Low-Impact Design Strategies

Practices

The basic Low-Impact Design (LID) strategy for handling runoff is to: 1) reduce the volume of runoff and 2) decentralize flows. This is usually best accomplished by creating a series of smaller retention/detention areas that allow localized filtration (rather than carrying runoff to a remote collection area) in conjunction with facilities addressing larger storm events as required. Common methods include:

• Bioretention Cells/Rain gardens
• Vegetated Swales
• Filter Strips
• Disconnected Impervious Areas
• Cistern Collection Systems

Site Design

Decreasing Impervious Surfaces can be a simple strategy to address water quality and avoid problems from stormwater runoff and water table depletion, by reducing surfaces that prevent natural filtration. Methods may include:

• Reducing Roadway Surfaces
• Permeable Pavement Surfaces
• Vegetative Roof Systems (Green Roofs)

Benefits versus Costs

Cost benefits to builders and developers utilizing LID strategies can be significant. According to the Center for Watershed Protection, traditional curbs, gutters, storm drain inlets, piping and detention basins can cost two to three times more than engineered grass swales and other techniques to handle roadway runoff. Choosing permeable pavement for a parking area may remove the need for a catch basin and conveyance piping. Small distributed filtration areas on individual lots can reduce site requirements for larger detention ponds that take up valuable land area.