A small-scale groundwater sustainability assessment based on the response of artificial mining:A case study of Da ′an City,Jilin Province
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Abstract:
Da′an City is located in the northwestern part of Jilin Province,an important grain-producing and also a water-scarce area.50% of the land surface in Da′an City is covered by arable land,and relies on groundwater irrigation.Under water supply and demand contradiction ,Da′an City urgently needs a convenient and reliable method to quickly grasp the distribution of local groundwater sustainability and guidelines for future groundwater management.Considering the complexity of numerical simulation methods a new method is needed to take the advantage of sufficient available groundwater level data which can be competent for smallscale groundwater sustainability. An artificial mining response-based groundwater sustainability index (AGSI) was proposed to highlights the impact of human mining activities on groundwater dynamics.The entropy TOPSIS method is used to determine the artificial mining degree of groundwater according to the data of groundwater exploitation in the study area.To achieve a spatial difference,it is necessary to decompose the pressure exerted by artificial mining on groundwater sustainability in each monitoring well through the decomposition coefficient,that could be correlated with the groundwater response state.Inverse distance weight interpolation method is used in ArcGIS to complete the conversion of AGSI value from point to surface. The average AGSI value of the whole aquifer,the Quaternary phreatic water and confined water,and the sustainability level subzones of each aquifer were obtained.Confined water was the main exploitation water source in the study area,and the analysis showed that the changing trend of the average AGSI value was the same as that of the exploited volume,indicating that the sustainability of confined water was significantly affected by it.The average AGSI value of phreatic water was similar to the trend of precipitation and was slightly affected by the amount of exploitation.Confined water′s average AGSI value was higher than that of phreatic water until 2015,and it continued to fall below phreatic water subsequent years due to unreasonable exploitation.The value of phreatic water increased with a trend of 0.01/a and the confined water decreased with a trend of 0.04/aindicate that the risk of damage to groundwater sustainability was shifting from phreatic water to confined water.This trend was not significant at 95% confidence level.The coverage rate of "Low" sustainability subzone of phreatic water reached its maximum value of 45.2% in 2010,because dry climate promoted evaporation that year,while the coverage rate of "Low" sustainability subzone of confined water reached its maximum value of 32.5% in 2017,which was related to the increasing mining volume in recent years. The average AGSI value obtained by the AGSI method can better quantify the overall state of a certain type of water body sustainability.The process of groundwater sustainability changing with time,helps to detect sudden increases and decreases of sustainability in time,and guides managers to implement correct plans to encourage or restrict extraction.This also reflects the multi-year trend and change rate of sustainability to identify the management objects that should be focused on to improve groundwater sustainability.The sustainability level subzones drawn by the AGSI method indicate that the development potential areas and mining protection areas of different types of groundwater consistent with the multi-year dynamic situation of groundwater level.The groundwater sustainability evaluated by this method pays more attention to the effect of human exploitation,and the evaluation results are more suitable for guiding exploitation activities.
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