An Integrated Conceptual and Modeling Approach for Studying Groundwater Recharge in Arid/Semi-arid Regions

Continued rapid population growth in arid/semi-arid regions like the southwestern U.S. is increasing the demand and reliance on groundwater resources each year. These resources are limited and require long-term management to ensure sustainability. Basin scale groundwater models are typically developed and used as the primary tool supporting management plans. Successful long-term .plans depend heavily on estimating realistic rates of recharge to the saturated zone. However, specification of basin recharge in typical groundwater models is often greatly oversimplified by assuming it is either spatially or temporally constant. In most cases, this is inappropriate because recharge is complex, it depends on many factors, and it exhibits pronounced spatial and temporal variability within a basin. Two key steps are proposed to obtain more accurate recharge estimates. First, important local and regional scale recharge mechanisms within the basin need to be identified. Second, important surface and subsurface hydrologic processes associated with these mechanisms must be evaluated and better understood. Physically based, integrated hydrologic codes are capable of simulating both surface and subsurface processes. A conceptual and modeling framework is developed based on a physically based integrated hydrologic code and GIS techniques to study recharge in semi-arid/arid basins. Within this framework, a step-wise approach is taken to identify, conceptualize and numerically analyze different relevant 'hydro-geomorphic' recharge mechanisms. This is an important step in developing a fully integrated hydrologic model for the basin flow system. Two different scale arid/semi-arid basin systems are used to demonstrate the approach.