Work on Beaver Creek Reservoir drain nearly done

Associated Underwater Services Inc. employees of Spokane, Wash., replace the hydraulic cylinder that opens and closes the "guardian gate" on the upstream end of Beaver Creek Reservoir Tuesday afternoon.

A second round of deep-lake diving is going on south of Havre, as divers are back in Beaver Creek Reservoir to repair a broken drainage gate.

"I think everything should be set by Saturday or Sunday, " Mark Yerger of the U. S. Department of Agriculture's Natural Resource and Conservation Service said Tuesday in a telephone interview from a boat on the reservoir.

The work is the final part of fixing a drain for the reservoir which was damaged last year when two bolts connecting the steel gate to the hydraulic cylinder used to open and close it sheared off, dropping the gate to an almost-closed position.

It remained in that position, with the county employees unable to either fully open or close it, until divers from Associated Underwater Services Inc. of Spokane, Wash. were able to dive last November, determining what was the problem, opening the gate and bringing up the hydraulic cylinder.

Divers from the company returned this week, starting their repair operation Monday. Yerger said he expects the work to be completed today.

This diagram, not to scale, shows where divers are working this week. Divers must dive about 45 feet to a 4½ by 4½ foot wide concrete riser, and then another 37 feet to the bottom of the riser to work on the malfunctioning drainage gate. The trip is deep enough that divers must decompress on their way to the surface, or risk decompression sickness, commonly known as the bends.

The level of the reservoir is down, with water released to drop it about 11 feet below the spillway. The reduced level lets the divers stay under longer, said Marvin Cross of the state Department of Natural Resources and Conservation. Five divers are working on the project, with each only able to dive twice a day and having to decompress each time they come up. Cross said the lower level allows them to stay down about 15 minutes longer on each dive.

Hill County Commissioner Kathy Bessette said that once the problem is fixed, the reservoir will be allowed to rise.

"We're going to try to get some back up there, " she said.

A complex drain system

The gate being repaired is called a guardian gate, actually used to shut off flow to a lower chamber where the main drainage gates are located.

The system was put in place when the dam was built in 1974. The dam and reservoir are multipurpose, used for irrigation water storage, flood control and recreation.

It is owned and operated by Hill County, with supervision by both state and federal agencies.

It was designed by USDA's Natural Resources Conservation Service. NRCS also helped provide funding for the construction, and is involved in oversight of its operations by the county.

The state Department of Natural Resources and Conservation also provides oversight. DNRC issues the permits to allow the dam's operation.

The drainage system is composed of the upper gate, about 400 feet upstream from the dam, and a compression chamber at the dam itself. Two gates at that chamber are used to regulate the water flow out of the dam.

The upper gate is used to shut off the flow, allowing work in the compression chamber.

The divers working on the gate are at the bottom of a 37-foot high, 4½-by-4½ foot concrete riser, located about 400 feet from the dam. The conduit that drains the dam, which originally rerouted Beaver Creek while the dam was constructed, runs into the riser, then back out and to the compression chamber at the dam.

Two sets of gates at the compression chamber are used to regulate the release of water from the reservoir.

Grant-funded work, special equipment

The county is using parts of grants from both NRCS and DNRC to pay for the work, $100,000 from DNRC and $75,000 from NRCS. The grants originally were made to do other work on the dam, upgrading the berm on the downstream side and drilling wells to observe water levels and reduce water pressure.

Most of that work has been completed. When the scope of that project was reduced, DNRC and NRCS agreed to allow the county to use some of the funds to repair the guardian gate.

Bessette said the parts for the repairs had to be specially made, all from special stainless steel. A company in Billings made the hydraulic cylinder, while another company from Big Timber made the plate to connect it to the gate.

"Actually, even the bolts and the fittings have to be stainless steel, " she said.

Bessette said the cylinder probably could have been used for a few more years, but the county decided to replace it due to its starting to wear down.

"We don't want anyone to have to go down there again, " she said.

Replacing, repairing and connecting

Yerger said the conditions are good for the repairs to be complete by the weekend. In addition to replacing the cylinder, the bottom of the hydraulic lines and the connecting plate and bolts, the divers will have to use a compound to repair some damage caused by shaking due to the flow of water from the gate being partially open.

The compound can only be used in temperatures greater than 40 degrees Fahrenheit. Yerger said it takes about seven days for it to cure at 41 degrees. The water is closer to 60 degrees, and the compound should cure in about three days, he said.

"It's a good temperature for curing, " he said.

Next projects in planning stages

Cross said that once the guardian gate is fully operational, the next project could begin in earnest.

He said most of the work on the berm and wells is complete. The next issue is repairing the exit gates at the compression chamber.

The Hill County Commission is in the process of hiring a firm to complete the first report that will be needed for that project.

Cross said work on the lower gates had to be delayed until the guardian gate, which is used to shut off the flow to the lower compression chamber, was repaired.

"We really can't do anything on those until this is operational, " he said.