A rain garden is a garden built specifically to capture stormwater runoff and let it seep slowly into the soil rather than running into the sewer system. When stormwater (runoff water and snowmelt) is absorbed into the ground, it filters and replenishes aquifers. However, much of the land surface in urban areas is covered by impervious, non-penetrable surfaces (like buildings and pavement) that prevent stormwater from being absorbed into the ground. Thoughtful landscape planning can help capture or divert stormwater during storm events. By controlling stormwater where it falls, the quantity of runoff will decrease.
More Facts about Stormwater
- Stormwater that does not seep into the ground flows into a combined sewer system or ends up directly in our streams and rivers. When it rains heavily or snow melts rapidly, the combined sewer system can overflow, resulting in the contamination of streams and rivers.
- A combined sewer system combines both sanitary sewage and stormwater in one piping system. When the capacity of the combined sewer system is exceeded, the excess flow is discharged into rivers and streams. Effective stormwater management can prevent the combined sewer system from overflowing.
- As little as one-tenth of an inch of rain can cause raw sewage to overflow into our rivers and streams in Pittsburgh.
- Stormwater that does not seep into the ground carries fertilizers, dirt, pesticides, grease, litter, and other pollutants into our streams and rivers.
- Stormwater runoff is nationally the most common cause of water pollution.
- When the combined sewer system overflows, Allegheny County issues river advisories if the water is too contaminated for contact. On average, nearly half of the days during the regular boating season are under advisory.
- 90% of Allegheny county residents use Pittsburgh’s rivers as the main source of drinking water.
Process
1. To design your lot to capture stormwater, the qualities of the vacant lot being used will have to be considered. Check out the site assessment page to see how different aspects of the site will affect how you will build your project. Because it takes some expertise to design a lot to capture stormwater, it’s a good idea to get input from an organization dedicated to stormwater issues, like Nine Mile Run Watershed Association, Stormworks, or Three Rivers Waterkeeper. For larger projects, it is necessary to seek help from an organization because any larger changes can affect the flow of water outside of your lot. Before going to one of these organizations, consider what stormwater issues exist right around your lot. Are there spots where water sits on the ground? Is there a roof nearby with a downspout that runs into the sewers? Below are some examples of strategies you may use:
- Rain Gardens or Bio-retention Cells: A rain garden is a planted recession that diverts runoff water from impervious surfaces, like rooftops and parking lots, around it into the ground, instead of the nearest storm drain.
- Rain Barrels and Cisterns: A rain barrel, or cistern, is a container used to collect and store rainwater, typically from rooftops via gutters and downspouts. Rain barrels store water that otherwise would have entered the sewer system or local waterways for future use on lot, and can help reduce water and sewer bills.
- Stormwater planters: A stormwater planter is a specialized vegetated planter box installed along sidewalks. They are designed to manage runoff. Water enters the planter through a curb cut or other inlet at street level, and excess volume beyond the capacity of the planter is directed to an overflow.
- Bioswales are landscape elements designed to remove silt and pollution from surface runoff water. By maximizing the amount of time water spends in gently sloped sides (typically planted with vegetation), more water can be filtered and infiltrated into the ground.
- Infiltration trenches are rock-filled ditches that collect stormwater and allow it to percolate into the ground through infiltration. They are often combined with other best stormwater management practices.
- Eliminate Curbs and Gutters: Curbs and gutters are designed to transport runoff to a stormwater drain as quickly as possible. By eliminating them, runoff can be diverted to a green area where it can infiltrate the ground. Furthermore, curbs and gutters create a concentrated flow of runoff. Their elimination can help establish a sheet flow, which will in turn help prevent erosion.
- Divert Downspouts: Downspouts in urban areas typically drain directly into the combined sewer system. By disconnecting downspouts and the drain, water can be diverted into pervious surfaces and filtered into the ground. A downspout disconnection can help reduce the quantity of roof runoff that enters into the sewer system.
2. Think about the overall purpose of your project. If, in addition to collecting stormwater, you’d like your lot to be visually appealing, to attract pollinators or provide some other environmental function, make sure you choose your plants according to that goal.
3. Check out the Department of Conservation and Natural Resources’ Plant Database for more information about what plants would be best for your site.
Benefits
- Keeps stormwater out of the sewer
- Keeps rivers cleaner
- Adds visual interest to a vacant lot
- Can increase neighborhood awareness of stormwater issues
- Habitat for native plants and wildlife
Suitability and Considerations
To do a Rain Garden or Stormwater Management project, the qualities of the vacant lot being used will have to be considered. Check out the lot assessment page to see how different aspects of the lot will affect how you will carry out your project
Vacant lots that have drainage issues or are adjacent to (and downhill from) impermeable surfaces. Check out the vacant lot you’re considering when it’s raining if you’re truly seeking to implement a project that will contribute to the stormwater management plan at a larger scale.
For more information, check out 3 Rivers Wet Weather’s website.
Materials
- Perennial native plants
- Mulch
- Soil
- Compost
- Gutter
- Rain barrel
- Landscaping stones
