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Numeric modeling for the Proposed Nimbus Hatchery Weir Replacement Project

by Jim Higgs

and Kathy Frizell

This is an on going project. As such, information presented here is primarily for communications with clients, it is a work in progress, and it is not complete or peer reviewed.

Objective: To investigate the hydraulic impacts on the proposed Nimbus Hatchery fishway and embankments after the removal of the Nimbus Hatchery Weir.

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.

Layout of proposed fishway and weir to be removed.


    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.


Mailing Address
Jim Higgs
Bureau of Reclamation
Mail Code 86-68460
PO Box 25007
Denver, CO 80225-0007

Phone/Fax Numbers
Phone: 303-445-2147
Fax: 720-544-6324

Package Delivery Address

Bureau of Reclamation
Bldg. 67, Rm. 152, 86-68460
Denver Federal Center
6th Avenue and Kipling St.
Denver, CO 80225-0007


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Last reviewed: 11/2/2008