Wetland Retention Basin in Superior

Reduces Stormwater Runoff

Constructing a wetland retention basin in Superior’s central business district is reducing damaging floods and the flow of pollutants into Lake Superior.


The City of Superior has recently seen several storms cause sewer overflows and flooding, resulting in significant property damage. During one large storm in 2012, hundreds of basements in the city’s Central Business District flooded. These fairly regular floods also overwhelm the city’s wastewater treatment plant, resulting in untreated stormwater carrying pollutants into the St. Louis River and Lake Superior. Thanks to several grants, including one from the Great Lakes Restoration Initiative, Superior installed a wetland retention basin to hold rain water so that it does not overwhelm the sewer system and flood people’s homes and neighborhoods. In 2016 workers began excavating the basin at a former parking lot in the Central Business District. During heavy rains the stormwater flows into a pool where pollutants can settle out of the water before into a meandering wetland, allowing more time for pollutants to be removed from the water. Workers also installed trees and native plants along the shoreline to absorb additional stormwater, which in turn created wildlife habitat and an appealing green space for residents. The City of Superior is designing informational packets on the basin and stormwater management for local schools. They also plan to provide funding for field trips that allow students to visit the basin for water quality testing and wildlife viewing.

Resource Challenges Addressed

  • Stormwater runoff
  • Flooding
  • Property damage
  • Pollution and sedimentation
  • Poor water quality


A person stands in front of a water retention pond

The retention basin holds excess water after a rain, allowing it to slowly filter into the soil. Credit: Kristy DeVera, City of Duluth.

Results and Accomplishments

Based on past results from earlier retention ponds installed in Superior, the city expects this project to almost completely eliminate basement flooding in the Central Business District. The project will also improve stormwater treatment by decreasing demand on the wastewater treatment plant during storms, which will enhance the water quality in Lake Superior. The plants and trees around the shoreline provide habitat for a variety of wildlife. The basin is also an attractive green space that people can visit in a part of the city without many natural areas.