Montana has 3,500 inventoried dams and possibly as many as 10,000 if stock ponds are included, says Michele Lemieux, manager of the Montana Dam Safety Program and civil engineer with the Montana Department of Natural Resources and Conservation.
Although most of those dams are too small or remote to endanger human life if they fail, it’s important that owners know how to inspect, maintain and operate them, Lemieux said. To provide that training, the DNRC hired Montana Watercourse at Montana State University to organize free workshops that will target the owners of small Montana dams.
“Failures have great impact on county resources, often involving local sheriff, county commissioners, county road crews and local emergency responders,” Lemieux said. “In many instances, local emergency responders are unfamiliar with the dams located in their areas and dam safety procedures. Providing county personnel with training and information on how to identify and respond to dam problems will improve response and minimize damage.”
Janet Bender-Keigley, program coordinator for Montana Watercourse, organized a May 31 workshop in Harlowton and said other workshops will be held this year.
Scheduled so far are an Aug. 3 workshop in Kalispell and an Aug. 16 workshop in Billings. Each will run from 11:30 a.m. to 3:30 p.m. and includes a free lunch. The Kalispell workshop will be held at the Montana Department of Fish, Wildlife and Parks headquarters at 490 N. Meridian Road. Participants must register by July 31. The Billings workshop will be held at the Northern Plains Resource Council at 220 South 27th Street. Participants must register by Aug. 13.
To reserve a spot, call (406) 994-6671 or email [email protected].
Plans are under way for fall workshops in Great Falls, Malta and Miles City, Bender-Keigley said.
Participants will learn how to inspect dams, rehabilitate outlet pipes and control aquatic weeds and invasive species, Bender-Keigley said. The workshops will also cover concrete repair and emergency actions in case of dam failure.
Lemieux recommends that owners of small rural Montana dams inspect their dams annually and after any noticeable earthquake. Northwest and southwest Montana have the highest probability of seismic activity, she said. Among other things, owners should examine concrete for cracks, rust stains and seepage. They should check corrugated metal pipes for corrosion, check the embankment for rodent holes, watch for new seepage and sinkholes, and periodically remove small trees.
“Trees are fine around reservoirs, but keep them away from the dam,” Lemieux said.
The design life of corrugated metal pipes ranges from 30 to 50 years, depending on the surrounding soils.
“When they fail, they can take out the whole dam,” Lemieux said.
She added that failure of corrugated metal pipes is the most common cause of dam failures in Montana.
Failures become more common as dams begin to age, and most of those failures are caused by a lack of preventative maintenance, Lemieux said. Some of Montana’s dams are more than 100 years old, with most of the older dams made out of earth and the larger made from concrete.
The Yankee Doodle Tailings Dam near Butte is Montana’s tallest dam, standing 570 feet high, Lemieux said. The Fort Peck Dam is the state’s largest.
Of all the dams in Montana, 150 are classified as “high hazard” and subject to strict state and federal regulations. The classification means their failure could endanger life downstream, but it doesn’t reflect the actual condition of the dams, Lemieux said.
Montana’s other dams are classified as “significant hazard” or “low hazard,” and it’s up to their owners to maintain them. Significant hazard refers to the potential for significant property or environmental damage downstream. Low hazard refers to limited or no property damage during failure. Most of Montana’s significant and low hazard dams are in Eastern Montana. The owners might be ranchers, cities or counties.
The DNRC issues permits for the high hazard dams, but not the others, Lemieux said. Since the Dam Safety Program focuses its outreach and education efforts primarily on high hazard dams, owners of low and significant hazard dams would benefit from the upcoming workshops, she added.
Montana’s dams serve a variety of purposes, including flood control, irrigation, water supply for livestock and recreation. Small ponds built for their aesthetic value tend to be located in Western Montana, while dams in Eastern Montana are more likely used for irrigation or livestock, Lemieux said.
Funding for the dam owner workshops came from a $17,000 grant awarded by the Federal Emergency Management Agency to the DNRC.
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