THREE-DIMENSIONAL HYDRODYNAMIC AND TOTAL DISSOLVED GAS SIMULATIONS OF ROCK ISLAND DAM SPILLWAY

摘要

Juvenile salmon have a difficult time passing dams in the Columbia River basin on their way to the ocean. Voluntary spill at the dams has improved non-turbine passage rates, but spillway operations cause increased levels of total dissolved gases (TDG) downstream. Plunging flow from the spillway carries entrained air deep into the stilling basin, where the bubbles experience a dramatic rise in hydrostatic pressure, and thus the gas contained within the bubbles is dissolved into the surrounding water. At Rock Island Dam, Public Utility District No. 1 of Chelan County (CCPUD) is implementing measures to achieve 95-percent survival for downstream migrating salmonids. A prototype spillway flow deflector was installed at the dam in late September 2000. Field tests evaluated its performance with respect to TDG reduction. The research contained herein describes a fully three-dimensional hydrodynamic simulation of the flow domain using U~2RANS, a CFD code that solves the three dimensional Navier-Stokes equations using the finite-volume method. A three-dimensional TDG production and transport model developed at IIHR - Hydroscience & Engineering was linked with the hydrodynamic solution and used to predict TDG levels downstream of the Rock Island Dam. The simulations were performed with and without spillway deflectors to demonstrate the potential improvement of TDG levels after the installation of spillway deflectors. The TDG parameters were then calibrated against the field data providing validation of the model.