Naturalizing a Stormwater Retention Basin

Improves Water Quality

Retrofitting and naturalizing a retention basin in Indiana improved water quality by filtering out sediments and pollutants from stormwater, decreasing the harmful impact of storms, and improving aquatic wildlife habitats.


One of the biggest threats to the Great Lakes is polluted runoff that occurs when heavy rains wash pesticides, fertilizer, sediment, animal waste, oil and other pollutants into nearby rivers and streams—and eventually the Great Lakes. Several years ago, to control stormwater flow within a local watershed, the City of Valparaiso, Ind., constructed a traditional concrete detention basin. The basin itself is roughly 2 acres in area, but is responsible for collecting stormwater from approximately 330 acres, most of which are commercial, industrial, or residential. The basin, as originally designed, only held excess water but did nothing to slow down flow or filter out sediments and pollution. Thanks to a grant from the Great Lakes Restoration Initiative, the City of Valparaiso and nonprofit Save the Dunes have partnered to naturalize and retrofit the Thorgren Basin by removing concrete and naturalizing landscaping and vegetation in the swale. They aim to expand the basin’s functionality, having it treat stormwater and provide aquatic habitat in addition to redirecting storm flows. At each inlet to the basin, sediment traps were constructed to remove much of the sediment picked up by the stormwater. The channels were reconstructed to give them a meandering path that slows down the flow of stormwater, allowing sediments and pollutants to settle out. Crews removed the concrete lining the channels, replacing it with bio-swales of native vegetation. Crews also landscaped the basin to provide a varied topography for wildlife habitats, creating clay-lined permanent pools, transitional wetland zones, and upland infiltration areas. Native vegetation was planted throughout the basin to naturalize its hydrology.

Resource Challenges Addressed

  • Sedimentation
  • Polluted storm runoff
  • Erosion
  • Lack of suitable aquatic habitats.


A water filtration basin with grass and plantings all around.

In addition to treating and redirecting stormwater, the retrofitted basin includes a varied topography with native vegetation to provide wildlife habitat. Photo credit: Save the Dunes.

Results and Accomplishments

This project is expected to annually prevent 402 pounds of nitrogen, 130 pounds of phosphorus, 3,590 pounds of biochemical oxygen demand, and 23 tons of sediment from entering the Salt Creek watershed, which eventually flows into Lake Michigan. This has significantly improved the water quality for both the people and wildlife in the area.

The Thorgren Basin before restoration is a low lying area in the landscape.

Prior to the retrofits, the Thorgren Basin was designed only to redirect, and not to treat, contaminated stormwater. Photo credit: Save the Dunes.

The Thorgren Basin under construction with low areas filled with water and higher areas with seedlings.

Meandering channels were constructed to slow down the rate of stormwater flow, and the concrete lining was removed. Photo credit: Save the Dunes.