Cowlitz Falls North Shore Collector
Tacoma Public Utilities (Tacoma Power) required engineering support for the design of a downstream fish passage facility mandated by their new Federal Energy Regulatory Commission (FERC) license.
Kleinschmidt was contracted by Tacoma Power to develop conceptual and final designs to improve downstream fish passage and to provide services during construction. The conceptual design process included the identification, study, design, and evaluation of numerous alternatives with the purpose of achieving fish survival goals. The recommended alternative was a 500 cfs (readily expandable to 750 cfs) surface collector located on the north bank of the dam and forebay in combination with improvements to the existing collection facility. Much of the facility is retrofit into the existing dam. Kleinschmidt’s primary responsibilities included the design of structural and mechanical features of the collector. Structural features included the concrete basin and steel framing of a 170 ft long channel, the overhead steel structure supporting a fish flume and walkway, and a pump back diffuser structure (for return flow into the forebay). Mechanical features include the intake, trashrack and trashrack cleaner, dewatering screens (fixed and traveling screens), screen and sump baffles, pump back pumps (4 at 130 cfs each), pump back discharge piping and diffusers, emergency breakaway floor panel, vacuum pump station, fish flume, and tailrace release gate (1,000 cfs capacity). Kleinschmidt also provided the 100% design cost estimate for this project, construction services, and assistance during the commissioning and screen balancing.
Kleinschmidt seamlessly took on additional structural components of the work and kept the FERC-mandated schedule on track when Tacoma Power’s resources were reduced. During the conceptual design phase, Kleinschmidt helped guide the decision to place the facility on the downstream side of the dam rather than within the forebay which would have required a very costly cofferdam. The new collector has proven effective at increasing collection for all species and more than doubling efficiency for spring Chinook over the original collector.