Lake Mead is one of a series of large Colorado River reservoirs operated and maintained by the Bureau of Reclamation. The Colorado River system of reservoirs and diversions is an important source of water for millions of people in seven Western States and Mexico. The U.S. Geological Survey, in cooperation with the Bureau of Reclamation, conducted a study from 1997 to 1999 to estimate evaporation from Lake Mead. For this study, micrometeorological and hydrologic data were collected continually from instrumented platforms deployed at four locations on the lake, open-water areas of Boulder Basin, Virgin Basin, and Overton Arm and a protected cove in Boulder Basin. Data collected at the platforms were used to estimate Lake Mead evaporation by solving an energybudget equation. The average annual evaporation rate at open-water stations from January 1998 to December 1999 was 7.5 feet. Because the spatial variation of monthly and annual evaporation rates was minimal for the open-water stations, a single open-water station in Boulder Basin would provide data that are adequate to estimate evaporation from Lake Mead.

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Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83).

Background The Las Vegas, Nev., metropolitan area (Fig. 1) experienced some of the worst flooding in recent years on July 8, 1999, when thunderstorms passed through Las Vegas Valley. Floodwaters from these thunderstorms caused damage to public property amounting to $20,500,000 and damaged or destroyed 369 homes (Manning, 1999). Also attributed to the floodwaters were two fatalities one by drowning in Flamingo Wash and the other in a traffic accident (Schoenmann, 1999). This fact sheet characterizes the atmospheric conditions and documents the peak-discharge estimates from this flood event. Las Vegas Valley is drained by Duck Creek, Tropicana Wash, Flamingo Wash, Las Vegas Wash, and several smaller tributaries. Water in these drainages generally flows eastward through Las Vegas to Las Vegas Wash and on toward Lake Mead, an impoundment of the Colorado River. Within the Las Vegas drainage basin are several flood-control facilities that were designed by the Clark County Regional Flood Control District to store water from flash floods temporarily to mitigate downstream flooding and property damage.

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