Decision Support Services and Impacts Associated with the Devastating Flash Flood in Moapa Valley, Nevada

Tropical moisture associated with the remnants of Hurricane Norbert in the Eastern Pacific Ocean and Tropical Storm Dolly in the Gulf of Mexico primed the Southwest United States for intense rainfall. Significant impacts occurred on 8 September across Moapa Valley, which is approximately 45 miles northeast of downtown Las Vegas. Moapa Valley stretches both north and south of Interstate 15 and includes the towns of Moapa, Glendale, Logandale and Overton, as well as the Moapa Paiute Indian Reservation. Rainfall amounts across this region ranged from 2.5 to 4.6 inches, measured from automatic rain gauges operated and maintained by the Clark County Regional Flood Control District. The National Weather Service WSR-88D estimated rainfall totals in excess of 6 inches for some locations outside of the rain gauge network. Substantial runoff from this rainfall flowed through the Meadow Valley Wash, Weiser Wash, and Muddy River, inundating and exceeding the capacity of the Interstate 15 drainage system. There were major damages to Interstate 15, which caused both north- and south-bound lanes to be closed to traffic for several days while the Nevada Department of Transportation officials evaluated the damage and implemented necessary repairs. Several earthen dams and levees were significantly eroded and subsequently failed, resulting in evacuations and damage to infrastructure and residential property. The damage to Interstate 15 cost $5 million to repair, while additional Clark County infrastructure and residential damages totaled nearly $1 million. This presentation will briefly illustrate key components that contributed to such a high impact event. Societal and economic impacts across Moapa Valley as well as National Weather Service Las Vegas decision support services will be highlighted.