Identification of suitable sites for managed aquifer recharge under semi-arid conditions employing a combination of numerical and analytical techniques

Abstract

Overpumping or overexploitation of groundwater is one of the major threats for aquifer systems in arid and semi-arid areas. Managed aquifer recharge (MAR) has been suggested by many researchers as a sustainable and effective method to alleviate negative impacts of overpumping. Optimizing artificial recharge considers the selection of suitable MAR sites in terms of surface and subsurface characteristics. While surface characteristics at potential MAR sites could be modified (e.g. slope, soil texture, etc.), subsurface characteristics cannot be changed through engineering work. Characteristics of the aquifer, such as depth to groundwater, play an important role in determining the capability of an aquifer to store a specific volume of infiltrated water. Currently, only a limited number of quoted researches are available that consider factors related to aquifer characteristics and the range of these factors to identify optimal MAR sites. In this study, a new approach is presented, that employs numerical groundwater modeling to generate MAR suitability maps considering sub-surface characteristics, such as depth-to-groundwater, aquifer transmissivity and specific yield. Multiple model-runs are conducted to simulate groundwater table response with respect to the volume of infiltrated water. Simulation results are used to calibrate a groundwater mound empirical equation that calculates the groundwater level increase as a function of the transmissivity and infiltrated water volume for a given value of aquifer’ specific yield, range of vertical hydraulic conductivities and a specific design and operation conditions of the MAR system. The empirical equation is employed in GIS to spatially calculate the height of groundwater mound beneath a hypothetical MAR site and to generate, based on that, suitability maps for MAR implementation. Assuming that MAR structures capture the median of monthly surface runoff rates at the respective wadi (catchment area), suitability maps are generated for different configurations/scenarios of aquifer hydraulic conductivity in a parameter study. The results highlight the importance of integrating aquifer characteristics (geometry and hydraulic parameters) and expected magnitudes and fluxes of infiltration water in delineating suitable sites for MAR.