OC Watersheds Glossary of Terms



Aquifer Water bearing layer of the earth's crust.


Best Management Practice (BMP) an engineered structure or management activity, or combination of these, that eliminates or reduces and adverse environmental effect of a pollutant.


Detention Basin Reservoir designed to slow the rate of flow in an open drainage facility.


Estuary Body of water at the lower end of a river which is connected to the ocean and semi-enclosed by land. In an estuary, sea water is measurably diluted by freshwater from the land.


Flood Control Channel Open waterway that is designed to carry large amounts of rain water. These structures are often lined with concrete to help control flood waters.


Gutter Area formed by the curb and the street to prevent flooding by channeling runoff to storm drains.


Illegal Discharge Any nonpermitted disposal into the storm drain system.
Illicit Connection Any connection to a storm drain system for which there is no permit or is used for an illegal discharge.
Indicator Bacteria Type of bacteria tested for in recreational waters as a means to ascertain the likelihood that harmful pathogens may be present. Indicator bacteria normally occur in the intestines of all warm-blooded animals and are excreted in high numbers in feces. There is no ideal indicator group of bacteria, so testing is currently done for three bacteria groups: total coliforms, fecal coliforms, and enterococcus. Most strains of bacteria within the three groups are not harmful themselves, but certain strains of E. coli, a fecal coliform bacteria are also pathogens.
Impervious Surface Paved surface or other land cover that does not allow water to percolate into the ground.


Nearshore Waters Coastal waters within a zone bounded by the shoreline and a distance of 1000 feet from the shoreline or the 30-foot depth contour, whichever is further from the shoreline.
Non-Point Source Pollution (NPS) pollution which does not come from a single, identifiable point but from a number of points that are spread out and difficult to identify and control.


Offshore Waters Coastal waters between the nearshore waters (see Nearshore Waters) and 3 miles from the shoreline
Outfall Opening at the end of a storm drain system that allows water to flow into a channel, lake, river, bay or ocean.


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Percolation Process where surface waters are absorbed through the soil into ground water.
Point Source Pollution Pollution from a single identifiable source such as a smoke stack or a sewage-treatment plant.
Pollutants Materials can include, but are not limited to, trash, paper, plastics, cleaning chemicals, animal waste, yard wastes, used oil, fertilizers, pesticides, sediment, metals, fuels, solvents, detergents and fecal coliform.
Pollution A human or naturally caused change in physical, chemical, or biological conditions that results in an undesirable effect on the environment.


Receiving Water Of a watercourse or waterbody that receives runoff or wastewater.
Runoff Water that flow over land surfaces and does not percolate into the ground.
Runoff Pollution (also stormwater, urban runoff, and storm drain pollution) rain and water from irrigation, garden hoses, or other activities that washes pollutants off of streets, parking lots, yards, and landscapes and into the storm drain system.


Sanitary Sewer System General term applied to waste water treatment plants that treat mainly household waste water supplied from plumbing/sewage lines. A series of biological and chemical processes are used at these treatment plants to remove many pollutants before the effluent is deposited into natural bodies of waters.
Source Control Action to prevent pollution at its origin.
Storm Drain System A system which includes grates, gutters, underground pipes, creeks or open channels designed to transport rain from developed areas to a receiving body of water.
Stream (also arroyo, barranca, creek) small natural waterway originating from underground springs, snow melt, runoff, or other natural sources which drains to lakes, rivers, channels or oceans.


Total Maximum Daily Load (TMDL) a numerical quantification of the pollutant loading that can be received by a waterbody. The TMDL consists of wasteload allocations for point sources (e.g., industrial and municipal discharges), load allocations for non point sources (e.g., agriculture, construction, siviculture), and a margin of safety so that any additional loading, regardless of source, would not produce a violation of water quality standards.


Water Quality Characterization Reports Are reference documents produced by Regional Board staff that describe the existing water quality conditions, data gaps, and sources of pollutants within a WMA. Strategies to resolve the water quality concerns, either in progress or proposed, are described. Preliminary versions of these reports are produced by the Regional Board in order to stimulate discussion and inputs on issues from other stakeholders. These documents will be updated as needed. First edition reports are available for Calleguas Creek, Santa Monica Bay, Los Angeles River, and San Gabriel River Watersheds.
Watershed Geographic area of land from which all runoff drains into a single waterway. Watershed Management Approach The watershed management approach is the specific method by which the Regional Board implements watershed management. Features include the targeting of priority problems, stakeholder involvement, developing integrated solutions, and evaluating measures of success. The entire watershed, including the land mass draining into the receiving water, is considered.
Watershed Management Areas (WMAs) are the geographically-defined watershed areas where the Regional Board will implement the watershed approach. These generally involve a single large watershed within which exists smaller subwatersheds but in some cases may be an area that does not meet the strict hydrologic definition of a watershed e.g. several small Ventura coastal waterbodies in the region are grouped together into one WMA.
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