PROVO — When the rains came and the waters rose, Carol Bird froze.

She stood in stunned silence as a river of brown water came rushing toward her Cedar Valley home. It descended upon her house with force — shattering the basement windows, collapsing a sewer pipe and sweeping away treasured mementos.

It's been nearly a month since flash flooding caused an estimated $350,000 in damage to some 32 homes in Cedar Valley, but the cleanup effort continues, and, as is evident by the remaining sandbags, the community remains wary.

"It's pretty scary. Before, when there was a thunderstorm, we would say, 'Oh good, we need the water,' " said Rita Bowers, Bird's neighbor. "Now every time the clouds start swirling and the rains come, we start calling people. We're just waiting on the edge."

Residents in Farmington, South Provo and Santaquin can relate. Folks in those Wasatch Front cities have recently endured at least one mudslide. Flash flooding — once considered a freak occurrence in Utah — is becoming increasingly common.

Why? There are several factors. A prolonged drought has contributed to forest fires, which in turn consume vegetation that would stop debris flow after a heavy downpour. But perhaps the greatest culprit is growth.

Flash floods in Santaquin, Farmington and Cedar Valley never would have happened with better city planning, geologists say.

"One of the biggest problems is the encroachment of subdivisions into Forest Service land," said Gary Christensen of the Utah Geological Survey. "We're building over alluvial fans where water and debris has flowed for years during rainstorms."

The Eagle View subdivision in South Provo, for example, is built on Buckley's Draw, a natural drainage. Last August, the city spent $180,000 on a 1,600-foot trench to protect the homes below from slides.

So far, the trench is working.

"We've been really lucky — or blessed — not to have a huge downpour. While someone else gets an inch or an inch and a half, we get a quarter inch," said Provo City Councilman Dave Knecht, who lives in the neighborhood. "If we were to get another large rainstorm, I think we could have an incident."

Both Christensen and Todd Nielson of the Natural Resources Conservation Service said cities should pay for geological studies to determine the likelihood of flooding before allowing hillside construction.

In cases of bad planning, there are several precautions city officials can take, Christensen said. A debris basin, essentially a small dam, is most effective for catching run-off above subdivisions. When that is not possible, a trench can be used to divert water away from homes. The trench at Buckley Draw channels water into an empty field.