Flash Flooding In Las Vegas

2 Pages 607 Words

Torrential rains produced severe and unprecedented flash flooding across the Las Vegas valley on July 8, 1999. Much of the Las Vegas valley experienced from 35%-70% of its annual rainfall(4.13 inches) over the course of 60-90 minutes. The resulting runoff from these rains caused widespread street flooding and record flows in normally dry washes and flood control detention basins. The floods caused over $20,000,000 in property damage and took 2 lives.
Flash floods are not unusual in the Las Vegas valley; however, this event was extreme in its scope and intensity. The purpose of this paper is to review the meteorological conditions that preceded this event and discuss how the urbanization of the Las Vegas valley contributed to the flash-flood threat.
In order for a flash flood to occur, heavy precipitation must fall in a region that has appropriate hydrological ingredients in place. The hydrological ingredients include antecedent precipitation, topographic relief, and land use. In order for heavy precipitation to occur, high rainfall rates must be sustained. High rainfall rates, in turn, result from rapid ascent of moist air. Long duration of high rainfall rates results from slow movement of the rainfall producing system.
The Las Vegas valley is located in the Basin and Range Physiographic Province. This region is characterized by a series of generally north-south trending mountain ranges and intervening valleys filled with eroded sediments.
The Las Vegas valley is very prone to flooding due to its geologic and orographic composition. The Spring Mountains are located on the west side of the valley, while the Sheep Range borders the valley on the north. Smaller mountains are on the east and southeast sides of the valley. The Spring Mountains are primarily composed of limestone rock. These factors, along with the amount of urban development in the area can often increase the severity of flash flooding.
The atmosphere ...