Key concepts


Cloudburst = An extreme amount of precipitation in a short period of time, sometimes accompanied by hail and thunder, that is capable of creating flood conditions.

Constructed conveyance system facilities = Gutters, ditches, pipes, channels, and most flow control and water quality treatment facilities.

Conveyance System = Drainage facilities and features that collect, contain, and provide for the flow of surface and storm water from the highest points on the land down to a receiving water course. Conveyance systems consist of both natural elements and constructed facilities.

Detention = Release of surface and storm water run-off from the site at a slower rate than is collected by the drainage facility system, the difference being held in temporary storage.

Drainage facility = A constructed or engineered feature that collects, conveys, stores or treats surface and storm water run-off. Drainage facilities shall include, but not be limited to, all constructed or engineered streams, pipelines, channels, ditches, gutters, lakes, wetlands, closed depressions, flow control or water quality treatment facilities, erosion and sedimentation control facilities, and other drainage structures and appurtenances that provide drainage.

Ecosystem services = Benefits people obtain from nature

Evapotranspiration = Evapotranspiration is the sum of evaporation from the land surface plus transpiration from plants.

Flood = the temporary covering by water of land not normally covered by water. In the urban context, this includes fluvial flooding from watercourses, flooding from sea surges in coastal areas, and pluvial flooding when the capacity of sewerage systems is exceeded. (EC 2007, Fratini et al 2012)

Groundwater = Underground water usually found in aquifers. Groundwater usually originates from infiltration. Wells tap the groundwater for water supply uses.

Hydrologic cycle = The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes, such as precipitation, interception, run-off, infiltration, percolation, storage, evaporation, and transpiration.

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.

Infiltration = The downward entry of water through a soil surface and into the soil

Natural conveyance system elements = Swales and small drainage courses, streams, rivers, lakes, and wetlands.

Natural onsite drainage feature = A natural swale, channel, stream, closed depression, wetland, or lake.

Precipitation = Water pouring down from the clouds. Precipitation is the source of all the water.

Retention = The process of collecting and holding surface and storm water run-off with no surface outflow.

Run-off = 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.

Run-off coefficient = A dimensionless coefficient relating the amount of run-off to the amount of precipitation received. It is a larger value for areas with low infiltration and high run-off (pavement, steep gradient), and lower for permeable, well-vegetated areas (forest, flat land).

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

Stormwater Management = The application of site design principles and construction techniques to prevent sediments and other pollutants from entering surface or ground water, source controls, and treatment of run-off to reduce pollution.

Storm drainage system = The system of gutters, pipes, streams, or ditches used to carry surface and stormwater from surrounding lands to streams and lakes. Also see Conveyance System.

Watershed = A watershed is the region draining into a river, river system, or body of water.