| Wulan is located at east Qaidam Basin. The climate in this region is semi-arid plateau continental continent with the features of strong and long-duration evaporation, and less and concentrated rainfall. Groundwater is widely distributed with good water quality and water stability. However, the distribution of surface water space in the study area is very uneven. Also, the freezing period is long. Therefore, it is urgent to find water supply scheme for groundwater resources. Taking groundwater dynamics theory as a guide, this thesis is aimed to explore the sustainable utilization of groundwater in Wulan basin. In this study, numerical simulation method is used to study the rules of lake degraded area and investigate the influence of surrounding ecological environment in different mining case. As a result, the threshold of sustainable groundwater exploitation and groundwater protection measures are put forward. Some major opinions and conclusions obtained from this study are showed below:(1)Defining the simulation area. The study area is surrounded by four mountains and one lake, which are Maoniu mountain, Amuneige mountain, Qinghai Nanshan, Buhete mountain and Chaikai lake, in the direction of southwest, northwest, north and west, respectively. In the vertical direction, the surface is upper boundary, and the lower boundary is bedrock.(2)Establishment of Wulan basin hydrogeological conceptual model. According to the Wulan basin hydrogeological, geological conditions and the actual flow field are used to simplify the boundary conditions. The western and northeastern boundaries could be conceptualized as confining boundary and the rest of the borders are the flow boundaries. Dulan lake, Keke Salt lake and Salt lake are the minimum base level of erosion, and therefore they are generalized as drainage boundary. The upper boundary is water table and the lower boundary is the water impermeable boundary. The basin is a intermontane rift basin, and its hydrogeological structure meets the typical characteristics of artesian; piedmont alluvial fan aquifers generally are single-structure gravel aquifers, but to the center of basin alluvial-lacustrine alluvial plain, the aquifers gradually transfer to sand and clay inter layer called confined water multi-layer structure. Therefore, the aquifer in the simulation area is divided into two layers. The basin groundwater is generalized as heterogeneous isotropic three-dimensional unsteady flow.(3)Establishment of numerical model of groundwater flow with the best simulation degree. Based on the groundwater system generalization and the conservation law of mass and energy, the Wulan basin groundwater flow mathematical model was established. Visual Modflow software is used to achieve the groundwater flow model in the research area. The result indicates that the model are reliable.(4)Determination for the quantity of regional groundwater resources and threshold of sustainable exploitation. Six different groundwater exploitation schemes are set up and run to forecast the groundwater flow field and the groundwater level drop. The threshold of sustainable utilization is 8.5×104m3/d, accounting for about 50% of the amount of water resources supply.(5) Proposal of a groundwater-resource exploitation mode. It is applied to preserve lake ecosystem. Firstly, The type of plum blossom is used to layout the wells with 1000 m well spacing. Secondly, the best choice is that the groundwater should be pumped from middle-deep-runoff zone and the mineralization degree is less than 1g/L. Thirdly, the groundwater are supposed to be pumped from the upstream of residential areas. Finally, the water supply sites are emplaced in the Amuneige alluvial-proluvial fan, Saishenke alluvial-proluvial fan, Dulan alluvial-proluvial fan and in front of the Saishenke alluvial-proluvial fan.These research achievements provide important guidance and scientific significance to the rational exploitation, utilization and protection ecological environment in Wulan basin and semi-arid areas in the northwest. |
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