Integrating Diffuse and Concentrated Recharge in Karst Models

Distributed parameter models of mature karst aquifers need to take into consideration both the dual character of flow in the saturated zone and the heterogeneous infiltration conditions. Usually, in the modeling of unconfined aquifers, recharge due to infiltration is considered as uniformly distributed over the entire domain. The present study evaluates the contribution of distinct infiltration zones and examines different hypotheses on the spatial distribution of recharge zones. The applied methodology comprises two parts: i) the development of a 3D transient model and ii) the development and examination of different scenarios on the spatial distribution of recharge. The model is developed using the finite element code FEFLOW which allows for the integration of discrete features such as channels in a porous matrix. The scenarios for the spatial distribution of the recharge zones describe three hypotheses. In the first scenario, recharge is exclusively introduced through faulted zones. In the second scenario, the entire model domain receives the recharge. In the third scenario, recharge is distributed in sub-areas selected based on geomorphological and hydrogeological criteria. For each scenario, simulation model results for the water table are compared with field measurements and discussed. The derived results indicate that greater model accuracy is achieved for Scenarios 2 and 3. Finally, a forth scenario, designed by combining Scenarios 2 and 3, exhibits the best fitting between simulation results and observation data. The methodology is applied to the karst aquifer of Palaikastro-Chochlakies in Eastern Crete, Greece, for the period 2008–2012.