Homeowners looking to enhance their landscape this year while managing stormwater have options available. Green infrastructure options include permeable pavement, rain barrels, large trees, green roofs, rain gardens, bioswales and more. Each is designed to utilize technologies or replicate natural systems in urban areas that create habitat, reduce the heat-island effect, improve air quality, enhance the visual appeal of communities, and/or manage stormwater. Rain gardens and bioswales are two powerful, accessible solutions for homeowners. Both help control runoff, reduce erosion, and create critical wildlife habitat, yet they differ in design and function. Understanding the differences is key to choosing the right option and implementation to achieve maximum results . Rain gardens are shallow, depressed areas in the landscape designed to capture stormwater runoff from adjacent land and structures. Stormwater is allowed to filter through the soil of these planting areas . Rain gardens can be designed and installed as attractive landscape beds, often planted with a mix of blooming plants that are well-adapted to enhance the water-infiltration task of a rain garden . Rain-garden design takes into account the infiltration rate of the soil and is built to a size that is capable of accommodating a specific amount of runoff from the surrounding landscape . It is recommended that rain-garden placement is, at minimum, 10 feet away from the foundation of an adjacent building with a slope of 1:12 percent away from the structure to insure adequate drainage . Down spouts, reinforced swales or a subdrain can be used to feed water directly into a rain garden. During heavy rainfall, rain gardens may reach capacity. To prevent damage, rain gardens need to be designed with an overflow outlet. An overflow pipe or a relief in the sidewall of the rain garden can serve this purpose. The height of the overflow is based on the depth of the rain garden, it is lower than the top edge of the garden but high enough to allow the garden to retain a calculated amount of water for infiltration. Bioswales differ from rain gardens in form and scale. Designed to capture and convey stormwater, bioswales are sloped channels that infiltrate water while it flows away from the source site. Typically, bioswales are capable of managing larger volumes of stormwater and are engineered to include a subgrade of amended soils. The objective of each garden is to capture stormwater and allow it to infiltrate into the soil by creating a space for stormwater runoff to slowly soak into the soil profile rather than quickly run over land, entering open water systems or storm sewers. Benefits of stormwater infiltration include pollutants and contaminants are removed; groundwater is recharged; water is cooled before entering local stream corridors, enhancing aquatic habitats; and it reduces strain on local stormwater sewer systems. Functioning rain gardens and bioswales utilize similar plant palettes. Native species are recommended for many reasons, particularly their robust, deep-reaching root systems. As native plants become established in a rain garden or bioswale, their roots penetrate deep into the soil profile, creating pore space that improves water-infiltration capacity. Additionally, they help protect soil from erosion, are capable of withstanding dry periods, and are tolerant of more challenging soil profiles. Choosing which native plants to include in a planting is based on sun exposure, soil type, garden size and personal aesthetic preferences. Depending on the size of the garden, trees, shrubs, perennial grasses and perennial flowers are options. Placement requires special consideration due to the slope of the gardens. Pay attention to the size of the plant, and place it in the garden so a layered look is achieved. Also note the moisture preferences of the species, use this information to locate the plants in the base of the garden where conditions will be moist, the top of the slope where soil conditions will be dryer, or the middle of the slope where soil moisture will be moderate as compared to the top and bottom of the garden . Rain gardens and bioswales, if designed and constructed properly, will not hold water for the length of time necessary for mosquitos to reproduce. Mosquitos require one to two days of standing water for eggs to hatch and another seven to 10 days for larvae to develop into adults. Rain gardens and bioswales aim to infiltrate water within 24 hours.
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