Forest Estates (Wheaton) Green Streets Help to Restore Sligo Creek

Just south of downtown Wheaton, the Forest Estates is a single-family-home residential neighborhood tucked between Dennis Avenue and Sligo Creek Parkway. This neighborhood is the site of a “green streets” roadway rehabilitation project, where landscaping installed along the curb helps to control and treat rainfall runoff. The small landscaped areas use plants to trap pollutants carried by the first flush of rainfall runoff (i.e., runoff from the first inch of rainfall–the amount of the majority of rainfall events in this region) and soaks the water into the ground or by slow percolation, into the stormdrain system. Excess volume (e.g. during larger rainstorms) is directly routed into the stormdrain system and into Sligo Creek.

Streetside bioretention holds stormwater rather than sending it through pipes into regional stormwater ponds

Many of the green street  installations are  “bioretention gardens” where water filters through plants; mulch; biomix–a mixture of planting soil, sand, and mulch; and a gravel layer, before entering into the perforated underdrain that leads to the storm drain system. In contrast rain gardens have the same filtering layers, but water infiltrates into the underlying soil.  The soil is tested to ensure proper infiltration.

Native plants and flowers used in bioretention swales help the ecosystem by being attractive to pollinators such as bees, moths, butterflies, and hummingbirds

Located in the street right of way between the curb and sidewalk, the green street installations are designed to receive street runoff from the curb into an inlet. There drought-tolerant plants, sturdy grasses and shrubs form a vegetative filter to absorb the water. The installations are designed to drain within 12–48 hours.

Ponding of water after rainfall event quickly soaks into the porous soil media used in the streetside bioretention garden

Residents in the neighborhood were given a tour of the completed green street practices with the Department of Environmental staff. They had questions about how the bio-retention gardens function, who maintains them (the County does) and whether they are effective at improving downstream water quality in our local streams.  Green street installations such as the ones in Forest Estates which control rainfall runoff pollution and reduce runoff volume, are expected to cumulatively result in a positive response in stream biological communities. Streams are monitored on an ongoing basis by the County’s Biological Monitoring Program.

Environmental Protection staff conducting a neighborhood walk to explain the stormwater landscaping

Residents were also encouraged to install raingardens or other stormwater control practices in their yards through technical assistance and financial subsidies offered by the RainScapes Neighborhoods Program offered by the County. The County has set a goal that a minimum of 30 percent of properties in a RainScapes Neighborhood will have some form of stormwater control project. The joint effect of the green streets and privately-owned RainScapes projects is expected to result in better stormwater control at the subwatershed scale, resulting in clean, healthy local streams while adding value through attractive neighborhood landscaping.

Next time you are in the Forest Estates neighborhood tell us how the bio-retention gardens appear to be faring and whether you feel they add value as landscaping.