Madison’s Engineering Division, in cooperation with Madison Parks, has proposed constructing a third storm water pond in Cherokee Marsh Conservation Park’s South Unit. The pond will be just north of Wheeler Road near Bonner Lane and Northland Drive. City staff presented the plans at a public meeting at Black Hawk School on April 11.

Like the ponds added along Wheeler Road in 2012, this pond’s purpose is to improve water quality in the Yahara River and downstream lakes. Storm water from 170 acres of neighborhoods now drains directly into ditches that run through the conservation park and empty into the Yahara River. The pond will capture grass clippings, sand, dirt, leaves, and other debris from the storm water before it reaches the river and lakes.

City Engineering estimates that the pond will capture 20,000 pounds per year of sediment and 50–60% of the storm water’s phosphorus, a nutrient that promotes algae growth. The city expects to dredge the collected sediments about every 20 years.

The pond’s shape will be long and narrow to preserve a wetland just north of the site. Engineering will scrape the wetland’s surface to improve the site for wildlife. The pond will have a clay liner and will be shallow along its edges, increasing to 5–7 ft at its deepest. Parks will add plantings in and around the pond. The existing path between the proposed pond and the wetland will be widened to 14 ft allow equipment access for dredging.

The city’s Storm Water Utility and a $100,000 matching grant from the Dane County Urban Water Quality Grant Program will fund the project’s estimated $329,000 cost. The project requires approval by Madison’s Board of Public Works, Board of Park Commissioners, and Common Council. The city will also request needed permits from the Wisconsin Department of Natural Resources and the U.S. Army Core of Engineers. The Friends of Cherokee Marsh have expressed support for the project due to the benefits it will provide for water quality and wetland restoration.