Learn about Naturalized Basins
Take a walk through a
naturalized basin

What is a naturalized basin:

Naturalized basins are stormwater control facilities that are planted with native vegetation rather than maintained as mown lawn. Both as detention basins, where the water drains out completely between storms, and as retention, or wet, basins, these facilities address stormwater quality. The stems and leaves of the native plants, and the detritus, or dead twigs and leaves, help filter stormwater. The plants may also take up certain pollutants, such as excess fertilizer, removing them before the stormwater is discharged to a creek.

Why do it:
Stormwater quality is becoming an issue for municipalities. The new NPDES permitting program and other water-quality related programs (such as source water area protection program) look at reducing pollutants in stormwater discharges. Stormwater quality is no longer just an environmental or ecological concern. Sediment in stormwater reduces the ability of the stream to convey stormwater, increasing flooding. Other pollutants in streams that supply drinking water to communities increase the cost of treatment, and the higher cost is passed along to residents and businesses.

Retrofitting basins brings returns to the municipality, residents and the environment. If the basins are owned by the municipality, maintenance costs will be reduced once the vegetation is established and mowing is no longer necessary. Sediments and nutrients are removed by the vegetation before the stormwater reaches a stream, maintaining the stream function of conveying flood flows and supporting fish and wildlife. The vegetation selected can greatly increase the esthetic appeal of a basin, providing color in all seasons and attracting birds and butterflies to the area.

Calculating the costs for retrofitting a basin is important. If sufficient funds are not set aside for site preparation, planting and inspection and maintenance, the project will not be as successful as it could be. Retrofitting cost is going to depend on the size of the basin, the number of basins being retrofitted, the level of detail, and the size and species of the plant material used.

Naturalizing a basin can eliminate the need for periodic mowing. A naturalized basin is not maintenance free, however. When first established, frequent inspection should be made to determine if the vegetation is becoming established properly. Once established, less frequent inspections can be made to see that the inlets and risers are clear and functioning well.

Trees, shrubs and grasses all can be used in naturalizing a basin. See the list of suggested plants. Shallow rooted plants should be used on the dam area of the basin.

After planting, a small amount of the vegetation may need to be replaced, but for the most part the basin should be less trouble than a typical grassed basin. Consideration should be given to the surrounding neighbors and businesses. Adjacent landowners may have the misperception that the basin is being ignored once vegetation starts to grow. A flier or article in the municipal newsletter explaining what is being done in the basin and why should alleviate any concerns.

Suggested plants:
Grasses: Warm Season Grasses and wildflower mixes. In wet areas, plant Sweetflag, Yellow Iris and Soft Rush for color and texture.
Shrubs: Red Chokeberry (Aronia arbutifolia), Silky Dogwood (Cornus ammomum), Arrowwood (Viburnun Dentatum), Cranberrybush (Viburnum trilobum).
Trees: Red Maple (Acer rubrum), River Birch (Betula nigra), Sweetgum (Liquidambar styraciflua), various Willows.