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