Analysis of spillway hydrodynamics for total dissolved gas prediction downstream of hydropower projects with free, plunging spillway jets Public Deposited


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  • During spring and early summer hydropower projects are often forced to spill water through their spillways due to increased river flows of the runoff season. Flows which are directed through spillways--instead of through turbines--contain a substantial amount of energy. Stemming from the high energy content, spillway flows entrain air at the point of impingement with the lower reservoir; furthermore, entrained air can be carried deep into the plunge pool. This process results in the transfer of mass from air to the liquid phase, which can ultimately cause supersaturation of Total Dissolved Gas (TDG) downstream of hydropower projects. Under certain conditions, high enough levels of TDG supersaturation can harm fish and other aquatic biota. For this reason, many hydropower facilities are currently studying methods to reduce dissolved gas generation caused by spillway flows. The present research effort utilizes Computational Fluid Dynamics to examine spillway jet characteristics for the prediction of TDG downstream of an arch dam. In seeking to make TDG predictions, flow at the spillway exit is analyzed and correlated to historical TDG data for known conditions at a specific hydropower project. Once this calibration step is complete, TDG predictions can be made by running numerical models of the spillway with potential structural modifications and analyzing hydrodynamic quantities at the spillway exit plane. Based on the results presented herein, the developed methodology appears to be a viable technique for analyzing structural alternatives for TDG abatement at hydropower projects with free, plunging jets. Results from the current work were compared to estimates made by another TDG prediction method, and similar trends were observed. Potential improvements to the developed methodology have been identified and suggested as future topics of research.
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