Groundwater Restoration through Recharge Dams in Arid Regions

The use of fossil freshwater resources in arid and semi-arid regions has quadrupled over the last few decades. The climate change phenomenon, in such regions, is associated with extended drought periods and frequent extreme rainfall events. Due to the lack of surface water during dry years, groundwater resources are overexploited to meet the agriculture water demands. Recharge dams are built across the main wadis to harvest the surface water runoff, restore the depleted groundwater resources, and mitigate the possible destruction of flash floods.
More than 150 dams have been built in the Northern Emirates of the United Arab Emirates (UAE) during the last four decades to enhance the groundwater recharge and improve the resilience of the downstream cities against flood hazards. The current study assesses the overall efficiency of dams in UAE in recharging the groundwater resources in the quaternary aquifer. The efficiency of the dam is defined as the actual volume of the water that reaches the saturated zone to the total volume of water in the ponding area. It is concluded that the efficiency of the recharge dams in UAE varies between 15 and 49%, with the lower end of that range being the most common. The remaining portion is either lost directly through evaporation or stored temporarily in the unsaturated zone causing an increase of the soil moisture contents. Based on the subsequent rainfall pattern, the water in the unsaturated zone might continue to percolate and reach the saturated zone or lost through evapotranspiration from vegetation. Several recommendations are proposed to maximize the groundwater recharge from extreme rainfall events.