Characterization of wet and dry weather flows from urban runoff in an arid region

The Las Vegas Wash receives runoff from the Las Vegas Valley which includes the City of Las Vegas, City of North Las Vegas, City of Henderson, and other outlying areas. The annual precipitation in this arid region is approximately four to five inches. In this study, intense spatial and temporal sampling of urban runoff was performed in washes located throughout the Las Vegas Valley. The source of these flows comes primarily from irrigating landscapes, shallow groundwater, and rainfall excess. The purpose of this study is to evaluate the quality of runoff at these locations and to characterize the temporal variability of urban runoff during wet and dry periods. This is critical since there is a lack of comprehensive data for arid regions. Preliminary dry weather runoff results show a clear difference between locations that are influenced by shallow groundwater and locations that have runoff generated only from urban areas. During wet weather, the water quality analysis suggests that the peak concentrations in many constituents (e.g., chemical oxygen demand, Nitrogen, and Phosphorous) occurs about one to two hours prior to the peak water level in the storm channels. This is important when suggesting solutions for minimizing the adverse impacts to water quality. There is also an increase in total suspended solids (TSS) during rainfall events which is important for determining the potential of contaminants being transported downstream. Contaminants can attach to suspended solids and travel to the receiving water body. Lastly, the phase of solids changes from predominately dissolved during dry weather flows to suspended during rainfall event