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Hillsboro Dam gets tested
City gathers data on dams ability to withstand water pressure
hillsboro dam
The City of Hillsboro is testing the dam on Hillsboro Lake to determine its ability to withstand water pressure. The Department of Natural Resources has rated the dam a high hazard over concerns that it may fail during a major flood and affect communities downstream. - photo by Hillsboro Sentry Enterprise archives

Hillsboro residents have been buzzing over testing being done at Hillsboro Lake to determine important data on the dam’s ability to withstand water pressure and the possibility of the construction of a spillway that would be used in the event of a major flood situation.

City Administrator Adam Sonntag discussed the situation in an interview with the Sentry Enterprise Tuesday afternoon.

He explained that the testing and eventual analysis will be used in future  meetings with the Department of Natural Resources (DNR), the state government agency that is responsible for the safety of other towns downstream that could be affected in the event of a major flood.

Sonntag and the City Council decided on the testing because the DNR has rated the Hillsboro Dam as a “high hazard.”

If the dam should fail during a major flood, the agency is very concerned about the towns downstream that would suffer a high cost in the loss of buildings and possibly lives.

As a result of that rating, the DNR has told the city that a spillway is needed and has set a 2018 deadline for the project.

In the event of a major flood, the spillway would divert water away from the dam and into another area, relieving pressure.

Construction of a spillway has been discussed by the Council but no decisions have been made, Sonntag reported.
“We’re talking about a major deal here, that would be costly and take plenty of planning time before work even started,” he stated. “We would need engineers and contractors.”

There is disagreement over the old data and some people think Hillsboro Lake is bigger than it really is. The differences have led to the newly established testing.

It is important to verify the dam’s capacity and the size of the lake.

The DNR is talking about the slim possibility of a 1,000–year flood in the future. The last major flood event in the area was apparently in 2008.

Sonntag reported that the Council has decided to hold back on some other projects while the spillway project is still in the exploratory phase, but the situation is certainly a community-wide issue.

“We’re trying to gather as much information as possible,” he said. “In the next year we plan on holding a public hearing and include the DNR and engineers along with our citizens.“We are going to be as responsible as possible and study the newest data. This could become very costly. We would like to avoid any construction that is not necessary.”

Sonntag stated that he believes part of this is an over-sell policy on the part of the DNR. He reported a similar situation is happening in the central Wisconsin community of Amherst, near Waupaca.

The City Administrator is well aware of the undercurrent in Hillsboro of residents who are troubled by the situation.

“Many people have told me that the loss of our lake would be catastrophic,” he reported. “This isn’t a disaster. We’re just doing some needed testing required by the DNR.”

For more information, contact Sonntag at City Hall at 489-2350.