A GIS Nonpoint Source Pollution Model for the Las Vegas Valley

The Las Vegas Valley is located in Southern Nevada where the average rainfall rarely exceeds five inches per year. The majority of rainfall is concentrated in the winter and summer periods, thus characterizing the region as semi-arid. The Las Vegas Valley watershed is divided into nine sub watersheds that form a 3968 km2 (1532 mi2) watershed. The entire watershed drains first to the Las Vegas Wash, and then to Lake Mead—the main source of drinking water for Southern Nevada. Approximately 85% of the watershed is undeveloped natural desert; however, some areas are highly developed. The nonpoint source pollution from urban runoff has direct water quality impacts on Lake Mead (the receiving water body). Excessive nutrients from nonpoint sources have been identified as one of the possible causes of excessive algae growth in the Spring of 2001. In this study, a Geographic Information System (GIS) -based model that uses the Simple Model is used to better understand how nonpoint sources contribute to total pollutant loads in the lake. The loads from the model are compared to waste water treatment loads for 2000 and 2001