Low Impact Development (LID) is a term being used today to describe a new engineering approach to land development and stormwater management. Low Impact Development focuses on conservation and on-site landscaping features to protect water quality. This approach is significantly different than modern drainage design which collects stormwater runoff in structures for treatment.
Why is Stormwater Runoff Bad?
Stormwater can pick up debris, chemicals, dirt, and other pollutants and flow into a storm sewer system or directly to a lake, stream, river, wetland, or coastal water. Anything that enters a storm sewer system is discharged untreated into the waterbodies we use for swimming, fishing and providing drinking water. Left untreated, stormwater pollution can damage natural habitats for wildlife, fish, plants and water supplies.
Typically storm water runoff is collected in detention ponds, catch basins and other drainage features. The water is stored in order to remove sedimentation and treat the water using biological and chemical means. Most stormwater detention structures are large and expensive to build. These structures usually require large pieces of land to be cleared and modified to build the structures.
Low Impact Development Features
There are quite a few low impact development features that can be used to reduce the stormwater runoff from a project. The most commonly used features are:
- Bioretention Cells (also known as rain gardens) – Bioretention is the process of biological removal of contaminants or nutrients as fluid passes through media or a biological system. Typically a rain garden is a depressed area that has a well draining soil and plant life (see photo above). These features are inexpensive to create and add aesthetically pleasing landscaping to the area.
- Cisterns and Rain Barrels – collecting rain water from gutters on buildings is a great way to reduce the amount of stormwater runoff. The cisterns can be used to store water for fire protection and irrigation. Smaller rain barrels are a great way to collect water for gardening and irrigation.
- Green Roofs – are roof surfaces covered with some type of vegetation and soil. The idea here is to capture rain water and hold it so it doesn’t run off the structure and create stormwater runoff from the impervious layer.
- Permeable Pavements – are porous pavements or pervious pavements that allow the movement of water through them to the soil below. Again the idea here is to reduce the stormwater runoff that you’d get from a traditional impervious pavement.
- Grassed Swales – or bioswales are designed to slow the flow of water and remove silt and pollutants. The swales have very gentle slopes with vegetation planted within it.
Benefits of Low Impact Development
The benefits to low impact development are fairly obvious. The biggest benefit is improved water quality and the protection of habitat for animals, fish and insects. LID also provides for much more aesthetically pleasing landscaping, reduced construction costs and a reduction in impervious surfaces. The other benefit to this approach is an improved rate of ground water recharge due to infiltration.
I hope you’ve found this brief discussion of Low Impact Development interesting and useful. If you have questions or comments I’d like to hear them. If this topic is of interest to my readers I can certainly provide future posts in more detail.
I wish that more attention had been paid to landscape/water management as the different subdivisions in our town were developed. A lot of our residents deal with stormwater issues on a very regular basis because developer after developer did “just enough” to pass legal muster without considering the overall impact of the development on the surrounding areas and the town overall. It’s a small town–it didn’t take long for water management to become a problem! My mom works for the town doing water billing (and handling the customer calls when water issues arise)– I often hear about the problems we’ve got, so I find discussions of how developers and communities can fix and avoid those problems VERY interesting and useful. Kudos on a good post (and on an underdiscussed topic!).