What is a Green Alley?
A green alley is constructed so that it reduces the impact on the environment. It may use methods to manage stormwater runoff that reduces the amount of runoff and improves the quality of the water before it runs into the storm sewers and the streams. A green alley can also be green space. Alleys that are not used for service or emergency access can be made into a neighborhood mini-park with trees and landscape, like the Q St NW Green Alley.
Why does the city want to install Green Alleys?
The city is striving to make all of its infrastructure and operations more sustainable. D.C. must improve the quality of the water running into rivers and streams to meet permits associated with the Clean Water Act. We want to reduce the amount of water that flows into the sewers and streams which causes stream bank erosion. We want to filter and clean storm water before it flows into the streams to improve the health of the streams for people, wildlife and the entire ecosystem. Permeable pavement allows water to infiltrate into the ground, which recharges groundwater, reduces the volume of runoff and improves water quality. D.C. will be constructing Green Alleys as pilot projects in 2011 and 2012 to determine the effectiveness and durability of the materials.
What is permeable pavement?
Permeable pavement has pores or openings that allow water to pass through the surface and percolate down through the existing soil. Permeable pavement can include porous asphalt, pervious concrete, and permeable pavers. A thick gravel layer under the pavement gives space to store the water and gradually filter into the surrounding soil. In areas where soils do not drain well, pipe under drains will be used to ensure the water can flow out before damaging the pavement.
How is construction of a green alley different from a conventional alley?
Normally, it takes about a week to pave an alley with conventional concrete or asphalt. An alley with permeable paving is excavated twice as deep as a conventional alley and the pavement needs 14 days to set before it can be driven on. We can expect a green alley to take about two months from start to finish, including time needed for pavement to firmly set (cure).
How will construction affect the residents?
Residents will not be able to have vehicle access their alleys for about two months. DDOT will notify you in advance of an alley improvement project and access to garages and driveways will be temporarily restricted. Garbage pickup will be temporarily relocated from the alley to the front of your house.
Green Alley Dos and Don’ts
- Keep your green alley clean of dirt and debris. Sweep leaves and plant debris off the alley.
- Install rain gardens, bioswales, and rain barrels on your own property to absorb and filter water before reaching the alley. DDOE’s River Smart homes program can help you implement these practices and provide financial assistance.
- Drive on the alley until curing time is complete and barriers are removed!
- Dump chemicals or toxic materials on or near the green alley
- Spread sand or dirt on or near permeable paving in the green alley
- Remove stone from between permeable pavers
- Seal permeable asphalt or concrete