Construction, operation, and evaluation of groundwater-fed side channels for chum salmon in British Columbia
Fisheries Bioengineering Symposium: American Fisheries Society Symposium 10
Colt J;White RJ;
American Fisheries Society
Since 1978, more than 40 groundwater-fed side channels have been built in British Columbia, totaling over 100,000 m2 of new or improved salmonid spawning and rearing area. The technique involves grading down, deepening, and widening of intermittent or relic side channels on river floodplains to intercept subsurface flow. The constructed channels are rock-armored and protected from floods by dykes or local landforms. The channels are unmanned and depend on volitional entry of spawners and self-regulation of fish density. Methods of site selection, design, and construction are discussed. Data collected from 1978 to 1987 from 24 channels showed an annual production of emergent chum salmon Oncorhynchus keta of over 290 fry/m2 of developed spawning area, and a mean survival to emigration of over 16% of potential egg deposition. Yearling production of coho salmon O. kisutch was as high as 30 g/m2 in one channel in 1 year. Increasing coho salmon populations did not coincide with declining chum salmon production. A conservative benefit/cost ratio calculated for the technique was 1.7. Channels constructed with introduced graded spawning gravel substrates (i.e. 0% fines of 9.5 mm or less in diameter) did not result in greater survival or annual production of chum salmon fry than those constructed with existing gravel substrate (containing up to 15% fines of 1.6 mm and smaller), although construction costs for graded gravel averaged $4.00 (Canadian)/m2 higher. Production and survival of chum salmon remained high for more than 4 years following construction.