Pattern And Degree Of Groundwater Recharge From River Leakage In A Karst Canyon Area Under Intensive Mine Dewatering

Most lead-zinc (Pb-Zn) deposits in southwestern China located in karst canyon areas are faced with difficulties to identify the connection between surface water and groundwater. Hydrological dynamics monitoring, tracer injection test, and riverbed dredging test were applied to discuss the contribution of river leakage to the mining area under intensive mine dewatering. The water level of surface water (-887 m asl), pore groundwater (-886 m asl), and karst groundwater (882-886 m asl) decreased in turn in the Maoping Pb-Zn deposit, which suggested the Luoze River as a losing stream. The groundwater temperature dynamics did not respond to rainfall events. Karst groundwater presented a peak delay and amplitude decay when compared with the overlying pore groundwater. Lower electrical conductivity (40-70 mu S/cm) was generated due to cation exchange process during vertical infiltration. It could be concluded firstly that pore groundwater ran horizontally and rapidly according to the synchronous response within an hour of groundwater level in the upstream and downstream boreholes to riverbed dredging test. Secondly, pore groundwater could supply the underlying karst groundwater vertically and slowly, which caused an increase of groundwater level lasting for one week during the dredging test until the recovery of decreasing trend in the dry season. Finally, the injected tracer cost more than seven months to eliminate, indicating a slow velocity around 0.01 m/d in the karst aquifer. Overall, it could be proved that surface water could be an indirect and limited water-filling source for the karst groundwater in the mining area under the control of the riverbed sediment structure. Despite the significant groundwater level drawdown caused by intensive mine dewatering, the mining area would not be threatened by the possible river leakage, and the river ecological system would not be reshaped greatly due to the weak interaction process between surface water and groundwater. (C) 2021 Elsevier B.V. All rights reserved.