Safety Evaluation of the Plunge Pool and the Downstream River of the Baihetan Hydropower Station Using Model Experiments

Abstract: As a part of the hydropower expansion in China, the Baihetan Hydropower Station is now being constructed in the southern parts of the country. This hydropower station will, when completed, become the third largest in the world in terms of installed power output.The construction of a hydropower plant of the Baihetans Hydropower Station’s size is not without problems and high standards of safety are essential as large land areas upstream and downstream of the dam are affected. One of the risks is that the flow of water through the dam can cause scour and erosion downstream of the dam which threatens the stability of both the dam and the riverbed. To evaluate this risk, studies of a model in the scale of 1:100 have been performed at the Department of Hydraulic Engineering at Tsinghua University in Beijing, China.This thesis evaluates whether the discharge through the dam causes a hydrodynamic pressure above the allowed limit in the plunge pool below the dam and which measures that can be made to reduce this pressure. Flow velocity measurements were conducted, both in the plunge pool and along the downstream riverbed, to further evaluate the risk of erosion.The experiments show that the use of nappe splitters in two of the surface spillways will reduce the hydrodynamic pressure in the plunge pool to well below the acceptable limit of 15 m H2O. However, the flow velocity downstream of the plunge pool is too large and protection measures are recommended to avoid riverbed erosion.The results obtained indicate that a shortening of the plunge pool is possible which would lead to a reduced construction cost. However, further studies would be necessary to determine if this increases the risk of erosion in the downstream river.