Glossary of Stormwater Control Measure Terminology

(A full Stormwater Glossary is available here.)

Berm: A constructed barrier of compacted, raised earth used to prevent and slow the flow of runoff.

Bioretention Cell: A landscaped depression designed to remove pollutants from stormwater runoff through infiltration.

Buffer: The vegetated area between a water body and adjacent land uses; provides soil stability, slows the flow of runoff, and improves water quality by filtering out pollutants.

Catch Basin: The underground pit beneath a storm grate that collects rainwater from streets and serves as an entry point to the storm drain system.

Channel: The natural path of water and sediment flowing within stream banks.

Cistern: A storage tank located above or below ground that holds rainwater for beneficial reuse.

Culvert: A tunnel, pipe or other structure that allows water to flow under a roadway, railroad or other obstruction.

Detention: Temporarily collecting and holding stormwater runoff while slowly draining to another location.

Discharge: 1. A flow of liquids from a source; can be made up of washwater, sewage, stormwater, wastes, tap water, spring water or other sources. 2. A measurement of the volumetric rate of water flow over a period of time, usually expressed as cubic feet per second.

Downspout: A typically vertical pipe that carries rainwater from a roof gutter to the ground level.

Drainage: The natural or artificial process of removing excess surface and sub-surface water.

Drainage Basin: All the land, surface water, and underlying groundwater that drains to a given point; also known as a watershed.

Dry Pond: A depression that temporarily holds stormwater and releases it at a slower rate until it enters a stream or collection system. Also known as a "detention pond."

Easement: A right to use and/or enter a specified area of land owned by somebody else; granted to utilities or municipal governments to maintain equipment or infrastructure, or to other private parties for a specified use.

Erosion: The process of detaching and moving soil from one location to another; caused by the action of wind, water, or other forces working on the earth's surface. 

Forbay: A sediment forebay is a post-construction practice consisting of an excavated pit, bermed area, or cast structure combined with a weir, designed to slow incoming stormwater runoff and facilitating the gravity separation of suspended solids.

Flooding: The rising and overflowing of a body of water, submerging land that is usually dry.

Floodplain: An area of land adjacent to a stream or river channel that is susceptible to natural flooding during periods of high discharge.

Grading: The cutting, filling or other alteration of the land surface to a desired slope or elevation.

Green Roof: A roof partially or completely covered with vegetation, designed to absorb and filter rainwater and provide other environmental benefits. 

Illicit Connection: Any connection to the storm drain system that is not permitted, or any legitimate connection that is used for illegal discharge.

Illicit Discharge: The release of any material into the stormwater conveyance system which is not authorized by the regulating body and/or contains pollutants or pathogens.

Infiltration: The process of water soaking into the ground from the surface, commonly referred to as percolation.

Infrastructure: The set of fundamental facilities, systems, and equipment serving an area for public benefit, such as roads, pipes, and buildings.

Inlet: A point where stormwater enters a stormwater conveyance system, such as a catch basin.

Level Spreader: An erosion control device, such as a concrete lip, designed to mitigate the impact of high-velocity stormwater runoff by evenly distributing flow.

MS4: Municipal Separate Storm Sewer Systems, a collection of structures designed to gather stormwater and convey it to local streams or rivers.

NCDEQ: North Carolina Department of Environmental Quality, a state agency whose purpose is to protect North Carolina's environment and natural resources.

NPDES: National Pollutant Discharge Elimination System, part of the Clean Water Act which requires permits for surface water pollution. In North Carolina, these permits are issued and enforced by NCDEQ.

Nutrient Load: The total input of nutrients into the ecosystem from human and non-human sources, which can become stressful to aquatic ecosystems in excess.

Outfall: A point where collected storm water runoff is discharged from an underground piped system or above ground conveyance into a receiving water body.

Permeable: Having pores or openings that permit liquids to pass through, also known as "pervious".

Rain Barrel: A storage device that collects stormwater, usually from a roof surface, which can be reused for irrigation, washing vehicles, or other uses not involving human consumption. 

Rain Garden: A bowl-shaped area in the landscape planted with native shrubs and flowers, where rain water collects and is absorbed back into the soil.

Rainwater Harvesting: The collection and storage of rainwater in a container or planted area, preventing excess runoff and redirecting the water for beneficial use.