| In recent decades,more and more studies have shown that the source and sink conditions of water quality in the middle reaches of the Yellow River have changed significantly,and the grown of human activities on water quality is also increasing.Coal mining is a vital reason for the change of water quality.Kuye River Basin is a coal concentrated distribution area in Northern Shaanxi.With the increase of coal mining amount year by year,the problem of water resources caused by coal mining will become increasingly prominent.Therefore,it is of great scientific and practical significance to quantitatively study the influence of coal mining on water resources in Kuye River for ensuring the ecological water quantity of the river.Based on the observation data of underground water level and spring discharge in mining area obtained through field investigation,the influence model of coal mining on water resources was studied by taking Kuye River as an example.The impact on regional water quality simulated and analyzed by constructing a coupling model of surface water and groundwater.It aims to provide decisions for water management and alleviate water problems caused by coal mining.The main results are as follows:(1)Since 1996,the annual coal production in the Kuye River Basin increased rapidly,approaching 350 million tons per year by 2018.Meanwhile,the water inflow from mines was 59.505 million m~3per year.The water inflow of coal mines mainly belonged to the grade of 1000-10000m~3/d or greater than 10000m~3/d.Although there was a large number of small coal mines,their distribution area was smaller than that of large coal mines as a whole.In general,the study area belonged to the region with more water inflow.(2)The runoff of Kuye River,Wulanmulun River and Boniuchuan River showed a decreasing trend in the past 60 years.Since 1996,the annual runoff of Kuye River reduced significantly,and the variation before and after the abrupt change was 406 million m~3.(3)The influence of coal mining on water resources in Kuye River Basin can be divided into two types:the development height of water-conducting fissure zone through the surface model and the non-penetration model.The calculation results show that,the water-conducting fracture zones in most coal seam mining areas are all developed in the overlying bedrock,and only a few of the coal seams in the slope area of gully area are buried shallowly.Besides,the water-conducting fracture zones have developed into the Quaternary subsurface layer to communicate with the surface water.(4)The semi-loose coupling SWAT model and MODFLOW model are used to simulate the impact of coal mining on water resources.The results show that the coupling model can accurately describe and simulate the runoff process and groundwater in the study area.(5)Coal mining can reduce the runoff in Kuye River Basin.The water reduction caused by coal mining is mainly discharged through the connection between the water-conducting fissure zone and the goaf.Coal mining resulted in 291 million m~3of runoff reduction in Kuye River,of which 185 million m~3was infiltrated through water-conducting fissure zone.From the perspective of spatial distribution,the runoff water reduction in the mining intensive area and the water infiltration into the water-conducting fracture zone are relatively large and wide.In addition,based on the classification model of coal mining's impact on water resources,Modflow model is used to analyze the impact of coal mining on groundwater.The results show that the groundwater level drops significantly under the condition of coal mining,and the phreatic water level decreases by 3.60-7.16m compared with the initial water level of the model The buried depth of the phreatic water level is distributed between 11.40-14.96m.Besides,the total impact of coal mining on groundwater in 2018 was 9.79×10~8m~3. |
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