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Drainage Terms A-Z

S

An equation developed in the 19th century by a French mathematician, which takes account of all the physical processes of fluid flow such as momentum and inertia to calculate depth for gradually varying flow states.

A device with openings, generally of uniform size, used to retain or remove suspended or floating solids in flowing water or wastewater.

A board or plate that dips below the top water level to retain scum and other floating debris.

The ratio of the weight of the sediment in a water-sediment mixture to the total weight of the mixture. Sometimes expressed as the ratio of the volume of sediment to the volume of mixture.

The movement of solids transported in any way by a flowing liquid.

The process of deposition and consolidation of suspended material carried by water, wastewater or other liquids, by gravity.

The minimum velocity in sewers necessary to keep solids in suspension, so preventing the deposition and subsequent nuisance from blockages or reduced capacity.

A drain or sewer system, normally of two pipelines, one carrying wastewater and the other surface water.

A structure for the collection and partial treatment of sewage.

Wastewater and/or surface water conveyed by a drain or sewer.

A pipe or conduit that carries wastewater or drainage water serving more than one property.

The unintentional escape from a sewerage system; the inability of drainage flows to enter a sewerage system because of surcharge.

Alternative term for “drainage collecting system” for foul and surface water systems.

A network of pipelines and ancillary works that conveys wastewater and/or surface water from drains to a treatment works o other place of disposal.

An organisation with the legal duty to provide sewerage services in an area. In England and Wales these services are provided by 10 water service companies, in Scotland by 3 water authorities, and in Northern Ireland by the Water Service of the Department of the Environment for Northern Ireland.

A diverting weir constructed on the side of a channel or conduit, usually at right angles to the centre-line of the main channel.

Sediment (often soil) consisting of particles between 0.002 mm and 0.02 mm in equivalent diameter.

The representation of specific conditions during a specific period in a sewerage system, treatment works, river etc, by means of a computer model.

The representation of a physical system and its time-related behaviour by a computer model.

A gate constructed to slide vertically and fastened into or against masonry of dams, (penstock) tanks or other structures under which flow takes place when open.

A pit into which surface water is drained to infiltrate into he ground.

The top of the inside of a pipe or conduit.

A measure of soil wetness, calculated by the Meteorological Office in the UK, to indicate the capacity of the soil to absorb rainfall.

The practice of reducing runoff and also pollutants at their source so that they do not enter the drainage system or become significantly delayed and attenuated.

A period when an overflow discharges to a watercourse/ spill frequency The number of spill events over a given period.

A small basin into which flow is discharged, which is used to either dissipate energy or trap solids.

The impounding of water, either in surface or in underground reservoirs.

An occurrence of a meteorological event, often of rainfall, snow or hail. Used in connection with a phenomenon that is either unusual or of great magnitude, rate or intensity.

Storage tanks designed to hold most of the stormwater in either sewers or treatment works such that downstream flooding or incomplete treatment respectively is minimised.

A weir, orifice or other device for permitting the discharge from a combined sewer of the flow in excess of that which the sewer is designed to carry.

The ground surface area drainage directly to one fully or a collection of gullies.

The process whereby the rainfall runoff carries surface sediments and dissolved pollutants into the drain or sewer system.

Water from precipitation that has not seeped into the ground and is discharged to the drain or sewer system directly from the ground or from exterior building surfaces.

A drain or sewer system that has been designed to carry only surface water.

Insoluble solids that either float on the surface of, or are in suspension in, water, wastewater or other liquids.

The application of drainage techniques that are considered to be environmentally beneficial, causing minimal or no long-term detrimental impact.

A grass channel for stormwater collection with shallow side slopes, which is normally dry except during rainfall.

Rainfall depths or intensities derived from rainfall statistics and not representing an individual real rainstorm.

Rainfall time series usually derived by stochastic processes for use in place of a recorded rainfall series.