100-year Storm Event

On July 8, 1999, the Las Vegas Valley experienced a 100-year storm event. Although the Valley frequently gets flash floods throughout the summer months, this event had a tremendous impact.

7/8/99 Northshore Road notice the muddy water

The Las Vegas Wash is the single drainage point for the entire Valley. This means that all of the stormwater, with the exception of the water absorbed into the soil, must exit the Valley through the Wash.

The Wash experiences approximately 150-200 cfs (cubic feet per second) of flow on a typical day. During this event, flows were recorded at approximately 16,000 cfs. The Wash channel widened as much as 300 feet at some points.
The property damage, both public and private, that resulted from this event was substantial. (Public property damage was estimated at over $20,000,000.) One mobile home actually fell into the Flamingo Wash because of the bank eroding beneath it. There were two deaths during this event. One death was a drowning and the other was in a weather related traffic accident

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Historic Lateral site much faster flows than on a typical day

When the flows reached the Lake Las Vegas intake pipes (where the Wash flows underneath Lake Las Vegas), there was so much debris being pushed against the grates and the flows were so fast that workers were unable to remove the debris fast enough. As a result, the water flowed up and over, into the lake at Lake Las Vegas. At the other end of the lake, the spillways were hard at work.

7/8/99 Las Vegas Bay confluence, notice the sediment

At Las Vegas Bay (the location of the confluence of the Las Vegas Wash and Lake Mead) the amount of sediment that entered from the Wash was tremendous.

Due to this storm, we now have a better understanding of how these events affect the banks of the Wash and, therefore, how we should approach stabilizing them. The following chart shows the peak discharges during the event as well as the previous maximum discharges for these locations: