金沙江溪洛渡水电站环境水文地质综合评价

Comprehensive Assessment of Environmental Hydrogeology in Xiluodu Hydropower Station

溪洛渡水电站是我国西南地区的一座大型水电站 ,其规模仅次于三峡水利枢纽规模。在分析坝区水文地质条件的基础上 ,从温度场、同位素、水化学场以及岩体地下水动力条件等多角度解释了溪洛渡水电站坝区两岸地下水埋深大、局部温度和局部承压等异常现象。通过分析认为 ,坝址区水文地质工程条件良好 ,岩体透水性较弱 ,无大的控水构造 ,坝区不存在危害性的渗漏问题 ,坝基及两岸谷坡均有相对抗水介质存在。

The planned Xiluodu Hydropower Plant is the second largest hydropower plant in China, next to the Three Gorges Power Station. It is situated on the upper reaches of the Jinshajiang River. There exist many problems related to groundwater around the dam district: (1) Groundwater level is buried deeply and its hydraulic gradient is gentle. (2) Temperature of groundwater is locally abnormal and the groundwater head is locally confined. (3) Modern karst is developed in the limestone of both banks and in valley. (4) Recharge source comprises precipitation, surface water, groundwater of other aquifers and water bodies of different altitudes and times. The fluctuation of groundwater levels of various holes on banks and in valley keeps synch onously with that of the Jinshajiang River. Furthermore, the synchronism of level rising is better than that of falling. In this paper, the groundwater flow system around the dam district is analyzed according to geologic structure and lithologic features. The environmental hydrogeological characteristics are studied in many aspects, such as temperature field, hydrochemical field, isotopes and dynamic conditions, etc. The major conclusions are as follows: The hydrogeological conditions are fine. The penetrability of rock mass is relatively weak. There is no potential leakage. The deep karst is developed weakly. There exist relatively water proofing strata at some depth of dam foundation and valley sides. Despite the groundwater level buried deeply and its gradient is gentle, it is estimated that the backwater level corresponding to reservoir level will be formed after reservoir ponding due to the special basin structure of the dam district. Finally, it is pointed out that the hydrogeological engineering problems may exist which include seepage deformation within inter layer and inner layer faulted planes and the effect of these planes under the action of uplift pressure to the safety and stability of hydraulic constructions after reservoir ponding. Especially, in the rock mass of dam abutments, the hydraulic gradient is large because the seepage tracking is short. The effect of seepage force will be strong after reservoir filling. So the effect scope of uplift pressure on the surrounding rocks will be large so that the overall load should not be underestimated. In order to assure the safety and stability of hydraulic constructions, seepage control and decompression of rock mass are of special importance.