1 IMPROVING STRATEGIC GROUNDWATER RESERVES IN UAE VIA MANAGED AQUIFER RECHARGE WITH RECYCLED WATER S. Al-Qaran and M. Mohamed Department of Civil and Environmental Engineering United Arab Emirates University, Al Ain, P.O.BOX 15551, UAE. Phone: 03-971-5163, Email: m.mohamed@uaeu.ac.ae Abstract In this study, we attempt to identify zones suitable for artificial-recharge in Abu Dhabi using (GIS). The solution has started by employing least cost analysis to produce two cost-impact parameters for expected pollution originating from septic tanks and pesticides. Data used includes hydraulic gradient and distribution map of source point pollutions. Cost analysis considered the hydraulic gradient as a friction layer to calculate the accumulative cost-impact over the whole basin and it produces a mapping of high/low cost layers. The high hydraulic gradient is considered the low cost for pollution associated with groundwater. Next, multi criteria of Fuzzy Overlay GIS technique have been introducing in order to integrate the producing cost impact parameters together with Hydro- geomorphic and geologic Indexes based on Analytical Hierarchy Process (AHP) to finally develop Suitability mapping showing the best choice for sites adapted for artificial recharge. The cartography of the groundwater pollution potential, combined to the repartition of favourable zones to artificial recharge, constitute a unique tool to decision making. Keywords: Artificial Recharge, Least Cost Analysis, Geospatial Mapping, Fuzzy Overlay, GIS. Introduction Groundwater is the main source of freshwater in arid regions. Arid regions are known for low rainfall, high potential evapotranspiration, and high intensity/low frequency seasonal rainfall events. The dramatic increase of population and the rapid development in the agriculture and industrial sectors put a huge stress on this already scarce natural resource (Mohamed and Almualla 2010a and b). The average annual groundwater recharge is about 4,875 Mm³. The contribution of groundwater to the total water usage in the region is more than 75% (Dawoud et al. 2005). Groundwater resources in UAE can be divided into renewable (shallow aquifers) and non-renewable resources (deep aquifers) (Elmahdy and Mohamed, 2012 and 2013a and b). The renewable water resources occur mostly in shallow alluvial aquifers formed by percolating rainfall (Sherif et al., 2011 a and b). On the other hand, the non-renewable deep groundwater aquifers were formed during two ancient wet periods (6000-9000 and 25,000-30,000 years ago) (Wood and Imes 1995). The recharge of shallow aquifers depends mainly on rainfall events and surface runoff, and thus may vary considerably from year to year. Due to the high evaporation rate and surface water runoff in mountains areas, only 10 to 14 % of the total precipitation percolates to recharge the shallow groundwater aquifers in UAE (ESCWA 2003). Yet, many groundwater aquifers in GCC countries are being mined in an uncontrolled and unplanned manner (Mohamed et al 2010 a and b). Unplanned groundwater mining erodes the economic and social sustainability of the communities that depend on the depleting storage (Dawoud et al. 2005; Elmahdy and Mohamed, 2015). Reuse of treated wastewater has recently been recognized as one of the dependable resources for water supply in the UAE (Daoud et al., 2005). It is mainly used to support the expansion of gardening and landscaping in the country. The annual increase in the use of treated water for irrigation is about 10% (Alsharhan et al 2001). Previous studies (e.g. Halcrow & Partners 1969; IWACO 1986; Entec 1996; JICA 1986; Sherif et al 2011b; and Elmahdy and Mohamed 2014 a and b) show that the groundwater is one of the strategic resources of freshwater in UAE.