Assessment Of Karst Groundwater Quality And Vulnerability In Jinci Spring Area Based On Catastrophe Theory

Shanxi province is one of the most widely distributed karst in northern China,and karst water has been consistently used as an important source of water supply for industrial and agriculture and domestic water.Jinci Spring is a famous karst spring in Shanxi province.Since 1980s,with the rapid economic development,the amount of karst groundwater exploitation has increased year by year.The karst water level has dropped significantly and the spring flow has decreased dramatically.At the same time,the karst water environment in the spring area has been seriously threatened due to the intensification of coal mining and discharge of wastewater.Therefore,it’s time to evaluate and protect the karst groundwater environment.Firstly,based on the analysis of the physical geography,geological and hydrogeological conditions of Jinci Spring,this thesis focused on the trends and causes of changes in water temperature along the groundwater flow in the spring field.Data on water samples showed that the water temperature gradually increased from 12°C in Louzitiao village Q087 of Gujiao City,northern part of the spring field to 56°C in the geothermal well Q093,of the Shentanggou village.The reason for the increase in water temperature may be due to the full exchange of heat between water and rock.Based on the literature research at home and abroad,this thesis uses the catastrophe theory which can directly deal with non-continuity issues without any special intrinsic mechanism.According to the multi-criteria evaluation method based on the catastrophe theory,7 indictors including total hardness,TDS,Cl^-、SO₄^2-、NO₃^-、NO2^-and F^-have been selected.The author constructed a karst water qualityevaluation system of Jinci Spring area.According to the 32 karst water samples from the karst spring hydrogeological survey investigation in 2016,the karst water quality was evaluated based on The Groundwater Quality Standard（GB/T 14848-2017）,and then a karst water quality zoning map of Jinci Spring area is drawn used ArcGIS.The results show:The karst groundwater quality of Jinci Spring area shows a gradual deterioration rule.From class I and class II in the north recharge area to class III in the middle runoff area,and then to the class IV and class V in the southeast discharge area.The karst water anions of Jinci Spring area are mainly SO₄^2-,this thesis states that one of the main source of SO₄^2-is the gypsum developed in the Ordovician.The interaction of water and rock makes the gypsum dissolved,so that the content of SO4^2-in karst groundwater continuously increased.The rest of SO4^2-may come from the coal system water in the overlying coal strata.Based on the above evaluation results and the European karst evaluation method（COP model）,combining the topography and geomorphology,geological and hydrogeological conditions and human engineering activities of Jinci Spring area,evaluation indicators are selected from the inherent（essential）vulnerability and specific（human activity）vulnerability.Then karst groundwater vulnerability evaluation system of Jinci spring area is constructed.Applying the multi-criteria evaluation method based on catastrophe theory,combining the Jenks optimization,catastrophe theory and fuzzy membership function to determine the weights of each evaluation index.And then ArcGIS was used to draw the vulnerability map of karst water in Jinci spring area.The results shows:The high-vulnerability areas are mainly distributed in the Fen River Valley,a small part of the northern limestone exposed area,the northeast of the Spring area and the eastern part of the Spring area.They mainly include the south of the Chaicun Street and most of the Huifeng Streets in Jiancaoping District;most of the Xiayuan Street,most of the Xinghua Streets,most of the Wanbailin Streets,most of the Heping Streets,most of the Changfeng West Streets,most of the Qianfeng Streets,the east of the Xiaojingyu Street,most of the Nanhan Streets,the middle east of Shentanggou Street in Wanbailin District;most of Yijing Street and the middle of Jinsheng Town in the northern part of Jinyuan District and some coal mine goafs of Wanbailin District.The low-vulnerability areas are mainly distributed in the middle parts of the Spring area and a few areas in the west and southwest.They mainly include the middle east of Xingjiashe Township,a small part of middle east of Hekou Township,the south of the Yuanxiang Township and most of the Dongqu Street in Gujiao City;the middle north of Mayu Township and a small part of north of Dongyu Township in Qingxu County.The vulnerability of other regions is of medium level.These regions are mainly distributed in the exposed areas of limestone in the northern part of the Spring area,a small amount of shallow karst-covered areas,the west of the Spring area,some of the coal mines in middle east of the Spring area and some areas in the south and southeast of the Spring.They mainly include the most of Jialequan Township,the north of Geshang Township,most of Suoyu Township,middle east of Chang’an Township,most of Zhenchengdi Township,west of Yuanxiang Township,middle east of Malan Township,most of middle west of Taoyuan Street,south of Xiqu Street and most of Tunlan Street in Gujiao City;middle west of Du’er’ping Street,middle south of Huaketou Street,west of Shentanggou Street;most of Baijiazhuang Street and most of Wangfeng Township in Wanbailin District;most of Jinci Town,southeast of Yaocun Town,middle west of Luocheng Street,west of Jinsheng Town and west of Jinyuan Street in Jinyuan District;south of Mayu Township,middle south of Dongyu Township and middle of Qingyuan Town in Qingxu County.The evaluation results can provide a basis for the rational development,utilization and protection of karst water in Jinci Spring area.