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Flood control and the pink and chum salmon of the Vedder River, B.C. : a method to estimate the effects… Peters, Neil Jacob 1978

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FLOOD CONTROL AND THE PINK AND CHUM SALMON OF THE VEDDER RIVER, B.C. A METHOD TO ESTIMATE THE EFFECTS OF EXTREME FLOWS AND CHANNEL MODIFICATIONS ON SALMON PRODUCTIVITY by NEIL JACOB PETERS BASc., University of British Columbia, 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES The Department of Civil Engineering We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1978 Neil Jacob Peters, 1978 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I a g ree tha the 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 tudy . I f u r t h e r agree 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 purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that 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 not be a l l o w e d w i thou t my w r i t t e n p e r m i s s i o n . Department o f tn^neerm The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date 7 W 1 M , H78 i i ABSTRACT Major flood control works for the Vedder River, presently in the planning stage, w i l l affect the productivity of the Vedder River's pink and chum salmon. In the past, flood control work has failed to provide long term flood protection and has reduced salmon productivity. This thesis presents the background and history of the interrelated flood control and fish resource problems, suggests apparently feasible solutions, and develops a method to determine the numbers of pink and chum salmon that would be produced from rehabilitated spawning areas. The Chilliwack River below Vedder Crossing (the Vedder River) is flowing across and is actively building an a l l u v i a l fan by a natural process of building up the channel bed and periodically breaking out into new channels. A long term flood control project w i l l have to both constrain the river laterally and provide for occasional sediment removal from the channel. Previous efforts to prevent bank erosion and flooding have reduced the width of the river channel and have eliminated many of the best pink and chum spawning areas. If constructed, wide dykes would provide a high factor of safety against flooding and would allow restoration of former • spawning areas. Rehabilitation projects should be closely coordinated with plans for sediment removal. Highly variable flows, particularly winter floods, appear to reduce the freshwater survival of pink and chum salmon in the Vedder River. Narrowing of the river channel has increased water velocities and river bed ins t a b i l i t y and has increased the detrimental effects of floods. To i i i quantify these effects, relationships between river flow and mortality are developed for the present narrow channel, a wide channel and a side channel development. These relationships are used in a method of calculation of adult salmon production that considers uncertainties due to environmental fluctuations and inaccuracies of data. Using estimates for the Vedder River chum salmon the calculations indicate that egg to fry survival in a wide Vedder channel and in a developed side channel would be 1 3/4 to 3 times higher than in the present narrow channel. Restoration of natural spawning areas would li k e l y increase the commercial chum catch by 40,000 to 65,000 fish. A policy of both rehabilitating natural spawning areas and constructing enhancement f a c i l i t i e s appears to be necessary to increase and stabilize the pink and chum salmon production from the Vedder-Chilliwack River. i v TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS iv LIST OF TABLES v i i LIST OF FIGURES . ix AKNOWLEDGEMENTS x i CHAPTER I INTRODUCTION . . . 1 II THE PHYSICAL SETTING 4 A. Location 4 B. Glacial History and Physical Features 6 C. Hydrology 7 D. Forests in the Watershed 13 E. The Chilliwack-Vedder River Channel 17 1. Description 17 2. Channel Stability 21 III THE HISTORY OF THE VEDDER CHANNEL 27 A. Channel SHifts during Native Occupation of the Chilliwack River A l l u v i a l Fan 27 B. Early White Settlement and Establishment of the Chilliwack River in the Vedder Channel . . . . 29 C. The Vedder River Diversion 32 D. Floods, P o l i t i c s , and Riprap, 1923-1976 34 E. Changes in the Vedder Channel 48 IV THE PINK AND CHUM SALMON OF THE VEDDER RIVER 51 A. Introduction 51 B. The Life Cycle of Pink and Chum Salmon and Factors Affecting Productivity 53 1. Migration and Spawning 54 2. Incubation 56 3. Emergence and Migration 59 4. Estuarine and Marine Life 59 5. The Commercial Fishery 60 V CHAPTER Page C. The Spawning Areas of the Vedder-Chilliwack River 61 D. The Spawning Areas of the Lower Vedder River . . . 65 E. The Distribution of Spawners 68 F. The Freshwater Productivity of the Vedder Stocks . 72 V ALTERNATIVES 79 A. Introduction 79 B. Alternative. Schemes for Reducing Flood Damage . . 79 1. Flood Control Objectives 79 2. Storage Reservoirs 80 3. Watershed Management 80 4. ' Stabilization of the Sediment Source . . . . 81 5. Sediment Traps 81 6. Flood Proofing, Insurance, Zoning, and Evacuation . . 82 7. Dyking and Dredging Alternatives 82 C. Alternative Schemes for Pink and Chum Salmon Development 88 1. Pink and Chum Salmon Management Objectives . 88 2. Incubation Boxes . . . 91 3. Spawning Channels 92 4. Side Channel Rehabilitation 93 5. A Wider Vedder Channel 95 6. Rehabilitation or Enhancement? 95 D. Example Alternatives for Evaluation 98 VI THE EFFECTS OF EXTREME FLOWS AND CHANNEL GEOMETRY ON EGG TO FRY SURVIVAL 101 A. Introduction 101 B. Mechanisms of Flow Induced Mortality 102 C. Observations of Flow Induced Mortality in the Vedder River and Other Streams 102 D. Relationships between Extreme Flows and Additional Mortality 112 1. A concept of Additional Mortality 112 2. Additional Mortality vs. Maximum Annual Flow during Spawning and Incubation . . . . 114 3. Additional Mortality vs. Minimum Annual Flow during Spawning and Incubation . . . . 117 E. Calculation of Expected Egg to Fry Survival . . . 118 1. Steps in the Calculation 118 2. Calculation of Expected Additional Mortality 118 3. Estimation of Stable Flow Survival 123 4. Calculation of Expected Egg to Fry Survival. 124 F. The Effect of Channel Geometry and Dredging on Expected Egg to Fry Survival 126 v i CHAPTER Page VII ESTIMATION OF ADULT SALMON PRODUCTION 135 A. Introduction 135 B. Description of the Method 136 1. The Basic Concept . 136 2. Application of the Method to Estimating Adult Salmon Production . . . .„ 137 C. Example Calculations 142 D. Estimation of Catch 146 VIII DISCUSSION AND CONCLUSIONS . 150 A. A Historical Perspective 150 1. Instability of the Chilliwack River below Vedder Crossing 150 2. The Flood Control - Fish Resource Conflict . 151 B. The Wide Dyke Alternatives 151 C. The Method of Evaluation 153 D. The Value of Restoring Salmon Habitat 154 BIBLIOGRAPHY 156 PERSONAL COMMUNICATIONS . . . 162 APPENDIX 163 v i i LIST OF TABLES TABLE Page I " Mean Monthly Contribution of Chilliwack Lake Outflow to the Flow at Vedder Crossing 15 II Calculated Bed Load Transport at Three Sections in the Vedder River 25 III Flood Protection Work Carried out on the Vedder River, 1923-19 76 36 IV Comparison of the Vedder River Escapements with the Vedder-Chilliwack River and Fraser River Escapements . . 52 V Approximate Capacity of Pink and Chum Spawning Areas in the Vedder-Chilliwack River System 64 VI Estimated Chum Spawning Area Capacity B.C. Hydro Bridge to Ford Road 67 VII : Egg to Fry Survival of Pink Salmon 1957-1965 75 VIII Average Annual Chum Salmon Escapements to the Total Fraser, Vedder-Chilliwack, and Harrison Spawning Areas . 75 IX Factors Affecting the Productivity of Ten Hypothetical Pink Salmon Spawners 76 X Comparison of the Sediment Control Problems of the Vedder River in a Narrow Channel and a Wide Channel 83 XI Examples of Channel Modification Alternatives for the Vedder River '. 84 XII Mechanisms of Flood and Low Flow Induced Mortality in the Vedder River 103 XIII Observations of Flow Induced Mortality in the Vedder River 104 XIV Discharge of the Chilliwack River During Pink Salmon Spawning and Incubation 108 XV Three Rough Estimates of Mortality Due to Floods . . . . 116 XVI Calculation of Expected Additional Mortality 121 XVII Expected Egg to Fry Survival for Different Stable Flow Survivals and Additional Mortality vs. Flow Curves . . . 125 v i i i TABLE Page XVIII Expected Egg to Fry Survival for Channels of Different Widths 130 XIX Expected Egg to Fry Survival for a Side Channel Development Project 134 XX Example Calculations of Adult Chum Salmon Production from Alternative Spawning Areas 143 XXI Comparison of the Risk of a Low Level of Production . . 145 XXII Estimation of Catch Contributed by Alternative Spawning Areas . '. 149 ix LIST OF FIGURES FIGURE Page 1. Vedder-Chilliwack River Watershed 5 2. Precipitation at Chilliwack, B.C 9 3. Maximum Recorded Daily Discharge and Mean Monthly Discharge for the Chilliwack River at Vedder Crossing . 10 4. Flood Hydrographs of the Chilliwack River at Vedder Crossing for 1975 * 11 5. Frequency and Magnitude of Minimum Daily Flows in the Chilliwack River at Vedder Crossing 14 6. Vedder-Chilliwack River Profile 18 7. Airphotograph of the Vedder River, June, 19 76 . . . . . 20 8. Former Channels of the Chilliwack River . 28 9. Map of Vedder River Showing Approximate Location of Major Floods 35 10. Airphotographs of the Vedder River, 1958 and 1969 . . . 49 11. Location of Major Pink and Chum Salmon Spawning Areas . 63 12. The Number of Spawners in the Vedder River as a Percent of the Total Escapement to the Vedder-Chilliwack 1935-1966 69 13. Pink and Chum Escapements to the Vedder River 1935-1966. 70 14. Proportion of Pink Salmon Spawning in the Vedder-Chilliwack River Below Allison Pool vs. Time 73 15. Sketch of AlternativeC Secondary Set-Back Dykes . . . . 86 16. Sketch of Alternative D Wide Armoured Dykes 87 17. Changes in Types of Uncertainty in Relation to the Degree of Environmental Control 97 18. Sketch of Side Channel Rehabilitation Project 100 19. Egg to Fry Survival vs. Difference Between Extreme Flows During Spawning and Incubation 109 X FIGURE Page 20. Big Qualicum River Chum Egg to Fry Survival vs. Peak Daily Discharge During Incubation I l l 21. Additional Mortality vs. Maximum Annual Flow During Spawning and Incubation 115 22. Additional Mortality vs. Minimum Annual Flow During Spawning and Incubation 119 23. Additional Mortality vs. Flow Curves used in Expected Survival Calculation 120 24. Additional Mortality vs. Maximum Annual Flow for Channels of Different Widths . . . 131 25. Additional Mortality vs. Flow for a Side Channel Development 132 26. Examples of Conversion of Estimates to Matrix Form . . . 138 2 7.v Schematic Diagram of Calculation 140 28. Adult Chum Salmon Production vs. Probability 144 29. Adult Chum Salmon Production vs. Probability for Examples of Side Channel Development 147 1A Multiplication of a 5 x 1 Fry Production Matrix by a 5 x 5 Flood Induced Mortality Matrix 164 2A Cumulative Probability vs. Additional Mortality due to Floods 166 xi ACKNOWLEDGEMENTS The author is very grateful to his supervisor Professor S. 0. Russell for his guidance and encouragement. Thanks are extended to those biologists and engineers of various agencies that gave freely of their time to provide information and criticism. The author would also like to thank Dave McLean, a fellow student, for sharing and discussing the results of his sediment transport study of the Vedder River and for his assistance in compiling the h i s t o r i c a l information. 1. CHAPTER I INTRODUCTION In British Columbia today the expansion of human activities associated with population and economic growth is leading to increased pressure on the environment. Massive hydro-electric projects, open p i t mines, port developments, pipelines and urban growth are some of the many developments we can expect. For each development we are faced with a problem in assessing environmental effects: how do we estimate what changes in the environment w i l l result from a proposed development? Frequently conflicts arise between government agencies or between government, industry and citizens groups. The uncertainties and d i f f i -culties in evaluating changes in the environment make both p o l i t i c a l and technical solutions d i f f i c u l t . There are too few methods available that can deal satisfactorily with the imperfect and incomplete data, the risk and uncertainty that are usually a part of an environmental analysis. This thesis presents the background and history of a current development vs. environment problem and describes an attempt to develop and apply a quantitative method that considers subjective opinion, risk and uncertainty directly in the analysis. The example chosen for this study is the flood control and fishery resource problem of the^Vedder River, British Columbia; specifically, to evaluate how the choice of different flood control schemes w i l l affect the production of pink and chum salmon. In December, 1975 the Vedder River caused moire than $700,000 flood damage to nearby property. The flood also caused an extensive loss of eggs of pink and chum salmon, the two main commercial species that u t i l i z e 2. the river. Debris and sediment deposited in the channel by the flood made emergency channel work necessary and government agencies initiated a reappraisal of long term solutions to prevent further flooding. The river i s an important producer of four species of salmon and trout but during the past several years the river has los.t spawning and rearing areas due to a combination of floods with associated natural channel changes and a r t i f i c i a l channel alterations. The long term solution should provide both flood protection and the capability for salmon and trout protection. The conflict that has existed between people concerned with flood control and people responsible for fisheries is illustrated by the following correspondence. In 1964, i n a letter to W.G.R. Simpson, the Reeve of the Municipality of Chilliwhack, W. R. Hourston, then the Director of the Pacific Area, Federal Department of Fisheries, writes, VI wish to bring to your attention a recent development which has resulted in the loss of many millions of chum salmon and pink salmon eggs. This has been the direct result of flood control measures in the lower Vedder River." The Reeve replies, "I realize the importance of the fishing industry to British Columbia. On the other hand, I have a great responsibility for the protection of l i f e and property in this municipality. When I think of this river in spate, on i t s mad terrifying plunge through our area, I thank the Almighty for the protection works carried out..." Since 1964 the decision making process has changed considerably and now more cooperation between government agencies is possible. The basic technical issues, however, have not been resolved. Flood control and pink and chum salmon production are not the only important aspects of the Vedder River problem. Coho salmon and steelhead 3. trout reared in the Vedder River support a portion of an important sport fishery. The potential of the river bank areas as recreational land i s only partly developed. Flood control and fisheries development schemes may require farmland. These aspects of the problem are not considered in this thesis even though they may have a significant influence on the eventual solution. In order to demonstrate a method of evaluation i t is desirable to evaluate f a i r l y r e a l i s t i c alternatives. For the Vedder River problem this requires understanding of the mechanisms and frequency of flooding, under-standing of changes in the river due to natural causes or human intervention, and understanding of the biological requirements, previous levels of abundance, and objectives of development of the Vedder-Chilliwack stocks of pink and chum salmon. Chapters II, III and IV present some of the history and background necessary for the suggestion of alternatives in Chapter V. Chapter VI presents evidence that variable discharge and narrowing of the river channel are a significant cause of inefficient spawning and egg and alevin mortality. A technique to estimate this mortality i s developed. In Chapter VII this technique is used in conjunction with a probabilistic method of calculation to estimate the production of chum adults for a few example spawning areas. Chapter VIII summarizes the history of the problem and discusses the method and implications for management of the Vedder River. 4. CHAPTER II THE PHYSICAL SETTING A. LOCATION The Chilliwack River joins the Fraser River f i f t y miles east of Vancouver and i s the largest tributary of the Fraser on the south side of the lower Fraser Valley. The Vedder River i s the name given to a four mile reach of the Chilliwack River that flows west from Vedder Crossing to the head of the Vedder Canal (Figure 1). The Chilliwack River drains a mountainous area of about 474 square miles of which 164 square miles are in the State of Washington. The head-waters originate in the rugged 8,000 foot high Border Peaks of the Cascade Range and flow ten miles north to Chilliwack Lake, just north of the Canada-USA border. The 3,000 acre Chilliwack Lake i s at 2030 feet above sea level (ASL) and from here the river follows a steeply graded glacial valley 28 miles to Vedder Crossing. There the river emerges from the Cascades on to an a l l u v i a l fan and f a l l s from 100 feet ASL to about 30 feet ASL where the Vedder Canal crosses the almost f l a t Fraser Floodplain. Local flooding and bank erosion occur from about four miles above Vedder Crossing to the head of Vedder Canal. There is also a more serious threat of a radical change of river course between Vedder Crossing and the canal which would cause widespread flooding of low lands. Salmon and trout use a l l the Vedder-Chillwack system except for the very steep headwaters and tributaries. The Vedder River and that part of the Chilliwack River just upstream of Vedder Crossing, the reach that is prone to flooding, provides a large proportion of the spawning and rearing capabilities of the river. v i - A.ppt2ox. LIMIT £>P - / \ —ALLUVIAL PAN / / \ . .CMILLIWACUC „v3 y LAKE i \ JtooL-7172 A -A LA.ICE • V-7 9 7 ® FIG. I - VEDDER-CHILLIWACK RIVER WATERSHED B. GLACIAL HISTORY AND PHYSICAL FEATURES The d i f f i c u l t y of controlling the Vedder River flooding is largely a result of features shaped by recent a l l u v i a l and glacial activity. The Vedder i s a stream flowing across and actively building an a l l u v i a l fan and as such i t i s subject to sudden and abrupt channel changes. This trouble-some fan building and channel switching behaviour occurs during high flows. The highest flows occur during flash floods that are generated by heavy rainstorms on the steep, relatively impervious drainage basin which has been shaped by alpine and valley glaciers. Prior to the most recent glaciation in southern BC, the Sumas Glaciation, the Fraser River is thought to have flowed through the Sumas Valley creating a flood plain between Vedder Mountain and Sumas Mountain (Armstrong, 1959). During the recession of the Sumas ice Armstrong proposed that a large ice block in the Sumas Valley diverted meltwaters and the Fraser River north of Sumas Mountain to near the present Fraser River channel. About the same time meltwaters from the Chilliwack Valley Glacier were flowing southwest down the Columbia Valley into the Nooksack River drainage (Munshaw, 1976). After the ice block wasted away a large 4 by 8 mile shallow lake remained in the Sumas Valley and the Chilliwack River pushed north through the Vedder Crossing gap to the Fraser River. For about the last 10,000 years the Chilliwack River has been building a sand and gravel al l u v i a l fan which now is about 70 feet thick at Vedder Crossing and extends into the Fraser River flood plain in the form of a flat cone ./ with a four mile radius. During the Sumas Glaciation the Chilliwack Valley Glacier flowed east to west following but modifying a valley shaped by former glaciations 7. (Munshaw, 1976). The glacier imposed a steep bedrock and rubble gradient of about 70 feet per mile on the Chilliwack River which has a lesser slope only in the lower reaches. Most of the previously deposited unconsolidated formations were removed by the last glaciation; however, the glacier did "smear" a thin mantle of t i l l on the valley walls and deposited up to 35 feet of sandy t i l l and d r i f t in the h i l l y Ryder Lake area, east of Vedder Crossing and north of the Chilliwack River (Armstrong, 1959) . Recessional outwash sand and gravel and glacial d r i f t were deposited in the valley bottom generally increasing in thickness toward Vedder Crossing. There are about nine major tributaries of the Chilliwack River below Chilliwack Lake draining 353 square miles or 73% of the total basin area. These tributary streams typically occupy steep sided valleys alpine glaciers. Throughout this drainage area bedrock is. at the surface or covered by a thin mantle of d r i f t (Armstrong, 1959). C. HYDROLOGY The Chilliwack River watershed characteristics and climatic factors produce extremely variable flows. For example, the max. daily flow of 27,000 cfs recorded at Vedder Crossing on December 29, 1917 i s almost 100 times the min. daily flow of 280 cfs on November 30, 1952. The central Fraser Valley experiences warm dry summers and cool moist winters. The mean annual total precipitation at Chilliwack is 68 inches per year of which 40 inches (water equivalent) i s precipitated as snow (BC Ministry of Agriculture, 1976). Since about 50% of the Chilliwack River Basin i s at greater than 3700 feet elevation the lack of precipitation recording stations above 2000 feet make i t d i f f i c u l t to estimate orographic 8. effects in the watershed. A rough calculation of annual basin precipitation can be made from the mean annual runoff of approximately 4.9 cfs per square mile at Vedder Crossing. This corresponds to about 66 inches of runoff per year. Considering that the probable evapotranspiration i s about 20 inches per year would indicate that the mean annual precipitation over the total watershed i s about 90 inches per year. The greatest precipitation over 24 hours recorded at Chilliwack was 4.81 inches (Atmospheric Environment Service). Storms precipitating over 4 inches in 24 hours can occur from October through March (Figure 2). The average annual discharge for the Chilliwack River at Vedder Crossing i s 2410 cfs based on 43 years records (Water Survey of Canada). From Figure 3 i t can be seen that the highest monthly mean flows occur in May, June and July whereas the largest daily flows occur from October to February. Two different mechanisms cause these spring floods and winter floods resulting in different requirements for.flood control and different effects on the salmon and trout. Figure 4 shows a typical spring flood hydrograph (return period approximately 2.5 years) and a winter flood hydrograph (return period approximately 10 years). The mean spring flood (41 year average) i s . 8600 cfs with a maximum of 15,400 cfs occurring on June 2, 1968. The mean winter flood (41 year average) i s 10,350 cfs with a maximum of 27,000 cfs occurring on December 29, 1917. The spring floods, due mostly to snowmelt, have only rarely caused extensive flooding. The rise of the hydrograph i s gradual and the instan-taneous peak i s usually from a few percent to 20 percent higher than the daily mean flow. Backwater from the Fraser River in spring can, however, 9. 10.0 I (O ) MAXIMUM RECORDED 24 HOUR PRECIPITATION (30 YEARS RECORDS) 8.0 MEAN MONTHLY PRECIPITATION 6.0 o M H <C H H PH H O W Pi P* 4.0 2.0 Aug S 0 N D J F M A M J J Aug FIGURE 2 PRECIPITATION AT CHILLIWACK, B.C. 10. 30,000 WINTER FLOODS SPRING FLOODS 25,000 20,000 DISCHARGE (cfs) 15,000 10,000 5,000 (O) MAXIMUM RECORDED DAILY FLOWS (40 years records) MEAN MONTHLY DISCHARGE APPROXIMATE FRESHWATER LIFE-CYCLE Aug S PINK SALMON CHUM SALMON SPAWNING INCUBATION EMERGENCE 1 FIGURE 3. MAXIMUM RECORDED DAILY DISCHARGE AND MEAN MONTHLY DISCHARGE FOR THE CHILLIWACK RIVER AT VEDDER CROSSING 11. 30,000 20,000 DISCHARGE (cfs) 10,000 8,000 6,000 4,000 2,000 0 MAXIMUM INSTANTANEOUS DISCHARGE DECEMBER 3, 1975 27,800 cfs DECEMBER 3, 19 75 18,700 cfs WINTER FLOOD JUNE 5, 1975 9,380 cfs SPRING FLOOD 10 15 DAYS 20 25 30 FIGURE 4. FLOOD HYDROGRAPHS OF THE CHILLIWACK RIVER AT VEDDER CROSSING FOR 1975 12. cause sustained high water levels in the lower, river that dyke designs must consider. A relatively high flow in spring is beneficial for some species of salmon. The freshet usually coincides with and assists the emergence and seaward migration of pink and chum fry (Figure 3). The high flows also remove some of the fines accumulated in the gravel over the winter. The spring floods, therefore, are not l a i major cause of flood damage. Figure 4 shows the winter flood hydrograph of December, .1975. Most of the precipitation, 4.05 inches of rain and snow at Chilliwack, f e l l on December 1. At higher elevations the precipitation would have fallen as snow. On December 2 and 3 a further 3.56 inches of rain was recorded at Chilliwack while temperatures rose from 30°F on December 1 to 48°F on December 2. This produced a "rain on snow" condition that generated a large volume of runoff from both melting snow and from direct r a i n f a l l . In contrast to the spring flood^note the steep rise of the December 1975 hydrograph and that the magnitude of the instantaneous peak i s 48% greater than the daily mean flow. This is the type of flood that causes channel shifting, transports large volumes of sediment and i n f l i c t s the greatest flood damage on nearby land and on the salmon and trout. Computer modelling of Chilliwack River floods using the UBC Water-shed Model revealed that Chilliwack Lake provides almost negligible flood control storage for the Vedder River (McLean, 1976). Several major t r i -butaries, receiving high intensity precipitation because of orographic effects, are below Chilliwack Lake. By September cooler temperatures and lack of snow effectively terminate snowmelt runoff. The normal series of rainstorms from the Pacific Ocean usually begin in f a l l ; however, i f this precipitation is 13. delayed, low flows result. Almost 50% of a l l the annual minimum flows occur in September and October (Figure 5). With further delay of f a l l precipitation extreme low flows can occur in November. The annual minimum flow also occurs frequently in January, February and March when precipitation f a l l i n g as snow produces l i t t l e runoff. Chilliwack Lake does not appear to provide any significant storage to maintain adequate flows at Vedder Crossing. A comparison of mean monthly flows at Vedder Crossing and at the outlet of Chilliwack Lake'does show,v. however, that the runoff contribution of the basin above Chilliwack Lake during the low flow months of January and February i s less than at any other time of year (Table 1). This probably reflects the higher elevation of the upper watershed and the greater fraction of the precipitation that would f a l l as snow. D. FORESTS IN THE WATERSHED The Chilliwack Valley and tributary valleys have supported a logging industry since about 1910 when a logging railroad was built as far as Chilliwack Lake (Goodyear, 1957). Favourable climate combined with relatively rich soils produce commercial stands of balsam f i r and hemlock on the upper slopes and cedar and douglas f i r at lower, elevations. The Chilliwack Forest is part of the Dewdney Public Sustained Yield Unit with a permissible annual cut of about 5 to 10 million cubic feet,.worth approximately $500,000 to $1,000,000 annually (Dreher, 1974). Two aspects of logging activity in the Chilliwack basin must be considered for their possible effect on flooding and water quality in the Vedder River: 10 ^ _ co u o o (U n CO r o 53 O 53 53 M W CJ 53 H S3 W P o P o Pi u w o 53 5ti APPROXIMATE FRESHWATER LIFE-CYCLE 800 CO 4-1 CJ 700 600 o co « °500 P o W cu P M o cn400 aj a) 53 H 200 100 Aug S ? PINK SALMON CHUM SALMON J F M M Aug SPAWNING INCUBATION EMERGENCE MINIMUM FLOW GREATER THAN 1000 cfs Aug S O N D J F M A M J Aug FIGURE 5. FREQUENCY AND MAGNITUDE OF MINIMUM DAILY FLOWS IN THE CHILLIWACK RIVER AT VEDDER CROSSING TABLE I MEAN MONTHLY CONTRIBUTION OF CHILLIWACK LAKE OUTFLOW TO THE FLOW AT VEDDER CROSSING MONTH i FLOW @ VEDDER CROSSING (43 year mean) FLOW @ OUTLET OF CHILLIWACK .LAKE (45 year mean) CONTRIBUTION OF CHILLIWACK ,. LAKE TO TOTAL FLOW % JAN 2010 450 18.3 FEB 1880 435 18.8 MAR 1430 . 355 19.9 APR 1920 522 21.4 MAY 4010 1150 22.3 JUN 5030 1550 23.6 JUL 3390 1080 24.2 AUG 1630 541 24.9 SEP 1310 382 22.6 OCT 1790 472 20.9 NOV 2070 535 20.5 DEC 2240 573 20.4 ANNUAL MEAN 2410 668 21.7 DRAINAGE AREA ABOVE VEDDER CROSSING ABOVE CHILLIWACK LAKE PERCENT ABOVE CHILLIWACK LAKE 2 474 miles . 127 miles 26.8 16. 1) has clearcutting significantly increased the peak flow of winter floods? and 2) has logging activity significantly increased s i l t deposition and accumulation of debris in the Vedder River? No attempt has been made to provide conclusive answers to these questions but some general observations can be made. The most damaging floods in the Vedder are the winter floods caused by sustained intense r a i n f a l l on snow. When these conditions prevail, interception, evapotranspiration and antecedent s o i l moisture become insignificant in determining maximum flows (Willington, 1967). The proportion of runoff generated by direct r a i n f a l l during extreme events i s , therefore, unlikely to be affected by clearcutting. The snowmelt pro-portion of runoff may, however, be increased by clearcutting as advected heat reaching the snowpack i s greater in clearcut areas (Gray, 1970). The commercial logging areas in the basin consist of about 45 square miles of mature stands of commercial timber and about 71 square miles of immature timber and areas regenerating following logging or fires (Fairbairn, 1973) . The remaining 358 square miles consist of non-commercial stands and unproductive areas due to steep slopes and poor quality soils. Since logging has been somewhat sporadic over about sixty years i t i s d i f f i c u l t to estimate the percentage of the basin subject to changed hydrologic conditions at any point in time but this fraction of the basin area probably has been less than 10%. It i s , therefore, unlikely that past logging has significantly increased the peak winter flows in the Vedder. 17. The suspended sediment concentration of the Vedder River during flows of less than 3000 cfs i s low, 0 to 40 ppm, however, i t can be 350 ppm during major floods (Water Survey of Canada). Slash burnt logged areas with poorly designed or maintained roads may contribute a significant proportion of the suspended sediment. Strict regulations concerning the protection of streams and the location of much of the present logging above Chilliwack Lake likely make current contributions less than past years. The presence of reject timber and rooted tree log jams in the Chilliwack-Vedder River can deflect the current against the banks causing bank erosion, bank caving and stream inst a b i l i t y . Since 1959 a l l timber sales issued have required the removal of rejects from the stream bed (Marr, 1964). Rooted trees, a product of natural erosion, w i l l continue to be a problem. Although individual tributaries may be seriously affected by increased flooding, s i l t a t i o n , and debris due to extensive logging of their small watersheds, present levels of logging activity do not appear to significantly increase the peak flows and suspended sediment load of the Vedder River. E. THE CHILLIWACK-VEDDER RIVER CHANNEL 1. Description From Chilliwack Lake to Liumchen Creek, a distance of 23 miles, the Chilliwack River Channel i s narrow, sinuous and steeply graded. Except for two short reaches of lesser slope where the river meanders on coarse gravel the river drops about 80 feet per mile down a valley slope imposed by glaciation (Figure 6). The river i s unable to erode the large boulders 2000 1500 ELEVATION (FEET ASL) 1000 5000 HEADWATER ELEV. APPROX. 9000 FT. 10 CHILLIWACK LAKE \ FOLEY CREEK e \ \ IUMCHEN CREEK VEDDER CROSSING B.C. HYDRO BRIDGE i — VEDDER CANAL 15 20 25 30 35 DISTANCE FROM HEADWATERS (MILES) 40 45 50 55 oo FIGURE 6. VEDDER - CHILLIWACK RIVER PROFILE 19. and occasional outcrop of bedrock that form the channel bed. Log jams are common in this reach; a few miles below Chilliwack Lake a log jam several hundred feet long blocks an old channel. Below Liumchen Creek the channel widens, and the slope decreases to about 45 feet per mile. The river meanders irregularly within a low terrace of i t s own alluvium which is protected by dumped rock in a few places. Secondary channels branch around frequent islands and bars which are . commonly formed or destroyed by currents deflected by log jams. The average active channel width for the mile long reach above Vedder Crossing is about 1200 feet with the slope decreasing to about 25 feet per mile at Vedder Crossing. At Vedder Crossing the river flows through a narrow 150 foot wide gap in bedrock. Bedrock on the south and the Department of National Defence dyke on the north continue to confine the river for an additional 1000 feet. For the remaining distance to Ford Road, about 2 miles, the river widens to an average active channel width of about 800 feet in a braided channel. Local expansions in the width coincide with the formation of large bars near Peach Road and Ford Road (Figure 7). From Ford Road to the BC Hydro Railway Bridge the river i s con-stricted by bank protection in a channel varying from 250 to 500 feet in width (Figure 7). Bars have formed in the expansion at Hopedale Road and just below the railway bridge. The water surface slope decreases rapidly over this reach from about 20 feet per mile at Ford Road to 13 feet per mile just below the railway bridge. Below the railway bridge the river widens slightly but the meanders are constrained by low protected banks within wide set-back dykes that 201. eventually form the 3.5 mile long Vedder Canal. The low flow channel meanders sinuously within the canal forming side bars at regular intervals. At the mouth of the canal, near the junction with the Sumas River, the Vedder River has deposited a bar composed of sand and s i l t . The grain size of bar material decreases from Vedder Crossing to the canal corresponding to the decrease in slope from about 25 feet per mile to about 2 feet per mile in the canal. The larger sizes, Dn , decrease from about 4 inches at Vedder Crossing to about 1% inches in the canal. Smaller sizes, _, decrease from about 1\ inches to 1 inch over the 5 mile long 65 reach (D. McLean, 1978). 2. Channel Stability The control of the Vedder requires answers to three questions:' 1. Where i s the channel aggrading or degrading and at what rate? 2. Where is the source of the sediment? 3. Are the channel processes understood well enough to predict what w i l l happen i f the channel i s modified by new dykes or bank protection? In an attempt to find answers to these questions the BC Water Resources Service surveyed a set of several cross-sections in 1958 and resurveyed them again in 1963. The cross-sections show that systematic deposition occurred-below Vedder Crossing (D. McLean, 1978). Extensive realigning of banks and channel clearing carried out by Chilliwhack Municipality during this period make calculation of the net aggradation from these cross-sections impossible. Furthermore, the small floods that occurred (less than 10,000 cfs) between surveys would have deposited relatively small amounts of sediment. From 1971 to 1973 the Sediment Survey Section of the Federal Department of the Environment annually surveyed 11 cross-sections from Vedder Crossing to the canal. They concluded that there was net aggradation of the study reach over the survey period, however, the cross-sections were too far apart to calculate a rate of accumulation (Sediment Survey Section, 1974). The BC Water Investigations Branch of the Water Resources Service surveyed a new set of some 20 cross-sections in July 1975 and again in January, 19 76 after the major 18,700 cfs flood of December 5, 1975. Between the two bridges the channel was found to have aggraded an average of 1 to 2 feet and the net sedimentation was calculated to be 258,000 cubic yards (W. Tempest, 1976). More evidence that the Vedder channel i s aggrading is provided by the Water Survey of Canada gauging station just downstream from the BC Hydro railway bridge. A specific gauge plot for flows of 5000 and 7500 cfs showed that the bed aggraded about 2% feet from 1953 to 19 73 in spite of gravel removal and bank realignment near the gauging station (D. McLean, 1978). The source of the sediment deposited in the Vedder River i s the 3 mile reach upstream of Vedder Crossing. Airphotos before and after the 19 75 flood show extensive erosion of banks, bars, and islands and the creation of new channels. Similarly, a comparison of airphotos of 1940 and 1952 show that the large floods of 1948, 1949 and 1951 removed most of the vegetation from the islands and caused major channel shifts. Ultimately some of the gravel must come from farther upstream, from the tributaries and from bank erosion where in a few locations the river has access to erodible materials. It is suggested that the coarse sediment i s eventually carried down to the bars and islands above Vedder Crossing and is stored here unt i l major floods shift this material into the lower river. Fine sediment from tributaries and from bank erosion contribute to a considerable suspended sediment load during large floods. Almost a l l of this material would be carried out to the Fraser River except for local deposition in backwaters and side channels. The suspended sediment load appears to have l i t t l e effect on channel s t a b i l i t y . Bed load transport i s generally accepted to begin at a threshold flow for a given size material. If this flow persists for some time a l l the threshold size material and smaller at the surface of the bed w i l l be removed providing no material is received from upstream. The removal of the finer material leaves the coarser stones to stabilize or "armour" the surface of the bed. For a higher flow the bed w i l l again stabilize, but with larger material. For extremely high flows even the largest materials of the river' own alluvium w i l l move and the stabilizing effect is lost. The bed load transport process i s complicated by local changes in river width, depth, slope and the size distribution of bed material. The sizes of material moved and the theoretical bed load transport capacity are different for each section. Generally, for moderately high flows, the wide sections have a relatively low bed load transport capacity and become sediment storage areas. The narrow sections, however, have a higher bed load transport capacity and carry material through the section. In extremely large floods even the wide sections transport bed load u n t i l decreasing flow or channel geometry downstream reduces the transport capacity and deposition occurs. Measurement of cross-section areas before and after the 19 75 flood showed greater deposition in the wide sections than in narrow sections (D. McLean, 1978). The erosion of bars and islands by this: flood indicate that even these wide sections transport material during large floods. Much effort has been spent trying to develop mathematical formulas to describe bed load transport. Formulas have been developed for sand bed rivers from flume experiments, but the formulas describe only a steady state condition for one homogeneous reach. These formulas, therefore, are d i f f i c u l t to apply to a river of variable slope, width, depth, flow and grain size distribution. The formulas do, however, give an indication of the relative transport potential at a section. D. McLean calculated the bed load transport rate along the Vedder River using a modified Einstein (1950) formula adapted for gravel rivers (D. McLean, 1978). The results show that the transport rate decreases considerably down the river due to the decrease in channel slope (Table II). The formula predicts that bed load transport i s roughly proportional to the slope cubed. Thus, only a small fraction of the bed load passing through Vedder Crossing i s transported below the railway bridge. The bed load formula was partially verified by agreement with bed load sampling done by the Sediment Survey of Canada in 19 72 at the railway bridge. The formula also predicted the 1975 aggradation between the two 3 bridges f a i r l y accurately. The calculated volume of 200,000 yards is 3 close to the surveyed volume of 258,000 yards . The formula was then used to predict the average annual deposition between the two bridges by using a flow-duration curve to estimate the average flood flows. The results showed that very l i t t l e deposition should TABLE II CALCULATED BED LOAD TRANSPORT AT THREE SECTIONS IN THE VEDDER RIVER 1 RIVER BED LOAD TRANSPORT (TONS/DAY) DISCHARGE (cfs) VEDDER CROSSING BROWNE ROAD BC HYDRO BRIDGE 7,000 2,500 250 30 :10,000 11,000 1,200 200 12,500 32,000 2,800 750 15,000 85,000 6,000 2,000 from D. McLean, 1978 26". occur below the railway bridge. The average annual deposition between the 3 two bridges is likely to be about 170,000 yards . Steeply sloped gravel bed rivers such as the Vedder are typically braided and unstable laterally. An explanation for braiding is given by Henderson (1966), "On steep slopes where the transporting power is high the banks are most vulnerable to attack and that in fact the river dissipates i t s surplus power by attack on the banks and the formation of multiple channels". Lateral instability is further increased in the Vedder River due to the aggradation of the bed. The instability of the Vedder River Channel presents three main problems: 1) The river frequently erodes i t s banks and washes away adjacent property. 2) The aggradation of the channel bed reduces the flow carrying capacity of the channel. The frequency and severity of flooding i s , thereby, increased. 3) Unchecked aggradation of the channel bed could result in a radical shift of the river to another location on the a l l u v i a l fan. The next chapter relates how people have dealt with these problems in the past. 27. CHAPTER III THE' HIS TORY..OF THE VEDDER CHANNEL A. CHANNEL SHIFTS DURING NATIVE OCCUPATION OF THE CHILLIWACK RIVER ALLUVIAL FAN The Stalo Indians occupied the Fraser Valley below the Fraser Canyon prior to the arrival of Europeans. Composed of 17 p o l i t i c a l l y independent tribes the Stalo shared a common language and culture, developed by trade along the Fraser and by contact during the annual salmon fishery at Yale (Duff, 1952). The Chilliwack, a Stalo tribe, controlled territory that included the Chilliwack River Basin, the Chilliwack Alluvial Fan and a northern portion of the Nooksack River drainage. The early shifts and changes of the river are remembered in the traditions and place names of the Chilliwack Tribe obtained from members of the Tribe by Duff (1952) and Wells (1965). Long ago, says the tradition the Chilliwack flowed straight west into Sumas Lake. After some time the river suddenly l e f t i t s channel at Vedder Crossing and flowed north-east and north to the Fraser. The Indians called the old channel "Thewlnum", meaning, "river that changed i t s course". The mouth of the river slowly worked i t s way westward along the Fraser as channel shifts occurred on the lower part of the fan, where the Indians named a place, "Soowahlihl", meaning, "large stream that dissappeared". The river also opened up two other major channels at Vedder Crossing, the "Coqualeetza" (later known as Luckakuk) through present day Sardis and the "Atchelitz" Channel. These two channels joined three miles north north-west of Vedder Crossing at "Atchelitz", meaning, "place where two rivers meet".(Figure 8). 29. The villages of the Chilliwack were constructed above Vedder Crossing before 1830. The building of Fort Langley in 182 7 and the presence of whites reduced the threat of raids from warlike coastal tribes and the Chilliwack were able to move out toward the Fraser without fear of harassment (Duff, 1952). Until 1830, therefore, the Chilliwack's villages were generally not endangered by the erratic behaviour of the lower Chilliwack River. One incident occurred, however, when the river washed away a large plank house built on a low river terrace near Vedder Crossing (Duff, 1952). B. EARLY WHITE SETTLEMENT AND ESTABLISHMENT OF THE CHILLIWACK RIVER IN THE VEDDER CHANNEL Simon Fraser, in 1808, was the f i r s t Caucasian to v i s i t the Chilliwack area during a quest to expand the territory of the fur trading North-West Company. The Hudson's Bay Company later b u i l t the f i r s t permanent settlement in the Fraser Valley, Fort Langley, i n 1827. Discovery of gold in the Fraser River gravel in 1858 brought thousands of goldseekers through the Chilliwack Area; during the years of the Fraser gold rush several travellers recognized the rich farming potential of the land and settled. The settlers found the climate and s o i l favourable for fruits, vegetables and dairying. By 1866 they were cultivating about 5000 acres finding markets for their products in New Westminster and i n the gold camps of the Caribou (Ramsay, 1975). One of the early settlers, Volkert Vedder, in 1865, took up 640 acres near present day Yarrow (Ramsay, 1975). From Vedder and his descendents came the names for Vedder Mountain, Vedder River, Vedder Cross-ing and Vedder Canal. 30. The early pioneers lived under the most trying hardships. Almost annually the Fraser River Flooded 15,000 - 20,000 acres of potentially good farmland. After the floods the remaining ponds and sloughs would breed swarms of mosquitoes. The people recognized the possibility of alleviating the flooding by dyking Chilliwack and Sumas but because of the magnitude and expense of the undertaking none of the early settlers were to see the dykes built (Sinclair, 1961). Adding to the hardship of the Fraser floods was the unpredictable winter flooding of the Chilliwack River. In 1872, at a meeting in Chilliwack, the settlers resolved to ask for government assistance to remove log jams from the river (Gibbard, 1937). During the f i r s t 15 years of settlement, 1858 to 1873, the Chilliwack River occupied the Chilliwack and Luckakuk channels (Figure 8). In 1873 Stewart Vedder reported,"There's muddy water in Vedder Creek!"; a part of the Chilliwack River had found i t s way into i t s former channel (Wells, pers. comm.). Two years later, in 1875, an intense winter storm generated a large flood that washed out a l l the bridges and used a l l four main channels: the Chilliwack, the Luckakuk, the Atchelitz and the Vedder (Gibbard, 1937). Casey Wells, a grandson of one of the earliest successful dairy farmers, A. C. Well's, said his grandfather lost his barns and 15 acres of his Sardis farm to the Luckakuk Channel during one night of this flood. After 1875 a portion of the flow of the river occupied a l l of the main channels, and the threat of flooding and having a troublesome...river to deal with was extended over a larger area than prior to 1875. The BC Government, i n an 1876 report by Edgar Dewdney, recommended keeping the Chilliwack River out of the Vedder Channel and confining i t to the Luckakuk 31. and A t c h e l i t z channels. This would ease the task of draining and dyking Sumas (Gibbard, 1937). The reclamation plan f o r Sumas, however, was too expensive for the province and region at that time, and the choice of channel was l e f t to the influence of the l o c a l residents and to the whim of the r i v e r . The Chilliwack area s e t t l e r s and the Sumas area s e t t l e r s argued over which channel should be the sole course of the r i v e r . H i s t o r i a n Gibbard reports, "... one knows that f o r years there were people i n Upper and Lower Sumas who believed the Chilliwack s e t t l e r s aided the diversion of the Chilliwack to the Vedder to the advantage of Chilliwack and disadvantage of the Sumas settlements." The dispute came to a head during the heavy flooding of 1894. "Colonel James Baker (then P r o v i n c i a l Secretary) t e l l s of h i s discovery of a l o c a l feud at Chilliwack which developed between residents of Chilliwack and residents of Sumas. A log-jam had formed i n Luckakuk Creek and prevented the main flow of the Vedder waters from going down the Luckakuk through what i s now Sardis. The Sumas people t r i e d to break the jam but were stopped by the Chilliwack people. Feelings ran high and both sides threatened to use arms. S p e c i a l Constables were sworn i n and dispatched to the scene, and trouble was averted on the promise of Colonel Baker to inve s t i g a t e and to see that j u s t i c e was done." (Dickson, 1946). Before anything could be done the r i v e r downcut the bed below Vedder Crossing and the complete flow of the Chilliwack River became w e l l established i n the Vedder Channel. 32. C. THE VEDDER RIVER DIVERSION Although the f i r s t o f f i c i a l plan to drain Sumas Lake and dyke the Sumas area was presented in 1876, construction on this large and expensive project was not started until 1919. During these 43 years there were at least eight separate attempts to construct the dykes, pumphouses, and canals (White, 1937). Several engineering firms surveyed the area and prepared plans. Of special interest are the engineer's concepts and plans for the diversion of the Vedder River. After 1894 the Vedder River carried the complete flow of the Chilliwack River into Sumas Lake. How could this flow be directed to the Fraser in a safe and permanent channel? The channel had to consist of two different sections. F i r s t l y , the river would f a l l steeply, about 70 feet, from Vedder Crossing to the Fraser Floodplain. Secondly, the channel would have to convey the flow across the Fraser floodplain at a very low gradient. The engineers' proposals differed in the location of the diversion, the protection required for the steep section and the amount and location of sediment deposition expected in the channel. The earliest plans called for turning the Vedder back into the Luckakuk Channel through Sardis. This was the shortest route, i t avoided crossing the low land near Sumas Lake, but the route has a very steep gradient. The channel would require extensive protection. The diversion plan for the Luckakuk was infeasible, however, because of the strong opposition of the people of Sardis and Chilliwack. At their instigation the Provincial Government built a strong rock-filled crib across the old entrance to the Luckakuk Channel (LeBaron, 1908). 33. In 1908 J. F. LeBaron proposed diverting the river from a point 3 ., miles downstream of Vedder Crossing near Hopedale Road to Wilson Slough and the Fraser River. The steep gradient and excessive velocity of the flow was to be overcome by three regulating dams in the channel. LeBaron recognized that the river could bring down an immense amount of sand and gravel in a flood but did not specify how this would affect the channel. He warned Sardis by stating that the Luckakuk crib and revetment were so low that they would afford l i t t l e protection against recutting of the Luckakuk channel in a flood. Later in 1908, J. D. Schuyler reviewed several of the previous plans. Schuyler noted that the low s i l t load of the river was not likely to f i l l in the canal quickly. He conjectured that sand deposited at the foot of the steep part of the grade could be excavated periodically (Schuyler, 1909). The plan that was eventually adopted and b u i l t , the Sinclair Plan, diverted the Vedder from a point just upstream of Sumas Lake to the Sumas River at the base of Sumas Mountain. The Vedder channel dykes extended up to the BC Electric Company's railway embankments. Upstream of the railway bridge the plan called for some minor bank protection work and clearance of log jams and debris from the channel (Sinclair, 1961). With the exception of LeBaron's report none of the early reports examined by the writer commented on the serious problem of the river breaking out of i t s channel between Vedder Crossing and the new diversion channel (LeBaron, 1908, Schuyler, 1908, 1909, H i l l , 1909, Rice, 1913, Sinclair, 1961). None of these engineers recognized that a channel s h i f t could be triggered by deposition of sand and gravel Q,n the a l l u v i a l fan. 34. D. FLOODS, POLITICS, AND RIP-RAP 1923-1976 The Vedder River has flooded large areas of land and property at l e a s t f i v e times since 1923 and has caused s u b s t a n t i a l damage by erosion almost every year. Figure 9 shows the approximate l o c a t i o n of the f l o o d routes. In response to the emergencies created by the flooding and erosion, many i n d i v i d u a l s , government departments and other groups undertook bank protection and channel work to protect t h e i r i n t e r e s t s (Table I I I ) . These people included i n d i v i d u a l r i v e r s i d e property owners, the Sumas Drainage and Dyking D i s t r i c t , the Corporation of the Township of Chilliwhack (abbreviated i n t h i s thesis to C.T.C.), the P r o v i n c i a l Government Department of P u b l i c Works, the Department of Highways, the Department of A g r i c u l t u r e , the Water Resources Service, the BC E l e c t r i c Company, the Yarrow Waterworks Board, and the Federal Government, f i r s t through Unemployment R e l i e f Funds, then through the Department of National Defense and l a t e l y through the Fraser River J o i n t Advisory Board. P r i o r to proposal of a comprehensive Fraser River flood c o n t r o l plan i n 1968, no one agency or group of agencies assumed f u l l r e s p o n s i b i l i t y for the flood c o n t r o l of the Vedder-Chilliwack River. The bank protection and channel work f a i l e d to reduce the s e v e r i t y of flooding and erosion because the work was c a r r i e d out i n a piece-meal hap-hazard manner. The d i f f i c u l t task of sharing r e s p o n s i b l i t y between interested groups and the lack of a widely accepted and technically sound flood control scheme prevented the planning of longer term floo d control measures. Despite e f f o r t s of i n d i v i d u a l s and governments during the passage of over f i f t y years the r i v e r i s s t i l l without a s a t i s f a c t o r y channel. In response to the floods of the 1920's and 1930's workers generally cleared log jams from the channel and covered them with gravel to protect FIG.9 - MAP OF VEDDER RIVER SHOWING APPROX. LOCATION OF MAJOR FLOODS TABLE III FLOOD PROTECTION WORK CARRIED OUT ON THE VEDDER RIVER 1923-1976* YEAR LOCATION - TYPE OF WORK APPROX. COST AT TIME OF CONSTRUCTION GROUPS RESPONSIBLE ": REFERENCE 1920 VEDDER - Clearance of log jams and debris UPSTREAM OF RAILWAY BRIDGE - bank pro^t tection $1,943- Sumas Drainage and Dyking District F.N. Sinclair, 1961 1930 DOWNSTREAM OF RAILWAY "BRIDGE - cut off bend -1932(?) NORTH VEDDER DYKE - extended 5000 f t . - - Marr, 1964 1933 VEDDER - channel clearing - Federal Government Unemployment Relief Marr, 1964 VEDDER - channel clearing, gravel removal - C.T.C. Marr, 1964 1949 HOPEDALE-YARROW AREA - gravel removal - — Dept. of Fisheries, 1949 DOWNSTREAM OF VEDDER CROSSING - buildup bank - Department of National Defense C.T.C. 1951 VEDDER - channel clearing ,7,338 C.T.C. C.T.C. 1952 BROWNE ROAD - gravel removal - H. P. Klassen C.T.C. 1952 1953 VEDDER - channel clearing, wing dams 1,721 2,756 C.T.C. and Provincial Department of Pub. Works C.T.C. 1954 SOUTH B.C.E. RAILWAY EMBANKMENT -Floodway Bridge - B.C.E. Co. and Yarrow Water Works Board C.T.C. * This l i s t is not complete. Records of gravel removal were generally, not kept. On a few occasions property owners have contracted trucks to haul rock to protect their own property (Klein, pers. comm.). TABLE III (continued) APPROX. COST YEAR LOCATION - TYPE OF WORK AT TIME OF CONSTRUCTION GROUPS RESPONSIBLEIT:: REFERENCE 1954 SOUTH BANK NEAR VEDDER. MTN. :.ROAD -channel clearing, timber piles, dredging FORD ROAD - channel clearing 4,537 BROWNE ROAD - channel clearing LICKMAN ROAD - channel clearing C.T.C. and Provincial Department of -Public Works C.T.C. 1955 BROWNE ROAD ) channel clearing, KEITH WILSON ROAD ) rock protection 13,152 -1956 BROWNEr.ROAD - wing dam SOUTH BANK NEAR VEDDER MTN. ROAD -bank protection 14,852 C.T.C. and Provincial Department of Highways C.T.C. 1957 VEDDER - gravel removal - - Dept. of Fisheries, 1957 1958 LICKMAN ROAD - channel clearing, 1500 WEBSTER ROAD of protection work f t 3,476 C.T.C. and Prov. Dept. of Highways C.T.C. 1959 TAYLOR HILL - rock wing dam 3,375 C.T.C. and Prov. Dept. of Agriculture C.T.C. 1960 VEDDER - channel clearing 3,000 C.T.C. and Provincial Government C.T.C. TABLE III (continued) APPROX. COST YEAR LOCATION - TYPE OF WORK AT TIME OF CONSTRUCTION GROUPS RESPONSIBLE.: f REFERENCE 1961 PEACH RD. TO LTCKMAN RD. - 2000 ft of bank protection UPSTREAM OF HOPEDALE RD. - 2000 f t of bank protection UPSTREAM OF VEDDER CROSSING - channel clearing BROWNE RD. - rock protection C.T.C. and Provincial Govt. C. T.C. 1962 1964 VEDDER - heavy rock protection - channel clearing UPSTREAM OF B.C.E. RAILWAY BRIDGE -dyked off Hopedale channel forming Hopedale slough 80,539 C.T.C. and Provincial Govt. C. T.C. DYKE ROAD - gravel removal - C.T.C. C. T.C. 1967 BC HYDRO RAILWAY BRIDGE TO HOPEDALE ROAD - dyke extended 10,135 C.T.C. and Provincial Govt. C. T.C. 1968 UPSTREAM OF B.C.H. RAILWAY BRIDGE -rock protection 3,630 BC Hydro and C.T.C. C. T.C. 1968 1969 VEDDER - Bank Protection 30,000 C.T.C and Provincial Govt. C. .T.C. 1974 PEACH ROAD - 1000 feet of rip-rap ro protection - Provincial Water Resources Service C. • T.C OJ 1 oo ;. TABLE III (continued) APPROX. COST YEAR LOCATION - TYPE OF WORK AT TIME OF CONSTRUCTION GROUPS RESPONSIBLE": '•' REFERENCE 19 75 FORD ROAD - rip-rap on l e f t bank - Provincial Water Resources Service IPSFC, 1977 19 75-1976 VEDDER - restore low banks channel clearing of debris 100,000 Provincial Water Resources Service (BC Water Resources, 19 76) 1976 VEDDER - Phase I - raise banks 3 f t - remove debris - scalp bars 473,000 . Fraser River Joint Advisory Board (J. Wester, 1976) 1976 VEDDER - Phase II - dredge and stockpile 750,000 cu.yds. of gravel 682,000 (H.R. Milton, Pers. Comm.) VO 40. the banks. Rock protection was added at Vedder Crossing (Marr, 1964) . To straighten the channel the Sumas Drainage and Dyking Di s t r i c t cut off a large meander in the river just downstream of the railway bridge (Sinclair, 1961). In 1935 floodwaters broke over the north bank, overtopped the railway embankment north of the BC Hydro Railway Bridge, washed out 1000 feet of track and released floodwaters into Sumas East Prairie. After this flood the upstream end of the north Vedder Dyke was extended about 5000 feet paralleling the railway track. Funding of work during this period was assisted by Unemployment Relief Funds (Marr, 1964). In 1948 floodwaters again overtopped the north railway embankment (Marr, 1964). In 1951 log-jams formed in the main channel causing the river to break out over both banks. Water overtopped the north railway embankment and for the f i r s t time flooded the area south of the river (Raudsepp, 1955). The water threatened to overtop the south railway embankment at Yarrow but flood fighters dynamited a gap in the railway embankment just north of the South Vedder Dyke and the embankment held (C.T.C., 1952). The unpredictable timing of the sudden winter flooding and the potential of the river to flood and erode the banks at any point between the two bridges made the river a constant threat to the local property owners. They urged their municipal government, the C.T.C, to control the river. Lacking sufficient resources for the construction of major flood control works the Municipality appealed to the Provincial Government for assistance. Since the river threatened Provincial Government interests^ the two governments * Vedder Mountain road, paralleling the south bank below Vedder Crossing, was the responsibility of the Provincial Department of Public Works. The conservation of farmland was the responsibility of the Department of Agriculture. 4(1. agreed to share 50:50 the cost of emergency channel clearing and bank protection up to a few thousand dollars per year. With this assistance the Municipality was able to operate a b u l l -dozer for several days per year and sometimes employed a mobile dredge, shovel, and trucks. Generally two methods of channel maintenance were used. F i r s t l y , contractors removed snags and bulldozed definedcchannels, and secondly, they constructed wing dams to divert the current when the river threatened to erode and undercut a bank. Frequently, however, the river adopted a new channel above the work carried out making i t a total loss. Wing dams sometimes diverted the flow against new banks downstream relocating the erosion. Realizing the inadequacies of temporary work the Provincial Depart-ment of Public Works, in 1952, proposed to build a 240 foot wide straight channel bordered by 12 foot high dykes from Vedder Crossing to the BC Hydro bridge for an estimated cost of $500,000. There were both engineering and p o l i t i c a l d i f f i c u l t i e s with this proposal. The proposed channel would have shortened the existing channel by 2000 feet and probably would have been excessively steep. Since the slope of the channel would gradually flatten from 0.004 at the upper end to 0.0015 at the BC Electric Company railway bridge control of scour upstream and deposition downstream would be d i f f i c u l t . A Provincial Government Hydraulic Engineer considered that the cost of maintaining the proposed channel would very l i k e l y be higher than maintenance of the existing channel (Raudsepp, 1955). Even i f the proposed channel design had been sound ,the problem of obtaining the cooperation of interested groups and achieving a fair dis-tribution of the cost defeated the proposal. The Provincial Government and 42. the Municipality of Chilliwack (C.T.C.) could not afford to assume f u l l responsibility and they attempted to involve the Municipality of Sumas, local property owners, the BC Electric Company and the Department of National Defense . The Provincial Government suggested further that the flood control works would protect the Federally operated Coqualeetza Indian Hospital. Although the hospital i s situated adjacent to the old Luckakuk channel the Federal Department of Public Works considered there was no flood threat to this f a c i l i t y . In addition, the National Defense training base had constructed and maintained i t s own dyke and had not experienced flood damage in 1948 or 1951 (C.T.C, 1952). The proposal to involve the Federal Government defeated, the Provincial Member of the Legislative Assembly, Ken Kiernans, stated, "We regret we must deal with this problem on a piecemeal basis but there does not appear to be any other course open to us." (C.T.C, 1953). In April, 1953 the Federal Government passed B i l l 109, "An Act to Authorize the Grant of Assistance to a Province for the Conservation of Water Resources". The Municipality and the Provincial Governments f e l t that under this b i l l the Federal Government might provide flood control assistance. The Federal Government, however, stated that the b i l l ' s purpose was to provide for development of use of water only, such as water supply or hydroelectric power and considered that, "The control (of the Vedder) •.,i. would rather be directed toward the objective of ensuring the water flowed away unused as a resource..." (C.T.C, 1954). The Department of National Defense maintains a training base on the north bank of the Vedder River just downstream of Vedder Crossing. 43. In the spring of 1954 the Vedder began to erode i t s south bank about one mile downstream from Vedder Crossing. One of the property owners affected, J. Connor, requested assistance from the municipality. The municipal clerk advised, "The entire responsibility for the protection of your own property l i e s in your own hands..." (C.T.C, 1954). Vedder Mountain Road was threatened, however, and the Municipality obtained Provincial Government cooperation to share the cost of $4,000.00 for emergency work that summer. In November, 1954, inspite of protection work the river seriously eroded Connor's and a neighbour's property removing up to 100 feet of land along several hundred feet of river bank (Chilliwack Progress, 1954). The spring freshet of 1955 and the winter flood of November, 1955 continued to cause river erosion problems. Then in June, 1956, four or five acres of land were lost approximately one half mile west of Vedder Crossing and the river again threatened Vedder Mtn. Road (C.T.C, 1956). Emergency work was carried out. In September, 1956, a wing dam constructed near Browne Road blocked the upstream migration of sockeye, coho, and chum salmon and the local Federal Fisheries Officer, E. S. Robertson, requested that a passage for salmon be made by removing the obstruction. The municipality complied with this.request but asserted that i f the Federal Department of Fisheries could direct removal of works and thereby hinder flood control then the Federal Government should assume some responsibility for the river. The Department of Fisheries, however, replied that the removal of man made obstructions or provision for passage of f i s h by these obstructions was required by the Fisheries Act. The Federal Government disclaimed further responsibility. 44. In 195 7, perhaps in another attempt to involve the Federal Government through B i l l 109, the Water Conservation Act, the BC Water Resources Service completed a study of "Flood Control and Hydroelectric Power on the Chilliwack River". The lack of suitable reservoir sites with enough storage capacity in the lower reaches of the river appeared to rule out flood control by storage reservoirs (Goodyear, 1957). Later in 1957 a committee of engineers was formed by the Provincial Government to evaluate flooding and erosion of the Vedder River. They initiated a series of surveys that would lead to bank protection proposals in 1964 (Marr, 1964) . From 1956 to November 1963 there were no floods greater than 10,000 cfs (approximate return period, two years) yet bank erosion remained a problem. In 1959 nineteen local property owners signed and presented a petition requesting the Municipality to extend the protection on the north bank (C.T.C, 1959). In 1960, property was endangered between Ford and Browne Roads on the south bank (C.T.C, 1960). In 1961 erosion was again a problem on the north bank one half mile upstream of the BC Electric railway bridge and was purported to be aggravated by dredging of the outside of the bend by a logging company (C.T.C, 1961). The Municipality provided rock protection for some of the worst areas but continued to press for more substantial assistance from the provincial government. Answering a request from the Provincial Government for the views of the Municipality on a solution to the control of the Vedder the Reeve of the Municipality, W.G.R. Simpson, writes, "Thank you for your letter of December 4th re Vedder River Control and for asking our views as to a solution. I have gone through reams of correspondence on the subject during the past week, and the answer has always been the same:- a lot of buck-passing and delays, ending up with a piecemeal, wasteful job being done, and the Provincial Govern-ment and the Township of Chilliwhack sharing the cost on a 50-50 basis. We are ready and anxious to provide leadership and management in this project and feel quite confident the river can be controlled. The last freshet has proven beyond a shadow of doubt that i f we more or less dyke the banks with gravel from the bars, and face those embankments with heavy rock - and I mean heavy rock - that such places resist the ravages of the river even in places where the river has flowed over the top of such protection work. It would be our intention to do only the danger spots as they become evident each freshet. We are confident that over a period of a few years i f we continue to do work of a permanent nature and keep the channel clear of debris, our worries w i l l be over. We don't need a staff of engineers, we don't need months of preparation, we're ready to go to work now. A l l we need is your assurance that up to $100,000.00 w i l l be available over the next five years, and we'll get results. It i s urgent that we get cracking, so how about putting up the money now and negotiate with the other interested parties while the job is being done. We could get another.freshet any time." (C.T.C., 1962) Mr. Kiernans, the local M.L.A. concurred with these views noting that the Department of Fisheries should be consulted on the flood control measures (Chilliwack Progress, 1962). The previous 50% cost sharing plan continued. Now, however, the Provincial Government assisted the Municipality for work costing up to $25,000 per year. Wing dams were reinforced, extended, and became new banks. The municipality rip-rapped the most threatened banks adding a few thousand feet of protection a year and establishing by bits and pieces the present bank alignment. 4.6. The Federal Department of Fisheries did not object to the 1963 program which consisted of rip-rapping along the banks. However, bulldozing operations in the river in the winter of 1963-64 resulted in "the loss of many millions of Chum Salmon and Pink Salmon eggs" (C.T.C, 1964). After this incident the Municipality cooperated with the Fisheries and no gravel was removed below water except from an area in the head of the canal near Dyke Road designated by the Fisheries as a "Flood Protection Removal Area" (C.T.C, 1967). The Water Resources Service completed i t s evaluation of the river in 1964 and released the report, "Proposed River Protection Work for the Chilliwack-Vedder River" (Marr, 1964). Marr proposed to build flood embankments between the two bridges and confine the river by armoured groins in a channel varying from 280 to 345 feet in width. The proposed work on the Vedder was estimated to cost $630,000 and the proposed channel modifi-cations upstream of Vedder Crossing was estimated to cost $180,000. It i s doubtful i f this proposal would have been a satisfactory long term solution. By narrowing the channel above Vedder Crossing the river would likely have increased the rate of scour here and displaced this sediment to locations downstream where the slope was substantially less. The sediment load to the lower river would have been increased adding to the existing problem of aggradation. During the period in which cross-sections were surveyed, 1958 to November, 1963, there were no floods greater than 10,000 cfs. In addition the channel clearing work and realignment of banks during these years by the Municipality made the comparison of cross-sections d i f f i c u l t . Marr did not detect a consistent pattern of change along the river and the aggradation of the bed with larger floods was not recognized at that time (Marr, 1964). No government committment was made on.this proposal and protection work on the river continued on a piecemeal basis until 1975. The flood of December, 1975 broke through both north and south banks in several places. This time, however, the south railway embankment did not hold back the flood and damage exceeding $700,000 was caused in Yarrow and Sumas West Prairie (Fraser River Joint. Advisory Board, 1976) . Deposition of sediment in the channel seriously reduced the channel capacity below Vedder Crossing. The Water Investigations Branch of the Provincial Government estimated the capacity of the Vedder Channel between Browne Road and the BC Hydro bridge to be reduced to 4500 cfs and estimated the probability of flooding during the spring freshet to be 50% (Tempest, I. 1976). The larger winter floods also posed the threat of serious flooding. The channel needed emergency maintenance, a situation similar to that following previous floods. The Water Investigations Branch immediately spent some $100,000 to partially- restore the low banks, then resurveyed cross-sections established before the flood and quickly prepared a program of_alternative plans to increase the flow carrying capacity. The agency responsible for the flood control of the Vedder, the Fraser River Joint Advisory Board, met with the Water Investigations Branch, the Provincial Fish and Wildlife Branch and the Federal Fisheries Service and reached a concensus on these alternative plans in March, 1976. It was resolved to carry out the work in two phases. Phase I consisted of raising the existing banks by 3 feet, providing rip-rap protection, and removing gravel from bars one foot above the waterline. Phase I increased the maximum channel capacity to 19,000 cfs bankfull. Phase II 48. consisted of dredging 750,000 cubic yards of gravel to further increase the channel capacity to 30,000 c f s . The f i r s t phase was completed p r i o r to the spring freshet and the second phase was ca r r i e d out in July and August, 1976 p r i o r to the winter floods. The work cost a t o t a l of $1,155,000 (H.R. Milton, pers. comm.). The Board considered that i n addition to Phase I and II the r i v e r would require a maintenance program of gravel removal, the amount varying from year to year, depending on flood flows (Fraser River Joint Advisory Board, 1976) . A Phase I I I program of set back dyking to provide flood protection for the 1 i n 200 year floo d was also discussed, however, the long planning period necessary for this project made i t unsuitable f o r the emergency s i t u a t i o n . E. CHANGES IN THE VEDDER CHANNEL • The many e f f o r t s to control the Vedder altered the width and length of the channel. An early d e s c r i p t i o n of the r i v e r i s given by LeBaron (1908) "The Vedder Pass i s a comparatively new stream and i s very i r r e g u l a r i n width. I t s width varies from 60 feet to 400 feet at low water, and i t i s f u l l of rapids and gravel banks. I t i s also much choked by f a l l e n trees and logs which appear to have been uprooted when the r i v e r broke out i n i t s present channel, about 15 years ago. The River appears to me to have not yet attained i t s s e t t l e d regimen and undoubtably i s continually widening." It can only be speculated what the Vedder Channel would be l i k e had i t been l e f t alone. Perhaps, by now, the Chilliwack River would have found some other course to the Fraser River. Figure 10 shows the channel i n 1958 and 1969. Over the approximately 1 3/4 mile long reach from Ford Road to the railway bridge the reduction of average active channel width at flood stage was about 44 percent from 630 feet in 1958 to 350 feet i n 1969. The thalweg length over this reach was reduced by about 7 percent from 9250 feet to 8580 feet. When the Chilliwack River adopted the Vedder Channel in 1894 land-ownership extended under the river and property boundaries were not resurveyed. Whenever the river shifted channels away from a landowners's property a few loads of rock could quite profitably recover land. One property of 18 acres (PCL K NE \ SEC.3. TWP.23) was reclaimed by construction of a wing dam in 1956 and more extensive bank protection i n 1964. In providing bank protection, the Municipality would try to build on the shortest distance of bank possible. In a river of irregular width this could be achieved only by cutting off side channels and "unnecessary" bends. The Provincial Government supported the narrowing of the channel financially and the Water Resources Service engineers approved of a narrow channel concept. One of the design c r i t e r i a adopted for the proposed river protection works of 1964 was , "to confine the river within a narrow strip of land and possibly reclaim land within the present erosion belt." (Marr, 196 The effects of the channel changes on the pink and chum of the Vedder River w i l l be discussed in the next chapter. 51. CHAPTER IV THE PINK AND CHUM SALMON OF THE VEDDER RIVER A. INTRODUCTION The local residents, the municipality, and province have traditionally been much more concerned with the river's flood threat than the river's production of salmon. It is also only relatively recently that the Fisheries and Marine Service, responsible for chum salmon, and the International Pacific Salmon Fisheries Commission (I.P.S.F.C.), responsible for pink salmon since 1957, have attempted to preserve the freshwater habitat of these valuable stocks. For example, the Fisheries Act of 1932 gave the Department of Fisheries broad authority to protect salmon from dams, pollution or water diversions, but the act was not extensively enforced in B. C. u n t i l the mid 1950's (Scott and Schouwenburg, 1977). The value of the salmon's freshwater habitat and the significance of physical factors controlling freshwater survival was not widely appreciated by the municipal and provincial governments when they were channelizing the river in the 1960's. In 31 years of observation (1935-1966) the pink and chum salmon escapement to the Vedder River averaged about 25% of the total Vedder-i v . Chilliwack system pink and chum escapement. The escapement to the Vedder River also makes up a significant proportion, 11%, of the total run of Fraser River chum salmon (Table IV). Since 1967, escapement estimates for the Vedder River have been combined with the Chilliwack River estimates, therefore, a separate record of recent escapements to the Vedder River i s not readily available. 52. TABLE IV COMPARISON OF THE VEDDER RIVER ESCAPEMENTS WITH THE VEDDER-CHILLIWACK RIVER AND FRASER RIVER ESCAPEMENTS SPECIES NUMBER OF SPAWNERS VEDDER RIVER VEDDER-CHILLIWACK RIVER (inc l . Sweltzer Creek) LATE FRASER RIVER RUN TOTAL FRASER RIVER PERCENT OF ESCAPEMENT TO THE VEDDER RIVER [VEDDER-CHILLIWACK RUN % LATE FRASER RUN % TOTAL FRASER RUN % PINK PINK CHUM 1 CHUM 39,000 (46,700)* 13,100 (20,200)* 168,000 202,890 45,700 69,800 430,764 1,629,000 319,510 23 23 29 29 11 PINK1 AND CHUM1 mean escapement 1935-1966, visual observation index, Salmon Stream Spawning Reports, Department of Fisheries. PINK 2 mean escapement 1957-1973, based on tag and recapture studies, International Pacific Salmon Fisheries Commission Annual Reports. CHUM mean escapement 1960-19 75, based on tag and recapture studies, (Palmer, 1972) (Anderson, 1976). Calculated proportion of Vedder-Chilliwack River runs using the mean percentages from visual observation 1935-1966, The largest escapements to the Vedder River have been frequently in the order of 50,000 to 100,000 pinks and 20,000 to 50,000 chums (Department of Fisheries, 1935-1975). Overfishing, loss of spawning area, floods, and other factors drastically reduced the escapements in the 1950's and early 1960's. Therefore, the 1935-1966 average, 39,000 pinks and 13,100 chums, is probably much lower than the potential size of the Vedder River stocks. An escapement of 39,000 pinks, every two years, and 13,100 chums every year, is estimated to be worth $294,408 annually (1975 dollars, gross value at wholesale)(P. Meyer, pers. comm.). The f i r s t part of this chapter reviews the l i f e cycle of pink and chum salmon, describes the spawning areas of the Vedder-Chilliwack system, and describes the changes that have occurred in the Vedder River spawning areas. The second part of the chapter describes the decline in numbers of spawners returning to the lower Vedder River and identifies the factors that are probably responsible for the low productivity. B. THE LIFE CYCLE OF PINK AND CHUM SALMON AND FACTORS AFFECTING PRODUCTIVITY The l i f e of migratory salmon and trout is a struggle for survival; the probability of a f e r t i l i z e d egg becoming an adult is about one in five hundred. Even i f a salmon has been lucky enough to avoid oxygen depri-vation, predators, high stream temperatures, floods, low flows, water pollution, and shortage of food i t faces a 25 to 80 percent chance of getting caught. Having escaped the fishery the salmon may have to contend with obstructions in the river, more pollution, and predators. Furthermore, the salmon may have to spawn in a damaged or limited area when the river is flooding or when the river is almost dry. 54. Development of each stage of the salmon l i f e cycle i s dependent upon specific river, estuary and ocean conditions. For example, the river must provide spawning gravel, adequate flow for spawning, protection and l i f e support for incubating eggs and developing alevins, feeding stations and hiding places for coho, chinook and steelhead fry, transportation to the estuary for pink and chum fry, and access back to the spawning ground for adult spawners. Similarily the estuary and ocean must provide food and a favourable physical environment. Any natural event or human activity that unfavourably alters environmental conditions can have a serious effect on the numbers of fish available for our use, that i s the numbers that can be safely caught without endangering the continuity of the species. 1. MIGRATION AND SPAWNING Pink and chum salmon have a virtually identical l i f e history in freshwater except for differences in migration timing and selection of spawning areas. Adult pink salmon destined for the Vedder River enter the Fraser River between late September and early October reaching the Vedder River spawning areas throughout October. Peak spawning activity usually occurs between October 17 and October 20 (I.P.S.F.C., 1975). An ideal spawning site would be in a r i f f l e between pools, with a water depth greater than about one foot, with water velocity between one and two feet per second and with stable clean gravel. The ideal gravel *' would have about 80% of the stone sizes between % inch and 2 inches and the balance up to 4 inches (Bell, 1973). Natural gravels, however, often have a significant percentage of fines. Adult Vedder chum,, salmon enter the Fraser River between the end of September and early December after a week or more in the estuary. They arrive at the spawning grounds from early October to mid December and show no well defined peak of spawning activity (Palmer, 1972) . In comparison to other species of salmon, chum salmon are not as capable of leaping over obstacles and generally use the lower reaches of streams. In the Vedder River, chum salmon prefer pools, stream margins,, and side channels rather than the main channel and w i l l heavily u t i l i z e gravel with upwelling flow (Tesky, pers. comm.). Like pink salmon, chum salmon require clean, stable gravel, but unlike pinks, the bigger chums can use larger gravel. A pair of chum salmon require about two square yards of spawning area and a pair of pink salmon about one and a half square yards (Clay, 1961). After selection of a suitable area the female carefully excavates a nest or redd.- The shape of the redd creates a favourable flow pattern so that eggs w i l l not be lost to the current. After the redd is completed spawning occurs and the eggs and sperm are deposited simultaneously. The female soon digs another depression immediately upstream thus covering the previously deposited eggs with gravel. After several sequences of nest building and deposition of eggs and sperm, over a period of a few days, the eggs are buried by a layer of gravel which may be one to two feet thick (Jones, 1959). Chums deposit a total of about 3,000 eggs per female and r pinks deposit about 2,000 eggs per female. The adults die within a few weeks of spawning. Many factors can signficantly reduce the numbers of eggs deposited successfully per female spawner. Fi r s t , the number of eggs per female 56. i s proportional to the length of the fish. Comparing two runs with an equivalent number of spawners, but with a distinct average size difference, the run of smaller fish would deposit considerably fewer eggs than the run of larger fish. Second, high water velocities during floods can sweep fish off their redds and disturb and delay spawning, or, prevent spawning a l -together. Third, both low flows and high flows induce crowding by limiting spawning area. Crowding results in egg retention and redd superimposition. Females usually retain less than 5% of their eggs after spawning. When the numbers of fish on the spawning ground at the same time are excessive egg retention may approach 40 percent (McNeil, 1969) . If spawning area is limited later spawners dig their redds in areas previously utilized and dislodge the eggs of the preceding spawners. Loss of eggs due to redd superimposition has been estimated to be about 50 percent when the density is two females per 1.2 square yards and about 70 percent when the density is three females per 1.2 square yards (McNeil, 1969). 2. INCUBATION Eggs successfully deposited in the Vedder gravels w i l l hatch into alevins in about three months. After about another three months of development fry w i l l emerge from the gravel. Because water temperature and dissolved oxygen levels control the rate of embryo development and flow conditions affect the timing of emergence the total period in the gravel can vary by a few weeks from year to year (D. Bailey, pers. comm.). Survival of eggs and alevins in natural streams is usually low and extremely variable. In seven years of measurement the egg to fry survival of Fraser River pink salmon has averaged 12.6 percent with a high of 18.4 percent in 1965 and a low of 9.2 percent in 1961 (I.P.S.F.C., 1975). In thirteen years of measurement the egg to fry survival of Fraser River chum salmon has averaged about 15 percent with a high of 38 percent in 1976 and a low of 7 percent in 1964 (M. Bailey, pers. comm.). Insufficient oxygen or disturbance of the eggs usually causes most of the egg to fry mortality. S i l t in the gravel and low flows can result in insufficient oxygen; later spawners, floods, and predators can disturb the eggs. During the six month incubation period flow of water through the gravel must supply the eggs and alevins with oxygen and must remove the toxic wastes of metabolism, these being carbon dioxide and ammonia. Low dissolved oxygen concentrations are most damaging just prior to hatching (Cooper, 1965) (McNeil, 1966). From hatching to emergence total oxygen consumption by an alevin increases by about 10 times, however, after hatching respiration across new g i l l membranes make an alevin slightly more tolerant of low oxygen levels than an egg (McNeil, 1966). The amount of oxygen delivered to an egg or alevin is a function of the dissolved oxygen concentration and the intragravel flow velocity (McNeil, 1966). Successful incubation in a r t i f i c i a l spawning channels i s accomplished with water near saturation level with an apparent flow velocity of 1100 mm/hr (Bell, 1973). In a study of four natural BC streams Wickett (1958) found that egg to fry survival was higher in gravels of higher permeabilities. Cooper (1965) describes an experiment with sockeye eggs that showed an increase in egg to fry survival from less than 10 percent to 80 percent when the apparent velocity of the intragravel flow increased from about 18 mm/hr to 400 mm/hr. 58. A serious reduction of intragravel flow and egg to fry survival can be caused by a small percentage of fines in the gravel. Cooper (1965) found that less than 10 percent by weight of fines added to a gravel sample reduced permeability from 100 mm/hr to less than 10 mm/hr. He also found that circulation of sediment laden water (200 ppm suspended solids) over a medium graded gravel reduced the egg to fry survival from 70 percent to 0 percent whereas circulation of water containing only 20 ppm suspended solids produced a negligible change in survival. Survival in coarse gravel was not as severely affected by circulation of sediment laden water (200 ppm suspended solids) as was the medium gravel. I n i t i a l l y , the female salmon's vigorous digging removes the fines from the redd. Flow of sediment laden water, as might occur during floods or dredging, would s i l t up the gravel and would reduce egg to fry survival. Factors that increase the interchange of oxygen-rich stream water with the intragravel water are a high stream gradient, moderately high stream flow, coarse bed materials and an uneven stream bed (McNeil, 1969) (Vaux, 1968) . Although coarse bed materials allow better interchange between stream and intragravel water than do fine bed materials, coarse bed material also allow predators better access to eggs than do fine bed materials (McNeil, 1969). McNeil suggested that an unaccountable loss of about 30 percent of the eggs from a coarse gravel spawning area in Sashin Creek, Alaska could have been due to sculpins (Cottus Aleuticus) and other fish predators. The extent and significance of predation of eggs in the Vedder River i s unknown. Floods can cause a very significant reduction in egg to fry survival by gravel shifting, channel switching and s i l t deposition. Low flows can 59. reduce the oxygen supply to embryos by reducing the stream flow - intra-gravel flow interchange. Egg mortality can be severe when water levels drop and eggs dry out, particularly affecting those eggs which were deposited along stream margins or on bars in the channel. These factors are significant in the Vedder River and w i l l be discussed in Chapter VI. 3. EMERGENCE AND MIGRATION Fraser River pink and chum fry emerge from the gravel between late February and early June (Palmer, 1972)(Northcote, 19 74). Fry generally leave the tributaries shortly after emergence and swim and d r i f t for a few days unt i l reaching the Fraser Estuary. The peak seaward migration usually occurs in April (Palmer, 1972). Predators are not thought to cause significant mortality in the Fraser River (Vernon, 1962), however, coho smolt predation of pink and chum fry in the Vedder-Chilliwack River could be in the order of 4 million fry per year (M. Bailey, pers. comm.). This is roughly 10 percent of the average fry output, but would be a larger fraction in years of low fry output. Predation could become a significant factor i f a proposed Chilliwack River hatchery is constructed and i f large numbers of coho smolts are released from the hatchery during the pink and chum fry migration (M. Bailey, pers. comm.). Pink and chum fry avoid predators by migrating at night. Losses in clearwater are reduced by schooling ( E l l i s , 1977). Turbidity reduces predation in the Fraser River (Vernon, 1962). 4. ES TUARINE AND MARINE LIFE L i t t l e is known of the movements of chum fry in the Fraser Estuary (Northcote, 1973). Observations of chum fry from the Big Qualicum River, BC 60. indicate that the fry school along shorelines, under wharves, and keep to shallow water for about eight weeks before moving out to deeper waters (Allen, 1974). The survival of fry during this period has been shown to depend on the ava i l a b i l i t y of adequate food which allows a rapid growth rate. In order to survive,the fry must l i t e r a l l y outgrow their predators (Parker, 1971). The estuarine stage is of v i t a l importance to the productivity of pink and chum salmon as mortality of pink salmon has been observed to be between 59 and 77 percent during the f i r s t 40 days in an estuary (Parker, 1968). Fraser River pink salmon spend 1*5 years at sea and attain a weight of 3 to 5 pounds. Although both even and odd year stocks are present in streams of central and northern BC, pink salmon return to the Fraser River only in odd years. Chum salmon spend 2h, 3h or 4% years at sea and attain an average weight of 8 to 18 pounds. Five year old chums make up less than three percent of the total return in any one year (Palmer, 1972). Fry to adult survival of pink and chum salmon is very low with most mortality occurring during early estuarine and marine l i f e (Parker, 1962). For five brood years, 1961 to 1965, the fry to adult survival of Fraser River chum salmon averaged 2.1 percent varying from 0.6 percent to 3.4 percent (Palmer, 1972). For seven brood years, 1961 to 1973, the fry to adult survival of Fraser River pink salmon averaged 2.9 percent varying from 0.8 percent to 5.0 percent (I.P.S.F.C., 1975). 5. THE COMMERCIAL FISHERY Exploitation rates of pink and chum salmon, commonly between 30 and 80 percent, are regulated in part to allow adequate escapements for repro-duction. For example, the Department of Fisheries was concerned over depressed Fraser River chum salmon stocks in the mid 1960's and reduced the exploitation rate to less than 10 percent in 1965 and 1966 (Palmer, 1972). Management of a mixed-stock fishery, like the Fraser River pink and chum fisheries, i s a complex task. One factor that contributes to the complexity i s described in the following paragraphs. Escapements are adjusted as much as possible to ensure that the optimum number of spawners return to each spawning area of the Fraser. If, however, the freshwater survival varies among the tributary stocks and i f the timing of migration of these stocks through fishing areas i s similar, a stock with lower freshwater survival w i l l be exploited at a greater rate. If there i s a consistent difference in freshwater survival between two stocks subject to a common fishery, fishery managers are faced with a dilemma. Either they fully exploit the productive stock at a cost of over-fishing and perhaps drastically reducing the size of the unproductive stock, or they protect the unproductive stock at a cost of underharvesting the productive stock. C. THE SPAWNING AREAS OF THE VEDDER-CHILLIWACK RIVER The area of the Vedder-Chilliwack stream bed that i s suitable for pink and chum salmon spawning i s only a small percentage of the total wetted area of the river channel. Steep gradients, high vei'dcity flows and coarse bed material limit spawning above Liumchen Creek and low gradients, s i l t , and poor gravel limit spawning in the canal up to about 1^ miles below the BC Hydro railway bridge. A survey of chum spawning areas in 1971 found that chum spawning areas made up less than four percent of the total river wetted area (Bailey, Van Tine, 1971). 62. Pink and chum have much the same requirements for spawning and much of the areas used by one species is used by the other. Pink salmon, however, tend to use the main channel, whereas Vedder River chums tend to use side channels and margins of the main channel. Although spawning areas of the two species overlap^estimates of the spawning capacity for one species are not directly indicative of the spawning capacity for the other species. There are four sections of the Vedder-Chilliwack System that contain over 95 percent of the spawning area (Figure 11, Table V). 1) Chilliwack Lake to Chipmunk Creek The upper river, from just below Chilliwack Lake to Chipmunk Creek, has a capacity for approximately 12,000 chums (Bailey, Van Tine, 1971). This reach has been used by up to 200,000 pinks although this number resulted in crowding (I.P.S.F.C., 1969). This section of the stream bed is relatively stable and fluctuations in flow are damped by Chilliwack Lake. However, because of the steep gradient and coarse bed materials even a small increase in flow can severely restrict spawning areas (I.P.S.F.C., 1969). Small populations of pink and chum, up to a few hundred fish, u t i l i z e the deltas of Nesakwatch and Centre Creeks (Walker et a l , 1972). Foley Creek and Chipmunk Creek were formerly utilized by pinks, however, extensive logging of these creeks' watersheds has caused sedimentation and ins t a b i l i t y of the creek beds and has destroyed much of these spawning areas (I.P.S.F.C., 1969). 2) Allison Pool to Liumchen Creek There is a relatively good section of spawning area below Allison Pool to Tamihi Creek. The gradient is about 50 feet per CEEETC LAKE" s\ SPAWNING AREAS err™ X. m 7172 A x i ca-uu-iwAC-K 7«s?a f<SCt ('A^L) •74<i>4 FIG II - LOCATION OF MAJOR PINK AND CHUM SALMON SPAWNING AREAS 1 TABLE V APPROXIMATE CAPACITY OF PINK AND CHUM SPAWNING AREAS IN THE VEDDER-CHILLIWACK RIVER SYSTEM LOCATION OF SPAWNING AREA LENGTH AVERAGE APPROXIMATE CHUM PERCENT OF CHUM OF GRADIENT WETTED AREA' 1 SPAWNING WETTED AREA CAPACITY RIVER (feetper (including Side AREA 1 USABLE (@ 1.1 yds 2/fish) (miles) mile) Channels)(yds2) (yds 2) (%) (no. of spawners) PINK CAPACITY (no. of spawners) VEDDER CANAL TO 1.5 10 108,533 4,958 _4.6 4,500 B.C. HYDRO RAILWAY BRIDGE TO 6.0 26 553,777 49,238 8.9 44,800 LIUMCHEN CREEK > 100,000 TO 3. 7 62 330,249 7,679 2.3 7,000 TAMIHT CREEK TO 6.1 52 538,959 15,517 2.9 14,100 SLESSE CREEK TO 3.4 118 230,045 1,000 0.4 900 CHIPMUNK CREEK TO 5.8 78 315,376 8,191 2.6 7,500 ' > CENTRE CREEK 200,000 TO 4.0 108 304,174 4,766 1.6 4,300 CHILLIWACK LAKE TOTAL 30.5 - 2,381,113 91,349 3.8 83,100 300,000 SWELTZER CREEK 1.6 25 43,044 14,791 34.4 13,400 15,000 TOTAL 32. 1 — 2,424,157 106,140 4.4 96,500 315,000 Bailey, Van Tine, 19 71 Estimate based on 1935-1975 escapement records and observations in "Proposed A r t i f i c i a l Spawning Channel for Chilliwack River Pink Salmon", I.P.S.F.C., 1969 65. mile and the river meanders in a coarse gravel bed. This reach has a capacity for about 14,000 chums (Bailey, Van Tine, 1971) and i s extensively used by pinks. There is virtually no suitable spawning area above Allison Pool to Chipmunk Creek (I.P.S.F.C., 1969) and only limited area below Tamihi Creek to Liumchen Creek. 3) Sweltzer Creek Sweltzer Creek is a stable, moderately sloped, 25 feet per mile stream with fine gravel that is subject to s i l t i n g (Tesky, pers. comm.). The chum capacity has been estimated to be 13,400 fish (Bailey, Van Tine, 19 71) with spawning concentrated in the area immediately downstream from Cultus Lake and in the lower half mile of the creek. The stream is consistently used by 10,000 to 20,000 pink salmon (Department of Fisheries, 1935-1975). 4) Liumchen Creek to Vedder Canal The lower Vedder-Chilliwack river from Liumchen Creek to the head of Vedder Canal provides a spawning capacity for about 50,000 chums (Bailey, Van Tine, 1971) and has been used by 50,000 to 100,000 pinks. Numerous side channels, both above and below Vedder Crossing provide a large proportion of the spawning area. The changes in spawning capacity brought about by flood protection work are described in the following section. D. THE SPAWNING AREAS OF THE LOWER VEDDER RIVER The municipality and provincial government, through the construction of flood protection works, have seriously reduced the available spawning area between the BC Hydro bridge and Ford road. The active channel area in 66. this reach was reduced by 45 percent from about 122 acres in 1958 to .67 acres in 1969 (Figure 10). Flood protection work has resulted in an estimated 2 loss of chum spawning area of 13,000 to 26,000 yds , capacity for approxi-mately 12,000 to 24,000 chum spawners (Table VI). The loss of production from the main spawning areas, the Hopedale, Browne, and Lickman channels, occurred over about 15 years. In the early 1960's, the municipality and provincial government extended previously constructed wing dams and bank protection to form f a i r l y continuous dykes. Fish were allowed access to the side channel spawning areas at the downstream ends of side channels through gaps in the bank protection. A l l direct surface flow from the main channel to the side channels was cut off at the upstream ends of the side channels. As spawning pink salmon prefer a water velocity of at least one feet per second, the reduced flow in the side channels would have immediately limited the area available for pinks. I n i t i a l l y chum salmon spawning was not affected. The gravel and rock used in the construction of bank protection allowed adequate seepage flow to the side channels as long as the river stage was sufficiently high. Within a few years, however, beaver dams,vegetation, dumping of f i l l and garbage, and compaction and s i l t i n g of the banks reduced both the quantity of seepage flow and the quality and quantity of spawning gravel (Resource Development Branch, 1968). Chum salmon spawned in the side channels in considerable numbers as late as the f a l l of 19 75 inspite of continued s i l t i n g and deterioration of the gravel. A major loss of productive area occurred when the flood of December 5, 19 75 deposited s i l t and debris in the channels. TABLE VI ESTIMATED CHUM SPAWNING AREA CAPACITY BC HYDRO BRIDGE TO FORD ROAD YEAR Hopedale Channels and Slough (yds 2) Browne Channel (yds 2) Lickman Channel (yds 2) Main River (yds 2) TOTAL AREA (yds 2) CHUM SPAWNING CAPACITY @ 1.1 yds /fish (no. of spawners) 19581 10,000 1,000 2,000 5,000 18,000 16,400 to-15,000 to-2,000 to-4,000 to-10,000 to-31,000 to-28,200 2 1971 4,700 150 1,350 5,000 11,200 10,200 3 1977 - - 5,000 5,000 4,500 Basis for estimates: a) Provision of flow and channel clearing of Browne and Hopedalg channels was estimated to provide 20,000 yds of spawning area (Resource Development Branch, 1969). Flow occurred naturally in these channels prior to 1960. b) The wetted areas of Hopedale, Browne and Lickman channels was measured in 1971 to be approximately 26,000 yd (Bailey, Van Tine, 19 71) even after loss of wetted area to l a n d f i l l and vegetation. A high percentage of this wetted area would have been productive chum spawning area. c) Spawning capacity of the main channel in 1958 would likely have been greater than the dyked and dredged main channel due to changes in st a b i l i t y of the streambed. A slightly greater percentage of the wetted area of the main channel would li k e l y have been usable in 1958. (Bailey, Van Tine, 1971) Hopedale, Browne and Lickman channels were almost completely unsuitable for spawning during f a l l of 1976 due to the lowering of the river grade in summer, 1976. This caused a loss of about 6,200 yds of spawning area. 68. Without subsequent flushing with clear water the channels have remained s i l t e d . In the summer of 1976 dredging reduced the average river" stage in this reach by about feet. During the f a l l of 1976 inspite of normal main channel flows, the flow in the side channel spawning areas was very low and many areas were dry. E. THE DISTRIBUTION OF SPAWNERS Prior to 1949 the pink and chum escapement to the Vedder River made up an average of about 50 percent of the total Vedder-Chilliwack River escapement. From 1949 to 1966 the escapement to the Vedder River made up an average of 22 percent of the total chum escapement and an average of 8 percent of the total pink escapement (Figure 12). The total escapement to the Vedder-Chilliwack River declined in 1949 and in the same year less than 10 percent of the stock u t i l i z e d the Vedder. There were extremely small escapements to the Vedder in the 1950's (FigureB). The sudden drop in the Vedder River escapement index could have been caused by the following: 1) The commercial chum fisheries reached a peak in the 1940's and 1950's. Overexploitation during these years led to a general collapse of the Fraser River chum stocks in .1955. (Palmer, 1972). Prior to 1949 i t is thought there was a big early run of chum salmon to the Vedder River (Tesky, pers. comm.). Possibly, the fishery wiped out this early run. 2) A sequence of unfavourable flow conditions in the late 1940's and early 1950's apparently caused generally poor spawning and ) 100 PERCENT VEDDER 1935 1940 1945 1950 1955 1960 TIME (years) FIGURE 12 THE NUMBER OF SPAWNERS IN THE VEDDER RIVER AS A PERCENT OF THE TOTAL ESCAPEMENT TO THE VEDDER-CHILLIWACK 1935 - 19661 Calculated from, "Salmon Stream Spawning Reports", BC 16, F381, Fisheries and Marine Service, Sweltzer Creek not included. 53 O o S r-j s < 00 < co H I PH o o O o o o o o O o o o o o O o o o P H W CM LO o o o o H i—l CNI LO o w i—l o W 1 | 1 1 1 1 CO o o o o o o o o o o o o PH o o o o o o PH 9 I—1 CM LO o o o PH I—l CM LO X Pi pq o O o o o o w o O o o o o p LO LO LO o o o & *> #» #\ M i—l ro r-~ LO LO LO 4-* r—1 ro 70. SEVERE CURTAILMENT OF FRASER RIVER CHUM j_ FISHERY FLOOD CONTROL WORKS COLLAPSE OF FRASER_ RIVER CHUM FISHERY 1955 FLOOD *»15,900 cfs NOV, 1952 LOW FLOW 2 80 cfs 1951 FLOOD NOV 27, 1949 FLOOD ~19,000 cfs JUNE 1, 1948 FLOOD — — ~~~ " L . LO VO cu C\ rH o •—1 VO •H vO i> o> rH cu CO 1 LO c ro •H o a\ r4 vo rH ca Q\ P^  a rH w > c H ca Pi CO Pi cu w •H p L-I LO p <U LO w r C as > CO rH •H PH M „ rH O 00 '—\ H ro CO. CO o H . LO W vO as W rH rH Vw/ a w u PQ w a o H oo . CO H w 4-1 U o p. LO <r £3 Pi CJ> rH p 00 c •H a a H ts & PH 00 o o- e a\ CO rH cu rJ ro 4-1 rH CO W a Pi Q s o rH LO H ca ro f*4 oo CT\ rH o o •o ON o 0 0 o o . vo o LO o -3-o ro 'O CM cn SH —^s tH cu o . cj o •CU rg 3 o *a ca rH d X H 3 CO ^—' incubating conditions for several years. Following the large spring flood of June 1, 1948 a flood on November 27, 1949 of approximately 19,000 cfs eroded one half to three quarters of a mile of good spawning ground and shifted great quantities of gravel (Department of Fisheries, 1936-1975). The large flood during the winter of 1951 caused further shifting of the already unstable stream bed. In November, 1952 the mean monthly flow was 474 cfs dropping to a low of 280 cfs on November 30. The extreme low water during spawning would have severely limited spawning area in the mainstem as well as side channels for chum salmon. Another large flood, 15,900 cfs, occurred in November, 1955. 3) The municipal and provincial government cleared the channel, protected banks and constructed wing dams during the 1950's, however, during the early 1960's they carried out the major channelization and gravel removal work. This work could only have aggravated the already poor spawning and incubating conditions. 4) The Chilliwack Fishery Officer was replaced in 1946 and again in 1949. The escapement index is based on periodic observations of the spawning grounds and estimates depend on the judgement and experience of the Fishery Officer. E. S. Robertson took over the position from 1949 to 1964 and supplied continuity of observation for that period. There is a small possibility that the change in observer could have influenced the escapement record. 72. The effects of overexploitation, poor flow conditions, and flood control work on escapement are impossible to separate. Most probably, a combination of these factors reduced the size of the Vedder stock. The bed of the upper Chilliwack River, from Foley Creek to Chilliwack Lake, has remained stable and in the 1960's larger numbers of both pink and chum salmon have spawned in this area (Palmer, 1972)(I.P.S.F.C.,11969). Of six brood years of pink salmon studied by the I.P.S.F.C., overcrowding occurred twice in the upper spawning area. A trend of lower utilization of the river below Allison Pool i s indicated in Figure 14. F. THE FRESHWATER PRODUCTIVITY OF THE VEDDER STOCKS The numbers of pink and chum salmon spawning in the Vedder River have declined and have remained low. The low escapements, however, were the result of a l l the factors that affected the survival of the salmon and were not necessarily a direct result of the channel modifications-raid extreme flows. To differentiate the effects of changed spawning and incubating conditions from other factors i t is necessary to examine the freshwater productivity of the Vedder stocks. Freshwater productivity can be established in at least two ways: 1) Fisheries biologists and technicians can determine the number of spawners, eggs and fry in f i e l d studies of several l i f e cycles. 2) If two stocks from different spawning streams are subject to similar marine mortality and fishing pressure escapement records can be compared. The freshwater productivity of one stock can, PERCENT SPAWNING IN. LOWER AREA 100 n 90 • 80 • 70 • 60 • 50 • 1957 59 61 63 65 67 69 71 73 75 TIME (years) PROPORTION OF PINK SALMON SPAWNING IN THE VEDDER-CHILLIWACK RIVER BELOW ALLISON POOL VS. TIME (I.P.S.F.C., 1969) TREND (Fitted by eye) 10 J 0 74. therefore, be established relative to the freshwater productivity of the other stock. From 1957 to 1965 the International Pacific Salmon Fisheries Commission measured the freshwater survival of pink salmon in the Vedder-Chilliwack River and in the Harrison River, a major tributary of the lower Fraser River. Except for 1957 there was consistently higher egg to fry 0 survival in the Harrison River (Table VII). The low survival in the Vedder-Chilliwack River was attributed to flash floods aggravated by logging, dike construction, gravel removal, and other encroachments of c i v i l i z a t i o n (I.P.S.F.C. 1969). The Fisheries and Marine Service recognized the low productivity of the Vedder-Chilliwack chum stocks when severe regulation of the Fraser River chum fishery in the mid 1960's failed to significantly increase the numbers of chum returning to the Vedder-Chilliwack System (Palmer, 1972). The Harrison River escapement, a chum stock having similar level of exploitation, showed greater than a two-fold increase over the same time period (Table VIII). The major spawning areas of the Harrison River have been relatively unaffected by human activity in the watershed or by extreme flows (Palmer, 1972). Channelization of the Vedder River and the prevalance of extreme flows in the Vedder would appear to be responsible for the difference in productivity. Table IX summarizes the main factors that would affect the productivity of 10 hypothetical pink salmon spawners and identifies the relative significance of the factors in the Vedder River. Fisheries managers can have some control over most of the major factors although probably at great TABLE VII EGG TO FRY SURVIVAL OF PINK SALMON 195 7-1965 (I.P.S.F.C., 1967) VEDDER- HARRISON % YEAR CHILLIWACK % 1957 8.60 3.67 1959 6.02 10.85 1961 9.00 11.08 1963 5.18 7.80 1965 12.85 22.20 MEAN 8.3 11.1 TABLE VIII AVERAGE ANNUAL CHUM SALMON ESCAPEMENTS TO THE TOTAL FRASER, VEDDER-CHILLIWACK AND HARRISON SPAWNING AREAS1 AVERAGE ANNUAL ESCAPEMENT 1960-1964 1965-1969 19 70-1975 TOTAL FRASER VEDDER-CHILLIWACK HARRISON 231,200 60,800 75,700 407,900 79,400 172,900 415,500 69,000 146,7002 Source: (Palmer, 19 72) (Anderson, 19 76) Harrison System spawning areas including Chehalis River and Squakum Creek. Weaver Creek not included TABLE IX FACTORS AFFECTING THE PRODUCTIVITY OF TEN HYPOTHETICAL PINK SALMON SPAWNERS* LIFE STAGE INITIAL NUMBER APPROXIMATE SURVIVAL NUMBER A FEW OF THE FACTORS REMAINING AFFECTING PRODUCTIVITY RELATIVE SIGNIFICANCE TO THE VEDDER EXAMPLES OF CONTROL EGG/ ALEVIN/ FRY 10,000 eggs 10% 1,000 fry FRY/ ADULT 1,000 fry 2% 20 adults Sex-ratio Fecundity (number of eggs per female overescapement - crowding loss of spawning area - causes crowding extremes of discharge - crowding - erosion, sedimentation drying of eggs temperature Low Low Low High High Low predators Unknown fines in gravel - main channel Low - backwaters and High old side channels discharge must be sufficient for fry o Low -to- emerge predators Low — coho pollution and loss of estuary Unknown — feeding areas predators - estuary High -food supply in ocean Unknown -high seas fishery Unknown -use non selective fishing gear none increase catch increase spawning area create spawning areas behind flood protection works, provide adequate flow control temperature of hatchery water supply unknown improve watershed sediment control clean by providing flow or by gravel cleaning equipment none control timing of hatchery releases of smolts restrict development and pollution unknown unknown -J control fishery by inter- • national agreement TABLE IX (continued) FACTORS AFFECTING THE PRODUCTIVITY OF TEN HYPOTHETICAL PINK SALMON SPAWNERS* RELATIVE LIFE STAGE INITIAL APPROXIMATE NUMBER A FEW OF THE FACTORS SIGNIFICANCE EXAMPLES OF CONTROL siHUJi N U M B E R SURVIVAL REMAINING AFFECTING PRODUCTIVITY TO THE VEDDER ADULT/ SPAWNER 20 adults 50% 10 ^ commercial catch High spawners pollution Unknown obstructions - in side channels Moderate and creeks - regulate escapement - control pollution of lower Fraser - remove, clear debris SPAWNER/ 10 ~2,000. eggs 10,000 EGG spawners per female eggs ^1,000 eggs per spawner The factors marked by an arrow are highly significant factors that could be controlled by fisheries managers - a l l could be costly. 78. expense. For example, loss of spawning area, sil t e d gravel, and extreme flows can be avoided by construction of an a r t i f i c i a l spawning channel. There are various methods of increasing the productivity of salmon by controlling or even eliminating the natural mortality factors. The next chapter describes several methods of increasing the numbers of salmon, describes alternative methods of flood control, and suggests combinations of schemes that would likely be successful in the Vedder River. 79. CHAPTER V ALTERNATIVES A. INTRODUCTION There are several alternatives for reducing flood damage from the Vedder and several alternatives for increasing the abundance of pink and chum salmon. The overall plan that is eventually adopted should provide a solution for both flood control and fisheries management problems. While the level of productivity of natural stocks of pink and chum salmon is an important economic component of an overall plan i t also appears to be highly dependent on choices of flood control schemes. Therefore natural productivity should be a major consideration. This chapter reviews the objectives of flood control and fisheries management and suggests apparently feasible solutions. Examples of spawning area rehabilitation schemes are suggested and w i l l be evaluated in later chapters. B. ALTERNATIVE SCHEMES FOR REDUCING FLOOD DAMAGE 1. FLOOD CONTROL OBJECTIVES In 1968 the Fraser River Joint Advisory Board agreed to approve the use of federal, provincial and municipal government funds for flood control on the Vedder River i f the project was economically ju s t i f i e d (BC Water Resources Service, 1968). A recent study concluded that benefits from increased flood protection are substantial and justify a major flood control project (Princic, pers. comm.). The return period of the design flood that w i l l provide the greatest net benefits is likely to be high. Only a very low risk of a radical shift in river course can be tolerated. 80/ Provision of sufficient flow capacity, bank protection, and control of riverbed aggradation are essential components of a successful flood control project for the Vedder River. Some of the advantages and disadvantages of commonly used flood control methods are discussed in general terms in the following sections. 2. STORAGE RESERVOIRS Storage reservoirs do not appear to be a feasible or desirable solution to the flooding problem for the following reasons: 1) There is a lack of suitable reservoir sites with sufficient storage capacity in the lower reaches of the river. 2) The costs of disruption of residential areas, logging, recreation, sport fishery and commercial fishery interests would appear to greatly outweigh the flood control benefits. 3. WATERSHED MANAGEMENT Logging of the Vedder-Chilliwack River Basin has increased the sediment load and has contributed to flooding in some of the tributaries of the Chilliwack River (I.P.S.F.C., 1969). Logging has l i k e l y increased the suspended sediment load of the Vedder River for minor floods and could possible have increased the severity and frequency of minor floods in the Vedder River. On the other hand, logging has probably not significantly increased the magnitude of major floods or increased bed load movement. Although stream protection regulations are l i k e l y to improve the tributary streambed environment for salmon and trout production, regulation of logging is unlikely to reduce the design c r i t e r i a for flood control. 81. 4. STABILIZATION OF THE SEDIMENT SOURCE The main source of bed material shifted below Vedder Crossing i s the bed, bar, island, and bank material in the three mile reach above Vedder Crossing. The I.P.S.F.C. has suggested that controlling this erosion would be beneficial in reducing the build up of river bed level below Vedder Crossing and would reduce the need for gravel removal to maintain the flood carrying capacity of the dyke system (I.P.S.F.C, 1977). Although stabilization of the banks with rip rap could reduce gravel movement over the long term, material from islands and bars would likely continue to shift into the Vedder Channel for several years. 5. SEDIMENT TRAPS The excavation and maintenance of a large depression in the channel just above Vedder Crossing could prevent the passage of bed load to the reach below Vedder Crossing. This scheme would appear to control sediment aggradation below Vedder Crossing as well as having the advantage of limiting the detrimental effects of dredging on salmon and trout to one location. The wide sections of the channel presently act as temporary sediment storage areas. This i s evident in Figure 7 where large bars have formed in the local expansions in channel width at Peach and Ford Road. This material w i l l continue to move and cause aggradation in the narrow reach downstream even i f the bed load supply from above Vedder Crossing is cut off. Excavation and maintenance of a similar sediment trap below the BC Hydro bridge has been suggested to increase the bedload transport rate above the bridge and thus control aggradation. Although a depression would locally increase the bed slope and water surface slope the bed would likely armour and stabilize immediately upstream of the depression and the channel slope 82. above the bridge would be unaffected. Because of the relatively steep slope of the existing water profile the water surface slope above the BC Hydro bridge i s insensitive to small changes in water levels below the bridge. Thus a depression below the bridge is unlikely to be successful in reducing aggradation above the bridge. 6. FLOOD PROOFING, INSURANCE, ZONING AND EVACUATION Flood proofing, insurance, zoning, and evacuation can be economical alternatives i f the cost of engineering works to provide a high level of protection is prohibitive. Since the location and severity of flood damage is impossible to predict for a radical shift in river course these methods appear d i f f i c u l t to apply. Evacuation would be ineffective because floods cannot be forcast with adequate warning. The Vedder-Chilliwack Basin i s relatively small and storms can produce severe floods within a few hours. 7. DYKING AND DREDGING ALTERNATIVES Modifications to the Vedder River Channel by schemes combining armoured dykes and dredging are likely to provide feasible alternatives. Since sediment traps are thought to be ineffective, gravel removal w i l l have to be carried out essentially throughout the length of the channel. The geometry of the channel w i l l limit the timing and method of gravel removal (Table X). The width of the channel also appears to determine the r e l i a b i l i t y , the i n i t i a l cost, and the maintenance cost of the scheme and determine the effects on users of the river and adjacent land. Some examples of channel modification alternatives for the Vedder River are presented in Table XI. Figures 15 and 16 are sketches rof two alternatives. A reasonable width for a wider active channel (Alternative D) i s estimated to be about TABLE X COMPARISON OF THE SEDIMENT CONTROL PROBELMS OF THE VEDDER RIVER IN A NARROW CHANNEL AND A WIDE CHANNEL SEDIMENT CONTROL PROBLEM NARROW CHANNEL WIDE CHANNEL Reduction of channel capacity by rapid aggradation of the bed during a flood or by debris jams could result in overtopping and perhaps failure of dykes emergency dredging and clearance of debris could be required to restore lost capacity in design of the channel for safety, additional flow capacity would require a substantial increase in dyke height sediment and debris can be safety stored in the channel gravel removal can be scheduled on a non-emergency basis in design of the channel for safety, additional flow capacity can be provided by a small increase in dyke height or further increase in width Bedload movement in a channel with a rapidly decreasing slope w i l l result in aggradation throughout the channel narrowing the channel is not likely to make the channel "self £scouring". Narrowing w i l l increase the bedload transport capacity at a section, but narrowing w i l l also increase the bedload transport capacity of sections upstream and downstream. Because there i s no relative change along the reach aggradation w i l l s t i l l occur. Because each section w i l l transport bedload at lower flows, instability of the bed is promoted. wide sections in the river w i l l promote sediment storage and bed stability dredging might be carried out in a way that would cause minimal disruption to a stable meander pattern Dredging should be located and scheduled to do the minimum damage to the salmon and trout production of the channel dredging w i l l maintain instability of the gravel emergency dredging may be needed during c r i t i c a l periods of spawning and incubation gravel can be removed from sediment stored in bars above the waterline gravel can be removed during non-c r i t i c a l periods for fish TABLE XI EXAMPLES OF CHANNEL MODIFICATION ALTERNATIVES FOR THE VEDDER RIVER ALTERNATIVE FLOW CONTROL SEDIMENT CONTROL CHANNEL WIDTH, STABILITY ADVANTAGES DISADVANTAGES COST ITEMS Present dredged to design flood capacity - Maintenance dredging to provide f u l l capacity - Present alignment - Relatively instable bed low i n i t i a l cost No land acquisi-tion Bed aggradation - I n i t i a l dredging during a large - Maintenance flood likely to dredging reduce capacity,- Emergency emergency dredg- dredging and ing w i l l be channel clearing required B - Present channel banks improved and raised to design flood capacity - as above - as above as above - as above - Raising and improving dykes - Maintenance dredging - Emergency dredging and channel clearing C - Present channel - Maintenance - as above - Large overbank - Land acquisition - Secondary dykes unimproved, dredging to flow capacity for secondary - Maintenance secondary set- provide present provides safety dyke right of dredging back dykes con- channel capa- factor i f pro- way - Land acquisition structed to city within tected channel - Land values-with-. - Emergency contain over- present armoured aggrades and in secondary armo.uring of set-bank flow, banks loses capacity dykes w i l l be back dykes may secondary dykes - Emergency reduced be required impermeable, dredging and - Restricts land unprotected clearing should use within not be required secondary dykes - High i n i t i a l cost 00 TABLE XI (continued) ALTERNATIVE FLOW CONTROL SEDIMENT CONTROL D Wide channel, new primary dyke south of river, improved north dyke, dykes perme-able, protected - Maintenance dredging to design flood capacity CHANNEL WIDTH, STABILITY ADVANTAGES DISADVANTAGES COST ITEMS About 1000 feet wide, meander-ing main channel with bars and islands Relatively stable bed Additional capa-city can be pro-vided with small dyke height increase Sediment storage capacity 1) pro-vides safety factor during large flood 2) eliminates emergency dredg-ing 3) increases stability, may reduce total dredging require-ment-Land acquisMonx> for channel and -new dyke, land lost for agri-culture and residential use. New dyke must be armoured, high i n i t i a l cost New south dyke Improve north dyke Land acquisition Remove part of present south dyke oo Ul FIG. 15 - SKETCH OF ALTERNATIVE C SECONDARY SET-BACK DYKES 00 88. 1,000 feet. Most of the area between the dykes would consist of land occupied by the river in 1958. The design of a new Vedder Channel poses virtu a l l y the same problem to hydraulic engineers of today as was.posed to engineer's of the early 1900's. Now, however, engineers should consider the compatibility of the flood control schemes with salmon rehabilitation and enhancement alternatives. C. ALTERNATIVE SCHEMES FOR PINK AND CHUM SALMON DEVELOPMENT 1. PINK AND CHUM SALMON MANAGEMENT OBJECTIVES There are several possible pink and chum salmon management objectives for the Vedder River. Here are a few examples: 1) to maintain the current level of production 2) to restore the stocks to their hi s t o r i c a l l y higher levels of production 3) to produce the largest number of salmon that i s biologically possible and economically feasible. As the Vedder stocks are harvested simultaneously with other Fraser River stocks, the goals for the Vedder River stocks management w i l l be similar to the goals for the Fraser River stocks. In the spring of 19 77 the Federal and Provincial governments initiated a ten year $250 million to $300 million dollar program to increase the pro-duction of Pacific salmonids through the application of enhancement technology. The physical objective of the program is to, "restore Canada's Pacific Coast salmon stocks to their pre-1900 level of abundance" (McLeod, 1977). The Fraser River chum stocks have been selected for extensive development, the goal being to approximately double the present catch (D. Bailey, pers. comm.). 89. The I.P.S.F.C. have also proposed a restoration and enhancement program for Fraser River pink salmon (I.P.S.F.C, 1972). A brief description of the Fraser stocks illustrates the complexity of mixed stock enhancement. There are five major chum stocks with average escapements greater than 35,000 spawners that make up 90% of the total Fraser River chum escapement (1965-1975 average) (Anderson, 1976). Thirteen smaller runs make up the other 10%. A l l eighteen runs intermingle during migration through the Johnstone Strait, the Georgia Strait and the Fraser River fisheries (Palmer, 1972). Two runs of pink, salmon, the Harrison and the Vedder-Chilliwack, make up the late run to the Fraser River. The late run, however, has a considerabl overlap in the fishery with the large early runs to the spawning areas in the main channel of the Fraser River, the Seton River, and the Thompson River. Although regulation of the fishery can provide some protection for the late run, the late run cannot be managed as a separate fishery (Woodey, pers. comm. It i s apparent that the degree of enhancement of individual stocks in the same fishery w i l l have to be considered carefully. Is i t practical to enhance a l l the stocks to withstand a high exploitation rate, or, is i t better to sacrifice some of the smaller natural stocks and enhance a few of the major stocks? C. J. Walters (1977) has raised some further difficulties;; that may trouble enhancement efforts. F i r s t , a r t i f i c i a l f a c i l i t i e s are prone to "mechanical" failure., Second, i f i t is realized that a large f a c i l i t y , after i t s construction, is causing severe management problems the irrever-s i b i l i t y of p o l i t i c a l decision making w i l l likely prevent closure of the f a c i l i t y . Third, increased fishing effort and investment in fishing gear 90/ could undermine the benefits of more fish. Fourth, there are li k e l y estuarine or marine limitations on production. For example, the amount of pink and chum fry habitat in the Fraser River Estuary is perhaps only a fraction of i t s former size. Finally, interactions between a r t i f i c i a l and natural stocks, including the risk of loss of genetic v a r i a b i l i t y , and interactions between species are not fully understood. Doubling the catch is not to be achieved easily by construction of a few large f a c i l i t i e s and ignoring the fate of natural stocks. Natural stocks, "can provide a cushion to f a l l back upon in the likely event of frequent enhancement f a c i l i t y failures" (Walters, 1977). The doubling of the Fraser River pink and chum catch is likely to be achieved by a combination of re-building natural stocks and building a r t i f i c i a l stocks where risks of management problems and interspecies conflict are low. The suggested objective for Vedder-Chilliwack River pink and chum management i s to increase the production of adults for the fishery to historical levels with a significant proportion of the production being from the natural stock. The largest consistently observed number of spawners in the Vedder-Chilliwack River was about 200,000 pinks and about 100,000 chums. The objective would be to achieve a stable production of approximately 600,000 pinks and approximately 250,000 chums before harvesting by the fishery.''" The task for fisheries managers is to find the least costly method of producing these fish and at the same time maintaining a productive natural stock. Typical return to escapement ratios are: pinks 3:1, chums 2.5:1 Several techniques are available to increase salmon production. For pink and chum salmon these include variations of hatchery or incubation techniques, spawning channels and rehabilitation of natural spawning areas. Generally, the a r t i f i c i a l techniques are capable of producing a large number of fish from one f a c i l i t y . Rehabilitation of the natural spawning areas may not produce as many fish but could s t i l l have considerable economic value and advantages for management. A few examples of how these techniques might be applied to the Vedder River are presented. 2, INCUBATION BOXES In recent years the Fisheries Service and the Fisheries Research Board of Canada have developed successful gravel incubators that provide a simulated natural environment for the alevins. Clean 3/4 to V% inch gravel and f e r t i l i z e d eggs are placed in layers in a 9 foot by 3 feet by 3 feet deep box. Filtered water flows in at the bottom of the box, flows upward through the eggs and gravel, and drains away from the top. Each box can accommodate approximately 500,000 chum eggs and the water requirement i s about one cubic foot per second for 6 boxes (Nielson, pers. comm.). Survival of the eggs to fry i s 90% or greater for chum salmon and about 75% in a similar incubator for pink salmon (Bams,. 1974). A typical f a c i l i t y to produce 270,000 pink adults and 160,000 chum adults would need about 20 incubation boxes for pink and about 18 incubation boxes for chum. The eggs from about 6,000 female pinks are needed and at least 10% as many males for f e r t i l i z a t i o n (McNeil, Bailey, 1975). Only about 3,000 female chums plus males are required to obtain the f e r t i l i z e d chum aggs. The main requirements of an incubation box site are: 92. 1) the availability of a brood stock that i s easily trapped 2) a high quality water supply, usually f i l t e r e d , of about 3 cubic feet per second. The Hopedale Slough area just upstream from the BC Hydro bridge i s a potential site with the development of a groundwater supply. An intake on the Vedder River adjacent to the site would likely f a i l during an extreme flood or low flow. An installation of 18 incubation boxes for chum salmon would cost in the order of $400,000 to $600,000 on this site. The main advantages of this hatchery system would be the small land :; and water requirement and low capital cost compared to a spawning channel. The disadvantages would include the necessity for a reliable sediment free water supply, the large labour requirement (for cleaning the gravel, trapping the fish, and loading the boxes) and the potentially detrimental genetic effects hatchery fi s h may have on natural stocks. Since the fishery would be regulated to protect natural stocks a surplus of spawners in excess of the small brooding requirement w i l l return to the hatchery site and may cause crowding in the natural spawning areas. 3. SPAWNING CHANNELS There are several successful spawning channels i n BC for sockeye, pink and chum salmon. Egg to fry survivals of 50% to 75% have been achieved con-sistently and optimal survival can be higher. High egg to fry survivals depend on a reliable supply of sediment free water, about 60 to 120 cfs, depending on the width of the spawning channel. For a spawning channel adjacent to the lower Vedder River this water would have to be obtained from a river intake located in the stable confined <;reach just below Vedder Crossing. An intake located in the instable lower reach could occasionally be blocked by debris or l e f t dry by a channel shift. Because of the water ." intake problem one to two miles of large diameter pipeline would be required. The water intake, settling basin, and pipeline could cost in the order of one to two million dollars. Added to the cost of flood protection for the channel, the cost of land, and the cost of construction of the channel the total investment would be in the order of four to six million dollars. To justify this investment the f a c i l i t y would have to accommodate a large number of spawners and achieve a high level of production.. In 1968 the Fisheries Service considered construction of a spawning channel along the south bank below Ford Road (Resource Development Branch, 1968). The channel would have had a capacity for 25,000 chum salmon to produce in the order of 500,000 adults annually. The uncertain r e l i a b i l i t y of an intake just upstream of the channel and the lack of a definite.-, flood control plan for the river apparently constrained planning of the project. The I.P.S.F.C. avoided the problems of intake location, flood pro-tection for the spawning channel and coordination with flood control plans by selecting a spawning channel site about five miles downstream from Chilliwack Lake adjacent to the upper spawning area (I.P.S.F.C, 1969). S t i l l under consideration, the proposed channel would have a capacity for 73,500 pink spawners and would produce in the order of 1,000,000 adults in odd numbered years. 4. SIDE CHANNEL REHABILITATION In 1969 the Fisheries Service proposed a project to rehabilitate the former spawning areas on the south side of the Vedder River downstream of Ford Road (Resource Development Branch, 1969). The proposal included purchase of 75 acres of land, cleaning and grading the former river bed, and construction of an intake and desilting pool. The proposed rehabilitated channels would have had a capacity for approximately 20,000 chum spawners. If the egg to fry survival was 25% and the marine survival 2%, the project would produce about 150,000 adults annually. The purchase of land and construction work was estimated to cost $200,000 in 1969. Present costs would be much greater than this amount, mainly due to the increased cost of land. The advantages:of side channel rehabilitation are: 1) low construction costs 2) increased egg to fry survival under partially controlled flow conditions. Survival would be slightly higher than natural survival yet not so great to cause a management problem from surplus spawners. 3) improved and increased rearing area for coho and steelhead fry. 4) low risk of genetic interference. The disadvantages of side channel rehabilitation are: 1) uncertain egg to fry survival. This makes justification of the project d i f f i c u l t 2) high land costs 3) occasional failure of the water supply intake 4) maintenance costs for intake repair and channel cleaning. 95. 5. A WIDER VEDDER CHANNEL The construction of wide primary dykes and removal of some of the present bank protection between the BC Hydro Bridge and Ford Road is a flood control alternative that should promote increased pink and chum salmon production. The channel might look similar to the channel in 1958 (Figure 10) and would have an approximate spawning capacity for at least the h i s t o r i c a l capacity of this reach (about 16,000 to 30,000 chums and an undetermined number of pinks). The advantages of a wider Vedder channel are: 1) low development costs ( i f wide armoured dyking is the preferred method for flood control and i s used regardless of consideration of the fishery) 2) increased egg to fry survival. A wider branching channel would provide varied spawning areas and more stable gravel. 3) improved and increased rearing area for coho and steelhead fry The disadvantages of a wider Vedder channel are: 1) uncertain egg to fry survival 2) high development costs ( i f wide armoured dyking i s not the preferred method for flood control but is used because of consideration of the fishery) 6. REHABILITATION OR ENHANCEMENT? Cost benefit analysis provides a framework for comparing alternatives. These comparisons, however, rarely consider the risk of occasional loss of production directly, but leave this important factor to the intuition of the 96. decision makers. Because r i s k i s d i f f i c u l t to evaluate, high r i s k projects w i l l often be rejected even i f they are inexpensive. A f i r s t step i n comparing high r i s k and low r i s k projects i s to examine the magnitude and types of uncertainty associated with each a l t e r n a t i v e . For salmon development projects i n general, as the cost and degree of a r t i f i c i a l environmental control increases, the p r o b a b i l i t y of a l o s s i n production decreases. However, the consequences of an i n d i v i d u a l f a i l u r e often become more serious. For example, a scheme r e h a b i l i t a t i n g a n a t u r a l spawning area i s subject to a high p r o b a b i l i t y of l o s i n g a percentage of the deposited eggs due to floods. This percentage w i l l never be 100% although could be close to i t with an extremely large f l o o d . In contrast, a hatchery water . supply from groundwater i s usually unaffected by flooding, however there remains a very low p r o b a b i l i t y of f a i l u r e of this supply and 100% loss of the yearns production. The types of uncertainty change as the degree of environmental control increases. For example, r i s k of genetic damage becomes a factor i n a f u l l y c o n trolled a r t i f i c i a l environment. A few more i l l u s t r a t i v e examples are shown i n Figure 17. Natural and a r t i f i c i a l production could work together to eliminate much of the uncertainty. For the Vedder Ri v e r : t h i s could be achieved by a combination of both r e h a b i l i t a t i n g n a t u r a l spawning area and operating a small pink and chum hatchery. A few of the advantages of t h i s combination are: 1) natural production would be increased and p a r t i a l l y s t a b i l i z e d because surplus hatchery spawners would be a v a i l a b l e for spawning i n natural areas 97. F A C T O R S FLOODS AND LOW FLOWS OVER EXPLOITATION 1 HIGH _ RISK OF FACTOR SERIOUSLY REDUCING PRODUCTION DURING LIFE OF PROJECT LOW MECHANICAL FAILURE INTERSPECIES INTERACTIONS GENETIC PROBLEMS LOW HIGH Natural Spawning Area DEGREE OF ENVIRONMENTAL CONTROL Natural Spawning Area with Partial Flow Control . A r t i f i c i a l Spawning Channel Hatchery FIGURE 17 CHANGES IN TYPES OF UNCERTAINTY IN RELATION TO THE DEGREE OF ENVIRONMENTAL CONTROL 98. 2) natural production would maintain the run i n the event of a hatchery accident 3) a large n a t u r a l spawning area would minimize crowding caused by surplus hatchery spawners 4) r e s t r i c t i o n of the f i s h e r y would not be necessary to protect or r e b u i l d the natural stock 5) l o s s of genetic v a r i a b i l i t y i n hatchery produced f i s h would be minimized by regular use of natural f i s h f o r brood stock. A productive natural stock would supply these breeders 6) i improved and increased rearing area would increase coho and steelhead production R e h a b i l i t a t i o n or enhancement? As long as the economics are favourable why not both? D. EXAMPLE ALTERNATIVES FOR EVALUATION There could be several p o s s i b l e combinations of flo o d control and salmon development schemes. Provision of flo o d protection for enhancement f a c i l i t i e s , sharing costs of land purchase and r e h a b i l i t a t i n g the n a t u r a l production of the lower Vedder could be benefits r e s u l t i n g from a coordinated development. An important input to the decision i s the value of salmon pro-duction from present and p o t e n t i a l n a t u r a l spawning areas. In the previous section i t was argued that natural spawning areas can provide several advantages when combined with a small hatchery. Some of these advantages are perhaps already provided i n the Vedder-Chilliwack System by the e x i s t i n g natural spawning area. Whether or not the present natural production and spawning area i s s u f f i c i e n t l y large to complement an 99. enhancement f a c i l i t y depends on the s i z e of the f a c i l i t y , the l o c a t i o n of the f a c i l i t y , and the degree of c o n t r o l over surplus spawners. In any case the l e v e l of salmon production from d i f f e r e n t types of natural or r e h a b i l i -tated spawning areas should be evaluated. The examples suggested f o r evaluation are the production from the present channel, the production from a wider channel and the production from a side channel r e h a b i l i t a t i o n project (Figure 18). Because one of the l a r g e s t sources of uncertainty for these examples i s the mortality due to floods and low flows the next chapter examines this problem i n more d e t a i l . FIG. 1 8 - S K E T C H OF SIDE C H A N N E L REHABILITATION P R O J E C T o o 101. CHAPTER VI THE EFFECTS OF EXTREME FLOWS AND CHANNEL GEOMETRY ON EGG TO FRY SURVIVAL A. INTRODUCTION The Fisheries Service and the I.P.S.F.C. have recognized the detri-mental effects of floods and low flows on the productivity of the Vedder River pink and chum salmon. The damage apparently has been increased by the narrowing of the river (Palmer, 1972)(I.P .S.F.C., 1969). No attempt, however, has been made to quantify these effects. Calculations of annual expected flood damage are routinely used to compare flood control alternatives. 1 This chapter attempts to apply a similar approach to evaluate the effects of floods and low flows on salmon runs. A major component of this type of analysis i s the "flood damage" curve or the relationship between damage and flow magnitude. Such curves for pink or chum salmon of the Vedder River.were not available and had to be synthesized. Because of the complexity of flow induced mortality and the lack of data, relationships had to be developed on the basis of evidence that was scanty and sometimes only indirectly relevant. The procedure involved identifying the mechanisms of flow induced mortality, reviewing the evidence 1 The basic method of computation of the average annual expected flood damage consists of the following steps: 1) Multiply the probability of occurrence of an annual flood by the estimated damage that this flood would cause. This gives the expected damage for one flood. 2) Repeat this calculation for the whole range of flows causing damage. 3) Sum the expected damages for the individual floods. 102. of flow induced mortality in the Vedder River, establishing relationships between high flows and mortality and between low flows and mortality, and calculating the expected egg to fry survival. Further analysis involved modifying the curves for various channel widths and for a side channel with partial flow control. B. MECHANISMS OF FLOW INDUCED MORTALITY In the Vedder River the highest and lowest flows occur during the f a l l and winter months coinciding with spawning and incubation (Figures 3 and 5). Extreme high or low flows.may cause mortality in several ways, the mechanism being dependent mainly on the timing of the flows (Table XII). Mortality effects can also be compounded by a sequence of high and low flows. For example, i f spawning occurred during high water, a low flow during incubation w i l l expose redds dug at higher water levels. C. OBSERVATIONS OF FLOW INDUCED MORTALITY IN THE VEDDER RIVER AND OTHER STREAMS Although fisheries agencies have not specifically studied flow induced mortality i n the Vedder River they have made observations during the course of other investigations. The longest record of observations (1925 to 1976) is the Fisheries Service's, "Salmon Stream Spawning Reports". Observations of the physical condition of the spawning ground, s i l t i n g , erosion, change of stream course, and water levels are contained in these reports. Table XIII contains extracts from these reports with an extreme discharge measurement i f available. Table XIII shows that flow induced mortality i s common in the Vedder River and that the extent of the damage i s related roughly to the magnitude of a flood or a low flow. 103. TABLE XII MECHANISMS OF FLOOD AND LOW FLOW INDUCED MORTALITY IN THE VEDDER RIVER1 EXTREME FLOW LIFE STAGE ENVIRONMENTAL FACTOR DIRECT CAUSE OF MORTALITY SPAWNER high water velocities - delays and disturbs spawn-ing - reduces spawning area causing crowding, super-imposition of redds, and egg retention FLOOD EGG erosion, scouring of the riverbed - loss of eggs and alevins from the gravel ALEVIN sedimentation, burying of embryos - oxygen deprivation - fry are unable to move out of the gravel AND turbidity, s i l t deposition - oxygen deprivation FRY channel switching - dessication, oxygen depri-vation, or trapping of fry old channels SPAWNER reduced wetted area - reduces spawning area causing crowding, superimposition of redds, and egg retention LOW FLOW ; EGG AND reduced intragravel flow velocity and interchange with surface flow - oxygen deprivation ALEVIN drop in water table - dessication FRY low flow during migration - fry are trapped where spawning occurred at higher water levels 1 For other streams, extreme.flows may also be a barrier to upstream migration 104. TABLE XIII OBSERVATIONS OF FLOW INDUCED MORTALITY IN THE VEDDER RIVER BROOD YEAR OBSERVATIONS DATE FLOW .. (cfs) 1929 Low water prevented ut i l i z a t i o n of creeks Oct 1/29 645 1945 Large numbers of pink salmon were lost when a flood h i t during spawning on October 24. Later pinks and chums spawned successfully no record 1949 "Approximately % to 3/4 of a mile of good spawn-ing ground was badly eroded during the flash floods of Nov. 26th and Dec. 1st. Below the BC Hydro bridge to the canal, the river has s changed i t s bed from the south to the north side. Great quantities of gravel have been deposited in the canal. The river rose over 9 f t . in a 24 hour period Dec 1st. Quantities of gravel have been removed getween the (BC Hydro bridge) and the canal for road work and this has had an adverse affect on the river bed. As a result the flash floods did a great deal more damage than would have occurred, had the river bed been untouched. The river has been murky for the greater part of this year..." Nov 2 7/49 2 Approx 19,000 /. 1950 "There is erosion in the Vedder River from Vedder Crossing through to the Vedder Canal. It i s heavy in the Bridging Area (below BC Hydro bridge) and Browne Road sections. The river has not held well to the main channel since the floods of last December. Spawning grounds are deteriorating in this river owing to the continuous erosion." no record Source: Salmon Stream Spawning Reports, Forms, B.C. 16 and F 381, Fisheries and Marine Service This estimate is apparently from the Dominion Hydrological Service based on a gauge reading at Vedder Crossing 105. TABLE XIII (cont'd) BROOD YEAR OBSERVATIONS DATE FLOW (cfs) 1951 "Light s i l t i n g and erosion occurred particularly in the Browne and Ford Road areas. Scouring of the spawning beds is often heavy during high water. Early runs of Pinks and Chums did not spawn in the Vedder this year but went directly through to the upper reaches of the Chilliwack River. Continued scouring and erosion has deteriorated spawning grounds in the Vedder River." no record 1952 "Light s i l t i n g and Erosion." Jan 31/53 7,820 1953 "Considerable scouring, some s i l t i n g and erosion." Oct 31/53 12,400 1954 "Heavy erosion in three sections between Vedder Crossing and Canal. Considerable s i l t i n g and scouring." Nov 22/54 10,600 1955 "Extremely heavy erosion and considerable s i l t i n g throughout the river. November floods distorted the main channel. An estimated 50-60% of spawn was lost during flood conditions in November but light runs of late Pink and chums seeded new channels." Nov 3/55 15,900 1956 "Heavy erosion, s i l t i n g and scouring, spawning grounds in this river have been virtu a l l y wiped out by heavy scouring..." Oct 20/56 9,300 1957 "Spawning grounds in this river are extremely poor owing to continuous scouring and erosion and conditions are being aggravated by the continuous removal of gravel from various bars." Jan 17/58 4,760 1958 Erosion, s i l t i n g and scouring "less than usual" Oct 10/58 8,810 1959 "Light erosion. Exceptionally rainy f a l l caused muddy water conditions throughout most of the spawning season." Nov 24/59 6,840 1960 "Light erosion", scouring "light" Dec 12/60 4,080 106. TABLE XIII (cont'd) BROOD YEAR OBSERVATIONS DATE FLOW (cfs) 1966 "Heavy" erosion and s i l t i n g . "25% of main channel" affected. "Very heavy scouring occurred during late November and December and some Chum spawn loss must be expected." Dec 16/66 11,600 1967 "The combination of low water and freezing temperatures in the winter w i l l no doubt contribute to some extent to chum and pink egg loss this year." Dec 8/67 1,390 "Jan., 1968 flood - erosion and scouring, Ford and Hopedale" road areas. Jan 24/68 11,400 1968 "There was a winter k i l l of chum salmon eggs in some areas due to low water and cold weather in Jan and Feb 1969." Mean flow during cold period approx 950 19 70 "High water in early spring washed out a spawning area below Browne Road." Jan 31/71 May 13/71 12,600 8,800 19 72 "High water in late Dec. changed river channel in the Browne road area and f i l l e d and scoured some spawning grounds with gravel." Dec 26/72 7,840 107. The I.P.S.F.C. measured the egg to fry survival of six brood years of Vedder-Chilliwack pink salmon from 1957 to 1967 (Table XIV). In 1959 low survival was thought to have been caused by low discharge during incubation. In 1963 low survival was apparently caused by floods during the peak of spawning activity and again during incubation. Relatively stable discharge in 1965 appeared to contribute to a high egg to fry survival (I.P.S.F.C, 1969). In Figure 19 the egg to fry survival i s plotted against the difference between the annual peak flood and the annual low flow during spawning and incubation. The plot shows a trend of decreasing survival with an increase in the fluctuation in flow. This plot only covers a portion of the possible fluctuations in flow as the largest flow recorded during this period was 13,000 cfs. In the winter of 19 75 shortly after the December 5th flood the I.P.S.F.C. sampled the river gravel in areas known to have been heavily utilized by pink spawners. No eggs were found i n the main channel of the Vedder above the BC Hydro bridge and only a few eggs were found below the bridge and in Hopedale Slough. The I.P.S.F.C. estimated that mortality caused by the 18,700 cfs flood was from 80 to near 100 percent (Andrew, pers. comm.). The extremely poor return of adult pinks to the Vedder-Chilliwack in 1977, approximately 15,000, was evidently a result of this flood. There are few studies of other salmon and trout streams directly concerned with salmonid mortality due to variable discharge, perhaps due to the d i f f i c u l t y of measuring these effects. "The problem of relating observed mortality levels to causative factors is complicated in most instances because of interactions among environmental factors" (McNeil, 1966). McNeil (1966) studied the environmental factors affecting egg to fry TABLE XIV DISCHARGE OF THE CHILLIWACK RIVER AT VEDDER CROSSING DURING PINK SALMON SPAWNING AND INCUBATION (I.P.S.F.C., 1969) BROOD YEAR NUMBER OF FEMALE SPAWNERS SPAWNING PERIOD PEAK SPAWNING PERIOD INCUBATION PERIOD DIFFERENCE BETWEEN EXTREME FLOWS (cfs) EGG TO FRY SURVIVAL % Oct. Mean (cfs) Nov Mean (cfs) Oct 10-31 Nov 1 - Mar 31 Max. frfs) Min (cfs) Max. (cfs) Min. (cfs) 1957 114,000 927 1,160 4,410 636 4,760 871 4,124 8.60 1959 53,000 2,620 2,920 5,070 1,560 8,930 388 8,542 6.02 1961 112,800 1,760 1,610 5,850 1,240 9,280 694 8,586 9.00 1963 191,300 2,070 3,600 7,070 876 13,000 994 12,124 5.18 1965 127,000 2,120 1,640 2,160 1,250 5,270 831 4,439 12.85 1967 149,300 3,070 1,600 12,000 1,690 11,400 1,390 10,610 9.03 109 EGG TO FRY SURVIVAL % 15. 10 15 1 TREND (Fitted by eye) 5,000 X X -, 1 1 i 1 r ' i 10,000 DIFFERENCE BETWEEN EXTREME FLOWS DURING SPAWNING AND INCUBATION (cfs) FIGURE 19 EGG TO FRY SURVIVAL VS. DIFFERENCE BETWEEN EXTREME FLOWS DURING SPAWNING AND INCUBATION (Data from I.P.S.F.C, 1969) 110. survival for five brood years of pink salmon in three southeastern Alaskan streams. High mortality, 60 to 90 percent, was due to low dissolved oxygen levels associated with low flows during and after spawning. Movement of gravel, during floods, was associated with the removal of 50 to 90 percent of eggs and alevins present in spawning beds. 50 percent mortality occurred several times during floods that did not extensively shift wood debris. Wickett (1959) observed the Big Qualicum River spawning areas before and after a heavy flood. He observed s i l t i n g of gravel and loss of permeability, loss of spawning area through gravel removal and direct erosion of coho and chum eggs. He estimated that the flood reduced the productivity of a section of the lower stream by one third. For the purpose of increasing chum, coho, and chinook salmon production in the Big Qualicum River the Fisheries Service b u i l t a storage dam, outlet works, and a tributary diversion channel to provide flow control for the spawning areas. Prior to the completion of the project in 1963 chum egg to fry survival averaged 13 percent under natural flow conditions. Under controlled flow conditions, 1963 to 1977, chum egg to fry survival has averaged 27 percent. For the Big Qualicum, "flow stability appears to have been the major factor inducing variability in the freshwater survival rate of chum salmon" (Lister and Walker, 1966). A plot of the egg to fry survival vs. the peak annual discharge indicates an inverse relationship (Figure 20 )• Although the effects of floods are largely negative high flows do flush the fines from a part of the riverbed. Without periodic high flows the riverbed s i l t s up gradually and egg to fry survival drops to a level which may be lower than before flow control. The high survival in the flow controlled Big Qualicum River i s maintained by annual cleaning of the natural 111. EGG TO FRY SURVIVAL (%) 30 20 -I 10 J X 1964 x 1963 X 1959 1961 x 1962 1960 — i 1 1 1 1000 2000 3000 4000 PEAK DAILY DISCHARGE (cfs) FIGURE 20 BIG QUALICUM RIVER CHUM EGG TO FRY SURVIVAL VS. PEAK DAILY DISCHARGE DURING INCUBATION,- (Lister and Walker, 1966) 112. gravel. To clean the gravel the flow i s increased at the control works then the gravel i s disturbed slightly by a bulldozer blade and the fines are carried downstream. A chum spawning ground inventory of East Vancouver Island streams revealed that extreme flow conditions have had detrimental effects in 12 out of 35 streams surveyed (Fraser, Lightly, Bailey, 1974). The streams with widely fluctuating flows were usually those with a recently logged watershed. Preliminary results from a study of chum egg mortality in natural spawning areas of southern coastal BC indicated that the most productive chum streams are those that have a large lake to stabilize flows (Marshall, pers. comm.). There are many references in the literature that indicate qualitatively the significance of flow induced mortality. For improved management of salmon streams subject to flow mortality the effects need to be quantified. D. RELATIONSHIPS BETWEEN EXTREME FLOWS AND ADDITIONAL MORTALITY 1. A Concept of Additional Mortality For the purposes of rough estimation of mortality effects, definition of the complicated: interactions of causes of mortality can be avoided by a simplifying assumption. Mortality due to extremes of discharge can be treated as an independent effect additional to mortality caused by other factors. In the controlled flow environment of the Big Qualicum River, these other factors, gravel conditions, spawning density, etc. limit egg to fry survival to approximately 25%. For a specific natural spawning area there i s , hypothetically, an average level of mortality.that would result i f the flow were controlled. If this "background" mortality under stable flow conditions can be estimated then separate estimates of additional mortality due to extreme flows can be added to calculate the total mortality. Estimates of expected additional mortality due to extreme flows can be obtained by a method similar to the calculation for average annual flood damage. There are, however, several d i f f i c u l t i e s in obtaining estimates of a level of additional mortality in relation to a maximum or minimum flow. 1) The "Flood damage" curves can only be based on judgement and indirect evidence as specific data relating mortality and discharge i s generally not available. 2) Mortality effects are commonly not just the result of one flow but of a series of low flows and high flows. 3) The mortality caused by a flood or low flow depends on the stage in the salmon l i f e cycle that i t affects. In spite of the second d i f f i c u l t y mentioned above extreme flows are s t i l l l i k e l y to control the magnitude of resulting mortality. The third d i f f i c u l t y mentioned above could be resolved, for example, by separating the spawning and incubating periods and calculating additional mortality for: these periods separately. For the purpose of demonstrating a method the spawning and incubation periods are considered together and the maximum and minimum discharge during spawning, and incubation are considered to be the significant events causing mortality. Because of the variability in a flow vs. mortality relationship, i.e., two floods of similar magnitude could cause quite different mortalities a range of mortalities must be considered. The following discussions w i l l therefore develop upper and lower bounds for a long term average relationship 114. This long term average relationship can be represented by a curve somewhere between the upper and lower bounds. 2. Additional Mortality vs. Maximum Annual Flow During Spawning and Incubation The main causes of flood induced mortality in the Vedder River, in apparent order of importance, are: 1) direct erosion of eggs and alevins 2) oxygen deprivation due to s i l t deposition from turbid water 3) reduction of spawning area and spawning efficiency High water velocities would begin to reduce spawning area at flows greater than approximately 3,000 cfs, especially in the narrower sections. Significant suspended sediment concentrations, greater than about 40 ppm, would not usually occur during flows less than 6,000 cfs. Concentrations of about 150 ppm would likely occur at flows of about 10,000 cfs (Water Survey of Canada). Erosion of eggs would be expected to occur when the bed began to move. At the narrow BC Hydro bridge section the bed has been found to begin moving at about 6,000 to 7,000 cfs (Sediment Survey Section, 1974). Mortality effects would apparently be negligible for flows of about 3,000 or 4,000 cfs and would not become significant u n t i l flows of at least 6,000 cfs. Observations of fishery officers have indicated that heavy scouring of the stream occurred with a peak flow as low as 8,000 cfs. Therefore, flows greater than 8,000 cfs would be expected to regularly cause some mortality. The construction of the upper and lower bounds for the flood damage curve (Figure 21) i s based on the above discussion and on a few other rough approximations of flood induced mortality (Table XV). 115. MAXIMUM ANNUAL FLOW .(cfs) (SEP 15 TO MAR 30) FIGURE 21. ADDITIONAL MORTALITY VS. MAXIMUM ANNUAL FLOW DURING SPAWNING AND INCUBATION 116. TABLE XV THREE ROUGH ESTIMATES OF MORTALITY DUE TO FLOODS YEAR PEAK DAILY FLOW (cfs) Sept 15 - Mar 30 ESTIMATED MORTALITY DUE TO FLOODS SOURCE OF ESTIMATE 1955 15,900 50- 60% "Salmon Stream Spawning Report", 1955. Fisheries Service Form B.C.16 1963 13,000 60% Roughly estimated from egg to fry survival data for Pink salmon1 (I.P.S.F.C., 1969) 19 75 18,700 80-100% F. Andrew, I.P.S.F.C, personal communication . V . The estimate was obtained by the following steps: 1) egg to fry survival with no large floods or low flows in 1965 was 13% 2) egg to fry survival in 1963 was 5.2% and low survival was attributed to floods 3) estimated mortality due to floods would therefore be 13-5.2 x 100 'V 60% 13 117. 3. Additional Mortality vs. Minimum Annual Flow During Spawning and Incubation The main causes of low flow induced mortality are: 1) reduction of available spawning area 2) reduction of the intragravel flow - stream flow exchange, and dissolved oxygen level in the intragravel water 3) dessication of eggs and alevins. Reduction in spawning area will begin when the flow drops below the optimum spawning flow, the flow that provides the maximum productive spawning area. Higher flow levels may provide greater spawning area for some sections of the river but subsequent reduction in stage will dry out the eggs and render these sections unproductive. The optimum spawning flow should, therefore, be near or slightly greater than the mean flow during incubation. The mean flow November 1 to April 30 is 1,925 cfs, thus, the optimum spawning flow should be in the order of 2,000 to 3,000 cfs. Flows during incubation can drop considerably without major mortality effects. A natural sequence of riffles and pools forms a series of reservoirs that maintain a hydraulic gradient for intragravel flow through the r i f f l e areas even though there may be no surface flow on the r i f f l e (Jones, 1959). Much lower flows, however, are likely to result in low dissolved oxygen levels as observed by McNeil (1966) which in the Alaskan streams resulted in 60 to 90 percent mortality. Low water levels in the Vedder-Chilliwack River in 1959 probably contributed to the low egg to fry survival rate of 6.02% (Table XIV). If the 1965 survival of near 13% is used as a value for survival without flow mortality the reduction due to the low flows would be about 13-6 x 100 =" 54%. 13 118. The low flow curves are sketched in Figure 22. Mortality would be expected to increase slowly with decreasing flow un t i l about 1,000 cfs, then increase quickly to near 100% at the lowest flow on record. E. CALCULATION OF EXPECTED EGG TO FRY SURVIVAL 1. Steps in the Calculation Calculation of the expected egg to fry survival involves: 1) determining the probabilities of flows from a frequency analysis of the maximum and minimum flows occurring during spawning and incubation 2) multiplying the probability of a flow by the additional mortality i t is estimated to cause and summing these products to find the expected additional mortality. 3) choosing a hypothetical "stable flow survival" 4) reducing the stable flow survival by the expected additional mortality to give the expected egg to fry survival. 2. Calculation of Expected Additional Mortality To determine the sensitivity of the shape and position of the curves the expected additional mortality was calculated for the upper bound, lower bound, and intermediate curves in Figure 23. This calculation is shown in Table XVI. The expected additional mortality due to low flows was calculated to be between 13% and 53% with an intermediate value of 33%. The expected additional mortality due to floods was calculated to be between 17% and 54% with an intermediate value of 31%. 119. ADDITIONAL MORTALITY % MORTALITY EFFECTS - serious reduction in intragravel flow —• drying of eggs 1959 (Vedder-Chilliwack Pink Salmon) MORTALITY EFFECTS BEGIN - i reduction in spawning area causing crowding - reduction in intra-gravel flow Mean flow ^ Nov 1 - Apr 30 2COO MINIMUM ANNUAL FLOW (cfs) (Sept 15 to Apr 30) FIGURE 22. ADDITIONAL MORTALITY VS. MINIMUM ANNUAL FLOW DURING SPAWNING AND INCUBATION too ADDITIONAL IORTALITY % lOOr UPPERBOUND. 50 H ADDITIONAL < MORTALITY % 2000 50 h MINIMUM ANNUAL FLOW (cfs) (SEP 15 TO APR 30) 10,000 20,000 • 30p00 MAXIMUM ANNUAL FLOW (cfs) (SEP 15 TO MAR 30) 40.0J FIGURE 23. ADDITIONAL MORTALITY VS. FLOW CURVES USED IN EXPECTED SURVIVAL CALCULATION MINIMUM ANNUAL FLOW SEPTEMBER 15 to APRIL 30 (1) FLOW (cfs) 200- 300 300- 400 400- 500 500- 600 600- 700 700- 800 800- 900 900-1000 1000-1200 >1200 TOTAL TABLE XVI CALCULATION OF EXPECTED ADDITIONAL MORTALITY (2) (.3) (4) (3)x(4) (5) (3)x(5) (6) (3)x(6) No. of YEARS 1 1 3 5 11 10 7 1 2 0 41 PROBABILITY .024 .024 .073 .122 .269 .224 . 171 .024 .049 .0 1.000 ADD. MORT. UPPER BOUND % 97 94 86 70 55 43 35 28 23 6 EXPECTED ADD. MORT. % 2.3 2.3 6.3 8.5 14.8 10.5 6.0 0. 7 1.1 0 53% ADD. MORT. LOWER BOUND % 76 37 25 17 13 8 4 2 0 0 EXPECTED ADD. MORT. % 1.8 .9 1.8 2.1 3.5 2.0 .7 . 1 0 0 13% ADD. MORT. INTERMEDIATE CURVE % EXPECTED ADD MORT. % 90 83 63 40 32 25 20 16 10 0 2.2 2.0 4.6 4.9 8.6 6.1 3.4 .4 .5 0 33% TABLE XVI (cont'd) FLOW (cfs) No. of YEARS PROBABILITY ADD. MORT. UPPER BOUND % EXPECTED ADD. MORT. % ADD. MORT. LOWER BOUND % EXPECTED ADD. MORT. . % : ADD. MORT. INTERMEDIATE CURVE % EXPECTED ADD. MORT. % <5000 7 .212 0 0 0 0 0 0 MAXIMUM 5000-:7000 3 .091 10 .9 0 0 0 0 ANNUAL i 7000- 9000 5 .152 50 7.6 0 0 15 2.3 FLOW 9000-11000 6 .182 70 12.7 10 1.8 30 5.5 SEPTEMBER 15 11000-13000 6 .182 85 15.5 22 4.0 45 8.2 to 13000-15000 1 .030 94 2.8 33 1.0 64 1.9 MARCH 30 15000-17000 1 .030 96 2.9 45 1.4 75 2.3 17000-20000 2 .061 97 5.9 58 3.5 82 5.0 20000-25000 1 .030 97 2.9 82 2.5 89 2.7 > 25000 A .030 99 3.0 94 2.8 96 2.9 TOTAL 33 1.000-.. - 54% - 17% - 31% Annual extremes of discharge are summarized by the Water Survey of Canada, however, for the years 1912, 1913, 1919, 1922 and 1923 the maximum annual flood occurred outside of the September 15th to March 30th period. As mean daily flow records for these years were not readily available the maximum winter flood could not be determined and these years could not be included in the frequency histogram. In order to avoid the bias created by selecting just those years in which the maximum flow did occur in the September 15th to March 30th period the block of years 1919 to 1924 was omitted from the frequency count even though 1920, 1921 and 1924 contained large winter floods. For a l l other years of record the maximum winter flood was found from the daily records i f i t did not coincide with the maximum annual flood. ,_ 123. 3. Estimation of Stable Flow Survival The average egg to fry survival in the Vedder River under stable flow conditions can be approximated by egg to fry survival measurements under stable flow conditions in the Vedder-Chilliwack River, the Fraser River System and the Big Qualicum River. In 1965 Vedder River flows ranged between 1640 and 2120 cfs during spawning, and between 831 and 5270 cfs during incubation. Egg to fry survival of Vedder-Chilliwack pink salmon was measured to be near 13% (I.P.S.F.C, 1969) . This value can only indicate roughly what the true average value might be because the production of fry is dependent on several variable factors as well as discharge. Additionally the measurement in 1965 is a composite measurement of the productivity of a l l the Vedder-Chilliwack spawning areas, not just the Vedder River spawning area. The average egg to fry survival for the Fraser System is about 13% for pink salmon and about 15% for chum salmon. Since a considerable proportion of the Fraser System spawning areas are subject to at least some flow induced mortality the stable flow survival for the Fraser System as a whole would be greater than 13%. Egg to fry survival of chum salmon in the Big Qualicum River has averaged about 25% during 14 years of stable flow conditions. Because the Big Qualicum River gravel i s cleaned a r t i f i c i a l l y each year the average egg to fry survival of 25% would be a maximum value for stable flow survival. The true value of the average stable flow survival for the Vedder appears to be between 13% and 25%. Lacking further information the mean of this range, 19%, w i l l be used. 124. 4. Calculation of Expected Egg to Fry Survival The survival rate after an extreme flow i s equal to the stable flow survival reduced by the additional mortality. This calculation can be best illustrated by an example. Given: 1) the stable flow survival i s 19% 2) the additional mortality due to floods i§. 31% 3) the additional mortality due to low flows is 33% Then: 1) the survival after floods would be 19% - 19% (31%) = 13% 2) the expected egg to fry survival after both floods and low flows would be 13% - 13% (33%) = 9%. To get a feel for the change in expected egg to fry survival for different stable flow survivals and for different curves i n Figure 23 a few calculation results are presented in Table XVIII„ Only one calculated survival (18%) was greater than the average egg to fry survival of Fraser River pink and chum salmon (about 13-15%). This value of 18% resulted from use of a high stable flow survival of 25% and the lower bound mortality curves, the smallest estimated effect of extreme flows in the Vedder. It appears, therefore, that the actual average egg to fry survival of the Vedder River pink and chum salmon must be lower than the Fraser System average. The analysis indicates the expected egg to fry survival of the Vedder River pink and chum salmon would probably be near 125. TABLE XVII EXPECTED EGG TO FRY SURVIVAL FOR DIFFERENT STABLE FLOW SURVIVALS AND ADDITIONAL MORTALITY VS. FLOW CURVES STABLE FLOW EGG TO FRY SURVIVAL % EXPECTED ADDITIONAL MORTALITY DUE TO LOW FLOWS % EXPECTED ADDITIONAL MORTALITY DUE TO FLOODS % ADDITIONAL MORTALITY VS. FLOW CURVES IN FIG. EXPECTED EGG TO FRY SURVIVAL % 13 53 54 UPPER BOUNDS 3 13 13 17 LOWER BOUNDS 9 13 33 31 INTERMEDIATE 6 25 53 54 UPPER BOUNDS 5 25 13 17 LOWER BOUNDS 18 25 33 31 INTERMEDIATE 12 19 33 31 INTERMEDIATE 9 126. F. THE EFFECT OF CHANNEL GEOMETRY AND DREDGING ON EXPECTED EGG TO FRY SURVIVAL The magnitude of mortality due to extreme flows i s substantially dependent on the channel geometry and the st a b i l i t y of the river bed. An extreme example of this would be that, for the same flood, more erosion and scouring of the channel bed and loss of eggs and alevins would be expected in a straight narrow ditch than in a wide meandering stream. Additional mortality vs. extreme flow curves, therefore, are different for different channel configurations. This chapter does not attempt to discuss a l l the various effects of channelization - and dredging on salmon production but serves to present enough background material so that distinct additional mortality vs. flow curves can be postulated for the present Vedder channel, for a wider Vedder channel and for a side channel rehabilitation project. The expected egg to fry survival is then calculated using these curves. Dredging can result in direct mortality of fish through mechanical injury and through clogging of g i l l s by excessive suspended sediment. The timing of dredging can usually be selected to avoid direct interference with pink and chum salmon, however, resident species, coho and steelhead, could sustain direct mortality. The major mortality effects on pink and chum salmons are, therefore, due to altered channel conditions. Some of these are: a) reduction in channel width b) decrease in density of riverbed gravel c) removal of bed armour d) disruption of a stable r i f f l e - p o o l sequence e) lowering of river grade - cutting off seepage to side channels 127. a) Reduction in Channel Width Generally, for a narrow section of a channel, water velocity increases rapidly as the flow increases. In a wide section, however, the flow spreads out over bars and into secondary channels and the average depth and velocity increase slowly as the flow increases. A wide channel provides two hydraulic advantages for salmon pro-ductivity: 1) the range of flows over which suitable spawning area is available is greater than in a narrow channel 2) the bed i s stable at higher flows than in a narrow channel. . In 1957 the I.P.S.F.C. measured water velocities in the Vedder River at 23 cross sections and remeasured these i n 19 77 during very similar flow conditions (600-900 cfs). The data show that the 1977 velocities (mean of two measurements in each section) were higher than the 1957 readings at a l l sections but three. Large increases in velocity (200 to 400%) were found to have occurred in the narrowest sections near Browne Road and Hopedale Road (I.P.S.F.C, 1977). b) Decrease in Density of Riverbed Gravel, and c) Removal of Bed Armour Dredging of a gravel riverbed appears to decrease the density of what naturally i s a f a i r l y compact gravel bed. After the dredging of the Vedder River in summer, 1976, several of the gravel bars were soft and spongy. Soft gravel i s avoided by spawners. "A female cutting in this type of gravel would find bed-making almost impossible, rather like trying to make a hole in dry sand" (Jones, 1959). 128. Dredging also appears to remove the natural armouring of the bed provided by larger stones. The f i r s t few high flows following dredging would be expected to result in extensive readjustment of the bed. If the riverbed is instable (loose, unarmoured), a given flood would cause greater mortality than i f the bed has stabilized. d) Disruption of a Stable Riffle-Pool Sequence Dredging of a channel disrupts the natural river bed topo-graphy, characterized by various bars, r i f f l e s and pools. The r i f f l e - p o o l sequence i s perhaps most important for i t s promotion of food production and provision of suitable habitat for stream reared species of salmon and trout (Mundie, 1974). However, the r i f f l e s and pools play a v i t a l role in promoting successful spawning and incubation. Pools serve at least three purposes: 1) help to stabilize the stream by their deaccelerating effect on the velocity of the water (Stuart, 1960) 2) provide resting places where the preliminary courtship for spawning can take place (Jones, 1959) 3) provide reserves of water in times of low flow which w i l l percolate downstream through the gravel from one pool to another (Jones, 1959) The r i f f l e - p o o l sequence of a natural channel apparently results i n an environment less susceptible to flow induced mortality than the environment of a narrow dredged channel. e) Lowering of River Grade - Cutting Off Seepage to Side Channels Dredging of the Vedder River in 1976 reduced the chum spawning 2 area in side channels by approximately 6000 yds . Dredging lowered 129. water surface levels below the level necessary to supply seepage flow to side channels. These side channel areas w i l l remain un-available for spawning as long as the dredged grade i s maintained or until improvements to the side channels are made. In chum salmon streams that are subject to frequent and severe flooding side channels in the lower reaches have been identified as important chum spawning areas (Marshall, pers. comm.). Many of these side channels are naturally blocked off at the upper end by log jams, sediment, and debris which provide some flow control during floods that scour the main channel. For example, eggs that have been previously deposited on bars in the main channel become exposed during low flows. Eggs that have been previously deposited in the bed of a side channel have a more dependable low flow water supply from seepage from the main channel. It i s thought that provision of a safe environment during moderately high and low flows makes side channels more consistently productive than main channel areas. Distinct additional mortality vs. flow curves can be postulated for the present Vedder channel and a wider channel. The change in the low flow curve, Figure 22, i s d i f f i c u l t to predict. The advantages of a wider channel, dependable seepage flow in secondary channels and pools providing intragravel flow through bars would likely be offset by the disadvantage of a wider channel, the large area of streambed and redds that would be exposed at low flow. The mortality vs. low flow curves would not be expected to be significantly different for various channel widths. 130. For flood flows, however, a wider channel would be expected to have a lower additional mortality for a l l flood flows. Hypothetical curves are shown in Figure 24 (these correspond to the upper, lower and intermediate curves of Figure 23),. Although there i s no quantita-tive basis for the actual difference between the curves i t i s interesting to postulate a curve and see how i t would affect the calculation of expected egg to fry survival. Considering a stable flow survival of 19% and an expected additional mortality due to low flows of 33%, an increase in channel width could increase the expected egg to fry survival by as much as 5% (Table XVIII). TABLE XVIII EXPECTED EGG TO FRY SURVIVAL FOR CHANNELS OF.DIFFERENT WIDTHS RELATIVE CHANNEL WIDTH STABLE FLOW SURVIVAL % EXPECTED ADDITIONAL MORTALITY DUE TO LOW FLOWS % EXPECTED ADDITIONAL MORTALITY DUE TO FLOODS % EXPECTED EGG TO FRY SURVIVAL 7 NARROW 19 33 54 6 INTERMEDIATE 19 33 31 9 WIDE 19 33 17 11 The mortality curves for both low flows and flood flows for a side channel development would be significantly different than the curves for main channel spawning areas. The curves would probably be something like those shown in Figure 25. In this 100 40,000 MAXIMUM ANNUAL FLOW (cfs) (SEE 15 TO MAR 30) FIGURE 24. ADDITIONAL MORTALITY VS. MAXIMUM ANNUAL FLOW FOR CHANNELS OF DIFFERENT WIDTHS KX) ADDITIONAL MORTALITY % 50 lOOr Water Intake Drys Up ADDITIONAL < MORTALITY % 50 Reduced flow begins to have detrimental effects 500 1000" 1500" FLOW (cfs) J 2000 Suspended sediment causes s i l t i n g of gravel 10,000 20,000 FLOW (cfs) TABLE 25... ADDITIONAL MORTALITY VS. FLOW FOR A REHABILITATED SIDE CHANNEL (WATER SUPPLY INTAKE OPERABLE BETWEEN APPROXIMATELY 500 cfs and 16,000 cfs) 133. example a water supply intake is designed to be operable between 500 and 16,000 cfs. Some mortality occurs between these limits and severe mortality occurs when these limits are exceeded. Using the same method of caluclation as in the previous sections: 1) The expected additional mortality due to both floods and low flows i s near 15% 2) Using a stable flow survival of 19% the expected egg to fry survival in a side channel is near 14% 3) Using a stable flow survival of 25% ( i f the gravel was cleaned regularly, for example) the expected egg to fry survival in a side channel i s near 18%. These results (Table XIX) indicate that the average egg to fry survival would likely be considerably higher in a side channel with par t i a l flow control than in the main channel. The relationships between mortality and extreme flows are based on interpretation of a variety of evidence for the simple reason that l i t t l e directly applicable data is available. The value of this exercise i s to demonstrate that changes in channel geometry do have a significant effect on salmon production. These effects can be further explored by incorporating the expected additional mortality calculation into a method of estimating adult salmon production. This i s described in the following chapter. 134. TABLE XIX EXPECTED EGG TO FRY SURVIVAL FOR A SIDE CHANNEL DEVELOPMENT PROJECT STABLE FLOW SURVIVAL % EXPECTED ADDITIONAL MORTALITY DUE TO LOW FLOWS % EXPECTED ADDITIONAL MORTALITY DUE TO FLOODS. % EXPECTED EGG TO FRY SURVIVAL % 19 15.2 15.1 14 25 15.2 15.1 18 (with gravel cleaning) 135."; CHAPTER VII ESTIMATION OF ADULT SALMON PRODUCTION A. INTRODUCTION There are several factors that complicate estimation of long term production of adults from a specific natural spawning area. First, there are usually no records of numbers of spawners or measurements of egg to fry survival for the specific area concerned; second, there i s a wide var i a b i l i t y of spawning and incubating success within the area that would make measurement d i f f i c u l t ; and third, egg to fry survivals can vary by a factor of two or three and fry to adult survival by a factor of six from year to year. The simplest approach i s to multiply the estimated spawning area capacity by the average return to escapement ratio. For example, i f the Fraser River chum population has an average return to escapement of 2.23:1, and the estimated spawning capacity of the present channel between the BC Hydro Bridge and Ford Road is 4500 chum then the number of adults produced per year should average somewhere near 2.23 x 4500 = 10,035 adults. This calculation, however, ignores any characteristics of the spawning ground other than the approximate spawning area capacity. The calculation can be improved i f more information about the specific spawning population i s available. If fecundity, sex ratio, egg to fry survival, and fry to adult survival data have been collected the calculation can be broken down into several parts using average values or best estimates for these parameters. For the same example, "(using typical numbers): 136. 4500 (spawners) x 3000 (eggs per female) x 0.5 (50:50 sex ratio) x 0.07 (egg to fry survival) x 0.02 (fry to adult survival) = 9450 adults. ... This calculation, however, gives no indication of the year to year va r i a b i l i t y or of the accuracy of the estimate. Uncertainty can be considered directly by incorporating in the calculation an upper and lower bound for each parameter as well as the average or most probable value. Production of adults can then be expressed in terms of a range of possible values which i s the result of the v a r i a b i l i t y and accuracy of each parameter in the calculation. The upper and lower bounds for parameters can be obtained from data, or, i f data are unavailable, from experts who are willing to volunteer estimates. This method of cal-culation has been applied to salmon management (Sheehan, 1976), estimating long term effects of lake pollution (Hershman, 1974), and estimating the effect of pollution on a salmon run (Brox, 1976). This chapter presents the method, modified, to estimate the pro-duction of chum salmon between the BC Hydro bridge and Ford Road for the present channel, for a wider channel, and for a side channel development. The results describe the magnitude and the r e l i a b i l i t y of production from each scheme. The f i n a l section of this chapter estimates the contribution of each scheme to the commercial fishery. B. DESCRIPTION OF THE METHOD 1. The Basic Concept (for more detailed descriptions see Sheehan (1976) and Brox (1976)) To apply the methods^the f i r s t step is to obtain upper, lower and most probable values for the parameters. If the parameters are described by non linear relationships^, curves are required. These can be obtained 137. either from an expert who w i l l volunteer estimates or from a regression analysis i f data are available. Then, using the computer, a probability distribution is fitted between the three points or the three curves. The most probable estimate forms the mode of the distribution and the upper and lower estimates are set a fixed number of standard deviations away from the mode. In this thesis, a skew normal distribution (Hershman, 1974) i s fitted to the estimates with the upper and lower estimates being two standard deviations away from the mode. In situations where more data are available i t may be appropriate to use other probability distributions and include more than two standard deviations within the upper and lower estimates (Brox, 1976). After a probability distribution i s f i t t e d ^ i t i s divided up into discrete classes, and probabilities are calculated for a value being in any one class. The probability distribution i s now in matrix form. Figure 26 shows examples of the conversion of estimates to matrices. The numbers and matrix dimensions shown are for the example only. 1 x 20 and 20 x 20 matrices were used in the actual calculation. A l l the components of a calculation are converted to matrix form and the matrices are multiplied together to calculate a resultant matrix. The resultant matrix expresses the answer in terms of probability. This matrix can either be reconverted to an upper, lower, and most probable value or can be converted to an expected value. 2. Application of the Method to Estimating Adult Salmon Production Application of the probability matrix method to estimating adult salmon production i s based on the "spawners x eggs per female x sex ratio Spawning Capacity (chum salmon) 10,000 , 8,000 6,000 4,000 2,000 . 0 . 1. OBTAIN ESTIMATES Upper bound 10,000 .Most probable •Lower bound FIT AND DISCRETIZE SKEW NORMAL DISTRIBUTION 10,000 8,000 6,000 4,000 2,000 0 131 .320 .451 ,098 probability of the spawning capacity being between 6,000 and 8,000' chum salmon CALCULATE PROBABILITIES FOR MATRIX No. of Fry (xl0 b) FIGURE 26. - i 1 1 1 2000 4000 6000 8000 10,000 No. of Spawners EXAMPLES OF CONVERSION OF ESTIMATES TO MATRIX FORM 0 2000 4000 6000 8000 10,000 No.oof Spawners 2.0 1.6 No. of Fry 1.2 (xl0 b) 0.8 0.4 0 .100 .550 .350 0 0 No. of "Spawners Probability that i f there are between 4000 and 6000 spawners they w i l l produce between 0.8xl0 6 and £ 1.2 x 106 fry » 139. x ... = adults" calculation. The matrix method, however, allows the uncertainty associated with the parameters and the effects of floods and low flows to be incorporated directly. A schematic diagram of the calculation is shown in Figure 2 7 and the following paragraphs explain the input to the computer calculation. Input 1 Spawning Area Capacity The long term average number of spawners u t i l i z i n g a given spawning area should be equivalent to the spawning area capacity. This statement assumes that the fishery w i l l be regulated so that the long term average escapement w i l l equal the optimum escapement. In any one year, however, the number of spawners w i l l vary because of variability i n : 1) success of the spawners' l i f e cycle 2) exploitation by the fishery 3) distribution of spawners within the river For the purposes of comparing alternative spawning areas over a long time period these factors can be ignored. On an annual basis, however, these factors increase the uncertainty of production. Unfortunately, no method of estimating this uncertainty was found and therefore the uncertainty caused by these factors was not included in the calculation. The uncertainty expressed within the upper and lower bounds of spawning area capacity is the inaccuracy of estimating this capacity. Input 2 Fry Production Curves (Ideal Flow Conditions) The va r i a b i l i t y of the number of eggs per female and of the sex ratio i s small when compared to the variability of other parameters in this calculation, therefore, only a most probable estimate for the number of eggs and sex ratio i s used. With these parameters constant the number of n INPUT SPAWNING AREA CAPACITY Upoer Most Prob. Lower ' FRY (IDEAL FLOW) o n SPAWNERS 3. 100. ADDITIONAL MORTALITY % FLOW (cfs) 2000 ioq ADDITIONAL MORTALITY % FLOW 40,000 (cfs) ADULTS-FRY COMPUTER CALCULATION m, FRY (IDEAL FLOW) n o SPAWNERS FRY BEFORE LOW FLOWS FRY AFTER LOW FLOWS m FRY BEFORE, FLOODS m FRY AFTER FLOODS ft ADULTS m FRY n SPAWNING AREA CAPACITY m FRY (IDEAL FLOW) MULTIPLY m FRY AFTER LOW FLOWS MULTIPLY m FRY V AFTER! LOW FLOWS AND FLOODS ADULTS 140. OUTPUT i ADULTS PROBABILITY FIGURE 27. SCHEMATIC DIAGRAM OF CALCULATION 141. fry produced, as expressed by the curves, is related directly to the number of spawners and to the egg to fry survival under ideal flow conditions. The upper and lower bounds express the v a r i a b i l i t y of the egg to fry survival under ideal flow conditions. Because crowding causes mortality the relationships deviate from a straight line when the number of spawners exceeds the estimated spawning capacity (Figure 26 ). Inputs 3 and 4 Additional Mortality vs. Extreme Flows In Chapter VI relationships were established between extreme flows and additional mortality. The probability of occurrence of a level of additional mortality i s , therefore, the probability of occurrence of the extreme flow. In order to incorporate the probability of flow induced mortality directly in the matrix multiplication^the probabilities of various levels of additional mortality had to be expressed in matrix form. The Appendix describes the method of construction of these matrices and presents an example multiplication. Input 5 Fry to Adult Survival The estimates for fry to adult survival for the Fraser population (Palmer, 1972) are used as the estimates for the fry to adult survival of the lower Vedder run. Since the impact of increased output from the spawning areas of the lower Vedder considered in this chapter w i l l be negligible on the total Fraser population's survival the adult versus fry relationship is a straight line. The upper and lower bounds express both the annual variability and r e l i a b i l i t y of the estimates. 142. C. EXAMPLE CALCULATIONS To demonstrate the method, the spawning area alternatives for chum salmon described in Chapter V are evaluated. These examples include the present channel, a wide channel, and a side channel-development. The estimates used in the calculation are based on information discussed in previous chapters, however, u n t i l biologists have reviewed the estimates the results are somewhat speculative. Rehabilitation schemes increase the spawning area capacity and reduce the mortality caused by extreme flows. Table XX shows that these changes could increase the chum salmon production six to nine times. The calculated probability distribution describes the uncertainty of production from a spawning area assuming that fisheries management was able to consistently allow the desired escapement. Regulation of the fishery i s far- from achieving optimum escapement in any one year and would make the:, spread of the actual probability distribution greater than calculated, but would make l i t t l e change to.the expected value. Figure 28 shows the number of adult chum produced versus the probability that the number w i l l be within a given range in any one year. An important consideration of fisheries management is the risk of a low level of production. Occasional low production could result in c u r t a i l -ment of the fishery to build back stocks. Table XXI shows that the wide river alternative has a lower probability of producing less than 8000 adults than has either side channel development. This can be explained by examining the magnitude of the flood or low flow that causes severe mortality. A wide channel provides a variety of spawning environments. It would take an extremely large flood or extremely low flow to affect seriously a l l the locations where spawning had taken place. TABLE XX EXAMPLE CALCULATIONS OF ADULT CHUM SALMON PRODUCTION FROM ALTERNATIVE SPAWNING AREAS ALTERNATIVE (B.C. Hydro Bridge to Ford Road) Spawning Area Capacity UB (no of chum MP spawners) LB No. of Eggs per Spawner Egg to Fry Survival (Ideal Flow) UB MP (%) LB Additional Mortality vs. Flow Curves Fry to Adult Survival UB MP (%) LB No. of Adults UB MP LB Expected No. of Adult Chum Present Channel 10,000 4,500 3,000 1,500 25 19 13 -Low Flows Fig. intermediate -Flood Flows Fig. narrow 3.44 2.12 0.59 32,000 5,000 800 12,500 Wide Channel 30,000 22,000 16,000 1,500 25 19 13 -Low Flows Fig. intermediate -Flood Flows Fig. wide 3.44 2.12 0.59 150,000 80,000 20,000 82,000 Side Channel Development (without annual gravel cleaning) 25,000 20,000 17,000 1,500 25 19 13 -Low Flows Fig. -Flood Flows Fig. 3.44 2.12 0.59 184,000 104,000 15,000 98,000 Side Channel Development (with annual gravel cleaning) 25,000 20,000 17,000 1,500 35 25 20 -Low Flows Fig. -Flood Flows Fig. 3 = 44 2.12 0.59 213,000 136,000 19,000 118,000 ESTIMATES UB - Upper bound MP - Most probable LB - Lower bound FIGURE 28. ADULT CHUM SALMON PRODUCTION VS. PROBABILITY TABLE XXI COMPARISON OF THE RISK OF A LOW LEVEL OF PRODUCTION ALTERNATIVE (B.C. Hydro bridge to Ford Road) PROBABILITY OF THE NUMBER OF ADULTS PRODUCED BEING BETWEEN 0 AND 8000 (in any one year) PRESENT CHANNEL 0.426 WIDE CHANNEL 0.006 SIDE CHANNEL DEVELOPMENT (without gravel cleaning) 0.027 SIDE CHANNEL DEVELOPMENT (with gravel cleaning) 0.020 146. Failure of the water supply intake for the side channel is responsible for the second lower peak in Figure 28. Even though the side channel development should produce on the average more fish than a wide channel, the side channel i s subject to more frequent low levels of production when the intake design limits are exceeded. Increasing the egg to fry survival by gravel cleaning only slightly decreases the probability of low levels of production, however, i t does increase the average production of adults substantially (Figure 29). This calculation suggests that i f the risk of low production i s s t i l l not acceptable a more dependable water supply intake for the side channel i s warranted. D. ESTIMATION OF CATCH For an isolated salmon run harvested by a single specific fishery, f a i r l y precise regulation of the catch would be possible. The average catch would be near the optimum catch, equal to the expected number of adults minus the desired escapement. For a salmon run harvested with other runs by a mixed stock fishery the exploitation rate w i l l not be optimal. Larkin (1972) described the management of a mixed stock fishery. "Present practice is in large part a haphazard conglomeration of biological considerations, his t o r i c a l precedents, and p o l i t i c a l compromises, and i t almost certainly does not coincide with either maximum biological or economic yield in any s t r i c t sense." The actual exploitation rate of Fraser River chum salmon varied between 13 percent and 69 percent and averaged 55 percent from 1970 to 1975 (Anderson, 1976). The average rate i s likely to increase somewhat as the 147. 240,000 J 160,000 J ADULT CHUM SALMON 80,000 40,000 32,000 24,000 16,000 8,000 0 WITH GRAVEL CLEANING EXPECTED NO. = 118,000 WITHOUT GRAVEL CLEANING EXPECTED NO. = 98,000 0.1 0.2 0.3 PROBABILITY OF NO. OF ADULTS BEING BETWEEN 0-8000, 8000-16000, IN ANY ONE YEAR FIGURE 29. ADULT CHUM SALMON PRODUCTION VS. PROBABILITY FOR EXAMPLES OF SIDE CHANNEL DEVELOPMENT 148. salmonid enhancement program develops stocks capable of withstanding higher exploitation. Table XXII compares both the optimum catch and the catch at 55 percent exploitation for the alternative spawning areas. The wide channel and side channel development alternatives would be exploited at a rate less than the optimal rate. This additional production provides a safety margin to prevent overexploitation. The rehabilitation schemes could increase the chum salmon catch by approximately 40,000 to 65,000 fish annually. In contrast the present channel production appears to be exploited at a rate greater than the optimal rate. Without some rehabilitiation or enhancement efforts, overexploitation could depress the production of the lower Vedder River to a very low level. TABLE XXII ESTIMATION OF CATCH CONTRIBUTED BY ALTERNATIVE SPAWNING AREAS — • ALTERNATIVE DESIRED , EXCAPEMENT EXPECTED NUMBER OF ADULTS OPTIMUM CATCH2 MAXIMUM ALLOWABLE (OPTIMUM) EXPLOITATION RATE % CATCH @ 55% EXPLOITATION PRESENT CHANNEL 6,000 12,500 6,500 52 % 66,900 WIDE CHANNEL 23,000 82,000 59,000 72 % 45,000 SIDE CHANNEL DEVELOPMENT 21,000 98,000 77,000 78 % 54,000 (without gravel cleaning) SIDE CHANNEL DEVELOPMENT 21,000 118,000 97,000 82 % 65,000 (with gravel cleaning) The desired escapement would equal the expected spawning area capacity. This was calculated from a skew normal distribution fitted to estimates for spawning area capacity in Table XX The expected number of adults minus the desired escapement 150. CHAPTER VIII DISCUSSION AND CONCLUSIONS A. A HISTORICAL PERSPECTIVE 1. Instability of the Chilliwack River below Vedder Crossing The Chilliwack River below Vedder Crossing i s flowing across and actively building an a l l u v i a l fan by a natural process of building up the channel bed and periodically breaking out into new channels. The f i r s t record of this behaviour is a part of the traditions of native peoples. The Chilliwack River was at one time located near the present Vedder Channel then suddenly shifted to the Chilliwack Channel. Subsequent channel shifts to the Luckakuck, Atchelifez and back to the Vedder channel demonstrate that the river has been laterally and vertically instable during recent geologic history. Analysis of cross-sections, water level gauge records, and approximation of the sediment transport process by bed load formulas show that the Vedder Channel has been aggrading and that the reach between the two bridges has been aggrading at the greatest rate. Engineers concerned with the draining of Sumas Lake did not recognize the aggradation of the Vedder Channel and in the 1920's failed to i n i t i a t e a channel maintenance program as a part of the Sumas Lake project. The necessary emergency maintenance of the channel was carried out mainly by the Municipality of Chillxwhackwith the aid of the Provincial Government. The extensive efforts to maintain the channel combined with a reasonable amount of good luck have prevented the river from shifting channels. Because of recent population growth and land development a channel shift 151. would now be a major disaster for the Chilliwack and Sumas area. Until the Fraser River Joint Advisory Board builds a safe channel and undertakes a long term maintenance program the river continues to threaten. 2. The Flood Control - Fish Resource Conflict Local residents and their municipal and provincial governments have been fighting the Vedder River's flooding and bank erosion since 1894. There is a tradition of frustrated attempts to raise funds to build a safe channel. The Fisheries agencies have been attempting to protect and rehabilitate the habitat of Vedder River salmon and trout since about 1960. The attempts have been frustrated by a lack of funds and delayed because of the uncertainty of what flood control schemes would be bu i l t . It i s expected that a period of confrontation would exist between narrow interest groups with seemingly conflicting objectives, each lacking the funds to solve their problems. It is fortunate that two recent (1977) p o l i t i c a l announcements have been made. The Fraser River Joint Advisory Board's stated intention to build a long term Vedder River flood control scheme and the Federal Government's committment to enhance British Columbia's salmonids provide an unprecedented opportunity for the agencies concerned to coordinate their objectives for the Vedder River. B. THE WIDE DYKE ALTERNATIVES The wide dyke alternatives appear to be the best flood control schemes. In review, these are: - : 1) .construction of set-back dykes (unarmoured) to contain overbank flow and maintenance of the present armoured channel 152. 2) construction of primary (armoured) wide dykes, removal of some of the existing channel protection and allowing the river to flow in a much wider channel. (An economical way to achieve this might be to build only a new south dyke, to remove the existing south dyke, and to reuse the riprap. The existing north dyke would probably need some upgrading.) The assumed objectives of groups concerned with the Vedder problem are: The Flood Control Agencies 1) want to build dykes so that the channel capacity provides an adequate level of protection 2) want to plan a convenient long term scheme for the removal of sediment The Local Land Cwners 1) want flood protection for their property 2) want fishery enhancement and flood control schemes to take up as l i t t l e land as possible The Fisheries Agencies and 1) want to rehabilitate natural spawning Citizens Groups and rearing areas 2) want to have sediment removed from exposed bars or occasionally from the riverbed at non c r i t i c a l periods 3) want to obtain land for enhancement schemes preferably with flood protection and a dependable water supply (a possible objective). 153. The wide dyke a l t e r n a t i v e s do provide a high f a c t o r of safety against fl o o d i n g regardless of deposition of sediment and debris during a large flood. Wide dykes are the only flo o d c o n t r o l method that would allow r e h a b i l i t a t i o n of former natural spawning areas. These schemes would appear to provide the framework f o r working out s a t i s f a c t o r y solutions to the r i v e r aggradation, f i s h h abitat and land use problems. I t i s stressed that b u i l d i n g of wide dykes i s only the f i r s t step towards r e h a b i l i t a t i o n of the n a t u r a l salmon production. The p r o d u c t i v i t y of the r i v e r w i l l depend on th.e development work c a r r i e d out and on the planned sediment removal program. C. THE METHOD OF EVALUATION The production of pink and chum salmon from a r e h a b i l i t a t e d side channel or from a recreated " n a t u r a l " r i v e r cannot be expected to r e g u l a r l y produce a design number of f r y . Because of v a r i a b l e flow and other factors the schemes can be expected to occasionally produce a small number of f r y and occasionally, a large number of f r y . Most t r a d i t i o n a l engineering engineering analysis assumes that a successful project should have a constant l e v e l of production. Expensive works are constructed to reduce the r i s k of production f a i l u r e . The t r a d i t i o n a l type of analysis i s of l i m i t e d use for evaluation of r e h a b i l i t a t i o n schemes which have a hi g h l y v a r i a b l e l e v e l of production. This thesis demonstrates a p r o b a b i l i t y method to c a l c u l a t e the production of pink and chum salmon i n spawning areas subject to v a r i a b l e discharge. I 154. The chief advantages of this type of approach are: 1) The estimate of production i s divided into several parts which can be evaluated separately by experts. 2) Uncertainty of natural variability and of error in estimation is shown by the probability distribution of the results. This is useful in comparing the risk of low levels of production of different schemes. 3) Highly sensitive parameters which warrant investigation in more detail can be identified. For example, the expected egg to fry survival in a side channel increased significantly when partial flow control was provided. A disadvantage of this approach is the d i f f i c u l t y of establishing the mortality versus flow relationships when no directly applicable data are likely to be available. This method, therefore, i s only as good as the quality of information used. Although some of the input can be based on physical data the experience and judgement of experts is necessarily the backbone of the method. D. THE VALUE OF RESTORING SALMON HABITAT The results of the example calculations are speculative but indicate that substantial economic benefits can be realized from rehabilitation of spawning areas. Rehabilitated chum spawning areas between the BC Hydro bridge and Ford Road could produce an average of 80,000 to 120,000 adults annually, depending on the extent of rehabilitation efforts. This production would increase the average Fraser River chum catch by at least 40,000 to 65,000 fish. If these fish are currently valued at 15 dollars per fish 155. (gross value at wholesale, 1975) there i s a potential benefit to the province in the order of one half to one million dollars annually. Increased production of pinks, coho and steelhead would provide additional fish for the commercial and sport fisheries. The benefits of rehabilitation cannot be described adequately in terms of money. Management and enhancement of the Fraser River pink and chum fisheries is a complex task challenged by uncertainty. The success of this task depends on building and maintaining both natural and a r t i f i c i a l stocks, a possibility only i f natural salmon habitat is restored. 156. BIBLIOGRAPHY Allen, B., "Early Marine Life History of Big Qualicum River Chum Salmon", Proceedings of the 19 74 Northeast Pacific Pink and Chum Salmon  Workshop, D. R. Harding, ed., Dept. of the Environment, Fisheries, Vancouver, B.C., 1974, pp. 137-148. Anderson, A. D., "The 1975 Return of Chum Salmon Stocks to the Johnson Strait - Fraser River Study Area, and Prospects for 1976", Technical Report No. PAC/T-76-17, Fisheries and Marine Service, Fisheries and Environment Canada, Vancouver, B.C., 1976, 12 p. Armstrong, J., "S u r f i c i a l Geology of the Sumas Map Area", Paper 59-9, Geological Survey of Canada, 1959. 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Palmer, R....N., "Fraser River Chum Salmon", Technical Report 1972-1, Pacific Region, Fisheries and Marine Service, Fisheries and Environment Canada, Vancouver, B.C., 1972, 284 p. Parker, R. R., "A Concept of the Dynamics of Pink Salmon Populations", Symposium on Pink Salmon, N. J. Wilimovsky, ed., H. R. MacMillan Lectures in.Fisheries, University of B.C., Vancouver, B.C., 1962, pp. 203-211. Parker, R. R., "Marine Mortality Schedules of Pink Salmon of the Bella Coola River, Central B.C.", Journal of the Fisheries Research Board of  Canada, Vol. 25, No. 4, 1968, pp. 757-794. Parker, R. R., "Size Selective Predation Among Juvenile Salmonid Fishes in a British Columbia Inlet", Journal of the Fisheries Research Board of  Canada, Vol. 28, No. 10, 1971, pp. 1503-1510. Ramsey, B., Five Corners - the Story of Chilliwack, Agency Press Ltd, Vancouver, B.C., 1975, 91 p. Raudsepp, V., "Flooding in the Lower Mainland in November, 1954: The Vedder River Problem", B.C. Water Resources Service, Victoria, B.C., 1955. Resource Development Branch, "Proposed Chum Salmon Development Project for the Vedder River", unpublished, Fisheries and Marine Service, Fisheries and Environment Canada, Vancouver, B.C., 1968, 22 p. 160. Resource Development Branch, "Vedder-Chilliwack River Chum Salmon Re h a b i l i t a t i o n Proposal", unpublished, F i s h e r i e s and Marine Service, F i s h e r i e s and Environment Canada, Vancouver, B.C., 1969, 16 p. Rice. L. M., "Report on Reclamation Work for the Sumas Dyking D i s t r i c t , B.C.", 1913, B.C. Water Resources Service Library, V i c t o r i a , B.C. Schuyler, J . D., "Report on the Proposed Reclamation Works of the Sumas Development Co. Ltd. f o r the Drainage of Sumas Lake and the Overflowed Lands Surrounding", 1908, B.C. Water Resources Service L i b r a r y , V i c t o r i a , B.C. Schuyler, J . D., "Review of the Various Reports on the Sumas Reclamation Project", 1909, B.C. Water Resources Service Library, V i c t o r i a , B.C. Scott, P. and Schouwenburg, W., "Environmental Foresight and Salmon: New Canadian Developments", P a c i f i c Salmon, Management for People, D. V. E l l i s , ed., Western Geographical Series, Vol. 13, Un i v e r s i t y of V i c t o r i a , V i c t o r i a , B.C., 1977. Sediment Survey Section, "Bed Load Study, Vedder River, B.C.", 19 73 Progress Report, Canada Department of the Environment, Ottawa, Ontario, 1974. Sheehan, S. W., "Decision Theory as a Tool i n Sockeye Salmon Management of the Babine System", thesis presented to the University of B.C. at Vancouver, B.C., i n 1976, i n p a r t i a l f u l f i l l m e n t of the requirements f o r the degree of Master of Applied Science. S i n c l a i r , F. N., A History of the Sumas Drainage, . Dyking, and Development  D i s t r i c t , Chilliwack H i s t o r i c a l Society, Chilliwack, B.C., 1961, 20 p. Stuart, T. A., "The Influence of Drainage Works, Levees, Dykes, Dredging, etc. on the Aquatic Environment and Stocks", 7th Technical Meeting, International Union for Conservation of Nature and Natural Resources, Vol. IV, 1960, pp. 337-345. Tempest, W., "Memorandum - Vedder River", F i l e No. 0281550-B17A, Water Investigations Branch, B.C. Water Resources Service, V i c t o r i a , B.C. 1976. Vaux, W. G., "Intragravel Flow and Interchange of Water i n a Streambed", Fishery B u l l e t i n , Vol. 66, No. 3, 1968. Vernon, E. H., "Pink Salmon Populations of the Fraser River System", Symposium on Pink Salmon, N. J . Wilimovsky, ed., H. R. MacMillan Lectures i n F i s h e r i e s , U n i v e r s i t y of B.C., Vancouver, B.C., 1962, pp. 53-58. Walker, C. E., et a l . , "Catalogue of Salmon Spawning Streams and Escapement Populations - Chilliwack S u b - D i s t r i c t " , F i s h e r i e s and Marine Service, F i s h e r i e s and Environment Canada, Vancouver, B.C., 1972. 161. Walters, C. J., "Management Under Uncertainty", Pacific Salmon, Management;: for People, D. V. E l l i s , ed., Western Geographical Series, Vol. 13, University of Victoria, Victoria, B.C., 1977, pp. 261-298. Water Survey of Canada, "Sediment Data - Canadian Rivers", Canada Department of the Environment. Water Survey of Canada, "Surface Water Data", Canada Department of the Environment. Wells, 0. N., A Vocabulary of Native Words in the Halkomelem Language, Copyright by 0. N. Wells, 6937 Vedder Road, Sardis, B.C., 1965, 47 p. Wells, 0. N., Indian Territory 1858, Copyright by 0. N. Wells, 6937 Vedder Road, Sardis, B.C., 1966, 3 p. Wester, J., "Memorandum - Vedder River", File No. 0281550-B17A, Water Investigations Branch, B.C. Water Resources Service, Victoria, B.C., 1976. White, G. B., "A History of the Eastern Fraser Valley Since 1885", thesis presented to the University of B.C., at Vancouver, B.C., in 1937, in partial fulfillment of the requirements for the degree of Masters of Arts. Wickett, W. P.,. "Review, of Certain. Environmental Factors Affecting, the Production of Pink and Chum Salmon", Journal of the Fisheries Research  Board of Canada; Vol. 15, No. 5, 1958, pp. 1103-1126. Wickett, W. P., "Damage to the Qualicum River Streambed by a Flood in January 1958," Progress Reports of the Pacific Coast Stations, Fisheries Research Board of Canada, No. 113, 1959, pp. 16-17. Willington, R. P., "Effects of Logging on Some Hydrologic Aspects of the Seymour River Watershed", A Problem Study for Forestry 482, Faculty of Forestry, University of B.C., Vancouver, 1967. 162. PERSONAL COMMUNICATIONS Andrew, F., Engineer, International Pacific Salmon Fisheries Commission, New Westminster, B.C., 1976. Bailey, D., Biologist, Fisheries and Marine Service, Vancouver, B.C., 1977. Bailey, M., Biologist, Fisheries and Marine Service, Vancouver, B.C., 1977. Klein, P.D., Owner of land adjacent to Vedder River, 1976. Marshall, D., Biologist, Fisheries and Marine Service, Vancouver, B.C., 1976. Meyer, P. A., Economist, Fisheries and Marine Service, Vancouver, B.C., 1976. Milton, H. R., Municipal Engineer, Corporation of the Township of Chilliwhack, Chilliwack, B.C., 1977. Nielspn, G. , Engineer, Fisheries and Marine Service, Vancouver, B.C., 1977. Princic, R., Economist, Inland Waters Directorate, Vancouver, B.C., 1977. Tesky, D., Fisheries Officer, Fisheries and Marine Service, Chilliwack, B.C., 1976. Wells, C , Long-time resident of Sardis, B.C. and member of the Chilliwack Historical Society, Chilliwack, B.C., 1976. Wilson, G.A.C, Biologist, Fisheries and Marine Service, Vancouver, B.C., 19 76. Woodey, J. C , Biologist, International Pacific Salmon Fisheries Commission, New Westminster, B.C., 1977. 163. APPENDIX The 5 x 5 matrix in Figure 1A i s ah example of the type of matrix used to incorporate the probability of flow induced mortality directly in the matrix multiplication. The numbers that make up the matrix are the probabilities that fry production w i l l be within a range after flood induced mortality i f the fry production is in the same or higher range before flood induced mortality. For example, i f the estimated fry pro-duction i s between 1.6 to 2.0 million fry before flood induced mortality then there is a .307 probability that the fry production w i l l be between 1.6 and 2.0 million fry after flood induced mortality, a .084 probability between 1.2 and 1.6 million, a .114 probability between .8 and 1.2 million, etc. The probability of being in a "box" of the matrix is the probability of the mortality of the "box" being within an upper and lower limit. For box ".307" the average number of fry before mortality is 1.8 x 10 . For this average number to f a l l below 1.6 x 10 and out of the box a mortality ft ft rate of 1.8x10 - 1 . 6 x 1 0 x 100% = 11.1% is needed. Thus the probability 1.8 x 106 of being in the box is the probability of the mortality being greater than or equal to zero and less than 11.1 percent. For box ".084", 1.8 x 1Q6 - 1.2 x 1Q6 x 100% = 33.3% mortality is 1.8 x 106 needed for the average number to f a l l below 1.2 x 10 . Thus the pro-bability of being in box ".084" is the probability of the mortality being greater than or equal to 11.1 percent and less than 33.3 percent. The 164. FRY PRODUCTION AFTER FLOOD INDUCED MORTALITY (x 106) 2.0 1.6 1.2 FRY PRODUCTION BEFORE FLOOD INDUCED MORTALITY <* i o 6 ) 0 100 550 350 2 .0 Ii. 6 1. 2 . 8 .L \ 0 2.0 2.0 1.6 . 30.7 0 0 0 0 1.6 .031 1.2 .084 .319 0 0 0 1.2 . 184 . 8 . 114 .109 .341 0 0 .8 . 191 .4 .226 .226 .205 .392 0 .4 .218 0 .269 .346 .454 .608 1.0 0 .376 FRY PRODUCTION UNDER CONDITIONS OF IDEAL FLOW (x 106) FRY PRODUCTION AFTER FLOOD INDUCED MORTALITY (x 106) FIGURE 1A MULTIPLICATION OF A 5 x 1 FRY PRODUCTION MATRIX BY A 5 x 5 FLOOD INDUCED MORTALITY MATRIX1 20 x 1 and 20 x 20 matrices were used in the computer calculation 165. probabilities are obtained from a plot of cumulative probability vs. additional mortality (Figure 2A). Figure 1A shows an example multiplication of a 5 x 1 fry matrix by a 5 x 5 flood induced mortality matrix. To find the probability of the number of fry being in a specified range after flood induced mortality multiply each probability of the fry matrix by the corresponding conditional probability and then add the products. For example, the probability of the number of fry being between 1.6 x 10^ and 2.0 x 10^ after flood induced mortality i s , (0.100 x .307) + (.550 x 0) + (.350 x 0) + (0.x 0) + (0 x 0) = .031 Similarly, the probability of the number of fry being between 1.2 x 10 and 1.6 x 10 i s , (.100 x .084) + (.550 x .319) + (.350 x 0) + (0 x 0) + (0 x 0) = .184 CUMULATIVE PROBABILITY (PROBABILITY OF MORTALITY BEING LESS THAN GIVEN VALUE) 1.0 .9 .7 .6 .5 .4 .3 .2 p - probability m - mortality FROM ESTIMATED ADDITIONAL MORTALITY VS. FLOW CURVE FOR PRESENT CHANNEL (Fig. 24 ) p ( l l . l % - m <33.3%) = .084 p(0 ^ m <11.1%) = .307 50 ADDITIONAL MORTALITY DUE TO FLOODS (PERCENT) 100 FIGURE 2A CUMULATIVE PROBABILITY VS. ADDITIONAL MORTALITY DUE TO FLOODS 


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