Green Streets


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.  


Intro to Green Streets Video:


Benefits of Green Streets:

  • Create aesthetically attractive streetscapes
  • Provide natural habitat for pollinators and birds
  • Reduce stormwater runoff
  • Help visually to connect neighborhoods, schools, parks, and business districts.  

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).



Image of Rain Garden


Types of Green Streets Practices

Rain Gardens and Bioretentions

  • 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

Image of a Bioretention


Tree Box Filters

  • 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

Image of Tree Box Filters

Tree Box

Pervious Sidewalk, Permeable Pavers & Pavement Removal

  • 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

Image of Permeable Driveway

Permeable Pavement

Curb Extensions

  • 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

Image of Curb Extension

Curb Extensions

Grass Swales

  • 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

Image of Grass Bioswale

Grass Swale

Help Maintain Right-of-Way Rain Gardens and Green Streets

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.



Frequently Asked Questions about Green Streets

Why are you Creating Green Streets in my Neighborhood?

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.  


Where are Green Streets Practices? 

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).


What will the Green Streets Practices Look Like?

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. 


Who is Responsible for Maintaining Green Streets? 

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

DEP will:

  • 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. 



Image of a Green Street

How do Green Streets Work?

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.

Where are Examples of Green Streets in the County?


How Can I Learn More?

Email for information on Green Streets in your community.