A new method to estimate annual and event-based recharge coefficient in karst aquifers; case study: Sheshpeer karst aquifer, south-central Iran

Abstract

Quantification of recharge is a fundamental issue in evaluation and management of karst water resources. Recharge coefficient (RC), which is the ratio of aquifer recharged water (VR) to the total precipitation, has been widely used for recharge estimation in karst catchments. Though the RC definition is straightforward, in practice, its application on a fixed short time scale (e.g., monthly or annual) is challenging, because of the problems in determination of change in groundwater storage (DVS) that is included in VR. Some researchers have neglected DVS, estimated VR as equal to the net aquifer outflows; hence they have over-or under-estimated the RC, ignoring the aquifer's antecedent storage condition. In this study, a new method is proposed to estimate the actual event VR, and consequently, the event-based RC, utilizing the MRC displacement method of Kavousi and Raeisi (2015). Applying the method, VR due to a specific event or a combination of events during a hydrological year can be directly estimated by decomposition of the observed hydrograph to the individual hydrographs induced by different events. The method is applicable for karst aquifers with no-flow boundaries, draining by a spring. The calculated event VR takes DVS into account, enabling an accurate event-based RC estimation. The method was applied to the Sheshpeer karst aquifer in Iran. The estimated RCs reasonably matched up to the catchment properties and former field studies. Results showed that the annual RCs would be underestimated if the DVS was neglected, because DVS was positive during the study period.