The Wingra Watershed
About watersheds
The boundaries of watersheds (and subwatersheds) are generally determined by surface topography, with water of course always flowing downhill. However, construction (e.g., dams, channels, buildings, streets, stormsewers) can change the flow of water, resulting in a change in the shape and size of watershed boundaries.
Wingra watershed boundaries
The original Lake Wingra watershed has been changed rather dramatically due to urbanization, largely a result of dredging and filling associated with the construction of Vilas Park, Wingra Creek, and Arboretum Drive. Prior to the dredging of what is now Wingra Creek, Lake Wingra probably drained to Lake Monona through a meandering wetland flowage. The original boundary between the watersheds of these two lakes was probably not precise, since the elevation change is very small and the direction of flow was probably subject to some change in response to varying local conditions. The USGS, using current topographic data, gives the eastern boundary at about where Wingra Creek flows under Beld Street.
As a result of the construction of the spillway (dam) at the current outlet of Lake Wingra (near the south end of Orchard Street) and of Arboretum Drive (that serves as a dike separating Gardner Marsh from the lake), much of the original Wingra watershed no longer flows into the lake itself but into Wingra Creek instead. If we see the shape of the original watershed as resembling a fish, the effect of these major hydrographic changes is to “cut off the nose of the fish.”
City “sewersheds” do not conform precisely to the natural watershed boundaries as defined by topography. Storm sewers carry water from buildings and streets in ways that can alter the original direction of water flow. Also, the City of Madison maps single parcels (properties) in only one sewershed, even if portions of that property are in adjacent sewershed. Thus, the city sewershed boundaries exhibit jagged edges which are to some extent artifacts of the pattern of individual parcel boundaries.
Who lives in the watershed?
The Wingra watershed is home to over 33,000 people in 14 different neighborhoods. The UW Arboretum, Vilas Zoo, Edgewood College, 6 parks, 2 golf courses, and numerous public schools, churches, and community centers also call the Wingra Watershed home. Because of protected natural areas like the UW Arboretum, the Wingra Watershed is home to diverse ecological communities. Forests, prairies, and several kinds of wetlands support a high diversity of plants including some rare species like the small white lady slipper and the prairie fringed orchid. The watershed is also home to numerous species of mammals, reptiles, amphibians, insects, birds, and fishes.
While the watershed is home for many native plants and animals, invasive species have degraded the native biodiversity of ecological communities and alter water quality in lakes like Lake Wingra. Urban landscapes are stressful environments for plants and animals, and invasive species are often better than native species at surviving and multiplying in these harsh urban environments. Invasives plant species can crowd out native plants by competing for resources such as light and nutrients. Invasive animals can alter native communities by feeding on native vegetation or animals. Invasives species may also cause declines in water quality in lakes. For example, Eurasian milfoil, an aquatic weed that is abundant in Lake Wingra, contribute to algal blooms in lakes by transferring nutrients from lake bottom sediments to the water. Carp, an exotic fish that is common in Lake Wingra, reduce water clarity by stirring up lake bottom sediments.
Watershed management issues
Lake Wingra has an altered watershed because of its urban setting. Urban watersheds differ from natural watersheds because much of the landscape is built by humans. In the Wingra Watershed, about half of the land use is residential neighborhoods and about 15% is commercial uses. Instead of native prairie, forest and wetland vegetation, most of the watershed is covered by elements of a “built environment”: roads, parking lots, buildings, and lawns. Many of these surfaces are impervious, meaning they do not allow rain water to infiltrate into the ground.
Impervious surfaces alter how water flows through a watershed and affect both water quantity and quality. When it rains on streets, parking lots, and lawns, runoff from these surfaces carries pollutants including dirt, oil, road salt, pesticides, fertilizers, and trash. Runoff becomes stormwater as it flows into gutters and storm sewers and eventually into Lake Wingra.