Stormwater Definitions
Understanding Stormwater: A-Z Glossary
Stormwater runoff is precipitation that does not infiltrate soil but flows over land areas or through storm drains into larger bodies of water. The following terms are commonly used to describe stormwater management practices and regulations.
# | A | B | C | D | E | F | G | H | I | L | M | N | O | P | R | S | T | U | W
#
- 303(d) body of water – The list of lakes, rivers, and streams designated impaired or threatened by pollutants.
A
- Adapted Plants – Non-native plants that adapt well to a given region or locality.
- Aquifer – A layer of rocks containing groundwater that is withdrawn and used for human purposes.
B
- Backwater – Water upstream that is deeper than it normally would be due to an obstruction.
- Baffle – A device to deflect, check, or regulate flow.
- Basin – Any area draining to a point of interest.
- Berm – A barrier constructed of compacted earth or other material used to restrict or direct water flow.
- Best Management Practice – A practice suitable for treating or reducing pollutants in stormwater runoff.
- Biofiltration – The use of plants and other organic materials to enhance the infiltration of water into soil.
- Bioretention – The process of collecting stormwater in a treatment area containing soil and plant materials.
- Bioretention Cell – A shallow depression used to capture and filter stormwater runoff in a short period of time.
- Black Water – Wastewater that contains fecal matter and urine.
- Buffer – A vegetated area between a body of water and adjacent land practices like farming or development.
- Built Environment – Buildings, roads, and other infrastructure constructed in an urban setting.
C
- Catch Basin – A depressed area where runoff enters a bioretention cell or other control structure.
- Channel – A surface feature through which water travels.
- Check Dam – A small dam built across a channel or ditch that slows runoff speed.
- Cistern – Large devices for storing captured stormwater.
- Clean Water Act – Federal legislation that establishes goals for eliminating the release of high amounts of toxic substances into water.
- Closed Depression – An area that is either low-lying or has no surface water outlet.
- Combined Sewer – Conveys domestic, commercial, and industrial wastewater and stormwater through a single-pipe system to a publicly owned treatment facility.
- Constructed Wetland – A manufactured basin that contains slowly moving surface or subsurface water and organisms like those found in natural wetlands.
- Conveyance System – Drainage facilities made of natural elements or constructed facilities that collect, contain, and provide surface and stormwater.
- Critical Drainage Area – An area with severe flooding, drainage, or erosion that resulted from development and urbanization.
- Curb and Gutter – Provides a defined drainage pathway along the edge of city streets or roadways for stormwater runoff.
- Curb Cut – An area of removed curb that allows an unobstructed pathway from street level.
D
- Daylighting – Where an underground drainpipe exits from underground and exits to the soil surface of a body of water.
- Detention Basin/Dry Pond – A structure where stormwater runoff is directed, held, and slowly released to a body of water.
- Disconnection – Refers to disconnecting stormwater runoff from direct entry via downspouts, gutters, and paved surfaces.
- Drainage – The collection, conveyance, containment, and discharge of surface and stormwater runoff.
E
- Embankment – A structure that forms the bank of a pond, road, or other structure made from earth, gravel, or similar materials.
- Engineered Soil – Soil that has been formulated with components for a specific purpose or application.
- Environmental Protection Agency – A federal agency that protects human health and the environment.
- Erosion – The process that moves material from location to location; caused by wind, water, or other forces on the earth’s surface.
- Evapotranspiration – The transportation of water into the atmosphere as a result of surface evaporation.
F
- Filter Strip – Vegetated areas used to reduce stormwater runoff velocity.
- First Flush – The concept that runoff water from the first half to one inch of rainfall in a storm is the most contaminated with pollutants.
- Flood Control Channel – The open portion of a storm drain system; often concrete-lined.
- Flow Control Facility – A drainage facility designed to reduce the impact of increased surface and stormwater runoff.
G
- Grading – Changing existing ground surfaces to desired slopes, elevations, and forms.
- Gray Water – Wastewater from baths, showers, washing machines, and sinks other than kitchen sinks.
- Green – A term describing a process, structure, or idea that integrates environmental considerations.
- Green Roof – A roof partially or entirely covered with vegetation.
- Groundwater – Water underneath the ground surface in soil and rock formations.
H
- Hardscape – Fabricated features of a landscape made from concrete and non-plant materials.
- Hydraulic Retention Time – The average amount of time required for water to pass through a stormwater treatment process.
- Hydrograph – A graphical representation of water flow rate as it’s related to time.
- Hydrologic Cycle – The movement of water through its phases above, on, and below the surface of the earth.
I
- Illegal Discharge – The release or placement of any material into the stormwater conveyance system which is not authorized.
- Illicit Connection – Any storm drain system connection that is not permitted.
- Impervious Surface – Any surface with very limited capacity to absorb or infiltrate water.
- Infiltration – The process of water moving down from the top of the soil.
- Infiltration Basin – A shallow impoundment designed to infiltrate stormwater runoff into the soil.
- Infrastructure – Public works like electrical and water distribution systems, sewage collection and treatment systems, components of the transportation system, stormwater collection and conveyance systems, and other constructed components that are required for the economy to function.
- Invert – The lowest elevation of a pipe, pond, or drainage facility where water is designed to flow out.
L
- Leadership in Energy and Environmental Design – A rating system from the U.S. Green Building Council that categorizes the level of environmental sustainability of construction and buildings.
- Level Spreader – A water control device designed to create sheet flow across a landscape area rather than concentrated flow.
- List of Impaired Waters – A list prepared by each state as a requirement of the Clean Water Act.
- Low Impact Development – A land development approach that emphasizes site design and planning techniques that mimic the natural infiltration-based hydrology of the historic landscape.
M
- Media Filter – A filter made from sand, peat, shredded tires, foam, crushed glass, or other material that is used to remove solids and certain other contaminants from stormwater.
- Municipal Separate Storm Sewer System – Also called an MS4, this is a system of conveyances owned by a given state, city, town, or other public entity that discharges to waters.
N
- National Pollution Discharge Elimination System – A part of the Clean Water Act that requires point source dischargers of pollution to apply for and be granted a permit, often referred to as a General Permit.
- Native Plants – Plants that occurred in an area before disturbance by humans are native.
- Nonpoint Source Pollution – Pollution is not easily traced to one source or property.
O
- Outfall – The point where runoff exits a drainage system and discharges into a receiving body of water.
P
- Peak Flow Rate – The maximum flow of water during a storm event.
- Percent Impervious – The percentage of a given area that will not allow water to infiltrate.
- Percolation – Describes the flow of water within the soil profile once it has moved through the soil surface.
- Permeable Pavement – Several methods and materials that allow water and air to move through the pavement and into the underlying soil.
- Point Source Pollution – Pollution that enters the environment from a single point like a factory, oil spill, or stormwater discharge pipe.
R
- Rain Barrel – A small storage device that collects stormwater, usually from a roof surface.
- Rain Garden – A shallow landscape depression designed to capture and treat stormwater runoff.
- Rainwater Harvesting – The collection or capture of rainwater on-site instead of letting it run off.
- Receiving Waters – Bodies of water that receive water from upstream sources.
- Retention – The process of collecting and holding stormwater runoff.
- Retention Basin – A stormwater control structure with a permanent pool of water where storm runoff is directed.
- Retention Practices – Techniques that hold or retain runoff water, allowing it to infiltrate and evaporate.
- Retrofit – A management practice constructed in an existing developed area.
- Riparian – Land immediately adjacent to a body of water like a river, stream, lake, or wetland.
- Runoff – Excess rainfall, snowmelt, or irrigation water that flows over the land’s surface.
S
- Sanitary Sewer – A system that collects and transports wastewater from building plumbing systems to wastewater treatment plants.
- Sheet Flow – Waterflow over a surface at a uniform depth.
- Soil Amendments – Any material added to soil to improve its properties.
- Source Control – Action to prevent pollution where it originates.
- Storm Drain – A series of underground inlets and pipes used to collect and convey stormwater to a discharge point.
- Stormwater – Water from rainfall or snowmelt.
- Stormwater Control – The management of stormwater on- or off-site.
- Swale – A shallow and gently sloped channel that allows for stormwater runoff.
T
- Total Maximum Daily Load – A calculation of the maximum amount of a pollutant or pollutants that a body of water can receive and still meet established water quality standards.
- Tree Box Filter – Containers typically installed beneath street or sidewalk level in which trees are planted.
U
- Underdrain – A slotted or perforated pipe beneath a constructed soil bed that removes excess water from the bed.
- Underground Detention – Vaults or piping systems used to store stormwater to eventually infiltrate or be used for irrigation or domestic purposes.
W
- Water Quality Rainfall Amount – A value used for design purposes that accounts for the majority of rainfall events in a given area.
- Water Quality Volume – The water volume needed to be captured and treated from a given area for a storm that is equal to the water quality rainfall event.
- Watershed – Land area from which water drains into a particular body of water.
- Wetlands – Complex ecosystems that exist in transition zones between land-based ecosystems and water-based ecosystems.