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Stormwater Management: BMPs
What is a BMP?
Best Management Practices (BMP) are permanent facilities designed to collect stormwater runoff prior to releasing the water into a natural water way. A BMP is required by state law during development or redevelopment of residential, commercial and industrial properties to reduce pollution and control flooding associated with stormwater runoff from rooftops or pavement.
Can I remove a BMP?
No. By law you may not remove or modify a BMP on your property without gaining permission from the City of Norfolk Storm Water Engineer or his designee. City code 41.1 requires storm water BMPs to be installed and maintained as established in the approved site plan for development of the property. Additionally, a “Declaration of Covenants” (Declaration) is filed with the Clerk of the Court and attached to the Deed of your property that requires owners to maintain the BMP at their expense. The Declaration also allows the City Inspector to access your property on a routine basis to perform inspections and may require discrepancies be corrected within an allotted timeframe.
Why should I maintain it on my property?
Stormwater BMPs are required by state law and local law to be installed and maintained. These requirements are in place to assist with managing localized flooding, preventing pollutants such as nutrients, sediment, oil, etc. from running off the site and polluting downstream waters, and, in some instances, encouraging infiltration for groundwater recharge.
If you have questions about your BMP, please contact:
Chrisi VanLear, Environmental Program Supervisor
Monday-Friday 7:00am-3:30pm at 757-823-4078
A grass channel (or ditch) is a broad, shallow area covered with turf or grass. Grass channels are typically located along the edge of a property, gently sloping toward the storm drain system. They are commonly found along roads, parking lots, or between residential properties.
Grass channels, or ditches, are usually found along the edge of a property. They are designed to slow stormwater and temporarily store runoff after it rains, allowing it to filter into the ground. The grass helps filter out pollutants as the stormwater soaks into the subsurface.
Maintenance of a grass channel, or ditch is the responsibility of the property owner.
- Keep leaves, trash, debris and sediment out of the channel.
- Keep grass mowed no shorter than 3 inches. Remove any grass clippings.
- Reseed any bare areas and repair eroded areas when needed.
A dry swale is a broad, shallow, vegetated channel that is located along the length of a property and gently slopes toward the storm drain system. Dry swales are designed to slow stormwater runoff an allow water to soak into the ground through layers of special engineered soil mix and stone. They increase pollutant removal through filtration and infiltration.
Dry swales can be seeded with turf grass or planted with more elaborate landscaping that includes tall meadow grasses or native plants and trees. They are designed to dry out between rain storms and typically hold water for up to six hours after a storm.
Dry swales rely on an engineered soil mix below a grass channel to temporarily store and filter stormwater. Water will pool in the dry swale for up to 6 hours after a rain event before soaking into the underlying areas. If underlying soils do not absorb water well, there may also be an underdrain to direct filtered stormwater into the storm drain system. Systems with an underdrain will have a capped pipe to access the drain.
Maintenance of a dry swale is the responsibility of the property owner.
- Keep grass mowed, no shorter than 3 inches. Remove any grass clippings.
- Prune, weed, water, and mulch as needed.
- Remove sediment, litter and debris, and leaves regularly or after a storm.
- Reseed any bare areas and repair eroded areas when needed.
An infiltration trench is a small trench filled with stone that collects runoff from paved or impervious surfaces such as driveways or roofs and allows it to absorb into the underlying soil.
An infiltration trench contains a perforated pipe in a stone trench. Stormwater runoff is directed into the pipe which then drains out into the trench. During small rain events, stormwater flows out of the pipe through the perforations into the gravel and then into the soil. During larger storms, stormwater will be stored in the stone trench, but water will also flow through the pipe to a larger BMP. Runoff that moves into the soil can help recharge groundwater.
Maintenance of an infiltration trench is the responsibility of the property owner.
- Keep grass mowed along the infiltration trench, no shorter than 3 inches. Remove any grass clippings.
- Remove any vegetation from the stone trench.
- Remove litter, debris, leaves, and sediment at least once a month and as needed after a heavy storm to prevent clogging.
- Check for erosion and bare spots regularly.
- Be careful not to regularly drive over the trench so as not to cause compaction or crush the perforated pipe.
- Check the access pipe annually to make sure that it isn't clogged.
Rain gardens are shallow landscaped gardens designed to temporarily store and treat stormwater runoff from your roof, driveway, walkways and lawn. They consist of several layers: a gravel bed, a special engineered soil mix and sand, mulch, and planted with native grasses, flowers, shrubs, and sometimes small trees.
Bioswales are similar in the way rain gardens are designed with layers of vegetation, soil and also have a perforated pipe, or underdrain, in the gravel bed to assist n filtering storm water into the soil and storm drain system.
When it rains, stormwater runoff flows into the rain garden or bioretention area and collects in the garden area. Runoff may pool 6 to 12 inches above the mulch, but filters through the plant bed within 48 hours. The specially selected native plants absorb some runoff and nutrients through their roots and the excess runoff soaks through the mulch and filter media layers to the gravel bed and underlying soils. This process helps filter out pollutants before the stormwater is released into waterways.
Maintenance of a rain garden or bioretention area is the responsibility of the property owner.
- Water during dry spells to promote plant growth.
- Prune and weed to maintain appearance.
- Replace mulch as needed to keep it 1 to 3 inches deep.
- Check vegetation to make sure that it is healthy. Remove any dead vegetation and replant with the right native plants for the light and moisture conditions.
Permeable (or porous) pavement are surfaces made from porous material that allows stormwater to flow through it into the underlying stone and soil below instead of flowing off it. Permeable pavement may be made from porous asphalt, pervious concrete, or permeable interlocking pavers.
Permeable pavement is used primarily for walkways, parking areas, driveways, and patios. It is typically designed to treat stormwater and prevent rain falling on the pavement from becoming runoff.
Maintenance of pervious pavement is the responsibility of the property owner.
- Monitor the surface for sediment buildup, remove as necessary.
- Vacuum-sweep pavement or interlocking joints when needed.
- Ensure voids are clean and free of non-compressible materials that may inhibit draining; remove weeds by the roots.
- Fill with new stones if needed.
- Planted areas near the permeable pavement should be well maintained to prevent soil from washing into the pavement.
Rain barrels come in many different sizes, but a 55-gallon tank is the most common. Cisterns are tanks of 200-gallons or more. Water is captured from a surface, such as a roof, and conveyed to the rain barrel or cistern through pipes or gutters. This prevents stormwater from entering the storm drain system and can help with localized flooding. There is an overflow system that diverts excess rainwater when full.
The stored water is then available for non-potable use through a spigot or hose. Gravity facilitates the water in the tank being dispensed, so the barrel may be elevated on a stand or blocks to improve flow through a hose.
Rain barrels are a low-cost stormwater management tool that can typically be added to any buildings with gutters or downspouts. The containers collect and temporarily store rainwater from roofs which can then be used for other non-potable (non-drinking) uses such as watering plants, gardens or your lawn.
Maintenance of a rain barrel or cistern is the responsibility of the property owner.
- Keep the screen clean by removing any leaves or debris that could block the flow of water into the barrel.
- Use the water in the barrel regularly so that it is empty and ready to collect runoff from the next rain event.
- During winter, empty the rain barrel before a freeze.
- Occasionally rinse out the barrel or tank to remove any accumulated sediment.
Stormwater ponds, or retention ponds, are permanent pools of water that collect and store stormwater runoff from roofs, roads, and parking lots. They reduce pollution and improve water quality by filtering the runoff before it enters our local waterways. They also control water quantity to reduce localized flooding.
Stormwater ponds collect water that drains off from impermeable surfaces. They are designed to hold a permanent level of water, above which stormwater runoff is temporarily stored and released at a slower or controlled rate. This allows sediment to settle out removing pollutants before the water is released back into a local waterway. Most ponds also have a buffer, or vegetation, around their perimeter to slow runoff and control erosion. Vegetation helps stabilize the bank and assists in filtering out pollution by absorbing excess nutrients. Native plants around a pond also provide wildlife habitat and aesthetic value.
Some stormwater ponds have an aerator system (fountain) that agitates and circulates the water to improve oxygenation and help prevent algae growth.
Maintenance of a stormwater pond is the responsibility of the property owner.
- Keep litter, yard waste and pet waste out of ponds. Conduct periodic shoreline cleanups to remove trash, debris and floatables.
- Keep vegetation around the banks maintained. This could include regular mowing of grass or annual trimming of woody vegetation.
- Remove any invasive plant species.
- Reseed aquatic plants if necessary.
- Monitor the pond for evidence of destructive wildlife that may cause banks to erode.
- Do not use excess pesticides, herbicides or fertilizer.
- Scoop the Poop - be sure to clean up after your pets.