201 4th Street SE, Room 108
Rochester, MN 55904
Stormwater Best Management Practices
Best Management Practice (BMP) is used to describe methods that are used to minimize or prevent water pollution. In the world of stormwater management, BMPs are used to reduce the quantity of stormwater runoff and to improve the quality of stormwater runoff. There are many examples of BMPs that can be selected and implemented, a few of which are explained below.
On this page:
- Stormwater Ponds, Infiltration Basins, & Infiltration Trenches
- Native Vegetation, Bioswales, & Rain Gardens
- Constructed Wetlands
- Green Roofs
- Pervious Pavements
Links to other pages:
Stormwater ponds, infiltration basins, and infiltration trenches are constructed for the purpose of capturing and storing stormwater runoff. Capturing water in a pond, basin, or trench will help mitigate water quantity or quality issues downstream. According to the Minnesota Pollution Control Agency, these BMPs remove pollutants from incoming stormwater runoff through physical, biological, and chemical processes.
Infiltration trenches are long, narrow, shallow trenches with very permeable soils or rock that encourage groundwater recharge. The water captured in infiltration trenches is stored out-of-sight in the soils while it soaks into the ground.
Stormwater ponds and infiltration basins can store water for an extended period of time (a "wet pond") or store water temporarily (a "dry pond"). The City of Rochester owns and maintains over 150 ponds. The remaining 200+ ponds located within the city limits are owned and maintained by various entities including: private businesses, the State of Minnesota, and Olmsted County.
Native plants are those that existed in Minnesota prior to the arrival of European settlement and are adapted to thrive in this area. Native grasses and wildflowers have deep, extensive root systems that hold the soil in place and prevent erosion. The roots help pull water into the ground rather than let it run off the landscape. Native vegetation also provides habitat and food for native wildlife.
A bioswale is formed when the landscape is intentionally shaped into a shallow channel that collects stormwater and allows it to infiltrate into the soil, typically within 24-48 hours. Bioswales are planted with native vegetation that increase the infiltration rates of the stormwater management feature. These stormwater management features can be used to direct stormwater to other BMPs.
A rain garden is a carefully planned depression in the landscape that collects rainwater and snowmelt. The garden will capture stormwater and allow it to soak into the ground with 24-48 hours. Rain gardens can be any size or shape and can easily integrate into landscaping plans.
Constructed wetlands, including floating wetlands, are designed to mimic natural bogs and can help clean nutrient-polluted water. Native plants and microorganisms grow through the recycled plastic matrix and act as a natural filtration system for the lake. The wetland also creates habitat above and below the surface of the water, providing a haven for fish, turtles, insects and birds.
You can see floating wetlands in Silver Lake and in a handful of stormwater ponds across Rochester. These floating wetlands have a base made of recycled plastic that is then covered in soil and wrapped in burlap. Native plants are placed into soil-filled cavities and fencing is installed to prevent geese and muskrats from damaging the plants.
Green roofs are becoming commonly accepted and installed on buildings of all shapes and sizes. They are to reduce costs associated with the life-cycle of conventional roofs, heating and cooling. In addition, they are being used to address stormwater management and large green roofs are being used to create spaces for public benefit in urban settings.
Green roofs offer numerous benefits including:
- Reduced runoff
- Prolonged roof life
- Reduced roof temperature
- Decreased energy costs
- Reduction of the urban heat island effect
- Providing habitat for birds and insects
- Carbon sequestration
- Improved air quality
- Enjoyment and increased productivity for adjacent building occupants
Green roofs have aesthetic qualities which help to meet landscaping requirements and they create additional living space if constructed properly. The possibilities of so many benefits, particularly in urban high-density environments such as downtown Minneapolis and St. Paul, have triggered the use of green roofs.
Structure of a green roof
While a green roof may cost 2-3 times that of a conventional roof, life expectancy is commonly estimated to be at least twice as long. In addition, when evaluating the cost effectiveness of green roofs, all related cost reductions should be tabulated. For example, these could include the reduced energy costs of the building under the roof, the runoff credits possible through local regulatory programs and the carbon sequestration that could be credited as part of local CO2 monitoring.
When rainfall hits hard surfaces such as conventional concrete and asphalt, the water runs off, collecting pollutants along the way and ends up in storm drains and waterways. Pervious pavements allow water to pass through the surface and infiltrate into the soil below rather than running off impervious surfaces and into surface water.
Benefits of using pervious pavement include:
- Increased infiltration and groundwater recharge
- Reduced runoff rates
- Decreased pollution
- Decreased need for sand and salt during winter months, as moisture seeps into the surface and ice formation is reduced.
Types of pervious pavement:
- Pervious asphalt consists of small and large stones bound together by an asphalt binder. This creates large spaces in the rocks, allowing water to move downward.
- Pervious concrete is a mixture of Portland cement, fly ash, washed gravel, and water. Unlike conventional concrete, pervious concrete usually contains 15 to 25 percent air space, which is achieved by the addition of a fine, washed gravel.
- Pervious interlocking concrete pavers form patterns that create openings through which rainfall can infiltrate. These openings are typically filled with pea gravel.
- Plastic grid systems, sometimes referred to as geocells, consist of flexible plastic interlocking units that allow for infiltration through large gaps filled with gravel or topsoil planted with turf grass.
Permeable pavement maintenance should include an annual vacuum sweeping. Additional vacuuming may be necessary if sediment is visibly accumulating and clogging the pores of the surface. Some restriction on the use of sand or anti-skid material might be needed if repeated use shows an accumulation is problematic.