Assessing the Effects of Epikarst on Groundwater Recharge and Regional Fast-Flow Pathways in a Karstic Aquifer via Impulse-Response Functions

Abstract

A statistical impulse-response model based on multiple-lag correlations was constructed to determine the delayed aquifer response of precipitation events due to the epikarst in a karstic aquifer. The model was used to identify the direction and travel time of slow-diffuse flows and bimodal flows including slow-diffuse and fast-concentrated flows in wet years. Fast-concentrated flows with 0–15-day delays between precipitation events and aquifer response indicated rapid drainage of recharged water from the epikarst. A computed 46–75-day delay in the aquifer response in slow-diffuse flows was the upper bound for the epikarst retention time. The model identified the activation of a new fast-concentrated flow path due to subsurface water storage beneath the precipitation-fed recharge area when the system had high antecedent moisture. For the wettest year following moderately low antecedent moisture conditions, the model identified regional flow pathways extending over a 50–180-km distance. These results suggest that impulse-response models can be used independently to gain insights into the location of preferential pathways and the role of epikarst retention time in aquifer recharge.