The impact of overland flow on the variation of discharge and hydrochemistry of karst spring in peak cluster

Many closed depressions distribute in peak cluster area. The overland flow occurring in the closed depression enters the conduit though sink holes during storms and finally becomes a part of karst spring. In this paper, the typical peak cluster depression landscape-Yaji experimental site was selected to study the role of overland flow in discharge and hydrochemistry of karst spring though monitoring the quantity of overland flow and tracer experiment. The monitoring results of runoff plot show that overland flow occurred when rainfall was more than 64.4mm/day with low discharge in 2010. The overland flow coefficients were between 0.48% and 0.71%. The rainfall-runoff process of 19 May was chose to do water balance and ions mass conservation. Though the water balance analysis of catchment of Spring S31, overland flow only accounted for 0.63% of total discharge of spring. Overland flow could hardly influence the discharge of karst spring. The results of ions mass conversation model show that the variation of electrical conductivity of spring S31 was caused mainly by fracture water. The overland flow contains abundant rainwater, but the effect to electrical conductivity is very limited. Because of high rainfall needs and low proportion of overland flow, we can ignore the impact of overland flow on the variation of discharge and hydrochemistry of karst spring under appropriate rainfall conditions.