Path Selection by Outmigrating Juvenile Chinook Salmon, Ramifications for Constructing and Operating Diversions
* Do river hydraulics play an important role in entrainment of fish?
Water diversion and conveyance structures are an integral part of Reclamation's operations. Developing techniques to minimize entrainment of fish has been an ongoing process. Louvers, screens, etc. have all found utility in reducing the take of many different species. Most structure designs deal with removing the fish at the structure--little consideration has been given to whether the structures or diversions have been put in places that may predispose them to entraining more or fewer fish. In designing and operating
Need and Benefit
Reclamation operates many diversions and intake structures. In recent years, many structures--if they were not built with them--have been retrofitted with devices to minimize the take of aquatic organisms. Often when these structures are designed, fish are dealt with at the point they contact the structure and are deflected via louvers, or fish may be captured and transported elsewhere.
There are relatively little data that has been collected on fish behavior that allows us to determine whether simply changing the location of, or operation of a diversion may actually minimize the number of fish entrained. For many years, the Delta Cross Channel (DCC) has been used as the primary way to move water from the Sacramento River into the central and southern delta. Numerous studies have indicated that outmigrating salmon smolts can be entrained in the cross channel and moved into other areas of the Delta. While ultimately these fish can reach the ocean, predation rates via this pathway are many times higher than if fish simply pass down the Sacramento River. A through Delta facility, which had been in the planning stages for years, aims to route water from the Sacramento River, around much of the Delta and straight to the State and Federal pumpng plants.
Previous work done by a cooperative group consisting of Reclamation, U.S. Fish and Widlife Service (FWS), U.S. Geological Survey (USGS) and the California Department of Game and Fish, suggest the location of the DCC with respect to the Sacramento River may actually increase the entrainment of fish into this facility. Several operational changes have been suggested that might minimize these impacts, but more data are still needed to help develop models of smolt hydraulic preferences in river bends and at junctions.
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