Vulnerability Assessment Of Karst Groundwater Base On GIS

Groundwater is an important part of water resources. It is a major source of human drinking water. In recent years, contamination resulting from industry, urbanization and agriculture poses a threat to water quality. Southwestern karst region is the largest distribution area of carbonate rocks. As karst region have a particular geological structure, external contaminants flow to karst systems by water infiltration or sinkholes. It impact on the karst system and groundwater. Therefore, it is very necessary to asses the vulnerability t in karst region.Laolongdong underground river developed in the rock landscape areas, and underground karst along river systems is anticline extending into NE-SW direction. A large number of residential areas factories and mines located this area. Many people even use swallow hole as a sewage hole, which leading to serious pollution in the underground river.The weather stations,monitoring stations is established to monitor the amount of underground rivers, and physical characteristics of the flow control output system and the main physical indicators include water temperature,electrical conductivity(EC), pH value variations. Through field survey and laboratory experiments to obtain soil depth. soil texture, land use types, the degree of karst development data. By topographic maps, we obtain the elevation, slope and other data.This article summarizes the research results of European approach and taking into account the range of precipitation which is little change in small area. In order to be more accurate assessment. S factor was introduced and established the COSK methods. Considering the actual situation of study area, this article select 4 factors, such as the runoff conditions (C), covering layer of protection (O), surface water (S), degree of karst development (K) to assess the groundwater resource. With ArcGIS which has a powerful spatial analysis and mapping functions, we generated the runoff conditions evaluation map. coverage vulnerability maps, the situation assessment map of surface water. karst development evaluation map. and ultimately generated Laolongdong underground river vulnerability assessment map of ChongQing.From the evaluation of soil thickness we can see that most soil depth are about 1-2m, but some places like the area above the underground river.residential areas and quarries thin layer, have the higher vulnerability. There has many heavy loam.but medium loam is small. light loam sand appears in the basin area. Surface water which is far away from the region has less vulnerability. Water near the pollution has high groundwater vulnerability. The very low class is used for sectors the aquifer where only runoff process are present or where the distance from a swallow hole or sinking stream is very considerable.Finally, the consequences are concluded in this paper:Compared to other agricultural types area, the vulnerability of this region were generally higher; the place within 100 meters far from swallow holes has extreme vulnerability; surface water factor can be used to evaluate the vulnerability; COSK method can be used to assess groundwater vulnerability. The results of chemical analysis are consistent with the final report; this method is suitable for the study area.