What is Stormwater? Zoning Definition

Stormwater is water from rain or melting snow that flows across the land surface instead of being absorbed into the soil. In natural landscapes, most rainfall soaks into the ground. But when land is developed with buildings, roads, parking lots, and other impervious surfaces, much more water runs off, picking up pollutants like oil, fertilizers, and sediment along the way. Managing this runoff is a major concern in land development and zoning.

Most cities and counties have stormwater management regulations that require new development to control the rate and quality of runoff leaving a site. Common requirements include building detention or retention ponds, installing rain gardens or bioswales, using permeable pavement, and limiting the total amount of impervious surface on a lot. These rules are typically enforced through the site plan review and building permit process.

For homeowners, stormwater regulations can affect projects like adding a driveway, building a patio, or constructing an addition. If your project increases the amount of impervious surface on your lot, you may need to include stormwater management features or demonstrate that your project will not increase runoff beyond what the site currently generates. Some jurisdictions also charge stormwater utility fees based on the amount of impervious surface on your property.

Federal regulations under the Clean Water Act require cities with municipal storm sewer systems (known as MS4s) to obtain permits and implement programs to reduce stormwater pollution. These federal requirements trickle down to local development codes and affect what property owners and developers must do to manage runoff on their sites.