Evaluation of a hydrodynamic threshold in the Zhaidi karst aquifer (Guangxi Province, China)

Understanding how the discharge-rate and the hydraulic gradient of a karst aquifer varies in response to rainfall events is important for the efficient management of water resources in these aquifers. The relationship between discharge and hydraulic gradient is related to aquifer properties such as the physical characteristics of the karstic matrix, hydraulic conductivity and the extent to which water is exchanged between conduits and the matrix. In this study, discharge and hydraulic gradient data were monitored at 4-h intervals for 476 continuous days in the Zhaidi karst aquifer located in Guilin, Guangxi Province, China. These data showed that the relationship between flow rate and hydraulic gradient in the aquifer became increasing non-linear with increasing flow rates. After analyzing the time series data, a hydrodynamic threshold between quickflow- and baseflow conditions was found to take place at a discharge rate of 0.80 m 3 /s. The linear law and nonlinear equations were obtained between discharge and hydraulic gradient which reflected the flow mechanism of groundwater flow in this karst aquifer.