Lumped and distributed approaches to model natural recharge in semiarid karst aquifers

Abstract

Recharge is a key component of the hydrological balance in groundwater systems. Particularly in arid and semiarid settings recharge often takes place during isolated rainfall episodes. As a result pumping might cause groundwater levels to fall continuously for long periods of time, even if yearly abstractions remain below the average replenishment rate. Recharge is naturally difficult to quantify, as it depends on a complex variety of factors. Indirect techniques based on mathematical models have long since been advocated as valuable means to estimate recharge. This paper presents a methodology to estimate groundwater recharge in quick-response semiarid karst aquifers. Lumped and distributed models are used to evaluate the fraction of rainfall that ultimately results in aquifer recharge, as well as the correlation between the magnitude of rainfall events and infiltration rates. Modelling results are then compared with direct observations of the recharge processes and discussed to evaluate the implications of time scales. This study is demonstrated through a case-specific application to the Ventós aquifer, an intensively exploited carbonate system located in one of the driest areas of peninsular Spain. Overall, both approaches perform similarly, although the lumped model exhibits a better agreement with field records. Results reflect the nonlinear nature of the rainfall/recharge ratio. The fraction of rainfall that ultimately recharges the aquifer seems to increase exponentially with the magnitude of the event.