EVALUATION OF THE PERFORMANCE OF SURFACE WATER-SPREADING AQUIFER RECHARGE FACILITIES BASED ON THEIR SITE GEOLOGY

Most water-spreading recharge facilities in the southwestern U.S. are sited in alluvial basins. They are emplaced in or near dry channels of ephemeral streams.This location within the domain of a river channel takes advantage of the higher permeability of the sediments in this part of the drainage system. Although this location provides good infiltration rates it does not guarantees a desirable advance of the wetting front in the vadose zone especially for deep aquifers. The deeper portions of the vadose zone will determine the storage capacity and groundwater mound dissipation rate that will determine the technical and economic viability of the recharge site. It is therefore important to obtain the adquate geologic information during the site selection process so that the operational performance of the facility is optimized. The operational performance of two large recharge facilities in Arizona will be used to show its strong dependency on the site geology. The GRUSP recharge facility is situated in the dry bed of the Salt River within an alluvial fan at the base of the Superstition Mountains. The NAUSP recharge facility is located in a lower reach of the Agua Fria River within a lower energy fluvial enviroment.