Concurrent Sessions D: Downstream Migrant Surface Collectors-What Works and What Doesn\u27t Work - Evaluation of the Hydraulic Performance of a Free Surface Fish Bypass

In 2004, following consultations with the Federal Energy Regulatory Commission (FERC), the National Marine Fisheries Service (NOAA Fisheries) issued a document that included a Biological Opinion relevant to Priest Rapids Dam. A subsequent Biological Opinion, issued by NOAA Fisheries in 2008, was incorporated with the new FERC license. The 2008 Biological Opinion contained the same requirements as the 2004 Biological Opinion with respect to the survival objectives for downstream migrating juvenile fish. These objectives are 93% survival of juveniles and a juvenile and adult combined survival of 91% for the species listed for protection. Grant PUD is seeking to achieve at least 95% juvenile survival past the Priest Rapids Dam. In the past, Grant PUD spilled roughly 61% of the total river flow at Priest Rapids Dam during the spring fish passage season with the aim of achieving the survival target. A study was undertaken to identify a number of different fish passage alternatives for Priest Rapids Dam including: screening systems, collecting and bypassing fish through surface-oriented openings, and/or through modified turbine passages. The study suggested several options that had the potential to provide high fish passage efficiency and survival in a more efficient manner than high-volume spill programs. Further work concentrated on fish bypass through surface releases with prototype tests being conducted to assess the efficiency of fish collection as a function of bypass flow. Physical and numerical modeling were also undertaken to support the design of surface bypass alternatives. The final bypass design consisted in a modified spillway with elevated ogee crest in bays 20, 21 and 22.This paper presents results of the reduced scaled laboratory and CFD models developed to evaluate different bypass conceptual designs. Two numerical models were used; the commercial code Fluent and the open source code Open Foam. Details of model development and validation with data obtained in the reduced scale laboratory model will be presented. Possible cavitation, loads and impact on the tailrace with the selected bypass were computed and will be discussed