Stormwater Terminology
- Basin - Any area draining to a point of interest.
- Berm - A constructed barrier of compacted earth.
- Catch basin - Curbside opening that collects rainwater from streets and serves as an entry point to the storm drain system.
- Channel - A long narrow excavation or surface feature that conveys surface water and is open to the air.
- Channel, natural - A channel which has occurred naturally due to the flow of surface waters.
- Conveyance - The process of water moving from one place to another.
- Culvert - Pipe or concrete box structure which drains open channels, swales, or ditches under a roadway or embankment typically with no catch basins or manholes along its length.
- CSO - Combined Sewer Overflow.
- Ditch - A constructed channel with its top width less than 10 feet at design flow.
- Detention - Release of surface and storm water runoff from the site at a slower rate than it is collected by the drainage facility system, the difference being held in temporary storage.
- Discharge - The volume of water (and suspended sediment if surface water) that passes a given location within a given period of time.
- Drainage - The collection, conveyance, containment, and/or discharge of surface and storm water runoff.
- Dry Season - May 1 to September 30.
- Erosion - When land is diminished or worn away due to wind, water, or glacial ice.
- Flood - A temporary rise in flow or stage of any watercourse or stormwater conveyance system that results in stormwater runoff exceeding its normal flow boundaries and inundating adjacent, normally dry areas.
- Floodplain - Areas adjacent to a stream or river that are subject to flooding or inundation during severe storm events (often called the 100-year floodplain, it would include the area or flooding that occurs, on average, once every 100 years). Sometimes referred to as the “FEMA Floodplain.
- Grading - The cutting and/or filling of the land surface to a desired slope or elevation.
- Groundwater - Underground water usually found in aquifers. Groundwater usually originates from infiltration. Runoff can seep into the soil and recharge groundwater that supplies drinking wells and springs.
- Habitat - The specific area or environment in which a particular type of plant or animal lives and grows.
- Infiltration/Inflow (I/I) - Clean storm and/or groundwater that enters the sewer system through cracked pipes, leaky manholes, or improperly connected storm drains, down spouts and sump pumps.
- Impervious surface - A hard surface area which either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development; and/or a hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development.
Common impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam, or other surfaces which similarly impede the natural infiltration of surface and storm water runoff. - Invert - Elevation to the inside bottom of the pipe.
- Outfall - The point where wastewater or drainage discharges from a sewer pipe, ditch, or other conveyance to a receiving body of water.
- Point discharge - The release of collected and/or concentrated surface and storm water runoff from a pipe, culvert, or channel.
- Retention - The process of collecting and holding surface and storm water runoff with no surface outflow.
- Riprap - A facing layer or protective mound of stones placed to prevent erosion or sloughing of a structure or embankment due to the flow of surface and storm water runoff.
- Runoff - Water originating from rainfall and other precipitation that ultimately flows into drainage facilities, rivers, streams, springs, seeps, ponds, lakes, and wetlands as well as shallow groundwater.
- Stormwater - Stormwater is 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.
- Storm drain system - The system of gutters, pipes, streams, or ditches used to carry surface and storm water from surrounding lands to streams and lakes.
- Swale - A shallow drainage conveyance with relatively gentle side slopes, generally with flow depths less than one foot.
- Storm drain - An opening leading to an underground pipe or open ditch for carrying surface runoff, separate from the sanitary sewer or wastewater system.
For more definitions, please see Appendix B of the Stormwater Regulations.