Storm water runoff is a significant environmental problem for the Los Angeles area, as it contributes to ocean pollution and exacerbates drought conditions. Low impact development (LID) is a development strategy that seeks to manage storm water runoff more effectively by dealing with runoff water on site, rather than trying to channel the water away as quickly as possible.
Low impact development principles embrace and utilize a variety of specific techniques and structures to accomplish this task. The United States Environmental Protection Agency uses the term “Best Management Practices,” or BMPs, to refer to some of the best-suited techniques and structures, for reducing the amount of surface pollutants carried by storm water runoff.
Vegetated Swales and Rain Gardens
One of the simplest ways engineers and city planners can help reduce runoff water is to break up extensive paved areas with small “islands” of vegetation. This allows the plants to absorb and store the water, before ultimately releasing it back into the atmosphere. Most often, these areas are installed in low-lying areas, to take advantage of the natural lay of the land.
Rain cisterns are valuable tools for managing rainfall and reducing an area’s runoff water. By storing rainwater, rain cisterns transform the surplus water from a liability to an asset. Cisterns collect the water pouring out of downspouts, thereby reducing the amount of storm water filling sewers and collecting pollutants. Additionally, they serve as a source of clean water, suitable for watering lawns, irrigating crops and other outdoor uses.
At first glance, the notion of sod-covered roofs (pictured above) seems like a joke. However, upon closer examination, it becomes obvious that the concept has many merits. The grass absorbs most of the rainfall landing on the roof, which helps to address runoff water problems, and it helps to keep homes cooler in the winter, courtesy of the insulating value of the plants and soil. Additionally, as the grass transpires – drawing water from its roots and releasing it into the atmosphere – it lowers the local temperature further.
Permeable Pavers and Pavement
Some places simply require extensive paved areas; shopping malls, municipal centers and grocery stores are rarely feasible without large parking lots and pavement. Fortunately, engineers have devised a solution for these areas, called permeable surfaces. Unlike traditional surfaces composed of solid concrete or asphalt, permeable pavements allow water to trickle through them, rather than run across the surface.
Curb Cuts and Bump-Outs
Curb cuts are a brilliantly simple solution to storm water. Whereas conventional curbs contain water, preventing it from reaching the vegetation and soil a few short inches away, curbs designed with low impact principles have periodic gaps cut into them. These cuts allow water to pass through to the planted areas, reducing the overall volume of water flowing along the curb, and use it in the immediate vicinity to water plants and trees.
Simply planting medium or large canopy trees along sidewalks and roads drastically reduces the amount of runoff water in the area. Trees absorb water from the soil, use what they need and allow the excess to evaporate into the air via small holes in the leaves. This process not only manages runoff water, but it provides all of the other benefits trees do, such as shading the area, cooling the environment through the process of transpiration, improving the aesthetics of the area and raising property values.