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Abstract Jinping II hydropower station is situated in a karst area with mountains and valleys. The excavation of large size tunnels will significantly change the conditions for groundwater flow，causing inflow in the tunnels and impacts on surrounding environment. As indicated by the discharge patterns of groundwater in the auxiliary tunnel during its construction，12 fractured zones with high vertical conductivity are existing in the Jinping mountain. Five three-dimensional stead state flow numerical models are built with MODFLOW. In the models，these fractured zones are typically considered. UCODE is employed to calibrate the models according to observations of groundwater inflow，and key parameters are identified and optimized for better modeling. Based on the waterproofing technique in the auxiliary tunnel，the models predict water inflows in all tunnels before and after waterproof protections，and the results are 40.35 and 31.19 m3/s，respectively. Excavation of the tunnels will causes drying of two major springs in the area，and the springs could not be recovered unless more effective waterproof protection is applied.
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Received: 16 December 2009
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