Officials Evacuate Area Below Dam Forest Also Closed After Cave-In Detected On Earthen Dam

Concerned that the East Fork Dam southwest of here might break, Granite County officials on Friday ordered the mandatory evacuation of an area immediately downstream from the earthen structure.

The order was a step up from a previous request for voluntary evacuations. The new evacuation order prevails from the dam to Squaw Rock Campground, a distance of about 21-1/2 miles dotted with ranch houses and recreation sites.

The Granite County Sheriff’s Department said it was unknown how many people left the area. Officials said there would be no citations for refusal to comply, but people choosing to stay would be asked to sign statements that they were told of risks.

The evacuation order was issued because of concern about a small cave-in detected Thursday at the dam 15 miles southwest of Philipsburg, said Jim Kelly, disaster services coordinator for Granite County.

Also on Friday, the Forest Service closed some federal forest lands in the area.

The chance of the dam failing remains small, said Rick Bondy, an engineer for the the Montana Department of Natural Resources and Conservation.

He said officials have not determined what’s wrong with the East Fork Dam, but one theory is that fine sand and silt are being eroded from the interior of the earthen structure. That type of problem can be fixed, but would require draining the East Fork Reservoir, Bondy said.

The reservoir is being lowered, and Bondy said emptying it is being considered. If the reservoir is drained, there will be an attempt to do so gradually, on a schedule that allows farmers to get the irrigation water they need this summer, he said.

Meanwhile, the Forest Service has suspended public use of the Rock Creek area of the Lolo and Beaverhead-Deerlodge national forests. The area covers about 50 miles, from the dam to Interstate 90 above Clinton.

“We’re hoping the situation doesn’t get any worse, but we want to stay on the safe side in case something bad does happen,” said Winnie Schreiber, a Forest Service spokeswoman.

A small cave-in about 100 feet up the face of the dam was detected on Thursday, heightening concern about the structure.

The cave-in measured 6 feet in diameter, and about 26 inches deep. The depth increased by an inch or so on Friday, but Bondy said that was expected and was not a serious concern.

Officials have been monitoring the dam closely since Sunday, when muddy water began flowing from a drain where the flow normally is clear.

On Wednesday, the Forest Service informally notified forest users of concerns about the dam, and many left at that time, Schreiber said. On Friday, there were relatively few people in campgrounds covered by the forest closure.

Roadblocks were set up Friday.

The dam, managed by the Flint Creek Water Users Association, was built in the 1930s.

The reservoir holds 16,040 acre-feet of water, 14,000 of it for irrigators.