Passage Improvements at the Glenn-Colusa Irrigation Diversion
Fish Passage Policy and Technology: Proceedings of a Symposium
American Fisheries Society
The Glenn-Colusa Irrigation District (GCID) diverts up to 3,000 cubic feet per second (cfs) from the Sacramento River near Hamilton City, California. A new fish screen at the canal intake was constructed in 1972. About the same time, changes to the channel of the river resulted in the river degrading more than 3 feet near the intake to the pumping plant. The reduced water depth on the face of the screen structure causes through screen velocities to increase dramatically. At the present design pumping flow of 2,800 cfs, the velocity component perpendicular to the screens has doubled the current criteria of 0.33 feet per second (fps). This and other problems on the existing screens result in the impingement and entrainment of winter-run chinook smolts, which are a listed endangered specie. A range of solutions were considered by GCID and the resource agencies including building a gradient restoration project, changing pumping amounts and schedules, to a new state-of-the-art screen. Design criteria for the screen were established and alternatives consisting of vertical V-screens, inclined modular screens, and/or drum screens at the existing and other locations, were analyzed. The bypass system was a critical consideration that represented a substantial part of the cost, and yet, was based on the most uncertain data. Each alternative was evaluated for its ability to meet the fishery criteria, hydraulic, predator, sediment and debris conditions, and cost.