Ecological water security impact of large coal base development and its protection

Abstract

The two main factors of groundwater system disturbance in coal mines are mine water inflow caused by overburden destruction and advance drainage projects as the main means of mine water hazard control. An urgent problem to be solved in the ecologically fragile area is how to minimize the impact of advance drainage on the groundwater ecological environment while reducing mine water inflow rate to ensure safe production. This paper proposes an optimal advance drainage technology based on multi-objective groundwater management. Based on the analysis of the respective relationship between the drainage groundwater level and the capture supply and mine water inflow rate, the concept and mathematical expression of the drainage threshold of the mine and the ecological environment are put forward for the first time. Based on the numerical simulation model, this technology fully describes the dynamic changes of the groundwater system and establishes a groundwater management model with multi-objective constraints such as mine production safety, ecological water resources protection and efficient drainage. The optimal drainage scheme for the boreholes location, the drainage volume and the time distribution is obtained through objective programming. While reducing drainage volume and ensuring mine production safety, the impact on the locally important phreatic groundwater is significantly reduced, effectively resolving the contradiction between ecological water resource protection and mine safety production. In the example of a coal mine in Northwest China, by comparing the traditional equal drainage scheme, the optimized advance drainage technology fully considers the water-richness characteristics and the dynamic changes of the groundwater system during the drainage process. The number of boreholes in the optimization scheme is reduced by 50 %, and the total drainage volume is reduced by 40.60 %. More importantly, under the condition that the decrease of mine water inflow rate in the two schemes is basically the same, the average increase of Quaternary leakage in the optimization scheme decreases by 53.36 %. Through this technology, the ecological critical value in the study area is evaluated. When the regional Quaternary groundwater level decreases by more than 0.73 m, the impact range of the drawdown funnel and the drawdown rate are obviously accelerated. It provides a scientific foundation for groundwater resource management and low-carbon mining in ecologically fragile areas.