The GCID Fish Passage Evaluation and Monitoring Program

The most important objective of the GCID fish screen improvement project on the Sacramento River near Hamilton City is to protect fish while concurrently ensuring a reliable water supply to the District. Therefore, state and federal agencies and GCID developed an extensive evaluation program to measure the biological and hydraulic performance of the new facilities. The involved agencies formulated a comprehensive Guidance Manual for the Fish Passage Evaluation and Monitoring Program prior to completion of the fish screen project. This Guidance Manual provides the detailed direction and protocols for evaluating the GCID Fish Screen Improvement Project. Field testing and data collection at the site will be performed under a range of riverine and pumping conditions over three years to establish that the project provides sufficient protection for fish under future, naturally occurring conditions at the site. These tests or experiments are designed to determine if maximal survival of fish and optimal fish passage conditions are achieved as a result of the project. The evaluation program will also determine where problem areas may occur so that site-specific conditions can be improved.

Guidance for the Evaluation Program

The Evaluation Program is performed under the direction, guidance, and review of the Fish Screen Evaluation Committee (Committee). The Committee is composed of representatives from the National Marine Fisheries Service, U.S. Fish and Wildlife Service, U.S. Bureau of Reclamation, U.S. Army Corps of Engineers, California Department of Fish and Game, and GCID. This Committee has the authority to modify the protocols described in the Guidance Manual based on real-time feedback as the field-testing proceeds. When preliminary results from field tests are obtained, the information is reported to the Committee in written report format. The Committee reviews the preliminary results and determines if any changes or modifications to the testing program are required. Final results of the overall evaluation program are ultimately submitted to the Committee for review and approval.


Fish Survival Tests

The largest component of the evaluation program is measuring fish survival as they pass the fish-screening project. This involves an extensive series of experiments using marked juvenile salmon and steelhead. The fish are released near the facility then recaptured at downstream locations to determine the survival rates. Because river and pumping conditions at the site are always changing, the tests are designed to occur over a wide range of river and pumping conditions during a three-year period to “bracket” the types of natural conditions that may occur in the future. Additionally, the fish screen improvement project was constructed with three optional internal fish bypass pipes to route the fish to areas downstream of the screens. Results of the fish-testing program will establish the most favorable conditions for fish (i.e., bypasses opened or closed). These experiments will be extensively replicated to ensure a comprehensive evaluation of the project.

Although overall fish survival is the primary evaluation objective, there are other related factors that could affect the performance of the project. These additional assessments will include:

  • Entrainment through the facility
  • Predation at different locations throughout the project
  • Physical injury on the screens or inside the internal fish bypass system

Each of these possible factors will be studied through a series of experiments and monitoring activities to ensure no adverse impact on fish. If the tests determine that negative effects on fish do occur, corrective actions will be made to reduce or eliminate the impacts.

Biological Performance Of The Gradient Facility

The gradient facility was designed to minimize the project’s effects on the upstream migration of all adult fish and the downstream migration of juvenile fish. It is intended to provide water depths and velocities along potential fish passage routes that do not differ substantially from those in natural riffles in the upper Sacramento River. The gradient facility will also be evaluated over the next three years to discover any potential impacts to fish.

Upstream Migration

To analyze any potential influence of the gradient facility on upstream migration, sturgeon will be captured downstream of the site and fitted with radio transmitters. Then their upstream movement through the area will be monitored with mobile and fixed-station radio receivers. Any changes from normal fish migration behavior, such as delays at the site, will be assessed. As with the tests at the fish screens, the gradient facility will be evaluated over a wide range of river flows.

Downstream Migration

The principal concern of possible adverse impacts to the downstream migration of young fish pertains to possible increases in predation rates. This can be caused by physical habitat alterations in the river channel where the gradient facility was constructed. The objective of the analysis will be to determine whether the gradient facility creates conditions that attract significantly higher concentrations of predators than would otherwise exist under natural channel and hydraulic conditions. Because pikeminnow (formerly called squawfish) and striped bass are known to be predators on juvenile salmon, this portion of the evaluation will focus on those two fish species. In this latter instance, extensive baseline monitoring of predatory fish abundance was performed at the gradient site and other natural sites prior to construction. Now that the gradient facility is complete, monitoring of predatory fish abundance and distribution within the facility and other nearby sites will discover where any changes take place.

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