What is a green street?

A green street is a natural stormwater management approach that uses plants and soil to slow, filter, and cleanses stormwater from streets. Traditional stormwater management directs runoff into pipes. A green street manages stormwater at its source, where rain falls.

Green streets protect water quality in rivers and streams by removing up to 90% of pollutants. They replenish groundwater supplies, absorb carbon, improve air quality and neighborhood aesthetics, and provide green connections between parks and open space. Vegetated curb extensions improve pedestrian and bicycle safety, and calm traffic.

Stormwater in Urban Areas

In rural areas, rainwater infiltrates into the ground. Water is then naturally filtered through the soil and recharges groundwater. This natural cycle becomes more difficult as areas are developed with impermeable surfaces or surfaces that water cannot move through, such as parking lots and asphalt roads. Urban areas, like Cities, have low permeability for water to infiltrate. Instead, water travels through roofs and streets, into a storm drain system before it is released into local creeks and oceans.

Runoff becomes contaminated with debris, sediment, automobile fluids, fertilizers, and other pollutants while making its way to the nearest storm drain. Streets are designed for stormwater to travel quickly into drains, so there is no opportunity to clean out any pollutants before they enter a water body. Therefore, the contaminants and pollutants picked up by the runoff find their way into storm drains, which drain directly to our local creeks and jeopardize water quality. Developed cities contribute high amounts of stormwater due to large paved surfaces. 

Citywide Green Streets Project

This project will use green infrastructure to redesign street locations within the City of Calabasas. The design will include storm-water capture for reuse or recharge of aquifers by adding bio-retention swales and basins, and increasing permeable surfaces. The implementation of this project will improve water quality by using different filtration systems to capture and treat stormwater surface flows before entering Calabasas’ water streams.

Along with treating surface flows, there will be the addition of native trees and plants along various roadways to reduce carbon dioxide emissions and provide soil stabilization. The added bio-swales and planted trees will provide an aesthetic enhancement by providing visually appealing landscapes. The Citywide Green Streets Project will incorporate educational outreach which will assist in educating the community about the main benefits associated with the venture. Green streets will also increase the safety of pedestrians and road users by slowing down vehicle speeds through the implementation of raised medians, established curbs, and painted bike lanes.  The City is actively seeking funding opportunities for the following proposed phases of the Citywide Green Streets Project. 

Existing Conditions

• Low permeability increases flooding and does not allow for water filtration
• Urban runoff picks up pollutants from roadways like metals, motor oil, and nutrients
• Increased sediment from unpaved locations
• Water damage on roadway due to poor water surface management

The primary objectives of Citywide Green Streets Project:

• Improve water quality by removing urban runoff pollutants
• Reduce urban runoff entering the City’s storm drain system
• Increase air quality by planting trees along the roadways
• Educating the community on the benefits of Green streets
• Increased water surface management with permeable surfaces

1. Malibu Hills Road

The project constructed bio-filtration medians with impermeable liners and an underdrain along the road. Four center medians were built and serve as a pretreatment BMP that capture and treat surface flows. Treated flows are discharged into downstream catch basins. Phase I consisting of one bio-filtration center median was completed in December 2017 and 3 more medians were completed in March 2020.
This project was financed under the Safe Drinking Water, Water Quality and Supply, Flood Control, River and Coastal Protection Bond Act of 2006 (Prop 84) administered by State of California, Department of Water Resources.

Multi-Benefit Description:
1) Water Quality: The project improves water quality by filtering flows through bio-filtration soil media.
2) Aesthetic Enhancements: The improvement includes a visually appealing landscape for the community.
3) Enhanced Traffic: The center medians enhance traffic patterns by reducing speed and providing space for bike lanes in the future.

2. Las Virgenes Road

The project proposes to add a vegetated swale on the west side of the road. The vegetated slope will serve as a pretreatment BMP that will capture and treat surface flows. Treated flows will discharged into bioswales and vegetated planters. This green infrastructure will serve as infiltration chambers that will hold and gradually infiltrates through the soil media. The remaining unpaved shoulder will be retrofitted to serve as parking for the residents of the area. Native trees will be planted along the slope for dust control and soil stabilization. This phase is expected to be completed in October 2024. 

Multi-Benefit Description:

1) Water Quality: The project will improve water quality by filtering flows through the vegetated swale and bio-filtration soil media and by reducing sediment due to the unpaved shoulder.
2) Aesthetic Enhancements: The proposed improvement will include visually appealing landscape for the community.
3) Community Outreach: The project incorporates educational outreach signage which will help to educate the community on the many benefits of the venture.

3. Calabasas Road (West)

The project proposes to remove the existing sidewalk and replace it with a permeable surface. The road will be designed to direct the surface flows into the curb to be treated with bio-filtration soil media. The treated flows will be discharged into downstream catch basins.

Multi-Benefit Description:
1) Water Quality:
2) Aesthetic Enhancements: The proposed improvement will include visually appealing landscape for the community.
3) Community Outreach: The project incorporates educational outreach signage which will help to educate the community on the many benefits of the venture.

4. Mureau Road

The project proposes to construct a total of three (3) raised medians that will provide refuges for pedestrians crossing Mureau Road.  The total distance of the project is 980 feet.  The roadway width will be reduced resulting in the reduction of vehicle speeds.  That, in turn, will improve both pedestrian and traffic safety on the roadway.  New bike lanes will be installed and native trees will be planted as part of the scope of this project.

The newly constructed medians will serve as a pretreatment Best Management Practice (BMP) which would capture and treat surface flows. The collected water will be filtered through the bio-filtration soil to remove urban runoff pollutants such as sediments, bacteria, metals, and trash, and improve the quality of the water entering the storm drain system.

Multi-Benefit Description:
1) Water Quality: The project will improve water quality by filtering flows through bio-filtration soil media.
2) Aesthetic Enhancements: The proposed improvement will include a visually appealing landscape of native vegetation for the community. The project also includes bike lanes and pedestrian refuge in the newly constructed, raised medians.
3) Community Outreach: The project will incorporate outreach which will help to educate the community on the many benefits of the proposed project. 

For more information:

Los Angeles Low Impact Development Manual:
https://dpw.lacounty.gov/ldd/lib/fp/Hydrology/Low%20Impact%20Development%20Standards%20Manual.pdf

Stormwater Pollution Fast Facts:
https://dpw.lacounty.gov/prg/stormwater/page_30.cfm

Learn about Green Streets:
https://www.epa.gov/G3/learn-about-green-streets