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Attenuation Storage

Volume used to store runoff during extreme rainfall events. Comes into use once the inflow is greater than the controlled outflow. Storing runoff during the peak flow and releasing it at a controlled rate during and after the peak flow has passed.

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Balancing Pond

A pond designed to act as storage for attenuation. The pond always contains water and is also known as wet detention pond.


A ground depression acting as a flow control or water treatment structure that is normally dry and has a proper outfall, but is designed to detain storm-water temporarily.


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 under-drain, thereby promoting pollutant removal.

Brown Roof

The rough surface provides a degree of retention, attenuation and treatment of rainwater, and promotes evapotranspiration. Plants and insects are allowed to colonise these areas over time.

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This is a term used to identify the different assets or features that come together to form a sustainable drainage system. An example of a component would be a swale, soakaway or wetland etc.

Control Structure

Structure to control the volume or rate of flow of water through or over it.


Movement of water from one location to another.

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Design Criteria

A set of standards agreed by the developer, planners, and regulators that the proposed development should satisfy.

Detention Basin

A vegetated depression that is normally dry except following storm events. Constructed to store water temporarily to attenuate flows. May allow infiltration of water to the ground.

Detention Pond/Tank

A pond or tank that has a lower outflow than inflow. Often used to prevent flooding by providing a temporary storage volume.


Rate of flow of water.

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The point at which the quantity of water from rainfall or snow melt is of a greater volume than the drainage system is designed to take. Therefore exceedance events are rare occurrences of extreme weather.

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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.

Filter Strip

A vegetated area of gently sloping ground designed to drain water evenly off impermeable areas and to filter out silt and other particulates.


The act of removing sediment or other particles from a fluid by passing it through a filter.

Flood and Water Management Act 2010 (FWMA)

Act which aims to improve both flood risk management and the way in which water resources are managed by creating clearer roles and responsibilities and instilling a more risk based approach. Available to view at

Flood Storage

The temporary storage of excess runoff or river flow in ponds, basins, reservoirs or on the floodplain during a flood event.

Flow Control Device

A device used for the control of surface water from an attenuation facility, e.g. a weir.

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Geo-cellular Structure

A plastic box structure used in the ground, often to attenuate runoff.

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.

Greenfield Runoff

The runoff that would occur from the site it its undeveloped and undisturbed state. Greenfield runoff characteristics are described by peak flow and volumes of runoff for rainfall events of specified duration and return period (frequency of occurrence).

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Will not allow water to pass through it.

Infiltration Basin

A dry basin designed to promote infiltration of surface water to the ground.

Infiltration Trench

A trench, usually filled with permeable granular material, designed to promote infiltration of surface water to the ground.

Internal Drainage Board (IDB)

An operating authority responsible for management of water levels within an establish drainage district.

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Lead Local Flood Authority (LLFA)

As defined by the Flood and Water Management Act 2010 this is the Unitary or County Council. A position created in response to the Pitt review.

Local Planning Authority

Local authority responsible for planning and development control. Has the meaning given in section 1 of the Town and Country Planning Act 1990(c);

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Main River

Watercourses where the main legislative body is the environment agency.

Management Train

A method of managing surface water drainage in as natural a process as possible. Looking at the quantity and quality of runoff as it is conveyed from the point of precipitation to the final receiving water body.

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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.

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Ordinary Watercourses

Watercourses where the main legislative body is the Local Authority; includes all streams and ditches not identified as either Main River or a Critical Ordinary Watercourse, but where there is a risk of flooding.

Overland Flow Flooding

Flooding caused by surface water runoff when rainfall intensity exceeds the infiltration capacity of the ground, or when the soil is so saturated that it cannot accept any more water.

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The passing of water (or other liquid) through a porous substance or small holes (e.g. soil or geotextile fabric).


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 permeable surface that is paved and drains through voids between solid parts of the pavement.

Permeable Surface

A surface that is 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, for example concrete block paving.

Pervious Surface

A surface that allows inflow of rainwater into the underlying construction or soil.

Pitt Review

Independent review of flooding occurring in June/July 2007 assessing what happened and what should be done differently in the future.


Permanently wet depression designed to retain storm water and permit settlement of suspended solids and biological removal of pollutants.


The percentage of the bulk volume of a rock or soil that is occupied by voids, whether isolated or connected.

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.

Porous Paving

A permeable surface allowing the passage of water through voids within, rather than between, the paving blocks/slabs.

Public Sewer

A sewer that is vested in and maintained by a sewerage undertaker.

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Rain Garden

A planted area providing storm water attenuation and infiltration.

Rainwater Harvesting

This refers to the capture and storage of rain water which is then used in households and businesses for day to day activities. These can vary between tanked systems which provide water for flushing toilets and water butts for watering plants in the garden. The reuse of rainwater reduces the demand on clean water supplies.

Reed Bed

Area of grass-like marsh plants, primarily adjacent to freshwater. Artificially constructed reed beds can be used to accumulate suspended particles and associated heavy metals, or to treat small quantities of partially treated sewage effluent.

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 for a sufficient time to allow settlement and biological treatment of some pollutants.


Open surface water channels with hard edges.

Runoff / Surface Runoff / Surface Water Runoff

Water flow (including flow from snow and other precipitation) over the ground surface which has not entered the drainage system. This occurs if the ground is impermeable, is saturated or rainfall is particularly intense. The Water Industry Act 1991 and the Flooding and Water Act use slightly different terminology. However, the runoff with which the National Standards and guidance are concerned includes all such runoff.

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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 (i.e. routing water from building roofs and car parks to a large soakaway, infiltration or detention basin).


A sub-surface structure into which surface water is conveyed, designed to promote infiltration.

Source Control

The control of runoff at or near its source.

SuDS Management Train

The management of runoff in stages as it drains from a site.

Surface Water

Water that collects above ground after falling as precipitation.

Surface Water Sewer

Drainage system designed to convey precipitation from property

Sustainable Drainage Systems – (SuDS)

Concept of surface water drainage which takes into account the quantity and quality of runoff, and the amenity value of surface water in the urban environment. The main focus is on source control and the mimicking of natural processes.

SuDS Approving Body – (SAB)

The Lead Local Flood Authority which approves and, where appropriate, adopts SuDS.


A shallow vegetated channel designed to conduct and retain water, but may also permit infiltration. The vegetation filters particulate matter.

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Treatment Stage

A sustainable drainage component that protects or improves surface runoff by reducing suspended sediments or contaminants.

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A term including all rivers, streams ditches drains cuts culverts dykes sluices and passages through which water flows.


A device to control the flow of water.


A pond that has a high proportion of emergent vegetation in relation to open water.

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