By Ellen Thompson/Havre Daily News/ethompson@havredailynews.com
State and federal regulatory officials have prioritized a single problem among Beaver Creek Dam's many bugaboos - seepage from the dam's eastern abutment.
Since the reservoir was filled in 1977, different engineers and regulatory agencies, all with some say over the dam, have suggested different responses to the dam's problems, sometimes working at cross-purposes. This month they sat at one table and developed a game plan.
For the next year, pressures at various test holes in the dam will be monitored to find the source of water that has been, at times, seeping from the eastern abutment. More test holes and a system of pipes will be installed to help accomplish this.
"There's quite a bit of liability having those pressures at the dam," state Department of Natural Resources and Conservation dam safety manager Michele Lemieux told the Hill County commissioners, referring to vertical underground water pressures that could cause erosion in the earthen dam.
The dam is classified "high hazard," which means that failure would flood the first level of homes, water would go over the top of a paved highway or an overnight campground would be covered by water, said DNRC engineering analyst Marvin Cross. In the case of Beaver Creek Dam, all three conditions are true. The area with homes that would be threatened by a dam failure is in Herron's Park, near Fort Assinniboine.
Cross said fine material found in the water seeping out of the dam would indicate a problem.
So far, in the test holes that already exist, fine material has not been found, Cross said. But the water being tested is coming from several sources. Pipes in the ground will separate water from different sources to give engineers a better idea of what is happening underground.
"As long as you don't have any material moving, you don't have a problem," he said.
When the dam was first filled, seepage in the western abutment was immediately apparent. A corrective drain was installed and has been working well since, Cross said.
In 1985, seepage on the eastern side of the dam was discovered and plugged. The problem has reoccurred, however.
Currently, the seepage is plugged, but "the problem is not fixed, not permanently," Cross said.
An inspection in 1999 also uncovered a problem with the dam's outlet gate, and for a few years it hogged the attention of local and state dam regulators. The dam has a small and a large gate. The large gate, which would need to be opened in the event of heavy runoff to prevent spillage over the top of the dam, is not operating properly.
In 1999, the county received a $75,000 grant to study the problem, said Bear Paw Development Corp. program director Annmarie Robinson, who has worked on writing grant proposals for the dam.
The county had more test holes drilled, and divers inspected the outlet gate as well as another problem, crumbling of the concrete base of some of the dam's structure.
In 2003, with the results of these studies in hand, the county commissioners went to the state Legislature to ask for a $100,000 grant through DNRC to have the outlet gate fixed.
The plan put forward was to install new outlet works for the dam, but the USDA Natural Resources Conservation Service, which oversees all high-hazard dams in the country, testified that it would only support a project to repair the current drains leading from the dam, said HKM Engineering water resources senior project manager Jason Thom. The firm was hired by the county to study the dam.
County Commissioner Doug Kaercher said the county was caught in an awkward position before the Legislature when not all the entities agreed on what should be done. The project wasn't funded.
Though the outlet problem was not fixed, it has been moved down in priority so that the seepage problem can be addressed first. One reason, Lemieux said, is that the state has seen similar vertical pressures in a dam elsewhere in Montana that caused DNRC to look at such pressures as an immediate threat.
