Green Streets are roadway landscaping designs that reduce and filter stormwater runoff.
Green Streets are part of a County initiative to capture stormwater runoff in neighborhoods with minimal stormwater controls and not enough open space for larger stormwater practices. They use Low Impact Development (LID) and are constructed within the street right-of-ways.
When the County considers installing a Green Street, they take into account factors like utilities, existing drainage patterns, soils, tree impacts, the amount of runoff volume, and many other considerations.
More information is available on the Green Streets brochure (PDF).
A shallow depression planted with native plants
Gravel layer has an underdrain pipe that is connected to a nearby storm drain to help drain the facility after rain events
Collects, stores and allows rainwater from roadway to absorb into ground
Adds beauty to your street, with maintenance that varies based on the plants you select
Mini bioretention boxes filled with a soil mixture, a mulch layer, under-drain system and a shrub or tree
Typically used when space is limited
Requires proximity to a storm drain system
Pervious sidewalk allows water to infiltrate into ground below
Permeable pavers can be used to create parking pads along the roadway, also allowing water to infiltrate
Pavement removal may be used in combination with a stormwater management technique depending on site conditions
Less pavement means less stormwater and pollutants entering local streams
Placed within the road right-of-way between the curb and the sidewalk
Sometimes curbs are extended into the parking lane and pavement is removed to widen the available footprint and treatable drainage area
Requires adequate space and minimal impact to parking
Allow runoff to percolate into the ground, reducing the amount of runoff leaving the roadway
Check dams can be used within a swale to slow the flow rate, promote infiltration, and create small, temporary ponding areas
The vegetation covering the side slopes and channel bottom provides a filtration surface for the water and helps to reduce the flow velocity
Do you have a Green Street in your neighborhood? DEP typically maintains these rain gardens monthly. You can also help DEP by performing a couple small tasks.
|Actions You Can Take||Actions You Shouldn't Take|
|✔ Mow outer edges.||✘ Don’t use fertilizer or pesticide.|
|✔ Water if it hasn't rained in 10 days and is within the first 18 month of planting, or, during extreme drought.||✘ Don’t plant or remove plants.|
|✔ Remove any trash that has washed into the bioretention area or the inlet channels or pipes.||✘ Don't mow the inside of the rain garden.|
|✔ Check the facility a few days after a rain storm to make sure that there is not standing water after 2 days.||✘ Prune or cut back plants.|
|✔ Regularly inspect the practice for signs of erosion, obstructions, or unhealthy vegetation. Contact DEP if you notice problems.|
This project is part of the County’s need to meet Federal and State mandates to control and treat stormwater runoff. The goal of Green Streets is to reduce stormwater runoff, minimize pollution, promote infiltration, and restore stream conditions throughout County watersheds and the Chesapeake Bay.
Green Streets facilities are typically constructed within the street or within the County right-of-way areas (i.e. the grassy strip between the sidewalk and the curb).
There are many different looking Green Streets and Low Impact Development features. In the case of a rain garden or bioretention, they are typically bowl-shaped, sometimes sodded, and sometimes landscaped with plants and mulch. Tree box filters look smaller, with a square inlet with a tree or small shrub(s) planted inside a filter box filled with a bioretention soil mix. Typically, landscape designers work with the County to develop aesthetically pleasing designs that help connect a neighborhood together and provide a sense of neighborhood identity.
For additional photos, visit the Stormwater Management Best Practices webpage or the DEP Flickr website . The general Green Streets Photo Album and the Dennis Avenue Green Streets Photo Album are two good examples.
DEP is responsible for the maintenance of Green Streets. DEP will monitor the practices monthly to make sure they are functioning properly. Contact DEP if you have any questions or concerns about the practices in your neighborhood by either calling 311 or email us at askDEP@montgomerycountymd.gov.
ensure the plants are healthy;
remove dead, diseased, or dying plants;
replace plants as needed;
replenish the mulch;
regularly weed; and
remove sediment and trash that accumulates in the facility.
It depends on the type of practice, but generally, stormwater runoff from the roadway is diverted into an inlet opening in the curb, and is filtered through a mixture of highly permeable soils (sand, mulch, compost), then stored in an underlying gravel layer before percolating into the groundwater and/or entering into an underdrain that flows to the storm drain system.
Runoff has an opportunity to cool down while the plants help absorb nutrients and microbes around the plant roots help break down pollutants. When certain facilities are full after rain events, water may pond up to six inches before draining within 12 to 48 hours, depending on the type of facility and site conditions.
Email askDEP@montgomerycountymd.gov for information on Green Streets in your community.