Water Entrainment and Mixing Due to Spillway Discharges

Development and Implementation of an Optimization Model for Hydropower and Total Dissolved Gas in the Mid-Columbia River System

“…As the high-energy surface jets from the spillway enter the tailrace, they draw water laterally into the jet region from the powerhouse release region through a phenomenon called water entrainment. High-fidelity numerical models that accurately predict water entrainment show that powerhouse flows accelerate toward the spillway region as the spillway jets decelerate, and the presence of bubbles suppresses jet turbulence, which leads to a slower decay in jet strength and thus stronger water entrainment for bubbly flows (Turan et al 2006;Politano et al 2009). For model simplicity, the dependence of water entrainment on the energy of spillway flows is taken as a linear relationship bounded by the total powerhouse flow, as proposed by Schneider and Hamilton (2009).…”

“…State and tribal mixing-zone provisions allow an area of maximum TDG immediately downstream of the structure to be excluded from WQ compliance (Pickett et al 2004), because fish move quickly through this region with no adverse effects. The presence of dynamic processes that persist a considerable distance downstream, including lateral TDG exchange and flow entrainment in the stilling basin, complex spill bay flow patterns, recirculation, intense mixing, and degassing (Turan et al 2006;Schneider 2012) introduce notable challenges in setting a location that obtains accurate and consistent measurements that reflect a true crosssectional average. Therefore, the downstream FMS may be located from 0.5 to 14.5 km downstream of the dam.…”