Leaks in the Iron Mountain Lake dam have officials on watch to make sure new rainfall does not push the dam past its limits.
Bismarck Fire Department called in Bob Clay, chief engineer for the Missouri Department of Natural Resources (DNR) dam and reservoir safety program, Saturday afternoon to inspect the dam after getting reports that water was leaking through several spots.
“We found several seeps along the toe (next to the road) of the dam,” Clay said. “We have a potentially dangerous situation.”
Drainage pipes located in the spillway about three feet below normal water level usually are opened in the winter, but were still closed when the rains drenched the Parkland Friday night and Saturday morning. That led to the water level in the lake rising over the top of the spillway. However, the higher level also caused water to leak through the earthen dam that was build in 1841. The concrete spillway was added in 1941, according to lifelong resident Mary Self.
“Dirt and sand were washing out of the holes,” said Joe Robinson, who has lived at the lake community for 37 years.
When the rain stopped, the spillway helped the lake level slowly drop.
Clay believes the leaks start near the top of the dam, because the flow lessened as the level dropped in the lake.
“They’re going to open the pipes when the water level goes down,” Clay said. “Hopefully that will before the next round of rain.”
Clay said up to 15 inches of rain is predicted to fall on the area by Wednesday. If that amount comes over a span of days, the lake level drops enough, and the pipes are opened, the dam should be able to handle it, even with the leaks, he said.
“But if we get 15 inches in a 12-hour period, the lake will overtop the dam and the leaks will be meaningless,” he added. “If the lake level goes up and those leaks start boiling again, they need to think about getting people out of those houses downstream.”
City workers will keep an eye on the lake level and leaks throughout the night.
If the dam were to collapse or be breached, water from the 55-acre lake would dump into Indian Creek, which runs into the St. Francis River. Houses along those waterways would be in danger of flooding.
The leaks you see often are not as big a problem as what you cannot see, Clay said.
“We see a little hole, but we don’t know how much damage there is inside the dam,” he explained. “If it’s big enough and collapses, there could be a rapid collapse of the dam.”
DNR dams staff have seen several sinkholes in dams that fell in without warning or prior indication of problems.
Clay theorized that the leaks in the Iron Mountain Lake Dam are due to large trees – some three feet in diameter – that used to grow on type of the dam. When the roots die and rot, they leave channels that water can run through.
Clay saw signs that muskrats have at some point burrowed into the dam on the lake side. They likely dug holes into the dam that also would allow water to seep through.
Once the rain stops, the city needs to address the leaks. Clay said he believes they can be repaired and it will not be necessary to replace the dam.
Paula Barr is a reporter for the Daily Journal and can be reached at 573-431-2010, ext. 172 or at firstname.lastname@example.org.