Underground karst development characteristics and their influence on exploitation of karst groundwater in Guilin city， Southwest China

Abstract

Abstract Exploitation and utilization of karst groundwater is an effective way of solving the imbalance between supply and demand of water resources in Guilin City, southwestern China. In this study, we carried out a systematic investigation of the underground karst developmental characteristics and their influence on the migration and occurrence of karst groundwater in Guilin city. The results show that the thick limestone formation of D3r is the most ideal aquifer because it has the highest karst development and the most abundant karst groundwater. The main karst development zone is above 90 m a.s.l., and it accounts for 88.5 % of the karst caves, 11.5 % karst caves are located in the weak karst developed zone of 40-90 m a.s.l, and below 40 m a.s.l., the karst is not developed. Thus, the borehole depth for groundwater extraction is suggested to be approximately 100-120 m owing to the ground-surface elevation of Guilin city being 140-160 m a.s.l. The zone above 120 m a.s.l. is not optimal for karst groundwater exploitation because of its high karst cave filling rate (82.89 %) and low water-filling cavity ratio (16.95-30.08 %), in which the karst groundwater easily connects with surface water therefore an increase of possibility of collapse when extracting groundwater. The zone between 120-90 m a.s.l. could be more optimal for groundwater extraction due to its medium scale of karst caves, relatively low karst cave filling rate (62.07 %), and high water-filling cavity rate (30.43 %-62.10 %) relatively. Meanwhile, a favorable groundwater exploitation and utilization region is located in the eastern study area, which has the highest underground karst development, with the highest percentage of boreholes encountering caverns (80.21 %), linear karst rates (8.58 %), and the lowest karst cave filling rate (65.61 %). This study provides a scientific basis for the exploitation of karst groundwater and construction of a backup emergency water sources for Guilin City.