.
By David S. Liebl, Chair, UW-MadisonArboretum Storm Water Committee
Reprinted from NewsLeaf, Dec. 2007
Two and a half miles northwest of Nakoma Road & Manitou Way, the landscape rises to a small hill just west of Research Park Blvd. From this vantage (43°03.382’N, 89°29.149’W), 272 feet above Lake Wingra, the far horizon features the State Capitol to the east and the driftless area to the west. Low in the landscape, the UW-Arboretum is hidden from view, as is the path of storm water runoff draining from this most western interfluve [divide] between the Mendota and Wingra watersheds.
A raindrop wending its way through the west Wingra watershed follows a constructed waterway that bypasses opportunities for infiltration and treatment as it passes beneath topographic barriers to drain to the lake. If we follow the path of runoff through the watershed, we can see both the past and future of upland storm water management, and its affect on the Arboretum and Lake Wingra.
This aerial photo shows one path of storm water runoff (dotted line) through the West Wingra Watershed (solid line).
To comply with current storm water regulations requiring new commercial construction to detain and treat runoff, a biofiltration facility (a hi-tech rain garden) has been built adjacent to the West Beltline Highway bike path by an expanding car dealership. However, existing businesses continue to contribute windblown and erosional soils, petroleum products, heavy metals and trash that are transported by the quickly intensifying flows of runoff entering the street drains.
A buried concrete storm drain running beneath the bike path conveys the runoff southeastward to the ponds at Odana Hills Golf Course (43°02.739’N, 89°27.992’W), where it commingles with runoff from the Orchard Hills and Midvale Heights neighborhoods. When the Piper family broke ground here in the 1850’s, these ponds were a wetland isolated by the glacial moraine.
A buried concrete storm drain running beneath the bike path conveys the runoff southeastward to the ponds at Odana Hills Golf Course (43°02.739’N, 89°27.992’W), where it commingles with runoff from the Orchard Hills and Midvale Heights neighborhoods. When the Piper family broke ground here in the 1850’s, these ponds were a wetland isolated by the glacial moraine.
As Madison’s west side began to develop, the resulting runoff led to fluctuating water levels, causing most of the natural vegetation to recede (as at Dunn’s Marsh). In the 1950’s, a drain was constructed beneath the moraine (under fairways 1 & 2) to pass the accumulating water to Lake Wingra.
Madison Gas and Electric, City of Madison and State of Wisconsin have built an engineered infiltration project here that intercepts over half of the 115 million gallons of runoff entering Odana Ponds each year, and returns it to the groundwater via drain fields beneath the moraine. Pre-treated to remove sediment and contaminants, this water now replenishes springs around the west end of Lake Wingra.
Madison Gas and Electric, City of Madison and State of Wisconsin have built an engineered infiltration project here that intercepts over half of the 115 million gallons of runoff entering Odana Ponds each year, and returns it to the groundwater via drain fields beneath the moraine. Pre-treated to remove sediment and contaminants, this water now replenishes springs around the west end of Lake Wingra.
Runoff that bypasses the infiltration project (including salt-laden winter melt from the West Beltline Highway, commercial and residential properties and peak flows from large rain events) passes through the Odana ponds, and is conveyed eastward along the Southwest Bikepath in a buried drain that daylights at the head of Chippewa Drive.
Now commingling with runoff from the steep slopes of the Nakoma Neighborhood, it follows an open channel of concrete and stone like the one in Cherokee Drive. These open conveyances collect leaves and debris that frequently clog the drains near their combined outlet at Thoreau Elementary School. During large storms, runoff overflowing across the roadway erodes the hillside along Chippewa Drive, carrying sediment and debris to the trash gate beneath the stone bridge at the foot of Oneida Place, and into a concrete box channel under Nakoma Road.
Nakoma’s steep slopes require managing storm water where it falls, before it can run off the landscape. In a fully developed neighborhood, residential rain gardens that collect, detain and infiltrate water from roofs and driveways are often the only practical management practice. If each household in the watershed created a rain garden, it would dramatically reduce volume, phosphorus and sediment in storm water entering the Arboretum.
Finally, after miles of conveyance and a drop of hundreds of feet in elevation, an annual 100 million gallons of contaminated storm water runoff, flowing at up to 300 cubic feet (2,244 gallons) per second, enters the Arboretum at the Manitou Way outfall (43°02.855’N, 89°26.306’W). In the 1930s, there was an unobstructed view from Manitou Way across a low open wetland to Lake Wingra. Over the years, runoff gradually cut a channel into the wetland, depositing its sediment as it flowed through the marsh to Lake Wingra.
Early attempts to control the flow of runoff through the wetland included a ditch leading from the outfall east toward Wingra Slough. But the ditch acted as a groundwater drain, encouraging trees and shrubs to become established in the now drier soils. In the 1980’s, Secret Pond was dug out of the marsh to collect sediment and moderate flows through the marsh. Recently, Secret Pond’s berm failed, creating a deep channel cutting through the marsh to Wingra Slough — carrying with it accumulated sediment and filling in the already shallow west end of Lake Wingra.
Today, the Arboretum storm water management committee is working with consulting engineers and the City of Madison to find a storm water management method for this area that is consistent with the Arboretum’s mission to conserve and restore Arboretum lands, advance restoration ecology and foster the land ethic.
It is proving to be a difficult challenge to manage so much runoff so low in the landscape. How much easier our job would be if the rain that fell across the landscape of the west Wingra watershed remained there, infiltrating into the soil as nature intended
Now commingling with runoff from the steep slopes of the Nakoma Neighborhood, it follows an open channel of concrete and stone like the one in Cherokee Drive. These open conveyances collect leaves and debris that frequently clog the drains near their combined outlet at Thoreau Elementary School. During large storms, runoff overflowing across the roadway erodes the hillside along Chippewa Drive, carrying sediment and debris to the trash gate beneath the stone bridge at the foot of Oneida Place, and into a concrete box channel under Nakoma Road.
Nakoma’s steep slopes require managing storm water where it falls, before it can run off the landscape. In a fully developed neighborhood, residential rain gardens that collect, detain and infiltrate water from roofs and driveways are often the only practical management practice. If each household in the watershed created a rain garden, it would dramatically reduce volume, phosphorus and sediment in storm water entering the Arboretum.
Finally, after miles of conveyance and a drop of hundreds of feet in elevation, an annual 100 million gallons of contaminated storm water runoff, flowing at up to 300 cubic feet (2,244 gallons) per second, enters the Arboretum at the Manitou Way outfall (43°02.855’N, 89°26.306’W). In the 1930s, there was an unobstructed view from Manitou Way across a low open wetland to Lake Wingra. Over the years, runoff gradually cut a channel into the wetland, depositing its sediment as it flowed through the marsh to Lake Wingra.
Early attempts to control the flow of runoff through the wetland included a ditch leading from the outfall east toward Wingra Slough. But the ditch acted as a groundwater drain, encouraging trees and shrubs to become established in the now drier soils. In the 1980’s, Secret Pond was dug out of the marsh to collect sediment and moderate flows through the marsh. Recently, Secret Pond’s berm failed, creating a deep channel cutting through the marsh to Wingra Slough — carrying with it accumulated sediment and filling in the already shallow west end of Lake Wingra.
Today, the Arboretum storm water management committee is working with consulting engineers and the City of Madison to find a storm water management method for this area that is consistent with the Arboretum’s mission to conserve and restore Arboretum lands, advance restoration ecology and foster the land ethic.
It is proving to be a difficult challenge to manage so much runoff so low in the landscape. How much easier our job would be if the rain that fell across the landscape of the west Wingra watershed remained there, infiltrating into the soil as nature intended
No comments:
Post a Comment