Wednesday, April 19, 2006

Flood threat keeps cities on alert

Big Wood River causes minor flooding near Gooding

Two Canada geese hunker down and peek out of their nesting box Monday near West Magic, near the Blaine-Lincoln county line. Recent high water has claimed nests and eggs that have been located in more unfortunate spots on the ground. At least for now, this nesting box is a safe place for egg survival. Photo by Willy Cook


Faced with the threat of flooding, communities in the Magic and Wood River valleys continue to prepare and keep a watchful eye on swollen rivers and streams.

Minor flooding was reported near Gooding on Monday as the lower Big Wood River overflowed its banks, unable to contain water released from Magic Reservoir, which is rapidly filling to near capacity for the first time in a decade.

"We didn't lose any houses, but we lost a few outbuildings," Gooding County Sheriff Shaun Gough said Tuesday. "We've got through the worst of it for now. The water peaked yesterday but it's going down today, we hope."

Water discharge from Magic Reservoir dropped to about 4,600 cubic feet per second on Tuesday, down from 5,500 cfs Monday.

A flood warning issued by the National Weather Service remained in effect for Gooding County. Flood watches were extended until today, April 19, for the Shoshone and Richfield areas in Lincoln County.

"All rivers and streams in the area remain high and have the potential to be dangerous," NWS advised Tuesday. "Persons should continue to take precautions and remain vigilant."

Gov. Dirk Kemptorne declared a statewide disaster flooding emergency on Friday as snowpack near 150 percent of normal melted off mountains and prairies. Flood warnings have also been issued for the Portneuf River in Bannock County and the Snake River in Washington County.

Although the Gooding area escaped serious flooding on Monday, Gough cautioned that the threat isn't over.

"A lot of it's going to depend on the weather. It was colder up there this morning, but we're preparing for warmer weather," he said.

Operators of Magic Reservoir in southern Blaine County began sending water over its seldom-used dam spillway Friday, prompting the National Weather Service to warn of expected flooding downstream.

Magic Reservoir managers were spilling the water to allow space for heavy runoff behind the century-old earthen dam, the top of which has been dry since 2000 due to six years of drought.

"We want to leave ourselves a little bit of room in the top part of that dam in case we get a ton of influx," said Lynn Harmon, manager of Big Wood Canal Co.

The reservoir rose to the level of the spillway Thursday evening. Officials were concerned that the volume through the spillway and outlet gates, where water is normally released, would reach 6,000 cfs by late Friday night. At 6,000 cfs, the Big Wood would most likely flood around Gooding near where the river passes under the Idaho Highway 46 bridge. Gooding is about 35 miles north of Twin Falls.

Officials also say that at 6,000 cfs the Big Wood could cross the desert and join with the Little Wood River near Shoshone. Workers also have been shoring up an area near the Shoshone Ice Caves to keep the Big Wood River from jumping its banks.

"We're looking at possible flooding along both rivers," said Todd Jaynes, Lincoln County disaster services coordinator.

He said some river water can be diverted at two places above the town, but if that isn't enough the county has evacuation plans.

"We have those things we can do in case it gets too deep," he said. "Then at that point we're mostly spectators."

Jaynes said sandbags will be used in Shoshone, which he said hasn't flooded in about a century.

"Shoshone city has some sandbags," he said. "The problem with the sandbags is just the sheer area you have to sandbag to have an impact."

Water volume in the reservoir reached about 172,000 acre-feet when it began spilling. The level of the spillway on Magic Dam can be raised so that the reservoir can hold about 190,000 acre-feet.

The canal company has been releasing the maximum 1,250 cfs possible through the reservoir gates since early April to try to avoid overfilling the reservoir, said Jay Breidenbach, a weather service hydrologist with the National Weather Service in Boise.

He said most of the water entering the reservoir now was from Camas Creek, which drains Camas Prairie.

The Big Wood River also flows into the reservoir and is fed by snowmelt from the Big Wood Basin. The snowpack in the basin is 150 percent of normal, Breidenbach said, and the spring melt hasn't yet started.

"We expect the highest flows on the Big Wood in May," he said. "That's pretty fortunate for what's going on right now."

Once those flows start, much of it could be siphoned off for irrigation if the weather remains dry, reducing flood threats downstream.

"That's the hope," he said. "Unless we have a very wet May."

Harmon said it's too wet for irrigators to use much more water now, but that could change with a dry spring.

Kempthorne made the statewide disaster flooding emergency declaration Friday evening, saying the state faced "peril to public safety and property which is likely to be beyond the control of Idaho's county governments."

On Saturday, the National Weather Service had issued flood warnings for Gooding, Blaine and Lincoln counties, as well as less urgent flood watches for Bear Lake, Bonneville, Caribou, Cassia, Franklin, Fremont, Oneida and Teton Counties.

The governor's flood declaration was a dramatic change from recent years, when several southern Idaho counties received drought emergency declarations each fall.

"Above-average snow pack in Idaho's mountains, above-average spring precipitation, and a rise in temperatures has created an imminent threat of flooding along rivers and streams in Idaho," Kempthorne said in a statement announcing the declaration.

The declaration allows state officials to administer disaster emergency account funds up to $50,000 to provide assistance to local agencies. The state of emergency lasts for 30 days, but it can be ended early or extended at the governor's request.

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