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UBC Theses and Dissertations

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 Peters, Neil Jacob


Major flood control works for the Vedder River, presently in the planning stage, will 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 alluvial fan by a natural process of building up the channel bed and periodically breaking out into new channels. A long term flood control project will 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 instability and has increased the detrimental effects of floods. To 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 likely increase the commercial chum catch by 40,000 to 65,000 fish. A policy of both rehabilitating natural spawning areas and constructing enhancement facilities appears to be necessary to increase and stabilize the pink and chum salmon production from the Vedder-Chilliwack River.

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