Evolution characteristics of groundwater and eco-environment in Yulin-Shenmu Mining Area

Generally, mining activities will cause the variation of hydrogeological conditions in the mining area, and then affect the groundwater flow field and ecological environment.The purpose of this article is to study the characteristics of groundwater level change and its environmental effects after 15 years mining in Yulin-Shemu Mining Area. Groundwater level change was analyzed by observed data before and after coal mining, simultaneously, land desertification process was monitored by two same period remote-sensing image. The results showed: more than 15 years mining had drained at least 3.22% of the total water resources, which had drawn groundwater level down more than 1m of 968 km2,accouting 18.4% of the mining area.The area where water level dropped over 8 m mainly located at Mahuangliang Town. Land desertification had tremendously rehabilitated from 2000 to 2016, the area of serve desertification land and moderate desertification land were reduced sharply, but the non- desertification land area was increased. There was no correlated coefficient between groundwater level change and land desertification, and groundwater level decline did not directly caused desertification development. The permitted variation ranges of groundwater level should be decided by relationship between groundwater and vegetation.The upper limit of depth to groundwater must be less than the maximum capillary height, and the lower limit should be determined by the sum of the length of vegetation root and the maximum capillary height of groundwater. Accordingly, the upper limit of depth to groundwater in Yulin-Shenmu Mining Area is 0.5 m, and the lower limit is 4.0 m. The min-depth of groundwater is 0.5 m. The obvious decrease of groundwater level in Yulin-Shenmu Mining Area has not caused the development of land desertification, because the vegetation in these areas has no dependence on groundwater.In the development and construction of mining areas in arid and semi-arid areas, it is still necessary to attach importance to the constraint of groundwater level threshold and carry out water-preserved coal mining technology.