Best Management Practices

BMPs, which are sometimes called stormwater control measures (SCMs), stormwater management practices, or green infrastructure, can take many different forms:

• 1. Runoff Disconnection

  Runoff disconnection redirects roof or pavement runoff to pervious areas where it can soak into the ground instead of flowing directly into storm drains. They’re common in low and medium residential lots, but can be limited by compacted soils and extreme storms.

• 2. Bioretention

  Bioretention areas – such as rain gardens – use engineered soil, mulch, and native plants to capture, filter, and infiltrate stormwater. Because of the variety of potential bioretention designs, they can be used as a landscape amenity – with routine landscaping maintenance. They are feasible on most sites with less than one acre of contributing drainage area.

• 3. Infiltration

  Infiltration practices, like infiltration trenches, french drains, or basins, allow stormwater to soak directly into the soil and filter nutrients. Infiltration practices have the highest runoff reduction capability, but need to be on sites with very permeable soil. Pretreatment, prior to construction, is crucial, as is erosion and sediment control.

• 4. Filters

  Filters are designed like a bioretention but without the plants. They use 100% sand for their media mix and have a defined pretreatment area. They often have underdrains included, and filter stormwater without relying as heavily on infiltration.

• 5. Swales

  Both dry swales and wet swales are gently sloped, vegetated channels that slow, convey, and treat runoff by promoting infiltration and settling of pollutants. Swales work well for low density residential areas and roadways. However, pollutant removal is limited by rapid flow velocity during storms – installing check dams, swale media, or underdrains can help slow the flow and enhance infiltration.

• 6. Permeable Pavement

  Permeable pavement systems allow water to pass through the surface into an underlying reservoir where it infiltrates or is slowly released. The surface material can range from porous asphalt, porous concrete, or interlocking paver products, and they are popular in urban areas. The ability of permeable pavement to filter stormwater depends heavily on proper installation and maintenance.

• 7. Wet and Extended Detention Stormwater Ponds

  Stormwater ponds capture stormwater and use settling, biological uptake, and extended storage time to remove pollutants. Wet ponds maintain a permanent pool, while extended detention ponds temporarily hold runoff to reduce peak flows. While not as popular, they remain one of the most common stormwater practices in the Chesapeake Bay region.

• 8. Landscape-scale restoration practices

  a. Stream Restoration

  Stream restoration stabilizes eroding banks, improves in-stream habitat, and reconnects streams to their floodplains. These projects can be technically complex, and require great care in selecting appropriate sites. They are highly visible and can be a community amenity, but only when done with early and meaningful community engagement. These projects can also be expensive, and require time for permitting and construction.

  b. Reforestation/Riparian Buffers

  Riparian buffers are vegetated areas – typically forest – planted along waterways to intercept runoff, stabilize banks, and filter nutrients. Reforestation involves planting trees and native vegetation to improve watershed resilience and restore natural hydrology.

  c. Constructed Wetlands

  Constructed wetlands are engineered shallow basins planted with wetland vegetation and have deeper areas providing storage capacity for stormwater. They provide excellent pollutant removal and habitat, but can be difficult to maintain long term.

  d. Shoreline Restoration

  Shoreline restoration uses living shorelines and other natural features to stabilize eroding coasts, reduce nutrient inputs, and improve habitat. These projects restore natural water-land interfaces while providing a buffer against storms.

• 9. Municipal Program BMPs

  a. Street Sweeping

  Street sweeping removes sediment, debris, and pollutants from road surfaces before they can enter storm drains.

  b. Urban Nutrient Management

  Urban nutrient management reduces excess fertilizer use on lawns, parks, and other managed landscapes through planning, soil testing, and education. This prevents nitrogen and phosphorus from washing into local waters.

  c. Advanced IDDE Programs

  Advanced IDDE programs go above and beyond MS4 permit requirements to locate and eliminate nutrient-rich discharges – such as sewage or industrial waste – entering storm drains. They rely on proactive monitoring, mapping, and rapid response to protect water quality.

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