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Geomorphic constraints to urban residential development in the Seymour area, District of North Vancouver,… Maynard, Dennis Edward 1978

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r.l GEOMORPHIC CONSTRAINTS TO URBAN RESIDENTIAL DEVELOPMENT IN THE SEYMOUR AREA, DISTRICT OF NORTH VANCOUVER, B.C. by DENNIS EDWARD MAYNARD B.Sc, University of B r i t i s h Columbia, 1972. A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1978 © Dennis Edward Maynard, 1978 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make it f ree ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th is thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my writ ten permission. Department of QeoLo 6-lcAL Sc/JfA/c£S The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date ft*<j V /lb ABSTRACT The o p p o r t u n i t y t o apply p r e v e n t i v e p l a n n i n g i s a v a i l a b l e i n the Seymour area of North Vancouver, B.C., the l a r g e s t p o r t i o n of Greater Vancouver p o t e n t i a l l y open, to urban expansion. N a t u r a l areas which have c e r t a i n geomorphic l i m i t a t i o n s t o r e s i d e n t i a l use can be i d e n t i f i e d and excluded from development, p r e s e r v i n g them as open space i n t e g r a t e d w i t h i n an urban r e s i d e n t i a l s e t t i n g . I n t r u s i v e bedrock of the Coast Mountains l a r g e l y determines the o v e r a l l landscape of the Seymour area, however, below about 650 f e e t (200 m.) the t e r r a i n i s subdued and u n d e r l a i n by t h i c k s u r f i c i a l d e p o s i t s r e l a t e d t o a t l e a s t two major g l a c i a t i o n s separated by a n o n g l a c i a l i n t e r v a l . Most of the sediments exposed a t the s u r f a c e were d e p o s i t e d e i t h e r d u r i n g the F r a s e r G l a c i a t i o n (Vashon D r i f t and C a p i l a n o Sediments) or i n p o s t - g l a c i a l time (HoloeeneoSediments) .. ••: R e s i d e n t i a l development of the land i s dependent on s u r f a c e and subsurface d i s t r i b u t i o n o f the g e o l o g i c a l m a t e r i a l s , on the p h y s i c a l c h a r a c t e r i s t i c s o f the m a t e r i a l s (which determine t h e i r s u i t a b i l i t y f o r urban use), and on the g e o l o g i c a l processes a c t i n g on the landscape. Topographic c o n d i t i o n s t h a t a f f e c t r e s i d e n t i a l development i n c l u d e e l e v a t i o n and degree of s l o p e . U r b a n i z a t i o n a t h i g h e r e l e v a t i o n s w i l l encounter i n c r e a s e d p r e c i p i t a t i o n , more snow, and c o o l e r temperatures, a l l of - i i i -which add to the c o s t s of d e s i g n i n g and m a i n t a i n i n g houses, roads, and drainage systems. Slopes l e s s than 20%, not a l i m i t i n g f a c t o r , are mainly u n d e r l a i n by s u r f i c i a l sediments. Steep sl o p e s ( g r e a t e r than 27 .1/2%), such as those -underlain by bedrock a t h i g h e l e v a t i o n s and those along deeply i n c i s e d v a l l e y s and r a v i n e s , s e v e r e l y r e s t r i c t development. U r b a n i z a t i o n i n t e r a c t s w i t h s u r f a c e hydrology i n two ways. S t r u c t u r e s c o n s t r u c t e d along the drainage channels may c o n s t r i c t or b l o c k flow, i n c r e a s i n g the f l o o d hazard. Development of s u b d i v i s i o n s can a l t e r s u r f a c e and subsurface flow, l e a d i n g to g r e a t e r s u r f a c e r u n o f f , h i g h e r peak flows, and i n c r e a s e d sediment y i e l d . As p e r e n n i a l streams w i t h t h e i r a s s o c i a t e d wetlands and f l o o d - s u s c e p t i b l e areas are the most s i g n i f i c a n t h y d r o l o g i c a l f e a t u r e s they should be r e s t r i c t e d from development. " A moderately s t r o n g earthquake (average i n t e n s i t y VII) i s a d i s t i n c t p o s s i b i l i t y i n the Seymour area. In such an event, h i g h e r i n t e n s i t i e s would be f e l t i n areas u n d e r l a i n by f i l l or s a t u r a t e d C a p i l a n o cohesive sediments. L i q u e f a c t i o n of the Maplewood mudflats and slope f a i l u r e s are p o s s i b l e secondary e f f e c t s of an earthquake. In order to e v a l u a t e the geomorphic c a p a b i l i t y of land f o r urban r e s i d e n t i a l use, l i m i t i n g p h y s i c a l f a c t o r s must be i d e n t i f i e d and d e f i n e d . C h a r a c t e r i s t i c s which can be r e s t r i c t i v e i n c l u d e s l o p e or landscape p o s i t i o n , depth to bedrock or impervious l a y e r , depth to water t a b l e , t e x t u r e - i v : -(and s t o n i n e s s ) , drainage ( i n c l u d i n g stream c h a n n e l s ) , c o n s o l i d a t i o n h i s t o r y , f l o o d frequency, s t a b i l i t y of s u r f i c i a l m a t e r i a l , and s e i s m i c c o n d i t i o n s . Areas of s i m i l a r p h y s i c a l c h a r a c t e r i s t i c s are d e l i n e a t e d and r a t e d a c c o r d i n g to the number and s e v e r i t y of t h e i r l i m i t i n g f a c t o r s . The l a r g e s t t r a c t s of land which have low c o n s t r a i n t to development are g e n t l e , t i l l - c o v e r e d s l o p e s or g e n t l e t o moderate slopes u n d e r l a i n by Capilano c o h e s i o n l e s s sediments. L i m i t a t i o n s i n these areas are minor and can be e a s i l y overcome a t minimum economic and environmental c o s t . The main areas w i t h medium c o n s t r a i n t are those where depth to bedrock and slope are l i m i t i n g and where s t e e p l y and moderately s l o p i n g land i s u n d e r l a i n by impermeable t i l l . P a r t s of the d e l t a of Lynn Creek and Seymour R i v e r are a l s o r a t e d medium. Moderate r e s t r i c t i o n s need to be r e c o g n i z e d but can be overcome by s p e c i a l p l a n n i n g , design, and maintenance. Areas of h i g h c o n s t r a i n t i n c l u d e steep bedrock s l o p e s , steep erodable or unstable s l o p e s , wetlands and f l o o d -s u s c e p t i b l e areas, r a v i n e drainage channels, t i d a l mudflats, and g e n t l y s l o p i n g land u n d e r l a i n by C a p i l a n o cohesive sediments. Development of these areas w i l l r e q u i r e s p e c i a l design, major r e c l a m a t i o n , and i n t e n s i v e maintenance which may pose severe economic and enivronmental l i m i t a t i o n s . - v -TABLE OF CONTENTS Chapter Page I INTRODUCTION 1. General Statement 1 2. L o c a t i o n and D e s c r i p t i o n o f the Study Area. . 2 3. Purpose and Scope 6 4. Previous Work 10 5. Method of Study 11 II URBANIZATION AND THE GEOMORPHIC ENVIRONMENT 1. U r b a n i z a t i o n and Geomorphic Problems.... 14 1.1 Earthquake Hazard 16 1.2 Urban Hydrology..... 17 1.3 Ground S t a b i l i t y 21 2. Geomorphology and Urban Land-Use P l a n n i n g 2 8 I I I HISTORY AND DISTRIBUTION OF THE GEOLOGICAL MATERIALS 1. I n t r o d u c t i o n 33 2. Prev i o u s Work 34 3. Bedrock Geology 37 4. Quaternary S t r a t i g r a p h y and H i s t o r y of the F r a s e r Lowland 41 5. D i s t r i b u t i o n o f G e o l o g i c a l M a t e r i a l s i n North Vancouver-Seymour 47 6. S o i l s 63 IV TOPOGRAPHY 1. I n t r o d u c t i o n 67 2. E f f e c t s of E l e v a t i o n on Climate 69 3. D i s t r i b u t i o n and S i g n i f i c a n c e of Slopes. 75 4. Summary of To p o g r a p h i c a l C o n s t r a i n t s to Development 80 - v i -Chapter Page r V SURFACE HYDROLOGY 1. I n t r o d u c t i o n 85 2. F l o o d Hazard 87 3. D i s t r i b u t i o n and S i g n i f i c a n c e of Surface H y d r o l o g i c a l Features 92 4. H y d r o l o g i c a l E f f e c t s of Development...• 102 5. Summary of H y d r o l o g i c a l C o n s t r a i n t s to Development I l l VI PHYSICAL CHARACTERISTICS AND ENGINEERING PROPERTIES OF THE GEOLOGICAL MATERIALS 1. -Physical C h a r a c t e r i s t i c s and Urban Use I n t e r p r e t a t i o n s 116 2. S t a b i l i t y o f Slopes 133 3. C o n s t r u c t i o n M a t e r i a l s 138 4. Summary of G e o l o g i c a l C o n s t r a i n t s to Development 142 VII SEISMIC RISK AND MICROZONATION 1. Seismic Risk 150 2. S e i s m i c i t y of North Vancouver-Seymour.. 153 3. Seismic M i c r o n z o n a t i o n . 156 4. Seismic Micronzonation of North Vancouver-Seymour. 159 5. Summary of Seismic C o n s t r a i n t s to Development 162 •VIII GEOMORPHIC CONSTRAINTS TO URBAN RESIDENTIAL DEVELOPMENT 1. I n t r o d u c t i o n 16 4 2. Rating Geomorphic C o n s t r a i n t s i n E s t a b l i s h i n g S u i t a b i l i t y f o r R e s i d e n t i a l Land-Use 165 3. Summary of Geomorphic C o n s t r a i n t s t to Development;' 170 BIBLIOGRAPHY 17 7 APPENDICES 1. D e s c r i p t i o n o f S t r a t i g r a p h i c Sections..191 - v i i -2. Summary of the G e o l o g i c a l Survey o f Canada Urban Geology F i l e Borehole and E x c a v a t i o n Records 199 3. S o i l T e x t u r a l C l a s s i f i c a t i o n .. . 203 4. Summary of Recorded F l o o d Damage on Ri v e r s and Creeks i n North Vancouver-Seymour. . . . 204 5. S o i l T e s t i n g Procedures 207 A. Mechanical Sieve A n a l y s i s 207 B. A t t e r b e r g L i m i t s 207 C. E x p l a n a t i o n o f the U n i f i e d S o i l C l a s s i f i c a t i o n System . . . 208 6. G r a i n S i z e D i s t r i b u t i o n , A t t e r b e r g L i m i t s , and U n i f i e d S o i l T e x t u r a l C l a s s i f i c a t i o n o f S u r f i c i a l Sediments... 211 7. E x p l a n a t i o n of Stoniness C l a s s e s 214 8. E x p l a n a t i o n of Drainage C l a s s e s . 215 - v i i i -LIST OF TABLES i Table Page I E f f e c t of land-use change on r e l a t i v e sediment y i e l d and channel s t a b i l i t y 20 II P o s s i b l e h y d r o l o g i c a l e f f e c t s of changes i n land-use. 22 I I I F a c t o r s l e a d i n g to an i n c r e a s e i n shear s t r e s s 2 4 IV F a c t o r s l e a d i n g to a decrease i n shear s t r e n g t h 2 4 V Quaternary s t r a t i g r a p h y of the F r a s e r Lowland, B.C 4 3* VI Main s o i l types developed from s u r f i c i a l m a t e r i a l s . . 65 VII Extreme annual 2 4-hour p r e c i p i t a t i o n . 73 V I I I Accepted d e n s i t y standards f o r development and standards f o r the percentage of area r e t a i n e d i n a n a t u r a l s t a t e a t v a r i o u s s l o p e s 82 IX Degree of l i m i t a t i o n of topographic f a c t o r s t o urban r e s i d e n t i a l land-use 8 3 X Drainage b a s i n c h a r a c t e r i s t i c s f o r some s e l e c t e d streams i n North Vancouver-Seymour 98 XI Percentage increases.; i n peak flows w i t h v a r i o u s r e c u r r e n c e i n t e r v a l s assuming conver s i o n s of 5 to 25 percent o f the b a s i n area to impermeable s u r f a c e connected to storm sewers 10 7. XII Degree of L i m i t a t i o n of h y d r o l o g i c f a c t o r s t o urban r e s i d e n t i a l land-use...... 113 XIII P h y s i c a l c h a r a c t e r i s t i c s and urban use i n t e r p r e t a t i o n s of the g e o l o g i c a l m a t e r i a l s ". 124 XIV O n - s i t e s e r v i c i n g c o s t estimates f o r h i l l s i d e development of r e s i d e n t i a l h ousing under i d e a l c o n d i t i o n s and i n areas of e x t e n s i v e bedrock 12 8 XV Degree of l i m i t a t i o n of g e o l o g i c f a c t o r s to urban r e s i d e n t i a l land-use 147 - i x -Table Page XVI Modified M e r c a l l i Scale of earthquake i n t e n s i t i e s with approximately corresponding Richter magnitudes 151 XVII Zone boundaries for the Seismic Zoning Map of Canada 15 3 XVIII North Vancouver-Seymour earthquake data 154 XIX Earthquake prediction for North Vancouver-Seymour 15 5 XX Microzonation of V i c t o r i a 158 .:XXI Microzonation of North Vancouver-Seymour 159 XXII Degree of l i m i t a t i o n of seismic factors to urban r e s i d e n t i a l land-use 162 XXIII Degree of l i m i t a t i o n of geomorphic factors to urban r e s i d e n t i a l land-use.. 16 7 - x -LIST OF FIGURES F i g u r e Page 1-1 L o c a t i o n Map 3 1-2 Land-Use * I I I - l Geology : L o c a t i o n s * III-2 S u r f i c i a l Geology * .  I I I - 3 Diagrammatic Composite G e o l o g i c a l Cross S e c t i o n s * IV-1 Optimum Ranges of Slopes (Grades) f o r V a r i o u s Urban I n s t a l l a t i o n s and A c t i v i t i e s 70 IV-2 Topography * IV-3 Slope Map * V - l S u r f a c e Hydrology * V-2 L o n g i t u d i n a l P r o f i l e s of S e l e c t e d Streams * Vl-^la D e s c r i p t i v e Use of the U n i f i e d S o i l C l a s s i f i c a t i o n P l a s t i c i t y Chart 119 V l - l b P l a s t i c i t y Chart f o r Pre-Vashon Sediments 120 V I - l c P l a s t i c i t y Chart f o r Vashon D r i f t . 121 V l - l d P l a s t i c i t y Chart f o r C a p i l a n o Sediments. 122 VII-1 Seismic M i c r o z o n a t i o n 160 VIII-1 Geomorphic C o n s t r a i n t s to R e s i d e n t i a l Development * VIII-2 Areas o f Geomorphic C o n s t r a i n t to R e s i d e n t i a l Development. 171 * denotes t h a t these f i g u r e s are i n the—b-ae-k— pocke-t-. CV-WWAT t - x i -LIST OF PLATES P l a t e Page 1. Steep, g r a n o d i o r i t e c l i f f s o v e r l o o k i n g Indian Arm 49 2. P o d z o l i c s o i l developed on dense, lodgement Vashon t i l l which o v e r l i e s g r a n o d i o r i t e bedrock i n a roadcut, Mt. Seymour Road 49 3. Probable Semiahmoo D r i f t o v e r l a i n by a t h i n bed of s i l t y peak (Cowichan Head Formation) i n Lynn,canyon: a r a i s e d Holocene g r a v e l f l o o d p l a i n caps the s e c t i o n 52 4. R h y t h m i c a l l y laminated s i l t c o n t a i n i n g s c a t t e r e d subrounded-subangular g r a n i t i c dropstones; probably a g l a c i o l a c u s t r i n e u n i t of Semiahmoo D r i f t 52 5. F o r e s e t pebbly sand beds, d i p p i n g about 10° south, which were de p o s i t e d by advance Vashon outwash. The exposure i s i n the R i v e r s i d e p i t 56 6. C a p i l a n o Sediments ( f i n e s i l t y sand and stony c l a y e y s i l t ) o v e r l i e Vashon D r i f t ( s u b s t r a t i f i e d sandy g r a v e l and dense, lodgement t i l l ) 56 7. C a p i l a n o outwash d e p o s i t c o n s i s t i n g of f o r e s e t d e l t a i c beds of sand, g r a v e l l y sand, and sandy g r a v e l . 62 8. Maplewood t i d a l mudflats a t low t i d e 6 2 9. Boulders i n Francis. Creek which have been eroded out of Vashon t i l l : t h i s i s a t y p i c a l bedload. of the steep r a v i n e drainage channels 9 6 10. R i v e r s i d e D r i v e sand and g r a v e l p i t . There has been no attempt to r e c l a i m t h i s area s i n c e o p e r a t i o n s ceased i n the l a t e 1960's 143 - x i i -ACKNOWLEDGEMENTS S p e c i a l thanks are accorded to Drs. J.L. Rau and R.E. Kucera f o r s u p e r v i s i o n o f the t h e s i s . I am g r a t e f u l a l s o t o Dr. 0. Slaymaker f o r encouraging the study i n i t s formative stages and to him and Dr. R.V. Best f o r c r i t i c i s m of the manuscript. I would e s p e c i a l l y . l i k e to thank Dr. W.H. Mathews f o r v a l u a b l e d i s c u s s i o n and c r i t i c i s m . A grant a d m i n i s t e r e d by Dr. Mathews and p r o v i d e d by the G e o l o g i c a l Survey o f Canada f o r urban g e o l o g i c a l s t u d i e s of M e t r o p o l i t a n Vancouver was used to reproduce c o p i e s o f the t h e s i s . Thanks are due a l s o t o members of the Resource A n a l y s i s Branch, M i n i s t r y of the Environment, V i c t o r i a , B.C. f o r d i s c u s s i o n of the use of geomorphology i n land-use s t u d i e s . Dr. M.C. Roberts of the Geography Department, Simon F r a s e r U n i v e r s i t y a l s o e n t h u s i a s t i c a l l y supported the p r o j e c t . A p p r e c i a t i o n i s extended to Messrs. W. Henderson, I. S e l l a r s , and T. Zuehlke who v o l u n t e e r e d o c c a s i o n a l a s s i s t a n c e i n the f i e l d and to Dr. M. Church of the Geography Department, U.B.C. f o r making a v a i l a b l e l a b o r a t o r y f a c i l i t i e s f o r analyses o f sediments. I am very g r a t e f u l to Diane S c o t t who undertook the lab o u r i o u s task o f t y p i n g the f i n a l manuscript. CHAPTER I INTRODUCTION General Statement The a p p l i c a t i o n o f geology to problems of the urban environment takes many forms. One of the important areas r e q u i r i n g b a s i c g e o l o g i c a l i n p u t i s urban design and p l a n n i n g . Planners and engineers need s u f f i c i e n t knowledge of e a r t h processes o p e r a t i n g i n t h e i r area of r e s p o n s i b i l i t y to f o r e s e e both the short-term and long-term consequences of these processes, and to p l a n a c c o r d i n g l y . They should be aware of the p o t e n t i a l geomorphic c o n s t r a i n t s and hazards produced by these processes and of methods and co s t s o f e i t h e r c o n t r o l l i n g them or l i v i n g w i t h them. G e o l o g i s t s should not make the economic d e c i s i o n s t h a t d e f i n e the use of the l a n d , but they can p r o v i d e a v a l u a b l e s e r v i c e by communicating the data r e q u i r e d f o r d e c i s i o n making to the r e s p o n s i b l e agencies. T h i s t h e s i s p r e s e n t s a method of a p p l y i n g geomorphic i n f o r m a t i o n , i n c l u d i n g data on g e o l o g i c a l , t o p o g r a p h i c a l , and h y d r o l o g i c a l f e a t u r e s and pr o c e s s e s , t o determine l i m i t a t i o n s , o f the land i n urban development. The proper r e a l i z a t i o n o f the i n f l u e n c e of geomorphic c o n d i t i o n s on urban development i s e s s e n t i a l t o i n t e l l i g e n t , p l a n n i n g and may r e s u l t i n s a v i n g c o n s i d e r a b l e sums of money. Pl a n n i n g boards may be unaware t h a t some of the land they i n t e n d to develop i s f r e q u e n t l y f l o o d e d or p o o r l y d r a i n e d , i s s u b j e c t to slope f a i l u r e or pr e s e n t s p a r t i c u l a r - 2 -c o n s t r u c t i o n problems. I t i s necessary to d e f i n e the geomorphic c a p a b i l i t y of the l a n d i n order to p r o v i d e an adequate environmental b a s i s f o r d i r e c t i n g u r b a n i z a t i o n . Geomorphic c o n s t r a i n t s to development i n c l u d e e x c e s s i v e s l o p e , poor foundation c o n d i t i o n s , poor drainage, e a s i l y eroded s o i l s , f l o o d p l a i n s , and l a n d e s s e n t i a l to complete the n a t u r a l process f o r groundwater recharge. Proper c o n s i d e r a t i o n of these f a c t o r s can only be undertaken by examining the i n t e r a c t i o n among such p h y s i c a l f e a t u r e s as geology, s o i l s , topography, c l i m a t e , and hydrology. L o c a t i o n and D e s c r i p t i o n of the Study Area The Seymour area of the C o r p o r a t i o n o f the D i s t r i c t o f 2 North Vancouver, B.C., c o n s i s t s of s l i g h t l y more than 25 km bounded on the west by Lynn Creek, on the south by B u r r a r d I n l e t , on the e a s t by Indian Arm, and on the n o r t h by a t r a n s m i s s i o n l i n e right-of-way and Indian R i v e r Road. (Figure 1-1). Immediately to the n o r t h of the area are the Greater Vancouver Regional D i s t r i c t (G.V.R.D.) Seymour R i v e r watershed and Mount Seymour P r o v i n c i a l Park. Two major east-west roads, D o l l a r t o n Highway and Mt. Seymour Parkway, t r a v e r s e the southern p a r t of the map-area while L i l l o o e t Road, ; R i v e r s i d e D r i v e , Berkeley D r i v e , and Mt. Seymour Road pr o v i d e the main north-south a r t e r i e s . North Vancouver-Seymour l i e s a t the boundary between two major p h y s i o g r a p h i c u n i t s , the F r a s e r Lowland and the - 4 -Coast Mountains. The lowlands c o n s i s t o f subdued, r o l l i n g topography u n d e r l a i n mostly by u n c o n s o l i d a t e d g l a c i a l , , g l a c i o f l u v i a l , g l a c i o m a r i n e , and f l u v i a l sediments. In the study area these d e p o s i t s have b u r i e d the southern f l a n k of the Coast Mountains up to an e l e v a t i o n o f about 650 f e e t (200 m.), although i n p l a c e s bedrock i s exposed down to sea l e v e l . Slopes are predominantly i n the range of 0% to 20% but commonly exceed 35% a t h i g h e r e l e v a t i o n s . The mountains r i s e a b r u p t l y from deep, U-shaped v a l l e y s which, i n the Seymour area, are occupied by Indian Arm, Seymour R i v e r , and Lynn Creek. B u r r a r d I n l e t , which extends eastward from the S t r a i t o f Georgia s e p a r a t i n g North Vancouver from the c i t y of Vancouver, occupies an o l d r i v e r v a l l e y which may be the former course of the P i t t R i v e r . (Armstrong, 1957). Seymour R i v e r and Lynn Creek, w i t h a combined watershed 2 area o f 235 km , are the p r i n c i p a l drainage channels f l o w i n g through the area. These major v a l l e y s and t h e i r main !. t r i b u t a r y v a l l e y s are U-shaped g l a c i a l troughs, although i n p l a c e s , V-shaped g u l l i e s have been c u t t s i n c e the m e l t i n g o f the P l e i s t o c e n e i c e . Numerous s m a l l streams, r a r e l y exceeding 4 km i n l e n g t h , d r a i n the study area. Most of these o r i g i n a t e as r u n o f f on bedrock exposed along the upper slopes of-Seymour Mountain and have i n c i s e d s m a l l V-shaped.^, r a v i n e s i n the s u r f i c i a l m a t e r i a l . The l a r g e r r i v e r s have average g r a d i e n t s of about 0.9% whereas many of the s m a l l e r streams cascade down g r a d i e n t s exceeding 11.5%. - 5 -The P a c i f i c Coast f o r e s t s of the Seymour area f a l l p r i n c i p a l l y i n t o two b i o g e o c l i m a t i c zones, the C o a s t a l Douglas F i r Zone which i s c o n f i n e d to d r i e r (1000 to 1500 mm. of annual p r e c i p i t a t i o n ) c o a s t a l areas between sea l e v e l and 1000 f e e t (300 m.) e l e v a t i o n and the C o a s t a l Western Hemlock Zone ( D r i e r Sub-zone) which i s found whease.-annual p r e c i p i t a t i o n exceeds 1800 mm. The two zones may be d i s t i n g u i s h e d on d i f f e r i n g p r o p o r t i o n s of Douglas f i r , western hemlock, western red cedar,.grand f i r , v i n e and b r o a d - l e a f maple, red h u c k l e b e r r y , Oregon grape, and s a l a l . (Environment Canada, 1973). Wit h i n these zones l o c a l f e a t u r e s of the p h y s i c a l environment, and consequently the c h a r a c t e r of the v e g e t a t i o n , may vary c o n s i d e r a b l y . For i n s t a n c e , where seepage occurs along the steep s i d e s of r a v i n e s and creek g u l l i e s , narrow s t r i p s develop, fed by n u t r i e n t - r i c h groundwater. Red cedar and Douglas f i r are c h a r a c t e r i s t i c of these s t r i p s , as are red a l d e r , dogwood,, and b r o a d - l e a f and v i n e maple. Depending on the wetness o f the s i t e , swordfern, deer f e r n , skunk cabbage, salmonberry, and red e l d e r b e r r y can be c h a r a c t e r i s t i c subordinate s p e c i e s . Maidenhair f e r n s t y p i c a l l y cover the steeper v a l l e y s i d e s . (Planning Dept., D i s t r i c t of North Vancouver, 1975). W i n d f a l l s are common i n these g u l l i e s and r a v i n e s because the s o i l i s f r e q u e n t l y shallow, and when s a t u r a t e d , bWolffeTs WeTfvy ^ n"s^t?ab'-l%'. Purpose and Scope - 6 -In general the process of urban development can proceed by either of two methods; by increasing the density within an e x i s t i n g urban area or by extending the periphery of developed areas. The l a t t e r method of growth continuously pre-empts the urban edge, causing undeveloped open areas to recede from the population centre. However, natural areas which have ce r t a i n physical l i m i t a t i o n s to development can be i d e n t i f i e d and designated as undeveloped open space within an urban se t t i n g . Thus the pattern of open space areas i s provided not by man, but by an i n t e r a c t i o n of natural processes. Rather then nature being destroyed to accommodate development, an area can be, as McHarg (19 69) stated, "designed with nature". With the expansion of the Vancouver Metropolitan Region considerable pressure for land-use development on the North Shore i s in e v i t a b l e . The slopes of the North Shore mountains are becoming an a t t r a c t i v e location for urban expansion, p a r t i c u l a r l y now that the need to conserve farmland i n the Fraser River delta area i s becoming more apparent. Forecasts for the year 1981 indicate a population of 1.25 m i l l i o n for metrololitan Vancouver and 2.0 m i l l i o n by the year 2000, with the population of the three North Shore municipalities expected to reach 205,000 by 1985 and 250,000 i n the year 2000. (Environment Canada, 1973). In 1975 the population of the North Shore stood at 140,000. - 7 -Urban development on the North Shore has been r e s t r i c t e d to the lower slopes. West of Lynn Creek r e s i d e n t i a l housing e x i s t s up to about 1150 f e e t (350 m.) e l e v a t i o n as f a r west as the B r i t i s h P r o p e r t i e s . Toward Horseshoe Bay, development has g e n e r a l l y occurred south of the Trans-Canada Highway. The area north of the highway has mainly been zoned f o r s i n g l e - f a m i l y dwellings&although the Corporation of the D i s t r i c t of West Vancouver has e s t a b l i s h e d a working l i m i t of 1200 f e e t (365 m.) e l e v a t i o n f o r u t i l i t y s e r v i c e s , thus r e s t r i c t i n g f u r t h e r upslope development. East of Lynn Creek the land use becomes dominantly "immature timber"? Large areas are zoned f o r s i n g l e - f a m i l y residences, but to date there i s only s c a t t e r e d development i n the lower t h i r d of the regi o n . On~ the b a s i s of zoned land and present use, i t appears that t h i s i s a l o g i c a l area f o r future development. The G.V.R.D. has assumed the r e s p o n s i b i l i t y f o r r e g i o n a l planning of the Lower Mainland, although i n d i v i d u a l m u n i c i p a l i t i e s r e t a i n c o n t r o l of t h e i r own l o c a l planning. Guidelines f o r expansion of the M e t r o p o l i t a n Vancouver Region have been e s t a b l i s h e d i n "The L i v a b l e Region Plan 1976-1986.',' (G.V.R.D., 1975). An important goal of t h i s plan i s to r e t a i n the character of the resource system i n as near i t s n a t u r a l s t a t e as p o s s i b l e through the concept of an "Open Space Conservancy." I t attempts to i d e n t i f y areas deserving a d d i t i o n a l developmental r e s t r i c t i o n s due to environmental c o n s i d e r a t i o n s . The o b j e c t i v e of the conservancy concept i s t o : - 8 -1. M a i n t a i n and enchance b i o t i c p r o d u c t i v i t y . 2. Promote p u b l i c s a f e t y . 3. Preserve a sense of n a t u r a l landscape*, which pr o v i d e s the r e g i o n w i t h i t s image and c h a r a c t e r . 4. Preserve n a t u r a l areas f o r e d u c a t i o n a l and s c i e n t i f i c study. 5. Preserve l a n d f o r r e c r e a t i o n a l use. 6. Provide an environmental b a s i s f o r d i r e c t i n g the u r b a n i z a t i o n of l a n d . ( i b i d . ) . The c r i t e r i a f o r i n c l u d i n g d e f i n i t i v e areas i n a conservancy r e g i o n c o n s i s t o f : 1. P h y s i o g r a p h i c c a p a b i l i t y of l a n d to be put to s p e c i f i c uses. 2. H a b i t a t requirements of the f l o r a and fauna. 3. The n a t u r a l design values of the r e g i o n a l landscape. 4. The r e c r e a t i o n a l p o t e n t i a l of the l a n d p a r c e l . T h i s open space conservancy concept o f p r e s e r v i n g n a t u r a l landscape f e a t u r e s and q u a l i t i e s i s not j u s t a p r e s e r v a t i o n of open space, but a l s o i n v o l v e s the i n t e g r a t i o n of urban development wi t h the n a t u r a l landscape. Any f u t u r e development i n the Lower Mainland should not be p e r m i t t e d to go ahead without adherence to these or s i m i l a r g u i d e l i n e s . N a t u r a l areas which have c e r t a i n p h y s i c a l c o n s t r a i n t s to urban use should be i d e n t i f i e d and development planned a c c o r d i n g l y . - 9 -The Seymour area p r o v i d e s an e x c e l l e n t o p p o r t u n i t y t o examine some aspects of how u r b a n i z a t i o n can be guided by r e c o g n i z i n g n a t u r a l l i m i t a t i o n s t h a t some areas o f l a n d pose to development. Previous development i n t h i s area has g e n e r a l l y been r e s t r i c t e d t o s c a t t e r e d r e s i d e n t i a l housing and i s o l a t e d s u b d i v i s i o n s . Much of t h i s was achieved by completely c l e a r i n g the land and then superimposing housing on i t . On .the b a s i s of past experiences where development was l o c a t e d on u n s u i t a b l e s i t e s , t h i s method of u r b a n i z a t i o n i s no l o n g e r a c c e p t a b l e . S l i g h t l y l e s s than h a l f o f the approximately 6000-acre Seymour area i s f o r e s t e d , undeveloped lan d which c o u l d be co n s i d e r e d f o r p o t e n t i a l urban expansion. Of the remaining area, 24% i s al r e a d y r e s i d e n t i a l , 10% i s commercial and i n d u s t r i a l , 14% i s park la n d , and 4% i s occupied by Indian Reserve No. 3. Most of the undeveloped lan d i s zoned mainly f o r r e s i d e n t i a l use ( R S . l ) , thus l i m i t i n g the range o f land-use p o s s i b i l i t i e s f o r the r e g i o n . (Figure 1-2). Geomorphic f a c t o r s which are important i n determining the s u i t a b i l i t y of land f o r urban r e s i d e n t i a l development i n c l u d e ; d i s t r i b u t i o n and c h a r a c t e r i s t i c s o f g e o l o g i c a l m a t e r i a l s ; g e o l o g i c a l hazards; s e i s m i c r i s k ; topography (both s l o p e and e l e v a t i o n ) ; and d i s t r i b u t i o n and s i g n i f i c a n c e o f s u r f a c e h y d r o l o g i c a l f e a t u r e s . - 1 0 -Previous Work The importance of t e r r a i n s c i e n c e i n h e l p i n g to d i r e c t the u r b a n i z a t i o n of l a n d i s now becoming q u i t e obvious. In the p a s t , such i n f o r m a t i o n was r a r e l y o b t a i n e d , or i f i t was i t came at a l a t e stage i n the development and had only a minor i n f l u e n c e on the d e s i g n . The North Shore r e g i o n of Greater Vancouver i s unusual i n the p r o v i n c e i n t h a t a number of such s t u d i e s have ,been c a r r i e d out i n the area i n the p a s t f i v e y e a r s . Environmental c o n d i t i o n s o f the B u r r a r d Inlet-Howe Sound area were f i r s t d e s c r i b e d by Environment Canada (1973). The r e p o r t p r o v i d e s p r e l i m i n a r y d e s c r i p t i v e notes on s e l e c t e d environmental and resource f a c t o r s , l a n d and water use, and l a n d s t a t u s . I n t e r p r e t a t i o n s were summarized i n s u i t a b i l i t y o r c a p a b i l i t y maps. In 1974, Watts wrote a t h e s i s d e s c r i b i n g the geomorphology, as a p p l i c a b l e to p l a n n i n g and r e s i d e n t i a l development, of a 150-acre area n o r t h of Hyannis Drive on the e a s t bank o f Seymour R i v e r . The P l a n n i n g Department, D i s t r i c t o f North Vancouver (1975) p u b l i s h e d a somewhat fragmented summary o f the n a t u r a l environment of the Seymour area as p a r t of a s e r i e s of p r e s e n t a t i o n s on p l a n n i n g f o r f u t u r e development i n the area. T h i s was not a f u l l - b o d i e d e c o l o g i c a l study, but a p r e l i m i n a r y survey o f n a t u r a l c o n d i t i o n s i n d e s i g n a t e d areas. On the b a s i s o f a r e c e n t study of p h y s i c a l f a c t o r s , Walmsley (1977b) d e s c r i b e d urban s u i t a b i l i t y f o r undeveloped areas of the North Shore between Horseshoe Bay and Lynn Creek. The f o u r resource themes are - 11 -c l i m a t e , bedrock geology, s u r f i c i a l geology, and aq u a t i c s (hydrology and f i s h e r i e s b i o l o g y ) . Method o f Study P r e l i m i n a r y study of the Seymour area i n v o l v e d s t e r e o s c o p i c examination of 20-chain (1:15,840) b l a c k and white a e r i a l photographs. (flown Aug.: 30, 1968). Surface drainage p a t t e r n s and g e n e r a l i z e d s u r f i c i a l g e o l o g i c a l u n i t s were d e l i n e a t e d . E x i s t i n g g e o l o g i c a l maps o f the area (Armstrong, 1956; 1957 and Roddick, 1965) were i n c o r p o r a t e d i n t o t h i s stage o f the study. F i e l d work was c a r r i e d out i n June and J u l y , 19 76 du r i n g which the d i s t r i b u t i o n o f g e o l o g i c a l m a t e r i a l s was mapped on the b a s i s o f exposures i n creek beds, on steep b a r r e n s l o p e s , i n sand and g r a v e l p i t s , and i n roadcuts and a s s o c i a t e d shallow e x c a v a t i o n s . L o c a t i o n s o f exposures were p l o t t e d onto the a i r photographs. M a t e r i a l s were d e s c r i b e d i n the f i e l d by n o t i n g such p h y s i c a l c h a r a c t e r i s t i c s as t e x t u r e , s t r u c t u r e , and drainage. Subsurface records from the G e o l o g i c a l Survey of Canada (G.S.C.) Urban Geology F i l e a i ded i n the i n t e r p r e t a t i o n o f v e r t i c a l and h o r i z o n t a l d i s t r i b u t i o n o f g e o l o g i c a l m a t e r i a l s . Contacts between the g e o l o g i c a l u n i t s were f i n a l i z e d on the photographs b e f o r e being t r a n s f e r r e d t o a base map. 65 r e p r e s e n t a t i v e samples of the s i g n i f i c a n t s u r f i c i a l sediments were c o l l e c t e d i n the f i e l d f o r l a b o r a t o r y analyses o f p h y s i c a l c h a r a c t e r i s t i c s . A c t u a l s i t e s sampled were f a r fewer than the number of f i e l d - 12 -o b s e r v a t i o n s recorded. During the g e o l o g i c a l f i e l d - c h e c k i n g a b a s i c i n v e n t o r y o f s u r f a c e h y d r o l o g i c a l f e a t u r e s was a l s o mapped on the a i r photographs. T h i s mainly c o n s i s t e d of, walking a l l the drainage channels and i d e n t i f y i n g seepage s i t e s and wetlands. H y d r o l o g i c a l i n f o r m a t i o n was a l s o t r a n s f e r r e d to the base map. Laboratory work i n c l u d e d mechanical a n a l y s i s f o r g r a i n s i z e d i s t r i b u t i o n o f the c o a r s e r f r a c t i o n o f the sediments. A t t e r b e r g L i m i t s ( l i q u i d and p l a s t i c l i m i t s ) were determined, where necessary, on the f i n e f r a c t i o n i n accordance w i t h the U n i f i e d S o i l C l a s s i f i c a t i o n System. I n t e r p r e t a t i o n s o f the p h y s i c a l c h a r a c t e r i s t i c s o f s u r f i c i a l sediments and bedrock f o r r e s i d e n t i a l use depends on g e o l o g i c a l h i s t o r y , t e x t u r e , s t o n i n e s s , drainage and p e r m e a b i l i t y , and c o m p r e s s i b i l i t y . The geomorphic i n v e n t o r y i s d i s c u s s e d i n separate chapters and presented on a s e r i e s o f maps prepared a t a s c a l e o f 1:9600 and reduced 50%. The topographic base map was compiled from reduced v e r s i o n s o f a number of l a r g e s c a l e 1(112400) mmapssheeiiS. Contours on these maps are i n f e e t thus any d i s c u s s i o n i n v o l v i n g e l e v a t i o n i s i n f e e t w i t h a m e t r i c e q u i v i l a n t b r a c k e t e d . A l l other measurements use onl y the m e t r i c system. Resource i n f o r m a t i o n presented on these maps i n c l u d e s l a n d - u s e , . l o c a t i o n o f s u r f i c i a l exposures and bedrock ou t c r o p s , s u r f i c i a l geology, topography, s l o p e , and s u r f a c e hydrology. Seismic r i s k and mi c r o z o n a t i o n o f the Seymour area were eva l u a t e d u s i n g i n f o r m a t i o n p r o v i d e d by the V i c t o r i a G e o p h y s i c a l Observatory. An estimate o f earthquake p r o b a b i l i t y f o r the area i s based on recorded earthquake h i s t o r y . Seismic m i c r o z o n a t i o n i s dependent on the d i s t r i b u t i o n o f g e o l o g i c a l m a t e r i a l s . A medium s c a l e map shows the zones of r e l a t i v e earthquake i n t e n s i t y . C o n s t r a i n t s to urban r e s i d e n t i a l development posed by geology, topography, s e i s m i c i t y , and hydrology are d i s c u s s e d i n a summary s e c t i o n a t the end of the a p p r o p r i a t e c h a p t e r s . The s e v e r i t y o f the l i m i t i n g p h y s i c a l c h a r a c t e r i s t i c s c o n t r i b u t i n g to these c o n s t r a i n t s are a l s o d e f i n e d . O v e r a l l geomorphic c o n s t r a i n t s to development are determined i n a t a b l e compiled from these l i m i t i n g f a c t o r s . D e f i n i t i v e c h a r a c t e r i s t i c s i n c l u d e s l o p e , depth to bedrock, m a t e r i a l t e x t u r e and s t o n i n e s s , depth t o water t a b l e , drainage, c o n s o l i d a t i o n h i s t o r y , f l o o d frequency, and s t a b i l i t y o f s u r f i c i a l m a t e r i a l . Areas of h i g h , medium, and low geomorphic c o n s t r a i n t are d i s c u s s e d i n the f i n a l chapter and summarized on two maps. - 14 -CHAPTER I I URBANIZATION AND THE GEOMORPHIC ENVIRONMENT U r b a n i z a t i o n and Geomorphic Problems The p h y s i c a l landscape has always been a major f a c t o r i n the l o c a t i o n and development o f s e t t l e m e n t s , p a r t i c u l a r l y i n the e v o l u t i o n o f t h e i r s p a t i a l p a t t e r n . Although parent m a t e r i a l and topography on which development occurs are major s i t e f a c t o r s , o t h e r elements such as water r e s o u r c e s , l a n d -water boundaries, and c l i m a t e are u s u a l l y important. D i r e c t i o n a l and a r e a l c o n s t r a i n t s t o u r b a n i z a t i o n are imposed by the economic, s o c i a l , and environmental c o s t s o f overcoming geomorphic o b s t a c l e s . (Legget., 1973). The n e g l e c t of t e r r a i n s t u d i e s i n urban and r e g i o n a l p l a n n i n g c o n t r i b u t e s to these c o s t s by f a i l i n g to i d e n t i f y n a t u r a l c o n d i t i o n s which may l a t e r l e a d to development-related problems. The e f f e c t s o f geomorphology on development are wide ranging i n type and degree o f s e v e r i t y . Some o f the more' common cases c i t e d by Gray (1972) and Legget (1973) i n v o l v e ground subsidence o r s e t t l i n g . When development moves onto h i l l s i d e s and r i d g e s a p a r t i c u l a r s e t of geomorphic f a c t o r s becomes important. S t a b i l i t y of slopes i s dependent on a combination o f elements i n c l u d i n g geology, topography, hydrology, and c l i m a t e . A n a t u r a l v a r i a t i o n i n any o f these f a c t o r s c o u l d l e a d to i n s t a b i l i t y as c o u l d any major n a t u r a l d i s t u r b a n c e such as an earthquake. (Eschman and Marcus, 1972). - 15 -However, what i s of concern here i s t h a t a number of man-made dis t u r b a n c e s a s s o c i a t e d w i t h u r b a n i z a t i o n can cause slope f a i l u r e . T r i g g e r i n g a c t i o n s i n c l u d e c u t t i n g and f i l l i n g f o r r e s i d e n t i a l h i l l s i d e developments, v i b r a t i o n s from machinery, and a l t e r a t i o n of h i l l s i d e hydrology. Removal of v e g e t a t i o n from s l o p e s , p a r t i c u l a r l y t r e e s and woody p l a n t s , can a l s o cause a c c e l e r a t e d e r o s i o n and slope f a i l u r e . (Gray, 1970). The c o a s t a l zone of C a l i f o r n i a , mainly around San F r a n c i s c o and areas to the south, i s a r e g i o n where urban development has taken p l a c e i n recent years without adequate s t u d i e s of the many geomorphic hazards t h a t e x i s t . ( W i l l i a m s , 1975; L e i g h t o n , 1975; 1976; and W i l l i a m s and B e d r o s s i a n , 19 76). Most of these geomorphic problems are manifested i n slope i n s t a b i l i t y which has been a c c e l e r a t e d by man's a c t i v i t i e s . ( S u l l i v a n , 1975; Meehan e t a l , 1975; and Pestrong, 1976). In the p l a n n i n g and development of urban areas not only must the subsurface geology be known, but the p o s s i b i l i t y of d i s t u r b a n c e of the s u r f a c e must a l s o be c o n s i d e r e d . Geomorphic hazards w i l l be r a r e however they must.be c o n s i d e r e d as p o s s i b i l i t i e s i n a l l urban p l a n n i n g . In some cases, n a t u r a l f a c t o r s w i l l l e a d to a s e r i o u s hazard, whereas i n other cases, the works of man may serve to i t e n s i f y the degree of n a t u r a l hazard. Legget (1973) i n c l u d e s the f o l l o w i n g as geomorphic hazards; v o l c a n i c a c t i o n , f a u l t s , earthquakes, tsunamis, f l o o d s , and slope i n s t a b i l i t y . Man's a b i l i t y to prevent l o s s e s from - 16 -some hazards i s g r e a t e r than i t i s f o r o t h e r s . Through a combination of land-use r e g u l a t i o n s , a p p r o p r i a t e c o n s t r u c t i o n t echniques, and means of h i l l s i d e s t a b i l i z a t i o n , l o s s e s caused by hazards such as l a n d s l i d i n g and f l o o d i n g may be g r e a t l y reduced. However, l o s s e s from earthquakes, tsunamis, and e r o s i o n are s t i l l only p a r t i a l l y p r e v e n t a b l e . Earthquake" Hazard Earthquake shaking, caused by the r e l e a s e of s e i s m i c energy, i s p o t e n t i a l l y the most hazardous geomorphic f a c t o r i n many areas because i t i s the most widespread and common e f f e c t o f any given earthquake. (Williams and B e d r o s s i a n , 1976). Earthquakes of h i g h R i c h t e r magnitude g e n e r a l l y produce ground motions of longer d u r a t i o n , h i g h e r a c c e l e r a t i o n and amplitude, and a g r e a t e r percentage o f lower f r e q u e n c i e s . (Housner, 1970). The i n t e n s i t y of ground shaking a t a p a r t i c u l a r l o c a t i o n depends on a number o f p a r t l y i n t e r r e l a t e d v a r i a b l e s i n c l u d i n g : R i c h t e r magnitude; d i s t a n c e from c a u s a t i v e f a u l t ; f o c a l depth; f a u l t plane geometry and d i r e c t i o n of f a u l t movement; type o f s u r f i c i a l and bedrock m a t e r i a l ; and g e n e r a l c o n d i t i o n s o f topography and geomorphology. ( W i l l i a m s , 1975) . Earthquake damage i s caused mainly by ground shaking as w e l l as by secondary e f f e c t s c h a r a c t e r i z e d by ground f a i l u r e . Types o f ground f a i l u r e induced by earthquakes i n c l u d e l a n d s l i d i n g , l i q u e f a c t i o n , l a t e r a l s p r e a d i n g , l u r c h i n g , - 17. -and d i f f e r e n t i a l s e t t l i n g . The Alaskan earthquake of 1974 p r o v i d e s a reeent example o f tremendous damage done to an urban area by the combination of ground shaking and ground f a i l u r e . (Gray, 1974; Legget, 1973; Seed, 1970; Seed and Wilson, 1967). Urban Hydrology The most f o r c e f u l land-use change which a f f e c t s the h y d r o l o g i c a l f u n c t i o n i n g of a stream b a s i n i s u r b a n i z a t i o n . V i r t u a l l y a l l watershed m o d i f i c a t i o n can be t r a c e d to changes i n land-use and geomorphology which accompany the t r a n s i t i o n of a stream b a s i n from a r u r a l to an urban one. These land-use and geomorphic t r a n s f o r m a t i o n s of a watershed come about by g r a d i n g p r a c t i c e s used to develop roads and b u i l d i n g s i t e s . Slopes are changed, both i n magnitude and s p a t i a l p o s i t i o n w i t h i n the watershed, c a u s i n g changing p a t t e r n s of o v e r l a n d flow. F i r s t and second order stream b a s i n s are o f t e n completely removed, and i n many cases, more than compensated f o r by the drainage network formed by newly c o n s t r u c t e d s t r e e t s and storm sewers. T h i s u s u a l l y leads to an i n c r e a s e d drainage d e n s i t y and consequently an i n c r e a s e i n e f f i c i e n c y Of the stream system i n removing water from the b a s i n . ( S a v i n i and Kammerer, 1961 and Roberts, 1972). The e f f e c t of man's a c t i v i t i e s i n urban development i s to a l t e r the f l o o d hydrology, sediment p r o d u c t i o n , and d i s c h a r g e - 18 -c h a r a c t e r i s t i c s of the watershed, as well as transforming the qua l i t y of the water. Increased flood magnitude and frequency caused by urbanization i s the main change i n stream flow regime as summarized by Leopold (1968) and Schaake (1972). They attributed t h i s increase i n flood p o t e n t i a l of an urban watershed to: an increase i n impervious surface area which increases surface runoff and decreases the amount of water which i n f i l t r a t e s into the ground; paving, straightening, or otherwise "improving" stream channels which reduces lag time between r a i n f a l l and stream runoff; landscaping and subdividing land into b uilding s i t e s which shortens the distance over which water flows before reaching a drainage channel, thereby reducing lag time; and f i l l i n g i n and developing flood plains which reduces space available for flood water i n the valley bottom so that the water i s forced to r i s e and flow more rapidly. Most of Leopold's (1968) discussion has been substantiated by numerous case studies which have examined the variation i n runoff volumes brought on by urban expansion. Studies such as those of Tholin and Keifer (1960), Carter (1961), TAnderson (1963) , Brater (1968), Brater and Sangal (1969) , Espey and Winslow (19 69) , and M i l l e r and Viessman (1972) examined the effects of changing the physcial c h a r a c t e r i s t i c s of a watershed on t o t a l runoff and peak flow. - 19 -They agreed t h a t the main e f f e c t on f l o o d r u n o f f i s i n c r e a s e d peak flow caused by decreased i n f i l t r a t i o n c h a r a c t e r i s t i c s of the b a s i n . Increased peak flows of 2 to 4 times t h a t of p r e - u r b a n i z a t i o n l e v e l s are caused by a c c e l e r a t i o n and c o n c e n t r a t i o n of f l o o d water by r u n o f f from impervious areas and by c o n s t r u c t i o n of storm sewers, g u t t e r s , c a t c h b a s i n s , and channel improvements which decrease l a g time by a f a c t o r of 3 to 4. Hammer (1972) s t a t e s t h a t stream channels respond to urban development by e n l a r g i n g i n roughly the same p r o p o r t i o n as the i n c r e a s e i n peak flow. H o l l i s (1975) r e p o r t s r t h a t s t u d i e s show an i n c r e a s e i n frequency and magnitude of s m a l l f l o o d s w i t h u r b a n i z a t i o n because paved s u r f a c e s produce r u n o f f and a r i s e i n stream flow from very modest rains t r o m s which would be completely absorbed by s o i l storage i f they were to occur over a non-developed catchment. He a l s o suggests t h a t the e f f e c t of u r b a n i z a t i o n on f l o o d s d e c l i n e s as f l o o d magnitudes i n c r e a s e . During severe and prolonged r a i n s t o r m s , a r u r a l b a s i n may become s a t u r a t e d and i t s channel network so extended t h a t i t responds h y d r o l o g i c a l l y as i f i t were an impervious catchment w i t h a dense network of s u r f a c e d r a i n s , consequently f l o o d s of a type and s i z e s i m i l a r to those of urban c o u n t e r p a r t s are produced. H o l l i s (1975) s t a t e s t h a t f l o o d s with a r e t u r n -p e r i o d o f g r e a t e r than 150 years are not m a t e r i a l l y a f f e c t e d by urban development. Martens (1968) claims the e f f e c t s of u r b a n i z a t i o n are n e g l i g i b l e f o r f l o o d s exceeding a 50-year r e t u r n - p e r i o d . - 20. -The i n c r e a s e i n sediment y i e l d s from b a s i n s p a r t i a l l y under development may range from 2 to 10 times the y i e l d s from n a t u r a l areas ( K e l l e r , 1962), whereas y i e l d s from areas completely under development range from 20 to 200 times n a t u r a l y i e l d s . (Guy, 1967; Guy and Ferguson, 1962; 1970; Wolman and Schick, 1967; and Schaake, 1972). In sma l l areas, denudation of n a t u r a l cover to expose u n d e r l y i n g s o i l i n a c t i v i t i e s such as i n t e n s i f i e d l o c a l c o n s t r u c t i o n or highway development may l e a d to sediment d e r i v e d by e r o s i o n from an acre of d i s t u r b e d ground to exceed 20,000 to 40,000 times the amount eroded from woodlands i n an e q u i v i l a n t time p e r i o d . (Leopold, 1968; V i c e e t a l , 1969; and P a r i z e k , 1971). * The amount o f sediment t r a n s p o r t e d at any time depends on the r a t e of stream flow. I t has been found t h a t most sediment c a r r i e d by a stream i s moved by i n f r e q u e n t , h i g h d i s c h a r g e flows. (Swenson, 1964; Dawdy, 1967; Leopold, 1968; and Schaake, 1972). TABLE I E f f e c t of Land-Use Change on R e l a t i v e Sediment Y i e l d and Channel S t a b i l i t y . ( a f t e r Guy, 1970). Land-Use Sediment Y i e l d Channel S t a b i l i t y N a t u r a l f o r e s t , g r a s s l a n d . Low Low R e l a t i v e l y s t a b l e , some e r o s i o n . H e a v i l y grazed area. Low-moderate > Less s t a b l e than above. Cropping Moderate-heavy Some aggradation and i n c r e a s e d bank e r o s i o n . Retirement of land from c r o p p i n g . Low-moderate Increased s t a b i l i t y . Urban c o n s t r u c t i o n . Very heavy Rapid aggradation, some bank e r o s i o n . S t a b l i l i z a t i o n . Moderate Degradation and severe bank e r o s i o n . S t a b l e urban. Low-moderate R e l a t i v e l y s t a b l e . The a l t e r a t i o n of stream d i s c h a r g e , peak flows and sediment y i e l d by u r b a n i z a t i o n w i t h i n the stream b a s i n i s a v a r i a b l e and t r a n s i e n t c o n d i t i o n . (Crippen, 19 69 and Graf, 19 75). No two streams w i l l r e a c t to urban development i n the same way nor w i l l there n e c e s s a r i l y be a p r e d i c t a b l e p a t t e r n i n the long-term d i s c h a r g e , f l o o d , and sediment y i e l d c h a r a c t e r i s t i c s of the streams. P r e d i c t i o n of the h y d r o l o g i c a l e f f e c t s o f u r b a n i z a t i o n must account f o r the f a c t t h a t streamflow i s not generated u n i f o r m l y over a watershed but i s dependent on v a r i a b l e source areas. (Gregory and Walling,1973). Runoff i s produced p r e f e r e n t i a l l y from c e r t a i n zones of a catchment depending on the l o c a l p h y s i c a l c o n d i t i o n s , causing d i f f e r e n t i a l o p e r a t i o n of f l u v i a l processes across a watershed. The f u n c t i o n i n g of a stream b a s i n a f t e r urban development w i l l depend on how much a l t e r a t i o n there has been to the n a t u r a l geomorphology, v e g e t a t i o n , and c l i m a t e of each source area which e x i s t e d p r i o r t o u r b a n i z a t i o n . G e n e r a l i z a t i o n s o f the p o s s i b l e h y d r o l o g i c a l e f f e c t s of changes i n land-use are summarized i n Table I I . Ground S t a b i l i t y A g e o l o g i s t who i s i n v e s t i g a t i n g an area f o r p o t e n t i a l l y u n s t a b l e ground must be prepared t o encounter an almost i n f i n i t e v a r i e t y o f g e o l o g i c and h y d r o l o g i c combinations. On the b a s i s of s u r f a c e i n d i c a t i o n s and l i m i t e d subsurface i n f o r m a t i o n , he should be able to i d e n t i f y - 22 -TABLE II Possible Hydrological Effects of Changes i n Land-Use, (after Savini and Kammerer, 1961). Change i n Land-Use Possible Hydrologic E f f e c t 1. Transition from Pre-Urban to Early Urban Stage. Removal of trees or vegetation. Construction of scattered houses and limited water and sewage f a c i l i t i e s . Decrease i n transpiration, increase i n streamflow. Increased sedimentation of streams. 2. Transition from Early Urban to Mid-Urban Stage. Bulldozing of land for mass housing, t o p s o i l removed, farm ponds f i l l e d i n . Mass construction of houses, paving of streets, b u i l d i n g of culverts. Accelerated land erosion and stream sedimentation and aggradation. Increased flood flows. Elimination of smallest streams. Decreased i n f i l t r a t i o n , increased flood flows, and lowering of water table. Flooding at channel contrictions on remaining small streams. Occasional overtopping or undermining of banks of a r t i f i c i a l channels. 3. Transition from Mid-Urban to late Urban Stage. Urbanization complete by addition of houses, streets, commercial and i n d u s t r i a l buildings. Stream channels r e s t r i c t e d due to a r t i f i c i a l channels. Construction of sanitary drainage systems and treatment plants for sewage. Improvement of storm drainage systems. Reduced i n f i l t r a t i o n , lower water table. Streets and gutters act as storm drains creating higher flood peaks and lower base flow of l o c a l streams. Increased flood peaks. Change i n channel geometry and sediment load. Aggradation. Removal of additional water from area, decreased i n f i l t r a t i o n , lower water table. Decreased i n f i l t r a t i o n . _ 23 _ favourable and unfavourable ground. In order to do t h i s he must understand not only the l o c a l geology but also the basic laws of s o i l mechanics. For land-use planning, slopes can generally be rated as having l i t t l e or no tendency to s l i d e , having a tendency to develop l o c a l and s u r f i c i a l f a i l u r e s , and having a p o t e n t i a l for slope f a i l u r e of a magnitude that i s d i f f i c u l t or unfeasible to prevent or repair. (Leighton, 19 76). At the l a t t e r two l e v e l s , c r i t i c a l strength parameters can be determined from subsurface exploration, and more detailed guidelines and geotechnical maps of land-use c a p a b i l i t y can be prepared. Areas where f a i l u r e has already taken place can be readi l y i d e n t i f i e d by indications of previous movement. Ground s t a b i l i t y can be thought of as the safety of an earth mass against f a i l u r e or movement. Every mass of s o i l located beneath sloping ground has a tendency to move downward and outward under the influence of gravity. (Terzaghi and Peck, 1967). If this tendency i s counteracted by the shearing resistance (shear strength) of the s o i l then the slope i s stable. However, i f the shear strength of the s o i l becomes less than the shear stress (disturbing force) acting over a continuous surface then f a i l u r e occurs. In general terms the s t a b i l i t y of a slope may be defined by a safety factor (F ) where: 1.) F = £ forces r e s i s t i n g slope f a i l u r e £ disturbing forces If F_ i s greater than 1.0 s t a b i l i t y i s probable, but i f F g i s less than 1.0 i n s t a b i l i t y e x i s t s . The c a l c u l a t i o n of F o depends - 24 -upon on-site measurements of the c r i t i c a l engineering parameters of the materials. However th i s stage i s only required af t e r good reasons have been found for suspecting that mass movement i s possible. (Cooke and Doornkamp, 1974). Predicting the p o s s i b i l i t y of mass movement i s usually based on an analysis of the geomorphic features and processes which may increase s o i l stress or decrease s o i l strength. I t i s important to note the e f f e c t of water which i s involved i n many of these factors. The main causes of i n s t a b i l i t y are summarized i n the following tables which are based on similar l i s t s found i n Sowers and Sowers (19 70), Terzaghi and Peck (1967), and Cooke and Doornkamp (19 74). TABLE III Factors Leading to an Increase i n Shear Stress 1. Removal of l a t e r a l or underlying support. - erosion by water (streams, waves) or g l a c i e r ice - weathering of weaker strata at the toe of a slope - erosion of granular material by seepage (piping) - man-made cuts and excavations; draining of lakes or reservoirs 2. Surcharge. - natural accumulation of water, snow, talus - human construction; f i l l , buildings 3. Transitory earth stresses. - earthquakes - continual passing of heavy t r a f f i c ; b l a s t i n g 4. Increased l a t e r a l pressure. - water i n v e r t i c a l cracks - freezing water i n cracks - swelling material - root wedging TABLE IV Factors Leading to a Decrease i n Shear Strength 1. I n i t i a l weak state of materials. - composition: inherently weak material - texture: looseness, roundness of grains - 25 -- s t r u c t u r e : f a u l t s , j o i n t s , bedding p l a n e s , massive beds o v e r l y i n g weak m a t e r i a l , s t r a t a i n c l i n e d toward f r e e face of a s l o p e , a l t e r n a t i n g permeable and impermeable beds, method of d e s p o s i t i o n ( g e o l o g i c s t r e s s h i s t o r y ) 2. Changes caused by weathering. - p h y s i c a l d i s i n t e g r a t i o n - h y d r a t i o n of c l a y m i n e rals - d e s s i c a t i o n of c l a y minerals - l e a c h i n g 3. Changes i n i n t e r g r a n u l a r f o r c e s caused by pore water. - buoyancy i n s a t u r a t e d s t a t e - l o s s o f c a p i l l a r y t e n s i o n upon s a t u r a t i o n - seepage p r e s s u r e of p e r c o l a t i n g groundwater 4. Changes i n s t r u c t u r e . - f i s s u r i n g o f p r e c o n s o l i d a t e d c l a y s because of the r e l e a s e of l a t e r a l p r e s s u r e - breakdown of loose or honeycombed s o i l s t r u c t u r e upon d i s t u r b a n c e The shear s t r e n g t h of a s o i l i s the maximum a v a i l a b l e r e s i s t a n c e t h a t i t has to movement induced by shear s t r e s s . Shear s t r e n g t h (s) is, .a f u n c t i o n of the f r i c t i o n a t g r a i n to g r a i n c o n t a c t , and i s r e l a t e d to the amount of g r a i n i n t e r l o c k i n g . T h i s i n t e r l o c k i n g i n c r e a s e s w i t h a n g u l a r i t y and d e n s i t y of packing ( c o n s o l i d a t i o n ) of the g r a i n s and these c o n t r o l the angle o f s h e a r i n g r e s i s t a n c e (0'). In a d d i t i o n , shear s t r e n g t h i s r e l a t e d to the e f f e c t i v e s t r e s s t r a n s m i t t e d between p a r t i c l e s (&') and t h e i r apparent cohesion ( c ' ) . (Cooke and Doornkamp, 1974). For normally c o n s o l i d a t e d cohesive and c o h e s i o n l e s s s o i l s : 2.) s = cr" tan 0' For o v e r c o n s o l i d a t e d cohesive s o i l s : 3.) s = c' + <T' tan 0' where s i s the shear s t r e n g t h a t the p o t e n t i a l f a i l u r e s u r f a c e . - 26 -The s t r e n g t h (and c o m p r e s s i b i l i t y ) of s o i l s depends very much on water pre s s u r e s as i n d i c a t e d by the f o l l o w i n g r e l a t i o n s h i p : 4.) a 1 = <r - u where <ry = e f f e c t i v e s t r e s s <T - t o t a l s t r e s s u = pore water p r e s s u r e Pore-water pr e s s u r e s are m o d i f i e d by the type o f m a t e r i a l . For example, i n c l a y s the pore p r e s s u r e w i l l vary from the i n i t i a l or immediate s t a t e to the long-term c o n d i t i o n . I n i t i a l l y when a c l a y i s loaded or unloaded (change i n t o t a l s t r e s s ) , the pore-water p r e s s u r e a l s o changes. Because of the low p e r m e a b i l i t y o f c l a y , excess pore p r e s s u r e s d i s s i p a t e s l o w l y , but, e v e n t u a l l y w i l l r e t u r n to t h a t d i c t a t e d by the l o c a l groundwater t a b l e . I n i t i a l l y then, pore-water p r e s s u r e i s a d i r e c t f u n c t i o n o f the t o t a l s t r e s s a p p l i e d to the s o i l but u l t i m a t e l y w i l l reach an e q u i l i b r i u m s t a t e where there i s no r e l a t i o n to the t o t a l s t r e s s . In sands however, the p e r m e a b i l i t y i s s u f f i c i e n t l y h i g h t h a t no change i n pore p r e s s u r e occurs f o r normal l o a d i n g r a t e s . Thus pore-water pr e s s u r e i s governed by groundwater t a b l e alone. Shear s t r e n g t h s o f s o i l s w i l l vary g r e a t l y depending on the p h y s i c a l c o n d i t i o n s , and p a r t i c u l a r l y on the degree of s a t u r a t i o n . A s p e c i a l case of i n s t a b i l i t y i n s a t u r a t e d c o h e s i o n l e s s m a t e r i a l ( s a n d and s i l t ) can r e s u l t from earthquake shock. Shear s t r e s s , induced by an earthquake, w i l l cause d e n s i f i c a t i o n or volume decrease of a l o o s e s o i l mass and a cor r e s p o n d i n g r i s e - 27 -i n pore-water p r e s s u r e . Depending on the time p e r i o d of shock-induced shear ( i e . r a p i d l o a d i n g ) , the p e r m e a b i l i t y may be i n s u f f i c i e n t to d r a i n the excess pore water. Consequently pore p r e s s u r e s i n c r e a s e w i t h each shock, thereby lowering the e f f e c t i v e s t r e s s . I f pore p r e s s u r e s i n c r e a s e to a value equal to the t o t a l s t r e s s , the e f f e c t i v e s t r e s s goes t o zero, c a u s i n g a complete l o s s of s t r e n g t h ( l i q u e f a c t i o n ) o f the s o i l . (Equations 4 and 2). When a s o i l l i q u e f i e s , water i s i n c o n t a c t w i t h a l l g r a i n s which; can l e a d to massive movement of the m a t e r i a l . I f a s o i l i s l i q u e f i e d a t depth, movement w i l l occur w i t h the o v e r l y i n g m a t e r i a l c a r r i e d r e l a t i v e l y i n t a c t . On slopes the e f f e c t i v e s t r e s s does not have to equal zero b e f o r e causing f a i l u r e . The r i s e i n pore-water p r e s s u r e w i l l cause a dramatic l o s s i n s t r e n g t h which, once i t drops below the shear s t r e s s , w i l l l e a d to i n s t a b i l i t y . When t h i s happens, movement al o n g a f a i l u r e plane can occur. Although t h i s movement may not n e c e s s a r i l y be l a r g e , c a u s i n g any s e r i o u s problems i t s e l f , i f i t occurs r e p e a t e d l y i t may remold the s o i l , i n c r e a s e pore p r e s s u r e s , and decrease s t r e n g t h , which w i l l u l t i m a t e l y l e a d to a l a r g e - s c a l e slope f a i l u r e . The cohesiveness o f c l a y prevents i t from responding to earthquake shock as d r a m a t i c a l l y as sand and s i l t . C oarser c o h e s i o n l e s s m a t e r i a l (gravel) has a s u f f i c i e n t l y h i g h p e r m e a b i l i t y to prevent any.buildup o f pore-water p r e s s u r e i f allowed to d r a i n p r o p e r l y . Unsaturated, loose sand and s i l t w i l l s t i l l tend to d e n s i f y under r a p i d shear s t r e s s , however - 28 -with no pore-water present, the main r e s u l t w i l l be compaction and s e t t l i n g o f the s o i l . S aturated c o h e s i o n l e s s sediments i n i t i a l l y i n a dense s t a t e w i l l tend to expand on s h e a r i n g , consequently n e g a t i v e pore p r e s s u r e s develop and s o i l s t r e n g t h t e m p o r a r i l y i n c r e a s e s . I t i s g e n e r a l l y agreed, the denser the s o i l the s a f e r the s l o p e . (Dr. P. Byrne, 1975. P e r s o n a l Communication). Geomorphology and Urban Land-Use P l a n n i n g When p l a n n i n g s t a r t s f o r an urban community the area to be developed must be co n s i d e r e d as an environment t h a t has been exposed f o r a long p e r i o d o f time to the e f f e c t s o f many n a t u r a l m o d i f y i n g f a c t o r s . The p r e s e n t day geomorphology o f an area i s the product o f complicated i n t e r a c t i o n s among g e o l o g i c , h y d r o l o g i c , topographic, c l i m a t i c and other processes and must be re s p e c t e d as such when c o n s i d e r i n g f u t u r e t e r r a i n changes. I t i s becoming much l e s s common f o r these processes to be n e g l e c t e d i n the development of c i t i e s or i n the p l a n n i n g of urban r e g i o n s . In f a c t , i n r e c e n t years much r e g i o n a l and l o c a l geomorphic mapping has been c a r r i e d out wit h the needs of r e g i o n a l and urban p l a n n i n g s p e c i f i c a l l y i n view. T h i s new tr e n d became popular w i t h the p u b l i c a t i o n o f "Design w i t h Nature" by Ian McHarg (1969). Through a s e r i e s o f examples he showed how urban s u i t a b i l i t y o f the land c o u l d be eva l u a t e d by c o m p i l i n g and mapping a l l b a s i c data p e r t a i n i n g to such f a c t o r s as c l i m a t e , h i s t o r i c a l geology, s u r f i c i a l geology, - 29 -physiography, hydrology, s o i l s , p l a n t ecology, w i l d - l i f e h a b i t a t , and land-use. Around the same time a number of s p e c i f i c i n t e r d i s c i p l i n a r y s t u d i e s were p u b l i s h e d which a p p l i e d geomorphic knowledge to land-use p l a n n i n g q u e s t i o n s . (Hilpman, 1968; M e t r o p o l i t a n Washington C o u n c i l o f Governments, 1968; and McComas e t a l , 1969). P r i o r to these s t u d i e s , p h y s i c a l problems i n the urban environment had been d e a l t w i t h by c o n c e n t r a t i n g on one p h y s i c a l parameter (eg. e n g i n e e r i n g geology) without always c o n s i d e r i n g the i n t e r a c t i o n among other f a c t o r s . (Radbruch, 1957 and Schlocker e t a l , 1958) . The I l l i n o i s S t a t e G e o l o g i c a l Survey has been very a c t i v e i n the a p p l i c a t i o n o f geomorphology to e n g i n e e r i n g , environmental, and p l a n n i n g problems. (Hacket and McComas, 1969; Gross, 1970; Jacobs, 1971; and Bergstrom e t a l , 1976) . These s t u d i e s c o n s i d e r geomorphology and n a t u r a l r e s o u r c e s to s o l v e land-use c o n f l i c t s between urban, a g r i c u l t u r a l , and min e r a l resource development. S i m i l a r s t u d i e s i n Alabama and Pennsylvania o u t l i n e the importance o f geomorphology to l a n d -use p l a n n i n g i n these s t a t e s . ( G e o l o g i c a l Survey of Alabama, 19 71 and Geyer and McGlade, 19 72) Perhaps the most comprehensive environmental study c a r r i e d out f o r a l o c a l urban area was a symposium compiled on the p h y s i c a l aspects of the environment o f T u l s a , Oklahoma. (Bennison, 19 73). The a p p l i c a t i o n o f land-use d e c i s i o n s based on n a t u r a l c o n s t r a i n t s i s w e l l i l l u s t r a t e d by Koons (1976) and Palmer (1976). V a r i o u s geomorphic f a c t o r s are d e f i n e d a c c o r d i n g to t h e i r developmental l i m i t a t i o n s and these are used to determine c o n f l i c t i n g and - 30 -compatible uses o f the l a n d . In C a l i f o r n i a u n c o n t r o l l e d urban sprawl has e n g u l f e d the landscape i n r e c e n t years w i t h l i t t l e r e g a r d f o r i t s a s s e t s or the hazards caused by i t s misuse. In r e c o g n i t i o n of t h i s problem the C a l i f o r n i a D i v i s i o n of Mines and Geology has made numerous c o - o p e r a t i v e s t u d i e s w i t h c i t i e s and c o u n t i e s i n the San F r a n c i s c o Bay area and has a l s o p u b l i s h e d an urban geology master p l a n f o r the s t a t e . ( A l f o r s e t a l , 19 73) . The Bay area l e a d s the United S t a t e s i n a c t i v e m u l t i - d i s c i p l i n a r y programs designed to understand and i d e n t i f y geomorphic hazards and to i n f o r m the p u b l i c i n such a manner t h a t the i n f o r m a t i o n may be r e a d i l y used i n land-use d e c i s i o n s . C a l i f o r n i a g e o l o g i s t s are a l s o i n v o l v e d w i t h s p e c i f i c u r b a n - r e l a t e d geomorphic problems. One p a r t i c u l a r area of concern i s the i d e n t i f i c a t i o n of unstable or p o t e n t i a l l y u n s t a b l e ground w i t h i n r e g i o n s of land intended f o r development. (Blanc and C l e v e l a n d , 1968; Brabb e t a l , 1972; and Hoexter e t . a l , 1977). Notable Canadian documents which d e s c r i b e the use of environmental geomorphology i n land-use p l a n n i n g include.works by S e r v i c e d' Urbanisme (1966) and P r e s t and Hode-Keyser (1977) who d i s c u s s the p h y s i c a l c h a r a c t e r i s t i c s of the Montreal r e g i o n and by C h r i s t i a n s e n (19 70) who d e s c r i b e s the p h y s i c a l environment of Saskatoon. In B r i t i s h Columbia there has been very l i t t l e i n i t i a t i v e on the p a r t of l o c a l governments to prepare p h y s i c a l s t u d i e s p r i o r to urban development. Most of the work i n v o l v i n g - 31 -geomorphic investigations i n the c i t y of Vancouver has been undertaken independently by the university as academic research, and as such, has had l i t t l e e f f e c t on further development. (Blunden, 1971; Cordonier, 1973; McLeod, 1973; Lim, 1974; and Watts, 1974). A major study on the physical environment of V i c t o r i a (Foster, 1976) examines s u r f i c i a l geology, seismic r i s k , waste disposal, and water resources of the c i t y , however, i t too i s a retrospective study of an area already urbanized. Land-use planning studies, based on natural environmental inventories and carried out p r i o r to large-scale urban development, have been prepared for Vancouver's North Shore region. (Environment Canada, 1973; Planning Dept., D i s t r i c t of North Vancouver, 1975; and Walmsley, 1977b). The Canada Land Inventory (C.L.I.) i s a comprehensive survey of land c a p a b i l i t y and use designed to provide a basis for resource and land-use planning. The objective of the C.L.I, i s to semi-quantitatively c l a s s i f y lands as to th e i r physical c a p a b i l i t y for use i n agricul t u r e , forestry, recreation, and w i l d l i f e . (C.L.I., 1970). The Resource Analysis Branch of the Ministry of Environment, Province of B r i t i s h Columbia has taken this an additional step and begun to c l a s s i f y land as to i t s s u i t a b i l i t y for urban development. (Beale and Rollerson, 19 75; Pattison, 19 77; Walmsley, 19 7 7a; 19 7 7b; and Block, 19 78). The geomorphic input i n such urban s u i t a b i l i t y studies consists of i d e n t i f y i n g t e r r a i n units and defining the - 32 -l i m i t a t i o n s t h a t some, p h y s i c a l c h a r a c t e r i s t i c s of these u n i t s pose to c e r t a i n urban land uses. The a p p l i c a t i o n of geomorphology to problems of urban land-use p l a n n i n g takes v a r i e d . f o r m s , not the l e a s t o f which i s communicating geomorphic i n f o r m a t i o n i n e a s i l y comprehensible terms to those i n v o l v e d i n the decision-making p r o c e s s . Mohorich (1971) and Baker (1975) d i s c u s s the r e s p o n s i b i l i t i e s o f g e o l o g i s t s i n a n a l y z i n g and p r e s e n t i n g data which c l e a r l y and simply show the p e r t i n e n t i n f o r m a t i o n . - 33 -CHAPTER I I I HISTORY AND DISTRIBUTION OF THE GEOLOGICAL MATERIALS I n t r o d u c t i o n Mapping and study of the geology was an e s s e n t i a l f i r s t step i n understanding the geomorphic c o n s t r a i n t s to urban development i n North Vancouver-Seymour. Because d i f f e r e n t types o f g e o l o g i c a l m a t e r i a l s are a p p r o p r i a t e f o r d i f f e r e n t urban uses, adequate data on t h e i r type and d i s t r i b u t i o n i s necessary i n the p l a n n i n g stage. Such c h a r a c t e r i s t i c s as t e x t u r e , drainage, s t o n i n e s s , d e p o s i t i o n a l h i s t o r y , and c o m p r e s s i b i l i t y can be used t o e v a l u a t e the m a t e r i a l s f o r use as fou n d a t i o n support, as a source of sand or g r a v e l , or f o r t h e i r s t a b i l i t y on s l o p e s . The p r e c i s i o n o f the g e o l o g i c a l map s u f f e r s from the i r r e g u l a r and v a r i e d q u a l i t y of s u r f a c e exposures. Areas a l r e a d y developed or f o r e s t e d areas w i t h deep s o i l had v i r t u a l l y no s u r f i c i a l exposures. The bes t s e c t i o n s were exposed i n areas of r e c e n t a c t i v e movement along the steep v a l l e y s i d e s of Lynn Creek and Seymour Ri v e r and i n the deeply i n c i s e d r a v i n e s o f the s m a l l e r streams. Most roadcuts, e x c a v a t i o n s , and creek beds only exposed t h i n s t r a t i g r a p h i c s e c t i o n s . Sand and g r a v e l p i t s , u s u a l l y a good p l a c e f o r s u r f i c i a l s e c t i o n s , have long been d i s u s e d and slope wash, r e v e g e t a t i o n , and r e g r a d i n g have covered much of the - 34 -s t r a t i g r a p h y . The G.S.C. Urban Geology F i l e p r o v i d e d numerous subsurface records which aided i n the i n t e r p r e t a t i o n s . However, these vary i n q u a l i t y from r e c o r d to r e c o r d and they are concentrated o n l y i n the Lynn Creek-Seymour R i v e r area. A g e n e r a l i z e d c o r r e l a t i o n o f Quaternary s t r a t i g r a p h y was a l s o h e l p f u l i n i n t e r p r e t i n g the d i s t r i b u t i o n o f s u r f i c i a l m a t e r i a l s . Throughout both t h i s chapter and Chapter VI, r e f e r e n c e should be made to the f o l l o w i n g maps and diagram: F i g u r e I I I - l f o r l o c a t i o n s o f bedrock outcrops, s u r f i c i a l exposures, boreholes and excavations (eg. GSC-374), s t r a t i g r a p h i c s e c t i o n s (eg. D-8), and samples of s u r f i c i a l sediments (eg. Sample 7); F i g u r e III-2 f o r s u r f a c e d i s t r i b u t i o n o f bedrock and s u r f i c i a l sediments; and F i g u r e I I I - 3 f o r v e r t i c a l d i s t r i b u t i o n o f the g e o l o g i c a l m a t e r i a l s . Information i n Appendices 1 and 2 i s a l s o p e r t i n e n t . Appendix 1 d e s c r i b e s the s t r a t i g r a p h i c s e c t i o n s l o c a t e d on F i g u r e I I I - l and Appendix 2 summarizes borehole, and e x c a v a t i o n logs recorded i n the G.S.C. Urban Geology F i l e . P revious Work The e a r l i e s t d e t a i l e d g e o l o g i c a l work i n t h i s area was by Burwash (1918) who d e s c r i b e d the s u r f i c i a l and bedrock geology o f the Greater Vancouver area and Howe Sound. In 1923, - 35 -Johnstone p u b l i s h e d the f i r s t map of s u r f i c i a l d e p o s i t s i n the Vancouver area as p a r t of a study of geology and sedimentation of the F r a s e r R i v e r d e l t a . The northern l i m i t of t h i s map-sheet i n c l u d e s the n o r t h shore o f B u r r a r d I n l e t up to about where Mt. Seymour Parkway cuts across the Seymour area. No f u r t h e r g e o l o g i c a l s t u d i e s p e r t i n e n t to North Vancouver-Seymour were p u b l i s h e d u n t i l Armstrong and Brown (1954) wrote a paper on the g l a c i o m a r i n e d e p o s i t s of the F r a s e r Lowland i n which they d e s c r i b e d s e c t i o n s from sand and g r a v e l p i t s i n the Seymour area. Roddick and Armstrong (1956) produced a p r e l i m i n a r y bedrock map of the Vancouver area (east h a l f ) which shows the g e n e r a l d i s t r i b u t i o n of Quarternary sediments. This was l a t e r r e p l a c e d by a r e v i s e d map and r e p o r t d e s c r i b i n g the bedrock, geology o f the North Shore. (Roddick, 1965). S u r f i c i a l geology o f the e n t i r e North Vancouver area was i n c l u d e d i n p r e l i m i n a r y s u r f i c i a l g e o l o g i c a l r e p o r t s of the Vancouver and New Westminster map-areas. (Armstrong, 1956; 1957). In 1961, Armstrong wrote a paper on s o i l s of the c o a s t a l area of southwestern B r i t i s h Columbia d e s c r i b i n g e n g i n e e r i n g and a g r i c u l t u r a l c h a r a c t e r i s t i c s of the v a r i o u s s u r f i c i a l d e p o s i t s . A c o r r e l a t i o n of l a t e P l e i s t o c e n e s t r a t i g r a p h y and chronology of the F r a s e r Lowland and northwestern Washington State was d e s c r i b e d i n a c l a s s i c j o i n t paper. (Armstrong e t a l , 1965). - 36 -Learning (1968) g e n e r a l l y d e s c r i b e s the d i s t r i b u t i o n of sand and g r a v e l i n the F r a s e r Lowland w i t h i n the context of the s u r f i c i a l geology of the r e g i o n . In a d d i t i o n to d i s c u s s i n g the technology of the sand and g r a v e l i n d u s t r y he a l s o b r i e f l y summarized the l o c a t i o n , geology, and h i s t o r y o f i n d i v i d u a l d e p o s i t s which were mined, i n c l u d i n g a number i n North Vancouver-Seymour. The complexity of po s t F r a s e r G l a c i a t i o n d e p o s i t i o n a l environments suggested by workers i n e a r l i e r s t u d i e s was confirmed by a study of p o s t - g l a c i a l c r u s t a l movement.in southwestern B r i t i s h Columbia and northwestern Washington S t a t e . (Mathews e t a l , 1970) . Recently Armstrong (1975a) r e p o r t e d on s t r a t i g r a p h i c s t u d i e s and r e - e v a l u a t i o n of h i s p r e l i m i n a r y s u r f i c i a l g e o l o g i c a l maps i n the F r a s e r Lowland. In the same year he a l s o b r i e f l y d e s c r i b e d the Quaternary geology of the Lowland f o r a f i e l d - t r i p guidebook.. (Armstrong, 1975b). Two major l i t h o s t r a t i g r a p h i c u n i t s u n d e r l y i n g Vashon t i l l have j u s t been r e d e f i n e d . (Clague, 1976; Armstrong and Clague,.1977). The most r e c e n t summary of the Quaternary s t r a t i g r a p h y of the F r a s e r Lowland,.discussed by Hicock (1976), was b r i e f l y p resented i n a G e o l o g i c a l A s s o c i a t i o n o f Canada f i e l d - t r i p guidebook. (Armstrong, 1977). There have been few l o c a l g e o l o g i c a l s t u d i e s c a r r i e d out i n North Vancouver-Seymour. P h i l i p (1961) d e s c r i b e d the geology and s t a b i l i t y o f a roadcut i n s u r f i c i a l sediments on Highway 401, about 1 km. west of Lynn Creek. (Figure 1-1). In 1974, Watts mapped the bedrock and s u r f i c i a l geology and d i s c u s s e d the e n g i n e e r i n g p r o p e r t i e s of the g e o l o g i c a l m a t e r i a l s f o r a s m a l l area e a s t o f Seymour R i v e r . The P l a n n i n g Dept., D i s t r i c t of North Vancouver's (1975) r e p o r t , d i s c u s s i n g the n a t u r a l environment of the Seymour area, c o n t a i n s a very g e n e r a l treatment of s u r f i c i a l geology, n e i t h e r showing the d i s t r i b u t i o n o f m a t e r i a l s nor f u l l y d e s c r i b i n g t h e i r c h a r a c t e r i s t i c s . A g e n e r a l i z e d d i s c u s s i o n of the s u r f i c i a l geology of North Vancouver-Seymour i s summarized from the w r i t e r ' s r e s e a r c h i n a f i e l d - t r i p guidebook. (Maynard, 1977). Bedrock Geology The Seymour area i s i n the southern end of the l a r g e complex of p l u t o n i c and metamorphic rocks comprising the Coast Mountains of B r i t i s h Columbia. S u r f i c i a l d e p o s i t s cover most of the bedrock to v a r i a b l e depths i n the southern p o r t i o n s of the study area, however at e l e v a t i o n s above about 650 f e e t (200 m.), bedrock i s g e n e r a l l y at or near the s u r f a c e , mantled by a t h i n cover of rubbly c o l l u v i u m or coarse t e x t u r e d s o i l . G r a n i t i c bedrock i s exposed i n p l a c e s along the deeply i n c i s e d lower v a l l e y s of Lynn Creek and Seymour R i v e r and at sea l e v e l around Deep Cove. P l u t o n i c r o c k s , Late J u r a s s i c to E a r l y Cretaceous i n age, have the o v e r a l l bulk composition of q u a r t z d i o r i t e , - 38 -c o n t a i n i n g both hornblende and b i o t i t e , the former dominant, and a sma l l amount of potassium f e l d s p a r . A c c o r d i n g to Roddick (1965) these i n t r u s i v e rocks are heterogeneous i n appearance, t e x t u r e , and composition, p a r t i c u l a r l y those t h a t are h o r n b l e n d e - r i c h ; j o i n t s and f r a c t u r e s are not c l o s e l y spaced nor uniform over l a r g e areas; the main minerals are p l a g i o c l a s e , hornblende, b i o t i t e , q u a r t z , and K - f e l d s p a r w i t h minor amounts of s e r i c i t e , e p i d o t e , and c h l o r i t e ; and a l t e r a t i o n i s g e n e r a l l y l i m i t e d to narrow zones of k a o l i n i z a t i o n o f the f e l d s p a r s . In the Seymour area p l u t o n i c rocks g e n e r a l l y seem to grade from west t o e a s t from a f i n e - g r a i n e d hornblende d i o r i t e through medium-coarse-grained hornblende b i o t i t e g r a n o d i o r i t e to c o a r s e - g r a i n e d hornblende q u a r t z monzonite. Near Lynn Creek the d i o r i t i c rocks are medium to very f i n e - g r a i n e d i n t e x t u r e and range from q u a r t z d i o r i t e to gabbro i n composition.. In the immediate v i c i n i t y of Lynn Creek canyon, bedrock i s c h a r a c t e r i s t i c a l l y f i n e - g r a i n e d , weakly f o l i a t e d , f r a c t u r e d , and i n t r u d e d by numerous a p l i t i c v e i n s and d i k e s . F o l i a t i o n i s not w e l l developed buteiapparently trends north-south. N o r t h e r l y t r e n d i n g f r a c t u r e zones are c h a r a c t e r i z e d by c l o s e l y spaced (10-25 cm.) j o i n t s and f r a c t u r e s . Bedrock exposed away from the canyon i s c o a r s e r g r a i n e d w i t h very widely spaced f r a c t u r e s . I t appears t h a t the canyons of Lynn Creek and Seymour R i v e r r e p r e s e n t zones of weakness i n the bedrock eroded by f l u v i a l downcutting i n p o s t - g l a c i a l time. - 39 -The south-west f l a n k of Seymour Mountain c o n s i s t s mainly of medium-fine to c o a r s e - g r a i n e d hornblende b i o t i t e g r a n o d i o r i t e . The c o m p o s i t i o n a l h e t e r o g e n e i t y seems to be due to a v a r i a t i o n i n b i o t i t e and K-keldspar content. Small mafic i n c l u s i o n s are common i n the u n f o l i a t e d rock. No r e g u l a r f r a c t u r e p a t t e r n was seen although many i n d i v i d u a l f r a c t u r e s are e n c l o s e d i n t h i n a l t e r a t i o n envelopes. On the south-east s i d e of Seymour Mountain and i n the Cove C l i f f area south of Deep Cove, bedrock i s mainly medium to c o a r s e - g r a i n e d hornblende q u a r t z monzonite with some g r a n o d i o r i t e . Rocks i n t h i s area are c o m p o s i t i o n a l l y and t e x t u r a l l y much l e s s v a r i a b l e than to the west, a l s o ' i n c l u s i o n s and f i n e - g r a i n e d m a f i c - r i c h bands are commoner i n the q u a r t z monzonite. B i o t i t e i s r a r e and much of the hornblende shows some degree of c h l o r i t i z a t i o n . The rock i s not f o l i a t e d and f r a c t u r e s are widespread and i r r e g u l a r . Roadcuts along Mt. Seymour Road near the t r a n s m i s s i o n l i n e show quartz monzonite and g r a n o d i o r i t e cut by many t h i n v e i n s of e p i d o t e w i t h a s s o c i a t e d zones of pink hydrothermal a l t e r a t i o n . Bedrock geology of the Lower Mainland i s not s o l e l y l i m i t e d to exposures of g r a n i t i c rock. T e r r e s t r i a l sedimentary rocks have long been i d e n t i f i e d i n the Vancouver area although they were i n i t i a l l y grouped i n t o a s i n g l e s t r a t i g r a p h i c u n i t of Cretaceous age. (Burwash, 1918). Johnstone (1923) remapped these rocks, d i v i d i n g the sequence i n t o an upper K i t s i l a n o - 40 -Formation o f Late Eocene-Early Oligocene age, disconformably o v e r l y i n g the B u r r a r d Formation of Mid-Late Eocene age. Recently the B u r r a r d Formation has been s u b d i v i d e d to i n c l u d e a Cretaceous member comp r i s i n g t h a t p a r t which r e s t s unconformably upon the deeply weathered g r a n i t i c rock of the Coast P l u t o n i c Complex. (Blunden, 19 71; 19 75; and Rouse e t a l , 1975). The C r e t a c e o u s - T e r t i a r y sedimentary s t r a t i g r a p h y of the area as summarized by Blunden (19 75) i s as f o l l o w s : Late Cretaceous Lions Gate Member (lower Burrard) c o n s i s t i n g o f a b a s a l conglomerate u n i t , a s a n d s t o n e - s i l t s t o n e u n i t , a shal e u n i t , and an upper coarse arkose u n i t ; Paleocene and Eocene P o i n t Ferguson beds (upper Burrard) c o n s i s t i n g of a sequence of sandstone and shal e and l o c a l l i g n i t e seams; and Eocene t o Miocene K i t s i l a n o and Boundary Bay Formations c o n s i s t i n g o f v a s t q u a n t i t i e s of cobble conglomerate w i t h interbedded sandstone and s h a l e , o v e r l a i n by a r e p e t i t i o u s sequence o f sandstone and s h a l e . The b a s a l u n i t of the Lions Gate Member i s i n f e r r e d t o l i e upon an i n c l i n e d p l a n a r s u r f a c e s t r i k i n g about east-west and d i p p i n g an average of 11° (20%) southward. I t has been concluded t h a t the present s o u t h e r l y slope o f the Coast Mountains near Vancouver corresponds c l o s e l y to the base of the Lions Gate Member, having been s t r i p p e d of subsequent sedimentary d e p o s i t s . (Rouse e t a l , 1975). - 41 -P r i o r to t h i s study no exposures of sedimentary rock had been d e s c r i b e d i n the Seymour area. Borehole records from the G.S.C. Urban Geology F i l e i n d i c a t e t h a t t h i c k sequences o f sedimentary s t r a t a are p r e s e n t beneath B u r r a r d I n l e t near the Second Narrows. The upper s u r f a c e of t h i s interbedded conglomerate, sandstone, and sha l e u n i t averages about 325 f e e t (100 m.) below sea l e v e l . On the beach around Roche P o i n t (Cates Park) are s u r f a c e exposures of a r k o s i c sandstone and pebbly sandstone. These rocks are reasonably w e l l s o r t e d , c o n s i s t i n g of c o a r s e - g r a i n e d , subrounded quartz and f e l d s p a r sand, with up to 25% subangular to subrounded rock fragments and subrounded pebbles. In p l a c e s the rock grades i n t o a conglomerate w i t h a subrounded coarse s a n d - f i n e g r a v e l matrix of q u a r t z , f e l d s p a r , and rock fragments c o n t a i n i n g up to 50% subrounded pebbles and cobbles. An important c h a r a c t e r i s t i c of these sedimentary exposures i s the f r i a b i l i t y o f the rock, p a r t i c u l a r l y on weathered s u r f a c e s : chunks of weathered sandstone can be crumbled i n the hand. Although bedding planes are i n d i s t i n c t they appear to d i p southward a t 10° to 12°. Quaternary S t r a t i g r a p h y and H i s t o r y of the F r a s e r Lowland In r e c e n t p u b l i c a t i o n s Armstrong (1975b, 1977) and Hicock (19 76) have d e s c r i b e d the Quaternary s t r a t i g r a p h y and h i s t o r y of u n c o n s o l i d a t e d sediments exposed i n the F r a s e r Lowland, of which North Vancouver-Seymour i s a p a r t . They - 42 -have suggested t h a t d u r i n g Wisconsin and probably e a r l i e r time, the Lowland was s u b j e c t e d to repeated g l a c i a t i o n s separated by n o n g l a c i a l i n t e r v a l s . These major g l a c i a l events each went through three main stages: an advancing stage c h a r a c t e r i z e d by c o a l e s c i n g . piedmont g l a c i e r s ; a maximum stage when the i c e a t t a i n e d a t h i c k n e s s of a t l e a s t 1800 m. and overrode much of the a d j o i n i n g mountainous areas; and a r e t r e a t i n g or d e g l a c i a t i o n stage when i c e was mainly r e s t r i c t e d to v a l l e y s and arms of the sea, p o s s i b l y readvancing l o c a l l y as s u r g i n g g l a c i e r s . I s o s t a t i c , e u s t a t i c , and probably t e c t o n i c adjustments accompanied each g l a c i a t i o n , r e s u l t i n g i n repeated sea l e v e l changes of a t l e a s t 200 m. Thick Quaternary d e p o s i t s , marine, non-marine, and g l a c i a l , were l a i d down and eroded as a r e s u l t of t h i s complex g e o l o g i c a l h i s t o r y . (Hicock, 1976). Armstrong (19 75a, 19 77) and Armstrong and Clague (19 77) have e s t a b l i s h e d t h a t f i v e major P l e i s t o c e n e f o r m a t i o n a l u n i t s , each probably r e p r e s e n t i n g a major g e o l o g i c - c l i m a t i c u n i t , are exposed i n the F r a s e r Lowland. These are summarized i n Table V. Westlynn D r i f t , the o l d e s t Quaternary sediment exposed i n the F r a s e r Lowland, was d e p o s i t e d more than 62,00 0 years ago under c o o l e r c l i m a t i c c o n d i t i o n s than e x i s t today. F o l l o w i n g an e r o s i o n a l p e r i o d and warming of the c l i m a t e , Highbury f l u v i a l sediments were l a i d down. - 43 -TABLE V Quaternary S t r a t i g r a p h y of the F r a s e r Lowland, B.C. ( a f t e r Armstrong, 1977 and Hicock, 1976). G e o l o g i c - C l i m a t i c U n i t Radiocarbon Ages. (Years B.P.) , E s t a b l i s h e d S t r a t i -|graphic Succession i f o r the F r a s e r Lowland. Holocene P o s t - G l a c i a l 11,000 to present Holocene Sediments ( S a l i s h and F r a s e r R i v e r Sediments) P l e i s t o c e n e Late Wisconsin F r a s e r G l a c i a t i o n 26,000 - 11,000 Capilano Sediments Vashon D r i f t Quadra Sand Coquitlam D r i f t Middle Wisconsin Olympia N o n g l a c i a l I n t e r v a l 60,000? - 26,000 Cowichan Head Sediments Middle or E a r l y Wisconsin Major G l a c i a t i o n p o s s i b l y g r e a t e r than 62,00 0 Semiahmoo D r i f t E a r l y Wisconsin? Major N o n g l a c i a l I n t e r v a l probably g r e a t e r than 62,000 Highbury. .Sediments E a r l y or Pre-Wisconsin Major G l a c i a t i o n g r e a t e r than 62,000 Westlynn D r i f t A f t e r another p e r i o d o f e r o s i o n and c l i m a t i c d e t e r i o r a t i o n , the next major g l a c i a l event began. Semiahmoo D r i f t , c o n s i s t i n g of p r o g l a c i a l and advance outwash and t i l l , was d e p o s i t e d by the advancing i c e sheet. During d e g l a c i a t i o n the sea l e v e l r ose as meltwater from r e t r e a t i n g and downwasting i c e flowed i n t o the sea. Glaciomarine d e p o s i t s were formed as m e l t i n g i c e b e r g s randomly dropped stones i n t o s e a - f l o o r mud. A f t e r the l a n d i s o s t a t i c a l l y rose above sea l e v e l , g l a c i o l a c u s t r i n e laminated s i l t s were l a i d down by meltwater ponded i n v a l l e y d e p r e s s i o n s . - 44 -The topography of much o f the F r a s e r Lowland has remained b a s i c a l l y the same s i n c e the e r o s i o n a l p e r i o d f o l l o w i n g the Semiahmoo G l a c i a t i o n , and has o n l y been l o c a l l y m o d i f i e d by l a t e r g l a c i a l and f l u v i a l a c t i o n . The sparseness of s t r a t i g r a p h i c r e c o r d s p r i o r to Semiahmoo time makes i t d i f f i c u l t to r e c o n s t r u c t the topography b e f o r e then. (Hicock, 1976). The Olympia N o n g l a c i a l I n t e r v a l i s r e p r e s e n t e d by n o n g l a c i a l sediments l y i n g between d r i f t o f the F r a s e r and Semiahmoo G l a c i a t i o n s . The Cowichan Head Formation, d e p o s i t e d d u r i n g t h i s time, c o n s i s t s o f a lower marine member and an upper f l u v i a l and e s t u a r i n e member. (Armstrong and Clague, 19 77). Marine and p o s s i b l y g l a c i o m a r i n e sediments o f the lower member were d e p o s i t e d d u r i n g the t r a n s i t i o n from g l a c i a l to n o n g l a c i a l c o n d i t i o n s a t the c l o s e o f Semiahmoo time. T h i s change accompanied a r e l a t i v e drop i n sea l e v e l as d e p o s i t i o n a l c o n d i t i o n s changed from a shallow marine to a t e r r e s t r i a l environment. P l a n t - b e a r i n g beds of the upper member of the formation were l i k e l y d e p o s i t e d as channel, overbank, and swamp sediments i n near-shore lowland areas. Subsequent e r o s i o n d u r i n g the F r a s e r G l a c i a t i o n removed much of these n o n g l a c i a l sediments. With the onset of the F r a s e r G l a c i a t i o n around 26,000 years ago, the c l i m a t e c o o l e d and p r o g l a c i a l Quadra Sand was d e p o s i t e d as d i s t a l outwash aprons a t s u c c e s s i v e p o s i t i o n s i n f r o n t o f , and perhaps along the margins of g l a c i e r s advancing from the Coast Mountains. (Clague, 1976). E a r l y i n the F r a s e r - 45 -G l a c i a t i o n , d e p o s i t i o n of Quadra Sand was p o s s i b l y i n t e r r u p t e d by advances of l o c a l piedmont g l a c i e r s i n t o some of the major v a l l e y s . Hicock (19 76) has suggested t h i s s t a d i a l event i s represented by Coquitlam D r i f t , thought to be mainly glaciomarine sediments, but may i n p a r t be t i l l . As the main Vashon i c e sheet advanced i n t o the F r a s e r Lowland, h i g h d i s c h a r g e meltwater streams emanating from the i c e f r o n t d e p o s i t e d sediments much more v a r i a b l e i n t e x t u r e and s t r u c t u r e than the u n d e r l y i n g Quadra Sand. During t h i s time i t i s l i k e l y t h a t flow t i l l s and i c e - c o n t a c t sediments were d e p o s i t e d a t the i c e margins. Vashon i c e e v e n t u a l l y overrode the area, reworking and r e d e p o s i t i n g i t s own advance outwash and d e p o s i t i n g lodgement t i l l . A t l e a s t t hree t i l l s h eets, separated by g l a c i o f l u v i a l sediments, are found i n the Lowland area and r e p r e s e n t l o c a l i c e advances d u r i n g the F r a s e r G l a c i a t i o n . (Dolmage, 1960). Laminated stony s i l t and f i n e sand l e n s e s i n the t i l l were formed by f i n e sediments and i c e - r a f t e d dropstones b e i n g d e p o s i t e d i n s m a l l meltwater ponds occupying d e p r e s s i o n s on the t i l l s u r f a c e . The c l i m a t e began warming and F r a s e r d e g l a c i a t i o n was under way by about 13,000 years ago although the Sumas G l a c i a l Stade was s t i l l to a f f e c t the e a s t e r n F r a s e r Lowland. As the sea c l o s e l y f o l l o w e d the r e t r e a t i n g Vashon i c e over the i s o s t a t i c a l l y depressed land c o n v e r t i n g major v a l l e y s i n t o f i o r d s , C a p i l a n o f o s s i l i f e r o u s marine and g l a c i o m a r i n e sediments were d e p o s i t e d . - 46 -With f u r t h e r r e t r e a t of Vashon i c e i n t o the Coast Mountains the lan d s t a r t e d i s o s t a t i c a l l y to r i s e f a s t e r than the e u s t a t i c a l l y r i s i n g sea l e v e l . Composite marine d e l t a s were formed a t the mouths of major v a l l e y s by southward f l o w i n g meltwater r i v e r s debouching from the r e t r e a t i n g i c e . S u p r a l i t t o r a l l a g g r a v e l s and l i t t o r a l sands, winnowed from Capilano g l a c i o m a r i n e sediments and Vashon D r i f t by storm waves and spray pounding a g a i n s t the emerging upland s l o p e s , were formed up to 650 f e e t (200 m.) above p r e s e n t sea l e v e l . (Mathews e t a l , 1970). At the same time t e r r a c e s were cut i n t o the composite d e l t a s . During the f i n a l stages of d e p o s i t i o n of the C a p i l a n o sediments, about 11,500 years ago, the western F r a s e r Lowland began another n o n g l a c i a l p e r i o d , w h i l e the e a s t e r n F r a s e r Lowland was s t i l l i n the Sumas Stade. S i n c e the P l e i s t o c e n e epoch the a n c e s t o r a l creeks and r i v e r s occupying the major v a l l e y s have cut deeply i n t o the v a l l e y sediment f i l l , and i n p l a c e s have eroded i n t o u n d e r l y i n g bedrock. Most o f the r e c e n t a l l u v i u m d e p o s i t e d a l o n g these v a l l e y s has been reworked from o l d e r sediments exposed i n the v a l l e y s i d e s . The major drainage channels have b u i l t e x t e n s i v e f l o o d p l a i n d e l t a s out from the lower upland s l o p e s to t h e i r p r e s e n t channel mouths. E r o s i o n and d e p o s i t i o n of u n c o n s o l i d a t e d m a t e r i a l s d u r i n g the Holocene have been a i d e d by s m a l l e r mountain streams, mass wasting, and man. - 47 -D i s t r i b u t i o n of G e o l o g i c a l M a t e r i a l s .in North Vancouver-Seymour Although the bedrock geology i s l a r g e l y r e s p o n s i b l e f o r determining the o v e r a l l landscape of the Seymour area, and i n f a c t dominates a t upper e l e v a t i o n s , i t i s the s u r f i c i a l g e o l o g i c a l m a t e r i a l s which account f o r the l a r g e v a r i a b i l i t y i n t h i s landscape. The topography of the area, as f o r the e n t i r e F r a s e r Lowland, has remained b a s i c a l l y the same s i n c e mid-Wisconsin time, however, the bulk of the s u r f i c i a l m a t e r i a l s now exposed were d e p o s i t e d d u r i n g the F r a s e r G l a c i a t i o n . Pre-Vashon sediments are exposed mainly i n the deeply i n c i s e d v a l l e y s of Lynn Creek and Seymour R i v e r w i t h l o c a l exposures i n the deeper g u l l i e s o f s m a l l e r streams. The s u r f i c i a l d e p o s i t s are r e l a t e d to a t l e a s t two major g l a c i a t i o n s separated by a t l e a s t one n o n g l a c i a l i n t e r v a l . Mesozoic g r a n i t i c bedrock occurs a t or near the ground s u r f a c e over most of the area above 650 f e e t (200 m.) e l e v a t i o n . Bedrock i s a l s o exposed i n the deeply i n c i s e d v a l l e y s of Lynn Creek and Seymour R i v e r , along a r i d g e extending down beside T a y l o r Creek, and along the steeper s l o p e s down to sea l e v e l n o r t h and south of Deep Cove. ( P l a t e 1). The bedrock topography i s complex (Figure IV-2, IV-3) and s l o p e s g e n e r a l l y exceed 15% as c o n t r a s t e d to the g e n t l e r s l o p i n g areas u n d e r l a i n by s u r f i c i a l m a t e r i a l . The diagrammatic g e o l o g i c a l p r o f i l e s (Figure III-3) i l l u s t r a t e the r e l a t i o n s h i p between topography and bedrock and s u r f i c i a l geology. Areas mapped as i n t r u s i v e bedrock are, f o r the most p a r t , - 48 -mantled by a t h i n cover ( g e n e r a l l y l e s s than 1.5 m.) of rubbly c o l l u v i u m and/or r e g o s o l i c s o i l . In p l a c e s , pockets of t i l l , mainly lodgement although some a b l a t i o n t i l l was noted a t h i g h e r e l e v a t i o n s , mantle the bedrock. ( P l a t e 2 ). These t i l l pockets are l o c a l i z e d and i r r e g u l a r i n t h e i r d i s t r i b u t i o n and thus are i n c l u d e d w i t h i n the bedrock map-unit. Although t h i s t i l l cover i s g e n e r a l l y t h i n , d e p o s i t s much t h i c k e r than 1.5 m. can be expected i n depressions on the bedrock s u r f a c e . Sedimentary bedrock, c o n s i s t i n g of Late Cretaceous to E a r l y T e r t i a r y a r k o s i c sandstone, i s exposed along the beaches around Roche P o i n t . These exposures are very t h i n , and because they r e p r e s e n t the o n l y outcrops i n the study area, are not c o n s i d e r e d important i n the s u r f a c e geology of the Seymour area. Diagrammatic c r o s s - s e c t i o n C-C (Figure III-3) shows the sedimentary bedrock s u r f a c e as i n t e r s e c t e d by d r i l l h o l e s near the Second Narrows (GSC-31, 33, 34, 35) and p r o j e c t e d onto the c r o s s - s e c t i o n l i n e ; by p r o j e c t i n g sedimentary bedding planes w i t h an average s o u t h e r l y d i p of 11° (20%) i t shows t h a t the rocks exposed a t Roche P o i n t are probably p a r t of the same sequence i n t e r s e c t e d by the d r i l l h o l e s . Assuming an east-west s t r i k e f o r these sedimentary beds (Rouse e t a l , 1975), the rocks i n t e r s e c t e d i n the d r i l l h o l e s and exposed a t Roche P o i n t probably correspond to the upper coarse arkose u n i t of the Lions Gate Member exposed i n S t a n l e y Park. - 49 -P l a t e 1. Steep g r a n o d i o r i t e c l i f f s o v e r l o o k i n g Indian Arm. P l a t e 2. P o d z o l i c s o i l (a) developed on dense lodgement Vashon t i l l (b) which o v e r l i e s g r a n o d r i o r i t e bedrock (c) i n a roadcut, Mt. Seymour Road. - 50 -T h i s sedimentary s t r a t i g r a p h y and s t r u c t u r e i s s i g n i f i c a n t f o r two reasons. F i r s t l y , because of the s o u t h e r l y p o s i t i o n of Roche P o i n t i n r e l a t i o n to the r e s t o f the Seymour area, the n a t u r a l d i p o f the sedimentary bedding planes p r o j e c t s above the p r e s e n t ground s u r f a c e i n d i c a t i n g t h a t a l l o f the h i g h e r sedimentary formations were eroded from the Seymour area p r i o r to d e p o s i t i o n of the s u r f i c i a l sediments. Secondly, Rouse e t a l (19 75) have shown t h a t a c o n s i d e r a b l e t h i c k n e s s of sedimentary rock e x i s t s below the arkose u n i t . T h i s suggests t h a t the Late Cretaceous sedimentary sequence c o u l d p o s s i b l y u n d e r l i e the Seymour area a t depth even up to about 400 f e e t (120 m.) e l e v a t i o n , where the p r e s e n t ground s u r f a c e i n t e r s e c t s g r a n i t i c bedrock. However, the occurrence of i n t r u s i v e bedrock i n the v a l l e y s of Lynn Creek and Seymour R i v e r , down to l e s s than 200 f e e t (60 m.) e l e v a t i o n and a l s o down to sea l e v e l e a s t of the mouth of Indian Arm, suggests t h a t i t seems l i k e l y t h a t most of the sedimentary rocks have been eroded from the g r a n i t i c s u r f a c e . A l l of the s u r f i c i a l m a t e r i a l s d e p o s i t e d p r i o r t o the l a s t major i c e advance are mapped together as Pre-Vashon sediments. The d i v i s i o n between Vashon D r i f t and Pre-Vashon sediments i s a a r b i t r a r y , one and f o r the purpose o f t h i s d i s c u s s i o n i s c o n s i d e r e d to be between p r o g l a c i a l Quadra Sand and Vashon advance outwash. The d e p o s i t i o n a l c o n d i t i o n s - 51 -o p e r a t i n g d u r i n g t h i s t r a n s i t i o n were h i g h l y v a r i a b l e , t h e r e f o r e the c o n t a c t between these m a t e r i a l s i s g e n e r a l l y g r a d a t i o n a l . Sandy t i l l and g l a c i o f l u v i a l g r a v e l s immediately o v e r l y i n g bedrock or a t stream l e v e l i n the v a l l e y s of Lynn Creek and Seymour R i v e r , appear to be the o l d e s t sediments exposed i n the area, and are very l i k e l y p a r t of the Semiahmoo D r i f t . (D-6) ( P l a t e 3). In p l a c e s t h i s d r i f t i s o v e r l a i n by massive c l a y e y s i l t ( c o n t a i n i n g s c a t t e r e d subrounded g r a n i t i c stones) which i s probably g l a c i o m a r i n e m a t e r i a l . (D-5). A t h i c k and f a i r l y e x t e n s i v e u n i t of Semiahmoo D r i f t i s a g l a c i o l a c u s t r i n e , r h y t h m i c a l l y laminated s i l t c o n t a i n i n g s c a t t e r e d subrounded g r a n i t i c dropstones, which i s exposed along the e a s t bank of Lynn Creek. (D-4) ( P l a t e 4 ) . Cowichan Head n o n g l a c i a l sediments are d e f i n i t e l y r e p r e s e n t e d i n a t l e a s t one l o c a l i t y i n Lynn Creek canyon. (D-6). Wood from a s i l t y peat bed 0.5 m. t h i c k , o v e r l y i n g probable Semiahmoo t i l l ( P l a t e 3), was dated a t 36,200 + 500 years B.P. ( F u l t o n , 1971). T h i s c o r r e l a t e s w i t h the Westlynn p a r a s t r a t o t y p e s e c t i o n l o c a t e d i n a roadcut.on Highway 401 about 1 km. west of Lynn Creek. (Armstrong and Clague, 1977). In t h a t s e c t i o n a 1.0 m. t h i c k compressed peat l a y e r , dated at 32,200 + 3300 years B.P. ( F u l t o n , 1971 and Clague, 1976), o v e r l i e s Semiahmoo t i l l and u n d e r l i e s Quadra Sand. F u r t h e r south i n Lynn canyon there are minor exposures of f i n e l y bedded s i l t and f i n e sand w i t h what appears to be a stony o r g a n i c c o l l u v i u m i n c l u d e d w i t h i n the d e p o s i t : these sediments - 52 -P l a t e 3. Probable Semiahmoo D r i f t (a) o v e r l a i n by a t h i n bed o f s i l t y peat (b) (Cowichan Head Formation) i n Lynn canyon: a r a i s e d , Holocene g r a v e l f l o o d p l a i n caps the s e c t i o n (c) P l a t e 4. R h y t h m i c a l l y laminated s i l t c o n t a i n i n g s c a t t e r e d subrounded-subangular g r a n i t i c dropstones; probably a g l a c i o -l a c u s t r i n e u n i t o f Semiahmoo D r i f t . - 53 -are a l s o l i k e l y p a r t o f the Cowichan Head Formation. L i m i t e d exposures of s i l t y c l a y diamicton and bedded c l a y e y s i l t , which seem to be d i r e c t l y beneath Vashon t i l l o r Quadra Sand, may r e p r e s e n t g l a c i o m a r i n e d e p o s i t s of the Coquitlam D r i f t i d e n t i f i e d by Hicock (1976). (D-12, 14; Samples 8,9). The o t h e r , and l e s s l i k e l y , p o s s i b i l i t y i s t h a t these d e p o s i t s r e p r e s e n t g l a c i o m a r i n e or shallow marine (estuarine) sediments o f the Cowichan Head Formation, d e p o s i t e d e a r l y i n the n o n g l a c i a l i n t e r v a l d u r i n g t r a n s i t i o n from the Semiahmoo G l a c i a t i o n . I f t h i s i s the case, subsequent g l a c i a l e r o s i o n must have removed a l l o f the o v e r l y i n g n o n g l a c i a l sediments. P o s s i b l y the t h i c k e s t and most e x t e n s i v e l y exposed Pre-Vashon sediment i s Quadra Sand. T h i s m a t e r i a l • c o n s i s t s l a r g e l y of w e l l s o r t e d , f i n e to c o a r s e - g r a i n e d , white sand with minor g r a v e l and s i l t which i s s u b h o r i z o n t a l l y l a y e r e d and e x t e n s i v e l y cross-bedded. Exposures of Quadra Sand are common i n the v a l l e y s of Lynn Creek (Q-5,7,8) and Seymour R i v e r (D-1,12). Although there i s no one complete s e c t i o n exposed i n these v a l l e y s , i t appears very l i k e l y t h a t the u n i t i s of comparable t h i c k n e s s to the 20 m. exposure of Quadra Sand at the Westlynn p a r a s t r a t o t y p e S e c t i o n to the west. (Armstrong and Clague, 1977). In addition,Quadra Sand i s exposed i n the R i v e r s i d e sand and g r a v e l p i t (D-15,17) where Learning (1968) r e p o r t e d t h i c k n e s s e s exceeding 30 m. and i n the deeply i n c i s e d g u l l y of McCartney Creek j u s t south of Mt. Seymour Parkway.(D-20). - 54 -Vashon D r i f t , c o n s i s t i n g p r i m a r i l y o f dense, grey, lodgement t i l l w i t h minor s u b s t r a t i f i e d m a t e r i a l , u n d e r l i e s , most o f the Seymour area. The s i l t y and sandy g r a i n s of the t i l l m a t r i x c o n s i s t mainly of subangular to angular q u a r t z , f e l d s p a r , and rock fragments whereas the c l a s t s are subrounded to subangular pebbles, cobbles, and boulders of g r a n i t i c o r g i n . Between or u n d e r l y i n g the t i l l sheets are g l a c i o f l u v i a l and i c e - c o n t a c t sediments c o n s i s t i n g o f : f o r e s e t pebbly sand beds (D-16) (P l a t e 5); c h a o t i c , s u b s t r a t i f i e d , dense, cobble g r a v e l c o n t a i n i n g b o ulders and lenses of sand and s i l t (D-12); and g r a v e l l y sand and g r a v e l l y t i l l - l i k e m a t e r i a l . (D-22). I t i s reasonable to expect t h a t Vashon D r i f t forms a mantle of v a r y i n g t h i c k n e s s roughly conforming to the pre-e x i s t i n g bedrock or s u r f i c i a l topography. (Figure I I I - 3 ) . Vashon D r i f t has been r e p o r t e d as v a r y i n g i n t h i c k n e s s from 1 to 30 m. (Armstrong e t a l , 1965), however i s g e n e r a l l y l e s s than 8 m.thick. In the Seymour area the d r i f t probably o n l y r a r e l y exceeds 10 m. t h i c k n e s s , although only i n two l o c a l i t i e s have the s m a l l e r streams managed to c u t through i t . In McCartney Creek where Quadra Sand i s exposed, the t i l l i s on l y 1 m. t h i c k . (D-20). Along the v a l l e y s i d e s of Lynn Creek and Seymour R i v e r where complete s e c t i o n s of the d r i f t are exposed, t h i c k n e s s e s commonly exceed 5 m. (D-3,7,8,10,11,12, 19). In F r a n c i s Creek the d r i f t i s a t l e a s t 8 m. t h i c k (D-22) and a d r i l l h o l e j u s t west of McCartney Creek (GSC-416) i n t e r s e c t e d 5 m. of t i l l w ithout going through the u n i t . - 55 -Throughout the area l o c a l i z e d and i r r e g u l a r l y -d i s t r i b u t e d l a y e r s of post-Vashon sediments, i n c l u d i n g g l a c i o m a r i n e stony c l a y e y s i l t , s u p r a l i t t o r a l l a g g r a v e l , and l i t t o r a l sand, mantle the t i l l . Where these m a t e r i a l s are d i s c o n t i n u o u s and l e s s than 1.5 m. t h i c k they a l s o have been i n c l u d e d w i t h i n the Vashon D r i f t map-unit. (D-3, 11; GSC-416) (Plate 6). Post-Vashon sediments of the F r a s e r G l a c i a t i o n are known as C a p i l a n o Sediments and c o n s i s t o f : marine and g l a c i o m a r i n e stony to s t o n e l e s s c l a y e y s i l t ; i n t e r b e d d e d sand, g r a v e l l y sand, and sandy g r a v e l d e p o s i t e d as outwash and d e l t a s ; f i n e to medium sand d e p o s i t e d as marine l i t t o r a l sediment; and s u p r a l i t t o r a l l a g g r a v e l . For the purpose of t h i s d i s c u s s i o n the C a p i l a n o Sediments have been sep a r a t e d i n t o two map-units, cohesive f i n e - g r a i n e d m a t e r i a l s and c o h e s i o n l e s s c o a r s e - g r a i n e d sediments. The cohesive sediments c o n s i s t of marine, g l a c i o m a r i n e , and probably g l a c i o l a c u s t r i n e u n i t s of c l a y e y s i l t , s i l t y c l a y , and c l a y c o n t a i n i n g v a r i a b l e amounts of subrounded g r a n i t i c dropstones. Armstrong and Brown (1954), d e s c r i b i n g g l a c i o m a r i n e sediments exposed i n the F r a s e r Lowland, suggested t h a t the stony c l a y s formed by stones dropping i n t o s e a - f l o o r mud from f l o a t i n g i c e . The only c o n c l u s i v e evidence of a g l a c i o m a r i n e o r i g i n f o r t h i s type of sediment, however, i s the occurrence of s c a t t e r e d stones and marine s h e l l s embedded i n a f i n e - g r a i n e d matrix. No marine f o s s i l s were observed d u r i n g the course of t h i s study, although Armstrong and - 56 -P l a t e 5. F o r e s e t pebbly sand beds, d i p p i n g about 10° south, which were d e p o s i t e d by advance Vashon outwash. The exposure i s i n the R i v e r s i d e p i t . l a t e 6. C a p i l a n o Sediments f i n e s i l t y sand (a) and stony c l a y e y s i l t (b)) o v e r l i e Vashon D r i f t ( s u b s t r a t i f i e d sandy g r a v e l (c) and dense, lodgement t i l l ( d ) ) . Brown (1954) r e p o r t e d f o s s i l i f e r o u s stony s i l t s i n a r a i s e d d e l t a i n the R i v e r s i d e p i t . In the western p a r t s o f the F r a s e r Lowland these d e p o s i t s are r a r e l y more than 15 m. t h i c k and g e n e r a l l y are l e s s than 8 m. L o c a l exposures along Lynn canyon show up to 9 m. of i n t e r l a y e r e d c l a y , s i l t y c l a y , c l a y e y s i l t , and sandy s i l t o v e r l y i n g Vashon D r i f t . (D-8,9). These two s e c t i o n s i l l u s t r a t e the d i v e r s i t y of t h i s type of d e p o s i t as ap p a r e n t l y marine c l a y s grade l a t e r a l l y and v e r t i c a l l y i n t o stony c l a y e y s i l t and i n p l a c e s are i n t e r l a y e r e d w i t h f i n e sand and s i l t beds. The most common type of occurrence of t h i s cohesive m a t e r i a l i s a brown or grey-brown, massive, c l a y e y s i l t o r s i l t y c l a y c o n t a i n i n g s c a t t e r e d subrounded pebbles, c o b b l e s , and boulders which g e n e r a l l y make up l e s s than 5% of the m a t e r i a l volume. In p l a c e s l a r g e b o u l d e r s up t o 2 m. i n diameter can be seen, whereas elsewhere the sediment may be s t o n e - f r e e . These sediments have a c h a r a c t e r i s t i c a l l y b l o c k y s t r u c t u r e , w i t h manganese-oxide-stained j o i n t s u r f a c e s . Large, reasonably l e v e l t r a c t s o f land i n the c e n t r a l Seymour area are u n d e r l a i n by a t l e a s t 1.5 m. of t h i s c h a r a c t e r i s t i c stony c l a y e y s i l t . (D-23). Because the s e a - f l o o r muds were l a i d down on an u n d u l a t i n g morainal s u r f a c e , i n f i l l i n g the depressions w i t h more m a t e r i a l , the t h i c k n e s s of these d e p o s i t s i s l i k e l y h i g h l y v a r i a b l e . An i n t e r e s t i n g type o f post-Vashon cohesive d e p o s i t i s exposed on the e a s t bank of the lower Lynn Creek v a l l e y . - 58 -(D-13,14). A varved s i l t and c l a y e y s i l t sequence, which may be up to 30 m. t h i c k , u n d e r l i e s C a p i l a n o outwash g r a v e l s and sediments d e p o s i t e d a f t e r i s o s t a t i c u p l i f t i n a meltwater pond formed i n a dep r e s s i o n on the t i l l s u r f a c e . C o h e s i o n l e s s C a p i l a n o Sediments range i n t e x t u r e from s i l t y sand to bouldery g r a v e l . They r e p r e s e n t d e l t a i c , channel, and f l o o d p l a i n d e p o s i t s o f p o s t - g l a c i a l meltwater r i v e r s which flowed from the Coast Mountains down the v a l l e y s p r e s e n t l y occupied by Lynn Creek and Seymour R i v e r . D e p o s i t i o n of sediment began when sea l e v e l was at l e a s t 200 m. hig h e r than pre s e n t . As r e l a t i v e sea l e v e l began f a l l i n g , d e p o s i t i o n o c c u r r e d a t p r o g r e s s i v e l y lower e l e v a t i o n s , and by the time i s o s t a t i c rebound was complete, a s e r i e s of r a i s e d outwash d e p o s i t s was l e f t . The b e s t examples of these l e v e l , r a i s e d t e r r a c e s can be seen i n the Seymour Heights area, n o r t h along the e a s t bank of Seymour R i v e r , and down the len g t h o f the r i d g e , between Lynn Creek and Seymour R i v e r . Thickness of these sands and gr a v e l s v a r i e s , depending on the u n d e r l y i n g Vashon t i l l topography, on c o n d i t i o n s which e x i s t e d d u r i n g d e p o s i t i o n of the outwash, and on the e f f e c t s o f p o s t - g l a c i a l e r o s i o n . The t h i c k e r sand and g r a v e l d e p o s i t s are found a t lower e l e v a t i o n s . The L i l l o o e t Road p i t (D-10) c o n s i s t e d of 1 to 2 m. of f l a t - l y i n g s u p r a l i t t o r a l l a g g r a v e l over up to 12 m. of f o r e s e t d e l t a i c beds of s i l t y g r a v e l , sandy g r a v e l , and sand. (Learning,1968) ( P l a t e 7). J u s t n o r t h o f t h i s p i t up to 8 m. of outwash sand and g r a v e l i s exposed along the h i l l s l o p e . (D-13). Most of the outwash g r a v e l s have been removed from the p i t on D o l l a r t o n Highway, however t h i s d e p o s i t a l s o appears to have f e a t u r e d a s u p r a l i t t o r a l boulder g r a v e l o v e r l y i n g d e l t a i c , f o r e s e t sandy g r a v e l . Borehold r e c o r d s (GSC-1010, 1013, 1016) i n d i c a t e t h a t up to 7 m. of C a p i l a n o Sediments o v e r l i e Vashon t i l l . S e c t i o n s exposed i n the R i v e r s i d e p i t (D-17) i l l u s t r a t e a d i f f e r e n t type of outwash. Channel d e p o s i t s t h a t are h i g h l y v a r i a b l e , both v e r t i c a l l y and h o r i z o n t a l l y , w i t h numerous d i s t i n c t l e n s e s of sandy g r a v e l , g r a v e l l y sand, and open-worked pebbly g r a v e l , l i e over and adjacent to Vashon D r i f t and Quadra Sand. Along the lower south-east slopes of Mount Seymour, n o r t h of Deep Cove, are a number of what appear to be s m a l l r a i s e d d e l t a i c , or i n p a r t , channel d e p o s i t s of sand and g r a v e l . These d e p o s i t s l i k e l y r e p r e s e n t l a t e stage outwash d e l t a s which formed as meltwater, f l o w i n g o f f the steep s l o p e s , d e p o s i t e d sediment i n t o the sea, or p o s s i b l y i n t o ice-dammed la k e s c r e a t e d between the c o a s t a l s l o p e s and a lobe of the waning Vashon i c e sheet. The e x t e n t and s t r u c t u r e of these l o c a l i z e d d e p o s i t s , because of t h i c k f o r e s t cover, i s not r e a d i l y apparent, although one exposed s e c t i o n (D-21) shows up to 12 m. of s u b s t r a t i f i e d sand and g r a v e l d i p p i n g 30° downslope. The lowland around Deep Cove was l i k e l y a r e c e i v i n g b a s i n f o r sediments d e p o s i t e d from meltwater f l o w i n g o f f the surrounding s l o p e s . The extreme v a r i a t i o n i n t e x t u r e , - 60 -s t r u c t u r e , and thickness of sediments exposed i n t h i s r e l a t i v e l y small area suggest th a t the d e p o s i t i o n a l environment was c o n t r o l l e d by complex d e g l a c i a t i o n c o n d i t i o n s . The sediments range from a dense, s u b s t r a t i f i e d , s i l t y sand (Samples 1,2) c o n t a i n i n g discontinuous pebble l a y e r s and sporadic rounded pebbles to poorly s o r t e d , bouldery, sandy g r a v e l . Holocene Sediments are those m a t e r i a l s deposited since the Fraser G l a c i a t i o n , and i n many cases are s t i l l being formed. They c o n s i s t , f o r the most p a r t , of c l a y to g r a v e l s i z e sediments deposited by present-day r i v e r s and streams i n bars, channels, f l o o d p l a i n s , and d e l t a s . The most extensive areas of Holocene Sediments are the f l o o d p l a i n d e l t a s of Lynn Creek and Seymour R i v e r . These d e l t a s , c o n s i s t i n g of sand and g r a v e l w i t h minor s i l t and c l a y , have b u i l t out from t h e i r r e s p e c t i v e mountain v a l l e y s to fornr a s i n g l e , l a r g e , d e l t a i c f l o o d p l a i n . The deposits are h i g h l y v a r i a b l e , both h o r i z o n t a l l y and v e r t i c a l l y (GSC-358,373,374, 445,449,458, 662), and are at l e a s t 50 m. t h i c k near the d e l t a f r o n t , although borehole records do not c l e a r l y d i s t i n g u i s h between Holocene and P l e i s t o c e n e sediments (GSC-31,33,34,35, 36, 320) . Small f l o o d p l a i n s e x i s t f u r t h e r upstream i n the v a l l e y s of Lynn Creek and Seymour River where stream erosion has cut l a t e r a l l y i n t o s u r f i c i a l sediments; they c o n s i s t mainly of cobbles and boulders eroded out of the o l d e r P l e i s t o c e n e - 61 r m a t e r i a l s . (GSC-39,697,793). Evidence o f pauses i n the downcutting a c t i o n of the r i v e r s i n p o s t - g l a c i a l time i s seen i n the v a r i o u s l e v e l s of flood p l a i n d e p o s i t s , p a r t i c u l a r l y i n Lynn canyon; they l i k e l y formed when a r e s i s t a n t m a t e r i a l was encountered and l a t e r a l e r o s i o n became t e m p o r a r i l y dominant. The l e v e l g r a v e l d e p o s i t a t the n o r t h end o f R i v e r s i d e D r i v e probably formed i n such a way. The p r e s e n t r i v e r channel i s entrenched i n a bedrock canyon a t l e a s t 30 m. below t h i s d e p o s i t , i n d i c a t i n g t h a t c o n s i d e r a b l e v e r t i c a l downcutting has o c c u r r e d s i n c e the r i v e r l a t e r a l l y eroded o v e r l y i n g s u r f i c i a l sediments. Maplewood t i d a l mudflats, a t the mouth of McCartney Creek ( P l a t e 8), i s made up of f i n e r g r a i n e d sediments (mainly s i l t and f i n e sand) than those i n the Lynn-Seymour d e l t a i n t o which i t grades. The upper and middle reaches of McCartney Creek flow through e a s i l y erodable C a p i l a n o c o h e s i o n l e s s m a t e r i a l thus p r o v i d i n g i t w i t h a l a r g e sediment source, but because of the low d i s c h a r g e of t h i s stream r e l a t i v e to e i t h e r of the major drainage ways and a low g r a d i e n t along i t s lower reaches, l i t t l e coarse m a t e r i a l i s t r a n s p o r t e d . S i g n i f i c a n t areas of man-made f i l l are found along Lynn Creek, i n two p l a c e s along the western end of D o l l a r t o n Highway, and along the w a t e r f r o n t a t the mouths of Lynn Creek and . Seymour R i v e r . The Lynn Creek f i l l i s a s a n i t a r y l a n d f i l l which i s a t l e a s t 10 m. t h i c k i n most p l a c e s . The two l o c a l i t i e s on D o l l a r t o n Highway r e p r e s e n t dumps of up to 5 m. of borrow m a t e r i a l . The w a t e r f r o n t area has a s u b s t a n t i a l but P l a t e 8. Maplewood t i d a l mudflats a t low t i d e . - 63 -unknown t h i c k n e s s of f i l l b u i l t up over the d e l t a f r o n t f o r dock l o a d i n g f a c i l i t i e s . I t i s a l s o l i k e l y t h a t many l o c a l c o n s t r u c t i o n s i t e s have emplaced t h i n l a y e r s of f i l l over the e x i s t i n g s u r f i c i a l m a t e r i a l . (GSC-358,373,445). S o i l s S o i l p r o f i l e s i n the Seymour area g e n e r a l l y appear to be p o o r l y developed, f o r the t e x t u r e of the parent m a t e r i a l i s s t i l l dominant. They are p o d z o l i c , developed from loamy g e o l o g i c a l m a t e r i a l s , w e l l to i m p e r f e c t l y d r a i n e d , h i g h l y leached, and reddish-brown i n c o l o u r . The b e t t e r developed s o i l s are l i k e l y h u m o - f e r r i c podzols which have formed on w e l l d r a i n e d s i t e s a t lower e l e v a t i o n s under mixed and c o n i f e r o u s f o r e s t cover. These s o i l s u s u a l l y have an o r g a n i c s u r f a c e h o r i z o n , a m i n e r a l -o r g a n i c h o r i z o n , and a d i s t i n c t , e l u v i a t e d , bleached h o r i z o n o v e r l y i n g the p o d z o l i c m i n e r a l h o r i z o n . C o a r s e - t e x t u r e d s u r f i c i a l m a t e r i a l s ; C a p i l a n o outwash, Vashon D r i f t , and s t a b l e c o l l u v i u m , are g e n e r a l l y o v e r l a i n by the h u m o - f e r r i c p o d z o l s . S l i g h t l y weaker p r o f i l e s are developed on the f i n e -g r a i n e d C a p i l a n o g l a c i o m a r i n e sediments. These ferro-humic podzols e x h i b i t a t h i c k s u r f a c e o r g a n i c h o r i z o n , a m i n e r a l -o r g a n i c h o r i z o n , and a t h i n , i n d i s t i n c t or n o n - e x i s t e n t , e l u v i a t e d , bleached h o r i z o n o v e r l y i n g a more o r g a n i c - r i c h - 64 -mineral h o r i z o n . In areas of poor drainage these s o i l s may have a mottled appearance i n t h e i r lower h o r i z o n , r e f l e c t i n g the r e d u c i n g c o n d i t i o n s ; brought on by water s a t u r a t i o n . P o o r l y developed m i n e r a l s o i l s w i t h l i t t l e or no h o r i z o n development, found on unstable c o l l u v i a l s l o p e s and r e c e n t a l l u v i a l d e p o s i t s , are c l a s s i f i e d as r e g o s o l s . Where f o r e s t -f l o o r o r g a n i c l i t t e r d i r e c t l y o v e r l i e s bedrock, the s o i l s are c l a s s i f i e d as f o l i s o l s . (Canada Dept. of A r g i c u l t u r e , 1974). The v a r i a t i o n i n s o i l p r o f i l e s found i n the Seymour area i s c e r t a i n l y much more complex than t h a t j u s t d i s c u s s e d , however a d e t a i l e d p e d o l o g i c a l survey was c o n s i d e r e d beyond the scope of t h i s study. Perhaps a more meaningful, y e t s t i l l rough, c l a s s i f i c a t i o n scheme i s to examine s o i l types developed from the d i f f e r e n t types of s u r f i c i a l m a t e r i a l s . (Table V I ) . S o i l drainage i s dependent on.the p e r m e a b i l i t y of the s o i l p r o f i l e and the u n d e r l y i n g parent m a t e r i a l , on s l o p e , and on depth t o the water t a b l e . G e n e r a l l y s o i l s can be d i v i d e d i n t o those with good downward drainage and those w i t h r e s t r i c t e d downward drainage. The l a t t e r group can be f u r t h e r s u b d i v i d e d on the b a s i s o f topography i n t o those w i t h good s u r f a c e drainage and those with poor s u r f a c e drainage. (Armstrong, 1961). The o n l y s o i l s w i t h good, u n r e s t r i c t e d downward drainage are on t h i c k d e p o s i t s of C a p i l a n o outwash m a t e r i a l . Other - 65 -coarse-textured s o i l s developed on colluvium, Vashon D r i f t , Capilano lag sand and gravel, or on Holocene a l l u v i a l material a l l have r e s t r i c t e d downward drainage due to some underlying ; geological feature. Impervious t i l l or bedrock underlie s o i l s developed on colluvium and lag gravel deposits, at r e l a t i v e l y shallow depths, thus r e s t r i c t i n g downward groundwater flow. However, l a t e r a l flow i s controlled by topography; therefore on slopes the surface drainage can be considered good. Where l o c a l i z e d f l a t - l y i n g or depressional areas occur, underlain by these materials, the surface drainage w i l l be poor. Generally a high water table i s present i n the Holocene a l l u v i a l sediments, permitting l i t t l e downward c i r c u l a t i o n of groundwater. TABLE VI Main S o i l Types Developed from S u r f i c i a l Materials (after Armstrong, 1961). S o i l textures are based on the S o i l Textural C l a s s i f i c a t i o n explained i n Appendix 3. Parent Material Main S o i l Types Colluvium rubbly loamy sand and rubbly sand Vashon D r i f t stony sandy loam Capilano glaciomarine sediments s i l t y loam, clayey s i l t y loam, and s i l t y clay a l l with scattered stones Capilano outwash sediments gravelly sandy loam, loamy sand, sandy loam Capilano l i t t o r a l sands s i l t y loam, sandy loam, loamy sand, and sand Capilano s u p r a l i t t o r a l lag gravels gravelly sandy loam and gravelly loamy sand Holocene mountain stream deposits gravelly loam, gravelly sandy loam, and sandy loam, however where stream gradients are low the s o i l s may be s i l t y loam or loam - 66 -S o i l s developed on impervious Capilano g l a c i o m a r i n e sediments have r e s t r i c t e d downward drainage due to the f i n e t e x t u r e of the s o i l i t s e l f . In a d d i t i o n , these d e p o s i t s g e n e r a l l y occupy f l a t - l y i n g or s l i g h t l y d e p r e s s i o n a l areas which causes poor s u r f a c e d r a i n a g e . In swampy or wetland areas i t i s not unusual to expect up to 0.5 m. of p a r t i a l l y decomposed o r g a n i c m a t e r i a l a t the top of the s o i l p r o f i l e . - 67 -CHAPTER IV TOPOGRAPHY Introduction Topography i s perhaps the most fundamental aspect of the physical environment of an area. Topographic conditions that a f f e c t urban r e s i d e n t i a l development include elevation and degree of slope. Elevation has a major e f f e c t on l o c a l c l i m a t i c conditions, which may be r e f l e c t e d i n the surface hydrology of the area. D i s t r i b u t i o n of geological materials may be dependent on changes in elevation. The amount of slope i s extremely important i n land-use a c t i v i t i e s . As slopes increase, conditions for r e s i d e n t i a l development become less favourable. I t i s not that development i s p h y s i c a l l y precluded on steeper slopes for, given s u f f i c i e n t f i n a n c i a l investment, engineering and a r c h i t e c t u r a l c a p a b i l i t y permits housing on v i r t u a l l y any s i t e . However, i n order to develop conventional r e s i d e n t i a l subdivisions with a minimum of environmental disturbance, urbanization i s limited to the less steeply sloping portions of h i l l s i d e s . Any development on sloping ground must consider the dynamic association of geologic, hydrologic, and c l i m a t i c conditions acting on the landscape. No r e a l consensus appears to have been formed on specifying areas unsuitable to urban development on the basis of slope alone. McHarg (1969) suggests slopes steeper than 20% should be prohibited from development whereas l o c a l - 68 -s t u d i e s (Planning Dept., D i s t r i c t of North Vancouver, 1975 and Hawksworth, 19 77) suggest 30% i s regarded as a reasonable maximum slope l i m i t f o r c o n v e n t i o n a l forms of h i l l s i d e development i n the Lower Mainland. Despite t h i s there are i n d i c a t i o n s t h a t s l o p e s i n the 25% to 30% range would r e q u i r e c a r e f u l l y designed c o n s t r u c t i o n techniques d u r i n g development. The 30% l i m i t may be a l i t t l e o p t i m i s t i c even though s p e c i f i c developments such as the B r i t i s h P r o p e r t i e s and S e n t i n e l H i l l i n West Vancouver are b u i l t on a maximum i n c l i n e of 3 5% w i t h some i n d i v i d u a l houses having been b u i l t on l o t s exceeding t h i s s l o p e . (Spearing, 1973). Powers (1974) suggests t h a t f o r slopes exceeding 20% the combination of s l o p e , heavy r a i n f a l l ( g r e a t e r than 1500 mm. per y e a r ) , f e a s i b i l i t y of r e v e g e t a t i o n , s o i l s t a b i l i t y , and s e r v i c e c o s t s and upkeep, forms a major l i m i t a t i o n . When v e g e t a t i o n i s removed and hard to r e p l a c e because of a t h i n s o i l p r o f i l e , h i g h p r e c i p i t a t i o n can i n c r e a s e e r o s i o n s i g n i f i c a n t l y on slop e s s t e e p e r than 15%. S p e c i f i c l i m i t s of slope f o r v a r i o u s urban uses have been d i s c u s s e d i n some s t u d i e s . The Un i t e d S t a t e s Dept. of A r g i c u l t u r e (19 73) has e s t a b l i s h e d very c o n s e r v a t i v e g u i d e l i n e s f o r urban use on s l o p i n g l a n d . Slopes w i t h g r e a t e r than 8% grade have moderate l i m i t a t i o n whereas a severe l i m i t a t i o n i s a p p l i e d to any sl o p e over 15%. These c r i t e r i a e s s e n t i a l l y apply to c o n v e n t i o n a l urban d e s i g n and p l a n n i n g i n " f l a t - l a n d " topography and are not p a r t i c u l a r l y w e l l s u i t e d t o mountainous areas such as B r i t i s h Columbia. However, i t i s important to note t h a t whereas development on slop e s exceeding 15% i s q u i t e f e a s i b l e , i t should proceed w i t h c a u t i o n a n d . i n c o r p o rate -the n a t u r a l contours of the land i n the urban des i g n . Spearing (19 73) has noted t h a t u n t i l now few s i t e s i n the p r o v i n c e having a slope of more than 10° (17.5%) have been c o n s i d e r e d s u i t a b l e f o r b u i l d i n g . In a d d i t i o n he recommends 17.5% be a maximum slope f o r driveways and notes t h a t l o g g i n g roads i n B.C. are l i m i t e d t o a slope of 20% by the Workman's Compensation Board. Hilpman (1968) p u b l i s h e d the most d e t a i l e d c r i t e r i a of slope l i m i t a t i o n to land-use. (Figure IV-1). T h i s c h a r t shows the optimum ranges of slopes f o r v a r i o u s urban i n s t a l l a t i o n s and a c t i v i t i e s . In p a r t i c u l a r g e n e r a l urban uses, c o n v e n t i o n a l housing, and a l l - w e a t h e r urban roads have low l i m i t a t i o n to development on s l o p e s l e s s than 15%. Engineered s t r u c t u r e s are a c c e p t a b l e on grades up to 25%. E f f e c t s of E l e v a t i o n on Climate Climate of a r e g i o n i s an important f a c t o r i n the development of a r e s i d e n t i a l area as i t has an impact on the c o s t o f d e s i g n i n g and m a i n t a i n i n g the s u b d i v i s i o n . Urban development a t h i g h e r e l e v a t i o n s w i l l encounter i n c r e a s e d p r e c i p i t a t i o n , g r e a t e r snow lo a d s , and c o o l e r temperatures. Main impacts o f these c l i m a t i c changes w i l l be i n c r e a s e d c o s t s f o r d e s i g n i n g s t r u c t u r e s and t h e i r s e r v i c e s , f o r h e a t i n g houses, to remove snow and i c e from roadways, and f o r d e s i g n i n g drainage systems which do not a p p r e c i a b l y a l t e r the Figure IV-1 Optimum Ranges of Slopes(Grades) for Various Urban Installations and Activit ies. ( f rom Hilpman, 1968 ) GENERAL RECREATION AREAS GENERAL URBAN USES SEPTIC FIELD SYSTEMS COMMERCIAL CENTRES ENGINEERED STRUCTURES CONVENTIONAL HOUSING AIRPORTS TRACKED VEHICLE OPERATIONS RAILROADS HIGHWAYS ALL-WEATHER URBAN ROADS I I I I I 10 COMMON GRADE LIMITATIONS 15 20 25 30 % GRADE 35 40 45 50 10" is 20" 25 n a t u r a l h y d r o l o g i c a l regimes. The Lower Mainland area o f southwestern B r i t i s h Columbia i s a f f e c t e d by p u l s a t i o n s of warm, moist a i r masses moving from the P a c i f i c , i n t e r a c t i n g w i t h c o l d , dry A r c t i c a i r masses t r a v e l l i n g from the e a s t over and between the Coast Mountains. Large s c a l e flow i s predominantly eastward, but l o c a l wind v e l o c i t y i s dependent on the s t r e n g t h and d i r e c t i o n of temperature and p r e s s u r e g r a d i e n t s . C l i m a t i c v a r i a t i o n s a t t r i b u t a b l e to l o c a l topographic i n f l u e n c e s are c o n s i d e r e d s i g n i f i c a n t . Hay and Oke (19 76) suggest t h a t topographic f e a t u r e s give r i s e to; u p l i f t ^ r e s u l t i n g i n c o o l i n g , p o s s i b l e condensation to form c l o u d s , and p o s s i b l e p r e c i p i t a t i o n ) ; c h a n n e l i n g and d e f l e c t i o n of a i r f l o w ; v a r i a t i o n s of s o l a r h e a t i n g o f the s u r f a c e owing to s l o p e angle and aspect; the p r o d u c t i o n of g r a v i t y winds (cold a i r - drainage downslope); and a g e n e r a l tendency toward c o o l e r temperatures w i t h i n c r e a s e d e l e v a t i o n . The North Shore mountains c o n t r o l the p r e c i p i t a t i o n p a t t e r n a c r o s s the Lower Mainland. Weather systems are f o r c e d to ascend t h i s b a r r i e r c a u s i n g i n c r e a s e d c l o u d cover and p r e c i p i t a t i o n c l o s e r to the mountains. In a d d i t i o n to i n c r e a s e d p r e c i p i t a t i o n w i t h e l e v a t i o n , p r e c i p i t a t i o n a l s o i n c r e a s e s more r a p i d l y up the major v a l l e y s o f Lynn Creek and Seymour R i v e r . T h i s has mainly been a t t r i b u t e d to the p o s i t i o n i n g of these v a l l e y s i n r e l a t i o n to the mountain f r o n t , as w e l l as a f u n n e l i n g e f f e c t of the g e n e r a l a i r f l o w - 72 -which leads to convergence and u p l i f t of the a i r . The mean annual p r e c i p i t a t i o n map f o r Greater Vancouver (Hay and Oke, 1976) shows t h a t y e a r l y r a i n f a l l i n c r e a s e s by 33% from downtown Vancouver (1500 mm.) to the mouth of T a y l o r Creek (2000 mm.) and f u r t h e r i n c r e a s e s the downtown amount by 66% a t the 1000 f o o t (300 m.) contour on Seymour Mountain (2500 mm.). The i n c r e a s e i n r a i n f a l l up Seymour V a l l e y i s shown by a mean annual amount of 1800 mm. a t Seymour F a l l s , some 19 km. upstream a t an e l e v a t i o n of 750 f e e t (230 m.). S h o r t - d u r a t i o n , h i g h - i n t e n s i t y r a i n f a l l , which i s a l s o c o n t r o l l e d by e l e v a t i o n change, i s important i n the s u r f a c e hydrology of an area. On a s m a l l s c a l e (of a l o t or l o c a l s t r e e t ) the extreme 2 4-hour p r e c i p i t a t i o n i s a u s e f u l parameter f o r i n d i c a t i n g the amount of water t h a t drainage systems must be a b l e to adequately handle. Bennett (1977) has produced a graph showing the v a r i a t i o n i n mean 24-hour p r e c i p i t a t i o n and 25-year r e t u r n - p e r i o d 24-hour p r e c i p i t a t i o n w i t h e l e v a t i o n . Data from h i s graph i n c l u d e d some Seymour area s t a t i o n s and t h i s i n f o r m a t i o n i s presented i n Table V I I . The mean value o f extreme 24-hour p r e c i p i t a t i o n i n c r e a s e s by more than 50% from sea l e v e l to 1000 f e e t (300 m.) e l e v a t i o n . The extreme 24-hour p r e c i p i t a t i o n w i t h a r e t u r n - p e r i o d o f 25 years i n c r e a s e s 35% between sea l e v e l and 650 f e e t (200m.) wit h only a s l i g h t i n c r e a s e up to 1000 f e e t (300 m.) e l e v a t i o n . P r e c i p i t a t i o n i n t e n s i t i e s i n the v a l l e y are s i g n i f i c a n t l y h i g h e r than the t r e n d shown f o r i n c r e a s e s due to e l e v a t i o n alone. TABLE VII Extreme Annual 24 - Hour P r e c i p i t a t i o n , ( a f t e r Bennett, 1977). S t a t i o n E l e v a t i o n i n f e e t (m.) Years of Record Mean (mm.) Standard D e v i a t i o n (mm.) 25-Year Return-P e r i o d (mm.) Second Narrows 13 (4) 17;(1958-74) 73 18 120 Seymour Ri v e r 590 (180) 23;(192 4-46) 112 25 173 Lynn Creek 625 (190) 10;(1965-74) 99 24 165 Seymour F a l l s 750 (229) 45;(1928-72) 143 48 253 Mount Seymour 2700 (823) 10;(1959-68) 123 24 191 T o t a l annual s n o w f a l l , maximum accumulated snowpack, and number of days w i t h s n o w f a l l i n c r e a s e w i t h e l e v a t i o n . A l l of these parameters are important i n determining the g e n e r a l a c c e s s i b i l i t y of an area f o r r e s i d e n t i a l use. Increased snowfall, w i t h e l e v a t i o n i s p a r t l y due to the gen e r a l o r o g r a p h i c i n c r e a s e but i s mainly c o n t r o l l e d by the decrease i n a i r temperature. On the North Shore, Bennett (19 77) has found t h a t t o t a l annual s n o w f a l l and days of snow i n c r e a s e s i g n i f i c a n t l y above 1150 f e e t (350 m.) e l e v a t i o n whereas a s u b s t a n t i a l i n c r e a s e i n maximum accumulated snowpack does not occur u n t i l an e l e v a t i o n of 2300 f e e t (700 m.) i s reached. The s i g n i f i c a n c e of t h i s i s t h a t v i r t u a l l y a l l the Seymour area l i e s below these c r i t i c a l e l e v a t i o n s and thus extreme c o n d i t i o n s and problems posed by e x c e s s i v e s n o w f a l l s w i l l be - 74 -r a r e l y encountered. T h i s i s not to say t h a t there w i l l be no d i f f i c u l t i e s w ith snow below these e l e v a t i o n s . T o t a l annual s n o w f a l l i n c r e a s e s 750 mm., days of snow i n c r e a s e by 13 days, and maximum snowpack i n c r e a s e s by 180 mm. from sea l e v e l t o 1000 f e e t (300 m.) e l e v a t i o n . (Bennett, 1977). The Atmospheric Environment S e r v i c e Climate S t a t i o n a t Second Narrows giv e s a mean annual s n o w f a l l of 600 mm. and a mean frequency of s n o w f a l l o f 8 days. T h i s i n c r e a s e i n s n o w f a l l w i t h e l e v a t i o n w i l l cause c o r r e s p o n d i n g l y g r e a t e r problems i n snow-removal and a c c e s s i b i l i t y . In a d d i t i o n i t has been found t h a t f o r each 1000 f o o t (300 m.) i n c r e a s e i n e l e v a t i o n ( f o r the i n t e r v a l from 500 f e e t (150 m.) to 3000 f e e t (900 m.)) there are about 45 more days wi t h f r o s t which w i l l c o n t r i b u t e to the c o s t and d i f f i c u l t y i n keeping roads open f o r v e h i c u l a r t r a f f i c . (Environment Canada, 1973). B u i l d i n g s must be c o n s t r u c t e d to support the g r e a t e s t weight of snow t h a t i s l i k e l y t o accumulate. Below 1300 f e e t (400 m.) snow loads do not i n c r e a s e a p p r e c i a b l y w i t h e l e v a t i o n . (Bennett, 1977). The p o s s i b i l i t y o f i n c r e a s e d snow loa d due to the a d d i t i o n of l a r g e amounts o f r a i n f a l l f o l l o w i n g a heavy s n o w f a l l i s the main concern a t lower e l e v a t i o n s , p a r t i c u l a r l y i n the major v a l l e y s . The e f f e c t s of topography on a i r temperature a l s o show c l e a r l y . Hay and Oke (19 76) suggest t h a t the mean annual temperature decreases about 1° C. per 1000 f e e t (300 m.) i n c r e a s e i n e l e v a t i o n . An important f a c t o r r e l a t i v e to - 75 -b u i l d i n g d e s i g n i s t h a t f u e l consumption f o r r e s i d e n t i a l h e a t i n g i s p r o p o r t i o n a l to the number of h e a t i n g degree-days, (the number of days the d a i l y mean temperature i s l e s s than 18° C. times the d i f f e r e n c e between each d a i l y mean temperature and 18° C ) . Based on l i m i t e d i n f o r m a t i o n , Environment Canada (19 73) found t h a t a 14% i n c r e a s e i n h e a t i n g degree-days can be expected per 1000 f e e t (300 m.) i n c r e a s e i n e l e v a t i o n . D i s t r i b u t i o n and S i g n i f i c a n c e of Slopes The importance of s l o p e magnitude on land-use a c t i v i t i e s has been d i s c u s s e d and i s summarized i n F i g u r e IV-1. In order to prepare a slope map there must f i r s t be a topographic base-map a v a i l a b l e . Two l e v e l s of topographic i n f o r m a t i o n have been compiled f o r North Vancouver-Seymour. The N a t i o n a l Topographic System 1:25,000 maps (92G/6a and 7d) w i t h a 25 f o o t contour i n t e r v a l g ive medium s c a l e coverage of the area. The D i s t r i c t o f North Vancouver commissioned Aero Surveys L t d . of Vancouver to prepare l a r g e s c a l e topographic coverage of the e a s t e r n d i s t r i c t , i n c l u d i n g most o f the Seymour area. These maps, a t a s c a l e o f 1:2400 wi t h a 5 f o o t contour i n t e r v a l , were compiled from v e r t i c a l a i r photographs taken i n A p r i l , 1956. H o r i z o n t a l and v e r t i c a l c o n t r o l was e s t a b l i s h e d by the F i e l d Survey D i v i s i o n of Aero Surveys L t d . The topographic map (Figure IV-2) was compiled a t a s c a l e of 1:960 0 w i t h a 2 5 f o o t contour i n t e r v a l from reduced v e r s i o n s of the o r i g i n a l l a r g e s c a l e map-sheets. Contour - 76 -l i n e s above 1200 f e e t , i n p l a c e s above 1000 f e e t on Seymour Mountain, and above 400 f e e t i n the i n t e r r i v e r area, were i n t e r p o l a t e d from the N a t i o n a l Topographic System 1:25,000 maps, as they were not i n c l u d e d i n the work done by Aero Surveys. There i s no doubt t h a t i n many p l a c e s on the map topography i s i n a c c u r a t e l y r e presented because of poor q u a l i t y photographs, heavy v e g e t a t i o n , and i n t e r p o l a t i o n . In p a r t i c u l a r , contour l i n e s through stream r a v i n e s are o f t e n erroneous. In a d d i t i o n , there have been some man-made m o d i f i c a t i o n s to slopes i n the p a s t 20 y e a r s . However, i t i s f e l t t h a t f o r the purpose and d e t a i l o f t h i s study the topography i s adequate and o n l y minor changes have been made where very obvious mistakes c o u l d be i d e n t i f i e d . For l o c a l development i t may be necessary to c a r r y out d e t a i l e d s u r f a c e topographic surveys. The slope map (Figure IV-3) was prepared from 1:9600 s c a l e reduced v e r s i o n s of the o r i g i n a l Aero Surveys contour maps w i t h a 5 f o o t contour i n t e r v a l . Slope c l a s s e s i n p ercent grade were determined from s c a l e s presented i n Thrower and Cooke (1968). Accuracy o f the slope map i s dependent on the accuracy of the o r i g i n a l contour l i n e s . A slope map i s a u s e f u l p l a n n i n g t o o l because the topography i s broken down i n t o p e r c e n t grade i n t e r v a l s which can be r e l a t e d to v a r i o u s urban-use a c t i v i t i e s such as those summarized i n F i g u r e IV-1. A p p l y i n g slope l i m i t a t i o n s to development i n North Vancouver-Seymour i n v o l v e s an assessment of p r e v i o u s s t u d i e s p l u s a knowledge of the d i s t r i b u t i o n of g e o l o g i c a l m a t e r i a l s i n r e l a t i o n to s l o p e s . In g e n e r a l , i t i s f e l t t h a t g e n t l e slopes up t o 15% grade p r e s e n t few problems to urban r e s i d e n t i a l use and thus have a s l i g h t l i m i t a t i o n to development. Steeper slopes i n the area g e n e r a l l y are e i t h e r u n d e r l a i n by bedrock c l o s e to the s u r f a c e or are the product of p o s t - g l a c i a l f l u v i a l e r o s i o n , t h e r e f o r e they are p o t e n t i a l l y s u s c e p t i b l e to i n s t a b i l i t y or e r o s i o n i f v e g e t a t i o n i s removed or the s u r f a c e h y d r o l o g i c regime i s a l t e r e d . In other s t u d i e s there appears to be some h e s i t a n c y about a c c e p t i n g a 30% slope as the lower l i m i t f o r severe l i m i t a t i o n , although 20% i s d e f i n i t e l y too low and even 25% i s q u e s t i o n a b l e . For the purpose of t h i s study i t i s f e l t t h a t slopes steeper than 27 1/2% pose a severe l i m i t a t i o n to urban use. Slopes between 15% and 27 1/2% are d e f i n e d as having moderate topographic l i m i t a t i o n . Depending on the g e o l o g i c a l m a t e r i a l s and h y d r o l o g i c a l c o n d i t i o n s o p e r a t i n g on a slope these l i m i t a t i o n i n t e r v a l s may be s l i g h t l y m o d i f i e d . For example, a w e l l d r a i n e d s l o p e u n d e r l a i n by t i l l i n the range of 15% to 20% grade may be more s t a b l e and s u i t a b l e f o r development than a bar r e n 10% slope c o n s i s t i n g of e a s i l y erodable sand. S t e e p l y s l o p i n g areas (greater than 27 1/2% grade) dominate those p a r t s of the landscape which are bedrock c o n t r o l l e d . Topography i s g e n e r a l l y more complex i n these areas as bedrock r i d g e s , hummocks, and i n t e r r i d g e v a l l e y s and depressions c r e a t e g e n t l y and moderately s l o p i n g ground w i t h i n the o v e r a l l s t e e p l y s l o p e d area. I n f i l l i n g of - 78 -s u r f i c i a l m a t e r i a l i n depressions on the bedrock s u r f a c e a l s o tends to modify l o c a l topography. Downcutting. of Lynn Creek and Seymour R i v e r i s mainly r e s p o n s i b l e f o r c r e a t i n g s t e e p l y s l o p i n g v a l l e y s i d e s i n the s u r f i c i a l sediments. Recent s l i d e s and washouts along the v a l l e y s have c o n t r i b u t e d to f u r t h e r steepening, p a r t i c u l a r l y along the upper slope s c a r p s . D i f f e r e n t i a l e r o s i o n has l e f t moderately and g e n t l y s l o p i n g areas w i t h i n the o v e r a l l steep v a l l e y s l o p e s , but these areas are i r r e g u l a r l y d i s t r i b u t e d and f o r the most p a r t , are s u s c e p t i b l e to c o n d i t i o n s which c o u l d l e a d to p o t e n t i a l i n s t a b i l i t y . Steep slopes n o r t h and west of Deep Cove, although mainly u n d e r l a i n by t h i c k Vashon t i l l , are c o n t r o l l e d by the same bedrock topography t h a t dominates the Woodlands area. Moderately and s t e e p l y s l o p i n g areas along B u r r a r d I n l e t , e a s t of T a y l o r Creek to Roche P o i n t , are mantled by t i l l which l i k e l y conforms to a p r e - e x i s t i n g topographic s u r f a c e . The many streams which flow down these t i l l - c o v e r e d s lopes are c o n f i n e d i n s t e e p - s i d e d r a v i n e s , which i n p l a c e s have bank slop e s exceeding 60%. Sand and g r a v e l removal i n some of the major p i t s has a r t i f i c i a l l y c r e a t e d s t e e p l y and moderately s l o p i n g areas. In p l a c e s these s l o p e s exceed a 60% grade. Moderately s l o p i n g areas (grades between 15% and 27 1/2%) are g e n e r a l l y a s s o c i a t e d with the t r a n s i t i o n from steep t o - 79 -gentle s l o p e s . As a l r e a d y d e s c r i b e d there are many areas o f moderate slope w i t h i n the o v e r a l l s t e e p l y s l o p i n g bedrock mountain s i d e and v a l l e y s i d e s of Lynn Creek and Seymour R i v e r . Other areas of moderate grade occur: where s u r f i c i a l sediments o v e r l a p the base of bedrock s l o p e s ; along the north shore of B u r r a r d I n l e t a t the b r e a k - i n - s l o p e between g e n t l y s l o p i n g uplands and steep lower s l o p e s ; along the middle reaches of some stream g u l l i e s ; and along the f r o n t edges of some r a i s e d , C a p i l a n o d e l t a i c outwash t e r r a c e s . Areas of g e n t l y s l o p i n g land ( l e s s than 15% grade) dominate the s u r f i c i a l landscape except i n regions m o d i f i e d by p o s t - g l a c i a l e r o s i o n . Vashon D r i f t covered ground i s the most t o p o g r a p h i c a l l y v a r i a b l e w i t h i n t h i s s u r f i c i a l landscape. The g e n t l y s l o p i n g and u n d u l a t i n g t i l l s u r f a c e f e a t u r e s s l o p e s r a n g i n g from 0% t o 15% w i t h numerous b r e a k s - i n - s l o p e . Large areas u n d e r l a i n by Ca p i l a n o g l a c i o m a r i n e sediments r a r e l y have slo p e s exceeding 10%, with a l a r g e p a r t having l e s s than 5% grade. F l a t - t o p p e d d e l t a i c t e r r a c e s of Ca p i l a n o outwash u n d e r l i e the g e n t l y s l o p i n g land a l o n g the e a s t s i d e o f Seymour R i v e r and along the i n t e r r i v e r r i d g e . The d e p r e s s i o n a l lowland south-west of Deep Cove, although g e n t l y s l o p i n g , has an i r r e g u l a r topographic e x p r e s s i o n . T h i s l i k e l y r e f l e c t s a t h i n d e p o s i t of outwash and beach sediments o v e r l y i n g t i l l and bedrock. The f l o o d p l a i n d e l t a s of Lynn Creek and Seymour - 80 -Riv e r are the l a r g e s t areas of l e v e l l a n d . Slopes along the d e l t a s u r f a c e are l e s s than 2 1/2% except immediately adjacent to the presen t channels. Summary of Top o g r a p h i c a l C o n s t r a i n t s to Development Top o g r a p h i c a l c o n s t r a i n t s to c o n v e n t i o n a l urban r e s i d e n t i a l development i n c l u d e both e l e v a t i o n and slope l i m i t a t i o n s . L i m i t a t i o n to development posed s o l e l y by e l e v a t i o n i s d i f f i c u l t to assess because i t i n v o l v e s more of a c o s t - b e n e f i t c o n s t r a i n t r a t h e r than a s t r i c t l y geomorphic c o n s t r a i n t . The only d e f i n i t e l i m i t i n g f a c t o r i s the maximum e l e v a t i o n to which pres e n t u t i l i t i e s are capable of s e r v i c i n g . E x i s t i n g s e r v i c e s i n North Vancouver are designed to s e r v i c e o n l y to 1150 f e e t (350 m.) e l e v a t i o n . However, i n order to operate s e r v i c e s a t t h i s maximum demand, major and c o s t l y improvements to the systems would be necessary. Development a t h i g h e r e l e v a t i o n s w i l l have to contend w i t h i n c r e a s e d t o t a l annual p r e c i p i t a t i o n and i n c r e a s e d s h o r t -d u r a t i o n , h i g h - i n t e n s i t y r a i n f a l l . These e f f e c t s are f u r t h e r magnified i n the major r i v e r v a l l e y s . Drainage f a c i l i t i e s to prov i d e f o r h i g h s u r f a c e r u n o f f w i l l have to be designed and maintained to prevent any s i g n i f i c a n t a l t e r a t i o n o f s u r f a c e h y d r o l o g i c a l regimes. Although dramatic i n c r e a s e s i n annual s n o w f a l l , number of days, of snowfall,and maximum accumulated snowpack do not begin u n t i l a l t i t u d e s a t l e a s t g r e a t e r than 1150 f e e t (350 m.) - 81 -have been reached, s i g n i f i c a n t i n c r e a s e s i n s n o w f a l l do occur between sea l e v e l and 1000 f e e t (300 m.) e l e v a t i o n . A l l of these parameters are important i n d e t e r m i n i n g the g e n e r a l a c c e s s i b i l i t y of an area f o r r e s i d e n t i a l use. Accompanying t h i s i n c r e a s e i n s n o w f a l l w i t h e l e v a t i o n , i s an i n c r e a s e i n the number of days w i t h f r o s t , which together combine to cause c o r r e s p o n d i n g l y g r e a t e r problems w i t h snow removal and d e - i c i n g of roads. Mean annual temperature decreases w i t h e l e v a t i o n , l e a d i n g to h i g h e r f u e l c o s t s f o r h e a t i n g houses. Other c o n s i d e r a t i o n s o f h i g h e r e l e v a t i o n development i n the Seymour area are t h a t more bedrock i s exposed, thus i n c r e a s i n g development c o s t s , and t h a t these areas are the headwaters f o r many of the s m a l l e r streams, consequently are very s e n s i t i v e to changes i n the h y d r o l o g i c a l regime. These f a c t o r s are d i s c u s s e d more f u l l y i n l a t e r c h a p t e r s . I t must be kept i n mind t h a t the technology to develop on steep s l o p e s and a t h i g h e l e v a t i o n s i s r e a d i l y a v a i l a b l e . However once s p e c i a l a r c h i t e c t u r a l and e n g i n e e r i n g designs are employed, c o s t s per housing u n i t begin to r i s e s i g n i f i c a n t l y . Another important f a c t o r i s t h a t i t i s now r e c o g n i z e d t h a t d e n s i t y of development must decrease as the slope becomes s t e e p e r . Hawksworth (1977) presented f i g u r e s which show accepted d e n s i t y standards f o r development and standards f o r the amount of area which should be r e t a i n e d i n i t s n a t u r a l s t a t e a t v a r i o u s slope grades. These are summarized i n the f o l l o w i n g t a b l e . - 82 -TABLE VI I I Accepted Density Standards f o r Development and Standards f o r the Percentage of Area Retained i n a N a t u r a l S t a t e a t Various Slopes, ( a f t e r Hawksworth, 1977) Average Percent Slope * U n i t s per Acre Percentage of Area i n N a t u r a l S t a t e 10% 2.0 - 3.5 30 - 32% 15% 1.5 - 3.0 32 - 40% 20% 1.2 - 2.5 43 - 55% 25% 0.8 - 2.0 57 - 70% 30% 0.4 - 1.5 72 - 90% * These f i g u r e s r e f e r to gross d e n s i t i e s , t h a t i s , they i n c l u d e roads, sidewalks, parks, e t c . Standards o f t h i s type r e f e r to c o n v e n t i o n a l s i n g l e -f a m i l y housing developed a t approximately even d e n s i t i e s over the h i l l s i d e and do not c o n s i d e r c l u s t e r type development. I t i s obvious t h a t on s t e e p e r s l o p e s , i f these standards are u t i l i z e d , the c o s t per housing u n i t f o r d e v e l o p i n g and s e r v i c i n g u t i l i t i e s and roadways would be a p p r e c i a b l y h i g h e r than f o r g e n t l y s l o p i n g areas. These h i g h e r c o s t s must be c o n s i d e r e d a l i m i t i n g f a c t o r to development. Geomorphic c o n s t r a i n t s imposed by topography are mainly l i m i t e d to steepness o f s l o p e , although landscape p o s i t i o n i s c o n s i d e r e d somewhat important. (Table I X ) . D e p r e s s i o n a l or f l a t - l y i n g areas a d j a c e n t to s l o p i n g ground can r e c e i v e c o n s i d e r a b l e seepage and r u n o f f , c a u s i n g poor drainage and a h i g h water t a b l e . - 83 -TABLE IX Degree of L i m i t a t i o n o f Topographic F a c t o r s to Urban R e s i d e n t i a l Land-Use. L i m i t i n g F a c t o r Degree of L i m i t a t i o n S l i g h t Moderate Severe slope 0 - 15% 15 - 27 1/2% g r e a t e r than 2 7 1/2% landscape p o s i t i o n — d e p r e s s i o n a l — Areas u n d e r l a i n by g r a n i t i c bedrock and where pos t -g l a c i a l f l u v i a l e r o s i o n has c r e a t e d s t e e p - s i d e d r i v e r v a l l e y s and stream r a v i n e s , make up most of the area having a severe slope l i m i t a t i o n . W i t h i n bedrock r e q i o n s l o c a l areas o f s u r f i c i a l m a t e r i a l and the hummocky nature o f the rock s u r f a c e c r e a t e s some p a r t s w i t h l e s s severe l i m i t a t i o n . A r t i f i c i a l l y over-steepened sl o p e s i n the abandoned sand and g r a v e l p i t s are p o t e n t i a l l y unstable and have severe l i m i t a t i o n to development. Regrading and s t a b i l i z a t i o n measures c o u l d modify these s l o p e s , removing t h e i r severe slope l i m i t a t i o n . The s i g n i f i c a n c e of d e s i g n a t i n g areas as having moderate s l o p e l i m i t a t i o n i s t h a t development on t h i s s l o p i n g ground c o u l d l e a d to e r o s i o n a l or s t a b i l i t y problems i f i t i s not done c a r e f u l l y arid c o ntained w i t h i n the l i m i t a t i o n s imposed by oth e r geomorphic parameters. In g e n e r a l , w e l l d r a i n e d ground u n d e r l a i n by t i l l and bedrock w i t h l e s s than 20% grade probably c o u l d be c l a s s i f i e d as s l i g h t l i m i t a t i o n areas w i t h r e s p e c t to s l o p e . S i m i l a r l y , r a s i e d d e t l a - t e r r a c e f r o n t s which s l o p e at l e s s than 20% can be f a i r l y e a s i l y developed p r o v i d i n g c o n s t r u c t i o n methods are used which do not expose l a r g e areas of the e a s i l y erodable c o h e s i o n l e s s sediment to e x c e s s i v e s u r f a c e r u n o f f . Moderately s l o p i n g l a n d , w i t h g r e a t e r than 20% grade, adjacent to the middle reaches of the s m a l l streams should not be developed because of h y d r o l o g i c c o n d i t i o n s . Areas of g e n t l e s l o p e have s l i g h t l i m i t a t i o n to r e s i d e n t i a l development. L o c a l i z e d areas of low slope contained w i t h i n an o v e r a l l s t e e p l y s l o p i n g r e g i o n , such as on the mountain s i d e , although not c o n s t r a i n e d d i r e c t l y by degree of s l o p e , are e s s e n t i a l l y i n a c c e s s i b l e because of the surrounding topography. Most of T the Seymour area u n d e r l a i n by s u r f i c i a l sediments has' s l i g h t s lope l i m i t a t i o n to development. - 85 -CHAPTER V SURFACE HYDROLOGY I n t r o d u c t i o n E f f e c t s on the h y d r o l o g i c regime of streams imposed by urban development i n n a t u r a l watersheds have been w e l l documented and shown to be s i g n i f i c a n t . Some of the e f f e c t s i n c l u d e : i n c r e a s e d peak flow, which can cause s e r i o u s f l o o d i n g ; decreased low flow and i n c r e a s e d sediment y i e l d , which can upset the stream ecology; and decreased water q u a l i t y , which can a f f e c t f i s h spawning and r e a r i n g , r e c r e a t i o n , and perhaps pose a s e r i o u s h e a l t h hazard. U r b a n i z a t i o n w i l l i n t e r a c t with h y d r o l o g i c systems a t two l e v e l s . L o c a t i o n and d e s i g n of s p e c i f i c s t r u c t u r e s along s u r f a c e channels can be r e l e v a n t i n terms of f l o o d hazard, whereas r e s i d e n t i a l s u b d i v i s i o n development (with accompanying road and drainage networks) can have a much gr e a t e r e f f e c t on the o v e r a l l h y d r o l o g i c regime, i n c l u d i n g i n c r e a s e d peak flow, i n c r e a s e d sedimentation, and i n c r e a s e d channel e r o s i o n . The h y d r o l o g i c a l s i g n i f i c a n c e of g e o l o g i c a l m a t e r i a l s i s important as i t determines drainage c h a r a c t e r i s t i c s of the area, e r o s i o n p o t e n t i a l , and types of f l o o d p r o c e s s e s . The Seymour area i s d i s s e c t e d by many r i v e r s and creeks which flow i n t o B u r r a r d I n l e t and Indian Arm. The two major watercourses, Lynn Creek and Seymour R i v e r , are used as p u b l i c water-supply sources. Watersheds of these two r i v e r s - 86 -2 comprise about 2 35 km., the majority of which i s closed to the public, s e l e c t i v e l y logged as a water conservation measure, and p a t r o l l e d and protected from f i r e s . Preservation of these basins since 1925 has given the area a superb water supply at r e l a t i v e l y low cost and has helped to prevent major flooding along the r i v e r flood p l a i n s . (Environment Canada, 197 3). Seymour River has a storage dam operating at Seymour F a l l s , 19 km. from i t s mouth. At certain times of the year the dam can be used for flood control. The l a s t damaging floods on Lynn Creek and Seymour River occurred i n 1961 and since that time much has been done to strengthen the channel banks and protect against future flooding. However, there w i l l always be po t e n t i a l danger to development near the main channels along the lower reaches of these drainage ways. Many other natural watercourses traverse the Seymour h i l l s l o p e and run to the sea; they range from minor depressions to deep g u l l i e s , some of which have perennial flow and others which are ephemeral. Watersheds of these streams vary from several hundred acres to less than ten acres. A l l of these however, are sim i l a r i n that they can occasionally reach flood stage very rapidly. During these p o t e n t i a l l y destructive high flows, the streams can carry large quantities of sediment and fl o a t i n g debris which exert powerful erosive forces on the channel banks and contribute to the i n s t a b i l i t y of man-made structures close to them. After such peak flows, sediment and debris w i l l be l e f t as bedload and overbank deposits. Some of the streams which are considered as important - 87 -watercourses d r a i n i n g the Seymour area, although t h e i r e n t i r e channel l e n g t h may not l i e w i t h i n the area, are McCartney Creek, T a y l o r Creek, an unnamed creek a l o n g s i d e Mt. Seymour Road, G o l f Course Creek, G a l l a n t Creek, Panorama Creek, F r a n c i s Creek, and A l l a n Creek. (Figure 1-1). For these streams, three main c o n d i t i o n s c o n t r i b u t e to q u a n t i t i e s and r a t e s of r u n o f f ; the c o n t r i b u t i n g area, the r a i n f a l l , and the imperviousness of the ground i n the c o n t r i b u t i n g area. F l o o d Hazard Areas a f f e c t e d by f l o o d i n g of the North Shore streams are r e l a t i v e l y l o c a l i z e d , however, i t i s because of the v i o l e n c e of f l o o d s and the frequent, o f t e n simultaneous occurrence i n many l o c a l i t i e s , which make these events noteworthy. The steep stream channels are h i g h energy environments, c h a r a c t e r i z e d by extreme f l u c t u a t i o n s i n d i s c h a r g e . F l o o d i n g i s not always simple overbank flow dependent on h i g h peak r u n o f f , but o f t e n i n v o l v e s c o n s t r i c t i o n or blockage, accompanied by channel d i v e r s i o n or downstream surges of h i g h d i s c h a r g e mixed w i t h d e b r i s . C o n s t r i c t i n g s t r u c t u r e s such as pipes and c u l v e r t s o f t e n are the i n i t i a t i o n p o i n t of such f l o o d s . The known h i s t o r y of f l o o d i n g on the North Shore has been compiled by Karanka (1977). Beginning i n 1896, n e a r l y 50 f l o o d s and 160 i n s t a n c e s of f l o o d damage have been recorded on the North Shore between Li o n ' s Bay and Deep Cove. - 88 -In The Seymour area, f l o o d damage was r e s t r i c t e d to the l a r g e r watercourses, Lynn Creek and Seymour R i v e r , u n t i l 19 55. (Appendix 4). Since t h a t time the frequency.of l o c a l i z e d f l o o d s on s m a l l streams has i n c r e a s e d and there i s no r e p o r t of f l o o d damage on the major r i v e r s s i n c e 1961. T h i s i s undoubtedly due to three f a c t o r s ; i n c r e a s e d r e s i d e n t i a l development near the s m a l l e r creeks i n the p a s t two decades, e f f e c t i v e c h a n n e l i z a t i o n of Lynn Creek and Seymour R i v e r through t h e i r f l o o d p l a i n s , and completion o f the Seymour F a l l s dam and r e s e r v o i r i n 1961. The most dramatic example of u r b a n i z a t i o n c a u s i n g f l o o d damage on the North Shore i s t h a t of Mosquito Creek i n the w i n t e r s of 1955 and 1956. F a l l f l o o d s had been a f e a t u r e of the creek f o r many y e a r s , but s i n c e the a d j a c e n t banks were s p a r s e l y s e t t l e d . they caused only minor damage. The main channel changed i t s p o s i t i o n many times, f l u c t u a t i n g over the wide f l o o d p l a i n along i t s middle reaches, n o r t h of Queens Road. In the e a r l y 1950's, l a r g e areas of the watershed were completely denuded f o r s u b d i v i s i o n expansion and r e s i d e n t i a l l o t s along the f l o o d p l a i n became very popular from the viewpoint of p r i v a c y and a e s t h e t i c appeal. On November 2 and 3, 1955 a very i n t e n s e r a i n f a l l combined wi t h m e l t i n g snow i n the upper watershed to produce 3 a r u n o f f estimated a t 37-40 m / s e c . (Greater Vancouver Sewerage and Drainage D i s t r i c t , 1963; 1964). The creek overflowed i t s banks a f t e r b e i n g jammed by logs c l e a r e d from the surrounding s u b d i v i s i o n development. Damage i n c l u d e d - 89 -washing out of three blocks of paved stre e t and sanitary-sewer, erosion of creek frontage, flooding of basements, st r u c t u r a l damage to two houses, and deposition of sand and gravel over gardens and streets. In December, 1956, another, less severe flood caused the loss of a l i f e . During the 19 55 flood the creek scoured through Capilano outwash sands and gravels and began rapidly downcutting into underlying, e a s i l y erodable Quadra Sand. The creek bed was observed to have been lowered by 2.5 m. between 19 55 and 1963. In the years following the floods, channel maintenance was car r i e d out i n the creek, c l e a r i n g out debris and placing heavier material along the banks. However, the ex i s t i n g channel was considered inadequate to handle any major storm runoff so, i n 1967, a flood control structure was b u i l t . I t consisted of a rectangular reinforced concrete channel, extending about 800 m. upstream from Queens Road, with a debris basin and earth dam at the i n l e t and an energy-d i s s i p a t i n g structure at the outle t : flooding has not recurred since the completion of the flood control measures. The common patterns of flood damage on the North Shore are point and li n e a r damage. (Karanka, 1977). The most frequent i s point damage, consisting of bank erosion and channel blockage where flooding i s l o c a l i z e d at stream crossings or other c o n s t r i c t i o n s . Linear damage, although less common i s more extensive, caused by flooding over large areas p a r a l l e l to the natural channel. Diversion and overbank flow - 90 -d u r i n g extreme peak d i s c h a r g e can l e a d to t h i s type of i n u n d a t i o n . S t r e e t s o f t e n form a path', o f l e a s t r e s i s t a n c e and can channel the d i v e r t e d flow a c o n s i d e r a b l e d i s t a n c e . On l a r g e r watercourses (Lynn Creek and Seymour: River) f l o o d i n g has not o n l y damaged numerous s t r u c t u r e s l o c a t e d on t h e i r a c t i v e f l o o d p l a i n d e l t a s , but a l s o c o n t r i b u t e d to l o c a l i z e d slumping where the v a l l e y w a l l s a d j a c e n t to narrow upstream f l o o d p l a i n s have been undermined. (Appendix 4). During extreme peak flows the lower reaches of Lynn Creek and Seymour R i v e r were c h a r a c t e r i z e d by s h i f t i n g of channels w i t h a tendency to complete d i v e r s i o n from channel to channel. P r i o r to 1910, Seymour R i v e r flowed i n two or more channels. Karanka (1977) suggested t h a t , based on an average frequency of f l o o d damage on these r i v e r s between the years 1902 and 1961, approximately a 4 to 8-year peak flow would l o c a l l y overtop or erode the channel banks, c a u s i n g minor damage to adjacent s t r u c t u r e s . Higher flows than the 4 to 8-year f l o o d were necessary b e f o r e channel d i v e r s i o n o c c u r r e d . However, when t h i s happened major damage o f t e n ensued to adjacent s t r u c t u r e s . The lower reaches of Lynn Creek and Seymour R i v e r have been s t a b i l i z e d i n t h e i r p r e s e n t p o s i t i o n by s t r a i g h t e n i n g and deepening the channels and r i p r a p p i n g the banks. Two types of f l o o d processes c h a r a c t e r i z e the s m a l l e r , steeper, h i g h energy streams which flow o f f the North Shore - 91 -mountains. (Karanka, 1977). Surging, the process of accumulation and b r e a c h i n g of temporary d e b r i s dams along the channel, was r e p o r t e d by R u s s e l l (19 72) as o c c u r r i n g i n the steep r a v i n e s along Howe Sound. Temporary dams can form a t c u l v e r t s and b r i d g e s which are in a d e q u a t e l y designed to handle • the combination o f high d i s c h a r g e , d e b r i s , and bedload moving down the channel. Upstream ponding behind t h i s blockage w i l l occur u n t i l the creek o v e r f l o w s , washing out the c r o s s i n g . Damage i s u s u a l l y r e s t r i c t e d to t h i s p o i n t although, i n l e s s c o n f i n e d channels, flow may be d i v e r t e d along an adjacent s t r e e t or lowland area. Surging along r a v i n e s can cause bank f a i l u r e , although i n some cases extremely l a r g e slumps may be the cause of s u r g i n g . The other main f l o o d process i s . u s u a l i n undeveloped areas along the steeper, upper s l o p e s . D i v e r s i o n of flow along o l d roadways (eg. l o g g i n g roads) can cause g u l l y i n g and unconfined s u r f a c e flow. Areas near the headwaters of streams, where channels are not w e l l d e f i n e d and there i s c o n s i d e r a b l e s u r f a c e and n e a r - s u r f a c e r u n o f f , are p a r t i c u l a r l y s u s c e p t i b l e to t h i s p rocess. In such areas roadbeds e f f i c i e n t l y i n t e r c e p t and d i v e r t water where they cross the slope a t an angle to the main d i r e c t i o n o f flow and r u n o f f . Even lower down the streams, roads which p a r a l l e l or angle downslope from-unconfined channels can be s u b j e c t to flow d i v e r s i o n from the creeks and wash out over a c o n s i d e r a b l e d i s t a n c e . - 92 -D i s t r i b u t i o n and S i g n i f i c a n c e of Surface H y d r o l o g i c a l Features The map of s u r f a c e hydrology (Figure V-l) i s an i n v e n t o r y of c e r t a i n s u r f a c e h y d r o l o g i c a l f e a t u r e s which are co n s i d e r e d important when p l a n n i n g urban r e s i d e n t i a l development. The drainage b a s i n i s g e n e r a l l y acknowledged to be a fundamental u n i t of study of the h y d r o l o g i c a l system. (Gregory and W a l l i n g , 1971). The f u n c t i o n i n g o f a drainage b a s i n i s dependent on many c h a r a c t e r i s t i c s which can be r e a d i l y i d e n t i f i e d , such as type of g e o l o g i c a l m a t e r i a l , topography of the b a s i n and the stream system, area of the b a s i n , and land-use. Because these i n f l u e n c e the amount of storage which a b a s i n can achieve, they determine the r a t e and extent a t which i n p u t ( p r e c i p i t a t i o n ) i s transformed i n t o output (streamflow). The drainage network r e p r e s e n t s the dynamic behavior of a drainage b a s i n and i n c l u d e s both p e r e n n i a l and i n t e r m i t t e n t streams. The form of p e r e n n i a l channels i n s m a l l systems ranges from meandering, unconfined streams t o deeply i n c i s e d , steep r a v i n e s . Depending on the l o c a t i o n , i n t e r m i t t e n t - c h a n n e l form a l s o v a r i e s : s t e e p - s i d e d g u l l i e s develop on steep s l o p e s where the drainage i s fed by seepage d u r i n g the wet season, whereas i n lowland areas or near the headwaters of the streams, i n t e r m i t t e n t drainage appears to f o l l o w shallow, unconfined, and i n d i s t i n c t channels. - 93 -Swampy areas or wetlands are i n d i c a t i v e of e i t h e r c o n d i t i o n s o f poor drainage or of constant s u r f a c e or subsurface seepage. P o o r l y d r a i n e d areas can be caused by a hi g h water t a b l e , a d e p r e s s i o n a l or f l a t - l y i n g impervious s u r f a c e , or both. Seepage zones are caused by p e r m e a b i l i t y d i f f e r e n c e s o f s u r f i c i a l sediments exposed on sl o p e faces or by groundwater flow through s a t u r a t e d s o i l . I d e n t i f i c a t i o n of seepage s i t e s i s important i n determining c o n d i t i o n s which can l e a d t o slope f a i l u r e . The t i d a l mudflats d i f f e r from other s u r f a c e h y d r o l o g i c f e a t u r e s i d e n t i f i e d because they are a s s o c i a t e d more wit h the marine, r a t h e r than the fresh-water environment. B i o l o g i c a l l y the mudflats are p o t e n t i a l l y important as they r e p r e s e n t an i n t e r a c t i o n o f fresh-water and s a l t - w a t e r eco-systems which have not been e x t e n s i v e l y damaged. Areas s u s c e p t i b l e to f l o o d i n g do not n e c e s s a r i l y o u t l i n e f l o o d p l a i n s of any p a r t i c u l a r r e t u r n - p e r i o d f l o o d , but r a t h e r are an i n d i c a t i o n of areas which c o u l d f l o o d given t h e i r p a r t i c u l a r topographic and g e o l o g i c c o n d i t i o n s and t h e i r r e l a t i o n t o c e r t a i n man-made s t r u c t u r e s . Some, but not a l l , of these areas p r o v i d e evidence of pr e v i o u s f l o o d i n g e i t h e r as overbank sediment d e p o s i t s , f l u v i a l e r o s i o n f e a t u r e s , or i n h i s t o r i c a l r e c o r d s . Lynn Creek and Seymour R i v e r occupy deeply i n c i s e d -•"9 4 -v a l l e y s cut i n t o s u r f i c i a l d e p o s i t s and bedrock of o l d U-shaped g l a c i a l troughs. Where these r i v e r s flow out of t h e i r c o n f i n i n g v a l l e y s onto t h e i r f l o o d p l a i n d e l t a s the channels are now reasonably c o n f i n e d by c h a n n e l i z a t i o n techniques. Only very s m a l l p r o p o r t i o n s o f the drainage b a s i n s of Lynn Creek and Seymour R i v e r l i e w i t h i n the Seymour area. The f l o o d p l a i n d e l t a s of these major watercourses are e a s i l y i d e n t i f i e d by t h e i r g e o l o g i c a l m a t e r i a l s and topographic s u r f a c e e x p r e s s i o n . F l o o d i n g of these lowlands was f a i r l y common u n t i l 1961. (Appendix 4). C o n t r o l measures have reduced the f l o o d hazard s u b s t a n t i a l l y , however, i t i s i m p o s s i b l e to say i t i s t o t a l l y e l i m i n a t e d . Wetlands on these f l o o d p l a i n s are where seepage or s u r f a c e r u n o f f from adjacent s l o p e s i s c o n s t a n t l y s u p p l y i n g water to those p a r t s which have a water t a b l e a t or near the s u r f a c e . The i n t e r r i v e r area, encompassing p a r t of the drainage d i v i d e between Lynn Creek and Seymour R i v e r , can be d i s c u s s e d as a h y d r o l o g i c a l e n t i t y . A f e a t u r e of t h i s f l a t - l y i n g upland, unique i n North Vancouver-Seymour, i s t h a t i t r e p r e s e n t s a l a r g e groundwater recharge area which i s , f o r the most p a r t , s t i l l i n i t s n a t u r a l s t a t e . Seepages and steep r a v i n e channels d r a i n i n g i n t o the major v a l l e y s d e r i v e t h e i r baseflow from groundwater o r i g i n a t i n g i n the permeable C a p i l a n o outwash sediments. Creeks are o n l y p e r e n n i a l where impermeable t i l l or Pre-Vashon m a t e r i a l i s exposed a t the s u r f a c e . Wetlands along the i n t e r r i v e r r i d g e occupy f l a t - l y i n g or d e p r e s s i o n a l areas, where impervious t i l l o r g l a c i o m a r i n e sediments u n d e r l i e - 95 -C a p i l a n o sands and g r a v e l s a t r e l a t i v e l y shallow depths. Most of the s m a l l e r streams west from F r a n c i s Creek to McCartney Creek e x h i b i t s i m i l a r development of t h e i r channels over the l e n g t h of t h e i r p r o f i l e s . (Figure V-2). Headwaters of these streams are mainly j u s t s l i g h t l y above the t r a n s m i s s i o n l i n e r ight-of-way. During p e r i o d s of h i g h r u n o f f , the upper s l o p e s are g e n e r a l l y s a t u r a t e d by s u r f a c e flow and numerous, s m a l l , i n d i s t i n c t , i n t e r m i t t e n t channels, which are not shown on the map, t r a n s m i t t h i s r u n o f f to the main drainage network. T r i b u t a r i e s are q u i c k l y amalgamated i n t o one or more main channels which then flow down the steep bedrock s l o p e s i n s l i g h t l y i n c i s e d g u l l i e s . Bedload i s made up predominantly of angular c o l l u v i a l r u b b l e . Near the base of the bedrock s l o p e s t h i c k e r s u r f i c i a l d e p o s i t s are deeply i n c i s e d by these s t e e p l y f l o w i n g streams. Bedload c o n s i s t s mainly of subrounded cobbles and b o u l d e r s eroded out of the s u r f i c i a l sediments. ( P l a t e 9 ) . Creeks f l o w i n g i n t o Deep Cove are c o n f i n e d i n steep r a v i n e s r i g h t down to near sea l e v e l . The r e s t of the streams have a major change of g r a d i e n t as they flow o f f the bedrock s l o p e s onto the g e n t l e r s l o p i n g s u r f i c i a l landscape. F l a t - l y i n g areas above Mt. Seymour Parkway and along Indian R i v e r Road are c h a r a c t e r i z e d by drainage channels which are only s l i g h t l y i n c i s e d , i n p l a c e s unconfined, which may flow through wide f l o o d p l a i n s and l a r g e wetlands. Bedload i n these low-gradient reaches i s g e n e r a l l y much more sandy, although pebbles, cobbles, and boulders are s t i l l common. - 96 -P l a t e 9. Boulders i n F r a n c i s Creek which have been eroded out of Vashon t i l l : t h i s i s a t y p i c a l bedload of the steep r a v i n e drainage channels. - 97 -Towards B u r r a r d I n l e t the t i l l - c o v e r e d s l o p e s steepen and the streams once more become c o n f i n e d i n s t e e p - s i d e d r a v i n e s . Cobbles and boulders make up the bedload over t h i s l e n g t h of the channels. Many s m a l l streams, l e s s than 1.0 km. i n l e n g t h , d r a i n these steep lower s l o p e s , i n t e r s p a c e d between the l a r g e r c r e e k s . Much of the D o l l a r t o n area i s d r a i n e d i n t o Indian Arm by t h i s type of s u r f a c e drainage, although most of the channels now e x i s t as c u l v e r t s which c o l l e c t t h e i r r u n o f f from r o a d s i d e d i t c h e s and storm sewers. Areas between watersheds which are not d r a i n e d by a s u r f a c e , channel probably d r a i n d i r e c t l y to the sea by s u r f a c e r u n o f f . Wetlands and seepage.sites on s l o p i n g ground c l o s e to some of the streams r e p r e s e n t s a t u r a t e d patches of s o i l where groundwater flows through t h i n s o i l over impervious t i l l or bedrock. Table X summarizes some measurable drainage b a s i n c h a r a c t e r i s t i c s of a few s e l e c t e d streams which d r a i n the Seymour area. These streams were chosen because they t y p i f y the v a r i a t i o n s i n b a s i n c h a r a c t e r i s t i c s which are caused by the d i f f e r e n t combinations of geology and topography and because most or a l l of the stream systems l i e w i t h i n the map-area. The l a c k of topographic c o n t r o l above the t r a n s m i s s i o n l i n e r ight-of-way makes i t d i f f i c u l t to a c c u r a t e l y d e f i n e the upper l i m i t of some of the drainage b a s i n s . However, f i e l d o b s e r v a t i o n s suggest that, most of the streams west of F r a n c i s Creek to McCartney Creek o r i g i n a t e c l o s e to the right-of-way. Those b a s i n s not completely d e l i n e a t e d on the map may, i n - 98 -f a c t , have watersheds up to 10% l a r g e r then t h a t g i v e n i n the t a b l e . T o t a l l e n g t h of p e r e n n i a l channels i n each of the stream systems i s probably very near to b e i n g accurate (w i t h i n the l i m i t of measuring e r r o r ) . 'TABLE X Drainage B a s i n C h a r a c t e r i s t i c s f o r Some S e l e c t e d Streams i n North Vancouver-Seymour. Stream Drainage Area i n m. (acres). 1. T o t a l Length of P e r e n n i a l Channels i n the Stream System i n m. 2. Drainage Density channel l e n g t h Stream G r a d i e n t i n % b a s i n area m. 2 m. McCartney Creek 3.75xl0 6 (925) 13,850 3.7xl0~3 9.0 T a y l o r Creek 1.30xl06 (320) 4,200 3.2xl0~ 3 6.3 Unnamed Creek 2.13xl06 (525) 5,650 2. 7 x l 0 ~3 11.3 G o l f Course Creek 1.40xl0 6 (345) 4,750 3.4xl0~ 3 5.3 G a l l a n t Creek l . O l x l O6 (250) 4,650 4 . 6 x l 0- 3 15.2 Panorama Creek 0.41xl06 (100) 3,350 8.3xl0~ 3 23.9 1. only i n c l u d e s the area o f the stream b a s i n w i t h i n the map-area. 2. p e r e n n i a l channels are those i d e n t i f i e d i n the f i e l d . B a s i n area and t o t a l channel l e n g t h ranges from McCartney 6 2 Creek a t 3.75x10 m. (925 acres) and 13,850 m. to Panorama 6 2 Creek a t 0.41x10 m. (100 acres) and 3,350 m. Drainage d e n s i t y and stream g r a d i e n t are more i n d i c a t i v e of the i n f l u e n c e of geology and topography on these b a s i n s . - 99 -T a y l o r and G o l f Course Creeks, which have low drainage d e n s i t i e s and the lowest g r a d i e n t s (Figure , o r i g i n a t e i n f l a t - l y i n g wetlands developed over impermeable g l a c i o m a r i n e sediments. The unnamed creek f l o w i n g o f f the mountain a l o n g s i d e Mt. Seymour Road has few t r i b u t a r i e s i n i t s narrow, elongate b a s i n which occupies the western s i d e of a low r i d g e forming the d i v i d e between drainage f l o w i n g i n t o B u r r a r d I n l e t and t h a t d r a i n i n g i n t o Indian Arm. Consequently the drainage d e n s i t y f o r t h i s stream system i s s i g n i f i c a n t l y lower than f o r the other c r e e k s . The upper reaches of McCartney and G a l l a n t Creeks flow down steep bedrock s l o p e s (Figure V-2), however, th e r e i s a s i g n i f i c a n t decrease i n g r a d i e n t along, the middle reaches of McCartney Creek and i t s t r i b u t a r i e s as they flow across an e x t e n s i v e area of C a p i l a n o outwash t e r r a c e s . The l a c k of s u r f a c e drainage from these l e v e l sand and g r a v e l d e p o s i t s decreases the o v e r a l l drainage d e n s i t y of McCartney Creek. G a l l a n t Creek flows i t s e n t i r e l e n g t h down steep, impermeable, bedrock or t i l l - c o v e r e d s l o p e s , consequently L i t has a h i g h e r drainage d e n s i t y and steeper g r a d i e n t . Panorama Creek i s t y p i c a l of the streams f l o w i n g o f f the steep bedrock and t i l l s l o p e s n o r t h of Deep Cove. They a l l have sma l l watersheds, h i g h drainage d e n s i t i e s , and steep g r a d i e n t s . The main channels, which occupy deep r a v i n e s r e c e i v i n g s u r f a c e r u n o f f from the impervious, w e l l d r a i n e d s l o p e s , dominate the b a s i n s . - 100 -F l o o d - s u s c e p t i b l e areas on the s m a l l e r streams are g e n e r a l l y l o c a t e d where a r t i f i c i a l c o n s t r i c t i o n s from blockages on semi-confined or unconfined channels and where n a t u r a l f l o o d p l a i n s e x i s t . A l l the major roadways; Mt. Seymour Parkway, D o l l a r t o n Highway, Deep Cove Road, Panorama D r i v e , Indian R i v e r Road, and Mt. Seymour Road, c r o s s n a t u r a l watercourses a t frequent i n t e r v a l s . Where these roads c r o s s streams a t p o i n t s where the channels begin to l e v e l out and become l e s s c o n f i n e d the p r o b a b i l i t y of s u r g i n g i s i n c r e a s e d . N a t u r a l f l o o d p l a i n s , mainly a s s o c i a t e d w i t h unconfined, low-gradient creek reaches, develop as streams and accompanying s u r f a c e r u n o f f flow o f f the steep bedrock or t i l l - c o v e r e d s l o p e s onto g e n t l y s l o p i n g , s u r f i c i a l t e r r a i n . Overbank flow w i l l occur d u r i n g p e r i o d s of h i g h r u n o f f as peak stream d i s c h a r g e s , t r a n s m i t t e d down the steep, c o n f i n e d r a v i n e s , cannot be accomodated i n the l e s s c o n f i n e d , low-gradient channels. F l o o d - s u s c e p t i b l e areas at the n o r t h end of R i v e r s i d e D r i v e and those near Mt. Seymour Parkway and Indian R i v e r Road formed because of these c o n d i t i o n s . The d e p r e s s i o n a l wetland south of Deep Cove i s a r e c e i v i n g b a s i n f o r c o n s i d e r a b l e s u r f a c e and subsurface r u n o f f . E x c e s s i v e drainage i n t o t h i s area c o u l d cause f l o o d i n g by r a i s i n g the groundwater t a b l e r a t h e r than from simple overbank flow. Surface drainage out o f the lowland i s not p a r t i c u l a r l y f a s t as a semi-confined channel flows through a v a l l e y of very low g r a d i e n t l y i n g between bedrock hummocks. - 101 -The response of stream r u n o f f to p r e c i p i t a t i o n i n the Seymour area has never been s t u d i e d i n d e t a i l , however, because most o f the s l o p e s are u n d e r l a i n by impervious t i l l o r bedrock at or near the ground s u r f a c e , r u n o f f i s probably extremely f a s t . In p a r t i c u l a r , the s h o r t , s t e e p - g r a d i e n t streams d r a i n i n g the impermeable slopes n o r t h of Deep Cove w i l l respond to p r e c i p i t a t i o n w i t h h i g h , s h o r t - d u r a t i o n peak flows and s h o r t l a g times. However, f o r streams such as McCartney Creek where there may a l s o be a s i g n i f i c a n t baseflow of groundwater from the Capilano outwash sediments c o n t r i b u t i n g to the t o t a l water y i e l d of the stream system, the r u n o f f p a t t e r n i s probably more complex. Discharge of the watercourses i s based on i n t e n s i t y and d u r a t i o n of p r e c i p i t a t i o n , however, i t can be s t r o n g l y i n f l u e n c e d by the o v e r a l l c l i m a t i c c o n d i t i o n s p r i o r to the storm. In g e n e r a l , h i g h - i n t e n s i t y , s h o r t - d u r a t i o n r a i n s t o r m s i n a f o r e s t e d area produce l a r g e r f l o o d d i s c h a r g e s than low-i n t e n s i t y r a i n f a l l s of long d u r a t i o n even though the t o t a l amount o f p r e c i p i t a t i o n may be the same. In summer months s h o r t - d u r a t i o n r a i n f a l l i n t e n s i t i e s are from 6 0% to 80% h i g h e r than w i n t e r i n t e n s i t i e s but the r u n o f f i s l e s s because of much g r e a t e r l o s s e s to a b s o r p t i o n , e v a p o r a t i o n , and t r a n s p i r a t i o n . (Greater Vancouver Sewerage and Drainage D i s t r i c t , 1964). A rough estimate of these l o s s e s d u r i n g summer months i s 70% and o n l y 20% f o r w i n t e r . (Environment Canada, 1973). - 102 -In l a t e f a l l or e a r l y w i n t e r , heavy r a i n s accompanied by warming temperatures which melt any e x i s t i n g snow can l e a d to r u n o f f exceeding t h a t caused by the storm p r e c i p i t a t i o n alone. T h i s may be f u r t h e r aggravated i f the ground i s f r o z e n p r i o r to the storm or i f i t i s s a t u r a t e d by e a r l i e r r a i n s . During c o l d w i n t e r s , p r e c i p i t a t i o n i s s t o r e d as snow and not r e l e a s e d u n t i l the f o l l o w i n g s p r i n g or e a r l y summer. The e f f e c t of these v a r y i n g c l i m a t i c c o n d i t i o n s on stream r u n o f f i s w e l l i l l u s t r a t e d by a g r a p h i c a l r e p r e s e n t a t i o n of monthly mean di s c h a r g e of Seymour R i v e r f o r the years 1968, 1969, and 1970. (Environment Canada, 1973). Discharge v a r i e d 3 from a monthly mean minimum o f l e s s than 2.8 m. / s e c . i n 3 summer to a maximum exceeding 28.3 m./sec. i n s p r i n g , autumn, or w i n t e r . Peak di s c h a r g e s from October to December r e f l e c t heavy f a l l r a i n s whereas peaks from May to J u l y r e f l e c t r u n o f f from s p r i n g snow melt. Minimum flows o c c u r r e d i n March and A p r i l when p r e c i p i t a t i o n was s t o r e d as snow and i n the dry summer months of August and September. H y d r o l o g i c a l E f f e c t s of Development Surface and subsurface flow p a t t e r n s over and through the land are a f f e c t e d as the s t r u c t u r e and h y d r o l o g i c a l p r o p e r t i e s of g e o l o g i c a l m a t e r i a l s are a l t e r e d by urban development. The main e f f e c t s are an i n c r e a s e i n the p r o p o r t i of s u r f a c e r u n o f f w i t h r e s u l t a n t i n c r e a s e i n peak flow and sediment y i e l d downstream i n the system. U r b a n i z a t i o n of an - 103 -upper watershed g e n e r a l l y has a g r e a t e r e f f e c t on flow d i s c h a r g e than development i n the lower b a s i n . Steep, upper, bedrock s l o p e s , i n p l a c e s covered w i t h a t h i n veneer o f s u r f i c i a l m a t e r i a l s , are d r a i n e d mainly by semi-confined or unconfined p e r e n n i a l and i n t e r m i t t e n t channels, with the l a t t e r dominant. Surface channels are g e n e r a l l y unable to become entrenched because of bedrock near the s u r f a c e and low d i s c h a r g e of the streams. In p l a c e s , creeks occupy g u l l i e s between bedrock hummocks although these are commonly s i t e s of seepage accumulation from subsurface flow through the s o i l . Any l i n e a r d i s t u r b a n c e across the s l o p e , such as a roadway, w i l l a l t e r the s u r f a c e r u n o f f p a t t e r n by i n t e r c e p t i n g unconfined s u r f a c e channels and s o i l groundwater flow. D i v e r s i o n o f t h i s r u n o f f along roadways i s common and p o s s i b l y causes g u l l y e r o s i o n and formation o f new channels. Development i n upper watershed areas a f f e c t s flow d i s c h a r g e s from s m a l l e r o r l e s s i n t e n s e storms more than from heavy, l o n g - d u r a t i o n r a i n s t o r m s . Areas o f deep t i l l u n d e r l y i n g moderate to steep slopes i n the mid to upper p o r t i o n s of the watersheds are a l s o h y d r o l o g i c a l l y a f f e c t e d by development. P e r e n n i a l streams are b e t t e r developed i n deep, r e l a t i v e l y uniform, s t e e p l y s l o p i n g r a v i n e s whereas unconfined, i n t e r m i t t e n t channels and areas o f seepage accumulation can be expected i n d e p r e s s i o n s . Runoff i s t r a n s m i t t e d to main channels by subsurface flow along the s o i l -t i l l i n t e r f a c e . Any development which a l t e r s the r u n o f f p a t t e r n can cause i n t e r c e p t e d flow and d i v e r s i o n c r e a t i n g new or a d d i t i o n a l g u l l i e d channels. - 104 -The'middle reaches o f streams t r a v e r s i n g the Seymour area are c h a r a c t e r i z e d by semi-confined and unconfined, low-g r a d i e n t channels, which i n many cases are a s s o c i a t e d w i t h wetlands. These areas, mainly u n d e r l a i n by impermeable t i l l o r gl a c i o m a r i n e sediments, are perhaps the most h y d r o l o g i c a l l y s e n s i t i v e to development. Any a l t e r a t i o n of the upper watersheds which causes i n c r e a s e d flow and sediment l o a d c o u l d l e a d to f l o o d i n g . In a d d i t i o n , development around the middle reaches would r e q u i r e d r a i n i n g the wetlands and c h a n n e l i z i n g the e x i s t i n g streams. The r e s u l t o f such measures would be much more e f f i c i e n t drainage systems and e l i m i n a t i o n o f s u b s t a n t i a l s u r f a c e storage areas. Consequently any i n c r e a s e d d i s c h a r g e and sediment l o a d i n the stream systems caused by upstream development would be e f f e c t i v e l y t r a n s m i t t e d t o the lower reaches o f the streams where f l o o d hazard and sediment d e p o s i t i o n c o u l d i n c r e a s e s i g n i f i c a n t l y . For the most p a r t , lower reaches o f a l l the creeks are w e l l c o n f i n e d i n s t e e p l y s l o p i n g , narrow r a v i n e s i n c i s e d i n s u r f i c i a l sediments. Consequently over most of these s e c t i o n s any i n c r e a s e d flow would be contained w i t h i n the pr e s e n t channels. However, near the stream mouths, the channels become l e s s c o n f i n e d and overbank flow caused by i n c r e a s e d d i s c h a r g e i s p o s s i b l e . Road c r o s s i n g s form a r t i f i c i a l c o n s t r i c t i o n s and c o n t r i b u t e to f l o o d hazard near the stream mouths. Development w i t h i n the lower watersheds, p r o v i d i n g i t i s s e t back from the r a v i n e s , should have l i t t l e e f f e c t on the h y d r o l o g i c a l f u n c t i o n i n g of the stream systems. - 105 -The most h y d r o l o g i c a l l y f a v o u r a b l e areas f o r development are those u n d e r l a i n by permeable Capilano outwash sediments. Because they are d r a i n e d mainly by subsurface flow, few s u r f a c e channels can be d i s t u r b e d . In the i n t e r r i v e r area, p e r e n n i a l and i n t e r m i t t e n t creeks d r a i n i n g the steep v a l l e y s l o p e s d e r i v e t h e i r flow from seepage of groundwater through outwash. Development on the r a i s e d t e r r a c e g r a v e l s would i n c r e a s e impervious s u r f a c e area, decrease groundwater recharge, decrease the amount o f seepage along the v a l l e y s i d e s , and reduce the flow i n the s u r f a c e channels. I t may have the e f f e c t o f e l i m i n a t i n g , or a t l e a s t r e d u c i n g , areas of i n s t a b i l i t y along the steeper s l o p e s , however,, the t r a n s i t i o n from subsurface to s u r f a c e r u n o f f means t h a t t h i s flow must be accomodated i n an a r t i f i c i a l network. Surface r u n o f f d e r i v e d from development i n the i n t e r r i v e r area should be conducted by a storm-sewer network d i r e c t l y to a r e c e i v i n g body and not di s c h a r g e d down steep, erodable slopes where l a r g e washouts c o u l d occur. Development on the outwash t e r r a c e s on the e a s t s i d e of Seymour R i v e r would mean s u p p l y i n g l e s s groundwater and more s u r f a c e r u n o f f d i r e c t l y to the l o c a l stream channels. This w i l l have the e f f e c t o f s h o r t e n i n g l a g time and i n c r e a s i n g instantaneous peak flows of the creeks. P o t e n t i a l e f f e c t s o f u r b a n i z a t i o n on f l o o d frequency are g r e a t e s t where f l o o d damage has o c c u r r e d i n the p a s t , as w e l l as at l o c a t i o n s where the t e r r a i n adjacent t o watercourses i s - 106 -f a v o u r a b l e f o r overbank flow or a h i g h water t a b l e . I t i s d i f f i c u l t to c a l c u l a t e changes i n d i s c h a r g e which c o u l d be caused by urban development i n the Seymour area. The impervious s u r f a c e would i n c r e a s e only i n areas u n d e r l a i n by permeable Ca p i l a n o sands and g r a v e l s . E i t h e r bedrock, t i l l , o r g l a c i o m a r i n e sediments, which are themselves v i r t u a l l y impermeable, are a t the s u r f a c e i n the r e s t of the Seymour area. However, t h i n s u p r a l i t t o r a l l a g g r a v e l d e p o s i t s and s o i l c o v e r i n g these impervious m a t e r i a l s accomodate subsurface flow and modify s u r f a c e r u n o f f to some ex t e n t . The p o s s i b l e changes i n peak flows caused by i n c r e a s i n g the impervious s u r f a c e area of a stream b a s i n or by i n c r e a s i n g the e f f i c i e n c y of the drainage network are shown i n "Table XI. U r b a n i z a t i o n has p r o p o r t i o n a l l y a much g r e a t e r e f f e c t on low-r e c u r r e n c e i n t e r v a l f l o o d s than on f l o o d s of h i g h - r e c u r r e n c e i n t e r v a l s . An i n c r e a s e i n impermeable, storm-drained s u r f a c e area of up to 5% o f a stream b a s i n should not a p p r e c i a b l y i n c r e a s e flow i n the stream system. Leopold (196 8) r e p o r t e d t h a t a t 2.5 housing u n i t s per a c r e , about 20% to 25% of an urbanized area i s covered by impermeable s u r f a c e s connected to storm sewers. Such a d e n s i t y of urban development i n a watershed w i l l cause a 9-to-10 f o l d i n c r e a s e i n the annual peak d i s c h a r g e of a stream. A h y d r o l o g i c a l p r i o r i t y of u r b a n i z a t i o n would t h e r e f o r e seem to be i n f i n d i n g ways to reduce the r a t e of t r a n s m i t t i n g t h i s i n c r e a s e d r u n o f f to the drainage, i n e f f e c t mimicking the n a t u r a l r u n o f f p a t t e r n . - 107 -TABLE XI P e r c e n t a g e I n c r e a s e s i n Peak F l o w s " w i t h V a r i o u s Recurrence I n t e r v a l s Assuming C o n v e r s i o n s o f 5 t o 2 5 P e r c e n t o f the B a s i n A r e a t o Impermeable S u r f a c e Connected t o Storm Sewers, ( a f t e r H o l l i s , 1975 and Karanka, 1977). P e r c e n t o f B a s i n N a t u r a l S u r f a c e C o n v e r t e d To Impermeable, Storm-Drained S u r f a c e :Annual F l o o d 5-year F l o o d 10-year F l o o d 25-year F l o o d 50-year F l o o d 100-y e a r F l o o d 5 0 0 0 0 0 0 10 100 40 20 0 0 0 15 300 90 60 40 30 0 20 900 120 100 60 50 30 25 1000+ 150 120 100 70 40 Another p o t e n t i a l problem which a r i s e s when storm sewers become the major means of t r a n s p o r t i n g b a s i n r u n o f f to the streams i s t h a t the n a t u r a l drainage b a s i n boundaries are a l t e r e d as the a r t i f i c i a l channels t r a v e r s e watershed d i v i d e s . Storm sewer development i n the western p a r t of North Vancouver i n t h i s way caused Mosquito Creek b a s i n t o i n c r e a s e i n area by 44%, Wagg Creek b a s i n to decrease by 36%, and a creek d r a i n i n g a 350-acre b a s i n being v i r t u a l l y e l i m i n a t e d . Development which s e r i o u s l y a l t e r s the n a t u r a l shape and area of a watershed should not be pe r m i t t e d . Changes i n drainage p a t t e r n can cause i n c r e a s e d d i s c h a r g e i n the en l a r g e d b a s i n and i n c r e a s e s i n sediment y i e l d , bank i n s t a b i l i t y , and f l o o d hazard. Streams d r a i n i n g watersheds which have been d r a s t i c a l l y reduced i n area o f t e n have lower flow which reduces t h e i r - 108 -a e s t h e t i c appeal and t h e i r a b i l i t y to s u s t a i n f i s h p o p u l a t i o n s . Although l i t e r a t u r e sources d i s c u s s e d i n Chapter I I may not e x a c t l y d e s c r i b e h y d r o l o g i c c o n d i t i o n s i n the Seymour area, there i s no doubt t h a t u r b a n i z a t i o n w i l l cause i n c r e a s e d sedimentation i n the l o c a l watercourses. Sediment and d e b r i s produced from urban development i n the upper b a s i n s w i l l c o n t r i b u t e to channel blockages and l e a d to more frequent surge f l o o d i n g . The Maplewood mudflats are probably very s e n s t i t i v e to i n c r e a s e d sedimentation. I f sediment p r o d u c t i o n i n the upper reaches of McCartney Creek was d r a m a t i c a l l y i n c r e a s e d , t h i s m a t e r i a l would u l t i m a t e l y be t r a n s p o r t e d downstream and d e p o s i t e d on the mudflats. Dumping l a r g e q u a n t i t i e s of sediment i n a s h o r t time c o u l d s e r i o u s l y a f f e c t the e c o l o g i c a l environment o f the t i d a l r e g i o n . A v a i l a b l e evidence i n d i c a t e s t h a t the major impact of u r b a n i z a t i o n on f i s h p o p u l a t i o n s i s g e n e r a l l y a s s o c i a t e d with s p e c i f i c stream-channel a l t e r a t i o n s and t h a t upper slope develop-ment i s only of minor importance. Karanka (1977) summarized the main e f f e c t s of u r b a n i z a t i o n on f i s h p o p u l a t i o n s i n North Shore streams: 1.) v i r t u a l e l i m i n a t i o n of chum and pink salmon p o p u l a t i o n s through dredging and c h a n n e l i z a t i o n of spawning areas and i n f i l l i n g o f e s t u a r i n e areas; 2.) severe r e d u c t i o n of coho, s t e e l h e a d , and sea-run c u t t h r o a t t r o u t p o p u l a t i o n s , mainly through e l i m i n a t i n g access to spawning areas a t impassable c u l v e r t s and dams; 3.) severe r e d u c t i o n s of - 109 -r e s i d e n t i a l c u t t h r o a t p o p u l a t i o n s i n some streams through e l i m i n a t i o n o f h a b i t a t by c h a n n e l i z a t i o n . Although a l t e r a t i o n s to some of the channels are l o c a l i z e d , the e f f e c t s may be f e l t throughout the stream system because o f s e l e c t i v e f a c t o r s such as o b s t r u c t i o n to m i g r a t i o n o r d e s t r u c t i o n o f spawning areas. H y d r o l o g i c a l amenities o f a stream are what might be c a l l e d the appearance o r impression which the stream, i t s channel, and i t s v a l l e y , leaves with the observer. (Leopold, 196 8). The amenity value o f the h y d r o l o g i c environment can be s e v e r e l y reduced by u r b a n i z a t i o n . I t s r e d u c t i o n can be a p h y s i c a l , b i o l o g i c a l , or v i s u a l p r o c e s s . Increased peak flows enlarge channels, c r e a t i n g u nstable and unvegetated banks and heavy d e b r i s accumultation i n scoured o r muddy creek beds. D e t e r i o r a t i o n o f water q u a l i t y can destr o y the balance o f stream b i o t a and i n c r e a s e growth o f a q u a t i c p l a n t s . Accumulation o f r u b b i s h i n stream channels may or may not a f f e c t the h y d r o l o g i c a l f u n c t i o n i n g o f the system but i s a e s t h e t i c a l l y unappealing. A unique h y d r o l o g i c e f f e c t o f urban development i s caused by the l o c a t i o n o f the m u n i c i p a l waste d i s p o s a l ground on the Lynn Creek f l o o d p l a i n . (Figure 1-2). This s i t e , f i r s t u t i l i z e d f o r waste d i s p o s a l i n 1945, p r e s e n t l y accepts garbage, i n c l u d i n g i n d u s t r i a l and commercial waste, from the C i t y and D i s t r i c t o f North Vancouver and the D i s t r i c t o f West Vancouver. The s a n i t a r y l a n d f i l l method of d i s p o s a l i s used i n which s o l i d wastes are d e p o s i t e d i n c e l l s 2 m. deep with 15 cm. of cover m a t e r i a l p l a c e d between c e l l s . A f t e r a t l e a s t t hree - 110 -c e l l s have been b u i l t up, 60 cm. of s o i l are compacted on top. The e n t i r e d i s p o s a l s i t e i s supposedly l i n e d w i t h a compacted, impermeable l a y e r t o prevent c o n t a c t between the u n d e r l y i n g groundwater t a b l e and the f i l l m a t e r i a l . Such a c o n c e n t r a t i o n o f s o l i d wastes i n t h i s type o f l a n d f i l l c r e a t e s a l o c a l pocket of p o t e n t i a l contamination. A p o l l u t i n g l e a c h a t e can be produced by r e f u s e i n c o n t a c t with water. T h i s water may o r i g i n a t e as groundwater or s u r f a c e water from p r e c i p i t a t i o n or r u n o f f and can d i s s o l v e s o l u b l e dry chemicals, l e a c h i r o n and v a r i o u s m i n e r a l s , and p i c k up s o l u b l e - f r a c t i o n s of o r g a n i c d e g r a d a t i o n . Where p r e c i p i t a t i o n and a s s o c i a t e d s u r f a c e r u n o f f are high , such as along the v a l l e y o f Lynn Creek, i t i s p o s s i b l e f o r the l a n d f i l l to become s a t u r a t e d and overflow the impermeable l i n e r . T h i s p a r t i c u l a r s i t e i s one of the worst p o s s i b l e l o c a t i o n s f o r such a l a n d f i l l . The u n d e r l y i n g f l o o d p l a i n i s composed of h i g h l y permeable, coarse, bouldery g r a v e l which i s s u b j e c t t o c o n s i d e r a b l e seepage and s u r f a c e r u n o f f from the adjacent s l o p e s . A number of c u l v e r t s and le a c h a t e seeps d r a i n d i r e c t l y i n t o Lynn Creek. P r e l i m i n a r y s t u d i e s o f water q u a l i t y and the i n t e n s e i r o n s t a i n i n g on rocks downstream from the l a n d f i l l i n d i c a t e t h a t c o n s i d e r a b l e p o l l u t a n t s are re a c h i n g the creek. (Dr. J . Rau, 1976. P e r s o n a l Communication). The e f f e c t on groundwater contamination i s unknown but a high water t a b l e probably i n t e r c e p t s the waste f i l l . - I l l -Summary of H y d r o l o g i c a l C o n s t r a i n t s to Development I t i s d i f f i c u l t to e v a l u a t e a l l the p o t e n t i a l e f f e c t s of urban r e s i d e n t i a l development on the h y d r o l o g i c a l systems i n the Seymour area and to assess where changes i n the h y d r o l o g i c regimes w i l l s e t r e s t r i c t i o n s on development. At p r e s e n t the bes t method i s to i d e n t i f y the s i g n i f i c a n t h y d r o l o g i c f e a t u r e s which are most s e n s i t i v e to changes i n the p h y s i c a l environment. By s e t t i n g l i m i t a t i o n s to urban development f o r these f a c t o r s i t i s p o s s i b l e to minimize d i s t u r b a n c e to the h y d r o l o g i c a l systems and to prevent downstream problems such as f l o o d i n g and sedimentation. H y d r o l o g i c a l f e a t u r e s which may r e s t r i c t development i n c l u d e depth to water t a b l e , drainage, f l o o d frequency, and s u r f a c e drainage channels. (Table X I I ) . Depth to water t a b l e w i l l a f f e c t drainage, p a r t i c u l a r l y on l e v e l o r g e n t l y s l o p i n g ground, and may cause d i f f i c u l t y i n e x c a v a t i n g f o r basements and u t i l i t i e s . Where the seasonal water t a b l e i s w i t h i n 0.75 m. of the ground s u r f a c e any type of e x c a v a t i o n w i l l experience drainage problems. Large areas with high water t a b l e s may be groundwater sources f o r p e r e n n i a l streams or act as storage areas d u r i n g peak r u n o f f p e r i o d s . A seasonal water t a b l e w i t h i n 0.75 to 1.5 m. of the s u r f a c e w i l l be a moderate l i m i t a t i o n t o excavations and drainage, however, d u r i n g the dry season there probably w i l l be no problem. The degree o f l i m i t a t i o n i s s l i g h t i f the water t a b l e i s not w i t h i n 1.5 m. of the ground s u r f a c e . - 112 -Severe drainage problems are g e n e r a l l y caused by; a water t a b l e a t or very near the s u r f a c e , an impervious h o r i z o n very near a g e n t l y s l o p i n g ground s u r f a c e , f i n e -t e x t u r e d s o i l developed on impervious m a t e r i a l , or constant seepage or r u n o f f c o l l e c t i n g i n a d e p r e s s i o n a l area. S i m i l a r c o n d i t i o n s can l e a d to i m p e r f e c t drainage (Appendix 8) and a moderate l i m i t a t i o n although g e n e r a l l y the water t a b l e and impervious m a t e r i a l w i l l be at g r e a t e r depth, s l o p e may be s t e e p e r , and seepage c o n s i d e r a b l y l e s s . W e l l d r a i n e d areas may be u n d e r l a i n by permeable sediments or by impermeable m a t e r i a l on moderate-steep s l o p e s . Although the degree of l i m i t a t i o n i s s l i g h t under these c o n d i t i o n s , care must be taken not to d i s r u p t the s u r f a c e r u n o f f p a t t e r n and cause downstream h y d r o l o g i c problems. The d e t e r m i n a t i o n o f f l o o d frequency i n t h i s study i s a s u b j e c t i v e , comparative measure based on f l o o d h i s t o r y and an e v a l u a t i o n of topographic, g e o l o g i c , and man-made c o n d i t i o n s a f f e c t i n g the h y d r o l o g i c systems. Any area which i s s u b j e c t to f l o o d i n u n d a t i o n should be c o n s i d e r e d u n s u i t a b l e f o r r e s i d e n t i a l development. In some of these f l o o d - s u s c e p t i b l e areas the p o s s i b i l i t y of f l o o d i n g i s remote and c o n s i d e r e d to be only a moderately l i m i t i n g f a c t o r . P a r t s of the f l o o d p l a i n d e l t a of Lynn Creek and Seymour R i v e r are so d e s i g n a t e d because f l o o d c o n t r o l by c h a n n e l i z a t i o n and water-supply storage have s u b s t a n t i a l l y reduced the t h r e a t of f l o o d i n g . Surface drainage channels are probably the most important - 113 -h y d r o l o g i c a l f e a t u r e i n the Seymour area and the most s u s c e p t i b l e to the e f f e c t s of development. Any a l t e r a t i o n i n the h y d r o l o g i c f u n c t i o n i n g o f a stream b a s i n w i l l be manifested i n changes i n flow regime, channel s t a b i l i t y , a n d sediment t r a n s p o r t and these changes w i l l be f e l t throughout the e n t i r e system. Because of t h i s , a l l major p e r e n n i a l stream channels should be s e v e r e l y r e s t r i c t e d from r e s i d e n t i a l development. Semi-confined or unconfined p e r e n n i a l and i n t e r m i t t e n t channels which can be e a s i l y i n t e r c e p t e d and d i v e r t e d by c r o s s - s l o p e c o n s t r u c t i o n are moderately l i m i t i n g . TABLE XII Degree of L i m i t a t i o n of H y d r o l o g i c F a c t o r s to Urban R e s i d e n t i a l Land-Use. L i m i t i n g F a c t o r Degree of L i m i t a t i o n S l i g h t Moderate Severe depth to water t a b l e g r e a t e r than 1.5 m. 0.75 - 1 . 5 m . l e s s than 0.75 m. drainage w e l l d r a i n e d i m p e r f e c t l y d r a i n e d p o o r l y d r a i n e d f l o o d frequency none r a r e o c c a s i o n a l or frequent drainage channel — s m a l l p e r e n n i a l or i n t e r m i t t e n t stream major p e r e n n i a l stream 1. Drainage C l a s s e s e x p l a i n e d i n Appendix 8. Areas wi t h severe h y d r o l o g i c a l l i m i t a t i o n s to development are mainly those occupied by p e r e n n i a l streams and a s s o c i a t e d wetlands and f l o o d - s u s c e p t i b l e areas. F l o o d p l a i n s and wetlands adjacent to unconfined channels a c t as sediment catchments and p r o v i d e s u r f a c e s t o r a g e . Leaving them i n t h e i r n a t u r a l s t a t e i s one of the b e s t ways to prevent downstream - 114 -f l o o d i n g and i n c r e a s e d sedimentation. D e s i g n a t i o n as g r e e n b e l t s t a t u s ensures t h a t the channel w i l l not be a r t i f i c i a l l y c o n f i n e d and reduces the p o s s i b i l i t y o f blockage, d i v e r s i o n , or s u r g i n g ; i t a l s o ensures t h a t f l o o d s o r i g i n a t i n g above an urban development can pass through the channel without causing severe damage; the channel then, w i l l remain i n a s t a b l e s t a t e , and the n a t u r a l channel, through r e t e n t i o n o f d e p r e s s i o n storage i n adjacent wetlands, w i l l h e lp r e t a r d the passage of peak flows. The d i s t a n c e development i s s e t back from streams should be determined by the p a r t i c u l a r channel and bank geometry and a s s o c i a t e d h y d r o l o g i c a l f e a t u r e s and not be a s t a n d a r d s p e c i f i e d d i s t a n c e from the channel. Maplewood t i d a l mudflats have severe h y d r o l o g i c a l l i m i t a t i o n s to development and are an important e s t u a r i n e environment which should not be a l t e r e d . Moderate r e s t r i c t i o n s - to development of seasonal wetland areas, caused by a moderately-high water t a b l e , i m p e r f e c t .drainage, or seepage, can be overcome by implementing proper drainage measures. Care must be taken not to cause s l o p e i n s t a b i l i t y o r e r o s i o n , s e r i o u s l y change the s u r f a c e flow regime, or a l t e r the groundwater hydrology, by d i s r u p t i n g s u r f a c e and subsurface r u n o f f p a t t e r n s . Areas of low h y d r o l o g i c a l c o n s t r a i n t are those u n d e r l a i n by t h i c k , w e l l d r a i n e d s o i l over a s l o p i n g t i l l or. bedrock s u r f a c e or by w e l l d r a i n e d C a p i l a n o sands and g r a v e l s . R e s i d e n t i a l development i n these areas w i l l not s e r i o u s l y a f f e c t the l o c a l hydrology i f i t i s s u f f i c i e n t l y s e t back from drainage channels and i f s u r f a c e and subsurface r u n o f f p a t t e r n s are not e x t e n s i v e l y a l t e r e d . - 116 -CHAPTER VI PHYSICAL CHARACTERISTICS AND ENGINEERING PROPERTIES OF THE GEOLOGICAL MATERIALS P h y s i c a l C h a r a c t e r i s t i c s and Urban Use I n t e r p r e t a t i o n s The p r o p e r t i e s of the g e o l o g i c a l m a t e r i a l s are important i n d e t e r m i n i n g the d e s i r a b i l i t y f o r c e r t a i n types of development and f o r p l a n n i n g use of the land. In e v a l u a t i n g s u i t a b i l i t y of the m a t e r i a l s f o r urban use, the main concern i n the Seymour area i s the ease of d e v e l o p i n g r e s i d e n t i a l s u b d i v i s i o n s . T h i s i n c l u d e s the a b i l i t y of m a t e r i a l s to support l o w - r i s e d w e l l i n g s ; t h e i r use as a road and s t r e e t subgrade; and the ease of e x c a v a t i n g them f o r underground u t i l i t i e s . Important c h a r a c t e r i s t i c s i n c l u d e genesis of the sediments and t h e i r d e p o s i t i o n a l h i s t o r y , t e x t u r e , s t o n i n e s s , drainage, and c o m p r e s s i b i l i t y . (Table X I I I ) . A most important c o n s i d e r a t i o n i s whether the m a t e r i a l has been preloaded by g l a c i e r i c e . Vashon t i l l and o l d e r d e p o s i t s have been o v e r r i d d e n by a t l e a s t 1800 m. of i c e a t v a r i o u s times d u r i n g the P l e i s t o c e n e epoch, whereas p o s t -Vashon sediments have been pre l o a d e d o n l y by the weight of the sediments o v e r l y i n g them and by the e f f e c t of d e s i c c a t i o n . Texture i s based on g r a i n s i z e d i s t r i b u t i o n and p l a s t i c i t y . Appendix 6 summarizes data o b t a i n e d from r e p r e s e n t a t i v e samples of the s u r f i c i a l m a t e r i a l s . (Figure I I I - l ; Appendix 1). The coarse f r a c t i o n ( g r e a t e r than 20 mm. - 117 -i n diameter) of the m a t e r i a l was estimated i n the f i e l d . Samples of the matrix ( l e s s than 20 mm. i n diameter) were c o l l e c t e d and analyzed i n the l a b o r a t o r y (see Appendix 5 f o r a d i s c u s s i o n o f s o i l t e s t i n g p r o c e d u r e s ) . Mechanical s i e v e a n a l y s i s p r o v i d e d g r a i n s i z e d i s t r i b u t i o n of the coar s e -matrix f r a c t i o n and A t t e r b e r g l i m i t t e s t s determined the p l a s t i c i t y and c o m p r e s s i b i l i t y o f the f i n e - m a t r i x f r a c t i o n . Based on t h i s i n f o r m a t i o n the sediments were c a t e g o r i z e d a c c o r d i n g to the U n i f i e d S o i l C l a s s i f i c a t i o n System f i r s t developed by Casagrande (1948). (Appendix 5). The system i s dependent on the i n h e r e n t p h y s i c a l p r o p e r t i e s which i n f l u e n c e the behaviour of s o i l . I t r e c o g n i z e s t h a t s o i l behaviour i s a f u n c t i o n of the s i z e , d i s t r i b u t i o n , and composition of the b a s i c c o n s t i t u e n t s common to s u r f i c i a l m a t e r i a l s and of the moisture content of the sediment. (Wagner, 19 57). S t o n i n e s s i s an estimate of the amount o f boulder s i z e fragments ( g r e a t e r than 256 mm. i n diameter) pre s e n t . (Appendix 7). Although t h i s p r o p e r t y was o r i g i n a l l y d e f i n e d f o r a g r i c u l t u r a l purposes i t can be s i g n i f i c a n t i n urban use. A h i g h p r o p o r t i o n of boulders or even a few, i s o l a t e d , very l a r g e b oulders can h i n d e r l i g h t machinery. Drainage and p e r m e a b i l i t y measure the a b i l i t y o f the sediment t o remove water from"the ground s u r f a c e . Taken together they c o n s t i t u t e a very important p r o p e r t y t o be c o n s i d e r e d when p l a n n i n g f o r r e s i d e n t i a l development: s u r f a c e and subsurface flow can s e r i o u s l y d i s r u p t e x c a v a t i o n work, f l o o d basements, and can l e a d to i n s t a b i l i t y o f s l o p e s . - 118 -P e r m e a b i l i t y d e s c r i b e s the ease with, which water flows through a m a t e r i a l and i s dependent on t e x t u r e and s t r u c t u r e (the s i z e , shape, and area of pore space i n the m a t e r i a l ) . R e l a t i v e p e r m e a b i l i t y depends on the type of g e o l o g i c a l m a t e r i a l and v a r i e s over a wide range. G r a v e l i s c o n s i d e r e d to be h i g h l y permeable ( g r e a t e r than 10 "*"cm./sec. ) , s i l t y sand -3 -5 has a low p e r m e a b i l i t y (10 to 10. c m . / s e c ) , and c l a y s are -7 con s i d e r e d t o be impermeable ( l e s s than 10 cm./sec.). (Sowers and Sowers, 1970 and Hodge, 1976). M a t e r i a l s which are n e a r l y impermeable and permit very l i t t l e downward p e r c o l a t i o n of water are d r a i n e d by s u r f a c e r u n o f f . In these cases drainage i s mainly a f u n c t i o n o f s l o p e . C o m p r e s s i b i l i t y o f a m a t e r i a l i s dependent on t e x t u r e and p r e c o n s o l i d a t i o n h i s t o r y . In g e n e r a l , c o m p r e s s i b i l i t y decreases w i t h i n c r e a s i n g d e n s i t y . (Sowers and Sowers, 1970). C o h e s i o n l e s s sediments such as sand, g r a v e l , and t i l l , which have n a t u r a l l y h i g h d e n s i t i e s , are c o n s i d e r e d to have n e g l i g i b l e t o s l i g h t c o m p r e s s i b i l i t y . F i n e - g r a i n e d sediments are much l e s s dense and, depending on t h e i r p l a s t i c i t y (Figures V l - l a to I d ) , have medium to h i g h c o m p r e s s i b i l i t y . P r e c o n s o l i d a t e d m a t e r i a l s , such as those o v e r r i d e n by g l a c i e r i c e , are g e n e r a l l y denser and l e s s compressible than s i m i l a r sediments which are normally c o n s o l i d a t e d . I d e n t i f y i n g compressible m a t e r i a l s i s an important step i n p r e v e n t i n g s e t t l i n g of founda t i o n s . - 119 -Figure V l - l a Descriptive Use of the Unified Soil Classification Plasticity Chart (after Legget, 1967) 1 cohesionless soils ( S M ; S Q S C - S M ) 2 inorganic clays of low plasticity ( C L ) 3 inorganic silts of low compressibility (ML) 4 inorganic clay-silt of low plasticity ( C I - M L ) 5 inorganic clays of medium plasticity (ci) 6 inorganic silts and organic clays of medium compressibility ( M L ; O L ) 7 inorganic clays of high plasticity ( C H ) 8 inorganic silts and organic clays of high compress ib i l i ty (MH ; OH) 40- I I | X Ui 30-• i i ' : i 5 o z 1 i i jt' > 1— V »— 20-1 ' < a. 10-7-4-1 1 2 | \ 8 ! f  6 ' ; • 4 / K i 1 / 3 ! ! 0 10 20 30 40 50 60 70 LIQUID LIMIT Figure VI—lb Plasticity Chart for Pre-Vashon Sediments e cohesive clayey silts and stony clays LIQUID LIMIT Figure V H c Plasticity Chart for Vashon Drift « lodgement till matrix o fine-grained drift LIQUID LIMIT Figure VI—Id Plast ic ity Chart for Capilano Sediments o cohesive stony to stoneless clayey silt and silty clay t cohesionless silty sand and sandy silt \ LIQUID LIMIT - 123 -The r e l a t i v e d e s i r a b i l i t y o f the v a r i o u s g e o l o g i c a l m a t e r i a l s f o r the s e l e c t e d urban uses (Table XIII) was compiled from s i m i l a r t a b l e s presented by numerous workers. (Casagrande, 1948; Wagner, 1957; Armstrong, 1961; The A s p h a l t I n s t i t u t e , 1969; Sowers and Sowers, 1970; and Hicock, 1976). Road subgrade d e s c r i b e s the u n d e r l y i n g l o c a l s u r f i c i a l m a t e r i a l over which roads and s t r e e t s , c o n s i s t i n g of paved s u r f a c e s on g r a v e l bases, w i l l be b u i l t . G e n e r a l l y roadways are l i m i t e d to shallow cuts and f i l l s . Use o f the m a t e r i a l s f o r support of foundations i s based on s i n g l e - f a m i l y or m u l t i - f a m i l y d w e l l i n g s of s i m i l a r f o u n d a t i o n requirements. S t r u c t u r e s r e q u i r i n g a foundation l o a d i n excess of t h a t of a t h r e e - s t o r e y b u i l d i n g are not c o n s i d e r e d . Ease o f e x c a v a t i o n p e r t a i n s to m a t e r i a l s r e q u i r i n g e x c a v a t i n g or t r e n c h i n g to a depth of 2 m. or l e s s by hand t o o l s o r l i g h t machinery. Shallow e x c a v a t i o n s are necessary f o r d w e l l i n g s w i t h basements, f o r cemeteries, and f o r underground u t i l i t y l i n e s such as sewers and water mains. (United S t a t e s Dept. o f A g r i c u l t u r e , 1973) . Bedrock p r o v i d e s e x c e l l e n t b e a r i n g f o r f o u n d a t i o n s , however ot h e r problems r e l a t e d to urban use render i t l e s s a t t r a c t i v e f o r development. Stud i e s have shown t h a t compressive s t r e n g t h of a l t e r e d , c o a r s e - g r a i n e d g r a n i t i c 5 5 rock ranges from 552 x 10 to 1104 x 10 p a s c a l s and w e l l -5 5 cemented sandstone ranges from 1104 x 10 to 2209 x 10 p a s c a l s . The s t r e n g t h . o f f r i a b l e sandstone i s much lower ( l e s s than 5 277 x 10 p a s c a l s i s common). (Deere, 1968 and Hendron, J r . , 196 8). L o c a l experience has shown t h a t the compressive s t r e n g t h TABLE XIII Physical Ch Interpretat a r a c t e r i s t i c s and Urban Use ions of the Geological Materials. Geological Materials Physical C h a r a c t e r i s t i c s Urban Use Interpretations Preloaded by Glacier Ice U n i f i e d Texture (App. 6) Stoniness (App. 7) Drainage and Permeability Compressibility and Expansion Value as Subgrade Bearing Value for Foundations Ease of Excavation Mesozoic D i o r i t e and Granodiorite Bedrock - - - impermeable to ground-water flow; rapid surface drainage none poor excellent requires b l a s t i n g Late Cretaceous-Early T e r t i a r y Sandstone - - -very low permeability to impervious; raoid surface drainage none poor excellent except for upper, decomposed or f r i a b l e surface can be done by machinery but may reouire b l a s t i n a Semiahmoo D r i f t s i l t y sandy lodgement t i l l containing lenses of laminated s i l t ; t i l l c l a s t s are mainly subrounded to subangular, g r a n i t i c pebbles. sandy gravel and gra v e l l y sand d r i f t ; subhorizontally bedded, containing subrounded to subangular, g r a n i t i c cobbles and pebbles. massive, stony clayey s i l t containing scattered subrounded g r a n i t i c stones. rhythmically laminated s i l t containing scattered subrounded g r a n i t i c stones. Yes t i l l matrix-SM silt - M L s l i g h t l y stony (1) very low permeability to impervious; surface drainage n e g l i g i b l e to s l i g h t i n s i l t s f a i r to good t i l l i s good to excellent low Yes matrix-SP-SM stone free (0) low permeability; mainly surface drainage n e g l i g i b l e to very low f a i r to good good to excellent low to moderate Yes ML-MH s l i g h t l y stonv (D . impermeable; surface drainage only medium to high poor f a i r low to moderate Yes ML s l i g h t l y stony (1) impermeable; surface drainage only s l i g h t to medium f a i r to poor f a i r low to moderate Cowichan Head Sediments interbedded fine sand and s i l t i n ho r i z o n t a l layers. organic s i l t ; peat with wood fragments Yes ML stone free (0) low to medium permeability; some surface drainage s l i g h t f a i r to poor f a i r to good high Yes PT stone free (0) impermeable ; peat can hold many tines i t s own weight of water very high not suitable not suitable moderate G e o l o g i c a l M a t e r i a l s P h v s i c a l C h a r a c t e r i s t i c s Urban Use I n t e r p r e t s t i o n s P r e l o a d e d by G l a c i e r I c e U n i f i e d T e x t u r e (App. 6) S t o n i n e s s (App. 7) Drai n a g e and P e r m e a b i l i t y C o m p r e s s i b i l i t y and E x p a n s i o n V a l u e as Subgrade B e a r i n g V a l u e f o r F o u n d a t i o n s E a s e o f E x c a v a t i o n C o q u i t l a m D r i f t ? l a m i n a t e d , b l u e - g r e y c l a y e y s i l t and m a s s i v e b l u e - g r e y s t o n y c l a y . Yes ML, CL s l i g h t l y s t o n y (1) impermeable; s u r f a c e d r a i n a g e o n l y s l i g h t t o medium f a i r t o poo r f a i r low t o moderate Quadra Sand medium t o f i n e s a n d c o n t a i n i n g sandy s i l t i n t e r b e d s , g r a v e l l e n s e s and i n t e r b e d s , and s c a t t e r e d p e b b l e s and p e b b l e c l u s t e r s ; s u b h o r i z o n t a l l y l a y e r e d and c r o s s -bedded . Yes SP s t o n e f r e e (0) medium t o l i g h p e r m e a b i l i t y ; good s u b s u r f a c e d r a i n a g e n e g l i g i b l e good t o f a i r good t o e x c e l l e n t h i g h Vashon D r i f t g r a v e l l y s a n d f o r e s e t beds and s u b s t r a t i f i e d c o b b l e g r a v e l c o n t a i n i n g s u b r o u n d e d g r a n i t i c s t o n e s . d e nse lodgement t i l l c o n t a i n i n g s u b r o u n d e d t o s u b a n g u l a r g r a n i t i c s t o n e s ; o c c a s i o n a l b o u l d e r s up t o 3 m. i n d i a m e t e r ; o c c a s i o n a l l e n s e s o f l a m i n a t e d , s t o n y s i l t and f i n e s and. c o a r s e , c o b b l y a b l a t i o n t i l l c o n t a i n i n g a h i g h p r o p o r t i o n o f s u b a n g u l a r t o a n g u l a r g r a n i t i c c l a s t s . Yes SP and G P ( e s t . ) s t o n e f r e e (0) t o s l i g h t l y s t o n y (1) medium t o v e r y h i g h p e r m e a b i l i t y ; good s u b s u r f a c e d r a i n a g e n e g l i g i b l e good good t o e x c e l l e n t m o d e r a t e l y h i g h Yes t i l l m a t r i x -SM s l i g h t l y t o m o d e r a t e l y s t o n y (1 t o 2) v e r y low p e r m e a b i l i t y t o impermeable; r a p i d s u r f a c e d r a i n a g e n e g l i g i b l e good t o f a i r e x c e l l e n t v e r y low; r e q u i r e s m a c h i n e r y No t i l l m a t r i x -SW s l i g h t l y t o moderate 1} s t o n y (1 t o 2) v e r y low t o low p e r m e a b i l i t y ; m a i n l y s u r f a c e d r a i n a g e n e g l i g i b l e good t o f a i r good low t o moderate C a p i l a n o S e d i m e n t s s t o n y t o s t o n e l e s s c l a y e y s i l t s and s i l t y c l a y ; g e n e r a l l y m a s s i v e and b l o c k y s t r u c t u r e b u t may be bedded i n p l a c e s ; s t o n e s a r e m a i n l y g r a n i t i c and s u b r o u n d No ML, MH, CL s t o n e f r e e t o s l i g h t l y s t o n y (0 t o 1) impermeable; s u r f a c e d r a i n a g e o n l y g e n e r a l l y s l i g h t t o medium b u t may be h i g h p o o r p o o r t o f a i r ; may s e t t l e e x c e s s i v e l y low t o moderate G e o l o g i c a l M a t e r i a l s P h y s i c a l C h a r a c t e r i s t i c s Urban Use I n t e r p r e t a t i o n s P r e l o a d e d by G l a c i e r I c e U n i f i e d T e x t u r e (App. 6) S t o n i n e s s (App. 7) D r a i n a g e and P e r m e a b i l i t y C o m p r e s s i b i l i t y and E x p a n s i o n V a l u e as Subgrade B e a r i n g V a l u e f o r F o u n d a t i o n s E a s e o f E x c a v a t i o n v a r v e d c l a y e y s i l t c o n s i s t i n g o f a l t e r n a t i n g l a y e r s o f s i l t and c l a y e y s i l t No ML s t o n e f r e e C O ) impermeable; s u r f a c e d r a i n a g e o n l y s l i g h t t o medium poor t o f a i r p o o r t o f a i r low t o moderate i n t e r b e d d e d sandy g r a v e l , g r a v e l l y s a n d s a n d , and s i l t y s a nd c o n t a i n i n g s u b r o u n d e d t o r o u n d e d g r a n i t i c p e b b l e s and c o b b l e s ; o c c u r s as s u b h o r i z o n t a l beds and l e n s e s and sou t h w a r d d i p p i n g f o r e s e t b e d s . No SM, SP, G P ( e s t . ) s t o n e f r e e (0) medium t o v e r y h i g h p e r m e a b i l i t y ; good s u b s u r f a c e d r a i n a g e n e g l i g i b l e t o v e r y s l i g h t good good h i g h s u b s t r a t i f i e d s i l t y s a n d c o n t a i n i n g s u b r o u n d e d g r a n i t i c p e b b l e s and p e b b l e l e n s e s . No SM s t o n e f r e e (0) low t o medium p e r m e a b i l i t y ; s u b s u r f a c e d r a i n a g e i s p o s s i b l e e x c e p t where the w a t e r t a b l e i s n e a r the s u r f a c e s l i g h t good t o f a i r good moderate t o h i g h r u s t y , sandy s u p r a -l i t t o r a l l a g g r a v e l c o n t a i n i n g a h i g h p r o p o r t i o n o f s u b r o u n d e d c o b b l e -s i z e m a t e r i a l and o c c a s i o n a l b o u l d e r s ; forms a m a n t l e u s u a l l y l e s s t h a n 1.5 m. t h i c k on C a p i l a n o S e d i m e n t s and Vashon D r i f t . No m a t r i x -SP and G P ( e s t . ) s l i g h t l y s t o n v (1) h i g h t o v e r y h i g h p e r m e a b i l i t y ; downward d r a i n a g e i s r e s t r i c t e d by u n d e r l y i n g impermeable m a t e r i a l s . n e g l i g i b l e good good h i g h H o l o c e n e S e d i m e n t s c o b b l e and b o u l d e r • g r a v e l s w i t h i n t e r s t i t i a l sand; d e p o s i t e d by p r e s e n t -day r i v e r s and s t r e a m s . No v e r y s t o n y t o e x c e e d -i n g l y s t o n y (3 t o 4 ) v e r y h i g h p e r m e a b i l i t y ; downward d r a i n a g e i s u s u a l l y r e s t r i c t e d by a h i g h water t a b l e n e g l i g i b l e good t o excellent good t o e x c e l l e n t moderate t o h i g h ; a h i g h w a t e r t a b l e w i l l h i n d e r e x c a v a t i o n work. G e o l o g i c a l M a t e r i a l s P h y s i c a l C h a r a c t e r i s t i c s Urban Use I n t e r p r e t a t i o n s P r e l o a d e d by G l a c i e r Ice U n i f i e d T e x t u r e (App. 6) S t o n i n e s s (App. 7) D r a i n a g e and P e r m e a b i l i t y C o m p r e s s i b i l i t y and E x p a n s i o n V a l u e as Subgrade B e a r i n g V a l u e f o r F o u n d a t i o n s E a s e o f E x c a v a t i o n f i n e s and and s i l t d e p o s i t e d by p r e s e n t -day s t r e a m s i n low, f l a t - l y i n g a r e a s and as t i d a l m u d f l a t s . No s t o n e f r e e (0) low p e r m e a b i l i t y ; a h i g h w a t e r t a b l e makes s u b s u r f a c e d r a i n a g e i m p o s s i b l e s l i g h t t o medium b u t may be h i g h i f s i l t and c l a y p r e d o m i n a t e f a i r t o p o o r p o o r t o f a i r ; w i l l s e t t l e e x c e s s i v e l y i n a r e a s u n d e r l a i n m a i n l y by s i l t and c l a y ; a r e a s u n d e r l a i n by f i n e sand and s i l t a re s u s c e p t i b l e t o l i q u e f a c t i o n h i g h ; a h i g h w a t e r t a b l e w i l l h i n d e r e x c a v a t i o n work c o l l u v i u m on b e d r o c k s l o p e s ; g e n e r a l l y l e s s t h a n 1.5 m. t h i c k and c o n s i s t i n g o f s u b a n g u l a r t o a n g u l a r f r a g m e n t s o f g r a n i t i c r o c k w i t h i n t e r s t i t i a l sand and s i l t . No s l i g h t l y s t o n y (1) h i g h t o v e r y h i g h p e r m e a b i l i t y ; downward d r a i n a g e i s r e s t r i c t e d by u n d e r l y i n g impermeable b e d r o c k n e g l i g i b l e t o s l i g h t p o o r t o f a i r p oor t o f a i r ; may be s u b j e c t t o mass movement moderate t o h i g h f i l l ; man-made d e p o s i t s o f a v a r i e t y o f m a t e r i a l s . u s u a l l y low p e r m e a b i l i t y ; ' i f l o o s e l y compacted the p e r m e a b i l i t y may be h i g h e r ; s u r f a c e d r a i n a g e i s poor on l e v e l a r e a s i f l o o s e l y compacted the c o m p r e s s i b i l i t y may be s l i g h t t o medium f a i r t o poo r p o o r t o f a i r ; may s e t t l e e x c e s s i v e l y moderate t o h i g h d e p e n d i n g on the d e g r e e o f c o m p a c t i o n - 127 -5 5 of the K i t s i l a n o sandstone ranges from 207 x 10 to 96 7 x 10 p a s c a l s and i s good foun d a t i o n m a t e r i a l f o r h i g h - r i s e b u i l d i n g s . (McLeod, 19 73). In Vancouver i t has been observed t h a t the eroded s u r f a c e and upper few metres of the sandstone i s o f t e n decomposed or f r i a b l e , consequently i t s s t r e n g t h i s s u b s t a n t i a l l y reduced. (Lim, 1974). J o i n t s and f r a c t u r e s e t s g e n e r a l l y comprise the dominant planes of weakness i n these types of bedrock and excavations or exposed steep s l o p e s must u t i l i z e and conform to these s u r f a c e s f o r optimum e f f i c i e n c y o f e x c a v a t i o n or s t a b i l i t y . Bedrock i n the Seymour area i s not f r a c t u r e d s i g n i f i c a n t l y enough to a l t e r the e n g i n e e r i n g p r o p e r t i e s . I t i s g e n e r a l l y i m p o s s i b l e to excavate i n areas immediately u n d e r l a i n by bedrock without b l a s t i n g and/or heavy machinery, consequently c o s t s are s i g n i f i c a n t l y h i g h e r . (Table XIV). Drainage from bedrock i s almost e n t i r e l y by s u r f a c e r u n o f f . Pre-Vashon sediments are exposed mainly a l o n g the s l o p e s of the major r i v e r v a l l e y s w i t h i s o l a t e d exposures i n s m a l l e r stream g u l l i e s and i n the R i v e r s i d e sand p i t . (Figure I I I - 2 ) . Because o f t h e i r d i s t r i b u t i o n these m a t e r i a l s are not important as p o t e n t i a l r e s i d e n t i a l areas except f o r t h e , l a t t e r s i t e . P r e l o a d i n g by a t l e a s t one major i c e sheet has caused c o n s o l i d a t i o n of the sediments w i t h corresponding changes i n r e l a t e d p r o p e r t i e s . B e a r i n g f o r foundations i s g e n e r a l l y good and ease of e x c a v a t i n g them i s low to moderate. - 128 -TABLE XIV On-Site S e r v i c i n g Cost Estimates f o r H i l l s i d e Development of R e s i d e n t i a l Housing Under I d e a l C o n d i t i o n s and i n Areas of E x t e n s i v e Bedrock, ( a f t e r Hawksworth, 1977; based on c o n s u l t a t i o n w i t h the B.C. Housing C o r p o r a t i o n ) . Type of S e r v i c e Minimum Cost Under I d e a l C o n d i t i o n s Minimum Cost i n Bedrock Area Watermains (15 cm. minimum pipe diameter) " $72/m. $130/m. S a n i t a r y Sewer (20 cm. minimum pipe diameter) $105/m.-$115/m. $164/m. Storm Sewers (25 cm.minimum pipe diameter) $66/m.-$72/m. $164/m.-$171/m. Roadworks (8.5 m. wide road i n c l u d i n g curb and boulevard t o p s o i l and seed) $100/m. $361/m. Sidewalk (1.5 m. wide concrete) $26/m. $26/m. Cost estimates exclude o f f - s i t e requirements and e n g i n e e r i n g c o s t s (eg. surveys, d e s i g n , and maintenance). Texture and genesis o f Quadra Sand make t h i s sediment h i g h l y s u i t a b l e f o r urban use. I t i s i n c o m p r e s s i b l e , of p e r m e a b i l i t y high enough to allow subsurface drainage, good to e x c e l l e n t f o r foundations t o r e s t on, good f o r subgrade, and easy t o excavate. Vashon lodgement t i l l i s an e x c e l l e n t foundation m a t e r i a l w i t h n e g l i g i b l e c o m p r e s s i b i l i t y . Depending on i t s c l a y content (usual range i s 2% to 8%), the t i l l has a d e n s i t y 3 ranging between 2.0 to 2.3 tonnes/m . (Cook and Brandon, 1956). Although the t i l l c o n t a i n s r e l a t i v e l y l i t t l e c l a y but a hig h p r o p o r t i o n o f sand, i t s coherency i s caused by the weight of - 129 -g l a c i a l i c e beneath which i t was d e p o s i t e d . T h i s dense, coherent m a t e r i a l allows very h i g h b e a r i n g loads, but i s v i r t u a l l y impermeable and d i f f i c u l t t o excavate. Some b u i l d i n g s i n Vancouver use loads as high as 6.7x10^ p a s c a l s although normal p r a c t i c e i s l e s s . (Cook and Brandon, 1956). Drainage i s by s u r f a c e r u n o f f and i s g e n e r a l l y very good on s l o p i n g ground but may be poor i n f l a t - l y i n g or d e p r e s s i o n a l areas. Large b o u l d e r s , which r e q u i r e b l a s t i n g t o make them sm a l l enough to excavate e a s i l y , may be encountered i n the t i l l . S u b s t r a t i f i e d Vashon d r i f t , c o n s i s t i n g of sand and g r a v e l outwash and i c e - c o n t a c t d e p o s i t s , i s g e n e r a l l y s u i t a b l e f o r urban use. Exposures of t h i s m a t e r i a l are i r r e g u l a r and d i s c o n t i n u o u s , consequently they can only be p r o p e r l y e v a l u a t e d by a d e t a i l e d subsurface study of the s i t e . Vashon a b l a t i o n t i l l i s a l s o i r r e g u l a r , r e s t r i c t e d to bedrock s l o p e s above the l i m i t of marine i n u n d a t i o n , a t l e a s t 650 f e e t (200 m.) above p r e s e n t sea l e v e l . The coarse, p o o r l y s o r t e d t i l l i s w e l l d r a i n e d , mainly by s u r f a c e r u n o f f , and has n e g l i g i b l e c o m p r e s s i b i l i t y , making i t f a i r l y w e l l s u i t e d as a foundation m a t e r i a l and road subgrade. Because i t i s l e s s compact i t i s more e a s i l y excavated than b a s a l t i l l , a lthough l i k e the l a t t e r , i t may c o n t a i n l a r g e b o u l d e r s . Post-Vashon g l a c i o m a r i n e and marine sediments are the l e a s t s u i t a b l e f o r urban r e s i d e n t i a l development. F l a t - l y i n g or d e p r e s s i o n a l areas u n d e r l a i n by such impermeable m a t e r i a l s - 130 -are p o o r l y d r a i n e d . They are not p r e c o n s o l i d a t e d and, depending on t h e i r s i l t and c l a y content, may be h i g h l y compressible and s u b j e c t to e x c e s s i v e s e t t l i n g under r e l a t i v e l y l i g h t l o a d s . The predominant cohesive sediment i n the area i s a stony c l a y e y s i l t or s i l t y c l a y of low to medium c o m p r e s s i b i l i t y or p l a s t i c i t y , however h i g h l y compressible c l a y e y s i l t s are to be expected i n the t h i c k e r d e p o s i t s . (Figure V l - l d ) . Klohn (1956) l i s t e d the unconfined compressive s t r e n g t h of s i m i l a r marine c l a y s i n the Vancouver area as 5 5 0.34x10 to 0.69x10 p a s c a l s . Major development on t h i s m a t e r i a l may cause l o c a l s e t t l i n g and encounter poor drainage such as r e p o r t e d i n the P o r t Coquitlam area by Hicock (19 76). The g l a c i o l a c u s t r i n e varved c l a y e y s i l t s may c r e a t e s i m i l a r problems. The more c l a y - r i c h varves are moderately compressible and, i n a t h i c k d e p o s i t , might s e t t l e s u b s t a n t i a l l y i f loaded. Areas u n d e r l a i n by t h i c k d e p o s i t s of C a p i l a n o sands and g r a v e l s are b e s t s u i t e d f o r r e s i d e n t i a l use. The c o h e s i o n l e s s sediments, because of good subsurface drainage and very low c o m p r e s s i b i l i t y , make e x c e l l e n t subgrade and foundation m a t e r i a l and are e a s i l y excavated. Present s u b d i v i s i o n s , such as Seymour Heights, were developed on these l e v e l t e r r a c e s because of the ease of i n s t a l l i n g underground u t i l i t i e s and foundations f o r d w e l l i n g s . The dense, s u b s t r a t i f i e d , pebbly s i l t y sand u n d e r l y i n g the lowland south and west of Deep Cove possesses s i m i l a r p r o p e r t i e s to the o t h e r c o h e s i o n l e s s sediments except t h a t - 131 -p e r m e a b i l i t y i s lower. T h i s m a t e r i a l i s g e n e r a l l y w e l l s u i t e d f o r urban use, however l o c a l drainage problems can be expected, p a r t i c u l a r l y i n p l a c e s where the water t a b l e i s near the s u r f a c e . S u p r a l i t t o r a l l a g g r a v e l s mantle most o f the Vashon D r i f t and Ca p i l a n o Sediments up to an e l e v a t i o n o f about 650 f e e t (200 m.). They are very permeable, p e r m i t t i n g e x c e l l e n t subsurface drainage down to the u n d e r l y i n g impermeable m a t e r i a l s . C o m p r e s s i b i l i t y i s n e g l i g i b l e , consequently they provide good foun d a t i o n support and make good road subgrade. Excavation i s u s u a l l y easy, except where l a r g e b o u l d e r s are encountered. As the g r a v e l s are g e n e r a l l y t h i n and d i s c o n t i n u o u s , any development must take i n t o account the type and c h a r a c t e r i s t i c s of the m a t e r i a l immediately u n d e r l y i n g them. Holocene a l l u v i a l g r a v e l d e p o s i t s which c o n s t i t u t e the f l o o d p l a i n d e l t a s o f Lynn Creek and Seymour R i v e r have few g e o l o g i c a l c o n s t r a i n t s to urban use. C o m p r e s s i b i l i t y i s . n e g l i g i b l e and p e r m e a b i l i t y i s very h i g h , although subsurface drainage can be r e s t r i c t e d by a sea s o n a l h i g h water t a b l e . These d e p o s i t s are s u i t a b l e as road subgrade and f o r found a t i o n support and can be excavated f a i r l y e a s i l y . A h i g h p r o p o r t i o n of boulders and a hig h water t a b l e may r e s t r i c t some d i g g i n g s . Toward McCartney Creek the d e l t a a l l u v i u m i s much f i n e r grained; the t i d a l mudflats a t the mouth of t h i s stream are made up. mainly o f f i n e sand and s i l t . S i m i l a r d e p o s i t s elsewhere i n the Lower Mainland have been c l a s s i f i e d as or g a n i c s i l t s although they range i n . c o m p o s i t i o n from s i l t y - 132 -sand to sandy s i l t c o n t a i n i n g s c a t t e r e d o r g a n i c matter and perhaps the o c c a s i o n a l t h i n o r g a n i c l a y e r . Klohn (19 56) has r e p o r t e d t h a t they have low to moderate c o m p r e s s i b i l i t y and 5 5 low b e a r i n g s t r e n g t h (0.21x10 to 0.83x10 p a s c a l s ) , however as c l a y and o r g a n i c content vary i t would not be unreasonable to expect h i g h c o m p r e s s i b i l i t y i n some p l a c e s . Because of a h i g h water t a b l e and low p e r m e a b i l i t y drainage i s poor. T h i s m a t e r i a l i s p o o r l y s u i t e d f o r urban use. A l a r g e p r o p o r t i o n of Vancouver i n d u s t r y i s l o c a t e d along the w a t e r f r o n t of B u r r a r d I n l e t . Almost i n v a r i a b l y development there r e q u i r e s s e v e r a l metres o f f i l l to c o n s t r u c t the yard: l e v e l a t a r e q u i r e d e l e v a t i o n and grade. S i m i l a r development over the Maplewood mudflats c o u l d cause e x c e s s i v e s e t t l i n g . In a d d i t i o n , these a l l u v i a l d e p o s i t s c o u l d l i q u e f y d u r i n g a major earthquake. C o l l u v i u m i s g e n e r a l l y t h i n and d i s c o n t i n u o u s , i r r e g u l a r l y d i s t r i b u t e d on the i n t r u s i v e bedrock s l o p e s . Good subsurface drainage i s r e s t r i c t e d by the u n d e r l y i n g bedrock so t h a t groundwater runs r a p i d l y down the bedrock s u r f a c e . Since the c o l l u v i u m i s s u b j e c t to g r a v i t a t i o n a l movement downslope i t should not be used as road subgrade or f o r foundation support. Any development would r e q u i r e removal of the c o l l u v i u m , so as to u t i l i z e the u n d e r l y i n g bedrock f o r support. F i l l c o n s i s t s of v a r i o u s man-made d e p o s i t s i n c l u d i n g - 133 -s o i l , s u r f i c i a l m a t e r i a l , broken rock, c o n c r e t e , even garbage and v e g e t a t i o n . The p h y s i c a l p r o p e r t i e s of each d e p o s i t , are t h e r e f o r e , h i g h l y v a r i a b l e . However, g e n e r a l l y t h i s m a t e r i a l i s more l o o s e l y compacted than n a t u r a l s u r f i c i a l sediments and may s e t t l e i f loaded. Major areas of f i l l which are s p e c i f i c a l l y designed f o r development are u s u a l l y a r t i f i c i a l l y compacted and allowed to s e t t l e p r i o r to c o n s t r u c t i o n . Since p e r m e a b i l i t y then becomes low, drainage can be poor on l a r g e , f l a t - l y i n g , compacted f i l l d e p o s i t s . Because of i t s mechanical composition, t h a t i s , f i n e p a r t i c l e s f i l l i n g v o i d s between coarse fragments, Vashon lodgement t i l l r e c o n s o l i d a t e s a f t e r emplacement as f i l l . In s p i t e of i t s r e l a t i v e i m p e r m e a b i l i t y , t i l l makes a good s t a b l e f i l l m a t e r i a l . S t a b i l i t y o f Slopes Over the years there have been many l a r g e s l i d e s and washouts i n the Lower Mainland. Most of these were i n u n c o n s o l i d a t e d sediments on steep slopes where heavy r a i n f a l l and e x c e s s i v e c l e a r i n g of the l a n d c r e a t e d u n s t a b l e s o i l c o n d i t i o n s . (Armstrong, 1956). Of the s l o p e f a i l u r e s i n s p e c t e d i n the Seymour area, most i n i t i a t e d i n drainage d e p r e s s i o n s , s m a l l seepage hollows, or on p o o r l y d r a i n e d p a r t s of open s l o p e s . I t i s obvious t h a t groundwater p l a y s an important p a r t i n the r e l e a s e of s l i d e s and washouts, probably by reducing normal e f f e c t i v e s t r e s s e s and by c r e a t i n g downslope seepage f o r c e s . In g e n e r a l , long uniform slopes appear to be more s u s c e p t i b l e to f a i l u r e than s h o r t , broken, or stepped ones. - 134 -Some of the more common combinations o f geology and hydrology which have caused slope f a i l u r e elsewhere i n the Lower Mainland have been documented by Armstrong (1956; 1957), A l l a n (1957), and Lapointe (1972). The main f a i l u r e types expected i n the Seymour area i n c l u d e : p i p i n g or sprea d i n g i n Semiahmoo laminated s i l t s caused by h o r i z o n t a l seepage; p i p i n g , slumping, or flow s l i d e s on steep s l o p e s i n Quadra Sand caused by e x c e s s i v e groundwater seepage; washouts i n Quadra Sand i n i t i a t e d by s u r f a c e e r i o s i o n ; flow of s a t u r a t e d Vashon D r i f t caused by high h y d r o s t a t i c p r e s s u r e under the t i l l sheets or by s u r f a c e e r o s i o n i n t o the t i l l ; p r o g r e s s i v e slumping i n Capilano cohesive sediments caused by h i g h pore-water p r e s s u r e ; flow s l i d e s or washouts i n C a p i l a n o c o h e s i o n l e s s m a t e r i a l i n i t i a t e d by undermining, s u r f a c e e r o s i o n , or oversteepened s l o p e s ; and flow of s a t u r a t e d s o i l over u n d e r l y i n g impermeable sediments or bedrock. I d e n t i f y i n g areas prone t o slope f a i l u r e (Figure VII-1) can be done on the evidence o f pr e v i o u s movement and/or a general understanding of the geology and hydrology o f the sl o p e . In the Seymour area most zones of i n s t a b i l i t y are i n d i c a t e d by numerous, but sm a l l f a i l u r e s . In many cases flow of s a t u r a t e d s o i l , i n d i c a t i n g an excess of groundwater seepage, i s the only evidence. Thick sequences of Semiahmoo laminated s i l t are exposed on steep s l o p e s along .Lynn Creek where the s o i l cover has flowed downslope. Groundwater i s c o n s t a n t l y seeping out of t h i s comparatively impermeable sediment and c o u l d l e a d to - 135 -subsurface e r o s i o n and subsequent s l o p e f a i l u r e . S l i d e s and washouts i n Quadra Sand are common along Lynn Creek, Seymour R i v e r , and McCartney Creek. T h i s sediment i s one of the most e a s i l y eroded m a t e r i a l s i n the area. Exposure on sl o p e s where there i s c o n s i d e r a b l e groundwater seepage, leads to r a p i d e r o s i o n and massive washouts. P h i l p (1961) d i d a s t a b i l i t y a n a l y s i s o f a roadcut on Highway 401, 1 km. west of Lynn Creek. He concluded t h a t the cut, made a t a 30° (60%) angle i n t o Quadra Sand, was s t a b l e w i t h regard to a c i r c u l a r a r c f a i l u r e s u r f a c e (the f a c t o r of s a f e t y was g r e a t e r than 1). However, the interbedded sands and s i l t s were s u s c e p t i b l e to s u r f a c e and subsurface e r o s i o n ( i e . p i p i n g ) which c r e a t e d numerous g u l l i e s and l e d to undermining and c o l l a p s e of l a r g e masses of s a t u r a t e d sediment. The p o s s i b i l i t y of p a r t i a l l i q u e f a c t i o n of these sediments was i n v e s t i g a t e d but they were found t o have hi g h enough p e r m e a b i l i t y and d e n s i t y t o r e s i s t t h i s type of f a i l u r e . N a t u r a l s l o p e s u n d e r l a i n by Vashon D r i f t are g e n e r a l l y s t a b l e . F a i l u r e o f the d r i f t i s p o s s i b l e where there are l a y e r s o r lenses of c o h e s i o n l e s s , s t r a t i f i e d , f i n e sediments i n or under the impermeable t i l l . During the wet season, high h y d r o s t a t i c p r e s s u r e s c o u l d develop i n the permeable u n i t s , and i f a roadcut or e x c a v a t i o n were to expose the t i l l - o u t w a s h c o n t a c t , r a p i d subsurface e r o s i o n might l e a d t o a washout or flow of the s a t u r a t e d m a t e r i a l . A f a i r l y l a r g e washout along the v a l l e y s l o p e of Seymour R i v e r was caused by s u r f a c e discharge down the steep slope from an a r t i f i c i a l drainage - 136 -d i t c h . The washout c r e a t e d a l a r g e , unstable g u l l y , exposing a t h i c k sequence of Ca p i l a n o g l a c i o m a r i n e sediments, Vashon t i l l and outwash, and Quadra Sand. (D-12). F a i l u r e by r o t a t i o n a l slump i s most probable i n massive Ca p i l a n o cohesive sediments, i n c l u d i n g the stony c l a y e y s i l t s and s i l t y c l a y s . In upper Lynn canyon, slump f a i l u r e s i n gl a c i o m a r i n e sediments have caused s m a l l s l i d e s along the steep e a s t e r n v a l l e y s i d e . (D-8,9). The f a i l u r e s were probably i n i t i a t e d by d i f f e r e n c e s i n p e r m e a b i l i t y between the sediments and culminated i n flow s l i d e s r a t h e r than r o t a t i o n a l slumps. Downward movement of groundwater through outwash sand and g r a v e l i s i n t e r c e p t e d by impermeable s i l t s and c l a y s , c a u s i n g seepage onto the s o i l - c o v e r e d s l o p e f a c e . A d d i t i o n a l groundwater seeps from a g r a v e l l a y e r which l i e s between the glac i o m a r i n e u n i t and impermeable Vashon t i l l . During p e r i o d s of high seepage and high pore p r e s s u r e s the s t r e n g t h of the cohesive m a t e r i a l s i s reduced, c a u s i n g f a i l u r e i n t h i s u n i t . O v e r l y i n g outwash i s undermined and f a i l s w i t h the c l a y e y s i l t s . A l l the f a i l e d m a t e r i a l moves downslope over the t i l l s u r f a c e as s a t u r a t e d , flow s l i d e s . A number of s l i d e s c a r s are a l i g n e d along t h i s s e c t i o n of v a l l e y s l o p e . Each c o n s i s t s of a steep headwall scarp through C a p i l a n o outwash and cohesive sediments and an exposed plane o f movement down the t i l l s u r f a c e . Along the v a l l e y slopes of lower Lynn creek the t h i c k sequence of varved c l a y e y s i l t has i n d i c a t i o n s of f a i l u r e : n e a r - v e r t i c a l s e c t i o n s of t h i s m a t e r i a l are exposed where - 137 -l a r g e b l o c k s have broken o f f the slope f a c e . (D-,13,14) . F a i l u r e i s p o s s i b l y caused by p i p i n g i n the s i l t l a y e r s or by high h y d r o s t a t i c p r e s s u r e s i n v e r t i c a l f r a c t u r e s . Constant seepage down the slope causes s a t u r a t e d flow of the o v e r l y i n g s o i l . F a i l u r e on n a t u r a l slopes u n d e r l a i n by Capilano sands and g r a v e l s i s uncommon because they are permeable and w e l l d r a i n e d . The main cause of i n s t a b i l i t y i n these i s by undermining or by a r t i f i c i a l l y o v ersteepening a s l o p e . Removal of sand and g r a v e l i n p i t - m i n i n g o p e r a t i o n s has d i s t u r b e d the n a t u r a l angle of repose of the c o h e s i o n l e s s sediments, making them p o t e n t i a l l y u n s t a b l e . Sand and g r a v e l p i t s o f f R i v e r s i d e D r i v e and D o l l a r t o n Highway both have n e a r - v e r t i c a l cut-banks. The D o l l a r t o n p i t i s p a r t i c u l a r l y s u s c e p t i b l e to f a i l u r e , as a s e c t i o n of the p i t scarp, which stands 8 to 10 m. hig h , i s c o n s t a n t l y s u b j e c t to smal l sand runs which are undermining a bouldery s u p r a l i t t o r a l l a g - g r a v e l capping. Removal of sand and g r a v e l exposes l a r g e areas of e a s i l y erodable m a t e r i a l t o s u r f a c e r u n o f f which can cause washouts and g u l l y e r o s i o n . The most common s i g n of i n s t a b i l i t y i s flow of s a t u r a t e d s o i l downslope over u n d e r l y i n g impermeable m a t e r i a l , u s u a l l y on steep s l o p e s below zones of groundwater seepage and on the steep g u l l y s i d e s o f the s m a l l e r streams. T h i s type of f a i l u r e p o s s i b l y i n d i c a t e s g e o l o g i c a l and h y d r o l o g i c a l c o n d i t i o n s which c o u l d l e a d to f u r t h e r i n s t a b i l i t y . In g e n e r a l , the p o t e n t i a l l y unstable areas are not i n - 138 -regions w e l l s u i t e d to urban development t h e r e f o r e they do not n e c e s s a r i l y pose a t h r e a t to man's a c t i v i t i e s . Slopes rendered unstable by the works of man, such as those i n the abandoned sand and g r a v e l p i t s , should be s t a b i l i z e d by d r a i n i n g , r e g r a d i n g , and r e p l a n t i n g w i t h v e g e t a t i o n . Excess water, e i t h e r as h i g h pore-water pressure or heavy s u r f a c e r u n o f f ; has a dramatic e f f e c t on the s t a b i l i t y o f s l o p e s . T h e r e f o r e i t i s not s u r p r i s i n g t h a t the b e s t method o f s t a b i l i z i n g s l o p e s i s by d r a i n i n g them. ( H e l l w i g , 1961). Surface d r a i n s prevent ground s a t u r a t i o n and subsurface d r a i n s remove excess groundwater from m a t e r i a l of low p e r m e a b i l i t y u n d e r l y i n g s l o p e s or from surrounding source areas. F i l t e r s can be p l a c e d along s l o p e faces to prevent seepage e r o s i o n . P l a n t i n g grass and t e r r a c i n g slopes g r e a t l y decreases s u r f a c e e r o s i o n and allows a n a t u r a l slope to r e - e s t a b l i s h . C o n s t r u c t i o n M a t e r i a l s Sand and g r a v e l are the only m a t e r i a l s which have been mined f o r c o n s t r u c t i o n purposes from Quaternary sediments i n North Vancouver-Seymour. An o l d , abandoned rock quarry of u n c e r t a i n age or purpose a t the mouth of F r a n c i s Creek, no r t h of Deep Cove (Figure 1-2), i n d i c a t e s t h a t i n t r u s i v e bedrock was removed from t h i s area. Sand and g r a v e l i n the area can be c l a s s i f i e d i n t o f o u r types: Quadra Sand; C a p i l a n o sand and g r a v e l ( r e p r e s e n t i n g - 139 -"raised d e l t a i c and channel deposi t s ) ; C a p i l a n o s u p r a l i t t o r a l l a g g r a v e l and sand; and Holocene d e l t a i c and channel g r a v e l s formed by present-day mountain streams. Quadra Sand i s l i m i t e d i n e xtent and g e n e r a l l y u n d e r l i e s t h i c k sequences of Vashon and Capilano sediments. Capilano outwash i s the b e s t s o r t e d of the P l e i s t o c e n e g r a v e l s , and forms an important g r a v e l source. The s u r f a c e exposure i s l i m i t e d and because the outwash g r a v e l s u n d e r l i e l e v e l , w e l l d r a i n e d t e r r a c e s which are h i g h l y s u i t a b l e f o r r e s i d e n t i a l development, they are r a p i d l y b e i n g covered by urban expansion. Minor amounts of C a p i l a n o g r a v e l are found along the s l o p e s n o r t h of Deep Cove • i n s m a l l d e l t a i c d e p o s i t s . C a p i l a n o l a g g r a v e l s are widespread but u s u a l l y too thin, and too d i r t y to be e c o n o m i c a l l y important. Where a s s o c i a t e d w i t h u n d e r l y i n g outwash sand and g r a v e l they may be minable. Sand and g r a v e l along the banks and a t the mouths of Lynn Creek and Seymour R i v e r c o n s t i t u t e l a r g e renewable r e s e r v e s . However, fores h o r e dredging was stopped i n 1963 by the N a t i o n a l Harbours Board to conserve g r a v e l f o r use i n b u i l d i n g up the w a t e r f r o n t . (Learning, 1968). Dry d i g g i n g s i n these Holocene g r a v e l s were a l s o c u r t a i l e d by zoning r e g u l a t i o n s and urban expansion. Learning (196 8) summarized the sand and g r a v e l workings which once operated i n North Vancouver-Seymour. The L i l l o o e t Road p i t (Figure 1-2) , above the s a n i t a r y l a n d f i l l , was the main source of g r a v e l f o r m u n i c i p a l use. F o r e s e t d e l t a i c beds of C a p i l a n o sand and s i l t y g r a v e l up to 12 m. t h i c k were - 140 -o v e r l a i n by 1 to 2 m. of f l a t - l y i n g , s u p r a l i t t o r a l l a g g r a v e l . T h i s o p e r a t i o n ceased i n the l a t e 1960's. Highland Sand and Grav e l L t d . operated a p i t , mainly i n C a p i l a n o outwash, o f f Seymour Boulevard west of Seymour R i v e r t i l l 1960 when pr o d u c t i o n was suspended even though the p i t was not d e p l e t e d . 3 At one time the p l a n t t r e a t e d as much as 137,000 m. of g r a v e l per year. A sand p i t o p e r a t i n g e a s t of R i v e r s i d e D r i v e mined Quadra Sand beds which were o r i g i n a l l y up t o 30 m. t h i c k ; Vashon t i l l and gl a c i o m a r i n e sediments p a r t i a l l y o v e r l a y the Quadra Sand; C a p i l a n o channel and d e l t a i c g r a v e l s o f unknown exten t i n t u r n l a y above the t i l l ; and a s u r f a c e veneer of la g g r a v e l capped the d e p o s i t . Operation of t h i s p i t ceased i n the l a t e 1960's. A t one time Capilano d e l t a i c g r a v e l s e a s t of Seymour R i v e r and nort h of D o l l a r t o n Highway were mined; 3 i n 1959, 226,900 m. of sand and g r a v e l were processed i n the treatment p l a n t . When t h i s source was d e p l e t e d the p l a n t was fed from dredged f o r e s h o r e d e p o s i t s of Holocene g r a v e l . The most common d i f f i c u l t i e s t h a t may be a t t r i b u t e d to g e o l o g i c a l c o n d i t i o n s i n the o p e r a t i o n o f sand and g r a v e l p i t s were d i s c u s s e d by Armstrong (1956; 1957) and Hicock (1976). These i n c l u d e : e x c e s s i v e overburden o f Vashon t i l l or C a p i l a n o g l a c i o m a r i n e sediments; d i s c o n t i n u i t y of g r a v e l and sand u n i t s , p a r t i c u l a r l y the l e n t i c u l a r nature o f many g r a v e l beds; o v e r s i z e d boulders up to 5 m. i n diameter, which cannot be handled by equipment without b l a s t i n g ; interbedded t h i n , f i n e sand and s i l t s t r a t a which make p r o c e s s i n g d i f f i c u l t and le a d to - 141 -washouts on steep s l o p e s ; i r r e g u l a r t i l l and/or stony c l a y e y s i l t s u r f a c e s which can make the o v e r l y i n g g r a v e l too t h i n to mine economically; and the presence o f a h i g h water t a b l e . Now t h a t f o r e s h o r e dredging i s stopped and the f l o o d p l a i n d e l t a s u r f a c e o f Lynn Creek and Seymour R i v e r i s mostly covered by some form o f development, the o n l y r e s e r v e s o f sand and g r a v e l l e f t i n the Seymour area are the Cap i l a n o outwash d e p o s i t s found between Lynn Creek and Seymour R i v e r and e a s t of Seymour R i v e r . The lower p a r t o f the i n t e r r i v e r area, a l r e a d y mined f o r sand and g r a v e l , i s now covered by m u l t i - f a m i l y r e s i d e n t i a l housing and Capilano C o l l e g e . A cemetery occ u p i e s a f a i r s i z e d area u n d e r l a i n by these g r a v e l s , although a s m a l l p i t c l o s e by i s operated i n t e r m i t t e n t l y by the m u n i c i p a l i t y . The main undeveloped area with e x t e n s i v e g r a v e l d e p o s i t s i n the i n t e r r i v e r r e g i o n l i e s between the cemetery and Lynn Canyon Park (Figure 1-1). Thickness o f these d e p o s i t s i s unknown although a borehole near the cemetery (GSC-1101) i n t e r s e c t e d at l e a s t 3.5 m. of g r a v e l . The Capilano sand and g r a v e l i s more e x t e n s i v e t o the no r t h , however, these r e s e r v e s f a l l w i t h i n the boundaries o f e i t h e r Lynn Canyon Park or the G.V.R.D. watershed. East o f Seymour R i v e r l i t t l e o f the Capilano outwash can be c l a s s i f i e d as g r a v e l r e s e r v e s because u r b a n i z a t i o n has pre-empted the la n d f o r r e s i d e n t i a l use. The main undeveloped area u n d e r l a i n by g r a v e l s l i e s n orth of Hyannis D r i v e , but most of t h i s a l s o f a l l s w i t h i n the G.V.R.D. watershed. Borehole records (GSC-1,214,215,274) i n d i c a t e s u b s t a n t i a l - 142 -th i c k n e s s e s o f s u r f i c i a l sediments i n t h i s area, however, the records are not d e t a i l e d enough t o gi v e a c c u r a t e s t r a t i g r a p h i c i n f o r m a t i o n . Up to 3.5 m. of C a p i l a n o sand and g r a v e l are exposed i n a c u t along the t r a n s m i s s i o n l i n e right-of-way (D^18) and i n a sm a l l p i t on the h i l l s i d e above Hyannis D r i v e . The o p e r a t i o n o f sand and g r a v e l p i t s i n the Seymour area has been dormant f o r ;some time. However, other than a t the m u n i c i p a l l y owned L i l l o o e t Road p i t , l i t t l e r e c l a m a t i o n work has been done on these s c a r s . There, r e g r a d i n g prepared the l a n d f o r development of r e s i d e n t i a l d w e l l i n g s , l i g h t i n d u s t r y , and p a r t of the Ca p i l a n o C o l l e g e campus. The D o l l a r t o n Highway and R i v e r s i d e D r i v e p i t s ( P l a t e 10) have remained u n a l t e r e d s i n c e o p e r a t i o n s ceased. Proper r e c l a m a t i o n methods such as those d i s c u s s e d by C a r r e i r o and R e i n i n g (1975) c o u l d be u t i l i z e d to make these p i t s s u i t a b l e f o r a l t e r n a t i v e uses such as r e c r e a t i o n a l , r e s i d e n t i a l , l i g h t i n d u s t r i a l , or commercial. In some p a r t s of the world, abandoned p i t s are used as waste d i s p o s a l s i t e s and then put to a l t e r n a t i v e use a f t e r they are f i l l e d . The p e r m e a b i l i t y o f the C a p i l a n o sands and g r a v e l s , groundwater seepage, and hig h r a i n f a l l i n t h i s area make t h i s l e s s a t t r a c t i v e . Summary of G e o l o g i c a l C o n s t r a i n t s to Development R e s i d e n t i a l development of the land i s dependent on - 143 -P l a t e 10. -Riv e r s i d e D r i v e sand and g r a v e l p i t . There has been no attempt t o r e c l a i m t h i s area s i n c e o p e r a t i o n s ceased i n the l a t e 1960's. - 144 -s u r f a c e and subsurface d i s t r i b u t i o n of the g e o l o g i c a l m a t e r i a l s , on s u i t a b i l i t y of the m a t e r i a l s f o r urban use, and on g e o l o g i c a l processes a c t i n g on the landscape. Each of these f a c t o r s must be c o n s i d e r e d w i t h the others to determine the s e v e r i t y of l i m i t i n g g e o l o g i c c h a r a c t e r i s t i c s . For example, a sediment w e l l s u i t e d to support d w e l l i n g s i s of l i t t l e importance i f i t i s only exposed on steep, unstable s l o p e s . G e o l o g i c a l f e a t u r e s which may r e s t r i c t development i n c l u d e depth to; bedrock or impervious l a y e r , t e x t u r e , s t o n i n e s s , c o n s o l i d a t i o n h i s t o r y , and s t a b i l i t y of the s u r f i c i a l m a t e r i a l s . (Table XV). Bedrock a t or near the s u r f a c e r e s t r i c t s development because i t i s d i f f i c u l t t o excavate and i s impermeable. Although bedrock has e x c e l l e n t b e a r i n g s t r e n g t h , d w e l l i n g s c o n s t r u c t e d on i t g e n e r a l l y r e q u i r e s p e c i a l foundation d e s i g n s . Because of the expense of e x c a v a t i n g and the p o s s i b i l i t y o f d i s t u r b i n g s u r f a c e drainage, bedrock w i t h i n 0.75 m. of the s u r f a c e i s a s e v e r e l y l i m i t i n g f a c t o r . Improved drainage and e a s i e r e x c a v a t i o n can be expected where s o i l , c o l l u v i u m , or other s u r f i c i a l sediments mantle the rock. A moderate l i m i t a t i o n i s given to areas where bedrock i s between 0.75 and 1.5 m. below the ground s u r f a c e . I f bedrock i s more than 1.5 m. below the s u r f a c e , the degree of l i m i t a t i o n t o r e s i d e n t i a l use i s s l i g h t . Texture ( U n i f i e d S o i l C l a s s i f i c a t i o n ) measures c o m p r e s s i b i l i t y , d e s c r i b e s p a r t i c a l s i z e d i s t r i b u t i o n , and - 145 -pro v i d e s a comparative measure of p e r m e a b i l i t y . S u r f i c i a l d e p o s i t s c o n t a i n i n g o r g a n i c matter, peat, and h i g h l y compressible s i l t s and c l a y s s e v e r e l y r e s t r i c t development becuase they are v i r t u a l l y impermeable and w i l l s e t t l e e x c e s s i v e l y i f loaded. A moderate l i m i t a t i o n i s given to s i l t s and c l a y s of low c o m p r e s s i b i l i t y and p e r m e a b i l i t y which may be s u b j e c t to minor s e t t l i n g . S l i g h t l y or non-compressible, c o a r s e - g r a i n e d sediments have on l y s l i g h t t e x t u r a l r e s t r i c t i o n s to de velopmen t . S t o n i n e s s i s an estimate o f the amount of boulder s i z e fragments. I f a sediment c o n t a i n s more than 40% boulders i t i s a severe r e s t r i c t i o n . A moderate l i m i t a t i o n i s given i f b oulders make up 10% to 40% of the d e p o s i t . Less than 10% boulder content i s only s l i g h t l y l i m i t i n g to r e s i d e n t i a l use. C o n s o l i d a t i o n h i s t o r y i s dependent on whether the m a t e r i a l has been preloaded by g l a c i e r i c e . . M a t e r i a l s t h a t are p r e c o n s o l i d a t e d , t h a t i s Vashon D r i f t and o l d e r sediments, are not r e s t r i c t e d by t h i s f a c t o r . Post Vashon m a t e r i a l s are normally c o n s o l i d a t e d a t depth as they have not been preloaded. A moderate l i m i t a t i o n i s given t o f i n e - t e x t u r e d , cohesive sediments, such as C a p i l a n o s i l t y c l a y s and stony c l a y e y s i l t s , and s a t u r a t e d Holocene s i l t s and f i n e sands. The c o n s o l i d a t i o n h i s t o r y of dense, c o h e s i o n l e s s , p o s t - g l a c i a l sediments i s not a l i m i t a t i o n . The presence of an impervious l a y e r w i t h i n 1.5m. of the ground s u r f a c e i s a moderately l i m i t i n g f a c t o r because of i t s - 146 -e f f e c t on drainage o f the o v e r l y i n g m a t e r i a l . Drainage and water t a b l e p o s i t i o n w i l l be more r e s t r i c t i v e i n areas of g e n t l e slope where the impervious l a y e r i s very c l o s e to the s u r f a c e . Impermeable sediments, such as Vashon lodgement t i l l , are u s u a l l y dense and compact which may a f f e c t the ease o f e x c a v a t i n g these m a t e r i a l s . The degree of l i m i t a t i o n f o r s t a b i l i t y of s u r f i c i a l m a t e r i a l s i s a comparative measure based on the type of sediments and the evidence of p r e v i o u s i n s t a b i l i t y . Slopes which should be r e s t r i c t e d from development are those which have p r e v i o u s l y f a i l e d and those immediately adjacent areas of s i m i l a r geology and hydrology. T h i s i n c l u d e s man-made, oversteepened s l o p e s i n roadcuts and sand and g r a v e l p i t s . A moderate l i m i t a t i o n i s given to areas of p o t e n t i a l i n s t a b i l i t y . These i n c l u d e steep slopes which have not p r e v i o u s l y f a i l e d but which have s i m i l a r geology and hydrology as other u n s t a b l e s l o p e s . C o h e s i o n l e s s sediments, where s u b j e c t to e r o s i o n on moderate or steep s l o p e s and i n stream v a l l e y s , have a moderate s t a b i l i t y l i m i t a t i o n . Areas w i t h severe g e o l o g i c a l c o n s t r a i n t s to development are those u n d e r l a i n by C a p i l a n o g l a c i o m a r i n e and marine sediments, and by Holocene sand and s i l t (Maplewood m u d f l a t s ) . C a p i l a n o cohesive sediments are normally c o n s o l i d a t e d and impermeable, which combined w i t h t h e i r t e x t u r a l l i m i t a t i o n s , can l e a d to poor drainage and e x c e s s i v e s e t t l i n g under foundation l o a d s . Such c o n d i t i o n s are not d e s i r a b l e f o r - 147 -i n t e n s i v e r e s i d e n t i a l use. F i n e - g r a i n e d , normally c o n s o l i d a t e d a l l u v i u m o f the mudflats probably c o n t a i n s h i g h l y compressible m a t e r i a l which, i f loaded, c o u l d cause e x c e s s i v e s e t t l i n g . TABLE XV Degree o f L i m i t a t i o n of Geo l o g i c F a c t o r s to Urban R e s i d e n t i a l Land-Use. L i m i t i n g Degree o f L i m i t a t i o n F a c t o r S l i g h t Moderate Severe depth to bedrock g r e a t e r than 1.5 m. 0.75 - 1.5 m. l e s s than 0.75 m. t e x t u r e 1. GW,GP,SW,SP,GM, GC,SM,SC. ML,CL. CH,MH,OL,OH,PT. st o n i n e s s 2. stone f r e e (0) or s l i g h t l y stony (1) moderately stony (2) or very stony (3) exce e d i n g l y stony (4) or e x c e s s i v e l y stony (5) c o n s o l i d a t i o n h i s t o r y p r e c o n s o l i d a t e d normally c o n s o l i d a t e d impervious h o r i z o n p r e s e n t a t l e s s than 1.5 m. depth s t a b i l i t y of s u r f i c i a l m a t e r i a l s t a b l e p o t e n t i a l l y u nstable evidence o f pr e v i o u s i n s t a b i l i t y 1. U n i f i e d S o i l Texture e x p l a i n e d i n Appendix 5. 2. Ston i n e s s C l a s s e s e x p l a i n e d i n Appendix 7 • D e p o s i t s o f man-made f i l l have h i g h l y v a r i a b l e p h y s i c a l c h a r a c t e r i s t i c s depending on the m a t e r i a l used and i t s degree of compaction. Large areas o f f i l l s p e c i f i c a l l y designed f o r i n d u s t r i a l development are a r t i f i c i a l l y compacted, consequently there should be l i t t l e or no s e t t l i n g although drainage may be poor.'. Other man-made d e p o s i t s , such as the s a n i t a r y l a n d f i l l , have h i g h l y v a r i a b l e c h a r a c t e r i s t i c s which c o u l d l e a d to - 148 -e x c e s s i v e d i f f e r e n t i a l s e t t l i n g under l o a d s . Such m a t e r i a l i s u n s u i t a b l e f o r r e s i d e n t i a l development. Development on bedrock i s p o s s i b l e p r o v i d i n g the s u r f a c e drainage i s not e x t e n s i v e l y a l t e r e d and the expense o f ex c a v a t i n g rock i s not r e s t r i c t i v e . T h i n s u r f i c i a l m a t e r i a l s (mainly t i l l and colluvium) over bedrock w i l l not a p p r e c i a b l y a f f e c t the s u i t a b i l i t y f o r development. Pockets of t h i c k t i l l , i r r e g u l a r l y d i s t r i b u t e d on the bedrock s u r f a c e , probably e l i m i n a t e some of the p h y s i c a l r e s t r i c t i o n s although s i t e -s p e c i f i c s t u d i e s are necessary to determine the degree of l i m i t a t i o n s i n these areas. Pre-Vashon sediments have few p h y s i c a l c h a r a c t e r i s t i c s which l i m i t development. The main c o n s t r a i n t to r e s i d e n t i a l use of these m a t e r i a l s i s t h a t they are exposed on l y on steep v a l l e y slopes.With p r e c a u t i o n s a g a i n s t s u r f a c e e r o s i o n , Quadra Sand, a w e l l d r a i n e d , p r e c o n s o l i d a t e d sediment wi t h n e g l i g i b l e c o m p r e s s i b i l i t y , i s w e l l s u i t e d f o r r e s i d e n t i a l use. Development i s p o s s i b l e i n the R i v e r s i d e p i t p r o v i d i n g proper r e c l a m a t i o n methods are u t i l i z e d to minimize e r o s i o n and slope i n s t a b i l i t y . Vashon D r i f t , which u n d e r l i e s much of the Seymour area, has few l i m i t a t i o n s to r e s i d e n t i a l development. The dense, compact lodgement t i l l , v i r t u a l l y impermeable, i s d i f f i c u l t t o excavate and may be p o o r l y d r a i n e d i n i s o l a t e d d e p r e s s i o n a l areas. - 149 -Areas u n d e r l a i n by t h i c k d e p o s i t s of C a p i l a n o outwash sediments have no g e o l o g i c a l r e s t r i c t i o n s to development. S u p r a l i t t o r a l l a g g r a v e l s are s u i t a b l e f o r r e s i d e n t i a l use although they are u s u a l l y t h i n and d i s c o n t i n u o u s , consequently are d i f f i c u l t to e v a l u a t e . Large boulders i n the g r a v e l or i n s t a b i l i t y on s l o p e s may be l i m i t i n g f a c t o r s to development. G e o l o g i c a l l i m i t a t i o n s to r e s i d e n t i a l development on Holocene a l l u v i a l g r a v e l s are s l i g h t , the main c o n s t r a i n t i s a h y d r o l o g i c a l one i n v o l v i n g poor drainage, h i g h water t a b l e , and s u s c e p t i b i l i t y to f l o o d i n g . - 150 -CHAPTER VII SEISMIC RISK AND MICROZONATION • Seismic Risk The problem of e s t i m a t i n g s e i s m i c r i s k i s fundamentally .that of p r e d i c t i n g f u t u r e ground motions or t h e i r c a u s a t i v e earthquakes. Earthquakes i n Canada are s u f f i c i e n t l y frequent and i n t e n s e to be of concern; two to three hundred occur each year w i t h about 2 7% of these l o c a t e d i n western Canada. (Whitham, 19 75). The s e i s m i c r i s k t o the major c i t i e s of B r i t i s h Columbia i s s i m i l a r t o t h a t of S e a t t l e . In 19 65 an earthquake k i l l e d s e v e r a l people and caused c o n s i d e r a b l e damage i n the Seattle-Tacoma area. The l a t e s t c o m p i l a t i o n o f earthquake data f o r western Canada demonstrates t h a t the most a c t i v e r e g i o n s a r e : 1.) along the Queen C h a r l o t t e - F a i r w e a t h e r f a u l t systems; 2.) west of Vancouver I s l a n d betweentthe Queen C h a r l o t t e I s l a n d s and the n o r t h e r n end o f the Juan de Fuca Ridge; and 3.) the Puget Sound-southern Vancouver I s l a n d r e g i o n . (Milne e t a l , 1977). S t r a i n r e l e a s e c a l c u l a t i o n s show t h a t most o f the energy i s r e l e a s e d along the Queen C h a r l o t t e - F a i r w e a t h e r f a u l t systems and suggest t h a t i n the Puget Sound-Vancouver I s l a n d r e g i o n a s i g n i f i c a n t amount of accumulated s t r a i n i s p r e s e n t l y a v a i l a b l e f o r r e l e a s e as earthquakes. Magnitude of an earthquake i s r e l a t e d to the amount of energy r e l e a s e d a t the hypocentre. I t i s measured on the - 151 -l o g a r i t h m i c Gutenburg-Richter S c a l e i n which an i n c r e a s e o f magnitude 1 r e p r e s e n t s about a t h i r t y - f o l d i n c r e a s e i n energy r e l e a s e d . I n t e n s i t y of an earthquake i s the amount of shaking, damage to p r o p e r t y , and e a r t h deformation f e l t or "observed a t a given p l a c e and which decreases away from the earthquake e p i c e n t r e . I n t e n s t i y i s measured i n terms of a r b i t r a r i l y d e f i n e d s c a l e s of which the most w i d e l y used i s the M o d i f i e d M e r c a l l i S c a l e . TABLE XVI M o d i f i e d M e r c a l l i S c ale of Earthquake I n t e n s i t i e s with Approximately Corresponding R i c h t e r Magnitudes. ( a f t e r Holmes, 1965). I n t e n s i t y D e s c r i p t i o n of c h a r a c t e r i s t i c e f f e c t s Magnitude approximately c o r r e s p o n d i n g to h i g h e s t i n t e n s i t y reached I I n s t rumental: d e t e c t e d o n l y by s e i sinography 3.5 to 4.2 II F e e b l e : n o t i c e d only by s e n s i t i v e people I I I S l i g h t : l i k e the v i b r a t i o n s due to a p a s s i n g heavy truck; f e l t by people a t r e s t , e s p e c i a l l y on upper f l o o r s IV Moderate: f e l t by people w h i l e walking; r o c k i n g of l o o s e o b j e c t s , i n c l u d i n g s t a n d i n a v e h i c l e s 4.3 to 4.8 V Rather Strong: f e l t g e n e r a l l y ; most s l e e p e r s are woken and b e l l s r i n g VI Strong: t r e e s sway and a l l suspended o b j e c t s swing; damage by o v e r t u r n i n g and f a l l i n g o f l o o s e o b j e c t s 4.9 to 5.4 VII Very Strong: g e n e r a l alarm; w a l l s crack; p l a s t e r f a l l s 5.5 to 6.1 - 152 -V I I I D e s t r u c t i v e : car d r i v e r s s e r i o u s l y d i s t u r b e d ; masonry f i s s u r e d ; chimneys f a l l ; p o o r l y c o n s t r u c t e d b u i l d i n g s damaged 6.2 to 6.9 IX Ruinous: some houses c o l l a p s e where ground begins to crack; pipes break open X D i s a s t r o u s : ground cracks badly; many b u i l d i n g s destroyed and r a i l w a y l i n e s bent; l a n d s l i d e s on steep s l o p e s 7.0 to 7.3 XI Very D i s a s t r o u s : few b u i l d i n g s remain s t a n d i n g ; b r i d g e s destroyed; a l l s e r v i c e s ( r a i l w a y , p i p e s , c a b l e s ) out of a c t i o n ; g r e a t l a n d s l i d e s and f l o o d s 7.4 to 8.1 XII C a t a s t r o p h i c : t o t a l d e s t r u c t i o n ; o b j e c t s thrown i n t o a i r ; ground r i s e s and f a l l s i n waves 8.1+ The N a t i o n a l B u i l d i n g Code of Canada (N.B.C.) p r o v i d e s minimum standards which, i f l e g a l l y adopted, are supposed to assure an a c c e p t a b l e l e v e l o f p u b l i c s a f e t y by d e s i g n i n g b u i l d i n g s to prevent major f a i l u r e and l o s s o f l i f e . S t r u c t u r e s designed i n accordance wi t h the earthquake-load p r o v i s i o n s o f the N.B.C. should r e s i s t moderate earthquakes without s i g n i f i c a n t damage and major earthquakes without c o l l a p s e , although there may be some s t r u c t u r a l damage. Seismic r i s k i n the b u i l d i n g code f o l l o w s the approach of Milne and Davenport (19691). They used the a v a i l a b l e earthquake h i s t o r y of Canada, i n c l u d i n g the 1,479. earthquakes which o c c u r r e d i n western Canada between 1899 and 1960, to produce a map of p e a k - a c c e l e r a t i o n amplitude. Earthquake r i s k - 153 -i n Canada was p u b l i s h e d as a s e i s m i c zoning map (Whitham e t a l , 1970) and i n c o r p o r a t e d i n t o . t h e 1970 N a t i o n a l B u i l d i n g Code. The r i s k a t any one l o c a t i o n was d e r i v e d from a l l known earthquakes which had i n f l u e n c e d t h a t s i t e , and was c a l c u l a t e d by determining the maximum, p e a k - h o r i z o n t a l g r o u n d - a c c e l e r a t i o n of each s e i s m i c event. Canada was su b d i v i d e d i n t o four zones, wit h those areas where s e i s m i c r i s k i s g r e a t e s t b e i n g p l a c e d i n Zone 3. (Table XVII). The re g i o n s where maximum a c c e l e r a t i o n s may be.expected i n southern Canada are the lower St. Lawrence R i v e r V a l l e y and western B r i t i s h Columbia, i n c l u d i n g Vancouver I s l a n d and the F r a s e r Lowland. TABLE XVII Zone Boundaries f o r the Seismic Zoning Map of Canada. ( A s s o c i a t e Committee on the N a t i o n a l B u i l d i n g Code, 1970). Zone Zone Boundaries (d e f i n e d as a c c e l e r a t i o n amplitude w i t h a r e t u r n - p e r i o d of 100 years (Acc.-lOO) and measured as a percentage of g r a v i t y ) 0 l e s s than 1% 1 1% to 3% 2 3% to 6% 3 g r e a t e r than 6% S e i s m i c i t y of North Vancouver-Seymour Seismic r i s k i n the Seymour area was i n v e s t i g a t e d w i t h the h e l p o f the V i c t o r i a G e o p h y s i c a l Observatory, E a r t h P h y s i c s Branch, Dept. o f Energy, Mines, and Resources. They examined 1,585 earthquakes i n southwestern B.C., recorded between 1899 - 154 -TABLE XVIII North Vancouver-Seymour Earthquake Data, (earthquakes of M e r c a l l i i n t e n s i t y II or more f e l t i n the area centred on 4 9°20'N.; 123°00' W.) Date Location Data Day/Mo./Yr. Lat. (°N.) Long. (°W.) Dist. (km.) Magnitude Intensity Ground Acceleration (%qravity) 10/9/1899 60.0.0 140.00 1603 8.6 III 0 17/3/1904 47.50 124.00 216 6.0 III 0 11/1/1909 49.00 122.70 42 5.6 VI 3 29/9/1911 48.80 122.70 63 4.3 II 0 18/8/1915 48.53 121.43 145 5.5 III 0 22/2/1916 48.80 122.60 66 4.3 II 0 1/7/1917 50. 00 128.00 367 6.4 II 0 23/12/1917 50 .00 128.00 367 6.5 III 0 6/12/1918 49.75 126.50 256 7.0 IV 1 10/10/1919 48.30 124.30 149 5.5 III 0 24/1/1920 48.70 123.00 70 5.0 IV 0 12/2/1923 49.00 122.70 42 4.3 III 0 7/9/1926 49. 00 124.00 81. 5.5 IV 1 1/11/1926 48.75 128.50 405 6.6 II 0 8/5/1927 49.00 124.00 81 •5.5 IV 1 26/5/1929 52.80 129.50 595 7.0 II 0 13/11/1939 47.50 122.40 208 5.7 II 0 29/11/1943 48.40 122.90 104 5.0 III 0 15/2/1946 47.30 122.90 226 5.7 II 0 23/6/1946 49.90 124.90 150 7.3 VI 4 17/7/1946 50. 00 129.00 437 6.5 II 0 13/4/1949 47.20 122.60 239 7.0 V 1 22/8/1949 53.75 133.25 860 8.0 III 0 26/1/1954 49.27 123.03 7 3.0 V 1 26/1/1956 48.33 122.43 ' 119 5.0 II 0 21/12/1956 51.80 129.20 516 6.7 II 0 10/7/1958 58.60 137.10 1376 7.9 II 0 14/7/1964 49.00 122.60 47 4.6 IV 1 29/4/1965 47.40 122.30 221 6.5 IV 1 14/2/1969 48.90 123.10 48 4.3 III 0 24/6/1970 51.74 131.00 624 7.0 II 0 30/11/1975 48.20 123.60 51 4.8 IV -16/5/1976 48. 80 123.30 61 5.3 V -- 155 -and 19 74 i n c l u s i v e , and determined t h a t 31 c o u l d have been f e l t i n the Seymour area. (Table X V I I I ) . In a d d i t i o n , Rogers (19 77) has r e p o r t e d on two r e c e n t earthquakes which a f f e c t e d the Seymour area, one i n November, 1975 and one i n May, 1976. An estimate of earthquake p r o b a b i l i t y f o r the Seymour area (Table XIX) i s based on a s t a t i s t i c a l a n a l y s i s of the data presented i n the preceeding t a b l e ( e x c l u d i n g the two earthquakes r e p o r t e d by Rogers (1977)). The l e n g t h of time of o b s e r v a t i o n i s too s h o r t f o r accurate p r e d i c t i o n of t e c t o n i c a c t i v i t y . However, the data has been processed to estimate the p o s s i b l e l e v e l of earthquake a c t i v i t y i n the near f u t u r e assuming a c o n t i n u a t i o n of the s t a t i s t i c a l p a t t e r n of the p a s t y e a r s . The values given i n Table XIX f o r r e t u r n - p e r i o d s g r e a t e r than 100 years w i l l probably be a l t e r e d by changing p a t t e r n s of s e i s m i c a c t i v i t y . TABLE XIX Earthquake P r e d i c t i o n f o r North Vancouver-Seymour P r o b a b i l i t y o f A c c e l e r a t i o n Amplitude b e i n g exceeded i n one year A c c e l e r a t i o n Amplitude (% g r a v i t y ) I n t e n s i t y ( M o d i f i e d M e r c a l l i Scale) E q u i v i l a n t r e t u r n -p e r i o d (years) 0.333 0 I I 3 0.100 1 IV 10 0.033 2 V 30 0.020 3 VI 50 0 .010 6 VII 100 0.005 13 V I I I 200 A c c - 1 0 0 f o r t h i s area equals 6.2% g r a v i t y . The values of i n t e n s i t y l i s t e d i n t h i s t a b l e are f o r f i r m s o i l . Other types of foundation m a t e r i a l may a l t e r the values by a t l e a s t a u n i t of I. - 156 -On June 23, 1946 an earthquake c e n t r e d west of Comox, Vanocuver I s l a n d (magnitude 7.3) produced a ground a c c e l e r a t i o n o f 4% g r a v i t y and an i n t e n s i t y of VI i n the Seymour area. (Table X V I I I ) . An earthquake of i n t e n s i t y VII or more w i l l cause damage to the ground and b u i l d i n g s . (Table XVI). I t i s probable t h a t such an event w i l l occur i n North Vancouver-Seymour once i n 100 y e a r s . (Table XIX). Seismic M i c r o z o n a t i o n The a c c e l e r a t i o n data used i n the Seismic Zoning Map of Canada were based on average ground c o n d i t i o n s . However, to assess the r e l a t i v e p o t e n t i a l f o r earthquake damage i n a l m i t e d area, i t i s necessary to take i n t o account d i f f e r e n c e s i n l o c a l geology. The b a s i c d i s t i n c t i o n between s e i s m i c zoning maps and microzoning maps i s t h a t the former estimate the r i s k of earthquakes over a wide area, whereas the l a t t e r show l o c a l v a r i a t i o n s i n the i n t e n s i t y w i t h which an earthquake may be f e l t over a s m a l l area. (Wuorinen, 19 76). A n a l y s i s o f data from microseisms (small earthquakes) and to a l e s s e r degree, l a r g e s e i s m i c events, has e s t a b l i s h e d t h a t s u r f a c e motions d u r i n g earthquakes vary w i t h ground c o n d i t i o n s i n a reasonably p r e d i c t a b l e way. Seed and I d r i s s (1969) r e p o r t e d t h a t ground a c c e l e r a t i o n s were a m p l i f i e d by a f a c t o r o f 0.8 to 4.0 depending on the type o f foundation m a t e r i a l . Wuorinen (19 76) c i t e s other s t u d i e s which show comparable v a r i a t i o n s i n i n t e n s i t y w i t h ground types. - 157 -Damage caused by earthquakes can be a f f e c t e d by ground c o n d i t i o n s i n s e v e r a l ways. Primary e f f e c t s are c o n s i d e r e d to be a c t u a l shaking of s t r u c t u r e s by s e i s m i c ground motion, w h i l e secondary e f f e c t s are those i n i t i a t e d by ground v i b r a t i o n , such as s e t t l i n g , l i q u e f a c t i o n , o r s l o p e f a i l u r e . Research on s e i s m i c m icrozonation of V i c t o r i a , B.C. (Wuorinen, 19 76) was based on the June 23, 19 4 6 earthquake. '(Table XVIII) . L o c a l v a r i a t i o n s i n response to t h i s earthquake were determined from i n t e r v i e w s and a comprehensive review of the s t r a t i g r a p h y and bedrock topographyoof V i c t o r i a . As only one earthquake was c o n s i d e r e d i n the study, ground motions caused by.uoither earthquakes may d i f f e r . The lowest i n t e n s i t i e s were recorded where bedrock appears w i t h i n 3 m. of the s u r f a c e : h i g h e s t i n t e n s i t i e s were f e l t i n marshy areas u n d e r l a i n by t h i c k u n i t s of V i c t o r i a c l a y (Capilano Sediment) or along the s h o r e l i n e where t h i c k f i l l has been d e p o s i t e d . A h i g h e r a m p l i f i c a t i o n of s e i s m i c waves i n t h i c k l a y e r s o f s a t u r a t e d , low d e n s i t y sediments probably causes the h i g h e r i n t e n s i t i e s . Intermediate i n t e n s i t i e s were p r e d i c t e d f o r ground u n d e r l a i n by u n c o n s o l i d a t e d sediments of d i f f e r i n g t h i c k n e s s e s . The c i t y was t e n t a t i v e l y d i v i d e d i n t o three zones (Table XX) based on the v a r i a b i l i t y of ground c o n d i t i o n s i n V i c t o r i a and the range of i n t e n s i t i e s •observed i n the 19 46 earthquake. - 158 -TABLE XX M i c r o z o n a t i o n of V i c t o r i a , ( a f t e r Wuorinen, 1976). Zone Re l a t e d Ground Type I n t e n s i t y Increment A bedrock w i t h i n 3 m. of the s u r f a c e -1 B other than A or C 0 C f i l l or former swamp u n d e r l a i n by V i c t o r i a c l a y + 1 Zones A, B, and C. r e p r e s e n t areas o f d i f f e r i n g a n t i c i p a t e d i n t e n s i t i e s f o r an earthquake of any s i z e and bear no r e l a t i o n to s e i s m i c r i s k zones. The former are based on the d i f f e r e n c e s i n a m p l i f i c a t i o n of s e i s m i c v i b r a t i o n by v a r i o u s s u r f i c i a l d e p o s i t s . Secondary e f f e c t s were not c o n s i d e r e d i n d e f i n i n g the zones, however i t would be wrong to d i s r e g a r d the p o s s i b i l i t y of compaction, l a n d s l i d e s , f a u l t i n g , o r l i q u e f a c t i o n d u r i n g a severe s e i s m i c event. The medium i n t e n s i t y r e p o r t e d i n the 19 46 earthquake was V, which corresponds to the mode of i n t e n s i t i e s f o r ground type B. T h i s zone r e p r e s e n t s the average s e i s m i c hazard i n V i c t o r i a and t h e r e f o r e i s given an i n t e n s i t y increment of zero. I n t e n s i t i e s a t l e a s t one u n i t lower than those i n Zone- • B might be expected i n Zone-A and i n t e n s i t i e s of one u n i t or h i g h e r than Zone-B might be f e l t i n Zone-C. Zones A and C are c o n s i d e r e d to be a c c u r a t e whereas a s l i g h t l y lower degree o f accuracy i s claimed f o r Zone-B. The most v a r i a b l e ground, Zone-B, i s c e r t a i n to c o n t a i n s m a l l areas which belong to the other two: boundaries between zones r e p r e s e n t i n t e r m e d i a t e bands where the i n t e n s i t y might be expected to vary w i t h i n the l i m i t s of both contiguous zones. - 159 -Seismic M i c r o z o n a t i o n of North Vancouver-Seymour Any attempt a t microzoning North Vancouver-Seymour i s t e n t a t i v e to say the l e a s t . There i s l i t t l e i n f o r m a t i o n to be had from experience d u r i n g the 19 46 earthquake, which caused the h i g h e s t recorded i n t e n s i t y i n the area, because the r e g i o n was s p a r s e l y i n h a b i t e d . However, because o f the s i m i l a r i t y i n s u r f i c i a l geology between the F r a s e r Lowland and southern Vancouver I s l a n d , the c r i t e r i a e s t a b l i s h e d by Wuorinen (1976) can be used f a i r l y c o n f i d e n t l y to determine s e i s m i c microzones i n the Seymour area. The-area i s d i v i d e d i n t o three i n t e n s i t y zones and areas prone to s l o p e f a i l u r e and l i q u e f a c t i o n are i d e n t i f i e d . (Figure VII-1 and Table XXI). These are determined by a combination of geology, s l o p e and hydrology. (Figures I I I - 2 ; IV-3; V - l and Table X I I I ) . TABLE XXI M i c r o z o n a t i o n of North Vancouver-Seymour. Zone Re l a t e d Ground Type I n t e n s i t y Increment A bedrock a t or near the s u r f a c e - 1 B other than A or C 0 C f i l l o r s a t u r a t e d wetlands u n d e r l a i n by C a p i l a n o cohesive sediments + 1 As w i t h the V i c t o r i a area, lowest s e i s m i c i n t e n s i t i e s would be f e l t where bedrock appears a t or near the s u r f a c e . I t i s not known what e f f e c t the f r a c t u r e zones i n the bedrock canyons of Lynn Creek and Seymour R i v e r would have on earthquake i n t e n s i t y . Zone-C i s d e f i n e d on the assumption AREAS PSONE TO SIOPE FAUOHE ABE* PPONE TO LIQUEFACTION NORTH VANCOUVER —SEYMOUR FIGURE Vl l — 1 SEISMIC MICROZONATION March. 1977 owe. D.E.M. - 161 -t h a t s a t u r a t e d C a p i l a n o c o h e s i v e sediments and f i l l are of low enough d e n s i t y to a m p l i f y s e i s m i c waves and so cause h i g h e r i n t e n s i t i e s . Intermediate i n t e n s i t i e s are p r e d i c t e d f o r ground c l a s s i f i e d as type B, a l l areas u n d e r l a i n by s u r f i c i a l d e p o s i t s other than the s a t u r a t e d g l a c i o m a r i n e and marine sediments. However, because of v a r i o u s ground c o n d i t i o n s w i t h i n Zone-B the i n t e n s i t i e s are l e s s c e r t a i n l y p r e d i c t e d than i n the other zones. Areas prone to slope f a i l u r e as a secondary e f f e c t of a s e i s m i c event are i d e n t i f i e d by evidence of p r e v i o u s movement or by g e o l o g i c a l and h y d r o l o g i c a l c o n d i t i o n s which can o b v i o u s l y l e a d to i n s t a b i l i t y . P o t e n t i a l i n s t a b i l i t y i s a l s o caused by o v e r s t e e p e n i n g of n a t u r a l s l o p e s by removal of sand and g r a v e l . C o h e s i o n l e s s sediments u n d e r l y i n g steep, b a r r e n scarps i n p i t s can f a i l as sand runs or as s a t u r a t e d flows d u r i n g severe ground shaking. Another p o s s i b l e secondary e f f e c t of a severe earthquake i s l i q u e f a c t i o n of the Maplewood' mudflats. In a r e c e n t study, Scotton (19 77) found t h a t c o h e s i o n l e s s sand and n o n - p l a s t i c s i l t which make up the top 2 5 m. o f the F r a s e r R i v e r d e l t a can l i q u e f y d u r i n g a s e i s m i c event. The c h a r a c t e r i s t i c s of the mudflat sediments (mainly f i n e sand and s i l t ) have not been i n v e s t i g a t e d , however, the p o s s i b i l i t y of l i q u e f a c t i o n should not be i g n o r e d . - 162 -Summary of Seismic C o n s t r a i n t s to Development A major earthquake a f f e c t i n g North Vancouver-Seymour, although not i m p o s s i b l e , i s improbable. Seismic data i n d i c a t e s t h a t a moderately s t r o n g earthquake (average i n t e n s i t y VII) i s a d i s t i n c t p o s s i b i l i t y . Earthquakes are more i n t e n s e where s e i s m i c waves are a m p l i f i e d by t h i c k l a y e r s of s a t u r a t e d , low d e n s i t y sediments. Areas u n d e r l a i n by r e c e n t f i l l and by s a t u r a t e d C a p i l a n o c o h e s i v e sediments, Zone-C ground types, have a moderate l i m i t a t i o n to r e s i d e n t i a l use. Bedrock of Zone-A and a l l o t h e r s u r f i c i a l sediments i n Zone-B have no s e i s m i c r e s t r i c t i o n s to development. Areas u n d e r l a i n by sediments which c o u l d l i q u e f y d u r i n g an earthquake should be s e v e r e l y r e s t r i c t e d from urban use. TABLE XXII Degree o f L i m i t a t i o n of Seismic F a c t o r s to Urban R e s i d e n t i a l Land-Use. L i m i t i n g F a c t o r Degree of L i m i t a t i o n S l i g h t Moderate Severe s e i s m i c microzone Zone-A; Zone-B Zone-C p o t e n t i a l to l i q u e f y The medium i n t e n s i t y f e l t on f i r m s o i l i n North Vancouver-Seymour d u r i n g the 1946 earthquake was VI (Table X V I I I ) . T h i s would correspond to i n t e n s i t i e s f e l t on ground type B. I f t h i s area were a f f e c t e d by,another i n t e n s i t y - V I earthquake, the Zone-C areas might be expected to reach i n t e n s i t y V I I , probably c a u s i n g some damage to b u i l d i n g s . Areas of Zone A might be expected only to reach i n t e n s i t y V. A 100-year r e t u r n - p e r i o d - 16 3 -earthquake i s predicted to cause an average i n t e n s i t y of VII i n the Seymour area (Table XIX). I f this happens, Zone-C areas could reach i n t e n s i t y VIII which i s described as destructive; where car drivers are seriously disturbed, masonry i s fissured, chimneys f a l l , and poorly constructed buildings are damaged (Table XVI). Seismic i n t e n s i t i e s necessary to cause liq u e f a c t i o n or i n i t i a t e slope f a i l u r e s are unknown. - 164 -CHAPTER VI I I GEOMORPHIC CONSTRAINTS TO URBAN RESIDENTIAL DEVELOPMENT I n t r o d u c t i o n The o p p o r t u n i t y to apply p r e v e n t i v e p l a n n i n g i s a v a i l a b l e i n the Seymour area of North Vancouver, the l a r g e s t p o r t i o n o f Greater Vancouver p o t e n t i a l l y open t o development. At presen t land-use i n the Seymour area i s g e n e r a l l y r e s t r i c t e d t o s c a t t e r e d r e s i d e n t i a l housing, i s o l a t e d s u b d i v i s o n s , and minor l i g h t i n d u s t r y and commerce. S l i g h t l y l e s s than h a l f o f the area i s f o r e s t e d , undeveloped l a n d which c o u l d be c o n s i d e r e d f o r p o t e n t i a l urban expansion. Most o f t h i s undeveloped area i s zoned f o r r e s i d e n t i a l use, which r e s t r i c t s the land-use p o s s i b i l i t i e s . N a t u r a l areas which have c e r t a i n geomorphic l i m i t a t i o n s to r e s i d e n t i a l development can be i d e n t i f i e d and perserved as open space i n t e g r a t e d w i t h i n the urban r e s i d e n t i a l s e t t i n g . The r o l e of the g e o l o g i s t i s to pro v i d e b a s i c i n f o r m a t i o n f o r p l a n n i n g of l o c a l . l a n d - u s e . T h i s r e q u i r e s i n v e n t o r y data and i n t e r p r e t a t i o n s a t a l e v e l a p p r o p r i a t e f o r use as a p l a n n i n g a i d , but not of s u f f i c i e n t d e t a i l to pr e c l u d e o n - s i t e i n v e s t i g a t i o n . In many cases s i t e s p e c i f i c i n f o r m a t i o n w i l l be necessary to v e r i f y or add to the e x i s t i n g i n v e n t o r y data. Under no circumstances should these data be c o n s i d e r e d a s u b s t i t u t e f o r s i t e - g e o l o g i c a l s t u d i e s where r e q u i r e d by b u i l d i n g codes. I t i s important t h a t the s c i e n t i f i c data and - 165 -i n t e r p r e t a t i o n s be communicated i n e a s i l y comprehensible terms to the n o n - s c i e n t i s t s i n v o l v e d i n the decision-making pr o c e s s . I n t e r p r e t i v e maps which c l e a r l y and simply show the p e r t i n e n t i n f o r m a t i o n are a very important means of communication. Ra t i n g Geomorphic C o n s t r a i n t s i n E s t a b l i s h i n g S u i t a b i l i t y •. f o r R e s i d e n t i a l Land-Use In order to e v a l u a t e the geomorphic c a p a b i l i t y of the l a n d f o r urban r e s i d e n t i a l use, p h y s i c a l c h a r a c t e r i s t i c s must be i n v e n t o r i e d and t h e i r degrees of l i m i t a t i o n determined. The presence o f bedrock a t or near the ground s u r f a c e ; steep slo p e s along the v a l l e y s of Lynn Creek and Seymour R i v e r , Indian Arm, and a t h i g h e r e l e v a t i o n s ; numerous p e r e n n i a l stream channels t r a v e r s i n g the area, w i t h a s s o c i a t e d wetlands, deep r a v i n e s , and f l o o d p l a i n s ; and a v a r i e t y of s u r f i c i a l sediments exposed a t the s u r f a c e , a l l pose l i m i t a t i o n s of v a r y i n g s e v e r i t y to c o n v e n t i o n a l r e s i d e n t i a l development. F i e l d and l a b o r a t o r y data and the maps were used to i n t e r p r e t geomorphic c o n s t r a i n t s to r e s i d e n t i a l land-use. For t h i s study, the term "geomorphic c o n s t r a i n t s to urban development" r e f e r s to the l i m i t a t i o n s of the p h y s i c a l landscape f o r c o n s t r u c t i n g detached s i n g l e - f a m i l y dwellings* i n c o n v e n t i o n a l s u b d i v i s i o n s together w i t h the a s s o c i a t e d road networks and shallow e x c a v a t i o n s f o r u t i l i t y s e r v i c e s . N a t u r a l v a r i a b i l i t y and complexity of the t e r r a i n , i n c l u d i n g g e o l o g i c , p e d o l o g i c , topographic, and h y d r o l o g i c v a r i a t i o n s - 166 -w i t h i n an area, l i m i t the r e l i a b i l i t y o f the i n v e n t o r y data. Consequently i n t e r p r e t a t i o n s based on the i n v e n t o r y data i are only an average f o r each des i g n a t e d area and might not r e f l e c t p o s s i b l e extreme c o n d i t i o n s . The general concept upon which the i n t e r p r e t i v e system i s based i s t h a t a l l areas are c o n s i d e r e d to have low c o n s t r a i n t to r e s i d e n t i a l use u n t i l one or more f a c t o r s d e t r i m e n t a l to t h i s use downgrade the area. The extent to which an area i s downgraded depends upon the number of f a c t o r s which l i m i t i t s use and the degrees of l i m i t a t i o n of these f a c t o r s . To ensure t h a t the area i s w e l l s u i t e d f o r r e s i d e n t i a l use the r a t i n g s of geomorphic c o n s t r a i n t tend to be c o n s e r v a t i v e . I d e n t i f y i n g the l i m i t i n g f a c t o r s a s s i s t s i n p l a n n i n g l a t e r d e t a i l e d s t u d i e s . The c r i t e r i a used to determine whether or not a geomorphic f a c t o r i s c o n s i d e r e d a s l i g h t , moderate, or severe r e s t r i c t i o n to r e s i d e n t i a l land-use (Table XXIII) have been developed from v a r i o u s sources. Many of these c h a r a c t e r i s t i c s i n c l u d i n g depth to bedrock, depth to water t a b l e , t e x t u r e , s t o n i n e s s , drainage, f l o o d frequency, and impervious h o r i z o n have been m o d i f i e d from a number o f other s t u d i e s which examined s p e c i f i c urban-use i n t e r p r e t a t i o n s such as d w e l l i n g foundations, shallow e x c a v a t i o n s , and l o c a l road and s t r e e t subgrade. (United S t a t e s Dept. of A g r i c u l t u r e , 1973; Fenger, 1977; P a t t i s o n , 1977; and Maynard, 1978). The degrees of l i m i t a t i o n of the remaining c h a r a c t e r i s t i c s , s l o p e , - 167 -TABLE XXIII Degree of L i m i t a t i o n of Geomorphic F a c t o r s to Urban R e s i d e n t i a l Land-Use. L i m i t i n g F a c t o r Degree of L i m i t a t i o n S l i g h t Moderate Severe slope 0 - 15% 15 - 21h% g r e a t e r than 27%% depth to bedrock g r e a t e r than 1.5 m. 0.75 - 1.5 m. l e s s than 0.75m. depth to water t a b l e g r e a t e r than 1.5 m. 0.75 - 1.5 m. l e s s than 0.75m. te x t u r e 1. GW,GP,SW,SP,GM, GC,SM,SC. ML, CL. CH , MH , OL, OH , PT. s t o n i n e s s 2. stone f r e e (o) or s l i g h t l y stony (1) moderately stony (2) or very stony (3) exc e e d i n g l y stony (4) or e x c e s s i v e l y stony (5) drainage 3. w e l l d r a i n e d i m p e r f e c t l y d r a i n e d p o o r l y d r a i n e d c o n s o l i d a t i o n h i s t o r y p r e c o n s o l i d a t e d normally c o n s o l i d a t e d -f l o o d frequency none r a r e o c c a s i o n a l or frequent landscape p o s i t i o n - d e p r e s s i o n a l -impervious h o r i z o n - p r e s e n t at l e s s than 1.5 m. depth -s t a b i l i t y o f s u r f i c i a l m a t e r i a l s t a b l e p o t e n t i a l l y unstable evidence of previ o u s i n s t a b i l i t y s e i s m i c microzone Zone-A; Zone-B Zone-C p o t e n t i a l to l i q u e f y drainage channel -s m a l l p e r e n n i a l or i n t e r m i t t e n t stream major perennial stream 1. U n i f i e d S o i l Texture e x p l a i n e d i n Appendix 5. 2. Ston i n e s s C l a s s e s e x p l a i n e d i n Appendix 7. 3. Drainage C l a s s e s e x p l a i n e d i n Appendix 8 . - 16 8 -c o n s o l i d a t i o n h i s t o r y , landscape p o s i t i o n , s t a b i l i t y o f s u r f i c i a l m a t e r i a l , s e i s m i c microzone, and drainage channels, have been adopted on the b a s i s o f f i e l d o b s e r v a t i o n , geomorphic h i s t o r y of the area, and s t u d i e s from s i m i l a r p h y s i c a l environments. A l l of these f a c t o r s have been f u l l y d i s c u s s e d and t a b u l a t e d i n the a p p r o p r i a t e c h a p t e r s . (Tables IX; X I I , XV; and XXII). Many, o f the p h y s i c a l l i m i t a t i o n s r a t e d as severe can be overcome, and i n numerous cases have been, by s p e c i a l designs or c o n s t r u c t i o n . F i n a n c i a l l y t h i s i s not always f e a s i b l e but i t i s p o s s i b l e . The r a t i n g o f geomorphic c o n s t r a i n t s to r e s i d e n t i a l development has been m o d i f i e d from the High-Medium-Low Urban S u i t a b i l i t y System developed by the Resource A n a l y s i s Branch, M i n i s t r y of the Environment, Province of B.C. (Beale and R o l l e r s o n , 19 75; Fenger, 19 77, P a t t i s o n , 19 77; and Maynard, 1978). D e s i g n a t i o n of areas as medium or h i g h c o n s t r a i n t does not mean t h a t there can be no development, but i s simply a comparative measure of the economic and environmental c o s t s of overcoming c e r t a i n geomorphic o b s t a c l e s . I t must be remembered t h a t a c o n s t r a i n t r a t i n g i s an average f o r i t s i n t e r p r e t i v e area. Low C o n s t r a i n t - Areas f e a t u r i n g minor l i m i t a t i o n s to r e s i d e n t i a l development. Degrees of l i m i t a t i o n of the p h y s i c a l c h a r a c t e r i s t i c s are s l i g h t and e a s i l y overcome. C o n s t r u c t i o n , development, s e r v i c i n g , and maintenance c o s t s - 169 -are r e l a t i v e l y low. Development of such areas i s not expected to cause s e r i o u s environmental damage. - L i m i t i n g f a c t o r s e i t h e r a l l have a s l i g h t degree o f l i m i t a t i o n or one moderately l i m i t i n g f a c t o r alone. Medium C o n s t r a i n t - Areas t h a t have p r o p e r t i e s moderately f a v o u r a b l e f o r r e s i d e n t i a l use. These moderate degrees of l i m i t a t i o n need to be r e c o g n i z e d but can be overcome or m o d i f i e d by s p e c i a l planning-;' design, and maintenance. - L i m i t i n g f a c t o r s have two or three moderate l i m i t a t i o n s alone, one severe l i m i t a t i o n alone, or one moderate and one severe l i m i t a t i o n . High C o n s t r a i n t - Areas t h a t have enough l i m i t i n g . c h a r a c t e r i s t i c s to make use q u e s t i o n a b l e . The degrees of l i m i t a t i o n may be overcome through major s o i l r e c l a m a t i o n , s p e c i a l d e sign, and i n t e n s i v e maintenance, however, economic f e a s i b i l i t y may then become l i m i t i n g . - L i m i t i n g f a c t o r s have four or more moderate l i m i t a t i o n s alone, one severe and two or more moderate l i m i t a t i o n s , or two or more s e v e r e l y l i m i t i n g f a c t o r s alone. - 170 -Summary of Geomorphic C o n s t r a i n t s to Development Geomorphic c o n s t r a i n t s to urban r e s i d e n t i a l development i n North Vancouver-Seymour are the r e s u l t o f an i n t e r a c t i o n of g e o l o g i c , topographic, and h y d r o l o g i c c h a r a c t e r i s t i c s and processes. A number of geomorphic f a c t o r s which pose c e r t a i n l i m i t a t i o n s to r e s i d e n t i a l use of the land are d e s c r i b e d and t h e i r degrees o f l i m i t a t i o n d e f i n e d . (Table X X I I I ) . Two maps (Figures V III-1 and 2.) summarize the c o n s t r a i n t s o f geomorphology to r e s i d e n t i a l use. These were compiled i r r e s p e c t i v e o f p r e s e n t land-use, t h a t i s , a l l lan d has been given c o n s t r a i n t r a t i n g s even though c e r t a i n areas are a l r e a d y s u b d i v i d e d or s e t a s i d e as parks. Areas o f s i m i l a r p h y s i c a l c h a r a c t e r i s t i c s can be d e l i n e a t e d from the i n v e n t o r y data. (Figures I I I - 2 ; IV-3; V - l ; VII-1 and Table X I I I ) . F i g u r e VIII-1 i s a d e t a i l e d map which r a t e s geomorphic c o n s t r a i n t s o f each area and i d e n t i f i e s the p h y s i c a l f a c t o r s and t h e i r degrees of l i m i t a t i o n to r e s i d e n t i a l use. T h i s i s v a l u a b l e i n a i d i n g the planner to determine the type and s e v e r i t y ' of l i m i t a t i o n s which can be expected i f development proceeds, and what remed i a l measures may be n e c e s s a r y c t o modify or overcome these geomorphic o b s t a c l e s . Areas of low, medium, and h i g h c o n s t r a i n t , i r r e s p e c t i v e of which geomorphic c h a r a c t e r i s t i c s l i m i t t h e i r use, are shown on F i g u r e VIII-2 (summarized from F i g u r e VIII-1). - 172 -Areas of low geomorphic c o n s t r a i n t are w e l l s u i t e d f o r r e s i d e n t i a l use. The p h y s i c a l c h a r a c t e r i s t i c s are only s l i g h t l y l i m i t i n g and can be e a s i l y overcome d u r i n g development at minimum economic and environmental expense. Present s u b d i v i s i o n s i n the Seymour area, f o r the most p a r t , occupy lands o f low c o n s t r a i n t . (Figures 1-1 and V I I I - 2 ) . The l a r g e s t t r a c t s o f land which have low c o n s t r a i n t to development are g e n t l y or moderately s l o p i n g areas u n d e r l a i n by C a p i l a n o c o h e s i o n l e s s sediments or g e n t l e , t i l l - c o v e r e d s l o p e s . There are no p h y s i c a l r e s t r i c t i o n s on l e v e l or near-l e v e l outwash t e r r a c e s , and even where sl o p e i s a moderately l i m i t i n g f a c t o r , these areas are s t i l l w e l l s u i t e d f o r r e s i d e n t i a l use. The o n l y moderate l i m i t a t i o n to development on g e n t l e s l o p e s u n d e r l a i n by Vashon t i l l i s i t s i m p e r m e a b i l i t y . I s o l a t e d d e p r e s s i o n s or r i d g e c r e s t s where depth to bedrock i s the o n l y moderately l i m i t i n g f a c t o r a l s o have low c o n s t r a i n t . Areas of medium geomorphic c o n s t r a i n t h a v e • c h a r a c t e r i s t i c s moderately f a v o u r a b l e f o r r e s i d e n t i a l use. These moderate r e s t r i c t i o n s need to be r e c o g n i z e d but can be overcome or m o d i f i e d by s p e c i a l p l a n n i n g , d e s i g n , and maintenance. Areas, i n which one f a c t o r i s s e v e r e l y l i m i t i n g w i l l be more d i f f i c u l t to develop without some environmental d i s r u p t i o n . The urban d e s i g n f o r these areas must allow f o r t h a t l i m i t a t i o n i n i t s p l a n . The main areas w i t h medium c o n s t r a i n t are those where - 173 -depth to bedrock and slope are l i m i t i n g and where s t e e p l y and moderately s l o p i n g l a n d i s u n d e r l a i n by impermeable Vashon t i l l . In p l a c e s , C a p i l a n o c o h e s i o n l e s s sediments have enough l i m i t a t i o n s to j u s t i f y a medium c o n s t r a i n t r a t i n g . On steep or moderate sl o p e s s u r f a c e i n s t a b i l i t y or e r o s i o n may r e s t r i c t development. On l e v e l areas the presence of an impervious l a y e r a t depth can cause a h i g h water t a b l e and i m p e r f e c t drainage to be moderately l i m i t i n g . Holocene a l l u v i a l d e p o s i t s , i n c l u d i n g much of the f l o o d p l a i n d e l t a of Lynn Creek and Seymour R i v e r , which are u n l i k e l y to f l o o d are given r a t i n g s of medium c o n s t r a i n t because of moderately l i m i t i n g f a c t o r s of water t a b l e , s t o n i n e s s , and f l o o d frequency. Thick f i l l used to r e c l a i m l a n d along the w a t e r f r o n t has low p e r m e a b i l i t y , i m p e r f e c t drainage, and might be a f f e c t e d by h i g h e r earthquake i n t e n s i t i e s . These c h a r a c t e r i s t i c s , although moderately r e s t r i c t i v e to r e s i d e n t i a l use, are not n e c e s s a r i l y l i m i t i n g to i n d u s t r i a l development, which i s the obvious use of t h i s land. Areas o f high geomorphic c o n s t r a i n t have enough l i m i t i n g c h a r a c t e r i s t i c s to make land use f o r r e s i d e n t i a l development q u e s t i o n a b l e . The degrees of l i m i t a t i o n may be reduced or overcome through s p e c i a l d e s i g n , major r e c l a m a t i o n , and i n t e n s i v e maintenance, however, economic f e a s i b i l i t y may then become l i m i t i n g . The u n s u i t a b l e t e r r a i n i s v a r i e d because of a combination of many geomorphic f a c t o r s . A r e a s c o f high c o n s t r a i n t i n c l u d e steep bedrock s l o p e s , steep erodable s l o p e s along the. v a l l e y s i d e s o f Lynn Creek and Seymour R i v e r , f l o o d -s u s c e p t i b l e areas, r a v i n e drainage channels, and g e n t l y s l o p i n g land u n d e r l a i n by Ca p i l a n o g l a c i o m a r i n e and marine sediments. P o s t - g l a c i a l f l u v i a l e r o s i o n o f Lynn Creek and Seymour Ri v e r has c r e a t e d deep, narrow v a l l e y s w i t h oversteepened, unstable s l o p e s . p f s u r f i c i a l sediments and bedrock canyons which are p o o r l y s u i t e d f o r r e s i d e n t i a l use. In p l a c e s , l a t e r a l e r o s i o n has formed widened f l o o d p l a i n s which are s e v e r e l y l i m i t e d by h i g h water t a b l e s , s t o n i n e s s , f l o o d frequency, and drainage channels. P a r t s o f the f l o o d p l a i n d e l t a , immediately a d j a c e n t to the main r i v e r channels, are given h i g h c o n s t r a i n t because f l o o d i n g i s p o s s i b l e . Wetlands on the d e l t a are r e s t r i c t e d by a h i g h water t a b l e , i m p e r f e c t drainage, s t o n i n e s s , and f l o o d frequency. P e r e n n i a l streams i n deep, s t e e p - s i d e d r a v i n e s w i l l be s u b j e c t to c o n s i d e r a b l e seepage and r u n o f f c a u s i n g i n s t a b i l i t y along the g u l l y s i d e s which, even without h y d r o l o g i c a l c o n s i d e r a t i o n s , warrant r e s t r i c t i n g developement of these channels. In many p l a c e s , a s s o c i a t e d w i t h the stream channels, are wetlands and f l o o d - s u s c e p t i b l e areas which are a l s o u n s u i t a b l e f o r r e s i d e n t i a l use. Large t r a c t s o f g e n t l y s l o p i n g l a n d u n d e r l a i n by cohe s i v e , Capilano g l a c i o m a r i n e and marine sediments are very p o o r l y - 175 -s u i t e d f o r r e s i d e n t i a l development. Texture, c o m p r e s s i b i l i t y , and c o n s o l i d a t i o n h i s t o r y of these m a t e r i a l s can l e a d to e x c e s s i v e s e t t l i n g under foundation l o a d s . Impermeability and ge n t l e s l o p e can cause a moderately high water t a b l e and im p e r f e c t drainage. Where the h y d r o l o g i c regime, e i t h e r by s u r f a c e drainage-or by downslope seepage, causes poor drainage and s a t u r a t e d ground, other f a c t o r s c o n t r i b u t e to r e s t r i c t i n g these areas from r e s i d e n t i a l use. Water t a b l e and drainage become s e v e r e l y l i m i t i n g and the l i k e l i h o o d of i n c r e a s e d s e i s m i c i n t e n s i t y i s a moderate l i m i t a t i o n . Maplewood t i d a l mudflats have many severe l i m i t a t i o n s to development. The l o o s e , s a t u r a t e d , normally c o n s o l i d a t e d , s i l t s and f i n e sands are h i g h l y compressible and have the p o t e n t i a l to l i q u e f y d u r i n g earthquake shock. In a d d i t i o n , the e s t u a r y i s probably b i o l o g i c a l l y important. In areas o f low or medium c o n s t r a i n t the n a t u r a l v a r i a b i l i t y o f the t e r r a i n can c r e a t e geomorphic c o n d i t i o n s which are u n s u i t a b l e f o r r e s i d e n t i a l development. A h i g h water t a b l e and poor drainage caused by an impervious h o r i z o n very near a d e p r e s s i o n a l or g e n t l y s l o p i n g ground s u r f a c e are the main r e s t r i c t i n g f a c t o r s . Man has c r e a t e d areas u n s u i t a b l e f o r development by a l t e r i n g the n a t u r a l landscape. Steep, b a r r e n s l o p e s i n abandoned sand and g r a v e l p i t s are o f t e n unstable and s u s c e p t i b l e to e r o s i o n . D e p o s i t s of f i l l , which are not s p e c i f i c i a l l y designed f o r development, are h i g h l y u n s u i t a b l e - 176 -f o r r e s i d e n t i a l use- Because of t h e i r h i g h l y v a r i a b l e t e x t u r e , c o m p r e s s i b i l i t y , and c o n s o l i d a t i o n h i s t o r y , these areas, such as the s a n i t a r y l a n d f i l l , are s u b j e c t ' t o i n c r e a s e d s e i s m i c i n t e n s i t y , poor drainage, and e x c e s s i v e d i f f e r e n t i a l s e t t l i n g . - 177 -BIBLIOGRAPHY A l f o r s , J.T.; Burnett,• J.L. ; and Gay, T.E.,Jr.; 1973. Urban Geology Master Plan f o r C a l i f o r n i a . C a l i f o r n i a D i v i s i o n of Mines and Geology. B u l l e t i n 198. 112 p. A l l a n , J.F.; 1957. L a n d s l i d e s , Washouts, and Mudflows i n the Lower F r a s e r V a l l e y , B.C. Unpublished B.A.Sc. T h e s i s , Dept. o f G e o l o g i c a l S c i e n c e s , U.B.C. 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F o s t e r ( E d . ) , V i c t o r i a : P h y s i c a l Environment and Development•. Western Geographical S e r i e s . Volume 12. Dept. of Geography, U n i v e r s i t y o f V i c t o r i a . V i c t o r i a , B.C. Dr. P. Byrne, Dept. o f C i v i l E n g i n e e r i n g , U.B.C; P e r s o n a l Communication, 1975. Dr. J . Rau, Dept. of G e o l o g i c a l S c i e n c e s , U.B.C; P e r s o n a l Communication, 1976. - 191 -APPENDIX 1 DESCRIPTION OF STRATIGRAPHIC SECTIONS V i s u a l d e s c r i p t i o n of the m a t e r i a l i n the f i e l d f o l l o w e d the t e x t u r a l c l a s s i f i c a t i o n scheme of Wentworth (1922) and mo d i f i e d by E.L.U.C. S e c r e t a r i a t (1976). R e l a t i o n s h i p of S i z e and Roundness i n the T e x t u r a l C l a s s i f i c a t i o n o f C l a s t i c Sediments. ^ ^ ^ S I Z E 1 1 1 1 1 SPE ROUNDNESS mm 256 64 2 .062 .0039 CIF ROUNDED 1 1 1 BOULDERY, COBBLY j PEBBLY, M o ROUND, or ANGULAR 1 1 SANDY 1 SI 1 LTY 1 CLAYEY 1 o ROUNDED GRAVELLY I o - 1 FINES O z ANGULAR BLOCKY I RUBBLY 1 1 1 S e c t i o n S i t e Sample Number Average Depth From Ground Surface (m.) D e s c r i p t i o n o f M a t e r i a l s D-1 0.0 - 2.0 2.0 - 5.0 5.0+ interbedded sandy g r a v e l , g r a v e l l y sand, and cobbly g r a v e l w i t h a cobbly bouldery g r a v e l cap. (Capilano) s u b h o r i z o n t a l l y bedded, medium-gra i n e d sand c o n t a i n i n g sandy g r a v e l lenses and i n t e r b e d s (Quadra Sand) r h y t h m i c a l l y laminated s i l t c o n t a i n i n g few s c a t t e r e d subrounded stones. (Semiahmoo) D-2 c o n t 1 d 0.0 - 1.5 pebbly s i l t y sand gra d i n g down-ward i n t o cobbly sandy g r a v e l . (Capilano) - 1 9 2 -1.5 - 3.0 3.0 + dense, grey lodgement t i l l c o n t a i n i n g about 25% cobble s i z e subrounded c l a s t s . (Vashon) sandy g r a v e l and coarse sand. (Vashon) D-3 0.0 - 1.0 1.0 - 8.0 8.0+ f i n e l y bedded, s t o n e l e s s c l a y e y s i l t . (Capilano) dense, grey lodgement t i l l c o n t a i n i n g about 15% cobble s i z e subrounded-subangular c l a s t s . (Vashon) sandy t i l l - l i k e m a t e r i a l c o n t a i n i n g l a r g e subrounded boulders and g r a v e l l e n s e s . (Vashon) D-4 G-48 15m,thickness 2m t h i c k n e s s r h y t h m i c a l l y laminated s i l t c o n t a i n i n g few s c a t t e r e d subrounded stones.(Semiahmoo) compact, low p e r m e a b i l i t y , s a n d y g r a v e l and g r a v e l l y sand. (Semiahmoo) D-5 G-41 G-42 G-43 0.0 - 1.5 1.5 - 5.0 5.0 - 9.0 9.0 - 13.0 13.0 - 14.0 14.0 - 18.0 18.0 - 23.0 23.0 + loose g r a v e l , c obbles, and b o u l d e r s . (Capilano) medium-fine sand c o n t a i n i n g sandy s i l t i n t e r b e d s , g r a v e l l e nses and i n t e r b e d s , and s c a t t e r e d stones; g e n e r a l l y s u b h o r i z o n t a l l y bedded and cross-bedded. (Quadra Sand) covered. massive brown s i l t and s i l t y f i n e sand c o n t a i n i n g few rounded pebbles. (Cowichan Head?) massive brown s i l t or c l a y e y s i l t w i t h dropstones.(Semiahmoo) r h y t h m i c a l l y laminated dense grey silt.(Semiahmoo) d r i f t comprised of t i l l w i t h f a i r l y dense s i l t y sand matrix c o n t a i n i n g about 20% cobble s i z e c l a s t s and f i n e l y laminated grey s i l t y c l a y and g r a v e l l e n s e s . (Semiahmoo) d i o r i t i c bedrock. D-6 cont'd 0.0 - 1.5 loose g r a v e l , c obbles, and b o u l d e r s . (Holocene) - 193 -G-65 GSC-93 1. 5 — 2. 0 or g a n i c s i l t , peat, wood (dated at 36,200 ± 300 years B.P.). (Cowichan Head) G-G-28 27 2. 0 3 . 5 s u b s t r a t i f i e d g r a v e l and g r a v e l l y t i l l c o n t a i n i n g up t o 40% subrounded cobble s i z e c l a s t s and boulders w i t h i n a coarse sandy matrix; numerous d i s c o n t i n u o u s l a y e r s and inte'rbeds o f s i l t and f i n e sand are i n c l u d e d w i t h i n the d r i f t . (Semiahmoo) D-7 0. 0 7. 0 s u b s t r a t i f i e d , p o o r l y s o r t e d mixture of c o a r s e - g r a i n e d sand, rounded pebbles, c o b b l e s , and boulders; i n p l a c e s interbedded, w e l l - s o r t e d l a y e r s of coarse sand and sandy g r a v e l . (Capilano) 7 . 0 — 10 . 0 stony c l a y e y s i l t ; bedded i n p l a c e s . (Capilano) 10. 0 16 .0 dense, grey lodgement t i l l c o n t a i n i n g about 15% cobble s i z e subrounded-subangular c l a s t s ; pockets of w e l l - s o r t e d g r a v e l occur w i t h i n the t i l l . ( V a s h o n ) 16. 0 - 30 -.0 covered. 30. 0 33 .0 w e l l - s o r t e d , medium-fine sand c o n t a i n i n g s i l t and g r a v e l lenses and i n t e r b e d s ; s u b s t r a t i f i e d and cross-bedded. (Quadra Sand) D-8 0. 0 — 2. 5 p o o r l y s o r t e d , s u b s t r a t i f i e d , c o a r s e - g r a i n e d sand, g r a v e l , cobbles, and! boulders . (Capilano) 2. 5 - 9 . 5 Ca p i l a n o marine and g l a c i o m a r i n e sediments: G- 32 2. 5 — 3 . 5 massive c l a y e y s i l t c o n t a i n i n g few pebbles; G- 33 3. 5 — 4. 5 w e l l - s o r t e d , f i n e s i l t y sand, s u b h o r i z o n t a l l y l a y e r e d ; G- 31 4. 5 - 5. 0 massive s i l t y c l a y ; G- 30 5. 0 - 5. 5 f i n e l y laminated c l a y e y s i l t ; 5. 5 — 6. 0 p o o r l y s o r t e d g r a v e l , c o b b l e s , and coarse sand; 6 . 0 - 8. 0 covered; cont'd G- 29 8. 0 — 9 . 5 f i n e l y laminated stony c l a y e y s i l t . - 194 -9. 5 — 12 .0 covered. 12. 0 15 . 0 dense, grey lodgement t i l l c o n t a i n i n g about 10%-15% subrounded-subangular cobble s i z e c lasts.(Vashon) 15. 0 - 22 .0 covered. 22. 0 22 22 5 + . 5 w e l l - s o r t e d , medium-grained sand wi t h s u b h o r i z o n t a l l a y e r i n g . (Quadra Sand) covered. D-9 0. 0 — 1. 5 p o o r l y sorted,non-bedded,rusty cobble g r a v e l w i t h some boulders i n a coarse sand matrix. (Capilano) 1. 5 3. 5 s u b s t r a t i f i e d and i n t e r l a y e r e d coarse sand, pebbly sand, pebbly g r a v e l , and cobbles. (Capilano) 3. 5 — 12 . 5 Cap i l a n o marine and g l a c i o m a r i n e sediments: G-40 3. 5 — 5. 0 w e l l - s o r t e d , f i n e s i l t y sand, f i n e l y l a y e r e d ; G-39 5. 0 - 7. 0 massive brown c l a y e y s i l t ; G-38 7. 0 — 8. 5 lens of moderately p l a s t i c , massive blue c l a y ; G-37 8. 5 - 10 ..'5 massive brown c l a y e y s i l t ; G-3 6 10. 5 — 11 .0 f i n e l y laminated blue-grey c l a y e y s i l t ; G-35 11. 0 — 12 .5 s u b s t r a t i f i e d s i l t y sand w i t h pebbly sand l e n s e s . D-10 0. 0 - 5. 5 Ca p i l a n o outwash sediments: 0. 0 1. 5 p o o r l y s o r t e d , s u b s t r a t i f i e d g r a v e l w i t h subrounded cobbles i n a coarse sand matrix; G-11, 12,13, 14,15, 17,18. 1. 5 4. 5 massive, compact, grey, medium-gra i n e d sand c o n t a i n i n g o c c a s i o n a l pebbles and pebble l e n s e s ; u n i t grades l a t e r a l l y i n t o i n t e r l a y e r e d f i n e sand, coarse sand, and g r a v e l l y sand with pebble l e n s e s ; f o r e s e t beds dip south-west a t about 10°; 4. 5 — 5. 0 well-cemented, f i n e , r u s t y sand forming an impervious h o r i z o n ; 5. 0 - 5. 5 coarse pebbly sand. cont'd G-16 5. 5 — 7. 0 i n t e r l a y e r e d sandy s i l t , s i l t , and stony s i l t y c l a y c o n t a i n i n g - 195 -dropstones. (Capilano) G- 19 7.. 0 11 .0 dense, grey lodgement t i l l c o n t a i n i n g about 15% subrounded cobble s i z e c l a s t s ; 2m diameter boulder i n the t i l l . ( V a s h o n ) D-11 0. 0 - 0. 5 c o a r s e - t e x t u r e d , w e l l - d r a i n e d red-brown s o i l . G- 54 0. 5 — 1. 0 massive f i n e s i l t y sand. (Capilano) G- 52 1. 0 2. 0 stony c l a y e y s i l t w ith a b l o c k y s t r u c t u r e ; numerous subrounded cobbles a t base of u n i t . (Capilano) G- 53 2. 0 3. 0 p o o r l y s o r t e d , u n s t r a t i f i e d , r u s t y , coarse sand and sandy g r a v e l w i t h few b o u l d e r s . (Vashon) G- 51 3. 0 + dense,grey lodgement t i l l c o n t a i n i n g about 20% subrounded cobble s i z e c l a s t s ; exposure of t i l l i s t h i n but approximately 10m downslope more t i l l i s exposed. (Vashon) D-12 G- 61 0. 0 - 3. 0 stony s i l t y c l a y c o n t a i n i n g dropstones. (Capilano) 3. 0 7. 0 dense, grey lodgement t i l l c o n t a i n i n g about 15% subrounded cobble s i z e c l a s t s . (Vashon) G- 60 7. 0 11 .0 s u b s t r a t i f i e d t o n O n - s t r a t i f i e d dense,cobble g r a v e l c o n t a i n i n g few boulders and l e n s e s of f i n e sand and laminated s i l t . ( V a s h o n ) 11. 0 - 35 .0 Quadra Sand?: G- 59 11. 0 15 .0 w e l l - s o r t e d , s u b h o r i z o n t a l l y bedded sand and s i l t y sand w i t h s i l t l a y e r s ; 15. 0 - 30 . 0 covered; G- 57, 58. 30. 0 32 .0 coarse g r a v e l l y sand o v e r l i e s s u b h o r i z o n t a l l y bedded, w e l l -s o r t e d , fine-medium sand; 32. 0 35 .0 s u b s t r a t i f i e d , coarse sandy g r a v e l c o n t a i n i n g g r e a t e r than 50% rounded pebbles. cont'd G- 56 35. 0 40 .0 very dense, massive, blue-grey c l a y c o n t a i n i n g numerous s m a l l stones and g r i t fragments and o c c a s i o n a l cobble s i z e c l a s t s . (Coquitlam D r i f t ? ) - 196 -G-55 40.0 - 65.0 65.0 - 67.0 67.0 - 70.0 70.0 + covered. dense cobble g r a v e l w i t h sand l e n s e s . (Semiahmoo?) f a i r l y dense, grey, s i l t y sandy t i l l c o n t a i n i n g about 20% subrounded-subangular cobble s i z e c l a s t s ; f i n e l y laminated s i l t y c l a y l e n ses w i t h i n t i l l . (Semiahmoo?) d i o r i t i c bedrock. D-13 G-2 3, 24. 0.0 - 2.0 2.0 - 8.0 8.0+ p o o r l y s o r t e d , n o n - s t r a t i f i e d , cobble boulder g r a v e l . (Capilano) i n t e r b e d d e d , s u b s t r a t i f i e d , w e l l -s o r t e d , pebble g r a v e l and coarse sand. (Capilano) varved c l a y e y s i l t ; a l t e r n a t i n g l a y e r s of s l i g h t l y p l a s t i c , g r e y c l a y e y s i l t and brown s i l t ; l a y e r s range i n t h i c k n e s s from 3-30 mm. (Capilano) D-14 The ex 50 m. s e c t i o G-6 4 G-25 posure i s low oelow the upla n D-13. 5m+ t h i c k n e s s 5m t h i c k n e s s 2m ..thickness 3m t h i c k n e s s 9m t h i c k n e s s lm 5m 3m 2m t h i c k n e s s down on the v a l l e y s l o p e , about nd s u r f a c e and about 30 m. below varved c l a y e y s i l t . (Capilano) covered. w e l l - s o r t e d , s u b s t r a t i f i e d , coarse pebbly sand. (Vashon) dense, grey lodgement t i l l c o n t a i n i n g about 5% subrounded cobble s i z e c l a s t s . (Vashon) Coquitlam D r i f t ? : massive,blue-grey c l a y c o n t a i n i n g few pebbles; covered; massive, b l u e - g r e y , s l i g h t l y p l a s t i c c l a y c o n t a i n i n g dropstones i n c l u d i n g a 1.5m diameter b o u l d e r . covered down to the pr e s e n t f l o o d p l a i n of Lynn Creek. D-15 cont'd G-50 0.0 - 2.0 2.0 - 10.0 p o o r l y s o r t e d , n o n - s t r a t i f i e d , bouldery cobble g r a v e l w i t h i n t e r b e d s of coarse pebbly sand. (Capilano) medium-fine sand c o n t a i n i n g sandy s i l t i n t e r b e d s , g r a v e l - 197 -i 10.0 - 12.0 12.0+ len s e s and i n t e r b e d s , and s c a t t e r e d pebbles; g e n e r a l l y s u b h o r i z o n t a l l y bedded and cross-bedded. (Quadra Sand) r h y t h m i c a l l y laminated s i l t c o n t a i n i n g s c a t t e r e d subrounded dropstones. (Semiahmoo) pebbly coarse sand. (Semiahmoo) D-16 G-62 2m t h i c k n e s s f o r e s e t beds of sandy g r a v e l and g r a v e l l y sand; beds d i p 10° south. (Vashon) D-17 0.0 - 1.0 .1.0 - 4.0 4.0 - 6.0 6.0 - 6.5 6.5 - 7.0 7.0 - 9.0 l o o s e , cobble boulder g r a v e l . (Capilano) s u b s t r a t i f i e d , cross-bedded, p o o r l y s o r t e d , coarse sand, pebbly sand, sandy g r a v e l , and •pebbly cobble g r a v e l . (Capilano) dense, grey lodgement t i l l c o n t a i n i n g about 15% subrounded cobble s i z e c l a s t s . (Vashon) s u b s t r a t i f i e d , g r a v e l l y sand g r a d i n g downward i n t o w e l l -s o r t e d , medium sand.(Vashon) laminated s i l t y c l a y . (Vashon) medium sand, s u b h o r i z o n t a l l y l a y e r e d and cross-bedded, c o n t a i n i n g s i l t and g r a v e l i n t e r b e d s and lenses.(Quadra Sand) D-18 0.0 - 3.5+ 0.0 - 1.5 1.5 - 2.0 2.0 - 3.5 3.5+ Ca p i l a n o outwash: l o o s e , r u s t y , cobble boulder g r a v e l w i t h coarse sand matrix; sandy g r a v e l w i t h few cobbles and s u b h o r i z o n t a l beds; s u b h o r i z o n t a l i n t e r b e d s of coarse sand, f i n e sand, and pebbly g r a v e l c o n t a i n i n g few bo u l d e r s ; compact,cobble b o u l d e r g r a v e l . D-19 c o n t 1 d 0.0 - 1.5 1.5 - 4.5 coarse sand and sandy g r a v e l . (Capilano) i n t e r l a y e r e d s i l t , c l a y e y s i l t f i n e sand, and g r a v e l l y sand l e n s e s ; massive, n o n - s t r a t i f i e d , few dropstones. (Capilano) - 198 -4,5 - 11.0 dense, grey lodgement t i l l c o n t a i n i n g about 20% subrounded cobble s i z e c l a s t s .and fragments of s i l t y c l a y . (Vashon) D-20 0.0 - 1.0 1.0 - 2.0 2.0 - 5.0 5.0 - 9.0 9.0 - 10.0 10.0 + c o a r s e - t e x t u r e d , w e l l - d r a i n e d , red-brown s o i l . dense, grey lodgement t i l l c o n t a i n i n g about 15% subrounded -subangular cobble s i z e c l a s t s . (Vashon) i n t e r l a y e r e d medium sand and pebble l e n s e s ; sand beds d i p 25° e a s t e r l y . (Vashon) covered. w e l l - s o r t e d , medium sand.(Quadra Sand) f i n e l y i n t e r l a y e r e d s i l t and f i n e sand. (Cowichan Head?) D-21 0.0 - 12.0 0.0 - 27.5 2.5 - 9.0 9.0 - 12.0 Ca p i l a n o outwash: p o o r l y s o r t e d , n o n s t r a t i f i e d , sandy g r a v e l and cobble g r a v e l ; s u b s t r a t i f i e d pebbly g r a v e l and g r a v e l l y sand; medium sand with pebbles and pebble l e n s e s , beds d i p 30° e a s t e r l y . D-22 0.0 - 8.0 0.0 - 1.5 1.5 - 3.5 3.5 - 8.0 Vashon D r i f t : dense, grey lodgement t i l l c o n t a i n i n g about 20% subrounded -subangular cobble s i z e c l a s t s ; f a i r l y w e l l - s o r t e d g r a v e l l y sand c o n t a i n i n g o c c a s i o n a l b o u l d e r s and le n s e s and i n d i s t i n c t l a y e r s o f f i n e sand and laminated s i l t ; p o o r l y s o r t e d , m a s s i v e , t i l l - l i k e m a t e r i a l , subrounded-rounded b o u l d e r s , c o b b l e s , and. pebbles make up 40% to 50% of the mass w i t h i n a dense, b l u e - g r e y , c l a y e y s i l t matrix. D-23 G-4 0.0 - 2.0 2.0+ stony s i l t y c l a y and s t o n e l e s s c l a y e y s i l t are exposed over a le n g t h o f 300 m. (Capilano) dense, grey lodgement t i l l . (Vashon) APPENDIX 2 SUMMARY OF THE GEOLOGICAL SURVEY OF CANADA URBAN GEOLOGY FILE BOREHOLE AND EXCAVATION RECORDS Information was submitted to the G.S.C. by the d r i l l i n g or e x c a v a t i n g c o n t r a c t o r . Borehole or Excav a t i o n Number E l e v a t i o n of Borehole C o l l a r or Excav a t i o n Borehole or E x c a v a t i o n Log Records Depth (m.) D e s c r i p t i o n of M a t e r i a l s GSC-1 512 f t . (156 m.) 0.0-2.4 2.4-6.4 6.4-22.0 22.0-27.4 27.4-27.7 27.7-34.1 b o u l d e r s , sand, g r a v e l , blue c l a y , coarse sand, g r a v e l b o u l d e r s . hardpan,sand,gravel, b o u l d e r s . decomposed rock, g r a n i t i c bedrock. GSC-31 -60 f t . (-18.3m.) 0.0-68.3 68.3- 70.4 70.4- 111.6 g r a v e l , sand, boulders minor c l a y ; c l a m s h e l l s a t 2 5.0m and 56.1m depth; wood a t 47.6m and 50.9m depth. conglomerate bedrock, interbedded s h a l e and sandstone bedrock. GSC-33 0 ft:, (ni.). 0.0-96.0 96.0 120.7 b o u l d e r s , g r a v e l , sand, sandstone, conglomerate, and s h a l e bedrock. GSC-34 -40 f t . (-12.2m) 0.0-55.5 55.5-69.8 69.8-84.1 84.1-95.1 gra v e l , b o u l d e r s , s a n d ; c l a m s h e l l s a t 43.0m and 5 4.3m depth; wood a t 43.0m and 45.4m depth, f i n e sand,clay, packed g r a v e l . f i n e g r a v e l , sand, s h a l e , conglomerate bedrock. GSC-35 c o n t 1 d -40 f t . (-12.2m) • 0.0-50.0 sand, g r a v e l , b o u l d e r s ; c l a m s h e l l s a t 28.3m,46.6m, 4 8.5m, and 49.4m depth; wood a t 2 8.3m and 46.6m - 200 -50.0-71.3 71.3-76.2 76.2-93.9 93.9-112.5 depth. f i n e g r a v e l (hard packed), sand, c l a y , sand, g r a v e l , conglomerate bedrock, sandstone,shale bedrock. GSC-36 -60 f t . (-18.3 m.) 0.0-99 .1 99.1-101.5 g r a v e l , b o u l d e r s , sand, c l a y ; c l a m s h e l l s a t 27.4m,46.0m 46.6m, and 60.5m depth; wood a t 24.7m, 26.2m, and 46.6m depth. conglomerate bedrock. GSC-39 300 f t . (91.5 m.) 0.0-5.5 : 5.5-18.3 bou l d e r s , g r a n i t i c bedrock. GSC-214 592 f t . (180.5 m.) 0.0-8.2 8.2-10.7 10.7-11.9 11.9-17.1 17.1-18.6 18.6-61.0 61.0-64.0 64.0-68.3 b o u l d e r s , coarse g r a v e l , sand. hardpan (6 5% c l a y ) . b o u l d e r s . hardpan (25% c l a y ) . g r a v e l , b o u l d e r s , b o u l d e r s , g r a v e l , coarse sand, hardpan. broken g r a n i t i c bedrock, g r a n i t i c bedrock. GSC-215 499 f t . (136.9 m.) 0.0-19.8 19.8-25.3 b o u l d e r s , g r a v e l , coarse sand. g r a n i t i c bedrock. GSC-274 597 f t . (182.0 m.) 0.0-54. 3 54.3-57.9 57.9-59.8 coarse sand, g r a v e l , b o u l d e r s , hardpan (up to 50% c l a y i n p l a c e s ) ; c l a m s h e l l s a t 53.4m depth, broken d i o r i t e . d i o r i t e bedrock. GSC-320 -60 f t . (-18.3 m.) 0.0-89.3 89.3-90.2 90.2-101.5 101.5-114.0 sand, g r a v e l , b o u l d e r s , c l a y , sandstone bedrock, conglomerate bedrock, sandstone, s h a l e bedrock. GSC-358 20 f t . (6.1 m.) 0.0-1.5 1.5- 4.6 4.6- 6.1 6.1-10.1 10.1-11.6 11.6-13.4 sand and g r a v e l f i l l , sandy g r a v e l , o r g a n i c sandy s i l t , sand, g r a v e l , o r g a n i c sandy s i l t , sandy g r a v e l . GSC-373 30 f t . (9.1 m.) 0.0-1.8 1.8-2.1 2.1-3.0 3.0-12.8 f i l l . o r g a n i c s i l t and sand, wood.. cobbles, b o u l d e r s , sand, g r a v e l , s i l t . 2 01 -GSC-374 2 6 . f t . (7.9 m.) 0.3-0.9 0.9-3.7 sand w i t h b o u l d e r s . sand, g r a v e l , b o u l d e r s . GSC-416 240 f t . (73.2 m.) 0.0-0.6 0.6-1.2 1.2-5.8 loos e s i l t y sand, g r a v e l , s i l t y sand, s u b s t r a t i f i e d g r a v e l w i t h s i l t l a y e r s , grey,very compact g l a c i a l •'.till";''.silty, sahd, g r a v e l , t r a c e c l a y , o c c a s i o n a l boulders GSC-441 -35 f t . (-10 . 7 m.>.) 0.0-8.8 sand, f i n e g r a v e l . GSC-445 0.0-1.5 1.5-6.1 f i l l . sand, g r a v e l , c o b b l e s . GSC-449 . 0.0-0.3 0.3-1.2 1.2-4.6 sand. sand; s h e l l s . sand, g r a v e l , o r g a n i c s , c l a y e y s i l t , c o b b l e s . GSC-458 0.0-4.6 g r a v e l , s a n d , s i l t , o r g a n i c s , peat. GSC-656 190 f t . (57.9 m.) 0.3-1.5 1.5-1. 8 p o o r l y graded g r a v e l , g r a v e l , b o u l d e r s . GSC-657 280 f t . (85.4 m.) 0.0-1.8 1.8-2.6 p o o r l y graded g r a v e l , g r a v e l , b o u l d e r s . GSC-658 280 f t . (85.4 m.) 0.0-2.4 p o o r l y graded g r a v e l , l a r g e b o u l d e r s . GSC-6 62 0 ft. ;(mv) 0.0-1.2 1.2-4.3 coarse g r a v e l , b o u l d e r s , c l e a n , w e l l graded g r a v e l . GSC-697 287 f t . (87.5 m.) 0.0-4.0 4.0-16.8 b o u l d e r s . g r a n i t i c bedrock. GSC-793 285 f t . (86.9 m.) 0.0-1.5 1.5-5.5 5.5-14.6 s o i l , . boulders. g r a n i t i c bedrock. GSC-1010 50 f t . (15.2 m.) 0.0-6.7 6.7-7.6 g r a v e l l y s a n d , s i l t y sand, s i l t y sandy t i l l . GSC-1013 30 f t . (9.1 m.) 0.0-0.9 0.9-1.5 1.5-3.4 s i l t y sandy g r a v e l , g r a v e l l y s i l t y sand, s i l t y sandy t i l l . GSC-1016 25 f t . (7.6 m.) 0.0-0.6 0.6-0.9 0.9-1.8 sandy g r a v e l , sand. s i l t y sand. GSC-1101 365 f t . (111.3 m.) 0.0-0.3 0.3-3.0 s o i l . w e l l graded g r a v e l , b o u l d e r s . GSC-1102 250 f t . (76.2 m.) 0.0-0.3 0.3-1.5 1.5-1.8 s o i l . p o o r l y graded g r a v e l , g r a v e l , hardpan. ' - • 2 0 3 ' -APPENDIX 3 SOIL TEXTURAL CLASSIFICATION Taken from "The System of S o i l C l a s s i f i c a t i o n f o r Canada". (Canada Dept. o f A g r i c u l t u r e , 1974). Coarse-textured group (1) Very coarse textured: sands and loamy sands (2) Moderately coarse tex-tured: sandy loams and f ine sandy loams Medium-textured group (1) Medium textured: loam, s i l t loam and s i l t (2) Moderately f ine textured: sandy clay loam, clay loam and s i l t y clay loam Fine-textured group (1) Fine textured: (2) sandy c lay, clay and s i l t y clay Very f ine textured: clay (more than 60% heavy clay) 90 100 PERCENT SAND The composition of family textural clay and sand in the main textural remainder of each class i s s i l t . groups. classes Percentages of of s o i l s : the - 2 04 -APPENDIX 4 SUMMARY OF RECORDED FLOOD DAMAGE ON RIVERS AND CREEKS IN NORTH VANCOUVER-SEYMOUR Taken from Karanka (19 7 7); based on r e p o r t s i n the Vancouver Sun and Vancouver P r o v i n c e . Lynn Creek Sept. 6-8, 1906 water i n t a k e dam washed away, even supports gone; i n t a k e blocked; west end of K e i t h Road b r i d g e washed out, creek changed course. 54 m. of flume c a r r i e d away; K e i t h Road b r i d g e c ut under by 4.5 m. undermining a g i r d e r . i n t a k e b l o c k e d by l o g s , dam damaged by a s l i d e ; K e i t h Road b r i d g e approaches damaged; D i s t r i c t L o t 204 (near mouth) f l o o d e d . new dam washed out; d i v e r s i o n upstream along a l o g g i n g road. l a n d s l i d e above water i n t a k e ; s h i n g l e m i l l c ut o f f ; 3rd S t r e e t b r i d g e s e c t i o n washed out. Nov. 5, 1908 Nov. 17, 1909 Jan. 1, 1918 Nov. 15, 1919 Oct. 28, 1921 K e i t h Road b r d i g e approaches again damaged. Oct. 8, 1934 overflow on 3rd S t r e e t . Oct. 9. 1941 overf l o w on e a s t bank. St. Denis S t r e e t to K e i t h Road, throuah gardens and over K e i t h Road: s i x homes and a s t o r e marooned. Nov. 26, 1949 Lynn Creek b r i d g e (3rd?) f l o o d e d and impassable; water i n t a k e blocked. Nov. 3, 1955 approaches to K e i t h Road b r i d g e damaged, Jan. 15, 1961 d e s t r u c t i o n of Lynn Creek sewage treatment p l a n t , (Hastings Creek c o n t r i b u t e d to the d e s t r u c t i o n ) . - 2 05; -Seymour R i v e r Jan. 8, 1902 Sept. 26, 1905 Nov. 5, 1918 Nov. 27, 1909 Jan. 1, 1918 Feb. 4, 19 24 Jan. 22, 1935 Oct. 18, 1940 Oct. 2, 1947 Nov. 26, 1949 Dec. 1, 1949 Feb. 16, 1950 Oct. 9, 1950 channel d i v e r t e d a t l o g jam through Capt. Thompson's Ranch. K e i t h Road b r i d g e c o l l a p s e d and washed away (weakened i n Sept. 8 storm, and f a u l t y d esign blamed). s l i d e s on p i p e l i n e road, l a r g e amounts of d e b r i s a t mouth. M o o d y v i l l e b r i d g e ( K e i t h Road?) washed out, D i s t r i c t Lots 193 and 204 inundated to depths o f 1.2 m., and Seymour d a i r y i s o l a t e d ; p i p e l i n e broken near mouth of r i v e r and road damaged by e r o s i o n and s l i d e s . s l i d e s and e r o s i o n a l o n g p i p e l i n e road. logs damaged water i n t a k e ; again s l i d e s and e r o s i o n along road. minor s l i d e s and e r o s i o n . overflowed n o r t h and south o f K e i t h Road, along Seymour Boulevard; 20 houses surrounded by 1 m. of water; some bank e r o s i o n and s l i d e c r i b b i n g a t S c o t t ' s Ranch i s damaged. dredge on C u t t e r I s l a n d i s swept downstream; work on Deep Cove c u t o f f i s r u i n e d . C u t t e r I s l a n d b r i d g e and D o l l a r t o n Highway undermined and damaged; Swedish Old People's Home on C u t t e r I s l a n d f l o o d e d and evacuated; R i v e r s i d e D r i v e , 50 f a m i l i e s evacuated between K e i t h Road and C u t t e r I s l a n d b r i d g e ; damage a l s o t o houses on 22 00 bl o c k K e i t h and Seymour Boulevard. second f l o o d along R i v e r s i d e D r i v e . C u t t e r I s l a n d again f l o o d e d , i n c l u d i n g basement of Swedish Old People's Home; R i v e r s i d e D r i v e and Seymour Boulevard, some basements and gardens are f l o o d e d . overflow on R i v e r s i d e D r i v e and C u t t e r I s l a n d ; channel t o be d i v e r t e d i n t o 1910 channel. Nov. 3, 1955 about 50 houses damaged or evacuated - 2,06 -alonq R i v e r s i d e D r i v e and Seymour Boulevard. Jan. 15, 1961 D o l l a r t o n Highway b r i d g e threatened; minor damage to s e v e r a l houses on D o l l a r t o n Highway and Seymour Boulevard. U n s p e c i f i e d Small Streams Indian R i v e r Road washed out and a number of houses i s o l a t e d . u n s p e c i f i e d f l o o d damage i n Deep Cove. Quarry Creek? overflowed near mouth and washed but a driveway. washouts on D o l l a r t o n Highway. M i l l e r Creek? f l o o d e d 4 houses. s e v e r a l hundred metres of Mt. Seymour Road f l o o d e d by blo c k e d c u l v e r t s . Nov. 3, 1955 Dec. 9, 1956 Oct. 11, 1958 Jan. 19, 1968 Oct. 25, 1971 Jan. 15, 1973 APPENDIX 5 SOIL TESTING PROCEDURES A. Mechanical Sieve A n a l y s i s T h i s method o f t e s t covers a procedure f o r the deter m i n a t i o n of the p a r t i c l e s i z e d i s t r i b u t i o n o f f i n e and coarse aggregates, u s i n g s i e v e s w i t h square openings. A s i e v e a n a l y s i s c o n s i s t s of shaking the m a t e r i a l through a stack of wire screens with openings of known s i z e s . D e t a i l s o f the procedure are o u t l i n e d i n American S o c i e t y f o r T e s t i n g M a t e r i a l s (1971) and Lambe (1951). G r a i n - s i z e l i m i t s of the U n i f i e d S o i l C l a s s i f i c a t i o n System used i n the l a b o r a t o r y p a r t < of the study are as f o l l o w s : M a t e r i a l P a r t i c l e S i z e U.S. Standard (mm.) Sieve No. cobbles coarse g r a v e l f i n e g r a v e l coarse sand 76.2 3 i n c h — 1 9 > 1 3/4 i n c h 4.76— #4 — #10 medium sand f i n e sand f i n e s ( s i l t and clay) 2.00 0.42 — — : #40 -0.074 #200 B. A t t e r b e r g L i m i t s A f i n e - g r a i n e d s o i l can e x i s t i n any of s e v e r a l s t a t e s depending on the amount of water p r e s e n t i n the s o i l system. Boundaries o f tithe se s t a t e s are d e f i n e d i n terms o f l i m i t s as f o l l o w s : l i q u i d l i m i t - the boundary between the l i q u i d and p l a s t i c s t a t e s ; and p l a s t i c l i m i t - the boundary between the p l a s t i c and s e m i - s o l i d s t a t e . The l i q u i d l i m i t o f a s o i l i s the moisture content a t which the s o i l has such a s m a l l shear s t r e n g t h t h a t i t flows to c l o s e a groove of standard width when j a r r e d i n a s p e c i f i e d manner. The p l a s t i c l i m i t i s the water content a t which the s o i l begins t o crumble when r o l l e d i n t o threads of s p e c i f i e d s i z e . Procedure f o r d e t e r m i n a t i o n of these A t t e r b e r g l i m i t s i s o u t l i n e d i n Lambe (1951). The d i f f e r e n c e between the l i q u i d and p l a s t i c l i m i t s i s a measure of the range o f water content through which a s o i l behaves as a p l a s t i c . T h i s d i f f e r e n c e i s termed the p l a s t i c i t y index. C. E x p l a n a t i o n of the u n i f i e d S o i l C l a s s i f i c a t i o n System The U n i f i e d S o i l C l a s s i f i c a t i o n System developed by Casagrande (1948) p l a c e s s o i l s i n t o three d i v i s i o n s ; coarse-gr a i n e d , f i n e - g r a i n e d , and h i g h l y o r g a n i c s o i l s . The co a r s e -g r a i n e d s o i l s are those having 50% or l e s s m a t e r i a l p a s s i n g the No. 200 s i e v e (0.074 mm.), and f i n e - g r a i n e d s o i l s are those having more than 50% p a s s i n g the No. 200 s i e v e . H i g h l y o r g a n i c s o i l s can g e n e r a l l y be i d e n t i f i e d by v i s u a l examination. The system r e c o g n i z e s 15 s o i l groups and uses names and l e t t e r symbols to d i s t i n g u i s h between groups. These symbols are d e r i v e d e i t h e r from terms d e s c r i p t i v e of the s o i l f r a c t i o n s , the r e l a t i v e v a l u e o f the l i q u i d l i m i t (high or low), or r e l a t i v e g r a d a t i o n (well-graded or p o o r l y - g r a d e d ) . The symbols are as f o l l o w s : Components and Corresponding Symbols boulders - none s i l t - M cobbles - none c l a y - C g r a v e l - G o r g a n i c - 0 sand - S peat - Pt Gradation Symbols L i q u i d L i m i t Symbols well-graded - W high - H p oorly-graded - P low - L These symbols are combined to form the group symbols which correspond to the names of t y p i c a l s o i l s as seen i n the accompanying c h a r t . G radation i s determined by s i e v e a n a l y s i s and a g r a i n -s i z e curve i s p l o t t e d as percent f i n e r by weight a g a i n s t a l o g - s c a l e of g r a i n s i z e i n mm. P l a s t i c i t y c h a r a c t e r i s t i c s are e v a l u a t e d u s i n g the l i q u i d l i m i t and p l a s t i c l i m i t t e s t s on the s o i l f r a c t i o n f i n e r than the No. 40 s i e v e (0.42 mm.). The p l a s t i c i t y c h a r t i s used t o c l a s s i f y the f i n e - g r a i n e d s o i l s and the f i n e - g r a i n e d p o r t i o n of c o a r s e - g r a i n e d s o i l s . T h i s c h a r t i s a p l o t of p l a s t i c i t y index versus l i q u i d l i m i t and i s used t o i n d i c a t e a s o i l ' s c o m p r e s s i b i l i t y . The a r b i t r a r y d i v i d i n g l i n e between low and high c o m p r e s s i b i l i t y i s a l i q u i d l i m i t value of 50. CO o _ Z c S s E Major Divisions 0) s O o 8 ° in o | S w i s ? »<5 a o 8 s 2 a III 6 _ 'E 1 0  0 = S :_ _ 8 « 8 B|.S < 5 ! u -- I Ii! Highly Organic Soils Group Symbols GW GP GM GC SW SP SM SC ML OL OH Typical Names Well-graded gravels and gravel-sand mixtures, little or no fines Poorly graded gravels and gravel-sand mixtures, little or no fines Silty gravels, gravel-sand-silt mixtures Clayey gravels, gravel-sand* clay mixtures Well-graded sands and gravelly sands, little or no fines Poorly graded sands and gravelly sands, little or no fines Silty sands, sand-silt mixtures Clayey sands, sand-clay mixtures Inorganic silts, very fine sands, rock flour, silty or clayey fine sands Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays Organic silts and organic silty clays of low plasticity Inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silts Inorganic clays of high plasticity, fat clays Organic clays of medium to high plasticity Peat, muck, and other highly organic soils Classification Criteria c _ co c 3 5 u-o ww g's L oTo-' u o S : - ."o : ! _ " at ' vi O > 1 n 0 fi ; " o g O 2 CM 1 2 J O ! i °-z (N JO CU A DQQ/D-\Q Greater than 4 - (D3Q)2 '10 Between 1 and 3 Not meeting both criteria for GW Atterberg limits plot below "A" line or plasticity index less than 4 Atterberg limits plot above "A" line and plasticity index greater than 7 Atterberg limits plotting in hatched area are borderline classifications requiring use of dual symbols CU = DQQ/D^Q Greater than 6 Between 1 and 3 Not meeting both criteria for SW Atterberg limits plot below "A" line or plasticity index less than 4 Atterberg limits plot above "A" line and plasticity index greater than 7 Atterberg limits plotting in hatched area are borderline classifications requiring use of dual symbols 1 T 1 1 1 PLASTICITY CHART For claudication ol f ina*grain*d . toil* and tint fraction ol coaria-Anerbarg L-mitt plotting in hatched araa are bcrrdarlina claitif icationt *raquiring uau Of dual lymboll. " PI • 0.73 ILL • 20! © / y 0 iOH) OL) 10 20 30 50 60 70 80 90 IOO Visual-Manual Identification, see ASTM Designation D2488. 0 M H X CD t) cn H cn P» H-Hi CD H- rt O H-fu 0 rt 3 H-O n 13 cn rt cn rt Hi (D 0 B i-S rt tr ro C| ti H-Hi H-CD O. Ol 0 H-M APPENDIX 6 GRAIN SIZE DISTRIBUTION, ATTERBERG LIMITS, AND UNIFIED SOIL TEXTURAL CLASSIFICATION OF SURFICIAL SEDIMENTS Sample Number Description of Sediment Estimated Percent Volume of Coarse Fraction Greater Than 20 mm. Diameter Percentage by Weight of Material Less Than 20 mm. Diameter Passing Sieve; Percent by Weight of Matrix (less than 20 mm.; Atterberg Limits Unified S o i l Texture #4 4.76 mm. #10 2.00 mm. #40 0.42 mm. #200 0.074 mm. Fine Gravel Sand Fines Plastic Limit Liquid Limit P l a s t i c i t y Index PRE-VASHON SEDIMENTS 8 laminated, blue-grey clayey s i l t 0 90 + • 90+ 25.2 33.0 7.8 ML 9 laminated, grey clayey s i l t 0 90+ 90+ 27.0 36.8 9.8 ML 25 massive, blue-grey stony clav 10 - 15 75+ 75+ 21.5 32.1 10.6 CL 27 laminated s i l t 0 90 + 90+ 22.2 22.6 0.4 ML 28 loose,poorly sorted d r i f t matrix 20 - 25 71.2 52.9 21.4 5.5 28.8 65.7 5.5 SP-SM 41 medium-fine sand, subhorizontally and cross bedded 5 - 1 0 96.6 91.2 40.5 0.6 3.4 96.0 0.6 SP 42 massive, p l a s t i c , stony clayey s i l t 0 - 5 90+ 90 + 41.6 50.7 9.1 MH 43 dense,laminated grey s i l t 0 75+ 75+ 23.3 25.2 1.9 ML 44 laminated,brown stony s i l t 5 - 1 0 75+ 75+ 29.3 29.8 0.5' ML 45 laminated, stony sandy s i l t 5 - 1 0 100.0 100.0 99.6 . 87.0 0.0 13.0 87.0. 25.6 26.1 0.5 ML 46 cense,grey t i l l matrix 15 - 25 87.8 79.5 65.8 46.0 12.2 41.8 46.0 15.8 17.4 1.6 SM 47 horizontally bedded fine sand and s i l t 0 100.0 100.0 99.2 55.3 0.0 44.7 55.3 17.1 13.1 1.0 ML 48 larcinated, stony sandy s i l t 5 - 1 0 100.0 100.0 100.0 64.5 0.0 35.5 64.5 21.8 22.3 0.5 ML • 50 medium sand,cross-bedded and subhorizontally layered 5 - 1 0 99.7 99.3 95.2 3.6 0.3 96.1 3.6 SP 55 dense,grey t i l l matrix 20 - 25 96.1 88.9 64.3 29.7 3.9 66.4 29.7 16.1 16.3 0.2 SM 5.6 massive,blue-grey stony clay . 5 - 1 0 75+ 75+ 20.3 34.6 14.3 CL 57 horizontally bedded fine sand 0 99.1 98.0 72.1 4.0 0.9 95.1 4.0 SP 58 subhorizontally bedded coarse-medium sand 5 - 1 0 90.0 67.2 13.5 1.5 10.0 88.5 1.5 SP Sample Number Description of Sediment Estimated Percent Volume of Coarse Fraction Greater Than 20 mm. 1»iam. Percentage by Weight of Material Less Than 20 mm. Diameter Passing Sieve; Percent by Weight of Matrix (less than 20 mm.) Atterberg Limits Unified S o i l #4 4.76 mm. #10 2.00 mm. #10 0.42 mm. #200 0.074 mm. Fine Gravel Sand Fines Plastic Limit Liquid Limit P l a s t i c i t y Index Texture 59 horizontally bedded sandy s i l t 0 99.1 98.2 95.6 63.8 0.9 35.3 63.8 18.4 21.3 2.9 ML 65 s i l t y peat with wood fragments PT VASHON DRIFT 3 dense lodgement t i l l matrix 2 0 - 2 5 83.1 70.8 40.6 13.0 16.9 70.1 13.0 14.9 17.4 2.5 SM 7 dense lodgement t i l l matrix 10 - 15 87.2 82.7 55.2 23.8 12.8 63.4 23.8 • 13.2 16.3 3.1 SM 10 dense lodgement t i l l matrix 15 - 20 93.0 84.9 56.2 22.3 7.0 70.7 22.3 13.4 16.5 3.1 SM 19 dense lodgement t i l l matrix 15 - 20 88.0 82.9 68.8 39.1 12.0 48.9 39.1 14.3 18.2 3.9 SM 34 dense lodgement t i l l matrix 20 - 25 91.1 82.1 56.0 25.2 8.9 65.9 25.2 . 13.0 14.4 1.4 SM 35 subs t r a t i f i e d s i l t y sand d r i f t matrix 5 - 1 0 94.0 90.6 70.5 14.5 6.0 79.5 14.5 9.0 15.0 6.0 SC-SM 49 loose,poorly sorted ablation t i l l matrix 40 - 50 65.6 42.7 13.4 2.8 34.4 62.8 2.8 sw 51 dense lodgement t i l l matrix 15 - 20 90.7 82.5 59.4 24.7 9.3 66.0 24.7 15. 3 16.5 1.2 SM 53 substratified fine sand d r i f t matrix 5 - 1 0 100.0 99.8 87.6 3.6 0.0 96.4 3.6 SP 60 laminated s i l t dri-ft 0 75+ 75+ 19. 8 22.0 2.2 ML 62 foreset medium-fine sand with pebbles 15 - 20 96.0 86.6 54.0 4.2 4.0 91.8 4.2 SP 64 dense lodgement t i l l matrix 15 - 20 84.8 78.3 62.3 36.8 15.2 48.0 36.8 12.9 15.8 2.9 SM CAPIU iNO COHESIVE SEDIMENTS 4 stony s i l t y clay 5 75 + 75+ .20.5 34.0 .13.5 CL 5 stony clayey s i l t 0 - 5 75 + 75+ 28.6 34.2 5.6 '•SL 16 stony s i l t y clay 0 - 5 75+ 75+ 22.5 36.4 13.9 CL 23 varved,grey s i l t 0 90+ 90 + 22.9 26.1 3.2 ML 24 varved,grey-brown clayey s i l t 0 90+ 90+ 36.0 42.4 6.4 ML 26 plastic,stony clayey s i l t 0 - 5 75+ 75+ 42.9 59.0 16.1 KH 29 laminated,brown,stony Cl<VSj«^  s i 1+ 0 - 5 75+ 75+ 22.6 24.1 1.5 ML 30 laminated,gritty clayey silt 0 - 5 75+ 75+ 18.4 21.6 3.2 ML 31 massive,brown s i l t y clay 0 75+ 75+ 19.0 24.4 5.4 CL-ML Sample Number Description of Sediment Estimated Percent Volume of Coarse Fraction Greater Than 20 mm. Diameter. Percenta Than 20 ge by Wei mm. Diame ?ht of. Ma :er Passi t e r i a l Less ig Sieve; Percent by Weight of Matrix (less than 20 mm.) Atterberg . Limits Unified S o i l #4 4.76 mm. #10 2.00 mm #40 0.42 iron. #200 0.074 mm. Fine Gravel Sand Fines Plastic Limit Liquid Limit P l a s t i c i t j Index - Texture T 32 massive,plastic,stony clayey s i l t 0 - 5 75+ 75+ 37.8 52.3 14.5 MH Jo laminated,blue-grey clayey s i l t 0 75+ 75+ - 23.4 27.5 4.1 ML ^ o massive,brown,gritty clayey s i l t 0 - 2 75+ 75+ 19.0 25.2 6.2 CL-ML J O I n blue-grey,gritty s i l t y clay lens 0 75+ 75+ 20.7 28.8 . 8.1 CL 52 massive, brown, stony clayey s i l t 0 - 5 75+ •75+ 17.8 20.5 2.7 ML 61 massive,brown,stony clayey s i l t massive,brown,stony clay 0 - 5 0 - 5 75+ 75 + 75+ 75+ 24.2 22.5 29.4 A 5.2 ML CAP I LA 1 NO COHESIONLESS SEDIMENTS dense,substratified s i l t v sand 0 - 5 97.3 94.1 79.5 42.8 2.7 54.5 42.8 16.3 J£. . H 17.1 i 9.9 0.8 CL SM 2 dense,substratified s i l t v sand 0 - 5 100.0 99.4 93.1 42.6 0.0 57.4 42.6 16.1 17.8 1.7 SM 6 dense,substratified sar.dy s i l t 0 - 5 100.0 99.2 91.6 58.8 0.0 41.2 58.8 17.1 17.4 0.3 ML 11 s i l t y sand foreset bed 0 100.0 99.9 99.5 48.1 0.0 51.9 48.1 19.0 20,. 1 1.1 SM 12 s i l t y sand foreset bed 0 100.0 100.0 99.6 35.5 0.0 64.5 35.5 18.3 19.1 0.8 SM 13 s i l t y sand, foreset bed 0 100.0 100.0 99 .0 46.3 0.0 53.7 46. 3 18.8 1.9.5 0. 7 £K 14 well-sorted sand foreset bed 0 - 5 100.0 99.4 28.2 1.0 0.0 99.0 1.0 SP 15 gravelly sand foreset bed 5 - 1 0 74.9 64.9 9.9 0.1 25.1 74.8 0.1 SP 17 s i l t y sand foreset bed 0 98.9 97.0 90.8 30.3 1.1 68.6 30.3 16.9 19.8 2.9 SM 18 s i l t y sand foreset bed 0 100.0 100.0 92.8 14.2 0.0 85.8 14.2 17.2 20.1 2.9 SM. 20 well-sorted sand foreset bed 10 - 15 97.9 93.0 40.1 1.9 2.1 96.0 1.9 SP 21 gravelly sand foreset bed 30 - 40 76.0 67.7 10.6 1.9 24.0 74.1 1.9 SP 22 s i l t y sand foreset bed 0 100.0 100.0 99.2 38.8 0.0 61.2 38.8 17.2 18.0 0.8 SM • 33 well-sorted,subhorizontal, clayey, s i l t y sand bed 0 100.0 100.0 96. 7 14.2 0.0 85.8 14.2 13.2 20.0 6.8 SC-SM 40 well-sorted,subhorizontal, s i l t y sand bed 0 100.0 100.0 96.9 16.3 0.0 83.7 16-3 18.3 22.1 3. 8 SM 54 subhorizontally layered 0 100.00 100.0 99.6 14.5 0.0 85.5 14.5 20.2 22.5 2.3 SM 63 | s i l t y sand foreset bed 0 100.00 100.0 99.2 36.2 0.0 63.8 36. 2 21.0 21.9 0.9 SM - -214 -APPENDIX 7 EXPLANATION OF STONINESS GLASSES Taken from "The System of S o i l C l a s s i f i c a t i o n f o r Canada" (Canada Dept. of A g r i c u l t u r e , 19 7 4). Stoniness C l a s s e s ( r e f e r s to stones l a r g e r than 25 cm. i n d i a m e t e r ) . 0 stone f r e e s l i g h t l y stony - stones cover 1% - 10% of the s u r f a c e area. 2 moderately stony - stones cover 11% -20% of the s u r f a c e area. 3, very stony - stones cover 21% - 40% of the s u r f a c e area. 4 e x c e e d i n g l y stony - stones cover 41% -80% of. the s u r f a c e area. 5 e x c e s s i v e l y stony - stones cover 81% -100% of the s u r f a c e area. APPENDIX 8 EXPLANATION OF DRAINAGE CLASSES Taken from "The System o f S o i l C l a s s i f i c a t i o n f o r Canada". (Canada Dept. of A g r i c u l t u r e , 19 74). W e l l Drained — Water i s removed from the s o i l r e a d i l y but not r a p i d l y . Excess water flows downward r e a d i l y i n t o u n d e r l y i n g p e r v i o u s m a t e r i a l or l a t e r a l l y as subsurface and s u r f a c e flow. Water source i s p r e c i p i t a t i o n . On s l o p e s subsurface flow may occur f o r s h o r t d u r a t i o n s but a d d i t i o n s are equaled by l o s s e s . I m p e r f e c t l y Drained — Water i s removed from the s o i l s u f f i c i e n t l y s l o w l y i n r e l a t i o n to supply to keep the s o i l wet f o r a s i g n i f i c a n t p a r t of the growing season. Excess water moves slo w l y downward i f p r e c i p i t a t i o n i s the main source, flow r a t e may vary but the s o i l remains wet f o r a s i g n i f i c a n t p a r t of the growing season. P o o r l y Drained — Water i s removed so s l o w l y i n r e l a t i o n to supply t h a t the s o i l remains wet f o r a comparatively l a r g e p a r t of the time the s o i l i s : not f r o z e n . Excess water i s e v i d e n t i n the s o i l f o r a l a r g e p a r t of the time. Subsurface flow and/or groundwater flow i n a d d i t i o n to p r e c i p i t a t i o n are the main water sources; there may a l s o be a perched water t a b l e with p e r c i p i t a t i o n exceeding e v a p o t r a n s p i r a t i o n . 

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