Hydraulic Engineer Bureau of Reclamation, Colorado, United States
Abstract Submission: Federally owned high head dams are being modified to provide fish passage which present several technical challenges. Starting at the upstream side, first the fish must enter the structure. High head dams typically have a wide range of lake operating levels which require an intake structure that functions across a range of water surface elevations to allow favorable entrance conditions. Once in the structure the flow will accelerate as it drops in elevation, then at the downstream end the flow much be slowed down before discharging into the downstream body of water. During the downstream fish passage design process for a facility, two unique hydraulics issues required design modifications to resolve. The first, jet detachment from an ogee spillway for gated flow regimes was addressed by incorporating trajectory curves into the vertical profile of the spillway. Second, reattachment of a free jet after an air gap was addressed by investigating the combined effects of deflectors coupled with inserts to better inform the effects of impact angle on the flow field. To support the design, both numerical (computational fluid dynamics or CFD) and a 1:10 Froude scaled physical hydraulic model were used to iteratively refine the design.
