Evaluation On The Reasonable Yield Of Groundwater In The Wulanmulun River Valley, Shaanxi Province

The research area is located in arid and semi-arid region in northwest China. In recent years, with the development of coal industry and its relevant industry, the local hydrogeology conditions have obviously changed, the groundwater level significantly decreased and scarcity of water resources is more striking. These problems have seriously restricted the local social and economic development. Therefore, it is particularly urgent to evaluate the available yield of groundwater in the research area and look for a more suitable project for the research area to exploit groundwater. Both of them have important theoretical and practical significance.The research focuses on the evaluation on the available yield of groundwater in the Wulanmulun river valley, Shaanxi Province in the paper. (1) On the basis of collecting, sorting and using the data, which are accumulated by predecessors, a hydrogeological conceptual model for the research area is established. (2) Based on the hydrogeological conceptual model, three-dimensional finite difference steady flow model and three-dimensional finite difference unsteady flow model for the research area are established to solve the water level and quantity in the area. (3) On the basis of full considering the factors that the thickness of the local aquifer is small, the ability of water storage is poor, the fluctuations in river flows are large and there is long zero flow, and the water demand, a new water collecting structure-infiltration gallery with underground reservoir is designed. (4) By combining water balance with numerical method, the available yield of groundwater in the Wulanmulun River Valley is evaluated and the guarantee level of it is demonstrated. (5) At last, preliminary programs for exploiting groundwater resources.and the relevant protection measures are proposed on the basis of the evaluation on the available yield of groundwater.The paper mainly comes to the conclusions as follows:(1) The research area is located in the transition zone of the Mu Us Desert and the Loess Plateau and belongs to typical arid and semi-arid continental climate. The alluvial distribution area in it is small and the thicknesses vary largely, but under the exploitation condition, the area can be supplied by the river leakage and the water is relatively abundant. So it is suitable to exploit groundwater along the riverside in the research area.(2) Due to the development of coal industry and its relevant industry, the hydrogeology conditions in the research area have obviously changed, mainly in runoff and discharge conditions of groundwater. Colliery exploitation causes the groundwater to flow to the nearby area of exploiting colliery and to be drained by the way of mine drainage. All of these lead to the waste and destroy on the water resource in the research area. Besides, a series of environmental geological problems, such as surface collapse and ground fissure, are caused.(3) Recently, infiltration galleries are often used in the Wulanmulun river valley, however, this kind of water-supplying projects cannot supply water resource normally during the dry season. In order to provide the solution to the problem mentioned above, we have designed a type of infiltration gallery which operates with an underground reservoir, which is connected to the downstream end of the infiltration gallery, based on the conventional infiltration gallery distributed along the river and under the riverbed.(4) Under the exploitation condition, the river leakage stimulated by the infiltration gallery flows into the reservoir along the gallery when the river maintains a certain flow rate and width in normal season. When the river is going to be dry, we can use the water reserved in the underground reservoir as well as the water collected by the infiltration gallery to maintain the normal water supply.(5) The model of infiltration gallery with underground reservoir was established by using the three-dimensional finite difference method. The results of simulation calculation using the model above reveal as follows:when four infiltration galleries with underground reservoir were built in the research area, the available yield of groundwater can increase by 0.92×104m3/d on the basis of current exploitation amount,1.676×104m3/d. Besides, the water supply project could be maintained normal so long as the cutoff time of Wulanmulan River was no more than 30 days in dry season.