Can Low Impact Development Fix our Stormwater Problem?
Low Impact Development (LID) for Stormwater Mitigation

What is Low Impact Development (LID)?
Low Impact Development (LID) is a principle of green infrastructure that is an important part of managing stormwater and improving sustainability. LID is development that works with nature to encourage infiltration and/or evapotranspiration of stormwater. LID can take advantage of natural features to direct stormwater and mitigate some of its negative effects.

What does LID look like?
You’ve probably seen LID before and perhaps not even realized it – part of the appeal of LID is that it works unobtrusively. Rain gardens, green roofs, rain barrels, vegetated swales, and using porous concrete or asphalt are all examples of LID. A side-benefit of LID is that it adds pleasant greenspace to urban environments. Parking lots, high-rises, highways, and office parks are all potential sites for LID.

Rain Gardens


Rain gardens work by collecting the rainwater that falls in a certain area and filtering it through layers of different sized gravel. It slows the water down so that it has a chance to infiltrate to the soil. Photo Source

Green Roofs


Green roofs use rainwater to water the plants that are growing on top of the building. Rain barrels collect rainwater and store it for later use. Photo Source

Vegetated Swales


Vegetated swales direct rainwater and also allow it to infiltrate to the soil using the vegetation. Porous asphalt and concrete turn a previously impervious surface into a permeable one, allowing water to trickle down to the soil. Photo Source

But why should we care about something that works in the background and simply encourages water infiltration?

For those in the Pittsburgh-area, LID may be an important way to combat damaging flooding during large storms and to improve water quality.

Pittsburgh’s stormwater problem comes from the amount of rainfall we receive and the CSO (combined sewer overflow) system. A CSO operates where both sewage and rainwater travel through the same pipes. When these pipes operate at- or below-capacity, the system operates as it should: all the water goes to a water treatment plant. When the pipes operate above-capacity, the system overflows, releasing both sewage and stormwater onto roadways and into waterways. While this scenario is obviously bad, it is common where CSOs exist.

Separating the storm system from the sewer system is one possible solution. This can be complex but would be feasible – cities larger than Pittsburgh have done it. A way to circumvent the problem entirely, however, would be to reduce the amount of stormwater entering the sewage system in the first place. LID can help achieve this.

LID is a promising solution because the more stormwater that enters the soil and atmosphere, the less there is to contribute to runoff on land. This not only reduces the strain on CSOs but also can help improve water quality. The soil and vegetation that are used in LID filter the stormwater that the LID captures.

We should strive to avoid CSO discharge into waterways because it can negatively affect water quality. In addition to the sticks, leaves, refuse, and oil that can run off of roadways, sewage has its own set of biological and chemical pollutants. CSO flooding releases this pollutant cocktail into local waterways and directly affects recreation and wildlife.

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