Wetlands are often described as the “kidneys of the landscape.” They help remove pollutants from runoff and moderate the flow of water to mitigate floods and drought. Wetland vegetation provides filtering, pollutant uptake, and slows down incoming runoff, allowing sediment and associated pollutants to settle out. The vegetative cover also provides shade, helping not only to cleanse, but to cool the water for temperature sensitive organisms downstream.
Wetlands also provide excellent wildlife habitat. Many species depend on wetlands at different points in their life cycle, including turtles, frogs, toads, salamanders, waterfowl, and songbirds. Flowering plants provide benefits to local pollinator populations.
Engineered Stormwater Wetlands build upon a standard stormwater management pond design to take advantage of the ecosystem services that natural wetland systems provide, such as food and habitat for wildlife, water quality improvement, flood protection, erosion control. Stormwater wetlands are designed with a variety of water depths. Shallow areas allow wetland vegetation to grow, which helps to slow down stormwater and filters out and uptakes nutrients and other stormwater pollutants. Deeper pools help settle out pollutants and provide temporary storage for stormwater runoff, which helps reduce erosion downstream. Rates of carbon accumulation measured in the soils of constructed wetlands suggest they also provide carbon sequestration benefits. The functional role of natural wetlands in improving water quality has been a compelling argument for the construction of stormwater wetlands.
DEP’s Kemp Mill Shallow Marsh Wetland project is located on Maryland National Capital Park and Planning property off Somersworth Way, just east of Wheaton Regional Park. The project is adjacent to the main stem of Northwest Branch and the property provides neighborhood access to the nearby Northwest Branch and Rachel Carson Greenway Trails.
“We enjoy looking at the aquatic flowers and animals. Since the pond was completed, we have seen cranes, wild turkeys, geese, ducks, turtles and frogs. It is rewarding to know that in addition to its natural beauty, the vegetation filters out the chemicals from the rain runoff.”
The project converted the original 1986 dry stormwater pond into the existing stormwater wetland facility in 2019. Most of the wetland is less than 2 feet deep to allow the wetland vegetation to grow and provide additional water quality benefits. A few deeper pools help dissipate runoff energy to reduce erosion downstream. The project was planted with over 2,000 native aquatic and wetland plants. Species include pickerel weed, soft rush, bristly sedge, and wool grass.
DEP selected a stormwater wetland for this location due to its proximity to Northwest Branch, a Maryland Class IV Recreational Trout Water. The shade from the wetland vegetation helps cool stormwater runoff before it leaves the wetland and reaches the cold-water dependent brown trout fishery downstream.
Learn more about DEP’s watershed restoration efforts at: MontgomeryCountyMD.gov/Water