Intake-induced Flow Field And Release Water Temperature Of Baihetan Dam, China

Flow field induced by hydropower intakes has significant influence on release water temperature and entrainment risk of fish in the reservoir forebay. Baihetan(BHT) hydropower station is located on lower reaches of Jinsha River in China. In the inertial design,9powerhouse intakes have been designing on the left bank as well as the right bank, and3tunnel spillways on the left bank side. The complex flow patterns upstream of intakes on BHT left bank related to the operations of intakes and spillway tunnels are investigated in the present study to enhance the understanding of hydrodynamic characteristics and to outline potential risk zones for fish entrainment. The second objective of this study is to predict the release water temperature, given the thermal stratified profile of the Baihetan (BHT) reservoir. Implications of the study of forebay hydraulics on risk assessment of fish entrainment are discussed first, and the results of three-dimensional (3D) Computational Fluid Dynamics (CFD) modeling under the thermal stratified scenarios then can be used to assist in making decisions regarding ecological and environmental management and operation optimization.Potential flow method, physical model experiments and three-dimensional computational fluid dynamics model (using ANSYS CFX) are employed to study the hydraulic performances upstream of left intakes under a number of operating scenarios. The Reynolds-averaged Navier-Stokes equations were solved in the numerical code and with k-s closure equations. For the verification and validation of this3D CFD model, experimental measurements were conducted using a physical model with a scale1:50in Nanjing Hydraulics Research Institute and the laboratory velocity measurements showed very good consistency with those in CFD modeling. Flow fields induced by multiple intakes and by a line sink tends to be the same at a distance beyond two times of the distance of the adjacent operating intake. Different operation scenarios were analyzed to improve the general understanding of characteristics of upstream flow and to reduce the risk of fish entrainment. The extent of the risk zone for fish entrainment defined by specified thresholds of velocity and acceleration indicate that smaller water depth over submerged intake means a higher risk of fish entrainment.The temperature of released water, which is a main controlling factor, may directly impact on downstream river eco-system. It should be regulated in order to obtain desirable water quality and reduce the risk of impairing fish. The previous research is briefly introduced herein. Under various stratification, selective withdrawal with9intakes located at each bank and3tunnel spillways are modeled using3D CFD in this investigation. The results of hydraulic characteristics and temperature profiles are presented and discussed for typical operation scenarios. It indicates that the release water temperature is higher under scenarios with a low water level in July or with spillway tunnels operating, and those of the left intakes are higher than the right in general.