Stormwater Glossary

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Stormwater is a complex issue with a number of technical terms. Here are some definitions to help explain many of the most common stormwater terms used by Durham County.

Adsorption	Attachment of pollutants in water to soil particles, resulting in retention of pollutants.
Base flow	Stream flow composed of groundwater seepage
Bioretention	The use of biological components such as plants, soil, and microbes to treat stormwater and remove contaminants and sedimentation
BMP/SCM	Best Management Practices/Stormwater Control Measures - Devices, practices, or measures that are designed, constructed, and maintained to remove pollutants from stormwater runoff; or to mimic the natural hydrologic cycle
(Riparian) Buffer	A vegetated area on either side of a stream of river, which helps shade and partially protect the stream from the impact of adjacent land uses
Culvert	A drain that directs unwanted water from open channels, swales, or ditches away from roads and other travel corridors or embankments.
Easement	The legal right to use a piece of land for a particular purpose - this does not include land ownership.
Ephemeral Stream	A stream that only flows for brief periods as a direct result of precipitation.
Erosion	The process in which earthen materials like sediment are worn away and transported by natural forces such as wind or water
GIS	Geographic Information Systems - a system that creates, manages, and analyses maps and data.
Groundwater	Water below Earth's surface that occupies empty space in soil and fractures in rock formations.
Illicit discharge	Any discharge into a storm drain system that is not entirely composed of stormwater.
Impervious surface	A surface which cannot be easily penetrated by fluids like water. Examples include sidewalks, roofs, decks, roads, etc.
Infiltration	The flow of a fluid (such as rainwater) through pores or spaces in a substance (such as soil).
Intermittent stream	A stream that only flows during certain times of the year, but not only in direct response to precipitation.
Non-point source pollution	Pollution that enters the environment from many indiscriminate sources (e.g. polluted runoff from city streets)
Nutrient Overload/Eutrophication	The process where too many nutrients, mainly nitrogen and phosphorus, are added to bodies of water and can act like fertilizer, causing excessive growth of algae which eventually results in low oxygen and blocked sunlight. This could come from fertilizer runoff or organic detritus like grass clippings ending up in waterways.
Perennial stream	A stream that has flowing water year-round during a typical year.
Point source pollution	Pollution from a single, identifiable source (e.g. discharge pipes or smokestacks)
Pollution	The introduction of harmful materials into the environment.
Rain Garden	A type of bioretention - a garden of native plants in a small slope that can hold and filter stormwater.
Retention	The process of collecting and holding surface and storm water runoff with no surface outflow.
Retrofitting	Modifying or upgrading an existing measure with a component not included when it was originally developed.
River Basin	An area of land where all flowing surface water converges to a single point, such as the Cape Fear River or Neuse River (typically larger than a watershed)
Runoff	Liquid that flows across the surface of the land and into nearby creeks, streams, or ponds when there is more water than the land can absorb.
Saturation Point	In soils, the point at which a soil or an aquifer will no longer absorb any amount of water without losing an equal amount.
Sedimentation	The process of sediment particles settling to the bottom of a body of water.
Storm Drain	A drain built to carry away excess groundwater in times of heavy rain. Typically drains directly to waterbodies without treatment.
Stormwater	Water from precipitation that runs off surfaces such as rooftops, paved streets, and parking lots. It can also come from compacted or saturated sediment and grassy surfaces like lawns, fields, and graveled roads.
Stream Restoration	The re-establishment of the general structure, function and self-sustaining behavior of the stream system.
Swale	A long, landscaped depression that collects and cleans stormwater. Can include grass swales, infiltration swales, bioswales, and wet swales.
Turbidity	The level of particulate matter such as sediment or organic by-products in a body of water (can usually be observed through the cloudiness of water)
Unincorporated	Areas within Durham County that do not fall within the City of Durham limits.
UNRBA	Upper Neuse River Basin Association - an organization for water quality protection and water resource planning and management within the Neuse River Basin.
Watershed	An area of land that drains all streams and rainfall to a common outlet, such as Ellerbe Creek or Little River (typically smaller scale than a River Basin)