ABSTRACT
Urban population growth is putting increasing demands on groundwater resources, especially in semi-arid regions like the southwestern United States with limited surface water supplies. Capturing urban storm runoff for focused groundwater recharge in ephemeral alluvial channels is one promising strategy for mitigating groundwater shortages; yet, little is known about the quality of urban runoff and potential impacts on shallow aquifers. In the Tucson Basin (Arizona), highly impervious urban watersheds generate more summer monsoon runoff events and have greater water yields, than less developed watersheds. Routing of urban runoff into local washes likely augments groundwater resources, as shown by rapid recharge beneath alluvial channels. The composition of wash substrates strongly controls nutrient transport. Low levels of trace metals and nutrients in storm runoff and shallow aquifers suggest that urbanization does not necessarily degrade water quality. Up to 6% of atmospheric nitrate may be transported to groundwater in areas of focused recharge.
