DUCHESNE — Three persistent leaks, in the Upper Stillwater Dam, first discovered just a year after the dam was completed in the fall of 1987, are going to be fixed once and for all this fall. But before that can happen the reservoir, about 30 miles northwest of Duchesne, will have to be drained.
Plans call for draining the dam in the late summer and early fall, said Tom Bruton, Strawberry Aqueduct coordinator for the Central Utah Water Conservancy District. The dam is being drained now but just under normal operations to prepare for incoming spring runoff
"What we plan on doing is operating it normally in the spring and once it fills, probably around the first week of July, then we begin draining until it is at the minimum level we can drain it. That will allow for the installation of PVC membrane over three cracks on the upstream phase of the dam," Bruton explained.
Two prior repairs on the cracks in the dam — one in 1988 and the other in 1992 — failed to adequately remedy the problem. The placement of the membrane is expected to be a permanent solution.
"The prior repairs were grouting contracts and the grout has deteriorated since it was injected in place. This is a different type of a repair, a membrane serves as a barrier between the water and the dam, and this should be a final fix. . . . That's what it's engineered for," said Bruton.
The Bureau of Reclamation will pay the cost of the repairs, which engineers have estimated at between $1 million and $5 million. The contract is pending negotiations but is expected to be officially awarded March 1 to Carpi USA.
Water in the dam will be drained down to 149 feet below the spillway at the crest. Work is expected to begin on Sept. 1 and be completed by Dec. 1, according to Bruton.
The early draining of the reservoir shouldn't impact downstream irrigators in the basin.
"If it's requested by the river commissioner, the natural inflow will be bypassed through the dam to satisfy senior water rights. The water we take out of Stillwater is then replaced by water out of Starvation for farmers on the lower Duchesne (river). We're preparing Starvation to be full as of April 1."
The storage water in Stillwater is primarily for supplementing Strawberry Reservoir, so Strawberry might be a little lower than normal if it becomes necessary to discharge water downstream. Strawberry filled in 1998, so it is not critical this year, Bruton said.
The Upper Stillwater Reservoir is expected to return to normal operations in 2001.