The City of Madison Engineering Division has announced its intention to re-grade and stabilize portions of the erosion-prone Cherokee Drive (Nakoma Park) storm water channel on the west side of Nakoma Park, just below Cherokee Drive. A public information meeting will be held on Tuesday March 10 in the cafeteria of the neighboring Thoreau School. Preliminary plans will be revealed at the public information meeting, so perhaps some background information beforehand might be helpful in evaluating alternative proposals to repair the situation.
City engineers cite channel erosion and unstable banks as reasons that make repairs necessary. Indeed. The Cherokee Drive storm water channel handles the single largest storm water flow in the watershed. It is the receiving channel for the Odana and Manitou sub-watershed or sewer sheds. The combined flows from the Odana and Manitou Way sub-watersheds total 165 million gallons of urban runoff per year—an enormous amount of water. One hundred sixty-five million gallons is equal to 513 acre-feet. That’s the amount of water that would cover 513 acres to a depth of one foot, or to visualize, you could imagine one half of the Arboretum under a foot of storm water.
Rainfall to Storm Water, or Where Does It All Come From
Precipitation that falls in the Lake Wingra Watershed either soaks into the ground or drains through the storm sewer system to Lake Wingra. Rain that does not infiltrate runs off into the storm sewer ( as opposed to the sanitary sewer) and through a series of above and below ground channels and pipes that make up a drainage subunit or sewer shed.
About 33 percent of each year’s rainfall in our neighborhood goes down the (storm) drain. With each rain, one-third of it is wasted before it has a chance to sink in to the soil, before it can quench the thirst of boulevard trees, or before it can replenish our groundwater. This calculation is based on figures contained in the Arboretum’s “Facility Storm Water Management Plan” (2006, p29) in the table “UW Arboretum Sewer shed Flows.”
The rainfall runs off into the storm drain because rooftops, driveways, parking lots, streets, and other paved surfaces are not permeable: they don’t absorb water. On its way into the storm drain, and eventually Lake Wingra, rainfall and snowmelt picks up the city’s residue and debris: leaves, small pieces of trash, oil and petroleum by-products deposited on streets, animal waste, heavy metals, and almost any other contaminant one can think of.
As you can see, not only is our precious natural resource squandered, it is contaminated with pollutants, and is thus rendered unfit for human or wildlife consumption. This wasted resource that was formerly known as rainfall is called storm water by city planners and engineers.
Storm Water and Lake Wingra Land and Water Community
There are 14 storm sub-watersheds or sewer sheds in the Lake Wingra Watershed. Combined, these storm sewer sheds funnel an estimated 470 million gallons of storm water (Arboretum Facility Storm Water Management Plan, 2006, p. 29) each year into Lake Wingra. That’s right, nearly one-half billion gallons of storm water runs off our landscape and into the Arboretum, its wetlands, and into Lake Wingra. That is enough water to cover 1,439 acres of land in water one-foot deep (a measure often called an acre foot)
Cherokee Drive (Nakoma) Storm Water Channel
As we said above, the Cherokee Drive storm water channel transports storm water from two source areas or sub watersheds into the UW-Madison Arboretum and Lake Wingra. One area (Odana Golf Course Ponds) collects storm water from the western one-third of the watershed and the other gathers storm water from the Manitou Way sub-watershed. A third, smaller sub-watershed, the Nakoma Neighborhood does not join the Cherokee Drive storm water channel but rather contributes its storm water to a natural spring-fed stream between the Nakoma Golf Club and the UW-Madison Arboretum, but never mind this one for now.
The Odana Golf Course ponds collect storm water from the far western reaches of the watershed—the area past Odana Road and Whitney Way. Storm water overflow is released from the Odana Ponds, flows under the SW Bike Path trestle and into the Cherokee Drive storm channel, where it joins more the locally generated storm water from the Manitou Way sub-watershed, and then flows past Throeau School and Nakoma Park. This storm drain then dumps its water into the Arboretum below the intersection of Nakoma Road, Manitou Way, and Huron Hill. You can’t see the outfall driving or walking by because it is obscured by the low stonewall and prairie vegetation at that point. But sometimes, after a heavy rainstorm, if you are walking or biking by, you can hear the roaring cascade of storm water as it tumbles into the Arboretum and heads towards Lake Wingra.
Public Information Meeting on Tuesday March 10
We will get a chance on Tuesday evening to see how city engineers plan to avoid, minimize, or mitigate this problem; in other words will they use the precautionary principle. We will get a change to learn if they plan to deal with rain where it falls or choose to send the problem downstream. The public information meeting will be in the cafeteria of Thoreau School starting at 6:30 pm.
Facility Storm Water Management Plan. 2006. UW-Madison Arboretum.
Lake Wingra: a vision for the future. 2009 Friends of Lake Wingra.
 The western portion of the Lake Wingra Watershed stretching westward from Nakoma Road/Manitou Way to just shy of West Towne Mall.
 UW-Madison Arboretum Facility Storm Water Management Plan, 2006, page 29