A Fish Passage Problem at the Seton Hydroelectric Project in Southwestern British Columbia

The Seton hydroelectric project, completed in 1956, is located near the Village of Lillooet, 300 kilometres north of Vancouver. During July to November each year, two discrete runs of adult sockeye salmon must migrate past the powerhouse tailrace and through a fishway at a low head dam on Seton Creek, to successfully reach their spawning grounds at Gates Creek and Portage Creek. From 1956 to 1969, Cayoosh Creek (the only tributary of Seton Creek) was diverted into Seton Lake to provide additional water for power generation. In 1969, the diversion was discontinued and Cayoosh Creek once again discharged into Seton Creek. In 1972, a decrease in the numbers of salmon reaching the spawning grounds was observed by the International Pacific Salmon Fisheries Commission (IPSFC). Subsequent investigations resulted in a five-year study program to determine the cause of the fish passage problem. This paper describes the study, with emphasis on the hydrological aspects and the operating procedures recommended to control flows in Cayoosh and Seton Creeks, to alleviate the problem.