基于人为开采响应的小尺度地下水可持续性评价--以吉林省大安市为例

A small-scale groundwater sustainability assessment based on the response of artificial mining:A case study of Da′an City,Jilin Province

为充分利用地表数据、小尺度考虑时空变异性评价地下水的可持续性,提出基于人为开采响应的地下水可持续性指标(artificial mining response-based groundwater sustainability index,AGSI),采用熵权TOPSIS(technique for order preferenceby similarity to ideal solution)法确定地下水人为开采程度,并通过分解系数将人为开采对地下水系统施加的压力分解至各监测井,进而与地下水响应状态关联。以大安市为研究区,使用Mann-Kendall检验法和Sen′s slope变化趋势分析法验证评价结果的准确性。结果表明:2008—2017年研究区地下水可持续性受到破坏的风险由潜水向承压水转移,而各含水层间、层内的地下水可持续性分布差异表明调控地下水开采布局是大安市未来地下水管理工作的重点;研究区地下水可持续性演变过程可被水位趋势分析结果验证,AGSI法强调了人工开采的作用效果,有助于更好地理解人类活动与地下水资源的相互作用过程,为评估地下水可持续性提供新思路。

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 small-scale 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/a indicate 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.