Analysis And Research On The Influence Of Reservoir Filling On The Ground Water Environment In The Inundated Area Of Reservoir In The Valley

The Guwa hydropower station is located in Xiangcheng county, Ganzi Tibetan autonomous prefecture, Sichuan province, which is the "bibcock reservoir" of the six-grade cascaded hydropower projects on the Shuoqu River mainstream from Xiangcheng to Derong. The reservoir is constructed in mountain canyon area, the maximum height of the dam is150m, and the normal water level is3398m. The water level uplifting about138m higher than that before dam impounding at the dam site, which reverses the flow of groundwater flow field in the dam site and will bring the problem of dam foundation seepage and seepage around the dam. Therefore, it has a great need to research the reservoir area groundwater environment with the effect of planned Guwa reservoir impoundment and the leakage of Guwa reservoir dam site.This paper analyzes the natural geography and hydrogeological conditions of the dam site area of Guwa reservoir which is constructed in mountain canyon area. The strata of the dam site area mostly consist of the Triassic Rana lower section of gray, dark gray thick-bedded metamorphic powder, plywood fine sandstone rock, the different causes of Quaternary sediments is mainly distributed in the riverbed, the two sides in the lower part and the left bank of the groove. We study the type of groundwater and the relation of the groundwater recharge, runoff and discharge in dam site, the groundwater type consists of layer of loose Quaternary pore water and bedrock fissure water, pore water occurs in the loosely packed layer, bedrock fissure water is mainly distributed in the cross-strait bedrock fissures. The groundwater of dam site mainly accepts precipitation recharge. The groundwater discharge to the river valley and downstream mainly through both sides of the river. The groundwater level changes with the seasons changing. And we analyzed the dynamical property and the chemical behaviors of the groundwater.Based on the above research and analysis, this paper establishs the hydrogeology conceptual model of the Guwa reservoir dam site area through the generalizations of the boundary conditions and the source sink term. By analyzing the pumping tests and the information from the injection and water-presure tests of the other well-drilling in the area, we preliminary determine the scope of the hydrogeology paramenters, then the groundwarer mumerical simulation software is used to make adjustments and computer imitation, and the three-dimensional numerical model of the groundwater flow in Guwa reservoir dam site is built. We compare the different simulations of groundwater flow in dam site before and after reservoir impoundment, and calculate the seepage of the dam site section after impoundmen. The results show that due to the dam construction, the ground water level of dam upstream will be uplifted, making the groundwater flow direction reversed, the change of the groundwater level which is near the dam site and the terraces on both sides is more obvious, the total leakage at the dam site section is1.9%of the average annual flow of the Shuoqu River at this part. It belongs to the weak leakage, and it would not produce significant effects on the normal operation of the reservoir by taking corresponding seepage control measures.