面向生态的矿区地下水位阈限研究

分布在干旱半干旱地区的植被,由于降水不足以维持其长期生存,需要地下水提供部分或全部水源,因而对地下水有一定的依赖性。煤层开采破坏含水层后地下水位会大幅降落,这在一定程度上会给依赖地下水植被造成水分胁迫,进而控制生态系统演化过程。针对榆神矿区煤层开采引起地下水位变化的基本特征,提出了生态安全约束下矿区地下水位控制阈值的确定方法。研究表明,植物根系与地下水毛细上升带保持接触时,植物就可以吸收利用地下水,因此本文将最大毛细上升高度与根系长度之和作为植被利用地下水的最大临界埋深。在毛管流理论指导下,以颗粒排列方式与孔隙直径大小的关系建立了最大毛细上升高度计算公式,并给出了通过颗粒级配曲线确定最大毛细上升高度的方法。据此计算的毛乌素风积沙最大毛细上升高度的取值区间为0.7～2.0 m,进一步确定了榆神矿区生态安全约束下的矿区水位控制下限为4.0 m。在此基础上,以2016年地下水流场基准,以水位埋深4.0 m为界将榆神矿区划分为生态约束区和无约束区。水位埋深小于4.0 m的区域植被对地下水依赖程度高,属于生态约束区,煤层开采造成地下水位下降极易使植被遭受水分胁迫,因而是矿区生态环境保护的重点。研究成果阐明了榆神矿区生态环境及地下水位对煤层开发的限制条件,为进一步推进保水采煤技术的发展奠定了理论基础。

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 underground 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 characteristics of groundwater level change caused by coal seam mining in Yushen mining area,and proposed a method to determine 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 capillary 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 between 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 mining 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.