Numeric modeling for the Proposed Nimbus Hatchery Weir Replacement Project

Nimbus Fish Hatchery is located on the American River approximately 1/4 mile downstream of the Nimbus Dam, in Fair Oaks, California. The hatchery facilities were built in the 1940's to compensate for spawning areas of salmon that were inundated by construction of the Folsom and Nimbus Dams.

Reclamation has decided to remove the Nimbus Hatchery Weir by providing a new ladder entrance near the base of Nimbus Dam and building a flume with embankment support across the Nimbus shoals, under the Hazel Avenue Bridge, and to the hatchery. The efforts included in this study are part of those tasks necessary to complete the final design concept phase of the overall project.

One major objective of the numerical modeling was to investigate the average velocity that the proposed fishway structure will be subjected to. The conceptual design includes supporting the concrete structures with embankment fill and riprap. It is desirable to have the structure withstand a flood release from the dam with flows that do not exceed the future downstream levee capacity of 160,000 ft³/s.

The 3D study is investigating 3 scenarios for the proposed modifications.
1. 160,000 ft³/s discharge
2. 115,000 ft³/s discharge
3. 66,667 ft³/s discharge
4. Ramping up discharges screening Animation.