What is low impact development?
Low impact development (LID) is a design approach for managing stormwater runoff. It emphasizes conservation and the use of on-site natural features to protect water quality. LID includes engineered practices that are designed to mimic natural hydrology by infiltrating stormwater runoff into the ground, evapotranspiration (uptake of water by plants) in landscaped areas, or capturing and reusing the runoff through rainwater harvesting techniques.
How is the City of Tuscaloosa implementing LID?
The City of Tuscaloosa has permitted over 200 LID sites since April 27, 2011. The City has been recognized as a leader in the state for LID implementation. Click below to view the National Low Impact Development Atlas and zoom into Tuscaloosa to see examples of LID elements that have been implemented locally. National Low Impact Development Atlas
Below are some examples of LID:
Permeable Pavers - Permeable pavers are a system of concrete pavers with layers of varying-sized stone – or aggregate – underneath that filter and direct storm water to underground aquifers. Permeable pavers are used as a way to control stormwater on developed sites. Any rain that falls on the permeable paver patio, walkway or driveway percolates between the pavers and, depending on the soil type, the water infiltrates back into the ground and/or slowly releases to the nearest storm sewer or waterway.
Rain Garden - A rain garden is a planted depression or a hole that allows rainwater runoff from impervious urban areas such as roofs, driveways, walkways, parking lots and compacted lawn areas to be absorbed. It reduces rain runoff by allowing stormwater to soak into the ground (as opposed to flowing into storm drains and surface waters which causes erosion, water pollution, flooding and diminished groundwater). Rain gardens can cut down on the amount of pollution reaching creeks and streams by up to 30 percent.
Sheetflow – Sheet flow is a flow that occurs overland in places where there are no defined channels and stormwater spreads out over a large area at a uniform depth. The flow typically drains toward a vegetated/grassed area to allow the stormwater to infiltrate into the ground or enter an inlet. As the stormwater flows through the vegetated/grassed area, pollutants and silt are removed.
Bioswales - Bioswales are landscape elements designed to remove silt and pollution from surface runoff water. They consist of a swaled drainage course with gently sloped sides (less than six percent) filled with vegetation, compost and/or riprap. The water's flow path, along with the wide and shallow ditch, is designed to maximize the time water spends in the swale, which aids the trapping of pollutants and silt. The two most common types of bioswales seen in the City of Tuscaloosa are grassed swales and infiltration swales.
Level Spreaders - A level spreader is a device designed to reduce water pollution by mitigating the impact of high-velocity stormwater surface runoff. It is used both on construction sites and for permanent applications such as drainage for roads and highways. The device reduces the energy level in high-velocity flow by converting it into sheet flow and disperses the discharged water so that it may be infiltrated into soil.
Underground Detention and Infiltration Systems – Underground detention systems are employed on a site to reduce the quantity of stormwater runoff leaving a site by temporarily storing the runoff that exceeds a site’s allowable discharge rate and releasing it slowly over time. Underground infiltration systems are incorporated to reduce the volume of stormwater runoff discharged from a site. Underground detention and infiltration systems are primarily used in newly-developed areas where land cost and/or availability are major concerns. Most systems are built under parking lots or other paved surfaces in commercial, industrial and residential areas. Perforated underground detention systems that release stored storm water into the subsoil are recommended only for areas with well-drained soils and where the water table is low enough to permit recharge. Some pretreatment such as sediment traps may be necessary for infiltration to eliminate sediment and other solids that could clog the system.
Storm Drain Snout – A storm drain snout structure is a catch basin with a plastic composite hood device attached to the inside wall of the catch basin structure designed to cover the outlet pipe in such a manner to prevent the exit of floating debris and oil. A catch basin with a snout structure installed also allows suspended solids to settle to the bottom of the basin while cleaner water from beneath the surface flows through the outlet pipe.