Lake Mitchell drawdown structure receives green light amid uncertainty of future dredging project

Aug. 11—MITCHELL — Despite the uncertainty of a proposed multimillion-dollar Lake Mitchell dredging project voters will decide in 2024, the city received a clear picture on a lake restoration related project this week.

On Monday, Aug. 7, the Mitchell City Council approved the $3.5 million drawdown structure that will construct a draining mechanism next to the Lake Mitchell spillway dam to control water levels for the wetland along Firesteel Creek and a potential future dredging project.

Although the council approved the drawdown structure, Public Works Director Joe Schroeder explained how it hinges on a future lake dreading project. For crews to mechanically dredge the phosphorus-rich soft sediment along the lake bottom that's contributing to the harmful algae outbreaks, the water must be drawn down in parts of the lake to expose the sediment.

"A drawdown project should not be finalized until after we know we are dredging the lake or not. For that reason, if we are dredging, it will include a wider cut out (pipe) for water to pass through on storms," Schroeder said.

While the drawdown structure is a vital component of the proposed lake dredging project, Mayor Bob Everson explained how the structure impacts the success of the city's wetland that's set to be built in 2024.

According to Everson, the water level of the lake will need to be lowered periodically for crews to maintain the wetland and sediment trap ponds along Firesteel Creek — the creek that flows into Lake Mitchell.

"We'll need to be able to get in there to manage the vegetation that's filtering the nitrogen and phosphorus out, and also clean out the sediment traps next to the wetland. We have to control the water level to be able to maintain those," Everson said.

The 35-acre wetland project is on schedule to begin in 2024. City leaders hope the improvements will drastically reduce the phosphorus and nutrients flowing into the lake via Firesteel Creek, which has been identified as a major contributor to the lake's algae woes.

For the cattail-filled wetland to better filter out runoff making its way toward the lake, Schroeder said the water levels of the lake — depending on whether it's been a dry or wet year — will need to be controlled through a drawdown.

"The wetland elevation is the same elevation as the spillway. If you have water going over the spillway, the wetlands would be under water. What the drawdown does is making sure the lake stays down for the wetlands when we have maintenance projects on the wetlands," Schroeder said.

Everson said one design of the drawdown structure is intended to have a large enough pipe that could drain a significant amount of water from a storm when portions of the lake are drained for dredging work.

"Let's say Wessington Springs gets a 12-inch rain, this pipe would handle that," Everson said.

The drawdown project could have entered the bidding stages in 2024 if the special election for the $25 million loan that would fund a future lake dredging project was moved up to November. But the council stuck with the June 4, 2024 date for the election during Monday's meeting, which will likely push the drawdown project construction into 2025.

If voters approve a $25 million loan application for dredging the lake on the June 4, 2024 special election, Everson said a drawdown of the lake will provide a better atmosphere for dredging bids.

"It would be beneficial for the contractors bidding the (dredging) project to see what they're bidding," Everson said.

Mike Bathke is one of the five council members who voted to maintain the special election date for June 4, 2024 instead of holding it in November 2023, but he supports the drawdown structure. He said the project will provide residents with "visible movement" on lake restoration efforts, which he believes will show the community that the city is making progress on tackling the declining water quality that saw record toxin levels this summer. This week, the Lake Mitchell water quality report moved down to an alert status after nearly a month at warning levels, which were brought on by the highest microcystin levels recorded in seven years of testing on the lake.

"We're not just talking about it, there's movement," Bathke said.