A local environmental advocacy group is calling for Dane County to lower the level of Lake Mendota by 2 feet to prevent future flooding after a County Board task force excluded the suggestion from its recommendations last month.
The Yahara Lake Level Task Force produced 46 recommendations to prevent future flooding along Lakes Mendota, Monona, Waubesa and Kegonsa and the Yahara River, including dredging the riverbed, removing aquatic plants to increase water flow and purchasing more land to manage stormwater. Land and Water Resources Department staff have said that increasing water flow is paramount to preventing the swells of water in the lakes.
The task force was created after torrential downpours flooded much of western Dane County Aug. 20, and continued precipitation overwhelmed the lakes of the Yahara River, breaching the shorelines and overfilling storm sewers.
Jon Becker, vice president of Capital Region Advocacy Network for Environmental Sustainability (CRANES), said the county needs to include consideration of reducing Lake Mendota’s level, which had been largely dismissed as ineffective by a technical work group including county Land and Water Resources Department staff.
“For the portion of the Isthmus community that is prone to flooding and the areas above Lake Mendota, it would be able to retain more of that water,” Becker said, following an Environment, Agriculture and Natural Resources Committee meeting Thursday where the committee reviewed the report.
CRANES says lowering Lake Mendota by 2 feet would put it closer to its natural level. Lake Mendota has been kept higher by the Tenney Dam for close to two centuries. Becker said reducing the lake back to its natural state could also return more of the natural habitat along the shoreline.
Sup. Yogesh Chawla, who was on the task force and is on the environment committee, said the recommendations do include somewhat lowering Lake Mendota and the other lakes by maintaining them at their summer minimum levels. Currently, he said, the Land and Water Resources Department maintains the lakes at the midpoint between the minimums and maximums.
“We felt it was important to manage our lakes as low as we can as a county,” Chawla said.
The lake level minimums and maximums were set by the state Department of Natural Resources in 1979, and the DNR would have to approve changes.
Lake Mendota had been over its DNR-stipulated maximum when the rainstorms hit in August. Land and Water Resources Department staff had kept more water in the upper lake to relieve the swells along Lake Kegonsa, which had flooded earlier in the summer.
Water levels in the lakes were already on average about half a foot over the summer maximums Thursday, according to data kept by the county Land and Water Resources Department. About an inch and a half more precipitation than typical had fallen in Madison by the end of March, according to the National Weather Service.
The dozens of task force recommendations include implementing several mitigation attempts — such as dredging the Yahara River, removing aquatic weeds and potentially pumping water out of the watershed. Once those recommendations are implemented and the county increases water flow through the system, the county would ask the DNR to review the lake levels, if necessary, Chawla said.
The recommendations also call for ensuring the Tenney Dam and its embankment can hold 100-year flood levels, studying how the county could potentially pump water out of the Yahara watershed and purchasing lands and wetlands to reduce stormwater runoff.
Some of the report’s recommendations — such as website updates and the creation of quarterly reports — could be implemented by county staff without County Board approval, Sup. Michele Ritt said at the committee meeting. Other recommendations would need to go through the County Board because they require funding. No resolutions have gone to the board based on the recommendations.