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Bull Lake Dam earmarked for $26 million addition

Jan 16, 2014 - By Eric Blom, Staff Writer

An old spillway is to be replaced, although it has never proved necessary in the history of the dam.

The Bureau of Reclamation is planning to build a $26.4 million spillway for Bull Lake Dam. The federal agency informed parties involved in the project and gathered comments at a public meeting Jan. 14.

"Reclamation wants to take action to fix it before something potentially fails out there," said Mahonri Williams, Wyoming Bureau of Reclamation water and lands coordinator.

Federal dollars would cover 85 percent of the project's cost, but the Midvale Irrigation District, which operates the dam and uses water from the Bull Lake Reservoir, would be responsible for the remaining $3.96 million.

BOR deputy area manager Lyle Myler said the bureau would have Midvale pay its share with a 50-year loan. There would be no reservoir restrictions during the anticipated two to three years of construction.

The project still must go through a National Environmental Policy Act process and receive Congressional approval. BOR hopes to have approval by April and award a contract in September.

Damaged dam

Bull Lake is a reservoir supplying the Midvale Irrigation District, holding 152,000 acre-feet of water and located about three miles west of the intersection of U.S. highways 26 and 287.

The spillway is a chute near the top of the dam that is able to pass 15,000 cubic feet per second of water and acts as a backup in case the regular outlet works cannot discharge water fast enough to prevent it from topping and damaging the earthen dam.

The spillway has never been used in the dam's 76-year history.

Freezing and thawing have weakened concrete supporting metal gates at the opening of the spillway so much that the gates eventually could stop working, Williams said. If they cannot open in an emergency, water could overrun the top of the dam.

Additionally, the Bureau of Reclamation found voids under the concrete of the chute, Williams said. If water ran over the chute, chunks of concrete could break out.

Seepage under the chute causing the voids eventually could erode the dam and cause it to fail, Williams said.

"The facility is to the point where you need to take corrective action now," he said

But Williams cautioned against panic.

"It's had water against those radial gates every year," he said. "It's still standing."

Construction

BOR's plan is to build a new spillway, with the same 15,000 cubic feet per second capacity, roughly 700 feet south of the current one, remove the existing spillway gates and bury the old chute. In an emergency, water would pass over the new safety feature, down a new 94-foot-wide chute and along a 650-foot earthen channel to rejoin Bull Lake stream near the dam's outlet works.

The project would employ about 15 to 20 people, Myler said. Any contractor selected would have to meet Tribal Employment Rights Office requirements.

Access to the south side of the dam would be closed during construction, because a bridge over the existing spillway would be removed and rehabilitated to cross the new spillway, Myler said. Recreationists could experience delays getting to the other side as well because of construction traffic.

In the end, though, the rebuilt bridge would be wider, Williams said. Equipment for the spillway gates blocks part of its width currently but would be removed when it is reinstalled.

The bureau hopes to receive permission to improve an existing road so construction vehicles could access the site more easily.

The route crosses tribal and Nature Conservancy land, and BOR would need approval from both groups.

The project also might have to work around wintering swans.

Mark Hogan, state coordinator for the U.S. Fish and Wildlife Service's Partners Program, said 20 to 40 birds spend the winter in Bull Lake Creek below the dam. He asked if the new road could be built out of their view and if some construction activities could take place when the swans are not there.

"At this point we definitely have the chance to look at that," Bureau of Reclamation's Wyoming manager Coleman Smith said.

An environmental assessment should be available for comment in February, he said.

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