Hard rain: Caution urged as monsoon season nears

Friday, June 29, 2001 | 10:45 a.m.

Aflash of lightning flares from a towering black cloud. Thunder rumbles in the humid air, accompanied by a downpour that drenches desert dwellers accustomed to clear blue skies.

Sunday officially starts what meteorologists call the monsoon season, which can bring flash floods to the desert.

The rains -- spawned by a collision of weather systems from Mexico and the California and Gulf coasts -- often start in the Spring Mountains, west of the Las Vegas Valley, trickling at first, then gaining strength as rivulets join to become streams. The streams turn into walls of water as the rain descends more than 2,800 feet in elevation to the valley's washes, taking roads, cars and some small homes.

When that scenario occurred in 1999, floodwaters rolled across Boulder Highway from the valley's major washes, closing intersections at Sahara Avenue, Flamingo Road, Russell Road and Tropicana Avenue.

The valleywide flood inundated the Miracle Mile Mobile Home Park on Boulder Highway south of Sahara Avenue, sweeping homes into the channel. Rampaging waters cut the valley in two, filling the Charleston Underpass and intersections along Main Street at Washington Avenue and Bonanza Road.

The total damage to public property added up to $22 million.

This year forecasters expect a normal year of precipitation, which means the valley could have its share of flash floods. Long-range forecasts predict that summer storms could come as early as Tuesday or Wednesday, Larry Jensen, chief weather service meteorologist in Las Vegas, said.

But even if it's a wetter than usual year, flood control experts say the Las Vegas Valley is better equipped to forestall damage from raging waters than it was two years ago.

Southern Nevada weather experts now have the instruments to spread warnings faster than they could on July 8, 1999, when two storms joined forces over the western half of the valley and created a 100-year flood.

The county's Regional Flood Control District also has completed more than 20 major projects since 1999.

One project includes a bridge at Boulder Highway straddling the Flamingo Wash. At a cost of $4.8 million, paid by the Nevada Department of Transportation, the bridge is accompanied by $1.2 million in channel work funded by the flood control district. The project was completed this month and will help protect the Miracle Mile Mobile Home Park.

Another project completed this month is the Duck Creek-Robindale Road Bridge, replacing an undersized culvert that allowed floodwaters to top the bridge. At a cost of $1.1 million paid by Clark County, the new structure protects about 29 acres with homes.

The next phase of the Flamingo Wash project includes a 3/4-mile concrete-lined channel between Boulder Highway and Mojave Avenue that will better protect the mobile home park. The project is expected to be completed by June 2002 at a cost of $7.7 million, paid by Clark County.

Meanwhile, flood control work continues on the Charleston Underpass, creating underground channels to direct water away from the flood-prone dip under the Union Pacific railroad tracks downtown. The $33 million project is due to be completed in about a year.

In all, about 57 detention basins and about 270 miles of channels and underground storm drains have been built since 1989, some of them massive channels and basins buried beneath roads for future protection from flash floods, flood district spokeswoman Betty Hollister said.

They have been paid for in large part by a quarter-cent sales tax in place for 12 years, which has raised more than $408 million.

It's a worthwhile investment, flood control officials say.

Since 1960 the area has experienced nine "million-dollar floods," meaning property damage was valued above $1 million. And most of those figures cover public property. The loss of private property could be much higher.

And the projects protect more than property, flood control officials note.

Floodwaters, once they engulf a car or person, are tough to escape. An Olympic champion cannot outrun floodwaters dashing at 30 mph, and less than a foot of water can float the family van, Hollister said.

Since 1977, 26 people have died in Southern Nevada floods.

While 12 square miles of the Las Vegas urban area is considered protected from flooding because of the projects, there is much more work ahead to flood-proof the rapidly growing area, Regional Flood Control General Manager Gale Fraser said. The flood control district works with Clark County and the cities to build each project.

While the local government agencies have done a good job of protecting people from floodwaters, until the Las Vegas Valley is fully developed around 2030 and all flood control projects are completed, there will always be a threat from a major thunderstorm, Jensen said.

"The Regional Flood Control District has done an absolutely fantastic job," he said. "But it will take many years for them to complete their work, and Mother Nature has many ways to circumvent those projects."

So what's the best advice experts have when you are caught in a thunderstorm in Southern Nevada? Avoid moving water, period, Fraser said.