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Recent Flooding and Environmental Change in Las Vegas Wash

Studies of sediment erosion and deposition over the past 3,000 years in Las Vegas Wash, as well as studies about how human activity affects river systems in the Southwest, have yielded new information on the responses of river basins to climate change and urban growth. In Las Vegas Valley, streamflow and precipitation data over the past decade show that urbanization has changed rainfall-runoff relations to produce more frequent flooding as well as more damage to private property and to the primary riparian ecosystem in the Valley.

During the past 20 years, several factors related to rapid urbanization of Las Vegas and surrounding areas have led to extensive changes in Las Vegas Wash, the main drainage from Las Vegas Valley into Lake Mead. The most damaging change is extensive erosion (9Mb PDF) that in places has caused downcutting of the Wash by as much as 30 meters and lateral expansion of the channel by as much as several hundred meters. Most erosion has occurred during floods caused by monsoonal, summertime downpours. The flooding not only damages marshes, but can be so severe that it endangers the main water pipeline into the city from Lake Mead. USGS studies are documenting the erosional effects from floods of the past decade. This information can be used to predict future changes to the actively eroding channel system, taken in light of projections for continued urban growth.

Photograph of the mouth of Las Vegas Wash entering Upper Las Vegas Bay in 2004. The delta has filled in a large volume of the Bay, causing abandonment of the principal marina and boat ramp at Lake Mead National Recreation Area. (Photo credit: Southern Nevada Water Authority)

For more information, contact John Whitney.