Instream flow needs study, Kerckhoff Hydroelectric Project, San Joaquin River, California

An instream flow needs study was conducted on a 12 km section in the foothill region of the San Joaquin River. Most of the flow is diverted for hydroelectric purposes. Four test release flows were maintained for one week each during the summer of 1977. Recording thermographs were used to monitor water temperatures. Weather conditions and water quality parameters were also investigated. A stepwise multiple regression computer program was used to analyze the flow, temperature, and weather data. A survey was conducted to determine the status of the fishery resource. Each of the test release flows caused the daily maximum water temperature at the downstream stations to drop several degrees. One regression model of maximum water temperature acheived a total explained variance of 89 percent. The ranges of weather variables encountered were not significant in the regression model. Acceptable values of the water quality parameters were maintained under all flow conditions tested. Smallmouth bass were the dominant species in the study area. Maximum water temperature was the most important smallmouth bass habitat parameter altered by flow releases. A constant release flow of 25 cfs is recommended to maintain water temperatures within the preferred range for smallmouth bass.