. 78. 83. 87. 91 . 97. 100.  I N D I C A T E D DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 17.5 30.6 45.9 59.0 84. 1 111.0 161.5 259. 1  L A K E  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 27.7 33.5 45.9 59.0 84. 1 111.0 161.5 259. 1  79 76 81 81 81 81 81 81  6 11 10 10 10 10 10 10  30 17 31 31 31 31 31 30  291  TIME  TABLE I I I . 8 D I S T R I B U T I O N OF  RAINFALL  BURNABY MTN BCHPA MAXIMUM  DATE YR-M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  1 6 16 1 7 17 1 7 17 17 17 1 7 17 17 17 1 7 1 7 17 17 1 7 1 7 17 17 17 17 1 7 17  HOUR  -  23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 1 6 1 7  18  19 20 21 22  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM) 1 .4 1 .6 2.8 2.4 4.0 4.8 5.2 4.8 5.6 6.0 9.4 7.6 9.4 9.6 8.0 6.8 4.0 8.8 4.0 3.4 3.0 3.6 2.0 4.0  FOR I N D I C A T E D MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 9.6 19.0 27.0 36.0 50.8 63.6 85.2 122.2  8. 16. 22. 29. . 42. 52. 70. 100.  RECORD CUM. RAIN (MM)  1 .4 3.0 5.8 8.2 12.2 17.0 22.2 27.0 32.6 38.6 48.0 55.6 65.0 74.6 82.6 89.4 93.4 1 02.2 106.2 109.6 112.6 116.2 118.2 122.2  PERCENT OF 24-HOUR RAINFALL 1 . 2. 5. 7. 10. 14. 18. 22. 27. 32. 39. 45. 53. 61 . 68. 73. 76. 84. 87. 90. 92. 95. 97. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 15.0 21 .9 27.2 36.0 50.8 63.6 85.2 122.2  78 77 77 79 79 79 79 79  6 11 11 12 12 12 12 12  13 28 28 17 17 17 17 16  - 292 -  TIME  TABLE I I I . 9 D I S T R I B U T I O N OF  RAINFALL  CAMPBELL RIVER BCFS MAXIMUM  DATE YR-M- D 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69 69  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7  1 2 3 4 6 8 12 24  RAINFALL  HOUR  HOURLY RAIN (MM)  20 21 22 23 24 1 2 3 4 ' 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 16 1 7 18 19  0.3 1 .3 3.3 7.9 3.0 6.6 7.4 10.9 9.7 6.1 3.6 3.3 2.0 1 .3 1.3 2.3 2.0 1 .5 0.5 0.8 0.3 0.0 0.0 0.0  DURATION  (HOURS)  24-HOUR  FOR  14. 27. 37. 46. 60. 73. 86. 100.  RECORD CUM. RAIN (MM) 0.3 1 .6 4.9 12.8 15.8 22.4 29.8 40.7 50.4 56.5 60. 1 63.4 65.4 66.7 68.0 70.3 72.3 73.8 74.3 75. 1 75.4 75.4 75.4 75.4  PERCENT OF 24-HOU] RAINFALL 0. 2. 6. 17. 21 . 30. 40. 54. 67. 75. 80. 84. 87. 88. 90. 93. 96. 98. 99. 100. 1 00. 1 00. 1 00. 1 00.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 10.9 20.6 28.0 34.6 45.5 55.2 65. 1 75.4  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 12.7 20.6 28.5 34.6 45.5 55.2 65. 1 75.4  75 75 75 69 69 69 69 69  8 26 8 26 11 14 1 1 7 1 1 6 1 1 6 1 1 6 1 1 6  - 293 -  TIME  T A B L E 111 . 1 0 D I S T R I B U T I O N OF R A I N F A L L CAMPBELL RIVER BCHPA  MAXIMUM  DATE YR--M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  24 24 24 24 24 24 24 24 24 24 24 24 24 24 24 24 24 24 24 25 25 25 25 25  .  1 2 3 4 6 8 12 24  ON RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 16 17 18 19 20 21 22 23 24 1 2 3 4 5  4.0 4.4 5.2 4.5 4.5 2.7 3.6 4.5 3.3 4.5 2.2 4.1 4.1 3.6 5.8 5.0 3.1 1 .6 0.3 1. 1 0.5 1 .6 2.0 1. 1  4.0 8.4 13.6 18.1 22.6 25.3 28.9 33.4 36.7 41.2 43.4 47.5 51 .6 55.2 61 .0 66.0 69. 1 70.7 71 .0 72. 1 72.6 74.2 76.2 77.3  DURATION  (HOURS)  24-HOUR R A I N F A L L  FOR I N D I C A T E D MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 5.8 10.8 14.4 18.6 25.7 33.4 47.9 77.3  8. 14. 19. 24. 33. 43. 62. 100.  PERCENT OF 24-HOUR RAINFALL 5. 11 . 18. 23. 29. 33. 37. 43. 47. 53. 56. 61 . 67. 71 . 79. 85. 89. 91 . 92. 93. 94. 96. 99. 100.  DURATION: MAXIMUM ON RECORD  'DATE YR-M-D  (MM) 23. 1 25.9 34.0 35.8 41 .2 47.0 59.3 77.3  79 77 77 77 80 80 77 79  9 12 12 12 3 3 10 2  1 12 12 12 13 13 31 24  - 294 -  TIME  T A B L E 111 . 1 1 D I S T R I B U T I O N OF R A I N F A L L CARNATION CREEK  MAXIMUM  DATE YR-M- D 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81 81  1 0 30 1 0 30 10 30 1 0 30 1 0 30 10 30 10 30 10 30 10 30 10 30 10 30 10 30 10 30 10 31 10 31 1 0 31 1 0 31 10 31 10 31 10 31 10 31 10 31 10 31 10 31  HOUR  1 2 13 1 4 1 5 1 6 17 18  19  20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0 1 1  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  RAINFALL  HOURLY RAIN (MM) 8.1 9.0 15.5 4.5 6.4 6.2 5.4 4.9 5.1 1 .5 1 .3 2.4 8.1 4.7 4.5 1 .9 4.5 10.7 15.4 9.4 8.8 7.9 7.9 8.3  FOR  10. 16. 22. 27. 37. 45. 57. 100.  RECORD CUM. RAIN (MM)  8.1 17.1 32.6 37. 1 43.5 49.7 55. 1 60.0 65. 1 66.6 67.9 70.3 78.4 83. 1 87.6 89.5 94.0 104.7 1 20. 1 1 29.5 1 38.3 1 46.2 1 54. 1 162.4  PERCENT OF 24-HOUR RAINFALL 5. 11 . 20. 23. 27. 31 . 34. 37. 40. 41 . 42. 43. 48. 51 . 54. 55. 58. 64. 74. 80. 85. 90. 95. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 15.5 26. 1 35.5 44.3 60. 1 72.9 92.1 1 62.4  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.0 26.4 38.6 50.8 67.4 83.9 97.8 1 62.4  80 77 77 77 77 77 77 81  1 1 1 2 11 2 11 2 11 2 11 2 11 2 11 10 30  - 295 -  TIME  T A B L E 111 . 1 2 D I S T R I B U T I O N OF R A I N F A L L CHILLIWACK  MAXIMUM  DATE YR-M- D 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  18 18 18 18 19 19 19 19 19 19 19 19 19 19 19 19 1 9 19 19 19 19 19 19 19  HOUR  21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 16 17 18 19 20  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  MICROWAVE R A I N F A L L ON  HOURLY RAIN (MM) 3.0 3.6 3.3 3.8 3.0 3.6 3.0 3.8 3.8 3.0 3.3 4. 1 5.1 3.6 4.3 3.0 2.8 2.5 2.8 2.5 3.3 2.8 3.3 4.3  FOR  INDICATED  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF(MM) 24-HR 5.1 9.2 13.0 17.1 23.4 31.0. 44.4 81 .6  6. 11 . 16. 21 . 29. 38. 54. 100.  RECORD CUM. RAIN (MM) 3.0 6.6 9.9 13.7 16.7 20.3 2 3". 3 27. 1 30.9 33.9 37.2 41 .3 46.4 50.0 54.3 57.3 60. 1 62.6 65.4 67.9 71.2 74.0 77.3 81.6  PERCENT OF 24-HOUR RAINFALL 4. 8. 12. 17. 20. 25. 29. 33. 38. 42. 46. 51 . 57. 61 . 67. 70. 74. 77. 80. 83. 87. 91 . 95. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 18.0 21 .3 24.9 29.0 39.4 44. 1 58.0 81 .6  66 69 63 63 63 69 69 66  1 1 1 10 10 10 1 1 1 1 10  6 4 21 21 21 4 4 18  - 296 -  TIME  TABLE III .1 3 D I S T R I B U T I O N OF R A I N F A L L CLOWHAM FALLS  MAXIMUM  DATE YR--M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  24 24 24 24 24 24 24 24 24 24 24 24 24 25 25 25 25 25 25 25 25 25 25 25  HOUR  1 2 13 1 4 1 5 1 6 17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM) 3.0 3.8 3.2 5.1 5.1 5.7 6.2 4.4 3.8 4.9 6.8 5.4 6.8 4.3 4.2 4.3 3.0 4.0 4.3 4.0 3.5 5.2 5.8 4.7  FOR  6. 11 . 17. 21 . 29. 39. 56. 100.  CUM. RAIN (MM) 3.0 6.8 10.0 15.1 20.2 25.9 32. 1 36.5 40.3 45.2 52.0 57.4 64.2 68.5 72.7 77.0 80.0 84.0 88.3 92.3 95.8 101.0 106.8 111.5  PERCENT OF 24-HOUR RAINFALL 3. 6. 9. 14. 18. 23. 29. 33. 36. 41 . 47. 51 . 58. 61 . 65. 69. 72. 75. 79. 83. 86. 91 . 96. 1 00.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 6.8 12.2 19.0 23.9 32.4 44.0 62.7 111.5  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 20. 1 26.0 32.2 42.7 54.2 64.8 72.3 111.5  75 80 78 78 78 78 78 79  8 28 11 6 1 1 7 1 1 7 1 1 7 1 1 7 1 1 7 2 24  - 297 -  TIME  T A B L E I IT . 1 4 D I S T R I B U T I O N OF R A I N F A L L COMOX A  MAXIMUM  DATE YR-•M-D 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83  2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  HOUR  10 10 10 10 10 10 10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1  18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 1 6 17  24-HOUR  RAINFALL  HOURLY RAIN (MM) 1 .2 3.2 2.6 2.5 3.7 1 .6 3.2 7.3 6.9 5.9 4.4 5.7 5.9 5. 1 4.8 3.0 4.2 3.8 3.2 3.0 2.4 2.2 1 .6 2.2  ON  RECORD CUM. RAIN" (MM)  PERCENT OF 24-HOU1 RAINFALL  1 .2 4.4 7.0 9.5 13.2 14.8 18.0 25.3 32.2 38. 1 42.5 48.2 54. 1 59.2 64.0 67.0 71.2 75.0 78.2 81.2 83.6 85.8 87.4 89.6  1 . 5. 8. 11 . 15. 17. 20. 28. 36. 43. 47. 54. 60. 66. 71 . 75. 79. 84. 87. 91 . 93. 96. 98. 100.  •  DURATION  (HOURS) 1 2 3 4 6 8 12 24  FOR  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24 -HR R A I N F A L L % OF (MM) 24-HR 7. 3 14. 2 20. 1 24. 5 36. 1 46. 0 60. 2 89. 6  8. 16. 22. 27. 40. 51 . 67. 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.8 24.8 27.0 32.0 37.2 46.0 60.2 89.6  83 83 62 81 81 83 83 83  11 1 1 6 11 11 2 2 2  3 3 1 14 14 11 11 10  - 298 -  TIME  T A B L E 111 . 1 5 D I S T R I B U T I O N OF R A I N F A L L COQUITLAM LAKE  MAXIMUM  DATE YR-M-D 81 -10 30 81 10 30 81 10 30 81 10 30 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31 81 10 31  1 2 3 4 6 8 1 2 24  R A I N F A L L ON  HOUR  HOURLY RAIN (MM)  21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 13 14 1 5 1 6 17 18 1 9 20  7.6 10.1 0.8 1. 1 1 .3 10.6 10.6 16.9 10.6 10.6 11.8 10.1 11.7 10.7 10.7 9.3 9.8 11.5 9.8 11.9 9.3 10.7 10.6 8.5  DURATION  (HOURS)  24-HOUR  FOR  7. 12. 17. 22. 32. 41 . 59. 100.  CUM. RAIN (MM) 7.6 17.7 18.5 19.6 20.9 31.5 42. 1 59.0 69.6 80.2 92.0 102. 1 113.8 124.5 1 35.2 1 44.5 154.3 165.8 175.6 187.5 196.8 207.5 218.1 226.6  PERCENT OF 24-HOUR RAINFALL 3. 8. 8. 9. 9. 14. 19. 26. 31 . 35. 41 . 45. 50. 55. 60. 64. 68. 73. 77. 83. 87. 92. 96. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 16.9 27.5 38. 1 49.9 71 .7 93. 1 1 34.3 226.6  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.9 28.0 39. 1 51.1 71.7 93. 1 1 34.3 226.6  81 73 77 73 81 81 81 81  10 10 11 10 10 10 10 10  31 13 13 13 31 31 31 30  - 299 -  TIME  T A B L E 111 . 1 6 D I S T R I B U T I O N OF R A I N F A L L COURTNEY PUNTLEDGE  MAXIMUM  DATE YR-M- D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  17 17 17 17 17 1 7 1 7 1 7 18 18 18  18 18 18 18 18 18 18 18 18 18 18 18 18  HOUR  17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 1 4 1 5 16  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR R A I N F A L L  ON  HOURLY RAIN (MM) 3.8 5. 1 3.6 2.3 5.3 5.8 5.6 4.8 4.8 7.9 5.6 6.9 6.4 7.6 5. 1 3.6 3.6 6.6 5.6 4.1 3.0 5.1 4.6 7.6  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.9 14.0 20.9 26.8 39.5 49.6 69.4 124.4  6. 11 . 17. 22. 32. 40. 56. 100.  RECORD CUM. RAIN (MM)  3.8 8.9 12.5 14.8 20. 1 25.9 31.5 36.3 41.1 49.0 54.6 61.5 67.9 75.5 80.6 84.2 87.8 94.4 100.0 1 04. 1 107. 1 112.2 116.8 124.4  PERCENT OF 24-HOUR RAINFALL 3. 7. 10. 12. 16. 21 . 25. 29. 33. 39. 44. 49. 55. 61 . 65. 68. 71 . 76. 80. 84. 86. 90. 94. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 14.0 23.8 29.2 36.4 53.6 64.0 86.8 124.4  80 80 83 83 83 83 83 68  7 7 9 9 11 11 11 1  1 0 10 10 10 14 14 14 17  - 300 -  TIME  T A B L E 111 . 1 7 D I S T R I B U T I O N OF R A I N F A L L DAISY LAKE DAM  MAXIMUM  DATE YR-M- D 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75 75  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  1 6 1 6 1 6 1 6 16 16 16 16 1 6 1 6 1 6 16 1 6 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7 1 7  HOUR  12 1 3 1 4 1 5 1 6 1 7 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0 1 1  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  RAINFALL  HOURLY RAIN (MM) 3.6 2.8 3.0 3.6 3.0 3.6 4.1 4.3 4.3 5.1 6.1 4.6 3.6 4.1 4. 1 7.1 6.4 4.8 3.6 3.6 3.8 3.3 2.3 3.0  FOR  7. 14. 19. 23. 31 . 42. 60. 100.  RECORD CUM. RAIN (MM) 3.6 6.4 9.4 13.0 16.0 19.6 23.7 28.0 32.3 37.4 43.5 48. 1 51 .7 55.8 59.9 67.0 73.4 78.2 81 .8 85.4 89.2 92.5 94.8 97.8  PERCENT OF 24-HOUR RAINFALL 4. 7. ' 10. 13. 16. 20. 24. 29. 33. 38. 44. 49. 53. 57. 61 . 69. 75. 80. 84. 87. 91 . 95. 97. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.1 13.5 18.3 22.4 30. 1 41 . 1 58.6 97.8  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 18.8 27.9 41 . 1 46.2 53.8 57.3 60.9 97.8  68 69 69 69 69 69 69 75  10 29 4 4 4 4 4 4 4 4 4 4 4 4 10 16  - 301 -  TIME  T A B L E 111 . 1 8 D I S T R I B U T I O N OF R A I N F A L L ESTAVAN  MAXIMUM  DATE YR-M- D 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78  1 1 1 1  1 1 1 1 1 1 1 1 1 1  1 1 1 1 1 1  1 1  1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1 1 1 1 1 1 1 1 1 1 1  6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 7  1 2 3 4 6 8 12 24  24-HOUR R A I N F A L L  HOUR  HOURLY RAIN (MM)  2 3 4 5 6 7 8 9 10 1 T 12 13 1 4 15 16 17 18 19 20 21 22 23 24 1  3.4 4.4 7.2 8.2 7.2 7.7 11.4 14.7 13.9 13.7 8.7 3.7 1 .4 3.9 3.7 12.1 15.9 11.9 12.4 8.2 15.9 9.7 6.9 4.1  DURATION  (HOURS)  POINT  FOR  8. 14. 20. 26. 36. 44. 55. 100.  RECORD CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  3.4 7.8 15.0 23.2 30.4 38. 1 49.5 64.2 78. 1 91 .8 1 00.5 1 04.2 1 05.6 1 09.5 113.2 1 25.3 141.2 1 53. 1 1 65.5 173.7 189.6 199.3 206.2 210.3  2. 4. 7.  11 . 14. 18. 24. 31 . 37. 44. 48. 50. 50. 52. 54. 60. 67. 73. 79. 83. 90. 95. 98. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 15.9 28.6 42.3 53.7 76.4 93.0 116.0 210.3  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 27.7 43.7 56.7 68. 1 80. 1 98.5 . 131.3 210.3  7111 2 7111 2 7111 2 7111 2 7111 2 69 11 19 69 11 19 78 11 6  -  TIME  302 -  TABLE I I I .1 9 D I S T R I B U T I O N OF R A I N F A L L HANEY MICROWAVE  MAXIMUM  DATE YR-M- D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  18 18 18 18 18 18 18 18 18 18 18 19 19 19 19  19  19 19 19 1 9 1 9 1 9 19 19  HOUR  14 15 16 1 7 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM) 4.8 6.6 5.6 5.8 4.3 3.6 4.6 4.6 3.8 3.0 4. 1 4.6 4.3 6.6 10.2 8.9 6.9 6.9 8.6 6.6 4.8 9.4 8.1 5.6  FOR  7. 13. 18. 23. 34. 44. 61 . 100.  CUM. RAIN (MM) 4.8 11.4 17.0 22.8 27. 1 30.7 35.3 39.9 43.7 46.7 50.8 55.4 - 59.7 66.3 76.5 85.4 92.3 99.2 107.8 114.4 119.2 1 28.6 1 36.7 1 42.3  PERCENT OF 24-HOUR RAINFALL 3. 8. 12. 16. 19. 22. 25. 28. 31 . 33. 36. 39. 42. 47. 54. 60. 65. 70. 76. 80. 84. 90. 96. 1 00.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 10.2 19.1 26.0 32.9 48. 1 62.3 86.9 142.3  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 19.3 27.9 35.6 40.7 50.6 63.0 87.4 142.3  65 69 64 64 80 80 80 68  1 1 1 11 11 12 12 12 1  3 1 29 29 25 25 25 18  -  TIME  303 -  TABLE I I I . 2 0 D I S T R I B U T I O N OF  RAINFALL  HANEY UBC MAXIMUM  DATE YR-M- D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1  1  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  18 18 18 18 18 18 18 18 18 18 18 19 19 19 19 19 19  19 19 19 19 19 19 19  HOUR  1 4 15 1 6 1 7 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  RAINFALL  HOURLY RAIN (MM) 5.8 5.6 5.3 5.3 5.8 3.6 3.0 4. 1 4. 1 5.6 5.6 5.6 5.1 6.9 7.9 5.8 5.3 6.9 6.1 6.9 7.1 6.4 6.9 7.1  FOR  6. 11 . 15. 20. 29. 38. 57. 100.  RECORD CUM. RAIN (MM)  5.8 11.4 16.7 22.0 27.8 31.4 34.4 38.5 42.6 48.2 53.8 59.4 64.5 71 .4 79.3 85. 1 90.4 97.3 1 03.4 110.3 117.4 1 23.8 130.7 1 37.8  PERCENT. OF 24-HOUR RAINFALL 4. 8. 12. 16. 20. 23. 25. 28. 31 . 35. 39. 43. 47. 52. 58. 62. 66. 71 . 75. 80. 85. 90. 95. 1 00.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.9 14.8 20.6 27.5 40.5 52.9 78.4 137.8  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 17.3 29. 1 34.9 40.7 53.2 63.3 84. 1 137.8  73 83 83 83 68 68 79 68  6 7 7 7 9 9 12 1  24 11 1 1 11 16 16 17 18  - 304 -  TIME  T A B L E 111.21 D I S T R I B U T I O N OF  RAINFALL  JORDAN RIVER DIVERSION MAXIMUM  DATE YR-M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  13 13 13 1 3 13 13 13 1 3 1 3 14 1 4 1 4 1 4 14 1 4 1 4 1 4 14 14 1 4 1 4 1 4 14 14  HOUR  16 17  18  19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 1 4 15  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR R A I N F A L L  ON  HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  17.3 11.2 5.6 6.6 9.1 11.7 10.2 11.7 10.2 13.5 12.4 18.0 17.3 15.7 19.8 18.5 7.9 14.7 10.2 15.2 13.2 21.3 21 .8 27.9  17.3 28.5 34. 1 40.7 49.8 61 .5 71.7 83.4 93.6 107. 1 119.5 1 37.5 154.8 170.5 190.3 208.8 216.7 231 .4 241 .6 256.8 270.0 291 .3 313.1 341 .0  5. 8. 10. 1 2 . 15. 18. 21 . 24. 27. 31 . 35. 40. 45. 50. 56. 61 . 64. 68. 71 . 75. 79. 85. 92. 100.  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 27.9 49.7 71 .0 84.2 109.6 132.2 203.5 341 .0  RECORD  8. 15. 21 . 25. 32. 39. 60. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 48.3 55.8 73.2 97.6 136.3 172.9 219.6 341 .0  76 80 80 80 80 80 80 79  1 1 12 12 12 12 12 12  14 12 26 26 26 26 25 13  - 305 -  TIME  T A B L E 1 1 1 . 22 D I S T R I B U T I O N OF R A I N F A L L JORDAN RIVER GENERATING  MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26 26  1 2 3 4 6 8 12 24  R A I N F A L L ON  HOUR  HOURLY RAIN (MM)  4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 16 1 7 18 19 20 21 22 23 24 1 2 3  1 .3 3.0 4. 1 5.1 15.0 9.1 8.4 6.6 5.1 4.3 6.9 6.1 3.6 7.6 15.7 15.0 13.5 7.6 9.9 7.9 12.2 6. 1 3.3 2.5  DURATION  (HOURS)  24-HOUR  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 15.7 30.7 44.2 51 .8 69.6 89.4 112.1 179.9  9. 17. 25. 29. 39. 50. 62. 100.  RECORD CUM. RAIN (MM)  1 .3 4.3 8.4 13.5 28.5 37.6 46.0 52.6 57.7 62.0 68.9 75.0 78.6 86.2 101.9 116.9 130.4 1 38.0 147.9 1 55.8 168.0 174.1 177.4 179.9  PERCENT OF 24-HOUR RAINFALL 1 . 2. 5. 8. 16. 21 . 26. 29. 32. 34. 38. 42. 44. 48. 57. 65. 72. 77. 82. 87. 93. 97. 99. 1 00.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 15.7 30.7 44.2 51 .8 69.6 89.4 112.1 179.9  72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25  - 306 -  TIME  T A B L E 1 1 1 . 23 D I S T R I B U T I O N OF  RAINFALL  KITIMAT MAXIMUM  DATE YR-M- D 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  1 4 1 4 1 4 1 4 1 4 1 4 1 4 1 4 1 4 1 5 15 1 5 15 15 15 15 15 1 5 15 1 5 1 5 15 1 5 15  HOUR  16 1 7  18 19  20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 13 1 4 1 5  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR  RAINFALL  RECORD  HOURLY RAIN (MM)  CUM. RAIN (MM)  3.0 2.5 4.8 5.6 4.8 4.6 5.1 5.8 5.3 7.4 6.6 7.6 8.9 10.2 9.4 7.9 8.4 7.6 4.8 3.0 5.8 3.6 3.3 2.5  3.0 5.5 10.3 15.9 20.7 25.3 30.4 36.2 41.5 48.9 55.5 63. 1 72.0 82.2 91 .6 99.5 107.9 115.5 120.3 123.3 1 29. 1 1 32.7 136.0 1 38.5  FOR  INDICATED  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 10.2 19.6 28.5 36.4 52.4 66.6 90.2 138.5  ON  7. 14. 21 . 26. 38. 48. 65. 100.  PERCENT OF 24-HOUR RAINFALL 2. 4. 7. 11 . 15. 18. 22. 26. 30. 35. 40. 46. 52. 59. 66. 72. 78. 83. 87. 89. 93. 96. 98. 100.  DURATION: MAXIMUM ON RECORD  DATE - YR-M-D  (MM) 18.5 33.5 47.5 60.5 82.6 1 02.7 120.4 138.5  66 66 66 66 66 66 66 74  10 10 10 10 10 10 10 10  23 23 23 23 23 23 23 14  - 307 -  TIME  TABLE I I I . 2 4 D I S T R I B U T I O N OF  RAINFALL  LADNER BCHPA MAXIMUM  DATE YR--M- D 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67  10 6 7 10 7 10 1 0 7 7 10 7 10 7 10 10 7 7 10 1 0 7 10 7 7 10 7 10 7 10 7 10 10 .7 7 10 1 0 7 7 10 7 10 1 0 7 1 0 7 10 7 7 10  1 2 3 4 6 8 1 2 24  ON  RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOU] RAINFALL  24 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 18 1 9 20 21 22 23  0.5 1 .8 3.8 5.6 4.6 3.8 3.3 3.6 2.5 4.6 2.8 3.0 0.8 2.8 3.8 4.8 3.8 1 .5 3.0 1 .3 2.3 1 .0 0.3 0.0  0.5 2.3 6.1 11.7 16.3 20. 1 23.4 27.0 29.5 34. 1 36.9 39.9 40.7 43. 5 47.3 52. 1 55.9 57.4 60.4 61.7 64.0 65.0 65.3 65.3  1 . 4. 9. 18. 25. 31 . 36. 41 . 45. 52. 57. 61 . 62. 67. 72. 80. 86. 88. 92. 94. 98. 100. 100. 100.  DURATION  (HOURS)  24-HOUR R A I N F A L L  FOR  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 5.6 10.2 14.0 17.8 24.7 31 .8 41.2 65.3  9. 16. 21 . 27. 38. 49. 63. 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 12.7 15.6 19.1 22.4 27.0 32.2 41 .2 65.3  69 78 78 64 64 63 67 67  4 7 7 11 11 12 10 10  17 10 10 29 29 23 7 6  - 308 -  TIME  TABLE 111.25 D I S T R I B U T I O N OF  RAINFALL  LANGLEY LOCHIEL MAXIMUM  DATE YR-M- D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26 26 26  24-HOUR  RAINFALL  HOUR  HOURLY RAIN (MM)  5 6 7 8 9 10 -1 1 1 2 13 1 4 15 1 6 1 7 18 19 20 21 22 23 24 1 2 3 4  1 .3 3.0 3.0 3.0 2.0 3.8 5.1 5. 1 3.3 3.0 2.8 6.4 7.6 9.9 9.4 7.4 4.3 4.6 3.3 4.8 3.0 2.8 1 .5 1 .0  ON  RECORD CUM. RAIN (MM)  1 .3 4.3 7.3 10.3 12.3 16.1 21.2 26.3 29.6 32.6 35.4 41.8 49.4 59.3 68.7 76. 1 80.4 85.0 88.3 93. 1 96. 1 98.9 100.4 101.4  PERCENT OF 24-HOUR RAINFALL 1 . 4. 7. 10. 12. 16. 21 . 26. 29. 32. 35. 41 . 49. 58. 68. 75. 79. 84. 87. 92. 95. 98. 99. 1 00.  •  DURATION  (HOURS) 1 2 3 4 6 8 12 24  FOR  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 9.9 19.3 26.9 34.3 45.0 52.9 68.9 101.4  10. 19. 27. 34. 44. 52. . 68. 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 17.3 21 .4 26.9 34.3 45.0 53.2 68.9 101 .4  73 73 72 72 72 79 72 72  10 10 12 12 12 12 12 12  6 6 25 25 25 17 25 25  - 309 -  TIME  TABLE I I I . 2 6 D I S T R I B U T I O N OF  RAINFALL  MISSION WEST ABBEY MAXIMUM  DATE YR-M- D 68 68 68 68 68 68 68 . 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  18 18 18 18 18 18 18 18 18 18 18 18 18 18 19 19 1 9 1 9 19 19 19 19 19 19  HOUR  1 1 1 2 13 1 4 15 16 17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  RAINFALL  HOURLY RAIN (MM) 3.8 3.6 3.6 4.3 4.6 4.8 5.3 4.8 3.8 3.6 4.6 3.0 4. 1 5.3 3.8 3.3 5.8 5.8 5.1 3.8 5.8 4.6 3.3 3.3  FOR  6. 11 . 16. 20. 30. 37. 53. 100.  RECORD CUM. RAIN (MM)  3.8 7.4 11.0 15.3 19.9 24.7 30.0 34.8 38.6 42.2 46.8 49.8 53.9 59.2 63.0 66.3 72. 1 77.9 83.0 86.8 92.6 97.2 100.5 1 03.8  PERCENT OF 24-HOUR RAINFALL 4. 7. 11 . 15. 19. 24. 29. 34. 37. 41 . 45. 48. 52. 57. 61 . 64. 69. 75. 80. 84. 89. 94. 97. 100.  I N D I C A T E D DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 5.8 11.6 16.7 20.5 30.9 38.7 55.0 103.8  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 24.4 31 .6 37.0 40.6 50.2 66.8 85.4 103.8  70 81 81 81 80 80 80 68  11 9 9 9 12 12 12 1  23 27 27 27 25 25 25 18  -  TIME  310 -  TABLE I I I . 2 7 D I S T R I B U T I O N OF  RAINFALL  NANAIMO DEPARTURE BAY MAXIMUM  DATE YR--M-D 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83  2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  10 10 10 10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  HOUR  21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 1 4 15 16 17  18  19 20  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR R A I N F A L L  RECORD  HOURLY RAIN (MM)  CUM. RAIN (MM)  3.6 1 .2 4.0 5.9 5.1 4.8 4.0 4.0 4.0 5.9 5.9 1 .8 0.4 1 .4 0.4 1.0 1 .0 1 .0 1 .6 3.2 2.4 2.0 2.4 2.0  3.6 4.8 8.8 14.7 19.8 24.6 28.6 32.6 36.6 42.5 48.4 50.2 50.6 52.0 52.4 53.4 54.4 55.4 57.0 60.2 62.6 64.6 67.0 69.0  FOR  9. 17. 23. 29. 41 . 57. 73. 100.  PERCENT OF 24-HOUR RAINFALL 5. 7. 13. 21 . 29. 36. 41 . 47. 53. 62. 70. 73. 73. 75. 76. 77. 79. 80. 83. 87. 91 . 94. 97. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 5.9 1 1 .8 15.8 19.8 28.6 39.6 50.2 69.0  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 28.4 37.0 37.0 37.0 37.6 44.2 50.4 69.0  72 72 72 72 75 75 83 83  8 8 8 8 2 2 2 2  21 21 21 21 12 12 10 10  - 311 -  TIME  T A B L E 1 1 1 . 28 D I S T R I B U T I O N OF R A I N F A L L -NORTH VANC. LYNN CREEK  MAXIMUM  DATE YR-M-D 81 81 81 81 81 81  81 81 81  81 81 81 81 81 81 81 81 81 81 81 81 81 81 81  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31  HOUR  1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 1 5 16 17 18 19 20 21 22 23 24  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM)  CUM. RAIN (MM)  6.8 13.6 12.3 10.0 19.6 13.8 17.9 16.8 12.8 14.0 14.7 11.5 10.8 10.0 11.9 9.1 8.9 5.7 5.3 2. 1 4.2 6. 1 8.7 4.7  6.8 20.4 32.7 42.7 62.3 76. 1 94.0 110.8 123.6 137.6 152.3 163.8 174.6 184.6 196.5 205.6 214.5 220.2 225.5 227.6 231 .8 237.9 246.6 251 .3  FOR  8. 14. 20. 27. 38. 48. 67. 100.  PERCENT OF 24-HOUR RAINFALL 3. 8. 13. 17. 25. 30. 37. 44. 49. 55. 61 . 65. 69. 73. 78. 82. 85. 88. 90. 91 . 92. 95. 98. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 19.6 34.7 51.3 68. 1 94.9 121.1 167.8 251 .3  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 19.6 34.7 51 .3 68. 1 94.9 121.1 167.8 251 .3  81 81 81 81 81 81 81 81  10 10 10 10 10 10 10 10  31 31 31 31 31 31 31 31  -  TIME  312 -  T A B L E 1 1 1 . 29 D I S T R I B U T I O N OF R A I N F A L L P I T T MEADOWS S T P  MAXIMUM  DATE YR-M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  16 16 16 1 6 1 6 1 7 1 7 17 17 17 17 17 17 1 7 1 7 1 7 17 1 7 1 7 1 7 17 1 7 17 17  1 2 3 4 6 8 12 24  RAINFALL  HOUR  HOURLY RAIN (MM)  20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 18 19  2.9 1.5 1 .0 2.1 2.7 2.1 3.2 5.1 6.3 6.3 7.0 8.0 9.3 7.8 7.8 9.3 9.5 8.3 2.0 4.1 2.9 2.5 3.1 2.5  DURATION  (HOURS)  24-HOUR  FOR  8. 16. 23. 30. 44. 57. 75. 100.  RECORD CUM. RAIN (MM)  2.9 4.4 5.4 7.5 10.2 12.3 15.5 20.6 26.9 33.2 40.2 48.2 57.5 65.3 73. 1 82.4 91 .9 1 00.2 102.2 106.3 109.2 111.7 114.8 117.3  PERCENT OF 24-HOUR RAINFALL 2. 4. 5. 6. 9. 10. 13. 18. 23. 28. 34. 41 . 49. 56. 62. 70. 78. 85. 87. 91 . 93. 95. 98. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 9.5 18.8 27. 1 34.9 52.0 67.0 87.9 1 1 7 ."3  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 24.6 37.6 45.2 51 .0 52.8 67.0 87.9 117.3  74 74 74 74 74 79 79 79  7 7 7 7 7 12 12 12  11 11 11 11 11 17 17 16  -  TIME  313 -  TABLE I I I . 3 0 D I S T R I B U T I O N OF  RAINFALL  PITT POLDER MAXIMUM  DATE YR-M- D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  18 18  18 18 18 18 18 18 18 18 19 19 19 19 19 19  19 19 19 19 19 19 19 19  HOUR  1 5 16 17  18  19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR R A I N F A L L HOURLY RAIN (MM) 5.8 6.1 5.6 5.6 3.3 3.6 3.8 5.1 5.6 6.1 5.8 5.8 6.9 8.1 6.9 5.6 7.1 8.1 6.9 8.1 6.6 6.9 5.8 5.1  FOR  6. 11 . 16. 21 . 30. 40. 57. 100.  RECORD CUM. RAIN (MM)  5.8 11.9 17.5 23. 1 26.4 30.0 33.8 38.9 44.5 50.6 56.4 62.2 69. 1 77.2 84. 1 89.7 96.8 1 04.9 111.8 1 19.9 1 26.5 133.4 1 39.2 1 44.3  PERCENT OF 24-HOUR RAINFALL 4. 8. 12. 16. 18. 21 . 23. 27. 31 . 35. 39. 43. 48. 53. 58. 62. 67. 73. 77. 83. 88. 92. 96. 1 00.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 8.1 15.2 23. 1 30.2 43.7 57.7 82.8 144.3  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.8 30.3 42.5 51.9 66.6 78.6 94.9 144.3  68 68 68 68 68 68 68 68  9 9 9 9 9 9 9 1  17 17 17 16 16 16 16 18  -  TIME  314 -  T A B L E 111.31 D I S T R I B U T I O N OF  RAINFALL  PORT ALBERNI A MAXIMUM  DATE YR--M- D 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83 83  2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  10 10 10 10 10 10 10 10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  HOUR  1 7 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 1 6  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR R A I N F A L L  ON  HOURLY RAIN (MM) 2.4 4.8 4.2 4.4 2.8 5.0 4.0 5.7 7.0 8.8 10.3 6.6 6.2 6.4 6.8 7.2 7.2 8.9 7.6 6.3 6.9 5.0 4.8 3.8  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 10.3 19. 1 26. 1 32.7 45.3 59.6 89.3 143. 1  7. 13. 18. 23. 32. 42. 62. 100.  RECORD CUM. RAIN (MM)  2.4 7.2 11.4 15.8 18.6 23.6 27.6 33.3 40.3 49.1 59.4 66.0 72.2 78.6 85.4 92.6 99.8 108.7 116.3 122.6 129.5 134.5 139.3 143.1  PERCENT OF 24-HOUR RAINFALL 2. 5. 8. 11 . 13. 16. 19. 23. 28. 34. 42. 46. 50. 55. 60. 65. 70. 76. 81 . 86. 90. 94. 97. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.7 29. 1 30.0 35.3 46.8 60.2 89.3 143. 1  78 78 78 73 75 79 83 83  5 5 5 10 11 12 2 2  24 24 24 27 13 17 11 10  - 315 -  TIME  T A B L E 1 1 1 . 32 D I S T R I B U T I O N OF R A I N F A L L PORT COQUITLAM CITY YARD  MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26  HOUR  3 4 5 6 7 8 9 10 1 1 1 2 13 14 15 16 17 18  19  20 21 22 23 24 1 2  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM) 0.5 3.0 5.1 5.1 5.3 6.1 7.6 7.4 6.6 5.8 5.3 6.9 6.1 6.1 6.1 6.9 5.6 8.4 8.9 5.8 3.3 1 .8 0.5 0.3  FOR  7. 14. 19. 24. 34. 44. 64. 100.  CUM. RAIN (MM) 0.5 3.5 8.6 13.7 19.0 25. 1 32.7 40. 1 46.7 52.5 57.8 64.7 70.8 76.9 83.0 89.9 95.5 103.9 112.8 118.6 121 .9 123.7 1 24.2 1 24.5  PERCENT OF 24-HOUR RAINFALL 0. 3. 7. 11 . 15. 20. 26. 32. 38. 42. 46. 52. 57. 62. 67. 72. 77. 83. 91 . 95. 98. 99. 100. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 8.9 17.3 23. 1 29.8 42.0 55.0 80. 1 124.5  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 12.0 19.8 28. 1 34.8 49.8 58.0 80. 1 124.5  82 77 79 79 79 79 72 72  7 11 12 12 12 12 12 12  3 25 17 17 17 17 25 25  - 316 -  TIME  TABLE I I I . 3 3 D I S T R I B U T I O N OF R A I N F A L L PORT HARDY  MAXIMUM  DATE YR-M-D 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  9 9 9 9 9 9 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  HOUR  19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 14 1 5 16 1 7 18  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM) 5.0 6.1 6.3 6.5 6.1 7.2 7.0 8.6 7.7 7.7 6.5 5.7 5.0 4.5 4.3 5.4 4.9 5.4 6.3 7.0 9.9 11.9 12.8 7.2  FOR  8. 15. 21 . 25. 33. 40. 51 . 100.  CUM. RAIN (MM) 5.0 11.1 17.4 23.9 30.0 37.2 44.2 52.8 60.5 68.2 74.7 80.4 85.4 89.9 94.2 99.6 1 04.5 1 09.9 116.2 123.2 1 33. 1 1 45.0 157.8 1 65.0  PERCENT OF 24-HOUR RAINFALL 3. 7. 11 . 14. 18. 23. 27. 32. 37. 41 . 45. 49. 52. 54. 57. 60. 63. 67. 70. 75. 81 . 88. 96. 1 00.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 12.8 24.7 34.6 41 .8 55. 1 65.4 84.6 165.0  _  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 12.9 24.7 34.6 41 .8 55. 1 65.4 85.4 165.0  80 80 80 80 80 80 80 80  6 12 12 12 12 12 12 12  8 10 10 10 10 10 10 9  -  317 -  T A B L E I I I . 34 T I M E D I S T R I B U T I O N OF R A I N F A L L PORT MELLON MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25  HOUR  1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  0.5 3.0 10.4 12.2 15.0 16.8 11.9 6.6 11.9 20.8 11.2 7.4 8.9 12.2 9.4 7.1 10.2 9.9 11.4 16.0 12.2 5.3 3.0 2.5  0.5 3.5 13.9 26. 1 41.1 57.9 69.8 76.4 88.3 109. 1 120.3 127.7 1 36.6 1 48.8 158.2 165.3 175.5 185.4 196.8 212.8 225.0 230.3 233.3 235.8  0. 1 . 6. 11 . 17. 25. 30. 32. 37. 46. 51 . 54. 58. 63. 67. 70. 74. 79. 83. 90. 95. 98. 99. 100.  FOR  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 20.8 32.7 44.0 55.9 83.0 106.4 1 45.3 235.8  RECORD  9. 14. 19. 24. 35. 45. 62. 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 20.8 34.8 44.7 55.9 83.0 1 06.4 145.3 235.8  72 70 70 72 72 72 72 72  12 4 4 12 12 12 12 12  25 9 9 25 25 25 25 25  -  TIME  318 -  T A B L E 1 1 1 . 35 D I S T R I B U T I O N OF R A I N F A L L PORT MOODY GULF OIL REF.  MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26  1 2 3 4 6 8 1 2 24  ON RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  3 4 5 6 7 8 9 10 1 1 12 1 3 1 4 15 1 6 1 7 18 19 20 21 22 23 24 1 2  1 .8 4.3 7.1 7.4 5.6 6.6 9.7 8.4 6.4 7.9 5.1 5.1 5.6 7.9 7.1 6.4 6.9 9.4 10.9 8.4 3.8 2.3 0.5 0.5  1.8 6.1 13.2 20.6 26.2 32.8 42.5 50.9 57.3 65.2 70.3 75.4 81.0 88.9 96.0 102.4 109.3 118.7 129.6 138.0 141.8 144.1 144.6 145.1  DURATION  (HOURS)  24-HOUR R A I N F A L L  FOR  8. 14. 20. 25. 34. 43. 60. 100.  1 . 4. 9. 14. 18. 23. 29. 35. 39. 45. 48. 52. 56. 61 . 66. 71 . 75. 82. 89. 95. 98. 99. 100. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 10.9 20.3 28.7 35.6 49. 1 62.6 87. 1 145. 1  PERCENT OF 24-HOUR RAINFALL  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 19.7 21 .8 29.2 36.3 51.6 67.3 92.3 1 45. 1  78 78 81 71 72 72 72 72  2 2 10 10 7 7 7 12  2 2 31 25 12 12 12 25  - 319 -  TIME  T A B L E 1 1 1 . 36 D I S T R I B U T I O N OF R A I N F A L L PORT RENFREW BCFS  MAXIMUM  DATE YR-M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  1 3 13 1 3 13 13 13 13 1 3 13 13 13 13 13 13 13 13 13 1 3 13 13 14 1 4 14 14  HOUR  5 6 7 8 9 10 1 1 12 1 3 1 4 1 5 16 1 7  18  19 20 21 22 23 24 1 2 3 4  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR  R A I N F A L L ON  HOURLY RAIN (MM)  CUM. RAIN (MM)  13.6 11.3 10.4 12.8 14.0 16.0 14.8 9.2 5.2 3.8 4.2 3.8 6.2 8.4 10.8 10.0 12.0 9.6 12.0 14.0 14.0 14.0 8.0 10.2  13.6 24.9 35.3 48. 1 62. 1 78. 1 92.9 102. 1 107.3 111.1 115.3 119.1 125.3 133.7 144.5 154.5 1 66.5 176. 1 188. 1 202. 1 216. 1 230. 1 238. 1 248.3  FOR  6. 12. 18. 23. 32. 41 . 52. 100.  PERCENT OF 24-HOUR RAINFALL 5. 10. 14. 19. 25. 31 . 37. 41 . 43. 45. 46. 48. 50. 54. 58. 62. 67. 71 . 76. 81 . 87. 93. 96. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % -OF (MM) 24-HR 16.0 30.8 44.8 57.6 79.3 102. 1 129.2 248.3  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 43.7 56.3 78. 1 99.7 117.6 1 25.2 153.6 248.3  77 78 78 78 78 78 75 79  1 1 1 1 1 7 1 1 7 1 1 7 1 1 7 1 1 7 10 16 12 13  - 320 -  TIME  T A B L E 1 1 1 . 37 D I S T R I B U T I O N OF R A I N F A L L PRINCE RUPERT A  MAXIMUM  DATE YR-M- D 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 9 9 9  1 2 3 4 6 8 12 24  RAINFALL  ON  RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 1 6 1 7 18 19 20 21 22 23 24 1 2 3  6.6 8.9 8.1 5.3 3.8 2.5 4.8 3.0 3.3 4.6 3.6 2.8 9.4 4.8 1 .8 1 .8 6.9 7.1 5.8 8.4 12.2 9.9 6.1 4.3  6.6 15.5 23.6 28.9 32.7 35.2 40.0 43.0 46.3 50.9 54.5 57.3 66.7 71.5 73.3 75. 1 82.0 89. 1 94.9 103.3 115.5 125.4 131.5 135.8  DURATION  (HOURS)  24-HOUR  FOR I N D I C A T E D MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 12.2 22. 1 30.5 36.6 50.3 60.7 78.5 135.8  9. 16. 22. 27. . 37. 45. 58. 100.  PERCENT OF 24-HOUR RAINFALL - 5. 11 . 17. 21 . 24. 26. 29. 32. 34. 37. 40. 42. 49. 53. 54. 55. 60. 66. 70. 76. 85. 92. 97. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.2 24.7 33.8 42.8 63.4 80.6 98.4 135.8  83 76 76 76 76 76 72 74  9 10 10 10 10 10 10 10  25 26 26 26 26 26 23 8  - 321 -  TIME  T A B L E I I I .38 D I S T R I B U T I O N OF  RAINFALL  SAANICH DENSMORE MAXIMUM  DATE YR-M- D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26  HOUR  3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 15 16 17 18 19 20 21 22 23 24 1 2  24-HOUR  RAINFALL  ON  HOURLY RAIN (MM) 1 .3 3.0 4.1 3.3 4.6 3.8 2.5 3.6 3.8 3.0 3.8 4. 1 4.6 7.1 4.8 4.1 4.3 4.6 4.3 6.6 7.6 4.8 3.6 1 .3  RECORD CUM. RAIN (MM)  PERCENT OF 24-HOU1 RAINFALL  1 .3 4.3 8.4 11.7 16.3 20. 1 22.6 26.2 30.0 33.0 36.8 40.9 45.5 52.6 57.4 61 .5 65.8 70.4 74.7 81.3 88.9 93.7 97.3 98.6  1 . 4. 9. 12. 17. 20. 23. 27. 30. 33. 37. 41 . 46. 53. 58. 62. 67. 71 . 76. 82. 90. 95. 99. 1 00.  *  DURATION  (HOURS) 1 2 3 4 6 8 12 24  FOR  INDICATED  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.6 14.2 19.0 23.3 32.2 43.4 60.7 98.6  8. 14. 19. 24. 33. 44. 62. 100.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 9.4 15.2 20.9 25. 1 32.2 43.4 60.7 98.6  72 72 65 67 64 72 72 72  2 2 10 1 9 12 12 12  16 16 5 2 30 25 25 25  - 322 -  TABLE I I I .39 TIME DISTRIBUTION OF RAINFALL SANDSPIT A  MAXIMUM 24-HOUR RAINFALL ON RECORD DATE YR-M-D 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78  10 31 10 31 10 31 10 31 10 31 10 31 10 31 10 31 10 31 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  HOUR 16 17 18 19  20 21 22 23 24 1 2 3 4 5 6  7 8 9 10 1 1 12 13 14 15  DURATION  (HOURS) 1 2 3 4 6 8 12 24  HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  2.9 3.2 1 .7 2.3 1 .5 1 .2 2.1 4.3 4.3 3.8 1.6 1.6 3.1 3.1 2.6 3.5 4.3 3.5 3.1 3.8 3.5 5.4 4.8 3.8  2.9  4. 8.  FOR INDICATED MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 5.4 10.2 14.0 17.5 24.4 32.2 44.5 75.0  7. 14. 19. 23. 33. 43. 59. 100.  6.1  7.8 10.1 11.6 12.8 14.9 19.2 23.5 27.3 28.9 30.5 33.6 36.7 39.3 42.8 47. 1 50.6 53.7 57.5 61 .0 66.4 71.2 75.0  10.  13. 15. 17. 20. 26. 31 . 36. 39. 41 . 45. 49. 52. 57. 63. 67. 72. 77. 81 . 89. 95. 100.  DURATION: MAXIMUM ON RECORD (MM) 12.7 22.0 32.3 38.8 42.8 47.0 51.8 75.0  DATE YR-M-D 75 80 80 80 80 75 79 78  10 10 10 10 10 10 11 10  5 31 31 31 31 4 20 31  - 323 -  TIME  TABLE 1 1 1 . 4 0 D I S T R I B U T I O N OF  RAINFALL  SPRING ISLAND MAXIMUM  DATE YR-M- D 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 7  1 2 3 4 6 8 12 24  R A I N F A L L ON RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 15 16 17 18 19 20 21 22 23 24 1  3.8 7.8 0.4 8.6 8.8 12.2 12.8 12.8 13.8 12.0 13.6 10.8 8.6 13.6 12.0 11.2 12.6 2.4 4.0 4.8 3.4 4.8 2.4 4.4  3.8 11.6 12.0 20.6 29.4 41.6 54.4 67.2 81.0 93.0 106.6 117.4 126.0 139.6 151.6 162.8 175.4 177.8 181.8 186.6 190.0 194.8 197.2 201.6  DURATION  (HOURS)  2 4-HOUR  FOR  7. 13. 20. 26. 38. 49. 72. 100.  2. 6. 6. 10. 15. 21 . 27. 33. 40. 46. 53. 58. 63. 69. 75. 81 . 87. 88. 90. 93. 94. 97. 98. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 2 4 - H R R A I N F A L L % OF (MM) 24-HR 13.8 26.6 39.4 52.2 77.2 98.0 146.0 201 . 6  PERCENT OF 2 4 - H O U R RAINFALL  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 22.6 30.4 40.6 52.2 77.2 98.0 146.0 201 . 6  79 75 78 78 78 78 78 78  9 4 11 2 5 10 2 2 11 6 11 6 11 6 11 6 11 6  -  324  -  TABLE 111.41 TIME DISTRIBUTION OF RAINFALL STAVE FALLS  MAXIMUM 24-HOUR R A I N F A L L ON RECORD DATE YR-M-D 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26 26 26 26 26 26 26 26 26  HOUR 1 1 12 13 14 15 16 17 18 19  20 21 22 23 24 1 2 3 4 5 6 7 8 9 10  DURATION  (HOURS) 1 2 3 4 6 8 12 24  HOURLY RAIN (MM)  CUM. RAIN (MM)  3.5 0.6 0.0 0.0 0.0 0.0 2.0 1 .4 2.9 3.1 4.7 7.1 6.1 10.6 11.0 10.8 8.9 12.8 8.5 7.7 10.6 9.7 5.5 5.3  3.5 4. 1 4.1 4.1 4.1 4.1 6.1 7.5 10.4 13.5 18.2 25.3 31.4 42.0 53.0 63.8 72.7 85.5 94.0 101.7 1 12.3 122.0 1 27.5 1 32.8  PERCENT OF 24-HOUR RAINFALL 3. 3. 3. 3. 3. 3. 5. 6. 8. 10. 14. 19. 24. 32. 40. 48. 55. 64. 71 . 77. 85. 92. 96. 100.  FOR INDICATED DURATION: MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 12.8 21 .8 32.5 43.5 62.6 80.9 109.3 132.8  10. 16. 24. 33. 47. 61 . 82. 100.  MAXIMUM ON RECORD (MM) 14.6 25.5 32.5 43.5 62.6 80.9 109.3 132.8  DATE YR-M-D 81  81 80 80 80 80 80 80  9 9 12 12 12 12 12 12  27 27 26 26 25 25 25 25  - 325 -  TABLE III .42 TIME DISTRIBUTION OF RAINFALL STRATHCONA DAM  MAXIMUM DATE YR-M-D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 17 1 17 1 17 1 17 1 17 1 17 1 17 1 17 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18 1 18  HOUR 17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR RAINFALL ON RECORD HOURLY RAIN (MM)  CUM. RAIN (MM)  5.1  5.1 14.8 22.4 29.0 41 .7 49.3 58.4 67.0 75. 1 85.3 92.4 100.5 104.6 114.8 118.4 1 24.0 128. 1 1 33.2 1 37.3 141.4 1 43.2 146.5 150.1 1 55.2  9.7 7.6 6.6 12.7 7.6 9.1  8.6 8.1 10.2 7.1  8.1 4.1 10.2 3.6 5.6 4. 1 5.1 4. 1 4.1 1 .8 3.3 3.6 5.1  FOR  8. 13. 19. 24. 36. 46. 65. 1007  3. 10. 14. 19. 27 . 32. 38. 43. 48. 55. 60. 65. 67. 74. 76. 80. 83. 86. 88. 91 . 92. 94. 97. 1 00.  INDICATED DURATION:  MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 12.7 20.3 29.4 38.0 56.3 71 .5 100.5 1 55.2  PERCENT OF 24-HOUR RAINFALL  MAXIMUM ON RECORD (MM) 23.9 26.0 29.4 38.0 56.3 71 .5 100.5 155.2  DATE YR-M-D 69 73 68 68 68 68 68 68  2 7 7 7 117 117 117 117 1 17 117  - 326 -  TABLE III.43 TIME DISTRIBUTION OF RAINFALL SURREY KWANTLEN PARK  MAXIMUM DATE YR-M-D 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68  1 1 1 1 1 1 1 1 1 1 1 1 1  18 18 18 18 18 18 18 18 18 18 18 18 19  1 1 1 1 1 1 1 1 1 1  19 19 19 19 19 19 19 19 19 19  1  19  HOUR 13 14 15 16 17 18  19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR RAINFALL ON RECORD HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  4.6 6.1 4.8 7.9 5.6 7.4 5.6 5.6 4.8 5.1 5.3 3.8 6.4 4.6 7.6 10.4 10.7 5.8 5.6 6.4 2.0 4.6 4.6 4.8  4.6 10.7 15.5 23.4 29.0 36.4 42.0 47.6 52.4 57.5 62.8 66.6 73.0 77.6 85.2 95.6 106.3 112.1 117.7 124. 1 1 26. 1 130.7 135.3 140. 1  3. 8. 1 1 . 17. 21 . 26. 30. 34. 37. 41 . 45. 48. 52. 55. 61 . 68. 76. 80. 84. 89. 90. 93. 97. 1 00.  FOR  INDICATED DURATION:  MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 10.7 21.1 28.7 34.5 46.5 57.5 77.3 1 40. 1  8. 15. 20. 25. 33. 41 . 55. 100.  MAXIMUM ON RECORD (MM) 18.2 28.2 35. 1 37. 1 46.5 57.5 81 .3 1 40.1  DATE YR -M-D 83 9 1 62 2 3 62 2 2 62 2 2 68 1 19 68 1 19 72 12 25 68 1 18  - 327 -  TABLE I I I . 4 4 TIME DISTRIBUTION OF RAINFALL SURREY MUNICIPAL  HALL  MAXIMUM 24-HOUR RAINFALL ON RECORD DATE YR-M- D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26  HOUR  HOURLY RAIN (MM)  3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 1 7 18 19 20 21 22 23 24 1 2  0.5 0.8 2.5 4.3 3.0 3.3 3.6 4.3 3.8 3.8 4. 1 4. 1 4.3 5.6 6.4 8.4 8.1 7.1 4.6 3.3 3.6 3.0 1 .5 1 .0  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  FOR  9. 17. 25. 32. 42". 51 . 68. 100.  0.5 1 .3 3.8 8.1 11.1 14.4 18.0 22.3 26. 1 29.9 34.0 38. 1 42.4 48.0 54.4 62.8 70.9 78.0 82.6 85.9 89.5 92.5 94.0 95.0  PERCENT OF 24-HOU1 RAINFALL 1 . 1 . 4. 9. 12. 15. 19. 23. 27. 31 . 36. 40. 45. 51 . 57. 66. 75. 82. 87. 90. 94. 97. 99. 100.  INDICATED DURATION:  MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 8.4 16.5 23.6 30.0 40.2 48.6 64.6 95.0  CUM. RAIN (MM)  MAXIMUM ON RECORD (MM) 17.5 21.5 26.0 31.6 44.9 56.6 64.6 95.0  DATE YR-M-D 68 81 80 80 67 67 72 72  8 7 7 7 12 12 12 12  27 29 11 11 22 21 25 25  - 328 -  TABLE III .45 TIME DISTRIBUTION OF RAINFALL TERRACE A  MAXIMUM 24-HOUR RAINFALL ON RECORD DATE YR-M- D 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  30 30 30 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31  HOUR 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 21  DURATION  (HOURS) 1 2 3 4 6 8 12 24  HOURLY RAIN (MM)  CUM. RAIN (MM)  2.3 3.6 4.3 5.3 4.5 5.5 6.3 8.1 7.3 7.5 9.7 6.5 5.1 4.1 4.7 4.7 4.0 3.8 3.4 3.4 3.2 2.8 2.6 2.8  2.3 5.9 10.2 15.5 20. 0 25.5 31.8 39.9 47.2 54.7 64.4 70.9 76.0 80. 1 84.8 89.5 93.5 97.3 100.7 104. 1 107.3 110.1 112.7 115.5  FOR  8. 15. 21 . 28. 39. 48. 65. 100.  2. 5. 9. 13. 17. 22. 28. 35. 41 . 47. 56. 61 . 66. 69. 73. 77. 81 . 84. 87. 90. 93. 95. 98. 100.  INDICATED DURATION:  MAX OCCURRING WITHIN MAX 24 -HR RAINFALL % OF (MM) 24-HR 9. 7 17. 2 24. 5 32. 6 45. 4 56. 0 74. 6 115. 5  PERCENT OF 2 4-HOU] RAINFALL  MAXIMUM ON RECORD (MM) 16.6 19.2 24.5 32.6 45.4 56.0 74.6 115.5  DATE YR-M-D 80 80 78 78 78 78 78 78  7 27 7 27 10 31 10 31 10 31 10 31 10 31 10 30  -  329 -  TABLE III .46 TIME DISTRIBUTION OF RAINFALL " TERRACE PCC  MAXIMUM DATE YR-M-D 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74 74  10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  14 14 14 14 14 14 14 14 14 14 15 15 15 15 15 15 15 15 15 15 15 15 15 15  HOUR  HOURLY RAIN (MM)  15 16 17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14  2.0 0.5 0.8 2.0 1 .3 1 .8 2.8 2.5 3.3 3.8 3.8 3.6 4.6 5.6 5.1 5. 1 6.6 8.1 5. 1 2.0 4.8 2.3 2.5 2.3  DURATION  (HOURS) 1 2 •3 4 6 8 12 24  24-HOUR RAINFALL ON RECORD CUM. RAIN (MM) 2.0 2.5 3.3 5.3 7. 1 8.9 1 1 .7 14.2 17.5 21.3 25. 1 28.7 33.3 38.9 44.0 49. 1 55.7 63.8 68.9 70.9 75.7 78.0 80.5 82.8  PERCENT OF 24-HOUR RAINFALL 2. 3. 4. 6. 9. 1 1 . 14. 17. 21 . 26. 30. 35. 40. 47. 53. 59. . 67. 77. 83. 86. 91 . 94. 97. 100.  FOR INDICATED DURATION: MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 8.1 14.7 19.8 24.9 35.6 43.8 58.2 82.8  10. 18. 24. 30. 43. 53. 70. 100.  MAXIMUM ON RECORD (MM) 19.1 30.5 41.9 45.7 50.2 54.3 62.9 82.8  DATE YR-M-D 80 68 68 68 68 68 68 74  9 11 11 11 11 11 11 10  19 19 19 19 19 19 19 14  - 330 -  TABLE III.47 TIME DISTRIBUTION OF RAINFALL TOFINO A  MAXIMUM 24-HOUR RAINFALL ON RECORD DATE YR-M- D 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  9 9 9 9 9 9 9 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10  HOUR  HOURLY RAIN (MM)  18 19 20 21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17  7.5 8.9 9.5 7.4 9.7 12.8 10.8 4.7 1 .6 1 .9 3.1 5.6 6.0 4.7 7.9 13.9 15.1 16.4 17.3 14.6 5.8 7.9 8.3 7.2  DURATION  (HOURS) 1 2 3 4 6 8 12 24  FOR  8. 16. 23. 30. 41 . 48. 60. 100. .  PERCENT OF 24-HOUR RAINFALL  7.5 16.4 25.9 33.3 43.0 55.8 66.6 71.3 72.9 74.8 77.9 83.5 89.5 94.2 102. 1 116.0 131.1 147.5 164.8 179.4 185.2 1 93. 1 201 .4 208.6  4. 8. 12. 16. 21 . 27. 32. 34. 35. 36. 37. 40. 43. 45. 49. 56. 63. 71 . 79. 86. 89. 93. 97. 1 00.  INDICATED DURATION:  MAX OCCURRING WITHIN MAX 24-HR RAINFALL % OF (MM) 24-HR 17.3 33.7 48.8 63.4 85.2 99.3 125. 1 208.6  CUM. RAIN (MM)  MAXIMUM ON RECORD  DATE —  (MM) 21.4 35.3 48.8 63.4 85.2 99.3 1 25. 1 208.6  YR-M-D 77 10 25 7111 2 80 12 10 80 12 10 80 12 10 80 12 10 80 12 10 80 12 9  -  TIME  331 -  TABLE 111.48 D I S T R I B U T I O N OF  RAINFALL  VANCOUVER A MAXIMUM  DATE YR-M-D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 16 12 16 12 16 12 16 12 16 12 17 12 17 12 17 12 17 12 17 12 17 12 17 12 17 12 17 12 17 12. 17 12 17 12 17 12 17 12 17 12 17 12 17 12 17 12 17  1 2 3 4 6 8 12 24  RAINFALL  HOUR  HOURLY RAIN (MM)  20 21 22 23 24 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 15 1 6 1 7 1 8 19  3.2 2.6 1 .8 3.6 3.6 3.0 5.2 5.4 5.7 6.5 5.9 6.7 9.9 10.9 13.1 9.4 3.2 2.3 2.5 4.7 3.5 3.2 1 .8 3.7  DURATION  (HOURS)  24-HOUR  FOR  11 . 20. 28. 36. 46. 56. 70. 100.  RECORD CUM. RAIN (MM)  3.2 5.8 7.6 11.2 14.8 17.8 23.0 28.4 34. 1 40.6 46.5 53.2 63. 1 74.0 87. 1 96.5 99.7 1 02.0 104.5 109.2 112.7 115.9 117.7 121.4  PERCENT OF 24-HOUR RAINFALL 3. 5. 6. 9. 12. 15. 19. 23. 28. 33. 38. 44. 52. 61 . 72. 79. 82. 84. 86. 90. 93. 95. 97. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 13.1 24.0 33.9 43.3 55.9 68. 1 85.3 121.4  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 23. 1 29.5 34.0 43.3 55.9 68. 1 85.3 121.4  81 81 81 79 79 79 79 79  6 6 6 12 12 12 12 12  13 13 13 17 17 17 16 16  - 332 -  TIME  T A B L E 1 1 1 . 49 D I S T R I B U T I O N OF R A I N F A L L VANCOUVER HARBOUR  MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26  1 2 3 4 6 8 12 24  R A I N F A L L ON  HOUR  HOURLY RAIN (MM)  2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 1 4 15 1 6 1 7 18 19 20 21 22 23 24 1  0.5 0.8 3.3 4.8 4.6 4.3 4. 1 3.6 4.3 3.0 3.0 4.8 4.6 4.3 6.4 5.1 7.4 6.1 5.3 4.3 4.3 2.5 1 .5 0.0  DURATION  (HOURS)  24-HOUR  FOR  8. 15. 20. 27. 37. 47. 63. 100.  CUM. RAIN (MM) 0.5 1 .3 4.6 9.4 14.0 18.3 22.4 26.0 30.3 33.3 36.3 41.1 45.7 50.0 56.4 61 .5 68.9 75.0 80.3 84.6 88.9 91.4 92.9 92.9  PERCENT OF 24-HOUR RAINFALL 1 . 1 . 5. 10. 15. 20. 24. 28. 33. 36. 39. 44. 49. 54. 61 . 66. 74. 81 . 86. 91 . 96. 98. 1 00. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.4 13.5 18.9 25.0 34.6 44.0 58.6 92.9  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 15.0 26.9 32.2 32.2 40.3 53.4 67.4 92.9  62 62 62 62 79 79 79 72  2 2 2 2 12 12 12 12  3 3 2 2 17 17 16 25  - 333 -  TIME  TABLE 111.50 D I S T R I B U T I O N OF  RAINFALL  VANCOUVER PMO MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26  HOUR  3 4 5 6 7 8 9 10 1 1 12 1 3 14 15 16 17 18 19 20 21 22 23 24 1 2  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR  RAINFALL  HOURLY RAIN (MM) 0.3 2.0 4.8 9.7 7.6 5.3 5. 1 8.4 7.6 5.6 7.1 5.6 4.6 5.3 6.9 8.1 7.6 6. 1 8.4 9.4 7.6 6. 1 2.3 0.0  ON  RECORD CUM. RAIN (MM)  0.3 2.3 7.1 16.8 24.4 29.7 34.8 43.2 50.8 56.4 63.5 69. 1 73.7 79.0 85.9 94.0 101.6 1 07.7 116.1 125.5 1 33. 1 1 39.2 141.5 141.5  PERCENT OF 24-HOUR RAINFALL 0. 2. 5. 12. 17. 21 . 25. 31 . 36. 40. 45. 49. 52. 56. 61 . 66. 72. 76. 82. 89. 94. 98. 1 00. 100.  FOR I N D I C A T E D . D U R A T I O N : MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 9.7 17.8 25.4 31 .5 47.2 60.2 82.8 141.5  7. 13. 18. 22. 33. 43. 59. 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 13.2 20.6 28.0 35.4 47.2 60.2 82.8 141.5  71 71 71 71 72 72 72 72  10 10 10 10 12 12 12 12  25 25 25 25 25 25 25 25  - 334 -  TIME  T A B L E 111.51 D I S T R I B U T I O N OF R A I N F A L L VANCOUVER UBC  MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26  24-HOUR  HOUR  2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 15 16 1 7 18  19  20 21 22 23 24 1  DURATION  (HOURS) 1 2 3 4 6 8 12 24  R A I N F A L L ON  HOURLY RAIN (MM) 0.3 1 .3 4. 1 5.8 6.9 6.4 4. 1 4.3 5.1 4.3 4.1 3.8 5.1 6.9 8.1 8.6 7.4 5.8 5.8 7.4 5.6 1 .8 1 .0 0.0  FOR I N D I C A T E D MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 8.6 . 16.7 24. 1 31.0 43. 1 55.6 72.9 114.0  8. 15. 21 . 27. 38. 49. 64. 100.  RECORD CUM. RAIN (MM)  0.3 1 .6 5.7 11.5 18.4 24.8 28.9 33.2 38.3 42.6 46.7 50.5 55.6 62.5 70.6 79.2 86.6 92.4 98.2 105.6 111.2 113.0 114.0 114.0  PERCENT OF 24-HOUR RAINFALL 0. 1 . 5. 10. 16. 22. 25. 29. 34. 37. 41 . 44. 49. 55. 62. 69. 76. 81 . 86. 93. 98. 99. 100. 1 00.  DURATION: MAXIMUM ON RECORD  DATE YR-M-D  (MM) 16.4 21 .4 27.3 31.0 43. 1 55.6 . 72.9 1 14.0  79 81 81 72 72 72 72 72  9 7 7 12 12 12 12 12  8 7 6 25 25 25 25 25  - 335 -  TIME  TABLE I I I . 5 2 D I S T R I B U T I O N OF  RAINFALL  -VICTORIA GONZALES HEIGHTS MAXIMUM  DATE YR-M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  1 3 1 3 1 3 1 3 13 1 3 13 1 3 1 3 13 13 13 1 3 13 1 3 1 3 1 3 1 4 1 4 1 4 1 4 1 4 1 4 1 4  1 2 3 4 6 8 12 24  RAINFALL  HOUR  HOURLY RAIN (MM)  8 9 10 1 1 1 2 1 3 14 15 16 17 18 19 20 21 22 23 24 1 2 3 4 5 6 7  3.4 5.0 8.3 6.9 6.1 4.5 4.5 3.8 4.8 4.0 5.9 6.1 6.4 5.6 4.8 5.4 4.3 1 .6 1 .0 0.3 0.0 0.3 0.3 6.9  DURATION  (HOURS)  24-HOUR  FOR  8. 15. 21 . 26. 35. 44. 67. 100.  RECORD CUM. RAIN (MM)  3.4 8.4 16.7 23.6 29.7 34.2 38.7 42.5 47.3 51 .3 57.2 63.3 69.7 75.3 80. 1 85.5 89.8 91 .4 92.4 92.7 92.7 93.0 93.3 1 00.2  PERCENT OF 24-HOUR RAINFALL 3. 8. 17. 24. 30. 34. 39. 42. 47. 51 . 57. 63. 70. 75. 80. 85. 90. 91 . 92. 93. 93. 93. 93. 100.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 8.3 15.2 21 .3 26.3 35.3 43.9 66.9 100.2  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 9.5 18.6 26.9 35.0 47.8 58.9 72.7 100.2  82 82 82 82 82 82 82 79  12 3 12 3 12 3 12 3 12 3 12 3 12 3 12 13  - 336 -  TIME  TABLE I I I . 5 3 D I S T R I B U T I O N OF  RAINFALL  VICTORIA INT. A MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26  1 2 3 4 6 8 12 24  RAINFALL  HOUR  HOURLY RAIN (MM)  2 3 4 5 6 7 8 9 10 1 1 1 2 1 3 1 4 1 5 1 6 1 7 18 19 20 21 22 23 24 1  1 .3 1.8 3.6 3.6 2.3 3.3 1 .3 1 .3 1.8 3.6 2.0 2.3 2.5 1 .8 5.6 7.6 4.6 4.8 5.1 5.8 6.9 9.9 4.3 2.3  DURATION  (HOURS)  24-HOUR  FOR  11 . 19. 25. 31 . 41 . 56. 68. 100.  CUM. RAIN (MM) 1 .3 3.1 6.7 10.3 12.6 15.9 17.2 18.5 20.3 23.9 25.9 28.2 30.7 32.5 38. 1 45.7 50.3 55. 1 60.2 66.0 72.9 82.8 87. 1 89.4  PERCENT OF 24-HOUR RAINFALL 1 . 3. 7. 12. 14. 18. 19. 21 . 23. 27. 29. 32. 34. 36. 43. 51 . 56. 62. 67. 74. 82. 93. 97. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 9.9 16.8 22.6 27.7 37. 1 50.3 61 .2 89.4  ON RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 1 1.9 18.5 23.3 27.7 38.2 50.3 61.2 89.4  74 74 74 72 80 72 72 72  11 9 1 1 9 1 1 9 12 25 11 21 12 25 12 25 12 25  - 337 -  TIME  TABLE 111.54 D I S T R I B U T I O N OF  RAINFALL  VICTORIA MARINE RADIO MAXIMUM  DATE YR--M- D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3  4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  HOUR  HOURLY RAIN (MM)  22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 13 1 4 1 5 1 6 1 7 18 1 9 20 21  1 .0 1 .5 3.6 3.3 5.3 4.3 6.9 8.4 6.9 6.6 10.7 2.3 1 .3 1 .5 5.1 6.6 4.8 5.8 6.6 5.8 5.3 1 .8 1 .0 1 .3  DURATION  (HOURS) 1 2 3 4 6 8 1 2 24  24-HOUR R A I N F A L L  FOR  10. 16. 22. 30. 41 . 49. 62. 100.  RECORD CUM. RAIN (MM)  PERCENT OF 24-HOUR RAINFALL  1 .0 2.5 6. 1 9.4 14.7 19.0 25.9 34.3 41 .2 47.8 58.5 60.8 62. 1 63.6 68.7 75.3 80. 1 85.9 92.5 98.3 103.6 1 05.4 1 06.4 107.7  1 . 2. 6. 9. 14.  18.  24. 32. 38. 44. 54. 56. 58. 59. 64. 70. 74. 80. 86.  91 .  96. 98. 99. 1 00.  INDICATED DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 10.7 17.3 24.2 32.6 43.8 52.4 66.9 107.7  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 17.8 24.8 29.0 35.7 45. 1 53.3 69.4 1 07.7  78 78 82 82 82 82 72 72  1 1 1 1 1 1 12 3  21 21 23 23 23 23 25 4  - 338 -  TIME  TABLE 111.55 D I S T R I B U T I O N OF  RAINFALL  VICTORIA SHELBOURNE MAXIMUM  DATE YR-M-D 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 26 26 26  1 2 3 4 6 8 12 24  R A I N F A L L ON  HOUR  HOURLY RAIN (MM)  4 5 6 7 8 9 10 1 1 1 2 13 1 4 1 5 1 6 17 18 19 20 21 22 23 24 1 2 3  1 .3 3.3 1 .5 2.8 3.6 4. 1 3.3 3.3 2.8 4.8 3.8 5.1 5.6 3.8 2.8 3.8 4.6 4.3 5.6 7.4 5.3 2.5 0.8 0.5  DURATION  (HOURS)  24-HOUR  FOR  9. 15. 21 . 26. 36. 44. 66. 100.  CUM. RAIN (MM) 1 .3 4.6 6.1 8.9 12.5 16.6 19.9 23.2 26.0 30.8 34.6 39.7 45.3 49.1 51.9 55.7 60.3 64.6 70.2 77.6 82.9 85.4 86.2 86.7  PERCENT OF 24-HOUR RAINFALL 1 . 5. 7. 10. 14. 19. 23. 27. 30. 36. 40. 46. 52. 57. 60. 64. 70. 75. 81 . 90. 96. 99. 99. 100.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.4 13.0 18.3 22.6 31 .0 37.9 56.9 86.7  RECORD  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 1 1 .7 14.7 18.3 22.6 31 .0 37.9 56.9 86.7  71 71 72 72 72 72 72 72  2 2 12 12 12 12 12 12  12 12 25 25 25 25 25 25  - 339 -  TIME  TABLE I I I . 5 6 D I S T R I B U T I O N OF  RAINFALL  VICTORIA U. OF VICT. MAXIMUM  DATE YR-M- D 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79  12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  13 13 1 3 1 3 1 3 13 13 1 3 13 13 1 3 13 V2 1 3 13 13 1 3 1 3 1 3 13 13 1 4 1 4 1 4  1 2 3 4 6 8 12 24  ON  RECORD  HOUR  HOURLY RAIN (MM)  CUM. RAIN (MM)  PERCENT OF 24-HOU1 RAINFALL  4 5 6 7 8 9 10 1 1 12 1 3 1 4 1 5 16 17 18 19 20 21 22 23 24 1 2 3  0.8 1 .4 2.4 3.9 3.3 3.0 6.4 5.6 5.0 5.2 3.8 3.2 4.2 3.2 4.8 5.6 5.6 4.8 4.6 4.2 4.0 1 .8 3.0 0.8  0.8 2.2 4.6 8.5 11.8 14.8 21.2 26.8 31 .8 37.0 40.8 44.0 48.2 51.4 56.2 61 .8 67.4 72.2 76.8 81 .0 85.0 86.8 89.8 90.6  1 . 2. 5. 9. 13. 16. 23. 30. 35. 41 . 45. 49. 53. 57. 62. 68. 74. 80. 85. 89. 94. 96. 99. 100.  DURATION  (HOURS)  24-HOUR R A I N F A L L  FOR  I N D I C A T E D DURATION:  MAX OCCURRING W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 6.4 12.0 17.0 22.2 29.6 37.0 57.4 90.6  7. 13. 19. 25. 33. 41.. 63. 100.  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 9.9 15.8 21.4 25.4 37.8 47.4 57.4 90.6  81 83 74 82 82 82 79 79  11 1 12 1 1 1 12 12  14 8 20 23 23 23 13 13  - 340 -  TIME  TABLE 111.57 D I S T R I B U T I O N OF  RAINFALL  WHITE ROCK STP MAXIMUM  DATE YR-M- D 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71 71  1 1 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11  2 2 2 2 3 3 3 3 3 33 3 3 3 3 3 3 3 3 3 3 3 3 3  HOUR  HOURLY RAIN (MM)  21 22 23 24 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 14 1 5 16 1 7 18 19 20  0.5 0.3 0.0 0.3 0.0 0.0 2.3 3.3 4.6 4.8 4.6 4.8 5.3 4.8 4.8 6.4 6.1 7.6 7.1 6.4 5. 1 2.3 1 .8 1 .0  DURATION  (HOURS) 1 2 3 4 6 8 12 24  24-HOUR R A I N F A L L  FOR  9. 17. 25. 32. 46. 58. 81 . 100.  RECORD CUM. RAIN (MM) 0.5 0.8 0.8 1. 1 1. 1 1. 1 3.4 6.7 11.3 16.1 20.7 25.5 30.8 35.6 40.4 46.8 52.9 60.5 67.6 74.0 79. 1 81.4 83.2 84.2  PERCENT OF 24-HOU1 RAINFALL  !. ] . 1 1 1 1  . . . .  4. 8. 13. 19. 25. 30. 37. 42. 48. 56. 63. 72. 80. 88. 94. 97. 99. 1 00.  INDICATED DURATION:  MAX O C C U R R I N G W I T H I N MAX 24-HR R A I N F A L L % OF (MM) 24-HR 7.6 14.7 21 . 1 27.2 38.7 48.5 67.8 84.2  ON  MAXIMUM ON RECORD  DATE YR-M-D  (MM) 15.2 24.3 25.8 27.7 38.7 48.5 67.8 84.2  72 7 72 7 72 7 78 1 1 7111 7111 7111 7111  9 9 9 3 3 3 3 2  - 341 -  APPENDIX IV WATER PERCOLATION THROUGH SNOW  - 342 -  APPENDIX IV WATER PERCOLATION  IV.1  THROUGH SNOW  VERTICAL UNSATURATED FLOW  A p h y s i c a l model f o r v e r t i c a l p e r c o l a t i o n o f water through a homogeneous ripe  snowpack has been developed by Colbeck  derived  by Colbeck  and r e s u l t s  of f i e l d  (1971, 1972). studies  Relationships  undertaken  to v e r i f y  t h e o r e t i c a l r e s u l t s a r e summarized i n t h i s s e c t i o n .  Development  of the theory  snowpack p e r m e a b i l i t y  requires  and water  the f o l l o w i n g  r e l a t i o n s h i p s between  saturation:  (iv..i)  k, = k S  z  u  where S = s a t u r a t i o n o f the snowpack; k u n s a t u r a t e d zone; and k  s  u  = intrinsic  = snowpack p e r m e a b i l i t y  permeability  i n the  a t some value o f S.  Also,  <t> = e  where and  0  4>{1 ~ Si)  0 = total e  porosity  (IV.2) of the snowpack;  Si = irreducible  saturation;  = e f f e c t i v e snowpack p o r o s i t y .  Colbeck shows the v e r t i c a l snow s u r f a c e  rate  of movement o f a water i n p u t ,  m, a t the  i s g i v e n by: (IV.3)  - 343 -  where  (dz/dt)  = speed o f p r o p a g a t i o n o f a wave with i n p u t r a t e m; p =  m  d e n s i t y o f water;  g = a c c e l e r a t i o n due t o g r a v i t y ;  and p. = v i s c o s i t y o f  water.  Experiments small  valley  compare and 5 m.  have  been  glacier  theoretical  f l o w measuring  conducted  by  Colbeck  i n the Cascade and measured  and Davidson  Mountains  field  i n Washington  results.  d e v i c e s were i n s t a l l e d  (1973)  Five  on a  State  h o l e s were  a t -depths r a n g i n g from  to  bored 1 m to  R e s u l t s o f the study are summarized on F i g u r e IV.1 and show e x p e r i -  mental d a t a agreed w i t h r e s u l t s d e r i v e d Similar  results  experimental British  were  studies  also  from t h e o r e t i c a l  o b t a i n e d by Colbeck  i n Vermont and C a l i f o r n i a ,  considerations.  and Anderson  (1982) from  and by Jordan  (1978) i n  Columbia.  Volume  F i g u r e IV. 1  Flux,  Wave Speed vs I n f l u x Rate  m/sec  ( a f t e r Colbeck and Davidson, 1973)  - 344 -  Eqn. by  IV.3 shows the r a t e of p e n e t r a t i o n the i n p u t  can  overtake  rate  a t which  preceding  (1973) demonstrated  of any i n p u t  i t was g e n e r a t e d .  smaller  analytical  ones  and  form  procedures  value  Therefore, a  shock  i s determined a large  front.  Colbeck  f o r c a l c u l a t i o n of f l u x  as a f u n c t i o n of time a t any snow depth f o r s p e c i f i e d water inputs snow s u r f a c e .  input  rates a t the  T h i s procedure was a p p l i e d by Dunne e t a l . (1976) to p r e -  d i c t snowmelt p e r c o l a t i o n c h a r a c t e r i s t i c s i n a s u b a r c t i c snowpack.  Tucker and Colbeck at  any depth  (1977) developed a computer program  f o r any i n p u t  a t the snow  Plotted  r e s u l t s are a v a i l a b l e f o r three  12-hour  duration:  depths ranging  double-peaked,  surface  to c a l c u l a t e  and  snow s u r f a c e  snow  input  s i n u s o i d a l and skewed.  from 1 m t o 8 m are shown on F i g u r e IV.2.  shapes over a a t snow  Common f e a t u r e s input  include  following:  i) a  shock  occurred  wave  formed  such  that  an  instantaneous  increase  in  flow  a t depth.  i i ) peak flow r a t e s decreased with  iii)  properties.  Flows  of the r e s u l t s of t h e o r e t i c a l c a l c u l a t i o n s f o r each s u r f a c e the  flow  depth.  d i f f e r e n c e s i n the shape of s u r f a c e ing depth.  inputs d i s a p p e a r s  with  increas-  - 345  F i g u r e IV.2.  -  Water P e r c o l a t i o n Through Snow ( a f t e r Tucker Colbeck, 1977)  and  - 346  In  instances  rapid  when  increase  important  Eqn.  in  to a l s o  rate i s less  IV.3  a  shock  wave  snowpack  -  forms  outflow  recognize  during  can  t h a t even  be  vertical  percolation,  observed.  i n these  cases,  However, the  peak  i t is outflow  than the peak r a t e i n p u t a t the snow s u r f a c e .  can be s i m p l i f i e d a =  ^—^  = 5.46  f u r t h e r by x 10  6  substituting  nT s~ 1  1  3m°-67(afeJ°-33  fdz\  'dz\  _ 3m  (iv.4)  (5.46 x I O )  0 6 7  6  m  0 3 3  jfej-  33  (IV.4a)  r e  (S -  (IV.4b)  529m067 A£33  Colbeck  and  Anderson  easily  measured  alone,  and  Eqn.  fornia ranging the  a  IV.4.  from  mean  in  value  Vermont  <t>  e  (1982) found experimental for  Snowmelt  and  a  this  grouping  studies  grouping  analysis yielded  the  to  undertaken  values  for  ku^ /3) 0e~ 1  than  either  be  adequate  v 1  0  0.00239 t o 0.00301 with a mean value  value  to  Eqn.  IV.4  yields  the  0  67  more p  1  for  in  snow a  o r  solution in  of 0.00270.  - 1 e  of  Cali-  narrow  following relationship  p e r c o l a t i o n and water i n p u t r a t e s to a r i p e  1.43m -  - 1 e  to be  ku^ /3)  f o r undisturbed ku /3)  1  band  Applying between  snowpack:  (iv.5)  - 347  Integration tion  of Eqn. IV.5 w i t h  describing  constant  depth  z=0 a t the snow s u r f a c e  of p e n e t r a t i o n  into  a snowpack  produces with  an equa-  time  input rate:  z= 1.43m - * 0  Solution  67  { I V  for  '  6 )  of Eqn. IV.6 i s shown g r a p h i c a l l y on F i g u r e IV.3 f o r a range of  water i n p u t s t o a snowpack from r a i n f a l l and snowmelt. consider  for a  snow depths  of 1 t o 2 m and t y p i c a l  the c o a s t a l r e g i o n ranging  F i g u r e IV.3 show  that  vertical  rain  from 5 t o 20 mm/hr. percolation  alone  3 hours t o the t r a v e l time of a water p a r t i c l e  For i l l u s t r a t i o n ,  and snowmelt Results  inputs  presented  can add about  through the b a s i n .  on  0.5 t o  - 348  F i g u r e IV.3.  -  P e r c o l a t i o n Rates f o r V e r t i c a l Unsaturated  Flow  - 349 -  BASAL SATURATED FLOW  IV.2 The  governing  base  of  a  envisioned vertical  equations  snowpack  have  a two-layer flow  f o r water  through  been  model  flow  through  developed  f o r water  an unsaturated  by  Colbeck  flow  layer  saturated  through  snow  (1974a).  a t the Colbeck  snow c o n s i s t i n g o f  and downslope  flow  along  a  boundary i n a s a t u r a t e d l a y e r .  For  constant  equation  slope  and  unit  width,  Colbeck  expresses  the c o n t i n u i t y  f o r the s a t u r a t e d l a y e r a s : (IV.7)  where  ks =  intrinsic  h = saturated to s a t u r a t e d  By  permeability  zone;  9 =  slope;  l a y e r t h i c k n e s s ; x = d i s t a n c e ; t = time; and I = n e t i n p u t zone.  c o n s i d e r i n g a new c o o r d i n a t e  the  o f the s a t u r a t e d  wave speed  solved d i r e c t l y  system  i n the s a t u r a t e d  (x', t ) which moves downslope a t 1  l a y e r , Eqn. IV.7 can be s i m p l i f i e d and  to y i e l d : (IV.8)  where  t o ' and t j j ' a r e time  limits  of water e n t e r i n g the s a t u r a t e d base, Eqn.  and q  (0,t ') L  t o the i n p u t  period length.  equal  i s the u n i t  discharge  which a p a r c e l  taken  a t the base  of the s l o p e .  from the base o f the s l o p e  t o the s a t u r a t e d  t o the time  during  l a y e r a t the top o f a s l o p e moves to the  IV.8 s t a t e s t h a t the o u t f l o w  lent  f o r the p e r i o d  layer  f o r water  integrated to t r a v e l  over along  i s equivaa  preceding the  slope  - 350 -  Experimental flow One  verification  has n o t been study  was  of  equations  as e x t e n s i v e  undertaken  by  Dunne  e t a l . (1976)  Snowmelt r u n o f f was measured  in  from  1 335  t o 2810 m  2  f o r basal  as t h a t f o r v e r t i c a l  arctic. area  developed  with  a t seven  downslope  saturated  unsaturated  flow.  i n the Canadian  hillslope lengths  plots  between  sub-  ranging 37 m and  85 m.  Comparison mated was  was  using  was e s t i m a t e d  ments  prediction of  time  to  remarkably  along  the h i l l s l o p e  theoretical  and v a l u e s  outflow  travel  r u n o f f was  A summary  was  time.  estimated;  Dunne  zone  of results  hydrograph  flow consideraand o u t f l o w f o r time  e t a l . concluded  generally excellent" was l e s s  esti-  to the s a t u r a t e d zone  t o the s a t u r a t e d  o f r u n o f f hydrographs  good".  a  runoff  the i n p u t hydrograph  of inputs  hillslope  o f peak  the t i m i n g  For example,  snowmelt  s u r f a c e m e l t and v e r t i c a l u n s a t u r a t e d  as the sum  equal  measured  as f o l l o w s : from  travel  calculated  between  Eqn. IV.8.  calculated  tions;  made  was  incre"the  and "the p r e d i c t i o n  satisfactory  though  still  f o r 20 hydrographs a n a l y z e d a t  these h i l l s l o p e p l o t s i s shown on F i g u r e IV.4.  Observed Peak Dlschorge (cm/hr)  F i g u r e IV. 4  Observed Lag to Peak (hrs)  Comparison o f P r e d i c t e d and Observed Outflow ( a f t e r Dunne e t a l . , 1976)  Hydrographs  -  Closer  examination  of  e v e r y i n s t a n c e observed contradict  when  plots  of r e s u l t s  F i g u r e IV.4 f o r l a g times  l a g times a r e l e s s than p r e d i c t e d .  one  ranging  considers  that  data  i n l e n g t h from  t o a l a r g e r watershed  be much l e s s tion  on  a r e from  only  These r e s u l t s  relatively  37 t o 85 m.  s c a l e suggests observed  than p r e d i c t e d by water p e r c o l c a t i o n  good, small  Extrapolation l a g times would  theory.  T h i s observa-  supports f u r t h e r the concept o f an i n t e r n a l d r a i n a g e network as the  dominant r o u t i n g mechanism f o r hydrograph  Examination to  shows i n  the c o n c l u s i o n t h a t e x p e r i m e n t a l r e s u l t s a r e e s p e c i a l l y  particularly hillslope  results  351 -  o f the s p e c i a l  illustrate  saturated  response  flow  existed  case  a n a l y s i s on a watershed  of steady  characteristics under  a  snowpack.  scale.  flow p r o v i d e s an o p p o r t u n i t y that  would  Colbeck  occur  (1974a)  i f basal showed f o r  steady f l o w :  flow depth  h = Ix(ctk,9)-  unit discharge  q = ak 6h  travel time  t = 4> x{ak 0)-  Even though runoff  IV  e  problems  (1974a)  i s limited,  9  (iv.11)  1  from  to a c t u a l water  Eqn. IV.11 n e v e r t h e l e s s a l l o w s f o r q u a l i t a -  o f the time frame f o r b a s i n r e s p o n s e .  and Dunne e t a l . (1976)  estimated  e q u a l t o 5.1 x 10~9 m2 f o r s a t u r a t e d flow through ranging  9  (iv.10)  s  the a p p l i c a b i l i t y o f a s t e a d y - s t a t e s o l u t i o n  t i v e assessment  Colbeck  < ->  1  1 mm  t o 2 mm.  Experimental  ks i s a p p r o x i m a t e l y snow w i t h g r a i n  sizes  data p r e s e n t e d by Colbeck and  - 352 -  Anderson  (1982) i n d i c a t e s 0e i s equal  to about 0.46.  Substituting  these  v a l u e s i n t o Eqn. IV.11 y i e l d s : _  16.5x  (IV.12)  9 Solution steep  o f Eqn. IV. 12 i s shown g r a p h i c a l l y on F i g u r e IV.5 f o r m i l d and  mountain  corresponding with of  slopes. travel  heavy ground  travel  times  where water  Also  times  litter  estimated  (Soil  shows b a s i n  i s routed  included  f o r overland  Conservation  response  through  on F i g u r e IV.5 f o r comparison are  would  flow  Service,  1974).  be more r a p i d  the b a s i n by o v e r l a n d  600 m  saturataed  and  hillside  F i g u r e IV. 5 show particle addition snowpack.  ranges to  flow  slopes  that from  the  along  time  Comparison  i n instances flow  For i l l u s t r a t i o n ,  the base of a snowpack f o r a d i s t a n c e o f  of  5  f o r basal about  forests  or c h a n n e l i z e d  than by s a t u r a t e d water p e r c o l a t i o n f l o w through snow. consider  through  and  15  degrees.  p e r c o l a t i o n the t r a v e l  10 t o 30 hours.  required  Results  for vertical  This  time  time  included  of a water  increment  percolation  on  is in  through  the  - 353 -  60 BASAL SATURATED FLOW ( F R O M E Q N . IV. 12 ) O V E R L A N D F L O W ( A F T E R SOIL C O N S E R V A T I O N S E R V I C E , 1974)  50  ~  40  JZ  o  UJ  IS rz  <n  /  30  UJ  > < cr  I-  V 20  SLOPE =5  200  400  °N^SLOPE  600  800  DISTANCE ( m )  F i g u r e IV.5.  T r a v e l Times f o r B a s a l S a t u r a t e d  Flow  1000  

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