This contract involved the construction of a state-of-the-art fish screening facility to minimize the impact of irrigation water diversions on the endangered winter-run Chinook salmon.  The Owner is Reclamation District No. 108, one of the largest agricultural water providers on the Sacramento River.  The screen facility is located at the District’s Wilkins Slough pumping plant about 45 miles northwest of Sacramento.  The project was the result of a cooperative effort between the District, the U. S. Bureau of Reclamation, U. S. Fish and Wildlife Service, National Marine Fisheries and the California Department of Fish and Game.

The fish screen is one of the largest screening facilities in the Sacramento basin.  It consists of a 250ft long by 45ft tall reinforced concrete structure spanning the entrance to the District’s pumping plant forebay.  The structure supports fourteen stainless steel screen panels each 16ft wide by 12ft tall with precise 3/32” openings between the screen wires which permit waterflow to the irrigation pumps, but obstruct passage of juvenile fish.  Total screen area is over 2,500 square feet accommodating irrigation flows up to 830 cubic feet per second.  Adjustable flow distribution louvers behind the screen panels control hydraulic uniformity through the screens.  The facility is also equipped with a continuous-travel brush mechanism which sweeps the entire screen surface once every five minutes cleaning off water-born debris.  Approximately 2,000 linear feet of temporary and permanent sheet pile was driven for the screen structure temporary cofferdam and has permanent retaining walls for the approach ramps to either side of the facility.  The screen and approach ramps are supported on 225 steel H-piles.

It was critical that construction of the fish screen facility be accomplished without interrupting irrigation water deliveries or interfering with fish migrations in the Sacramento River.  These challenges were successfully met despite the torrential rains and river level increases of up to 20ft encountered during “El Nino” storms of the winter of 1997-98.  Shimmick Construction was also responsible for the generation and implementation of a “value engineering” proposal that eliminated the need for a 5ft thick tremie concrete slab beneath the screen structure resulting in a savings of both time and money to the Owner.