The amount of impervious surfaces – roads, parking lots, driveways, sidewalks, patios, and rooftops – increases as land is developed. As naturally pervious areas are replaced by impervious surfaces, a greater percentage of rainfall flows off the land as stormwater runoff instead of infiltrating into the ground. The increased volume and velocity of runoff flowing off of impervious surfaces may harm natural resources. Stormwater runoff also picks up pollutants – including car oil, fertilizers, pesticides, sediment, pet waste, and trash – and carries these pollutants to waterways and the ocean.
Low Impact Development (LID) is an approach to stormwater management that aims to replicate the site’s natural hydrologic balance. LID emphasizes site design strategies that protect the site’s natural capacity to retain stormwater, integrated with small-scale distributed Best Management Practices (BMPs) that rely on on-site infiltration, evapotranspiration, harvesting, detention, or retention of stormwater runoff. Coastal Commission Water Quality Program staff recommends giving precedence to an LID approach to stormwater management in all development.
Examples of LID site design strategies include minimizing impervious surface area, preserving natural vegetation, conservation and use of natural drainage features, maintaining the infiltration capacity of the soil, and directing runoff from impervious surfaces into pervious areas. Examples of LID BMPs include rain gardens, grassy swales, permeable pavements, rain barrels, green roofs, soil amendments, planting native plants, and bioretention systems.