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Above-ground planter – A large box of topsoil with timber sides. A raised bed provides accessibility to plants and is beneficial if there is limited space to grow plants.


Best Management Practices or BMPs – Multiple treatment methods, activities, facilities and structures that, used together, help protect water quality by preventing or reducing pollution of stormwater and removing pollution from runoff before it is discharged to ground or surface water.

Bioretention cells, swales, planters – Shallow, engineered landscape depressions that receive stormwater runoff from an area, with soil media and plants designed for specific pollutant removal; may or may not have underdrains.

Biofiltration swale – A broad, open, vegetated channel that filters flowing stormwater. The most common form is a wide, shallow, inclined depression planted with grasses. 


Catch basin – An underground concrete structure, typically fitted with a slotted grate, to collect stormwater runoff and route it through underground pipes. It allows sediment and debris to settle out of the runoff and can have inserts or other fittings to trap oils and floatables. A catch basin also can be used as a junction in a pipe system and have a solid lid. Maintaining a catch basin often requires special expertise and equipment.

Cistern or rain barrels – A tank or barrel used to collect and store rain from roofs and gutters. 

Closed detention system – An underground structure, typically a concrete vault or series of large diameter pipes, that temporarily stores stormwater and releases it slowly. A system typically is used for sites that do not have space for an above-ground system. It is accessed through a manhole lid.

Covenants, Conditions, and Restrictions (CC&Rs)– Non-governmental rules and requirements specific to a condominium or homeowners association. Requirements for residents range from lawn upkeep to financial responsibility for maintaining common areas, potentially including stormwater management facilities. 

Curb inlet or storm drain – A catch basin that collects and conveys stormwater runoff. Usually found along a curb, a storm drain has a slotted cover and a curb inlet has an opening in the curb.

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Detention facility – A pond, vault or pipe which temporarily stores stormwater runoff and slowly releases it through a specially designed outlet. Detention facilities are designed to drain completely within a few hours or days.

Detention pond – An open basin built by excavating below ground or constructing above-ground embankments. It temporarily stores stormwater runoff and slowly releases it through a specially designed outlet.

Discharge point – The place where a stormwater system empties into a stream or other body of water.

Drywell – An underground, concrete structure that allows stormwater to soak into the ground through holes in the walls and/or open bottom. Maintenance often requires special expertise and equipment.


Filter strip – A strip of grass, usually along edges of parking lots and roads, that filters stormwater by removing sediment and oils before the water soaks into the ground.

Filter vaults or stormwater filters – Underground vaults, manholes or specialized catch basins that include a series of filter cartridges to capture sediment and pollutants before stormwater flows into a pipe system.  Types of pollutants removed depends on the medium used in the filter cartridge

Flow control structure/flow restrictor – A structure that restricts or slowly releases stormwater at a specific rate to reduce flooding and stream erosion and filters pollutants.


HOA – Home Owner Association.

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Impervious – Not allowing water to pass through the surface material.

Infiltration basin – An open basin built by excavating below ground or constructing above-ground berms, or embankments. It temporarily stores stormwater runoff and disposes of it by letting it soak into the ground.


Lawn alternative – Low, ornamental perennials, groundcovers and native meadow grasses.


Manhole – An underground, concrete structure that provides maintenance access to pipes that transport stormwater runoff. It is usually found in paved areas and has a solid lid.

Mulch – A layer of decomposed organic materials used to blanket an area where vegetation is desired. The materials enrich the soil for better plant development while preventing erosion and decreasing evaporation from the ground.

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Native plantings and trees – Using native plants reduces the amount of impervious surface and provides increased infiltration and interception of rainfall, wildlife habitat and aesthetic elements.

Nonpoint source (NPS) pollution - Unlike pollution from industrial and sewage treatment plants, NPS pollution comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground.


Oil-water separator – An underground vault that treats stormwater by mechanically separating oil from water. The oil rises to the surface and floats on the water and sediment settles to the bottom. Oil/water separators are typically used where high oil concentrations are anticipated in the stormwater runoff. For example, parking lots, service and fuel stations.


Permeable pavers – Manufactured modular systems of various materials, sizes and types with gaps between blocks; gaps are filled with permeable material to allow water infiltration.

Permeable surface – Specially constructed paving surfaces that allow water to pass through and soak directly into the ground.

Pervious concrete – Rigid pavement containing a cementitous material to bind aggregate without fine material; used to create large spaces for water infiltration.

Porous asphalt – Flexible pavement containing a bituminous binder to adhere aggregate without fine material; used to create large spaces for water infiltration.

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Rain garden – Specially designed, site-specific stormwater facility that use plants and soils to capture pollutants and allow stormwater to soak into the earth. 

Rainwater harvesting – Collection of surface rainwater for non-potable uses such as irrigation or grey-water flushing.

Retention facility – A drywell, vault, infiltration basin or pond that holds stormwater while it soaks into the ground.


Site planning and design – A multi-disciplinary approach to site design that locates buildings, roadways and other features away from critical habitat areas and to minimize impervious surfaces and the impacts of development.

Soil amendments – Products such as gypsum and lime that are added to soil to improve its physical qualities, especially its ability to provide nutrition for plants. 

Storm drain or curb inlet– A type of catch basin that collects and conveys stormwater runoff.

Stormwater - The water that runs off surfaces such as rooftops, paved streets, highways, and parking lots. It can also come from hard grassy surfaces like lawns, play fields, and from graveled roads and parking lots.

Stormwater treatment facility – A landscaped feature or structure that captures, conveys, slows, detains and/or treats stormwater. They include detention facilities and retention facilities.

Stormwater runoff – Water from rainstorms, irrigation or other sources, that flows across and off a hard area, such a street, paved lot, roof or sidewalk, that prevents it from soaking into the ground.

Stormwater system– A system of catch basins, pipes and/or facilities for conveying, detaining or treating stormwater. Not to be confused with a sanitary sewer, which carries wastewater to a treatment facility.


Treatment train – A combination of two or more treatment facilities connected in series. 

Treatment wetland – A shallow man-made pond designed to treat stormwater through the biological processes associated with aquatic plants. These facilities use dense wetland vegetation and settling to filter sediment and other pollutants out of stormwater.

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Underdrain – Perforated plastic pipes installed on the bottom of a stormwater feature, which is used to collect and remove excess runoff.


Vegetated swale – A landscape element designed to remove silt and pollution from surface water runoff.It is a drainage course with gently sloped sides, vegetation, compost and/or rock. 

Vegetated roofs – An engineered system of a thin layer of soil and plants designed to capture rain on a roof.


Watershed - An area of land that drains rain and water to a common outlet such as a stream, river, lake or ocean.  Watersheds are usually named after the outlet to wich it drains (i.e. Salmon Creek Watershed).  The word watershed is sometimes used interchangeably with drainage basin or catchment.

Wetpond – An open basin, built by excavating below ground, that has a year-round pool of water. The volume allows sediment to settle out. Wetponds also have additional temporary storage above the permanent water level to detain and slowly release stormwater.

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Xeriscaping and water-efficient plants – Landscaping and gardening in ways that reduce or eliminate the need for irrigation.

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