Assessment of Artificial Recharge Efficiency Against Groundwater Stress in the El Khairat Aquifer

Abstract

The El Khairat aquifer located at the eastern center of Tunisia is mainly recharged by infiltration of flood water through beds of ephemeral streams. Since late 70s, the aquifer showed a continuous water table decline due to an excessive increase of groundwater extraction. The situation worsened by the damming of the El Khairat wadi which is the most important wadi of the region. Artificial recharge campaigns were carried out by Tunisian water agency to re-establish the natural groundwater recharge of the aquifer. They consisted of releasing water from the dam reservoir to the natural downstream bed of the wadi channel. This paper aims to assess the efficiency of the artificial groundwater recharge operations by developing a conceptual rainfall-runoff model. The model input consists of the daily water volume released from the dam. The wadi bed is divided into several serial reaches. For each reach, the production function is represented by a soil store and four transfer reservoirs. The model calibration consists of reproducing the daily surface runoff volume measured at the runoff gauging stations and the water table level measured at the piezometers located in close proximity of the wadi course. The modelling results indicate an infiltration coefficient ranging from 40 to 80%. Despite this high infiltration rate, the mean annual recharge in artificialized regime remains below the natural recharge. The construction of El Khairat dam could be a good resource management alternative under certain constraints as increasing the recharge campaigns frequency and avoiding releases with high discharge rate.