Historic Lateral Grade Control Structure

The Historic Lateral Weir was originally built as a temporary grade control structure by the Colorado River Commission in 1984 to protect the Las Vegas Lateral bringing water to the Valley from the Southern Nevada Water System. The existing pipe was later relocated deeper downstream and is now over one hundred feet below the Wash. The weir was left in place after the pipe was moved, but received significant damage from several storm events in the late 1990s, particularly the 100-year flood event of July 1999.

During the July 8, 1999 storm, the flow of stormwater throughout the Valley was tremendous. Approximately 16,000 to 20,000 cfs (cubic feet per second) made its way down the Las Vegas Wash during this storm, whereas the normal flow is 220 cfs or 153 million gallons per day.

Erosion during this storm widened the Wash by 300 feet in some areas and carried tons of sediment into Las Vegas Bay. The temporary grade control structure eventually gave way to the rushing flows.

Construction of the current, permanent structure began in July 2000 and was completed by December 2000. The weir was designed as a three stage, dumped rock riprap chute spillway. The structure has a 4.5 feet minimum and 8.5 feet maximum height, and is 518 feet wide as it crosses the Las Vegas Wash. The dumped rock riprap configuration was chosen over more conventional gabion or concrete designs due to flexibility, constructability, maintainability, and cost considerations.

Historic Lateral during construction, November 2000.

December 2000

April 2004

May 2006