Groundwater level threshold under the constrain of ecology security in mining area

Vegetation distributed in arid and semi-arid regions,due to insufficient precipitation to maintain long-term survival,requires groundwater to provide part or all of its water demand,and thus is phreatophyte. When the under- ground mining destroys the aquifer, the groundwater level will drop significantly, which will cause water stress to phreatophyte,and control the ecosystem evolution process. In this paper,the authors investigated the basic characteris- tics of groundwater level change caused by coal seam mining in Yushen mining area,and proposed a method to deter- mine groundwater level threshold under ecological constraints in mining area. As long as the roots are in contact with the groundwater capillary rise zone,the groundwater can be utilized by plants. Therefore,the sum of the maximum cap- illary rise height and the root length is regarded as the maximum critical depth of the groundwater. Under the guidance of capillary flow theory,the formula to calculate maximum capillary rise height is established by the relationship be- tween particle arrangement and pore diameter,and the method of determining the maximum capillary rise height by particle gradation curve is given. According to the calculation,the maximum capillary rise height of the Mu Us aeolian sand is 0. 7-2. 0 m and the lower limit of the water level under the ecological constraints in the mine area is 4. 0 m. Based on the groundwater flow field in 2016,the Yushen mining area is divided into ecologically restricted areas and unconstrained areas with a water depth of 4. 0 m. Vegetation with a water depth of less than 4. 0 m is highly dependent on groundwater and belongs to the ecological confinement zone. The decline of groundwater level caused by coal seam mining is very likely to cause water stress on vegetation,which is the focus of ecological environment protection in min- ing areas. This illuminates the limitations of ecology and water level on coal mining in Yushen mining area,which lays a theoretical foundation for further promoting water-preserved coal mining technology.