A storm canal project along Fort Apache Road south of Russell Road is one of several flood control projects under way in the Las Vegas Valley. Roughly $136 million in flood control work has been finished in the past 12 months. Photo by Clint Karlsen.

Flood control work over the past year will probably help lessen the impact of annual monsoonal storms in Southern Nevada but it won't eliminate the risk of flash flooding, authorities say.

Roughly $136 million in flood control work has been finished in the past 12 months, with $61 million in more work under way in the Las Vegas Valley, Boulder City and Mesquite, according to officials with the Clark County Regional Flood Control District.

"It's an ongoing process," Betty Hollister, a district spokeswoman, said recently, adding that the district has 73 basins and 445 miles of canals, with plans for an additional 62 basins and 413 miles of canals to be built over the next 30 years.

Although the northwest valley has been a recent frequent target of flooding, Hollister said it's tough to predict a specific problem area.

"It's hard to say. We don't know where it's going to rain," she said. "While we're better protected today than last year or three years ago or five years ago, there's still a potential for problems. To say there's a particular problem area, no," there isn't.

Southern Nevada's desert climate disguises the valley's susceptibility to severe flash flooding in July, August and September, when the annual monsoon pushes moist air from the gulfs of Mexico and California into the valley, according to the National Weather Service.

The weather shift results in sudden thunderstorms. Although the monsoon months see less precipitation than January, February and March, storms are more intense during the monsoon.

The valley averages 14 thunderstorm days a year, and nine of those days are in monsoonal months, according to Weather Service statistics.

Rock-hard dry ground and uneven topography turn the downpours into fast walls of water that move from west to east, toward Lake Mead.

This year, various agencies coordinated by the flood district finished 21 flood control projects, including the construction of or improvements to three detention basins and 12 drainage canals in the valley.

Those facilities include basins along Rainbow Boulevard, Ann Road and in the Lone Mountain area; and the Duck Creek, Flamingo Wash, Red Rock Channel, Sloan Channel, Upper Blue Diamond Channel and Upper Las Vegas Wash canals.

Projects still under way and expected to be completed before next monsoon season include an expansion of the Upper Flamingo basin and construction of the Lower Blue Diamond Channel.

Hollister advises residents to watch for flooding if they live in houses lower than street level or in a house built before 1990, when flood-related zoning rules were more lax.

She also asks that residents consider getting flood insurance, even if their house is thought to be in a safe area.

"Even when we're finished (with all flood control work), there's always the potential for a flood larger than what we built for," Hollister said.

Residents also should watch for debris blocking inlets and canals, and alert authorities as needed.

Drivers are warned not to drive through streets with rushing water, or where the water is over the curb. Cars can hit debris hidden in floodwaters or be swept away with surprising ease by even a few inches of fast-moving water.

"More people die in floods than any other natural disaster. Most of those people die in cars," Hollister said. "We want people making smart decisions."

As part of the flood district's annual awareness campaign that uses slogans based on fictitious vanity plates, this year's slogan is "UNOBETR," or "you know better," than to drive through floodwaters, Hollister said.

More information is available by calling the flood district at 455-3139 or going online at www.regionalflood.org.