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Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Amenity: The quality of place being pleasant or attractive; agreeableness. A feature that increases attractiveness or value, especially of a piece of real estate or a geographic location
Attenuation: Reduction of peak flow and increased duration of a flow event.

Balancing pond: A pond designed to attenuate flows by storing runoff during the peak flow and releasing it at a controlled rate during and after the peak flow has passed. The pond always contains water. Also known as wet detention pond.
Basin: Flow control or water treatment structure that is normally dry.
Biodegradation: Decomposition of organic matter by micro-organisms and other living things.
Biodiversity: The diversity of plant and animal life in a particular habitat.
Bioretention area: A depressed landscaping area that is allowed to collect runoff so it percolates through the soil below the area into an underdrain, thereby promoting pollutant removal.
Brownfield site: A site that has been previously developed.

Brown roof: A roof that incorporates a substrate (laid over a waterproof membrane) that is allowed to colonise naturally. Sometimes referred to as an alternative roof.

Catchment: The area contributing surface water flow to a point on a drainage or river system. Can be divided into sub-catchments.
Combined sewer: A sewer designed to carry foul sewage and surface runoff in the same pipe.
Contaiminated ground: The area contributing surface water flow to a point on a drainage or river system. Can be divided into sub-catchments.
Controlled waters: Waters defined and protected under the Water Resources Act 1991. Any relevant territorial waters that extend seaward for 3 miles from the baselines, any coastal waters that extend inland from those baselines to the limit of the highest tide or the freshwater limit of any river or watercourse, any enclosed dock that adjoins coastal waters, inland freshwaters, including rivers, watercourses, and ponds and lakes with discharges and groundwaters (waters contained in underground strata).For the full definition refer to the Water Resources Act 1991.
Conveyance: Movement of water from one location to another.
Curtilage: Land area within property boundaries.

Design and Access Statement: Formal documents explaining the design philosophy which is behind a planning application.
Design criteria: A set of standards agreed by the developer, planners and regulators that the proposed system should satisfy.
Design Statement: In the context of a planning application, a written statement to a local authority prepared by an applicant setting out the design principles adopted in relation to a proposed design for a site and its wider context.
Designing for exceedance: An approach that aims to manage exceedance flows during rainfall events, eg the use of car parks during extreme events.

Detention basin: A vegetated depression, normally is dry except after storm events constructed to store water temporarily to attenuate flows. May allow infiltration of water to the ground.

Detention pond: A pond that has a lover outflow than inflow. Often used to prevert flooding.

Diffuse pollution: Pollution arising from land-use activities (urban and rural) that are dispersed across a catchment, or sub-catchment, and do not arise as a process effluent, municipal sewage effluent, or an effluent discharge from farm buildings.

Dry: Free of water under dry weather flow conditions.

Ecology: All living things, such as trees, flowering plants, insects, birds and mammals, and the habitats in which they live.
Ecosystem Services: The multitude of resources and processes that are supplied by natural ecosystems.
Environmental Footprint: A measure of environmental impact based on the distance that resources for a development are transported.
Environmental management: A management agreement for an area or project set up to plan and make sure the declared management objectives for the area or project are met. Environmental Management Plans are often undertaken as part of an environmental impact assessment and are set out in several stages with responsibilities clearly defined and environmental monitoring procedures in place to show compliance with the plan.
Evapotranspiration: The process by which the Earth's surface or soil loses moisture by evaporation of water and by uptake and then transpiration from plants.
Extended detention basin: A detention basin in which the runoff is stored beyond the time normally required for attenuation. This provides extra time for natural processes to remove some of the pollutants in the water.


FEH: Flood estimation handbook, produced by Centre for Ecology and Hydrology, Wallingford (formerly the Institute of Hydrology)
Filter drain: A linear drain consisting of a trench filled with a permeable material, often with a perforated pipe in the base of the trench to assist drainage, to store and conduct water, but may also be designed to permit infiltration.
Filter strip: A vegetated area of gently sloping ground designed to drain water evenly off impermeable areas and filter out silt and other particulates.
Filtration: The act of removing sediment or other particles from a fluid by passing it through a filter.
First flush: The initial runoff from a site or catchment following the start of a rainfall event. As runoff travels over a catchment it will pick up or dissolve pollutants and the "first flush" portion of the flow may be the most contaminated as a result. This is especially the case in small or more uniform catchments, however, in larger or more complex catchments pollution wash-off may contaminate runoff throughout a rainfall event.
Flood frequency: The probability of a flowrate being equalled or exceeded in any year.
Floodplain: Land adjacent to a watercourse that would be subject to repeated flooding under natural conditions (see Environment Agency’s Policy and practice for the protection of flood plains for a fuller definition).
Flood routeing: Design and consideration of above-ground areas that act as pathways permitting water to run safely over land to minimise the adverse effect of flooding. This is required when the design capacity of the drainage system has been exceeded.
Flow control device: A device used to manage the movement of surface water into and out of an attenuation facility, eg a weir.
Flood and Water Management Act: Legislation to clarify the framework for managing flood risk (particularly surface water management) in England and Wales.
Forebay: A small basin or pond upstream of the main drainage component with the function of trapping sediment.

Geocellular structure: A plastic box structure used in the ground, often to attenuate runoff.
Greenfield runoff: This is the surface water runoff regime from a site before development, or the existing site conditions for brownfield redevelopment sites.
Green infrastructure: Green Infrastructure is a strategically planned and delivered network of high quality green spaces and other environmental features (often including water features).
Green roof: A roof with plants growing on its surface, which contributes to local biodiversity. The vegetated surface provides a degree of retention, attenuation and treatment of rainwater, and promotes evapotranspiration. (Sometimes referred to as an alternative roof).
Greywater: Wastewater from sinks, baths, showers and domestic appliances this water before it reaches the sewer (or septic tank system).
Groundwater: Water that is below the surface of ground in the saturation zone.

Habitat: The area or environment where an organism or ecological community normally lives or occurs.
Highways Agency: The government agency responsible for strategic highways, ie motorways and trunk roads
Highway authority: A local authority with responsibility for the maintenance and drainage of highways maintainable at public expense.
Highway drain: A conduit draining the highway. On a highways maintainable at the public expense it is vested in the highway authority.
Hydrograph: A graph illustrating changes in the rate of flow from a catchment with time
HOST (Hydrology of Soil Types): A classification used to indicate the permeability of the soil and the percentage runoff from a particular area

Impermeable: Will not allow water to pass through it.
Impermeable surface: An artificial non- porous surface that generates a surface water runoff after rainfall.
Infiltration - to the ground: The passage of surface water though the surface of the ground.
Infiltration - to a sewer: The entry of groundwater to a sewer.
Infiltration basin: A dry basin designed to promote infiltration of surface water to the ground.
Infiltration device: A device specifically designed to aid infiltration of surface water into the ground.
Infiltration potential: The rate at which water flows through a soil (mm/h).
Infiltration trench: A trench, usually filled with stone, designed to promote infiltration of surface water to the ground.
Interflow: Shallow infiltration to the soil, from where it may infiltrate vertically to an aquifer, move horizontally to a watercourse or be stored and subsequently evaporated.
Interim Code of Practice: An agreed provisional document within the existing legislative framework that establishes good practice.

Lagoon: A pond designed for the settlement of suspended solids.
Lateral drain: (a) That part of a drain which runs from the curtilage of a building (or buildings or yards within the same curtilage) to the sewer with which the drain communicates or is to communicate; or
: (b) (if different and the context so requires) the part of a drain identified in a declaration of vesting made under section 102 or in an agreement made under section 104.
Local development framework: A non-statutory term used to describe a folder of documents which includes all the local planning authority’s Local Development Documents (LDDs). The local development framework will also comprise the statement of community involvement, the local development scheme and the annual monitoring report.


Master Plan: A masterplan includes both the process by which organisations undertake analysis and prepare strategies, and the proposals that are needed to plan for major change in a defined physical area.
Model agreement: A legal document that can be completed to form the basis of an agreement between two or more parties regarding the maintenance and operation of sustainable water management systems.

National Standards for Sustainable Drainage: Referred to as the National Standards.
A regulatory document providing Standards and guidance on the design, construction and maintenance of SuDS for approval and adoption by the SuDS Approval Body.
Natural Capital: The natural resource stocks from which resources useful for livelihoods are derived e.g. water, land, environmental resource

Offstream: Dry weather flow bypasses the storage area
Onstream: Dry weather flow passes through the storage area.

Pavement: Technical name for the road or car park surface and underlying structure, usually asphalt, concrete or blockpaving. NB the path next to the road for pedestrians (colloquially called pavement) is properly termed the footway.
Permeability: A measure of the ease with which a fluid can flow through a porous medium. It depends on the physical properties of the medium, for example grain size, porosity and pore shape.
Permeable pavement: A paved surface that allows the passage of water through voids between the paving blocks/slabs.
Permeable surface: A surface formed of material that is itself impervious to water but, by virtue of voids formed through the surface, allows infiltration of water to the sub-base through the pattern of voids, eg concrete block paving.
Pervious surface: A surface that allows inflow of rainwater into the underlying construction or soil.
Piped system: Conduits generally located below ground to conduct water to a suitable location for treatment and/or disposal.
Pollution: A change in the physical, chemical, radiological or biological quality of a resource (air, water or land) caused by man or man’s activities that is injurious to existing, intended or potential uses of the resource.
Pond: Permanently wet basin designed to retain stormwater and permit settlement of suspended solids and biological removal of pollutants.
Porous paving: A permeable surface allowing the passage of water through voids within, rather than between, the paving blocks/slabs.
Porous surface: A surface that infiltrates water to the sub-base across the entire surface of the material forming the surface, for example grass and gravel surfaces, porous concrete and porous asphalt.
Pound: A section of a swale designed to detain runoff.
Prevention: Site design and management to stop or reduce the occurrence of pollution and to reduce the volume of runoff by reducing impermeable areas.
Proper outfall: An outfall to a watercourse, public sewer and in some instances an adopted highway drain. Under current legislation and case law, the existence of a proper outfall is a prerequisite in defining a sewer.
Public sewer: A sewer that is vested in and maintained by a sewerage undertaker.

Rainwater harvesting or rainwater use system: A system that collects rainwater from where it falls rather than allowing it to drain away. It includes water that is collected within the boundaries of a property, from roofs and surrounding surfaces.
Recurrence interval: The average time between runoff events that have a certain flow rate, e.g. a flow of 2 m/s might have a recurrence interval of two years in a particular catchment.
Regional Control: Management of runoff from a site or several sites, typically in a balancing pond or wetland.

Retention pond: A pond where runoff is detained (e.g. for several days) to allow settlement and biological treatment of some pollutants.
Rill: Open surface water channels with hard edges.
RoSPA: Royal Society for the Prevention of Accidents.
Runoff: Water flow over the ground surface to the drainage system. This occurs if the ground is impermeable, is saturated or if rainfall is particularly intense.

Section 38: An agreement entered into pursuant to Section 38 Highways Act 1980 whereby a way that has been constructed or that is to be constructed becomes a highway maintainable at the public expense. A publicly maintainable highway may include provision for drainage of the highway. (Drainage of highways is defined in Section 100 (9) of the Highways Act 1980).
Section 102 or 104: Section within the Water Industry Act 1991 permitting the adoption of a sewer, lateral drain or sewage disposal works by the sewerage undertaker. Sometimes referred to as S102 or S104.
Section 106 (Town and Country Planning Act 1990): A section within the Town and Country Planning Act 1990 that allows a planning obligation to a local planning authority to be legally binding.
Section 106 (Water Industry Act 1991): A key section of the Water Industry Act 1991, relating to the right of connection to a public sewer.
SEPA: Scottish Environment Protection Agency.
Separate sewer: A sewer for surface water or foul sewage, but not a combination of both.
Sewer: A pipe or channel taking domestic foul and/or surface water from buildings and associated paths and hardstandings from two or more curtilages and having a proper outfall.
Sewerage undertaker: This is a collective term relating to the statutory undertaking of water companies that are responsible for sewerage and sewage disposal including surface water from roofs and yards of premises.
Sewers for Adoption: A guide agreed between sewerage undertakers and developers (through the House Builders Federation) specifying the standards to which private sewers need to be constructed to facilitate adoption.
Site Control: Management of water in a local area or site (eg routing water from building roofs and car parks to a large soakaway, infiltration or detention basin).
Site and regional controls: Manage runoff drained fro several sub-catchments. The controls deal with runoff on a catchment scale rather than at source.
SNH: Scottish Natural Heritage.
Soakaway: A subsurface structure into which surface water is conveyed to allow infiltration into the ground.

SOIL: Soil Index Value obtained from the WRAP soil classification, used in the Wallingford Procedure to calculate the treatment volume.
Source control: The control of runoff or pollution at or near its source.
STORM: A computer model based on equations used in the California Stormwater Best Management Practice Handbook. Used to assess detention basin performance.
Sub-base: A layer of material on the sub-grade that provides a foundation for a pavement surface.
Sub-catchment: A division of a catchment, allowing runoff management as near to the source as is reasonable.
Sub-grade: The surface of an excavation prepared to support a pavement.
Subsidiarity: The principle that an issue should be managed as close as is reasonable to its source.
SuDS (Sustainable Drainage Systems): Sustainable drainage systems or sustainable (urban) drainage systems: a sequence of management practices and control structures designed to drain surface water in a more sustainable fashion than some conventional techniques (may also be referred to as SuDS).
SuDS management train: The management of runoff in stages as it drains from a site.
Surface water management: The management of runoff in stages as it drains from a site.
Suspended solids: Undissolved particles in a liquid.
Swale: A shallow vegetated channel designed to conduct and retain water, but may also permit infiltration; the vegetation filters particulate matter.

Treatment: Improving the quality of water by physical, chemical and/or biological means.
Treatment volume: The volume of surface runoff containing the most polluted portion of the flow from a rainfall event.

Watercourse: A term including all rivers, streams ditches drains cuts culverts dykes sluices and passages through which water flows.
Water Framework Directive: A European Community Directive (2000/60/EC) of the European Parliament and Council designed to integrate the way water bodies are managed across Europe. It requires all inland and coastal waters to reach “good status” by 2015 through a catchment-based system of River Basin Management Plans, incorporating a programme of measures to improve the status of all natural water bodies.
WRAP (Winter Rain Acceptance Potential): Classification used to calculate the permeability of soils and the percentage runoff from a particular area.
Wet: Containing water under dry weather conditions.
Wetland: A pond that has a high proportion of emergent vegetation in relation to open water.

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