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Managing fall floods in the Lower Skenna region, British Columbia Urquhart, James Michael 1981

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c- / MANAGING FALL FLOODS IN THE LOWER SKEENA REGION, BRITISH COLUMBIA by JAMES MICHAEL URQUHART B.A., U n i v e r s i t y of Toronto, 1 9 6 8 M.A., U n i v e r s i t y of Toronto, I969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS THE FACULTY OF GRADUATE STUDIES i n the School of Community and Regional Planning We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1 9 8 1 ^ JAMES MICHAEL URQUHART In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a gree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . School of Community and Regional Planning Department o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 _^  A p r i l 2 3 , 1981 Date DE-6 (2/79) i i ABSTRACT This study i n v e s t i g a t e s f l o o d c h a r a c t e r i s t i c s and management st r a t e g i e s i n the Lower Skeena River Region. Rivers i n the region exhibit two annual f l o o d seasons i n which d i f f e r e n t types of floods occur. T y p i c a l l y , r i v e r s tend to f l o o d during spring freshet i n May and June as a r e s u l t of snowmelt runoff within the Skeena basin. However, intense and sustained rainstorms contribute to another type of f l o o d i n the f a l l months i n the Lower Skeena Region. Although the most extensive and l a r g e s t f l o o d of record occurred as a r e s u l t of regional snowmelt runoff i n the spring of 1936, "the f l o o d i n f l i c t i n g the greatest damage occurred i n the f a l l of 1978 as a r e s u l t of three days of continuous heavy r a i n . In contrast with the remainder of the Skeena basin where spring freshet floods are c r i t i c a l , f a l l f l o o d s i n the Lower Skeena occur more frequently than spring floods and f o r the same return period are greater i n magnitude. Despite the implementation of f l o o d damage prevention measures i n the Lower Skeena Region, f l o o d damage continues to increase and t h i s i s l a r g e l y the r e s u l t of f a l l f loods. Analysis of the meteorologic and hydrologic features of f a l l floods i n d i c a t e s important differences i n the duration and pattern of f l o o d i n g throughout the Lower Skeena as compared to spring freshet floods. The i n t e r v a l between the time when the p o s s i b i l i t y of a f l o o d i s known and when i t a c t u a l l y occurs i s shorter f o r f a l l f l o o d s , d i f f e r e n t properties are subject to f l o o d i n g and the frequency of f l o o d i n g of most f l o o d prone areas i s greater. This i n d i c a t e s the need f o r a d i f f e r e n t strategy to manage the f l o o d problem. The current program of f l o o d damage prevention measures i n the Lower Skeena i s based on the phys i c a l c h a r a c t e r i s t i c s associated with spring i i i freshet flooding. The exi s t i n g approach i n the region i s part of a blanket strategy toward managing floods province-wide. The strategy r e l i e s almost e n t i r e l y on nonstructural measures of f l o o d forecasting, floodplain regulation and floodproofing. The design flood, with a 1 i n 200 year return period adopted as a basis f o r the current strategy i s derived from the features of the 1936 spring freshet flood. These measures provided no assistance i n reducing damages during the f a l l f l o o d of 1978. A framework f o r developing a comprehensive fl o o d management strategy to handle f a l l floods i s applied to New Remo, a Lower Skeena f l o o d prone community. The strategy e n t a i l s the following f i v e steps: I Define the Spatial D i s t r i b u t i o n of Flood Damages II Design a Flood Forecasting Service I I I Design an Emergency Plan f o r Action During Floods IV Assess Remaining Practicable Alternatives f o r Reducing Flood Damage V Develop a Financing P o l i c y f o r the Program P o t e n t i a l l y f e a s i b l e adjustments to the flo o d hazard i n New Remo include; ( l ) f l o o d forecasting, (2) emergency action, (3) floodproofing and (4) permanent evacuation of some homes. However, to develop an optimum combination of altern a t i v e adjustments w i l l require s i t e s p e c i f i c information on f l o o d damage r i s k , which currently i s not available f o r properties i n New Remo. The f l o o d management strategy developed f o r New Remo would be applicable to other communities i n the Lower Skeena, prone to f a l l flooding. However, regional application of the approach requires t a i l o r i n g the strategy according to the physical, s o c i a l and economic features within each community affected by f a l l floods. i v TABLE OF CONTENTS PAGE CHAPTER 1 INTRODUCTION 1. I The Flood Problem i n the Skeena 1. I I Flood Management Strategies 3« A. Flood Control to Flood Damage Reduction 3 -B. A Framework f o r Flood Damage Reduction P o l i c y 9. I I I Study, Objectives and Scope 9« CHAPTER 2 THE FLOOD HAZARD IN THE LOWER SKEENA RIVER REGION 12. I Environmental Characteristics 12. A. Setting 12. B. Hydrology and Flood Conditions 1 6 . C. Flood Types 18. I I The Human Dimension 21. A. Flood Prone Lands and Communities 21. B. History of Floods and Damages 25. C. Recent Flood Experience 29. (a) Characteristics of the 1978 Flood 29. (b) Patterns of Flooding and Damages 3 3 . (c) Implications 35 • I I I Assessment of Flood Risk 3 7 -A. Flood Frequency Analysis 3 7 -B. Spring Freshet Floods vs F a l l Rain Floods 3 9 -IV Implications f o r Flood Management 4 1 . CHAPTER 3 CRITIQUE OF THE CURRENT FLOOD MANAGEMENT APPROACH IN THE LOWER SKEENA REGION 4 5 . I Scope of Pr o v i n c i a l Management of Floods 4 5 -A. Flood Damage Prevention Objectives 4 5 . B. Program Elements and Implementation Mechanisms 4 6 . V I I Effectiveness of Current Measures i n Dealing with F a l l Floods 49 A. Flood Forecasting 49 B. Design Flood Frequency and Floodplain Mapping 51 C. Floodplain Regulation and Floodproofing 54 I I I Implications 55 CHAPTER 4 TOWARD A STRATEGY FOR MANAGING FALL FLOODS IN NEW REMO 58 I Community Features and Flood Hazard 58 A. Flood Experience 58 B. Landuse and Flood Patterns 60 C. Developments Affe c t i n g the Flood Hazard 62 D. Community Regard Toward Flood Management 63 I I Developing a Comprehensive Strategy to Manage F a l l Floods i n New Remo 6 4 A. The Framework f o r Choice 6 4 B. Strategic Elements 65 Step I Define the Spatial D i s t r i b u t i o n of Flood Damages 65 Step I I Design a Flood Forecasting Service 66 Step I I I Design of An Emergency Plan f o r Action During Floods 68 Step IV Assessing Remaining Alternatives f o r Reducing Damages 71 Step V Development of a Financing Po l i c y 76 I I I Discussion and Implications 78 IV Study Conclusions 79 A. The Flood Hazard 79 B. The Current Management Approach 80 C. Flood Management Strategy f o r New Remo 80 REFERENCES 82 v i LIST OF TABLES PAG1 TABLE 1 STRATEGIES AND TOOLS FOR ACHIEVING FLOOD HAZARD REDUCTION 7 2 FLOOD PRONE COMMUNITIES IN THE LOWER SKEENA REGION 24 3 INSTANTANEOUS PEAK DISCHARGES, 1978 FLOOD 32 v i i LIST OF FIGURES PAGE FIGURE 1 SKEENA RIVER DRAINAGE BASIN 13 2 MEAN MONTHLY TEMPERATURES AND PRECIPITATION IN THE SKEENA 15 3 HYDROGRAPHS FOR THE SKEENA AND TRIBUTARIES 17 4 RUNOFF vs DRAINAGE AREA IN THE SKEENA 19 5 COMMUNITIES OF THE LOWER SKEENA REGION 22 6 ISOHYETAL MAP OF THE OCTOBER, 1978 STORM 30 7 FLOOD FREQUENCY CURVES FOR THE SKEENA AND TRIBUTARIES 38 8 RELATIONSHIP BETWEEN FALL AND SPRING FLOODS 40 9 FLOOD HAZARD IN NEW REMO 6 l 10 FLOOD ZONES IN NEW REMO 69 1 CHAPTER 1 INTRODUCTION I The Flood Problem i n the Skeena This thesis focusses on the problem of f a l l floods i n the Lower Skeena River Region of B r i t i s h Columbia with a view toward developing a strategy to reduce f l o o d damage. The study deals with the physical features of the floo d hazard i n demonstrating the importance of f a l l floods i n contributing to annual fl o o d damage. The current f l o o d management approach i s assessed i n l i g h t of the f a l l f l o o d problem to point out important l i m i t s i n i t s a b i l i t y to prevent flood damage. A strategy geared toward the physical features of f a l l floods i s developed to achieve comprehensive flood damage reduction f o r communities of the Lower Skeena Region incurring t h i s type of flood problem. The Lower Skeena River Region, from Hazelton to the coast has a history of flooding. Minor floods are regular events, occurring almost annually i n some l o c a l i t i e s , while i n a few communities, floods have occurred twice i n a single year. At l e a s t s i x major floods have i n f l i c t e d costly damage and severe disruption within the region during t h i s century. The e a r l i e s t , devas-t a t i n g f l o o d occurred i n 1936, when excessive and sustained snowmelt produced extensive damage during spring along the lower course of the Skeena. This fl o o d was severe enough to s t a l l floodplain encroachment i n some l o c a l i t i e s and redirect other townsites toward building on le s s haz-ardous s i t e s . To date, the 1936 f l o o d i s the largest recorded event of i t s type on the Skeena River but not the most damaging. In 19^8 another spring f l o o d i n f l i c t e d devastating losses and disruption as renewed 2. floodplain encroachment had prevailed i n the intervening period, free from severe floods. Damaging snowmelt floods occurred once again i n 1964 and 1972 and i t was evident a f t e r the l a t t e r event, second only i n magnitude to the f l o o d of 1936 that recurrent and increasing flood damage was impeding optimal use of floodplains and threatening the s o c i a l well-being of the regional population. Something had to be done to deal with the flood problem. In recognition of the v i t a l nature of floodplain resources i n the settlement and development pattern of B r i t i s h Columbia, and the problem of mounting fl o o d losses, the Province i n i t i a t e d a program of flood damage prevention f o r provincewide application i n 1973- The program designated nonstructural measures to cope with flood problems. Flood forecasting, emergency action plans, floodplain regulations c o n t r o l l i n g development i n flood zones and floodproofing requirements f o r new construction were devel-oped f o r communities and d i s t r i c t s facing f l o o d problems. The emergent approach i s geared s o l e l y toward the physical features associated with snowmelt floods generally occurring i n spring, as these are regarded as a pervading common problem throughout the province. For example, i n the Fraser, Columbia and Okanagan River Systems, as well as the Skeena, spring freshet floods continue to be a primary focus f o r concern i n managing flo o d losses (Province of B r i t i s h Columbia, 1980). In the Skeena River system, an apparently unrecognized f l o o d problem emerged during the past ten years. In 1974, heavy sustained r a i n f a l l generated severe floods along many of the t r i b u t a r i e s of the Lower Skeena and on parts of the Skeena floodplain during autumn. Not only was the timing different but the floodwaters affected different l o c a l i t i e s from those having had experience with spring, snowmelt floods. Flood damage, although l o c a l i z e d i n small communities i n the Lower Skeena Region, t o t a l l e d 3. s l i g h t l y i n excess of $1 m i l l i o n . In 1978 another f l o o d occurred i n response to heavy f a l l r a i n f a l l , but t h i s time the damages were more extensive and expensive, exceeding $50 m i l l i o n . Despite the prevailing f l o o d damage prevention program, f l o o d damages within the Lower Skeena Region exhibit an increasing trend, and raise c r i t i c a l questions about the scope of the current f l o o d management approach. The pr e v a i l i n g flood damage prevention program appears to f a i l i n incompassing the f a l l f l o o d problem. The current strategy focusses on the characteristics of the spring f l o o d hazard i n the Lower Skeena Region and the measures designated toward managing i t do not a s s i s t i n reducing f a l l f l o o d damages i n the region. This study focusses on the f a l l f l o o d problem evident i n the Skeena and suggests an approach toward i t s management. The strategy proposed here i s not new, but emerges from a synthesis of the l i t e r a t u r e on f l o o d management, i n l i g h t of the nature of the flo o d hazard i n the Lower Skeena, and the backdrop of the prevailing program operating i n the region. I I Flood Management Strategies A. Flood Control to Flood Damage Reduction Flood management l i t e r a t u r e abounds with studies describing and evaluating p o l i c i e s and programs i n numerous American floodplain settings. In the United States, population, development and floods interact to generate f l o o d hazards of a more extensive nature and greater severity than i n Canada. Furthermore, constitutional differences have contributed toward different i n s t i t u t i o n a l arrangements and organizational features applied i n the management of floods i n each country. Despite these and other differences, conceptual strategies have evolved along s i m i l a r l i n e s i n seeking a s o c i a l l y optimum use of floodplain resources. Flood management strategies have s h i f t e d gradually from single purpose fl o o d control projects, through the incorporation of multiple objectives i n planning water resource programs, to the contemporary approach involving multiple means management described by White (1975, 1979). U n t i l 1936, the problem of floods i n the United States was regarded primarily as a l o c a l or at most a state concern. The Flood Control Act of 1936, devised i n the wake of devastating floods of national concern, acknowledged the federal r e s p o n s i b i l i t y to manage flo o d problems. More than t h i s , the l e g i s l a t i o n encouraged the development of multiple purpose water resource planning and provided the c r i t e r i a of economic ef f i c i e n c y as a basis f o r assessing proposed projects (James, 1972). Despite i t s l i m i t a t i o n s and c r i t i c i s m s made of i t the conceptual framework of maximizing net economic benefits as a c r i t e r i o n provided the foundation f o r the evolu-t i o n of current procedures f o r considering the s o c i a l and environmental tradeoffs i n resource evaluations. For almost 30 years, the strategy f o r managing floods embraced a narrow range of structural adjustments. Flood control, achieved by dams, levees, floodways were d i s t i n c t technical solutions within the mandate and competance of the government agencies responsible f o r managing floods. Consideration and implementation of alternative nonstructural adjustments, such as floodproofing and floodplain regulations were frustrated by the ease of implementation of physical solutions and i t s apparent success. Nonstructural adjustments appeared too i n t r i c a t e , and were viewed as requiring extensive administrative overhaul to achieve f e a s i b i l i t y . Flood management programs tended to follow i n the wake of disasters, and r e s u l t i n highly v i s i b l e s t r u c t u r a l panaceas which i n turn were dramatic testa-ments to the competance of the design agency and the power of the community. 5. Critics of the flood control strategy pointed to the large expenditures on flood control and protection works and the prevailing increase in annual flood damages. According to White (1975) over $7 b i l l i o n i n 30 years had been spent on flood control works in the United States and yet annual flood damages demonstrate an increasing trend. Piatt (1979) conservatively estimates the b i l l for American flood damage to exceed $50 b i l l i o n during the 1980's based on the prevailing trend. Gilbert White in 1945 was f i r s t to allude to the cause of the problem and others (Kates, 1962;. Kates and White, I96I; Sewell, I965 and James, 1973) have confirmed that encroachment into floodplains was a major factor in contributing to an increase in flood damage potential. The need for supple-mentary, and i n some cases alternative measures of flood damage mitigation became increasingly apparent. Efforts by White ( i 9 6 0 ) , Kates and White ( l 9 6 l ) and Kates (1962) assisted in widening the choice among alternative flood management adjust-ments by pointing to the apparent advantages of floodproofing, landuse regulation and flood warning systems. Kates (I962) was instrumental i n demonstrating the factors involved i n constraining the choice of adjustments to floods made by private and public floodplain managers. Individual perception emerged as a c r i t i c a l factor in conditioning response to flood hazards. Adjustments made to a flood problem are conditioned by the managers'perception of the physical characteristics of the hazard and the perceived technical and economic f e a s i b i l i t y of various adjustments available to cope with i t . The studies of White and his co-workers assisted in shifting the emphasis from structural flood management toward a behavioral approach emphasizing integrated choice from among a broad range of flood management 6 . tools (Table l ) . According to White (1979) the trend i s currently away from reliance on manipulating floods to a comprehensive consideration of various measures to di s t r i b u t e losses, a l t e r floodplain use as well as possible f l o o d control. Nonstructural f l o o d management strategies have only recently been given the encouragement required to achieve comprehensive fl o o d damage reduction ( P i a t t , 1979)-Perhaps more s i g n i f i c a n t i n directing the emphasis away from fl o o d control has been the application of economic evaluation to demonstrate the economic e f f i c i e n c y of nonstructural flood management strategies r e l a t i v e to f l o o d control. Debate over optimum floodplain investment and use r e l i e d on economic analysis to resolve issues (Lind, 1 9 6 7 ; Whipple, I 9 6 8 ) . James ( 1 9 6 7 ) described a systematic procedure f o r determining the optimum combination of structural and nonstructural measures f o r f l o o d control according to the c r i t e r i o n of economic efficiency. James and Lee ( 1 9 7 1 ) demonstrate the design framework f o r evaluating t e c h n i c a l l y f e a s i b l e f l o o d management alternatives i n combination f o r p a r t i c u l a r f l o o d hazard types. Advocating the use of an economic approach f o r floodplain planning, James ( 1 9 7 2 ) demonstrates that benefit-cost c r i t e r i a i s essential i n determining the elements i n a u n i f i e d program f o r managing f l o o d losses. Economic c r i t e r i a are applied to determine whether development should be permitted i n a given floodplain as well as to determine whether structural measures should be b u i l t to protect the floodplain. Rising costs of structural measures and continued increases i n annual flood damage as well as environmental and other s o c i a l concerns have given further encouragement toward nonstructural strategies through the 1970's. These are viewed to off e r f l e x i b i l i t y , and adaptive c a p a b i l i t i e s over t r a d i -t i o n a l f l o o d control and more importantly, seek to treat the root of the 7 . TABLE 1 STRATEGIES AND TOOLS FOR ACHIEVING FLOOD HAZARD REDUCTION NONSTRUCTURAL A. Modify S u s c e p t i b i l i t y to Flood Damage and Disruption 1 . Floodplain Regulations a. state regulations f o r f l o o d hazard areas b. l o c a l regulations f o r f l o o d hazard areas ( 1) zoning ( 2 ) subdivision regulations ( 3 ) building codes (4) housing codes ( 5 ) sanitary and well codes ( 6 ) other regulatory tools 2 . Development and Redevelopment P o l i c i e s a. design and location of services and u t i l i t i e s b. land r i g h t s acquisition and open space use c. redevelopment and renewal d. permanent evacuation 3 . Disaster Preparedness and Response Planning 4 . Floodproofing 5 . Flood Forecasting and Warning Systems and Emergency Plans B. Modify the Impact of Flooding on Individuals and the Community 1. Information and Education 2 . Flood Insurance 3 . Tax Adjustments k. Flood Emergency Measures 5 . Postflood Recovery STRUCTURAL C. Modify Flooding 1 . Dams and Reservoirs 2 . Dykes, Levees and Floodwalls 3 - Channel Alterations 4 . High Flow Diversions and Spillways 5 - Land Treatment Measures 6 . On-Site Detention Measures SOURCE: A Unified National Program f o r Floodplain Management, January 1979 U.S. Water Resources Council, Washington, D.C. 8. problem rather than the symptoms. Local f a c t o r s have become i n c r e a s i n g l y important, and consequently, the information requirements f o r evaluating f l o o d p l a i n plans have changed. S i t e s p e c i f i c information i s required f o r the f l o o d hazard but, i n addition s o c i a l features of the target population must also be incorporated i n t o the i n v e s t i g a t i o n (James, 1973)- P u b l i c involvement i s viewed as prime r e q u i s i t e to developing successful f l o o d management plans. The trend, evident i n the s t r a t e g i e s evolved to manage floods high-l i g h t s at l e a s t f i v e important features: ( l ) Program design can draw from a wide conceptual range of f l o o d damage reduction measures, and these can be implemented i n various combinations, and at various times within the planning frame of reference. (2) The designation of program elements depends upon some systematic means of evaluating s o c i a l b e n e f i t s r e l a t i v e to costs. (3) Although the s t r u c t u r a l approach i s not regarded with the same esteem i t once held, i t i s not r u l e d out from consideration. More often i t i s used i n combination with other measures. (4) Long term planning tends to favour the nonstructural approach predominantly because of i t s p o t e n t i a l f o r f l e x i b i l i t y , a d a p t a b i l i t y , r e v e r s i b i l i t y and e f f e c t i v e -ness demonstrated i n v a r i e d s e t t i n g s . (5) Emphasis on nonstructural f l o o d management s t r a t e g i e s have i n t e n s i f i e d the information requirements f o r planning, n e c e s s i t a t i n g more l o c a l i z e d refinements i n formulating p o l i c y elements. Flood management p o l i c i e s appear to have evolved to a point where they seek optimal s o c i a l adjustments to various f l o o d hazards, not by s t r u c t u r a l control alone but through such measures i n combination with nonstructural approaches. 9. B. A Framework f o r Flood Damage Reduction P o l i c y In l i g h t of the foregoing review, i t i s advantageous at t h i s point to set out the conceptual framework f o r t h i s study. Flood management p o l i c i e s seek to designate a strategy which endeavors to provide f o r an appropriate l e v e l and pattern of adjustments to a flood hazard. These include practicable nonstructural and structural elements, designated i n l i g h t of the flo o d hazard. The appropriate combination and degrees of the practicable alternatives are derived by weighing the benefits and costs i n both quantitative and qu a l i t a t i v e terms, and comparing them with a view toward maximizing human welfare. In so doing, relevant information i s set f o r t h f o r choice i n the p o l i t i c a l process f o r the design of a s o c i a l l y optimal flood management policy. The policy may not seek to minimize or reduce fl o o d damages but at least the benefit-cost framework w i l l provide an objective way to i n d i -cate the trade-offs to be made i n the process. Flood damage reduction p o l i c i e s seek to develop the best rather than the least use of the floodplain. Comprehensive fl o o d damage reduction programs incorporate: a l l measures f o r planning and action that are needed to determine, implement and revise plans f o r the wise use of floodplain lands and t h e i r related water resources f o r the welfare of society (Goddard, i n Dougall, 1969). I l l Study, Objectives and Scope This study has four sequential objectives i n investigating f a l l floods i n the Lower Skeena River Region. These are: ( l ) to describe the physical characteristics of the f a l l f lood hazard i n the Lower Skeena Region, 10. (2) to describe and assess the current approach for managing floods in the region of the Lower Skeena, (3) to exemplify the current situation i n the Lower Skeena Region using New Remo as a case study, (4) to devise and describe a strategic approach to manage f a l l floods at New Remo. Hydrologic analysis of the flood problems in the Lower Skeena comprises the essence of Chapter 2 . Hydrologic data i s derived from Water Survey of Canada records of streamflow for Br i t i s h Columbia to 1979- Meteorologic characteristics of the 1978 flood on the Skeena are obtained from a report by Schaefer (1979) while hydrologic features of the same flood are taken from a congruent Water Survey of Canada ( 1 9 7 9 ) report. Flood frequency analysis i s applied to streamflow data for the Skeena and i t s tributaries i n assessing the relative magnitudes of spring and f a l l floods i n the Lower Skeena Region. Annual reports of the Water Investigations Branch have been instru-mental i n describing the features of the Province's flood damage prevention program. Synthesis of the current management approach in the Lower Skeena Region was also f a c i l i t a t e d by information provided personally by staff involved with Floodplain Planning and Management in the Waters Investigation Branch. Chapter 3 deals with the current flood damage prevention program in the Lower Skeena Region. Information on the human dimension of the flood problem i s based on unpublished data and documents provided by the staff of the Regional D i s t r i c t of Kitimat-Stikine in Terrace. Personal interviews with staff planners of the Regional D i s t r i c t and Municipality contributed significant information on the flood hazard and i t s management in local communities of the Skeena 11. Region, especially New Remo. Personal observations were made in the New Remo community and Lower Skeena Region during summer fieldwork of the previous year. Interviews conducted among residents in the community have been helpful i n supporting the conceptualization of the flood problem in New Remo for this study and in framing the limits of current flood management approach i n Chapter 4. In ligh t of the f a l l flood features i n New Remo, a new strategy for selecting the appropriate pattern and degree of adjustments to reduce flood damage from f a l l floods i s set forth i n the la t t e r half of Chapter 4. The flood damage framework synthesized i n Section II of this chapter i s used as a guide in designating suitable measures to manage the problem. Evaluation of alternative adjustments for New Remo i s based on qualitative technical-economic c r i t e r i a reflecting the primary objective of flood damage reduction. CHAPTER 2 12 THE FLOOD HAZARD IN THE LOWER SKEENA RIVER REGION I Environmental Characteristics A. Setting The Skeena, a major coastal r i v e r , 510 kilometres long, draining approximately 52,000 square kilometres, yields a mean monthly discharge of 900nrVsec. Headwaters r i s i n g i n the Skeena Mountains of northern B r i t i s h Columbia, flow south to merge with the flow of the Satsut River from the Omineca Mountains (Figure l ) . The Kispiox, draining the eastern flank of the Coast Mountains meets the Skeena while just downstream the Babine, r i s i n g from lakes on the Nechako Plateau, provides drainage from the east. The Bulkley, the southern major t r i b u t a r y of the Skeena, meets i t at Hazelton completing drainage of the Nechako Plateau Lakes. The Skeena turns west at Terrace and i s joined by a number of t r i b u t a r i e s including the Zymoetz, Kitsumkalum, Zymagotitz and Exchamsiks Rivers which r i s e with short steep courses i n the Coast Mountains. From Terrace to Chatham Sound, the Skeena meanders ribbon-like f o r 100 kilometres across a broad a l l u v i a l f l o o d p l a i n , 2 to 10 kilometres wide inset within a f j o r d , rimmed by 2000 metre high peaks of the Coast Mountains. Drainage within the Skeena River system incorporates runoff from two broadly d i s t i n c t i v e physiographic regions. The I n t e r i o r Plateau repre-sented by the Skeena and Omineca Mountains, Nass Basin and Nechako Plateau provide discharge to the Skeena upstream from Terrace. Rocks within t h i s physiographic diversion are l a r g e l y f l a t l y i n g and gently folded metasedi-mentaries and volcanics of Jurassic age (Holland, S.S., 1976). Rivers F IGURE I Skeena River D r a i n a g e Bos in 14. have established deeply i n c i s e d , s t r u c t u r a l l y controlled valleys i n response to post - g l a c i a l i s o s t a t i c u p l i f t and drainage. Numerous large and small lakes have been integrated within the present stream pattern through stream piracy and capture, p a r t i c u l a r l y i n the v i c i n i t y of Nechako Plateau i n the headwaters of the Bulkley. The Coast Mountains, a d i s t i n c t batholith of intruding granodiorite run northwest to southeast across the lower portion of the Skeena basin. Streams r i s i n g within t h i s region are short, steep and r e l a t i v e l y young i n r e l a t i o n to the lapse of post g l a c i a l drainage. Modified maritime conditions p r e v a i l throughout the basin a l l year as a result of westerly winds forcing mild, moist a i r masses inland from the P a c i f i c . Orographic influences related to the mountainous t e r r a i n cause temperatures to decrease and p r e c i p i t a t i o n to increase with a l t i t u d e and at the same time they produce an easterly moisture gradient across the Skeena basin. A coastal climate extends over the lower region of the Skeena to near Terrace while northern and eastern parts experience a more seasonal and d r i e r climate. Climatic stations within the Skeena region demonstrate the variable nature of temperature and p r e c i p i t a t i o n from west to east (Figure 2). At Kitimat and Prince Rupert mild wet winters are accompanied by cool s l i g h t l y d r i e r summers. Terrace, however, located 120 kilometres inland, experi-ences s l i g h t l y colder winters (mean January temperature -6 C) and hot summers (mean July temperature 16 C) reminiscent of greater climatic extremes within the i n t e r i o r parts of the Skeena basin (Figure 2). Along the coast and dnland through the Coast Mountains, p r e c i p i t a t i o n reaches a maximum i n l a t e autumn and early winter, with snow becoming the predominant form as winter sets i n . Inland, p r e c i p i t a t i o n i s lower and more evenly d i s t r i b -uted through the year. However, due to subfreezing temperatures throughout November to March, snow accumulates potential runoff u n t i l l a t e spring. Mean FIGURE 2 Monthly Tempera tures and Prec ip i t a t i on 15. the Skeena 4004 2004 4004 20 0 K i t i m a t J • F M -A M J j A S O N D 1 • • 1 « 1 ~ I • 1 » * J F M A M j j A S O N D -10 e r r a c e 400 2004 400 m m 200 i 1 — • — i — « — > — i i —i t—i— ~1 o J F M A M J J A S O N D J F M A M J J A S O N D 400 i S m i t h e r s 400 4 200 4 J F M A M J J A- S O N D 1 6 . B. Hydrology and Flood Conditions Seasonal cli m a t i c conditions together with the physiographic nature of the Skeena River basin combine to produce two peak runoff situations. The 'spring freshet', an annual high flow condition, usually occurs i n the months from May to July. During t h i s time of year streams within the head-waters of the Skeena swell with snowmelt runoff. The volumes carried depend lar g e l y on antecedent snow pack accumulation over the previous winter and the rates at which melting occurs during the months of A p r i l and May under the influence of sustained maritime polar a i r masses. These bring unsea-sonably warm and moist weather to the region which often r e s u l t s i n rapid melting of the snowpack. Severe floods, as a re s u l t of these conditions, are regional i n extent and have occurred i n 1 9 3 6 , 19^8 and 1 9 7 2 . These spring freshet floods appear to correlate with high flow conditions through-out the P a c i f i c Northwest i n these years and i n p a r t i c u l a r with those i n the Fraser System (Sewell, I 9 6 5 ) . Annual hydrographs f o r the Skeena and i t s t r i b u t a r i e s demonstrate the predominance of the spring freshet, peak flow season (Figure 3). However, on most of these r i v e r s there i s a second high runoff season i n autumn, when r i v e r s swell i n response to intense r a i n f a l l , p a r t i c u l a r l y i n the Coast Mountain region of the Skeena basin. These storms are c h a r a c t e r i s t i c of the coastal climate of B r i t i s h Columbia and the orographic effects gen-erated by the Coast Mountains (Hare and Thomas, 1 9 7 ^ ) . An upper atmo-spheric s h i f t i n c i r c u l a t i o n to a southwesterly flow brings unseasonably mild and moist weather toward the coast. Weakening of the a r c t i c front and orographic l i f t i n g pushes freezing l e v e l s above 3 0 0 0 metres which f a c i l -i t a t e s the onshore movement of disturbances. As a result these take the form of deep cyclonic depressions, edging slowly eastward across the Coast Mountains and the Skeena basin. R a i n f a l l i s intense and sustained f o r a 17. FIGURE 3 Hydrographs for the Skeena and Tribute r i e s 1 0 0 0 0 0 SKEENA 18. number of days as a number of such storms are,drawn into the c i r c u l a t i o n pattern. Storms of t h i s type have been responsible f o r r a i n f a l l s i n excess of 10 centimetres within a 24 hour period (Schaefer, 1979)- Such intense r a i n and i t s consequent effects within small steep catchments of coastal streams produces f l a s h floods; some of these have been devastating i n other parts of the P a c i f i c Northwest. C. Flood Types In the Skeena River system, headwater t r i b u t a r i e s predictably produce freshet snowmelt peak flows i n l a t e spring while lower t r i b u t a r i e s i n the v i c i n i t y of Terrace add another dimension to flooding by contributing peak runoff during l a t e autumn. Both effects are apparent i n the hydrographs compiled from mean monthly discharges f o r the Skeena and i t s t r i b u t a r i e s (Figure 3). In these graphs most of the v a r i a b i l i t y i n peak flows i s concealed by averaging. The v a r i a b i l i t y through the range of discharges f o r many of the lower t r i b u t a r i e s amounts to a factor of 10 times. Conse-quently flood peaks i n autumn periods can and often do exceed those asso-ciated with the spring freshet (Figure 3)> However t h i s i s not the case f o r the Skeena and i t s t r i b u t a r i e s upstream from Terrace. Sig n i f i c a n t differences are also apparent i n the duration and inundation patterns of spring compared to autumn floods. Spring freshet runoff requires a longer period to b u i l d toward peak flow conditions as discharge i s gathered by the Skeena from i t s upper basin over many days or even weeks of snowmelt. When i n flood, the r i v e r s spread excessive discharge from the main channel by s p i l l o v e r onto the adjacent floodplain. Low l y i n g swales and sloughs f i l l as both s p i l l o v e r and r i s i n g water table conditions extend floodwaters toward the floo d p l a i n margins on both sides of the r i v e r . The hydraulic 1 9 . FIGURE 4 Flood Runoff vs Drainage Area in the Skeena / < z &r / <W xrf " t r r LU <& * w / / / O / BULK LEY « s I l.ll Ml. • 1 IM ol / S 7 ^ / ZYMQETZ < Z ) CO H o / o / ' T / ' / / G- / HAMS IKS M AGQT1TZ Or l © x Ul © >-N •9/ O r / o o o o C N O O O O o o o m o o o C N o o m o o CN o o o o o C N o in © • [ L u b s / s p v a y v / ddONny a o o i d o n o CN wnwi xvw c h a r a c t e r i s t i c s of r i v e r channels, upon which i t s discharge capacity depends, often become modified through erosion of saturated and weakened bank materials along the main stem of the flooding current. Thus during sustained, high discharge, flooding and erosive damage emanates from the permanent r i v e r channels and i s l a r g e l y confined within a narrow floodplain zone. Moreover, fl o o d potential during the spring freshed period can be anticipated with considerable certainty by monitering r i v e r flows upstream and assessing the impact of p r e v a i l i n g weather conditions on snowpacks within contributing catchments. F a l l floods are a different matter. Severe and often l o c a l i z e d r a i n -storm runoff requires s i g n i f i c a n t l y l e s s time f o r i t s peak flows to appear i n mountainous streams whose catchments are i n the Coast Mountains. Thin s o i l cover, steep slope gradients, outcrops of impervious rock and at high a l t i t u d e s antecedent snow accumulation combine with the intense r a i n f a l l rate to produce a flashy runoff response. Often accompanying the high run-off are slope f a i l u r e s and mudflows clogging and diverting stream courses with debris. Although smaller i n area, these catchments are capable of producing instantaneous peak flows i n the autumn that exceed those occurring during the spring freshet. Flooding occurs i n association with impeded surface runoff and streamflow debris accumulation. The pattern although not necessarily random, i s highly disorganized occurring on t r i b u t a r y floodplains, stream confluences and i n g u l l i e s which were ess e n t i a l l y dry before the storm. Much of the flooding l i e s outside the common areas flooded by the Skeena River and i s not readily disclosed by monitering i t s flow. Furthermore, anticipation of these f l a s h floods i s hampered by t h e i r short f l o o d to peak r i s e of a matter of hours and the complex influence of washouts and debris damming t h e i r downstream conveyance of flow. Thus, i n the Skeena River system, two d i s t i n c t types of flooding takes place at di f f e r e n t times of the year. Each type arises from a different set of contributing conditions and produces a d i s t i n c t i v e type of flood. The spring freshet floods involve extensive runoff and y i e l d a low rate of flo o d discharge per unit drainage area (Figure 4). Such streams i n the Skeena River system r e f l e c t drainage from the I n t e r i o r mountains and plateaus. Higher rates of runoff to drainage area occur on Coast Mountain t r i b u t a r i e s of the Skeena primarily associated with flashy autumn floods. The Human Dimension A. Flood Prone Lands and Communities Approximately 16,000 people reside i n the Lower Skeena region i n the v i c i n i t y of Terrace, which i n 1976, had a population of just over 10,000 (Province of B r i t i s h Columbia, 1977t>). The remainder of the population reside on small farms, Indian Reserves and towns along the banks of the Skeena and i t s t r i b u t a r i e s (Figure 5 ) -The majority of residents, including those l i v i n g i n Terrace, inhabit floodplain lands. V i r t u a l l y every type and size of settlement within the region i s affected by flooding. Some, however, are extremely f l o o d prone, having experienced numerous severe floods i n t h e i r history. Despite fl o o d experience and the incursion of damages, these communities continue to persist and thr i v e . H i s t o r i c a l l y , settlement was attracted to the floodplains of the region and the enhancement and expansion of landbased transportation has reinforced floodplain settlement. The Skeena and Bulkley valleys have served the region as a natural transportation corridor and have even given added emphasis i n t h i s regard 23. by developments during the l a s t 30 years. Both highway and r a i l l i n e follow the course of the r i v e r s from Prince Rupert on the coast to Prince George i n the i n t e r i o r of the province. These frequently are situated on floodplains and often cross the major r i v e r s and t h e i r t r i b u t a r i e s i n transecting the region. Recent developments i n the fore s t , mining and marine resource industries i n the region have placed added value on the connective linkages (Province of B r i t i s h Columbia, 197?b). A c c e s s i b i l i t y afforded by transportation developments and opportunities associated there-with have assisted i n spreading settlement along floodplains of the Skeena and i t s t r i b u t a r i e s . Many of the smaller communities i n the v i c i n i t y of Terrace offer lower cost land and amenity values not accessible i n the municipality. Rapid population growth, although concentrated l a r g e l y i n Terrace (Province of B r i t i s h Columbia, 1977b), produces s p i l l o v e r effects i n many of these communities. Floodplain occupance not only persists but has been increasing through the past decade. Approximately 17,000 hectares of po t e n t i a l l y arable land occur on the a l l u v i a l s o i l s i n the v i c i n i t y of Terrace; less than one t h i r d of t h i s area occurs i n Class I I I or better (Province of B r i t i s h Columbia, 1977t>). The residual area remains forested. Approximately 200 residents i n the region are classed as farmers and 30 farms u t i l i z e on 500 hectares. Much of the farming i s carried out to supplement seasonal income i n resource industries. Many of these farms are located on the floodplains of the Skeena and i t s t r i b u t a r i e s and hence are prone to flooding. Within the v i c i n i t y of Terrace there are nine communities i n which flooding poses a problem (Table 2 and Figure 5) . Floods occur either i n spring or f a l l and affect s i g n i f i c a n t parts of each of these communities situated on the floodplains. Major, regional floods, occurred i n spring COMMUNITY TABLE 2 FLOOD PRONE COMMUNITIES IN THE LOWER SKEENA REGION RIVERS RESPONSIBLE FLOOD SEASON(S) MAJOR  FLOOD YEARS COMMUNITY OCCUPYING POPULATION FLOODPLAIN Hazelton Bulkley Skeena April-June 1 9 3 6,48,64 , 7 2 1000 50 Cedarvale-Kitwanga Skeena April-June 1 9 3 6,46,64 , 7 2 500 20 Usk Skeena April-June 1 9 3 6 , 4 8 , 7 2 500 75 Lakelse Lake Lakelse Lake & Tributaries Oct-Dec 1935,58 65,74,78 500 10 Terrace Skeena April-June 1936,48 ,72 11,000 20 Dutch Valley Kitsumkalum & Tributaries April-June Oct-Dec 1964,72 1923,74,78 50 100 New Remo Skeena Zymagotitz April-June Oct-Dec 1936,46 ,72 1961,74,78 150 100 Copperside-K i t s e l a s Zymoetz & Tributaries April-June Oct-Dec 1974,78,79 500 50 Old Remo Skeena April-June 1936,4S,72 100 100 •"•Estimates based on i d e n t i f i c a t i o n and delineation of approximate geomorphic floodplain l i m i t s without regard to flo o d frequency. These have been taken from maps of the floodplains i n the region and data from the Kitimat-Stikine Regional D i s t r i c t . during 1936, 19^8 and 1972 when the Skeena was responsible f o r flooding communities such as Hazelton, Gedarvale, Usk and Old and New Remo. Sign i f i c a n t f a l l floods occurred i n 197^ and 1978 i n f l i c t i n g damage on communities situated on the trib u t a r y floodplains of the Skeena, Gopperside, Dutch Valley, Remo and Lakelse Lake communities are affected by the Zymoetz, Kitsumkalum, Zymagotitz Rivers and Lakelse Lake t r i b u t a r i e s respectively. New Remo, situated at the junction of the Zymagotitz and Skeena Rivers, displays a unique s u s c e p t i b i l i t y to flooding on two counts within a given year. Population growth and associated development pressures have tended to aggravate f l o o d problems i n many of these communities. Economic advantages have encouraged the further conversion of floodplain land to agriculture, r e s i d e n t i a l and other land uses which have a greater potential f o r f l o o d damage. Collective action was taken by the pro v i n c i a l government to control and manage the development of floodplains i n the early 1970's. Their mandate i s to a s s i s t i n achieving f l o o d damage reduction. The current p o l i c y i s directed toward t h i s end but has c r i t i c a l shortcomings based on events and actions occurring since the 1978 floods. B. History of Floods and Damages At least ten.damaging floods have occurred during the past 50 years, recurring on average every four to f i v e years. Some communities have experienced damage from floods twice within the same year (Table 2 ) . The largest magnitude fl o o d on the Skeena River, near Terrace, occurred i n 1936 while the most damaging flood occurred i n the same area during 1978. Floods i n some years such as 19^8 and 1972 correlate with floods which occurred simultaneously on other r i v e r s i n B r i t i s h Columbia, especially 26. the Columbia and Fraser. Snowmelt runoff generated these floods i n response to delayed and rapid melting of extensive mountain snowpacks within the P a c i f i c Northwest Region. Other floods i n 1961, 1974 and 1978 were l i m i t e d to the Lower Skeena Region and these occurred i n response to sustained, heavy f a l l r a i n s , accompanying above normal seasonal temperatures. Although the gaging station of Usk has the longest record of Skeena River discharge, extending from 1928 to the present, no observation i s recorded f o r the f l o o d conditions during 1936 as the gage was removed by floodwaters (Water Survey of Canada, 1979"b; Asante, 1972). Correlations with Fraser and Columbia River flood conditions and flood routing simulation have been used to estimate the flow magnitude involved i n the 1936 f l o o d i s believed to have a 200 year recurrence i n t e r v a l (Marcellin and Beg, 1974) and r e l i c s of i t s impact derived from interviews and surveys have been employed-to compile information necessary f o r the construction of floodplain maps f o r the Lower Skeena Region. However the exact magnitude of the f l o o d i s unknown as the gage was destroyed during the 1936 flood (Asante, 1972). During the 1936 f l o o d , water depths exceeded 2 metres on the lower terrace i n Hazelton causing minor damage while major damage was incurred downstream and west of town where floodwaters eroded s o i l and removed almost one dozen homes (Marcellin and Beg, 1974). Near Cedarvale floodwaters extended to depths of 1 to 2 metres with erosion l o c a l i z e d on the north bank of the Skeena River. Farther downstream at Usk, the 1936 f l o o d breached the railway embankment separating the town from the r i v e r and reached d e a t h s of 4 to 5 metres throughout the main streets of town. At Terrace, only the lowerest most parts of the floodplain were flooded. Floodwaters covered Braun's Island, Ferry Island and L i t t l e Island and most of the land south of Graham Avenue to depths of 2 to 3 metres while downstream the 27. e n t i r e community of Remo was inundated by the combined floodwaters of the Skeena and backwater e f f e c t s on the Zymagotitz River to depths exceeding 2 metres. Recession of the floodwaters took almost two weeks at some of the s i t e s i n 1936. Damages were severe and extensive throughout the Lower Skeena Region (Asante, 1972). Communities were i s o l a t e d by a severed r a i l l i n e and the only bridge across the Skeena, at Terrace took almost one year to restore. Probable impacts within the region would have been even more severe, were i t not f o r the small number of inhabitants at the time. Floods i n 1948 and 1972 s i m i l a r i n nature were not as severe but corre-l a t e d with widespread f l o o d conditions i n the Fraser and Columbia River basins. In 1948 floodwaters inundated only two small communities at Hazelton and Remo while i n 1972, the second l a r g e s t f l o o d of record on the Skeena, inundation was more extensive but damages remained r e l a t i v e l y minor (M a r c e l l i n and Beg, 1974). By 1972, population i n Terrace and communities along the Skeena had grown beyond 10,000, heightening the impacts of floods and aggravating the hazard condition through f l o o d p l a i n encroachment. A f l o o d of s i m i l a r magnitude to that of 1936 would have been devastating ( M a r c e l l i n and Beg, 1974). 1974 brought the onset of a d i f f e r e n t set of f l o o d conditions through-out the region. Heavy, sustained r a i n f a l l during an unseasonably mild s p e l l i n October generated widespread f l o o d conditions on many of the t r i b u t a r i e s of the Skeena near Terrace. The Kitsumkalum, Zymagotitz and Zymoetz Rivers reached the highest stages experienced during t h e i r short record of hydrologic observation (Water Survey of Canada, 1979^ 0• Flooding along these r i v e r s a f f e c t e d communities which had grown up aware of the Skeena River f l o o d hazard and apparently enjoyed a r e l a t i v e l y safe, f l o o d f r e e l o c a t i o n p r i o r to 1974. Although the floodwaters were not as deep as 28 . those encountered i n e a r l i e r spring floods, i t t r a v e l l e d with greater v e l o c i t i e s causing extensive erosion and building numerous debris dams which aggravated the extent of floodwater inundation. Claims f o r f l o o d damage compensation were lodged from numerous communities within the region, however the' majority were submitted from Remo where flooding was severe as the Skeena and Zymogotitz combined to inundate almost the same area flooded i n 1978. The 1978 f l o o d occurring only four years l a t e r and s i m i l a r i n nature to that of 1974, caused the most-extensive f l o o d related damages to date. Despite previous f l o o d experience, floodwaters caught residents and public o f f i c i a l s by surprise. As i n 197^ , the Skeena River was not involved d i r e c t l y i n flooding and the meteorologic circumstances were reminiscent of those p r e v a i l i n g i n 197^ (Shaefer, 1979)- The actions taken i n the wake of the 1978 f l o o d , l i k e those following 197^, tended to maintain and restore community momentum i n the region. Pervading attitudes regarded the f l o o d as a 'freak', circumstance and community s p i r i t sought to maintain the status quo (Scanlon, et a l , 1979). P r o v i n c i a l programs of restoration and compensation along with federal funding reacted to community concerns and harriedly buttressed the status quo. I t i s highly l i k e l y that i f a f l o o d of s i m i l a r magnitude were to occur i n the near future, flood damage would exceed the figure f o r 1978. The scope of the prevailing f l o o d management strategy may require extensive a l t e r a t i o n to f a c i l i t a t e i t s achieving a more comprehensive reduction i n f l o o d damage. A f i r s t step i n t h i s regard i s an assessment of f l o o d r i s k s (Linsley, Kohler and Paulhus, 1 9 78 ) . In regard to the Lower Skeena Region, t h i s implies a d i s t i n c t i o n between the hydrologic characteristics of f a l l and spring floods involved within the dual nature 29. of the fl o o d problem. Although the seasonal nature of flooding i n the region seems to be a common understanding, fl o o d frequency assessments, designating f l o o d r i s k s have often not acknowledged the differences between r a i n floods and snowmelt floods i n the annual fl o o d series (Water Survey of Canada, 1979t>; Water Survey of Canada, 1972). Consequently, s i g n i f i c a n t uncertainty i s associated with p r o b a b i l i t i e s assigned to floods experienced within the h i s t o r i c a l record. C. Recent Flood Experience (a) Characteristics of the 1 9 7 8 Flood Serious flooding on the lower t r i b u t a r i e s of the Skeena River near Terrace during l a t e October, 1 9 7 8 occurred i n response to a multi-day r a i n -f a l l event (Shaefer, 1979). The storm dropped 221.1 mm of r a i n at the Terrace Airport while up to 4-07 mm f e l l near i t s centre around Kitimat to the south. An area of almost 52,000 square kilometres received over 220 mm through the storm's two day duration. The return period was estimated to be i n the 80 to 100 year range (probability .013 to . 0 1 0 ) . The anticedent weather conditions through the month of October played a major role i n the development of the storm characteristics (Schaefer, 1979). However these conditions are not unusual f o r t h i s time of year i n t h i s region of the Coast Mountains (Hare and Thomas, 1974-). The antecedent meteorologic conditions contributed to i n t e n s i f y i n g orographic effects by slowing the storm's passage and concentrating i t s track south of Terrace (Figure 6 ) . Through October freezing l e v e l s had averaged near 1500 metres, r i s i n g to 3000 metres during two short mild s p e l l s , while p r i o r to the storm of October 2 9 , they had f a l l e n to 1000 metres. During the month l i t t l e snow had f a l l e n . At the beginning of the storm, the freezing l e v e l was l y i n g 30. F I G U R E 6 Isohyetal Map of the October„1978 S t o r m (after Schaefer,1979) 31. above 3000 metres. On October 2 9 , a high pressure ridge lay across the north coast fo r c i n g a strong f r o n t a l zone southward ahead of a deep low over Alaska. On October 3 0 , the front was situated over the Queen Charlotte Islands and aligned from northeast to southwest, beneath a warm flow of moist a i r a l o f t . The front remained quasi stationary as at least three d i s t i n c t f r o n t a l waves moved inland across the Coast Mountains. F i n a l l y on November 2 , the front s h i f t e d and cold a i r invaded the region with freezing l e v e l s returning to 1000 metres and surface a i r temperatures cooling to near freezing. I n s t a b i l i t y associated with the cold front produced moderate showers i n the days that followed. However, the amounts were small compared to that which f e l l during October 29 to November 2 . Near Terrace, r a i n f a l l was measured on October 30 to be f a l l i n g at an average rate of 1 mm per hour (Shaefer, 1979). By the next morning the rate had increased steadily to 9 . 6 mm per hour. Over the 24 hour period (10 p.m. October 30 to 10 p.m. October 31) 114.8 mm f e l l , exceeding previous record f a l l s . Added to t h i s t o t a l a further 89.1 mm f e l l on November 1 producing a second record 24 hour f a l l . The recurrent p r o b a b i l i t i e s f o r the one day f a l l s ranged from .025 to .014 while the two day f a l l had a return pr o b a b i l i t y of .01 to .008 (Shaefer, 1979). On the basis of the magnitude of r a i n f a l l s , t h i s storm has a long recurrence indeed. However, these recurrence p r o b a b i l i t i e s are well within expectancy based on floodplain zoning c r i t e r i a aimed toward the 1 i n 200 year f l o o d on the Skeena and other r i v e r s (Sloan, 1974). By t h i s standard, the f a l l storm of 1978 cannot be regarded i n i t s e l f as extraordinarily severe and certainly not unique. The s t a l l e d low pressure system, responsible f o r the intense r a i n f a l l generated immediate hydrologic response within the catchments of the lower 3 2 . t r i b u t a r i e s of the Skeena and i n the adjacent Kitimat watershed. A l l of the streams carried peak flows on November 1 which exceeded those previously recorded during t h e i r r e l a t i v e l y short gaged history. The Skeena at Usk peaked l a t e r and di d not reach mean annual floodstage. Instantaneous peak discharges are tested f o r some of the streams near Terrace i n Table 3-TABLE 3 Instantaneous Peak Discharges, 1978 Flood November 1* Mean Annual Flood** Zymoetz River above Ok Greek 111,000 cfs 22 ,000 cfs Zymagotitz River near Terrace 18,700 cfs 5 ,900 cfs Exchamsiks River near Terrace 30,500 cfs 9 ,500 cfs Skeena River at Usk 150,000 cfs 159,000 cfs Estimates of return periods f o r the Zymoetz flood discharge range from 25 to 100 years (p = .04- to .01) while f o r the Exchamsiks, between 25 and 4-0 years (p = .04- to .03) and the Zymagotitz only 20 years (p = . 0 5 ) . The ^-Obtained from Water Survey of Canada, 1979, Preliminary Report on Terrace-K i t imat Flood of November, 1978 Environment Canada, Vancouver **Mean annual f l o o d i s the discharge exceeded every 2 to 3 years and represents the bankfull discharge. I f peak discharge exceeds mean annual f l o o d magnitude, r i v e r flow w i l l s p i l l onto the floodplain s i g n i f y i n g a flood. Estimates here are graphically determined from f l o o d frequency curves presented i n Figure 7 (Section I I I ) . 33-Skeena as mentioned above was not i n f l o o d during the storm but did receive higher volumes of flow than normally occur i n l a t e October (Water Survey of Canada, 1979a). Although the peak flows experienced i n the region were extreme, they do not represent discharges beyond the 1 i n 100 year return period, l e t alone the 1 i n 200 year recurrence i n t e r v a l . Using correlation methods to extend short gaging records over e a r l i e r years within the region, floods of greater magnitude can be inferred. These have return periods between 100 and 200 years (see Section I I I ) . Despite t h i s d i f f i c u l t y , the flood of 1978 was responsible f o r substanial and serious damage, unequalled during previous flooding. (b) Patterns of Flooding and Damages Strong, gusty winds associated with the rainstorm on October 30 and again on November 1 were responsible f o r numerous power outages, downed telephone l i n e s and windfelled trees. These developments preceded the flooding and contributed to a disruption of communications which may have further aggravated the impact of the storm (Scanlon et a l , 1979). Storm runoff damage began early on October 31 and i n t e n s i f i e d over the next three days i n direct response to the f a l l i n g r a i n . Early on the morning of October 31 a mudslide occured on Highway 16, approximately 40 kilometres east of Terrace. By mid-day a 60 metre segment of the road from Terrace to Lakelse had been washed out by floodwaters. In the afternoon, rains had washed rock onto the CN mainline between Terrace and Prince Rupert, d e r a i l i n g a passenger t r a i n . Later i n the day, problems had spread as small bridges were continuously washed out by floodwater and logging roads and power transmission l i n e s undermined. By the next day, Highway 16 had been affected by washouts and s l i d e s making i t impassible • 34. and small s l i d e s and washouts were common along the r a i l l i n e s . On the evening of November 1, a natural gas pipeline through the Telkwa Pass had been broken i n several places by floodwaters and s l i d e s . Flood effects and damages were culminating on Thursday as two men were k i l l e d when flood-waters washed two cars of a t r a i n into the Skeena River on the l i n e to Hazelton. At t h i s time road and r a i l transportation had been cut i n a l l directions from Terrace along with the supply of natural gas. Floodwaters j o i n i n g the Skeena had i s o l a t e d communities on tr i b u t a r y r i v e r s and flooding along Highway 16 had stranded t r a v e l l e r s . The floodplain lands resembled a c o l l e c t i o n of islands (Scanlon et a l , 1979). Most of the damages i n f l i c t e d by the floodwaters and associated erosion and mudslides occurred within approximately 35 kilometres of Terrace along the Skeena, Kitsumkalum, Zymoetz, Zymagotitz Rivers and other small stream floodplains and v a l l e y s . * Communities at Lakelse, New and Old Remo, Cedarvale, Rosswood and Greenville were severely flooded. Local residents sustained minor damages to residences and establishments. The bulk of the damage was incurred, by the i n f r a structure of the regional economy and components of the business and i n d u s t r i a l sectors which r e l i e d on communi-cation and transportation. Approximately $38 m i l l i o n of the t o t a l compen-sation expenditure by the B r i t i s h Columbia government was directed to restore transportation and communication f a c i l i t i e s and services. Although t h i s paper i s not intended to evaluate the economic impact of the f l o o d on the Terrace community and regional economy, some measure of the degree of disruption i s suggested by the length of time, restoration of f l o o d damages required. Complete normalization of power services took •^ Damages occurred i n the Kitimat Region, however, they are not investigated i n t h i s study. 35. almost two weeks. Telephone "communications were not as severely affected and were restored within a few days of the flood crests. Natural gas how-ever, required s i x days to be restored. The G.N. mainline was out of service f o r over a month. The roads and highways were plagued with over 25 bridges l o s t or damaged beyond repair. Restoration and repair efforts were hampered by i n a c c e s s i b i l i t y and further adverse weather conditions and i n many cases necessitated the costly use of helicopters i n place of conventional equipment. Although l o c a l labour was employed along with available equipment i n the repair e f f o r t s , the floods had a severe disruptive effect on employment and business i n the region. Forestry operations were cu r t a i l e d and l a y o f f s followed. Natural gas shortages l i m i t e d m i l l i n g operations. Stranded trucks and supplies on the highway and roads halted other businesses as well (Scanlon et a l , 1979). Some businesses, previously stocked, such as hardware and l i q u o r stores received a l i f t i n trade during the aftermath. As i s the case with many community adversities, some ind i v i d u a l s , i n p a r t i c -u l a r repair workers, gained while others l o s t . Some of the losses could not be adequately compensated i n f i n a n c i a l terms. (c) Implications The pattern of flooding and associated damages generated by the storm and f l o o d of 1978 were severe, p a r t i c u l a r l y along the Skeena and i t s t r i b u t a r i e s . The heaviest f l o o d damages were incurred i n the v i c i n i t y of the t r i b u t a r i e s of the Skeena; the Zymoetz, Zymagotitz, Kitsumkalum and Exchamsiks. On the v a l l e y slopes and on the floodplains of these r i v e r s much of the damage was caused by sl i d e s and debris clogging channels and re s u l t i n g i n washouts and inundation of flood prone land. Flood peaks rose very rapidly while r a i n was continuing to f a l l i n the area and produced 36. floodstages and discharges which exceeded previously recorded maxima on most of the t r i b u t a r i e s downstream from Terrace. The flooding, although severe and damaging, cannot be regarded as r e s u l t i n g from an extraordinary set of meteorologic conditions. Storms of t h i s type are common throughout the region of the P a c i f i c Northwest from Alaska to Northern C a l i f o r n i a . They generally occur i n the autumn and early winter months as moist, mild a i r intrudes the Coastal Mountain ranges pro-ducing intense, sustained orographic r a i n f a l l or snow (Hare and Thomas, 1979). Their magnitude varies temporally and s p a t i a l l y i n a random manner. The 1978 storm has a probable recurrence of 80 to 100 years while the flood discharges experienced on the r i v e r s of the Lower Skeena region have a return period of between 25 to 100 years. The magnitudes associated with these floods appear to be large enough to warrant attention and on the basis of t h e i r p r o b a b i l i t i e s floods of t h i s type should not be regarded as excep-t i o n a l l y rare events. In the f a l l of 1974, flooding occurred i n the Lower Skeena region under s i m i l a r meteorologic conditions and involved many of the same t r i b -u taries. Flood magnitudes were very near the discharges experienced i n 1978 (Water Survey of Canada, 1979a) .* The Skeena carried a larger discharge during t h i s f l o o d and s p i l l e d onto the floodplain at Terrace i n f l i c t i n g only minor damage as most of the floodwaters inundated lands to within the l i m i t s of the 1 i n 200 year flood. Downstream, minor flooding occurred, mainly at the confluences of the t r i b u t a r i e s with the Skeena. Landslides and washouts were not as widespread i n 1974 as they were four years l a t e r , * 0 c t o b e r 15, 1974 Zymoetz River 104,000 cfs October 15, 1974 Zymagotitz River 19,400 cfs October 15, 1974 Exchamsiks River 25,800 cfs October 10, 1974 Skeena River at Usk 209,000 cfs 37. probably due to the r a i n f a l l accumulating within the mountain catchments of streams over a two week period, rather than 2 to 3 days as i n 1978. The pattern of flooding i n 197^ resembled that which i s often associated with 'spring freshet* floods. The flood, therefore, may have reinforced ingrained perceptions concerning the timing and manner i n which r i v e r s i n the region f l o o d t h e i r banks. Furthermore, since i t s impact was r e l a t i v e l y minor i t may have l e d to a f a l s e sense of confidence i n existing flood damage reduction measures, a l l a y i n g floodplain managers' concerns f o r added flood control. Yet there i s reason to suspect that i n the recent history of the Skeena basin, r i v e r s have risen i n autumn at other times. The impact of the 1978 f l o o d suggests c r i t i c a l l i m i t a t i o n s p r e v a i l within the scope of the current f l o o d management approach i n the Lower Skeena region i n coping with the dual nature of the f l o o d problem. The p r e v a i l i n g strategy i s geared predominantly toward preventing damage from spring freshet floods and seems to ignore the features and impacts of f a l l r a i n floods. The extent and expense of damages incurred i n 1978 further suggests that floods of t h i s type might be of increasing regional importance, i f potential f l o o d damage i s allowed to mount through floodplain encroachment. I l l Assessment of Flood Risk A. Flood Frequency Analysis Flood: frequency "-curves derived from streamflow data i n Water Survey of Canada (1979b) are i l l u s t r a t e d on Gumbel probability paper i n Figure ?• The pattern among the Skeena and i t s t r i b u t a r i e s i s most s t r i k i n g . Headwater t r i b u t a r i e s ( i e . those r i s i n g i n the I n t e r i o r Plateau) consistently have gentler sloping frequency curves that those flowing to meet the Skeena from the Coast Mountains, implying associations with two d i s t i n c t p r o b a b i l i t y FIGURE 7 Flood Frequency Curves for the Skeena and Tributaries 1 0 1 M 1-5 2 - 0 5 10 20 5 0 - 100 R E C U R R E N C E INTERVAL y e a r s 39. d i s t r i b u t i o n s . In f a c t , there i s no l o g i c a l reason to lump spring freshet and f a l l r a i n floods into a single, annual series of instantaneous discharges. Resolution remains l i m i t e d by the short hydrologic records despite inclusion of both flood types i n a single series and most importantly, a smoothing effect i s introduced which suggests unfounded certainty i n the frequency d i s t r i b u t i o n . Despite the apparent c l a r i t y i n f i t t i n g a l i n e a r i z e d d i s t r i -bution to the annual f l o o d data, considerable uncertainty resides i n the sp e c i f i c a t i o n of recurrent f l o o d magnitudes, especially those large floods. Furthermore, there i s a sound argument, based on meteorologic factors, seasonality and hydrologic behaviour f o r retaining the d i s t i n c t i o n between spring freshet and f a l l r a i n floods i n assessing flood r i s k . Since these floods have been shown to be different i n these respects, there i s good reason to deal with them i n two different annual flood series, compiled by ranking the largest floods i n each seasonal series and subsequently computing recurrence i n t e r v a l s f o r p l o t t i n g positions on extreme value graph paper. In t h i s way the r i s k s of both spring and f a l l flooding can be assessed more r e a l i s t i c a l l y . B. Spring Freshet Floods vs F a l l Rain Floods Spring freshet floods are consistently greater than f a l l floods on the Skeena River. Tributaries such as the Zymoetz, Zymagotitz and Kitsumkalum experience larger floods i n f a l l during some of the years of record. Figure 8 i l l u s t r a t e s composite f l o o d frequency curves f o r these r i v e r s derived by separation of recorded floods into seasonal, annual series f o r f a l l and spring floods. F a l l f l o o d frequency demonstrates a different d i s t r i b u t i o n to that derived f o r spring floods. Furthermore, for.a given recurrence i n t e r v a l R E C U R R E N C E INTERVAL years 41. or frequency, the magnitude expected f o r f a l l floods i s consistently greater than spring floods above the mean annual f l o o d p r o b a b i l i t y of 0 . 5 0 . Beyond a recurrence i n t e r v a l of 20 years, the curves may inter s e c t , however, the short lengths of gaging records and the s t a t i s t i c a l uncertainty associated with curvelinear extrapolation, l i m i t the d e f i n i t i o n of these relationships to the observed f l o o d record. Figure 8 demonstrates that the Lower Skeena t r i b u t a r i e s experience f a l l floods of greater magnitude than spring floods. For the same frequency, rain generated floods are greater than those r e s u l t i n g from snowmelt. Although the a v a i l a b i l i t y of the hydrologic data l i m i t s some of the s t a t i s t i c a l r e l i a b i l i t y within these relationships, the pattern i l l u s t r a t e d i n Figure 8 confirms the importance of f a l l floods within the region. This i s p a r t i c u l a r l y important f o r floods recurring r e l a t i v e l y frequently, espe-c i a l l y those with frequencies of 5 to 20 years. Implications f o r Flood Management Floods occurring i n f a l l are physically different to those associated with regional snowmelt conditions i n spring through the Lower Skeena. These differences are important i n developing a practicable and ultimately an e f f i c i e n t strategy to manage flood problems i n the region. The physical nature of the flo o d hazard places a primary constraint on the feasible range of flood adjustments that can be made to reduce flood damages. From a management standpoint, i t i s c r i t i c a l to recognize the dual nature of the flood problem i n the Skeena Region and as well to appreciate the s p a t i a l and temporal variations i n the degree of the flo o d hazard. A strategy designed to reduce f l o o d damages should consider not only the t o t a l i n t e n s i t y of the f l o o d problem but also the r e l a t i v e i n t e n s i t i e s of i t s seasonal facets while facing variations i n the degree of the problem i n different l o c a l i t i e s . 42. Strategic f l o o d management i s based on an accurate and effective f l o o d forecasting and warning system (White, 1 9 7 5 ) ' Recognition of diagnostic meteorologic and hydrologic conditions i s fundamental i n regard to providing s u f f i c i e n t lead time to allow managers i n the flo o d prone areas to take emergency action against the l i k e l y f l o o d conditions and thereby reduce some of the damage that might otherwise occur. The characteristics exhibited by f a l l floods i n the Skeena demonstrate that diagnostic conditions are c l e a r l y different to those associated with snowmelt floods. Spring floods can be forecast up to a few days i n advance of the freshet crest moving down the Skeena. Extensive evacuation and emergency action can be e f f e c t i v e l y organized and employed to mitigate some of the damaging effects of the pending flood. In contrast, f a l l floods generated by rapi d l y moving rainstorms, are not as re a d i l y diagnosed nor i s there the same amount of lead time f o r emergency a c t i v i t i e s once pending f l o o d conditions are recognized. These differences imply that a new flood forecasting and warning system would be required to handle f a l l floods. A much t i g h t e r and e f f i -cient communication network would be needed to relay information on flood conditions throughout the Lower Skeena Region. Moreover, different i n s t r u -mentation f a c i l i t i e s would be needed to monitor r a i n f a l l and storm condi-tions as opposed tooheadwater snowpack and d a i l y weather conditions i n r e l a t i o n to snowmelt flooding. Structural f l o o d control measures to control spring floods w i l l probably not work very well against f a l l floods. Dyking along the Skeena does not prevent flooding from i t s lower t r i b u t a r i e s during high runoff conditions i n f a l l . F a l l floods affect different areas than those affected by spring floods. In some communities which experience both types of floods, l i k e New Remo, dyking of the entire community might be necessary to reduce f l o o d damage. Where f a l l floods are of greater magnitude and socio-economic significance, the design and i n s t a l l a t i o n of structural measures should be based on t h e i r physical characteristics. Nonstructural measures such as floodproofing, floodplain regulation and f l o o d insurance designed i n accord with spring freshet flooding w i l l necessitate some changes f o r communities where f a l l flooding i s a greater problem. I f f a l l flooding damage potential i s taken into account i n the determination of f l o o d insurance premiums, the premiums w i l l be more expensive than i f they were based on spring f l o o d features alone. In view of the more frequent f a l l floods of s i m i l a r magnitude, more costly flood-proofing measures would be j u s t i f i e d . For s i m i l a r reasons, evacuation measures, may prove more economically e f f i c i e n t i n reducing f l o o d damage, especially i n those communities where there i s a dual, seasonal f l o o d problem. Since f a l l floods have a greater magnitude f o r a given frequency s than spring floods, measures taken to reduce associated damages can be more expensive than those aimed at spring floods. Benefits f o r communities derived by averting f a l l f l o o d damage should exceed those f o r spring floods, making c o s t l i e r measures, economically e f f i c i e n t . In communities where there i s a dual f l o o d problem i t may be necessary to design appropriate f l o o d adjustments i n l i g h t of both f a l l and spring flood characteristics. Taking both types of floods into account could suggest a different mix of adjustments than treating each fl o o d problem separately. From the foregoing, three important points emerge: ( l ) Communities affected by f a l l flooding require different treatment to those affected by spring floods. L o c a l i t i e s where there i s a dual f l o o d problem comprise a t h i r d category. (a) Flood warning systems f o r f a l l floods need to be different than the spring freshet warning system and s p e c i f i c a l l y designed to take into account the short i n t e r v a l available. (b) Since potential damages from f a l l flooding are large, these damages combined with spring f l o o d damage potentials j u s t i f y much larger investments i n flo o d damage reduction measures than could be j u s t i f i e d on the basis of spring flooding alone. This would be p a r t i c u l a r l y s i g n i f i c a n t f o r the design of struc-t u r a l controls and evacuation. (2) The mix of adjustments appropriate i n coping with spring floods w i l l be different to that suited f o r f l o o d damage reduction associated with f a l l floods. (3) The design of strategies to deal with these different f l o o d problems within the Lower Skeena Region w i l l require s i t e s p e c i f i c information on both types of hazard f o r the design of e f f i c i e n t flood damage reduction. 45 CHAPTER 3 CRITIQUE OF THE CURRENT FLOOD MANAGEMENT APPROACH IN THE LOWER SKEENA REGION I Scope of P r o v i n c i a l Management of Floods A. Flood Damage Prevention Objectives Although the flo o d problem i n the Lower Skeena i s regarded by some (Scanlon et a l , 1979) as a national concern, management of the problem remains i n pr o v i n c i a l hands. To date, federal involvement has been ad hoc, p a r t i c u l a r l y following the 1978 flood event within the region. Federal funds provided much of the resources used i n restoration and assisted f l o o d victims i n compensating t h e i r f l o o d losses. However, the provincial government, by constitutional j u r i s d i c t i o n , assumes the r e s p o n s i b i l i t y of managing flood problems i n the region of the Skeena. Since 1976, the prov i n c i a l government has implemented a program of flood damage prevention within the Lower Skeena Region. The purpose of t h i s chapter i s to review the elements of the program, and to assess t h e i r effectiveness i n dealing with the f a l l f l o o d problem within the Skeena Region. The program currently applied i n the region i s nonstructural, r e l y i n g on flood forecasting and warnings, floodplain regulation and floodproofing. Outside of minor dykes around part of the old townsite of Hazelton, long since f a l l e n i nto disrepair, non of the fl o o d prone communities are protected from floods by dykes. In New Remo, recent construction has been completed on a t r a i n i n g berm f o r the Zymagotitz River. However, t h i s structure i s not designed to provide f l o o d control (Province of B r i t i s h Columbia, 1980). 46. The program of f l o o d damage prevention i s designated and implemented province-wide to achieve the following objectives: (1) To reduce the public danger due to flooding. (2) To reduce public costs associated with flood damages. (3) To achieve a poli c y within the l e g a l framework and implement i t province-wide. (4) To control development on f l o o d susceptible lands (Province of B r i t i s h Columbia, 1974). Although some may f i n d f a u l t with the stated objectives i n r e l a t i o n to t h e i r l i m i t e d scope, and even, perhaps i n terms of t h e i r constraining effects on p o l i c y , these are not assessed e x p l i c i t l y i n t h i s study. They are presented here as a basis f o r framing the features of the flo o d damage prevention program elements. The focus, i n l i g h t of these objectives, w i l l be with the designation and implementation of the program elements i n the Lower Skeena Region. B. Program Elements and Implementation Mechanisms Current f l o o d forecasting i n the Lower Skeena involves extensive monitoring of snowpack, weather and streamflow conditions to determine the magnitude of the spring freshet. Meteorologic and streamflow stations on the Skeena River System together with snow course stations throughout B r i t i s h Columbia are integrated by telecommunication f a c i l i t i e s to provide data f o r the Water Investigation Branch i n V i c t o r i a , on the potential and prevailing r i v e r and watershed conditions over the province (Province of B r i t i s h Columbia, 1976). During spring freshet, continuous d a i l y forecasts are made f o r r i v e r s and streams. Warnings are issued v i a regional water managers within the various d i s t r i c t s of the province when r i v e r s near c r i t i c a l floodstages. 47. By 1976, floodplain regulations and floodproofing requirements were established by the Floodplain Planning Division of the Water Investigation Branch f o r communities within the Lower Skeena (Province of B r i t i s h Columbia, 1980b). These measures consist of a flo o d damage prevention clause included i n zoning bylaws pertaining to floodplain development. Bylaw #37, Section 1 .10.0 f o r Greater Terrace t y p i f i e s the format of these r e s t r i c t i o n s : Not withstanding any other provisions of t h i s Bylaw, no building s h a l l be constructed, nor mobile home located: (a) With the underside of the f l o o r system of any area used f o r habitation, business or storage of goods damageable by floodwaters, the ground l e v e l on which i t i s located, lower than: i ) Two (2) feet above the one i n 200 year fl o o d where t h i s l e v e l can be determined, i i ) Twenty (20) feet above the natural boundary of the Skeena River where the one i n 200 year floodplain has not been determined by the Water Investigation Branch, i i i ) Five (5) feet above the natural boundary of a lake, i v ) Ten (10) feet above the natural boundary of any other water course. (b) Within: i ) Two hundred (200) feet of the natural boundary of the Skeena River, i i ) Twenty-five (25) feet of the natural boundary of a lake, i i i ) One hundred (100) feet of the natural boundary of any other water course. I f l a n d f i l l i s used to achieve the required elevation, the toe of the f i l l slope s h a l l be no closer than the above distance(s) from the natural boundary, and the face of the f i l l slope must be adequately protected against erosion from fl o o d flows and/or wave action. Provided that, with the approval of the Deputy Minister of Environment, these requirements may be reduced. Similar Bylaws are applied i n the flo o d prone communities of Lakelse, Dutch Valley, Remo, Usk, Cedarvale and Hazelton. Moreover, the Regional D i s t r i c t of Kitimat-Stikine has adopted ordinances f o r floodplain lands outside of municipalities and existing towns i n the Skeena Region. 48. These regulations generally apply to new development on floodplains i n the Skeena Region. Although there i s no specified penality f o r contra-vention, enforcement of the regulations i s achieved through the denial of building permits or service connections unless codes i n the zoning bylaw are adhered to. Developers, within r i g h t s under the Land Act, appealing to the Ministry of Environment f o r a relaxation or change i n subdivision requirements, now face a covenant attached to the Land Registry T i t l e , releasing the Province from r e s p o n s i b i l i t y toward flood problems associated with the s i t e . The covenant applied to flo o d prone lands i n the Municipality of Terrace reads as follows: The owner agrees to save harmless, the Province of B r i t i s h Columbia and D i s t r i c t of Terrace i n the event of any damage being caused by flooding to any building, improvement or other structure b u i l t , constructed or placed upon said lands and to any contents thereof ( D i s t r i c t of Terrace, Land Registry Office, 1980). Although the purpose of the covenant seems clear, i t i s not certain whether i n the event of widespread fl o o d damage throughout the Lower Skeena Region, the Province w i l l not provide compensation or restoration assistance to property owners. At present, the Pr o v i n c i a l Emergency Program, administers a substantial disaster fund, which no doubt would be drawn against i n the event of extensive f l o o d damage i n the region (Province of B r i t i s h Columbia, 1980). F i n a l l y , communities have the opportunity under the Water Act to form Water Management D i s t r i c t s f o r administration and funding of special projects i n r e l a t i o n to water development and problems. These d i s t r i c t s provide cohesive management units to define the framework and scope f o r dealing with l o c a l i z e d problems and issues concerned with water (Province of B r i t i s h Columbia, 1980b). The Water Management Branch of the Ministry 49. of Environment uses these as a basis f o r administering A g r i c u l t u r a l Redevelopment Act projects within the province. Such an application assisted i n financing the construction of erosion protection works i n New Remo during 1980 (see Chapter 4, Section IC). A number of such projects have been implemented i n the Lower Skeena Region, developing flood control structures, notably dykes and berms to protect and enhance a g r i c u l t u r a l land productivity. However, t h i s avenue of f l o o d damage prevention i s not e a s i l y u t i l i z e d unless there i s s i g n i f -icant a g r i c u l t u r a l land of Class 4 or better threatened by floodwaters. Moreover the degree of protection deemed feasible i s usually much lower than that which might seem so i n the r e s i d e n t i a l and commercial section of floodplain communities. Yet, i n few of the floodplain communities i s there an awareness of t h i s adjustment. Even where i t has been brought to the attention of residents, a major d i f f i c u l t y has been the achievement of consensus among participants i n the project (Marcellin, 1980, pers.comm.). The issues involved are examined i n Chapter 4 i n r e l a t i o n to c o n t r o l l i n g floods i n the Community of New Remo. I I Effectiveness of Current Measures i n Dealing with F a l l Floods A. Flood Forecasting The current f l o o d forecasting system within the Skeena Region i s part of the province-wide network established to deal with spring freshet, snow-melt floods. In the past these floods have at times resulted i n devastating effects on other r i v e r s as well as the Skeena. From past records, these floods have been coincident events on the Skeena, Fraser and Columbia Rivers as well as i n the Okanagan Valley. Considerable experience i n forecasting spring freshet conditions has contributed to the current, 50. highly effective monitoring of runoff and streamflow throughout the province i n r e l a t i o n to these floods (Province of B r i t i s h Columbia, 1973, 1976, 1980). The threat of severe, province-wide flooding has assisted i n encouraging te c h n i c a l l y e f f i c i e n t refinements i n the network and predictive models, such that antecedent freshet conditions can be noted and streamflow fore-cast at least two days i n advance of peak runoff f o r most large r i v e r s (Province of B r i t i s h Columbia, 1980b). The flood forecasting system i s only effective and e f f i c i e n t where i t can be l i n k e d to action toward reducing f l o o d damage (White, 1975)• The warning system contingent on forecasts of spring freshet flows seems to work e f f e c t i v e l y . During high runoff and flooding i n 1972, the warning system assisted i n reducing some flo o d damage (Province of B r i t i s h Columbia, 1973). However, these floods were noticeably smaller i n magnitude and less extensive than those i n 1948 (Water Survey of Canada, 1979). Flood fore-casting and warnings to generate emergency action works best where flooding occurs regularly. Spring freshets occur each spring during May and June on almost a l l r i v e r s of B r i t i s h Columbia. Despite the lack of flooding, communities are given annual reminders of the persistent threat of f l o o d damage, i n the seasonal r i s e of r i v e r l e v e l s during l a t e spring. The ex i s t i n g forecast and warning system has no relevance to the f a l l f l o o d problem. A different meteorologic prognosis i s required i n fore-casting the r i s e of r i v e r s i n response to f a l l rainstorms. The s p a t i a l and temporal features of these rainstorm floods bears l i t t l e r elationship to the behaviour and pattern of spring freshet floods (Chapter 2 ) . In forecasting these floods, time i s of the essence as storms move with speeds ranging between 30 and 50 kilometres per hour from west to east across the t r i b u t a r y watersheds of the Lower Skeena. Flooding begins i n many of these 51 . catchments before the Skeena River begins to show any sign of r i s i n g to floodstage. During the f a l l of 1978, forecasts and flow measurement of the Skeena near Terrace provided contradictory indications of developing f l o o d condi-tions i n the region downstream. At Terrace, the Skeena remained well below floodstage, yet at Remo, a few kilometres downstream, half of the community was under 2 metres of water. Not u n t i l near the end of the f l o o d were warnings issued from Terrace f o r the surrounding f l o o d prone communities. By t h i s time most of the damage had been i n f l i c t e d (Scanlon et a l , 1979). The forecasting network employed to deal with spring floods i s not operational i n r e l a t i o n to f a l l floods. In i t s current form and d i s t r i b u t i o n i t provides too broad coverage within the province to provide comprehensive d e t a i l relevant to f a l l rainstorms and flooding. Moreover, the instrumen-t a t i o n , data and a n a l y t i c a l approaches would have to be modified i n fore-casting f a l l floods (Linsley, Kohler and Paulhus, 1978). Under present arrangements, the f l o o d forecasting system i n the Skeena Region could not be expected to accurately and e f f i c i e n t l y forecast pending f a l l floods. B. Design Flood Frequency and Floodplain Mapping The design f l o o d frequency selected f o r managing floods i n the Skeena River system i s the 1 i n 200 year flood. The magnitude and associated depth and area of flooding associated with t h i s frequency i s highly uncertain, especially when estimated from short hydrologic records, such as those available f o r the Skeena and i t s t r i b u t a r i e s (Chapter 2 ) . The reasons f o r selecting a 1 i n 200 year f l o o d frequency f o r the Skeena are not c l e a r l y evident i n the rationale set f o r t h i n Water Investigation Annual Reports (Province of B r i t i s h Columbia, 1973 to 1980). However, t h i s f l o o d frequency seems to be one that has been designated f o r other r i v e r s 52. i n the province and may r e f l e c t the Province's objectives i n developing a uniform policy of f l o o d damage prevention (Sloan, 1974). The 1 i n 200 year f l o o d i n the Skeena River System e s s e n t i a l l y coin-cides with the magnitude of the h i s t o r i c flood of 1936. The procedure used by the Hydrologic Section of the Water Investigation Branch i s b r i e f l y described as a modelling process incorporating correlation, simulation and a strong judgemental component i n deriving the design flood magnitude by Sloan (1974) . Despite assigning the 1 i n 200 year frequency to the 1936 f l o o d , the precise magnitude of Skeena River flow during the h i s t o r i c event remain uncertain. The f l o o d swept away gages when the bridge at Terrace was washed away (Asante, 1972). In addition, i n attempting to map the area affected by these floodwaters, Marcellin and Beg (1974) i l l u s t r a t e d examples of the uncertainty and contradictory evidence associated with using markings on the floodplain and resident accounts of the f l o o d effects of the past. Most of the f l o o d effects from the 1936 flood have been erased by time and by more recent flooding i n 1972. Setting these concerns aside, the design f l o o d f o r management bears no relationship to the frequency d i s t r i b u t i o n derived f o r f a l l floods (Chapter 2 ) . On the Zymoetz and Zymagotitz Rivers, f a l l floods appear to be of consistently larger magnitudes than those of spring. Clearly the 1 i n 200 year f l o o d f o r these r i v e r s and t h e i r floodplains should be derived from the f a l l f l o o d series, not the overall annual fl o o d series as i s done f o r the Skeena where spring floods predominate. This d i s t i n c t i o n i s important when considering the design flood magnitude and subsequently becomes c r i t i c a l i n d i r e c t i n g the focus of floodplain mapping programs. The complex, terraced and sloughed a l l u v i a l floodplain of the Skeena, especially i n the v i c i n i t y of lower t r i b u t a r i e s make i t c r i t i c a l to accurately 5 3 . determine design f l o o d l i m i t s i n r e l a t i o n to topography. Maps of the flood hazard zone within a community are essential bases f o r effective planning implementation (Kates and White, 1961). In the Lower Skeena, floodplain maps r e f l e c t only the inundation pattern of the 1 i n 200 year f l o o d of the Skeena River. Tributary r i v e r s have not been analysed nor mapped to date (Province of B r i t i s h Columbia, 1980b). The short length of gaging records, watershed land use changes and the general lack of gage s i t e s has impeded the designation of the 1 i n 200 year f l o o d fo r these r i v e r s . However, i t appears from evaluations conducted i n t h i s study f o r t r i b u t a r i e s i n the Lower Skeena Region that primary focus should be towards f a l l r a i n floods rather than spring floods despite the i n a b i l i t y to precisely define a 1 in. 200 year f l o o d magnitude. The floodplain mapping program i n the Lower Skeena, spurred by flooding i n 1972, has only recently been completed, taking well over four years to provide maps of the f l o o d hazard i n communities from Hazelton to New Remo (Province of B r i t i s h Columbia, 1980a). The completed maps present the fl o o d hazard i n a l i m i t e d way. Although 2 foot (0.8 metres) contours have been used throughout, only the 1 i n 200 year f l o o d l i m i t i s shown on these. More frequent floods, presumably occur within t h i s l i m i t but t h i s assumption may not be the case, especially where t r i b u t a r i e s l i k e the Zymoetz and Zymagotitz or Kitsumkalum j o i n the Skeena. In these l o c a l i t i e s , t r i b u t a r i e s generate larger magnitude f a l l floods, which when combined with high stages on the Skeena produce flooding beyond the 1 i n 200 year l i m i t on these parts of the floodplain. Thus, the design flood frequency and the nature of the Skeena and i t s trib u t a r y floodplains contribute toward an apparent uncertainty i n d e l i n -eating experienced and potential f l o o d l i m i t s . Furthermore the exclusion 54. of f a l l f l o o d effects seems to compound the degree of uncertainty within the current f l o o d management approach. G. Floodplain Regulation and Floodproofing The f l o o d damage prevention clause, added to the zoning regulation f o r the Regional D i s t r i c t of Kitimat-Stikine i n 1976, was designated p r i o r to the floodplain mapping i n the region being completed. Without maps, i t i s often d i f f i c u l t f o r l o c a l area planners to convince floodplain developers of t h e i r value i n preventing f l o o d damage (White, 1975)- Moreover, since the regulations i n s t i t u t e d p r i o r to 1978 did nothing to minimize f l o o d damage fo r floodplain residents during the recent flood, there seems to be l i t t l e confidence i n t h e i r a b i l i t y to do so i n the future. Local residents i n New Remo frequently express a view that current regulations are unfair and i n e f f e c t i v e i n dealing with floods i n t h e i r l o c a l i t y and regard them as an impediment to community development (Chapter 4 ) . Floodplain regulation and floodproofing requirements could prove to be the most effective measures i n coping with f a l l as well as spring f l o o d damage. Once regulations have been implemented and enforced they can r e a d i l y be supplemented with s i t e s p e c i f i c information on the f a l l hazard and enforced i n the same way as they are now f o r spring f l o o d r i s k s . Flood-proofing measures taken toward spring floods are not as effective i n mitiga-t i n g f a l l f l o o d damage. Although these adjustments either prevent fl o o d -waters from entering buildings or provide protection to the contents of buildings against the one type of f l o o d i n spring, they could provide p a r t i a l protection against the f a l l type of flood. However, despite the prevalence of floodproofing requirements i n zoning bylaws f o r subdivision development, measures of t h i s type have not been implemented i n the Lower Skeena Region 55. p a r t i c u l a r l y with respect to existing buildings within the 1 i n 200 year flood l i m i t . They only apply where a building permit i s requested. L i t t l e technical advice accompanies floodplain regulations, other than the implied means of r a i s i n g the f i r s t f l o o r of the building above the specified eleva-t i o n on the floodplain. Alternative means of floodproofing could be imple-mented i f encouragement and advice were provided (Shaeffer, i 9 6 0 ) . Conse-quently there are few available means of reconciling residual f l o o d damages i n currently developed communities through the Skeena Region other than to have floodplain residents bear the loss or seek compensation by the government. Floodproofing f o r existing development i s relegated to in d i v i d u a l i n i t i a t i v e s i n the Lower Skeena Region. Taken i n t h i s l i g h t , together with some of the preceding problems evident i n the current approach, i t i s not surprising that many residents i n communities l i k e New Remo, Dutch Valley and Lakelse Lake avoid taking floodproofing action. In such communities, where there i s a perception of the high f l o o d r i s k and no f a i t h i n the effectiveness of the current management approach, residents press public o f f i c i a l s f o r flood control measures. Such has been the case i n New Remo, where the residents sought to have the community dyked. When structural measures of t h i s type are increasingly used to f i l l voids i n the current program, serious shortcomings are suggested i n the strategy. I l l Implications Structural f l o o d protection measures have not been implemented i n the Lower Skeena Region. Despite the reliance within the current f l o o d manage-ment approach on nonstructural flood damage prevention measures, f a l l floods are not encompassed by t h i s strategy. 56. Flood forecasting, fundamental to any strategy of flood management, i s aimed only at spring freshet floods. The current approach i s not designed to deal with f a l l floods. F a l l flood forecasting requires a different network of meteorologic and hydrologic stations as well as designing instrumentation and predictive models aimed at recording, processing and forecasting developing flood conditions within a relatively short lead time. Forecasts w i l l have to be issued more frequently, rather than daily, as they currently are developed for spring floods. Data on rainstorm, precipitation potential together with temperature profile of approaching a i r masses and ground surface conditions w i l l be required to predict l i k e l y r a i n f a l l totals and intensities. Runoff models w i l l be required for the rivers draining into the Skeena through the flood prone communities. I n i t i a l l y , the program w i l l have to address i t s e l f to identifying the information needs and evaluate the relative costs of enhancing the data base within the region compared to the benefits derived in dealing with the f a l l flood problem. Evidence presented earlier in the study indicates that the problem i s l i k e l y to increase i f i t continues to elude management. Some measures applied to spring floods have the capacity to be effective, i f only i n part against f a l l floods. This i s apparently true for floodplain regulation and floodproofing. However, these are not currently implemented as ef f i c i e n t l y as they might be. To work effectively these measures require community understanding, approval and action (James, 1973). Under the current approach, these measures are not explicitly encouraged within the frame of reference set out in the designated program. Inherent uncertainties in designating the design flood and identifying i t s limits on the floodplain are not acknowledged. The 1 in 200 year flood 57. boundary i s implied on maps of the Lower Skeena to s i g n i f y certain flooding within i t s l i m i t s . Studies of floodplain occupants i n other settings (Kates, 1962; Shanks, 1972; James, 1973; M i t c h e l l et a l , 1978) have shown that many of these do not perceive the nature of p r o b a b i l i t i e s and hence the significance of the design f l o o d boundary. Furthermore, with the l i m i t e d range of alterna t i v e adjustments perceived available to deal with the f l o o d problem and with f i r s t hand experience with f l o o d damages, many residents may develop a sense of f r u s t r a t i o n i n t r y i n g to do anything about the flo o d problem (White, i 9 6 0 ) . The current strategy applied to flo o d damage prevention i s too l i m i t e d i n scope to deal with f a l l floods. Moreover, the existing implementation mechanisms are not as e f f i c i e n t as they may have been presumed i n designating the program. The prevailing approach appears to have shortcomings i n dealing with spring freshet floods. The current approach cannot be simply extended to cover the f a l l f l o o d problem. A new strategy w i l l have to be developed f o r the region based on assessment of the entire range of flo o d hazards and the varied alternative adjustments possible within the setting of the Lower Skeena. New Remo offers an i l l u s t r a t i v e case f o r the devel-opment of such a strategy. 58 CHAPTER 4 TOWARD A STRATEGY FOR MANAGING FALL FLOODS IN NEW REMO I Community Features and. Flood Hazard A. Flood Experience New Remo i s situated approximately 8 kilometres west of Terrace on the north side of the Skeena River (Figure 5 ) - The community i s spread over floodplain land shared by the Zymagotitz and Skeena Rivers (Figure 9 ) -The fl o o d hazard within the community i s regarded as chronic as both r i v e r s i n f l i c t f l o o d damage (Marcellin and Beg, 1974). The community dates back to the early 1930's when completion of the CNR l i n e to Prince Rupert offered the opportunity f o r settlement (Asante, 1972). However, most of the current population located within the area since the early 1 9 5 0 ' s following the completion of Highway 16 to Prince Rupert. Approximately 150 people l i v e i n New Remo, occupying approximately 50 land-holdings (Figure 9)« The Zymagotitz River, known l o c a l l y as the Zymacord, drains approx-imately 377 square kilometres, flowing out of a deep, glacier-fed v a l l e y on the eastern flank of the Kitimat Range of the Coast Mountains. The floodplain of the Zymagotitz at Remo i s extensive, resembling a delta or fan deposit where the valley i n which i t flows widens to meet the Skeena. I t s surface i s gently undulating to f l a t with scattered oxbows and sloughs throughout. A large slough, a r e l i c from an e a r l i e r course of the Skeena, runs through the community. Most of the homesites i n New Remo are b u i l t on past islands of the Skeena or Zymagotitz Rivers, divided by these old w a t e r - f i l l e d back channels. 59. Disastrous floods occurred i n 1936, 1948 and 1972 when the Skeena River breached the CNR embankment separating the town from the r i v e r . In 1936, floodwaters inundated the entire townsite of New Remo and other parts of the floodplain around i t to depths of 2.5 metres (Marcellin and Beg, 1974). Although not as deep, floodwaters i n 1948, caused even more extensive damage as more people had located and b u i l t homes i n the community by t h i s time. Minor floods, referred to as i n d i r e c t by Marcellin and Beg (1974) i n t h e i r study, occur almost annually i n either spring or f a l l as a result of combined high runoff on both the Skeena and Zymagotitz Rivers. This hazard occurs when the Skeena River backs the Zymagotitz flow onto i t s floodplain. This type of f l o o d occurred i n 1972 (Marcellin and Beg, 1974) and may have been associated with part of the flood impact i n 1974 and again i n 1978 (Province of B r i t i s h Columbia, 1980a). F a l l floods, generated by heavy warm rains, however, usually send the Zymagotitz on the rampage. Floodwaters enter the floodplain north of the community and flow into the large, abandoned slough, attempting to j o i n the Skeena east of town (Marcellin and Beg, 1974). The combined highway and railway embankments block t h i s natural floodway from merging with the Skeena, backing floodwaters onto adjacent properties (Figure 9). In I 9 6 I , floodwaters up to 1 metre i n depth inundated properties i n New Remo. These were situated nearest the Zymagotitz River on the west side of town and near the southern bank of the slough (Marcellin and Beg, 1974). The most severe flooding occurred i n 1978 when rain - f l o o d conditions prevailed throughout the Lower Skeena Region. New Remo was one of the communities hardest h i t and given the most attention by media and public o f f i c i a l s (Scanlon et a l , 1979). Although a s i m i l a r flood occurred i n 1974, few people were prepared i n 1978. The floodwaters appeared to r i s e so 60. suddenly that emergency mitigative action seemed f u t i l e and even evacuation was impeded. Observers, who witnessed the r i s e of floodwaters i n the commu-n i t y were astounded by the speed at which i t t r a v e l l e d and the heights to which i t rose. The floodwaters, carrying extensive debris and s i l t , reached a height of over 3 metres on the western part of town. One resident escaped his home by cutting through the roof and t r a v e l l i n g by boat to the highway (Scanlon et a l , 1979). Direct f l o o d damage i n the community exceeded $200,000. However, long term effects have been even more destructive. Property values i n New Remo have shown a rapid decline since 1978 (Marcellin, 1980, pers.comm.). B. Landuse- and Flood Patterns Land on the floodplain at New Remo i s generally devoted to r e s i d e n t i a l use. Approximately 45 homes have been b u i l t on properties ranging i n size from about 0 .5 hectares to 10 hectares and these s i t e s comprise the major portion of the townsite (Figure 9 ) . On the northern and western periphery, farming i s practiced on the f e r t i l e a l l u v i a l s i l t s deposited by the Zymagotitz River. Mixed a g r i c u l t u r a l production predominates i n these areas with vegetable crops destined f o r l o c a l marketing i n Terrace and small amounts of milk provided f o r dairy production. Most residents maintain domestic poultry and cult i v a t e small gardens and orchards f o r some degree of s e l f - s u f f i c i e n c y . No commercial establishments are situated i n the community other than a carpentry shop and autobody repair firm. The f l o o d hazard within the community varies i n accord with the type of flooding and season. D i s t i n c t i o n i s evident i n the pattern of flooding associated with the Skeena and that i n f l i c t e d by the Zymagotitz. Skeena 6 1 . FIGURE 9 Flood Hazard in New R e m o (after Province of B.C., 1980 62. floods occur when the r a i l l i n e embankment i s breached south of the town-s i t e . Floodwaters spread evenly northward through the community, covering properties up to the 1 i n 200 year f l o o d l i m i t (Figure 9 ) . Skeena River floods, however, have not inundated the New Remo community since 1948. Flooding, associated with the Zymagotitz River, affects the community i n different ways. Floodwaters cover those properties west and south of the slough (Figure 9 ) . Flood depths are greatest i n the west nearest the r i v e r during these events and i n those areas nearest the r i v e r such as on DL2265 and DL1717, flooding due to backwater effects of the Skeena occur almost annually to varied depths. The d i s t i n c t i o n between these flood patterns i n New Remo provides the basis f o r different measures to cope with the f l o o d hazard. However, maps available which delineate pr o b a b i l i t y l i m i t s f o r various magnitude floods depict the entire community within a 1 i n 70 year f l o o d l i m i t . This f l o o d type i s a Skeena River Flood (Province of B r i t i s h Columbia, 1980a). C. Developments Affecting the Flood Hazard Flood control i n New Remo dates back to the construction of the CNR mainline to Prince Rupert. The railway embankment offers protection from Skeena River floods up to a 1 i n 70 year magnitude (Province of B r i t i s h Columbia, 1980a, Figure 9 ) . The Highway 16 embankment alongside reinforces the protection at the same flo o d frequency. A flood equal i n magnitude to the 1 i n 200 year f l o o d (or 1936 flood) would r i s e over these apparent dykes to a height of 1 metre and flo o d the entire community. Floodplain regulations were adopted by the Regional D i s t r i c t of Kitimat-Stikine i n New Remo i n 1976 designating setbacks and floodproofing requirements f o r new construction. These, however, are based on character-i s t i c s of Skeena River floods and do not relate to the pattern of flooding 63. associated with the Zymacord. About one half dozen new homes have been constructed since that time and most of these have been s i t e d on land south of the slough. During the summer of 1980, a r o c k - f i l l e d and earthen berm was constructed along the east bank of the Zymacord River, north of the townsite to provide erosion protection and ensure the r i v e r does not break i t s course during f l o o d and occupy the old slough through the town. Although the works are designed to keep the Zymacord i n i t s present channel and to a l l a y l o c a l residents' fears of a breakout developing a new course through the area, no protection against backwater flooding from the Skeena River i s provided by these works. Protection against flooding i n general by dyking i s regarded as unfeasible (Province of B r i t i s h Columbia, 1980). The report suggests: Future building i n the New Remo Subdivision Area should either be discouraged, or structures must be designed, s i t e d and b u i l t to conform to the requirements of the Kitimat-Stikine Regional D i s t r i c t Bylaw No.73. Recognizing the l i m i t e d protection that affordable dyking can provide, e x i s t i n g homeowners at New Remo would be wise to also consider plans f o r floodproofing to protect t h e i r property against future floods (Province of B r i t i s h Columbia, I98O). D. Community Regard Toward Flood Management Despite the r e a l and diverse f l o o d hazard, residents remain i n New Remo. Yet, few have taken i t upon themselves to floodproof t h e i r buildings i n accord with Regional D i s t r i c t recommendations. However, floodproofing requirements, i f adhered to, would not mitigate direct f l o o d damage from the Zymacord. They are based on Skeena fl o o d patterns. Few residents within the community appear to have the resources or display the i n i t i a t i v e to do much about flooding on t h e i r property. Following the 1978 f l o o d , property values have declined markedly i n New Remo. 64. Yet, most residents choose to remain located i n the community despite t h e i r experience with f a l l floods. The majority of residents favour dyking as the "best means of dealing with the fl o o d problem. Residents who occupy land south of the slough demonstrate a continued concern over the threat of f a l l flooding. Although the t r a i n i n g berm has removed the threat of the Zymacord River breaking out of i t s course the southwestern part of the community continues to face the annual threat of backwater flooding from the Skeena during both spring and f a l l seasons. Despite the actions taken i n the community toward the f a l l f l o o d hazard the need remains f o r a comprehensive strategy to contend with the complete scope of the f l o o d problem. F a l l flooding should be i t s focus and i t should provide the scope and means f o r framing a practicable and feasib l e range of adjustments to reduce f l o o d losses. The strategy should provide f o r residents of the community to make adjustments and take action against the hazard while minimizing the application of public funds. I I Developing a Comprehensive Strategy to Manage F a l l Floods i n New Remo A. The Framework f o r Choice In Chapter 1 a conceptual framework was i d e n t i f i e d as a basis f o r selecting the appropriate l e v e l of flood damage mitigation and designating the combination of f l o o d damage reduction measures to achieve i t . This approach i s followed here i n dealing with the f a l l f l o o d problem i n New Remo. The purpose, i m p l i c i t i n the approach, i s to provide an evaluative frame-work i n which to f a c i l i t a t e the selection of a s o c i a l l y optimal set of management alternatives and to generate evaluative information pertinent to public choice. 65. The strategy i s i n i t i a t e d by considering the f u l l range of alternatives (Table 1, Chapter l ) and s i f t i n g out the practicable adjustments, i n l i g h t of the flood hazard characteristics and the technical f e a s i b i l i t y of these measures. The second step i n the process involves a comprehensive evaluation to designate the optimum combination of alternative measures from those determined to be practicable. Evaluation at t h i s step i s to determine the so c i a l benefits r e l a t i v e to costs so that an optimal choice can be made to determine the l e v e l and degree of fl o o d management. Thus the implications of choosing one alternative or set of alternatives can be expressed i n values relevant to public decisionmaking. B. Strategic Elements The f l o o d problem at New Remo, necessitates immediate and continued planned action to achieve flood damage reduction. As a minimum, immediate steps should be taken toward defining the s p e c i f i c degrees of the dual f l o o d hazard i n the community and simultaneously undertaking actions to develop a floo d warning service and link e d emergency a c t i v i t i e s . Beyond these actions, ef f o r t s could be directed to evaluating remaining alternatives f o r reducing f l o o d damage. The strategy would comprise the following steps: Step I Define the Spatial D i s t r i b u t i o n of Flood Damages The analysis would commence with a d i s t i n c t i o n between spring freshet and f a l l r a i n floods i n the annual f l o o d series f o r the Zymacord River at New Remo. Although the streamflow record i s short, a probable frequency can be established f o r each type of flood, defining magnitudes and return periods (Chapter 2). In l i g h t of topographic information on the floodplain, depths and f l o o d areas f o r different return periods can be derived f o r s p e c i f i c s i t e s i n the community. Based on these data i t i s not only possible 66. to estimate the potential damages f o r each designated return period f o r the community as a whole hut ind i v i d u a l property owners w i l l he able to estimate t h e i r r i s k of fl o o d damage (James, 1973)• This i s a c r i t i c a l step f o r two reasons: F i r s t , i t a s s i s t s i n making private and public floodplain managers aware of fl o o d hazard and the s p e c i f i c flood damage potential associated with properties i n the community. Some of the managers may choose to take immediate, mitigating action to minimize t h e i r r i s k s and thereby contribute to flood damage reduction (Kates, I962). Second, s p a t i a l data on flood damages can ass i s t long range planning by serving as the evaluative base i n comparing the costs of alternative adjust-ments to the fl o o d hazard i n the community. Step I I Design a Flood Forecasting Service The need f o r a f a l l f l ood forecasting service extends beyond the commu-ni t y of New Remo, to the entire region of the Lower Skeena and i s regarded as fundamental to mitigating some damage during severe floods but more impor-t a n t l y , information provided i n advance of flooding may save l i v e s . I f anticipated storm conditions and r a i n f a l l accumulation can be provided early enough, warnings can be issued and emergency action taken to mitigate some damage. Forecasting f a l l floods requires comprehensive information on both atmospheric weather conditions and ground l e v e l conditions over the Coastal Mountain catchments of the Skeena. Currently, weather observation data i s assembled at Prince Rupert as a basis f o r developing regional weather fore-casts. Observations pertaining to atmospheric freezing l e v e l s , v e r t i c a l temperature p r o f i l e s , storm areas, humidity and precipitable water content and prevailing wind conditions are made on advancing P a c i f i c disturbances 67. (Shaefer, 1979). Such information i s v i t a l to forecasting potential r a i n -f a l l pattern, duration and inte n s i t y . However, a flood forecasting system requires l i n k i n g meteorologic conditions to runoff potential within the catchments of the Lower Skeena to predict anticipated r i v e r flows and ultimately f l o o d depths i n the communities of the region. This type of information i s currently unavailable f o r New Remo. The Ministry of Environment should assume r e s p o n s i b i l i t y i n regard to developing the f l o o d forecast system f o r the Lower Skeena Region. Fore-casting f l o o d depths f o r New Remo would appear to be only a part of the service as there are other communities i n the region facing the f a l l f l o o d problem. The Water Investigation Branch i n conjunction with the Water Survey of Canada would be required to determine storm r a i n f a l l - r u n o f f relations f o r the Zymacord and other r i v e r s of the region generating a f a l l f lood threat. The Water Investigation Branch would be call e d on further to establish f l o o d stage-streamflow relationships f o r communities l i k e New Remo so that they might anticipate l i k e l y f l o o d l e v e l s based on storm conditions. With t h i s information at hand, i t i s then possible to develop an i n t e -grated forecast and flo o d warning system. Such a service would be envisaged as operating through the f a l l months, p r i o r to the season when efforts commence on forecasting spring freshet f l o o d potential. The fl o o d forecast and warning service probably should be based i n Terrace where the Regional Manager of Operations i n the Ministry of Environment currently has a task of co-ordinating a c t i v i t i e s on water related problems. In a co-ordinative capacity, the Regional Manager i s i n a strategic position to integrate the f l o o d information and make i t relevant and useful to communities of the Lower Skeena. A n a l y t i c a l f a c i l i t i e s i n the regional o f f i c e are currently l i n k e d by telecommunication and computer to V i c t o r i a i n providing the ca p a b i l i t y f o r fl o o d monitoring. Inter agency linkages i n 68. disseminating forecast information w i l l require strengthening. Although the R.C.M.P, Pr o v i n c i a l Emergency Program and Ministry of Highways are regarded as important, the Regional D i s t r i c t Office should be involved and equipped to provide f l o o d warnings to c r i t i c a l l y f l o o d prone communities l i k e New Remo through the media as well as by c i t i z e n band radio transmission. In t h i s way f a l l f l o o d forecasts can be made e f f i c i e n t l y , and warnings issued that are accurate and relevant to communities of the Lower Skeena. Furthermore such a comprehensive service i s fundamental to effective emergency planning with regard to the flo o d problem. The nature of the f a l l f l o o d hazard and i t s relationship to l o c a l i z e d hydrologic and s e t t l e -ment characteristics necessitate a regional strategy aimed at forecasting potential f l o o d conditions i n each community. Effec t i v e emergency fl o o d damage mitigation i s only possible when t h i s type of information i s available to residents of these communities. Step I I I Design of An Emergency Plan f o r Action During Floods This step i s contingent upon successful completion of the two preceding actions. Emergency action can be e f f i c i e n t l y undertaken by residents of New Remo only i f they perceive a threat of flooding and translate the f l o o d magnitude into l i k e l y damaging effects. Residents require not only timely and accurate information on the pending f l o o d conditions but must be able to r e l a t e these to probable f l o o d l e v e l s on t h e i r properties. Furthermore, effec t i v e emergency action requires that residents be aware of what they should do to mitigate damage during the short time i t takes the floodwaters to r i s e onto t h e i r land. Currently, the Pr o v i n c i a l Emergency Program (Ministry of Environment) co-ordinates emergency planning f o r spring freshet floods within the region through a m i n i s t e r i a l representative i n Terrace. I t seems' reasonable to 6 9 . F IGURE 1 0 Flood Zones in New Remo F E E T 1 extend the duties of t h i s position to f a l l f l o o d emergency planning i n the Lower Skeena. However, t h i s type of flood problem i s c l e a r l y more l o c a l i z e d and requires different actions to mitigate damage than those appropriate f o r spring floods. The non-uniform pattern evidently associated with the flood hazard i n New Remo suggests that varied actions among residents w i l l be necessary to provide f o r appropriate mitigative e f f o r t s during f a l l floods (Figure 1 0 ) . Under a p a r t i c u l a r set of flo o d conditions, the r i s k of fl o o d damage varies i n three d i s t i n c t zones within the community. Flood zone A has the largest r i s k of flooding and properties i n t h i s flood zone experience the greatest depth of flooding. Flood zone B, currently unoccupied, has a moderate flo o d r i s k while zone G experience s the lowest f l o o d depths of a l l three areas. Flood conditions s i m i l a r to those of 1978 would probably allow res-idents i n zone G to remain on t h e i r property during flooding and take mitigative action to reduce damage by moving valuables and furniture from ground l e v e l to higher locations i n t h e i r homes and buildings. Residents i n Zone A would be advised to evacuate homes immediately. The plan f o r action within the community would need to be co-ordinated but at the same time provide f o r the d i v e r s i t y evident i n the hazard and the potential mitigative actions to reduce f l o o d damage. Developing a community based emergency plan f o r New Remo and other communities of the Lower Skeena facing f a l l f l o o d problems requires that residents be involved i n the planning process and the plan ultimately be t a i l o r e d to the p a r t i c u l a r community. Residents of New Remo w i l l have to be informed as to the p a r t i c u l a r f l o o d hazards they face on t h e i r homesite and instructed as to what they should and can do to prevent flood damage on t h e i r properties. Some type of public forum may be necessary, perhaps i n workshop format to f a c i l i t a t e the flow of information, education and ultimately the organization of the community toward the f a l l f l o o d problem. As i n d i v i d u a l residents c l e a r l y perceive t h e i r personal r i s k s from flooding they are more l i k e l y to want to do something about i t and adhere to desig-nated actions to minimize impacts (White, 1975). Planning toward probable f a l l f l o o d emergency i s but one step i n the strategy to manage floods however, consultation with community residents at t h i s stage can influence perceptions of the hazard and strategic actions which may serve to increase awareness and strengthen willingness to follow long term planning measures toward the flo o d problem. Step IV Assessing Remaining Alternatives f o r Reducing Damages Having taken these steps, the investigation i s open to evaluation of remaining adjustments to reduce f l o o d damage i n New Remo. Although these comprise a wide range of t h e o r e t i c a l l y applicable structural and nonstructural measures, some are not practicable to the situ a t i o n i n New Remo. Flood insurance i s ruled out at t h i s time, since i t i s not generally available from private insurance companies, nor i s there a government flood insurance program available to residents i n the region of the Lower Skeena. Any of the remaining nonstructural measures could be applied i n New Remo (Table 1, Chapter l ) . Structural control of f a l l floods at New Remo i s practicably l i m i t e d to dyking. Dams on the Zymacord are ruled out because i n d i r e c t flooding by the Skeena would continue to affect the community, even i f the flow of the Zymacord i s e f f e c t i v e l y regulated. Yet even with dykes protecting New Remo, since they offer only p a r t i a l f l o o d protection and frequently encourage encroachment, nonstructural measures, such as floodplain regulation and floodproofing', may be necessary to contend with the residual f l o o d damage potential. 72. The practicable range of alternative adjustments f o r New Remo would appear to e n t a i l : (1) Dyking the Entire Community (2) P r o h i b i t i n g Further Building i n the Floodplain (3) Floodproofing E x i s t i n g Buildings (4) Permanent Evacuation of Some Homesites A comprehensive evaluation of these alternatives i s beyond the scope of t h i s study and must await s i t e - s p e c i f i c data on flo o d damage potential derived i n Step I . However, i n l i g h t of the flo o d hazard and community features i n New Remo i t i s advantageous to investigate these alternatives further toward suggesting better adjustments to the flood problem than those currently being made. Ultimately the selection of an,optimum set of flo o d damage reduction measures would be made on the basis of providing an acceptable degree of fl o o d protection at least cost. The current management standard within the Lower Skeena Region i s the 1 i n 200 year flood. The approximate costs of each of these measures determined to achieve t h i s l e v e l of flood protection are compared to i n d i -cate the least cost alternative combination. ( l ) Dyking the Entire Community The e x i s t i n g berm provides p a r t i a l protection against f a l l floods (Province of B r i t i s h Columbia, 1980a). I t i s designed to prevent direct inundation up to the 1 i n 200 year f l o o d height. However, i t offers no protection against i n d i r e c t flooding when the Skeena backs the Zymacord flow onto the floodplain i n New Remo. Dyking the entire community along the Zymacord i s estimated to cost $500,000 (Province of B r i t i s h Columbia, 1980a). The protection provided, however, i s only up to the 1 i n 70 year Skeena 73. spring freshet f l o o d height as the highway and r a i l embankment along the southern side would be breached above t h i s height (Figure 9 ) . To achieve protection up to the 1 i n 200 year flood, not only the dyke would require modification but the highway embankment would have to be raised and but-tressed as w e l l as modifications carried out on the bridge across the Zymacord (Province of B r i t i s h Columbia, 1980). The costs of such a scheme would probably exceed the t o t a l value of property i n the floodplain at New Remo, estimated at $2 m i l l i o n at most (Marcellin, pers. comm., I98O). (2) P r o h i b i t i n g Further Building i n the Floodplain Currently t h i s measure i s applied by the Regional D i s t r i c t of Kitimat-Sti k i n e through Zoning Bylaw 73* New buildings are required to have the l i v i n g space s i t e d at least 2.6 metres (8.6 feet) above ground l e v e l . However, t h i s regulation i s based on Skeena f l o o d heights and not those associated with the Zymacord. The 1 i n 200 year flood height, related to the Zymacord requires s i t i n g the f i r s t f l o o r of some buildings above 3«2 metres (10.6 f e e t ) , while others might require l e s s elevation as flood-proofing. However, the precise degree of floodproofing must await s i t e s p e c i f i c evaluation of buildings i n New Remo. Prohibition of new construction would serve to halt the growth of future flood damages. However, on i t s own, t h i s measure does nothing to reduce existing f l o o d damage potential. I t s effect might not be f e l t f o r some time and then i t may depend on the e f f e c t i v e implementation of other adjustments to the f l o o d problem. 74, (3) Floodproofing E x i s t i n g Buildings Floodproofing would e n t a i l r a i s i n g some homes at least 3>2 metres ( 1 0 . 6 feet) while other buildings would require l e s s floodproofing to provide protection up to the 1 i n 200 year f l o o d l i m i t . Some of the buildings, p a r t i c u l a r l y older homes located i n f l o o d zone A, may not be st r u c t u r a l l y f i t to be raised. These have incurred extensive f l o o d damage and the costs of r e t r o f i t t i n g them would probably exceed t h e i r current market value (Figure 1 0 ) . However, f o r the northern part of the community i n f l o o d zone G, some homes would not have to be floodproofed to the same degree and r a i s i n g these buildings would probably be feasible. However, accurate cost estimates f o r each property would be needed i n either case to assess the s u i t a b i l i t y of floodproofing buildings. Assuming i t costs approximately $10,000 per home to raise the f i r s t f l o o r , the aggregate cost should not exceed $500,000 f o r the community but t h i s figure would not include floodproofing older homes i n zone A. (4-) Permanent Evacuation of Some Homesites Although i t may be the most economically e f f i c i e n t measure f o r some of the properties south of the slough i n Zone A, complete evacuation of the community i s probably out of the question. Obviously a property by property appraisal w i l l be required to assess the need to permanently evacuate or floodproof each s i t e . Information i n t h i s regard i s contingent on data derived i n Step I above. However, permanent evacuation should be considered as po t e n t i a l l y applicable, p a r t i c u l a r l y f o r those homesites which cannot be e f f i c i e n t l y floodproofed. In f l o o d zone A there may be as many as f i f t e e n such homes involved. Residents of these could be relocated with equivalent size and valued properties i n zone C. Compensation could amount to as much as $50,000 per household. Aggregate cost of evacuation would probably exceed $500,000 but would eliminate s i g n i f i c a n t f l o o d damage. (5) Comparing and Combining Adjustments I f dyking the entire community i s taken as the standard f o r comparison, t h i s measure w i l l achieve protection from Zymacord River floods up to the 1 i n 200 year return period at a cost of about $500,000. However, to e l i m i -nate a l l flooding i n New Remo, including backwater flooding related to the Skeena, the costs would exceed $2 m i l l i o n to achieve 1 i n 200 year fl o o d protection (Province of B r i t i s h Columbia, 1980a). For t h i s l e v e l of fl o o d protection, floodproofing and permanent- evacu-ation of some homes i n an appropriate combination would probably be more economically f e a s i b l e . Assuming the costs of floodproofing averages $10,000 per homesite and approximately 25 homes would be floodproofed i n zone C t o t a l l i n g $250,000. Evacuation of the remaining properties i n zone A might average $50,000 per household, t o t a l l i n g just over $750,000. Floodproofing and permanent evacuation would cost approximately $1 m i l l i o n to achieve the same degree of protection as dyking the community. Both floodproofing and permanent evacuation offer other advantages to dyking the community. Dyking would encourage further encroachment and development i n the floodplain increasing community size and property values. Nonstructural measures, such as floodproofing, permanent evacuation and floodplain regulation, encourage more e f f i c i e n t use of floodplain land. These measures would tend to curb over-development. Measures taken to floodproof dwellings not only minimize fl o o d damage but can also serve as reminders within the community of potential f l o o d severity and subtly keep residents and newcomers aware of the problems they must face i n building on fl o o d prone land. Permanent evacuation removes the problem completely, provided floodplain regulations are implemented preventing subsequent occupation of evacuated land. The nonstructural approach also encourages individuals within the community to assume r e s p o n s i b i l i t y f o r taking action toward the f l o o d problem while structural measures appear to work i n the opposite d i r e c t i o n . Step V Development of a Financing P o l i c y P o l i c i e s to accommodate Steps I , I I and I I I are available within the current set of i n s t i t u t i o n a l arrangements to manage floods within the Lower Skeena Region. Although these are geared toward spring freshet floods, resources might be supplemented to provide services toward the f a l l f l o o d problem. Moreover since f a l l flooding i s regional i n extent, the costs of a program to carry out steps I through I I I should be undertaken on a region-wide basis f o r the Lower Skeena with due consideration to the s p e c i f i c features of the f l o o d problem associated with i n d i v i d u a l communities. Currently, the Ministry of Environment handles f l o o d problems and the complete scope of the strategy proposed here would f i t within i t s mandate. Step I could be added to the present tasks of the Water Investigation Branch i n mapping and assessing floodplains. A f a l l f l o o d forecasting and warning service could be handled e f f i c i e n t l y by the Hydrologic Section while Step I I I could be developed by the Pr o v i n c i a l Emergency Program within the Lower Skeena Region. The costs involved with these steps i n the strategy should be borne by the Province since the benefits would extend beyond the Lower Skeena Region and these measures are fundamental to achieving f l o o d damage prevention. 77. Financing floodproofing and permanent evacuation of parts of the New Remo community could be accommodated under the River Protection Assistance Program. A 25 per cent l o c a l contribution i s required i n sharing the costs of r i v e r protection works with the Province. Although this, formula has only been applied to f l o o d control projects such as dyking, there i s l i t t l e preventing i t s use to encourage other types of adjustments to f l o o d hazards. In New Remo, a p o t e n t i a l l y better adjustment to the flood hazard could be achieved through floodproofing and permanent evacuation. I f the funds required to dyke New Remo against the 1 i n 200 year Zymacord fl o o d were available to residents to floodproof t h e i r homes instead, they might achieve a greater degree of protection against the complete f l o o d hazard. The cost of such a dyking project amounts to $500,000 (Province of B r i t i s h Columbia, 1980a). However, i t only achieves protection up to a 1 i n 70 year Skeena River flood. I f the 75 per cent provincial share of the project's cost ($375,000) was made available to the property owners of New Remo to carry out floodproofing measures, they would have approximately $9,000 per household. Adding t h e i r 25 per cent contribution to the figure should provide adequate funds to floodproof up to the Regional D i s t r i c t standard f o r New Remo i n regard to the 1 i n 200 year Skeena River f l o o d height. In t h i s way, the funds which would have paid f o r p a r t i a l protection with the dyke, provides f o r comprehensive f l o o d protection to a higher standard i n the community and i n l i n e with f l o o d damage prevention i n other parts of the Lower Skeena. 78. I l l Discussion and Implications The application of a comprehensive strategy to determine an appropriate set of adjustments to the f l o o d problem i n New Remo, systematically demon-strated the steps to be followed i n dealing with the f a l l f l o o d problem. The procedure i l l u s t r a t e d the simple l o g i c required to designate measures to reduce f l o o d damage i n the community. Evaluation of practicable a l t e r -natives f o r New Remo indicated that floodproofing and permanent evacuation are p o t e n t i a l l y better measures to achieve^ f l o o d damage reduction than dyking the community , s p e c i a l l y i f standard f l o o d protection up to the 1 i n 200 year regional f l o o d l i m i t i s applied to the consideration of costs. The strategy recognizes the non-uniform features of the flood hazard i n New Remo. The steps proposed f o r management suggests a l o c a l i z e d , community-based approach. Residents of New Remo would have to f u l l y p a r t i c i p a t e i n the implementations of the strategy. They should be informed and educated regarding the r i s k s of flooding and instructed as to practicable short and long term adjustments to the hazards i n the community. Such an approach requires a change i n the perspective toward managing floods i n the Region of the Lower Skeena which can f a c i l i t a t e the development of diverse e f f i c i e n t adjustments to f l o o d problems l i k e those i n New Remo. The primary step i d e n t i f i e d i n the strategy i s fundamental to those which follow i t . However, i t involves a different type of.hydrologic investigation than that which i s t y p i c a l l y involved to design structural f l o o d control measures. To provide relevant information f o r the consideration of both structural and nonstructural measures requires information on the hazard as a function of frequency and on the average annual damages at every location i n the floodplain (James, 1973). In dealing with i n d i v i d u a l property owners, the only relevant information i s the flo o d hazard f o r that p a r t i c u l a r property and the damages that hazard can be expected to cause. 7 9 . Making such information available to residents of New Remo should a s s i s t i n generating successful response to subsequent steps i n the strategy and encourage committment toward reducing f l o o d damage i n the community. At the same time, the strategy c a l l s f o r a different approach to managing floods on the part of the Ministry of Environment. In dealing with New Remo residents, agency s t a f f charged with developing a flo o d management plan would be required not only to communicate data on the flo o d hazard but to i n s t r u c t residents i n techniques to reduce damage. Moreover, i n evaluating the potential long term measures to be taken against the floo d hazard, a broad range of structural and nonstructural alternatives would have to be set f o r t h , i n understandable terms f o r l o c a l consideration, with a l l of the f i n a n c i a l implications on the table and decision c r i t e r i a evident from analyses of the f l o o d problem se t t i n g , i t w i l l then be possible f o r the community of New Remo to approach a s o c i a l l y optimal adjustment to the f l o o d hazard. Study Conclusions A. The Flood Hazard Persistent f a l l floods i n the Lower Skeena have contributed to increasing f l o o d damages despite the prevailing program of flo o d damage prevention i n the region. F a l l floods a r i s i n g from heavy r a i n f a l l are more hydrologically s i g n i f i c a n t than spring freshet floods on some of the Lower Skeena t r i b u -t a r i e s . They pose a severe hazard i n communities l i k e New Remo. Although these floods are not as extensive as the spring problem they are l o c a l l y severe, and as pressures f o r floodplain development continue i n the region, ensuing encroachment w i l l contribute to a continued r i s e i n damage potential from f a l l floods. The f a l l f l o o d hazard requires a different strategy f o r management than spring floods. 80. B. The Current Management Approach E x i s t i n g nonstructural f l o o d damage prevention measures applied i n the Lower Skeena Region do not incompass the f a l l f l o o d problem. Flood-p l a i n regulation and floodproofing requirements f o r communities i n the region are too uniform to take into account the diverse problem settings within the region and apply only to new development i n floodplains. Flood forecasting and warning systems along with emergency plans are geared toward flooding i n spring as a resu l t of coincident high runoff from snow-melt. The current si t u a t i o n i n Lower Skeena communities, i l l u s t r a t e d by New Remo, suggests the need f o r a comprehensive strategy to manage f a l l floods. C. Flood Management Strategy f o r New Remo A systematic, step by step procedure i s applied to the complex flood problem i n New Remo, based on a framework f o r considering a broad range of potential adjustments to the fl o o d hazard. Floodproofing and evacuation are suggested as more f e a s i b l e and e f f i c i e n t alternatives to dyking the community. Moreover, the strategy points out the information required i n the development of a comprehensive f l o o d management program f o r New Remo. Procedural steps i n the strategy include: I Defining the s p a t i a l and temporal characteristics of the fl o o d problem i n New Remo. I I Developing a f l o o d forecasting service. I l l Designing an emergency plan. IV Evaluation of practicable adjustments to the fl o o d hazard. V Developing f i n a n c i a l arrangements f o r f e a s i b l e adjustments. 81. Such an approach can be accommodated within the scope of current po l i c y and i n s t i t u t i o n a l arrangements i n the Lower Skeena Region. However, a prime requisite would be the involvement of New Remo residents i n the management process. Although floodproofing i s suggested as a p o t e n t i a l l y e f f i c i e n t adjustment to the fl o o d hazard i n New Remo, elsewhere i n the region, i t may prove unfeasible. To e f f e c t i v e l y evaluate floodproofing along with other alternatives requires accurate s i t e s p e c i f i c data on flo o d l e v e l s and potential damages. Even though f a l l flooding emerges as a c r i t i c a l problem i n other communities of the Lower Skeena, such as Lakelse, Dutch Valley, Gopperside, Rosewood and Greenvale, the s p e c i f i c formula developed f o r New Remo may not necessarily apply. This i s especially so i n regard to structural and nonstructural f l o o d damage adjustment combinations. For each f l o o d problem se t t i n g , i t w i l l be necessary to generate a strategy to provide s i t e s p e c i f i c information on the degree of the flood hazard as a basis f o r determining the appropriate combination of adjustments. REFERENCES Asante, N. 1972 Burton, I. 1970 Colton, D.E. 1978 Burnash, R.J.C. Dingman, M.L. 1977 P i a t t , R.H. Dalrymple, T. i 9 6 0 Dougal, M.D. (ed) I969 Downing, T.E. 1977 Hare, F.K. 1974 Thomas, M.K. Holland, S.S. I976 R o l l i n g , C.S. 1978 James, D.L. I967 James, D.L. 1971 Lee, R.R. 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White, G.F. 1969b "From Multiple Purpose to Multiple Means: Flood Loss Reduction" i n White Strategies  of American Water Management, University of Michigan Press, Ann Arbor White, G.F. 1975 "Flood Damage Prevention P o l i c i e s " , Nature and Resources, Volume IX, January - March White, G.F. 1979 Nonstructural Floodplain Management Study: An Overview, United States Water Resources Council, Consultant's Report, Washington 

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