Decay of Turbulence Downstream of a Stilling Basin

Turbulence must be modeled accurately to simulate river processes, particularly transport of aqueous oxygen and nitrogen. Spillway operations affect downstream turbulence, but there has been little research on turbulence intensities downstream of stilling basins. For this study, laboratory measurements were taken on a three-dimensional, physical model of McNary Dam, Columbia River, United States to determine how the turbulence, initially generated by spillway flow, decreases with distance downstream. The experiments also examined how flow rate, tailwater depth, and the presence of spillway deflectors affect turbulence. A mathematical analysis was used to predict turbulent kinetic energy with distance, and good agreement was found between laboratory measurements and numerical predictions. Turbulence production generated by channel bed roughness was found to be small compared to turbulent energy dissipation, and the effect of flow separation related to bed irregularities on turbulence production was found to be negligible.