Friday, May 30, 2008

Heavy rains lead to flooding fears

Castle Rock Fire area remains susceptible to flash floods and debris flows

Express Staff Writer

Heavy rainfall led to the formation of several large pools of water on Warm Springs Road west of Ketchum this week. On Wednesday, the National Weather Service released a flash-flood watch for portions of south-central Idaho that also covered the 48,520-acre Castle Rock Fire area. Photo by David N. Seelig

A flash-flood watch released by the National Weather Service on Wednesday serves as a continuing reminder of the ongoing possibility for severe landslides and debris flows in the aftermath of last summer's Castle Rock Fire.

Officials with the weather service office in Pocatello issued the flood watch for a portion of Idaho's south-central mountains. The advisory, which extended through 10 p.m. Wednesday, covered the Big and Little Wood river drainages, as well as the Lost River, Pahsimeroi and Sawtooth mountains.

The advisory cautioned that portions of Idaho's central mountains received moderate to heavy amounts of rainfall early Wednesday morning, which further saturated already soaked soils. It went on to say that expected showers and thunderstorms and locally heavy rainfall could further exacerbate the problem.

"Areas that have received heavier rains in the past 24 hours and recent days will have soils that are saturated, thus leading to runoff and possible flash flooding," the agency warned.

By Thursday, National Weather Service officials had lifted the flash-flood watch, though they were still calling for a slight chance of continued rainfall and thunderstorms in the Wood River Valley region throughout the remainder of this week and into the weekend.

The flood watch advisory noted that flash flooding is of particular concern within the 48,520-acre Castle Rock Fire area west of Ketchum.

The weather service said the fire area will be "highly susceptible" to flooding as well as to mudslides and debris flows.

"If you encounter floodwaters please do not drive into these areas," the advisory stated. "Please turn around and find an alternative route."

The advisory explained that flash flood watches mean that conditions may develop that lead to flash flooding and mudslides and debris flows. Flash flooding is a very dangerous situation, the advisory stated.

Blaine County Commissioner Tom Bowman said the weather service had notified him that .37 inches of rain fell early Wednesday in the Rooks Creek drainage west of Ketchum. The drainage, heavily burned in the first few days of last summer's fast-moving Castle Rock Fire, has a remote weather station installed near its lower end. The weather station was installed after the fire to monitor for dangerous rainfall events that may lead to flash flooding and landslides.

Lands burned within the Castle Rock Fire perimeter will be especially susceptible to flash floods for several years to come, due in part to their lack of vegetative ground cover, which typically helps soak up moisture during periods of heavy rainfall. After heavy rainfall last fall, large amounts of mud, rock and organic debris swept off burned hillsides and down into the gullies in much of the Warm Springs Creek drainage.

The Sawtooth National Forest has installed signs on roads and trails throughout the fire area warning of the danger of flooding and landslides.

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