Mining-affected water resources and ecological effects in ecologically fragile mining areas of western China

The ecologically fragile mining area in the west is an important coal production base in China, and the current scale and intensity of coal mining has far exceeded its environmental carrying capacity, which is very likely to cause irreversible damage to the ecological environment. The restoration of surface ecology in the post-coal mining stage will be the most prominent environmental problem facing the region, while water resources play a fundamental role in this process, and the contradiction between "water-environment" is prominent. Mining-affected water resources refers to the water resources transferred, pooled and effectively stored due to mining activities, which are artificial aquifers, and play a pivotal role in the surface ecological restoration from the point of view of the regional water cycle. On the basis of summarizing the existing research results, the calculation methods of the total amount of mining-affected water resources and the storage capacity of mining space were proposed, the relationship between them and the influencing factors such as overburden structure, hydrogeology, coal mining and the stability of water storage space were elaborated, and the evaluation system of the potential of mining-affected water resources, which contains 15 parameters in three aspects, was established. The regional water cycle pattern and the ecological damage process under the influence of mining were analyzed, the calculation method of the total amount of mining-affected water resources required to maintain ecological balance was explored, the concepts of the optimal, reasonable and minimum ecological water demand in the region were defined, the indicators for evaluating the effect of surface ecological environment restoration were proposed, and the mine planning and design ideas and technical system based on the whole cycle of coal mining were constructed. Taking a mine in an ecologically fragile mining area in the west as an example, the state of water balance/overbalance under the regional water cycle was described, and the effect of surface ecological restoration was assessed and predicted. The results shows that even in dry years, the current volume of mining-affected water resources can provide reliable and sufficient water resources for the surface ecosystem, and the ecological restoration level is Class II. The surface ecosystem of 1.53-2.26 times the area of the goaf can be restored at the level of Class I in both common and abundant years, and the functional integrity of the ecosystem can be maintained over a larger area, with the ratio coefficient of up to 9.03 in an abundant year. The volume of mining-affected water resources increases step by step with the increase of coal mining area, and under the premise of meeting the regional ecological water demand, it is the next key research direction to store it as a strategic reserve resource for a long period of time and use it for national defense, people's livelihood and industry in due time. Water is the most critical influencing factor in the process of changing regional ecological environment elements, and the protection and utilization of mining-affected water resources have important strategic values for both safe and efficient coal mining and ecological environment restoration.