work underway on a water-discharge structure we designed for poor soil conditions
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stormwater treatment wetland

stormwater treatment wetland
Carleton College
Northfield, Minnesota

stormwater treatment wetland and wildlife corridor meet ecological restoration goals

The Cowling Arboretum at Carleton College comprises 880 acres of land adjacent to the college. As part of its master planning in 1998, the arboretum worked on long-term restoration of its woodland, prairie, savanna, and floodplain plant communities and built parking lots and a new recreation center near the arboretum, requiring a stormwater detention pond.

The pond had to meet functional requirements—treating water before it discharged into the Cannon River—as well as fit into the natural landscape. Barr recommended a constructed wetland, which would be both effective and attractive in the arboretum setting.

Barr performed hydrologic and ecological analyses to determine the new wetland's size and its potential fit with the natural topography and vegetation. Working with the college to site the wetland, Barr recommended reclaiming a former dumping area, where heaps of old blacktop were overgrown with invasive, exotic trees. By constructing the pond there, the college lost an eyesore and ecological liability, and gained valuable wildlife habitat and a visual amenity because this was a wetland system, not a typical stormwater detention basin.

Later, Barr worked with the college to design an ecological corridor connecting the upper and lower segments of the property. Wildlife and pedestrian movement was considered while the corridor’s integrity was reinforced by establishing low-maintenance native vegetation in the adjacent recreation center, including oak savanna between ballfields, at entry points, and throughout parking lots. A pedestrian circulation plan limited human impact and featured interpretive nodes about the site’s natural and cultural history.