- aesthetic pollution
Solid sewage-related materials that are visible but create little environmental impact.
- antecedent conditions
The condition of a catchment before a rainfall event.
- antecedent precipitation
The relevant rainfall that takes place before the point in time of interest.
- antecedent precipitation index
An index determined by the summation of weighted daily rainfalls for a period preceding the start of a specific event.
- anti-flooding device
A device specifically designed to be installed in gravity drains or sewers to prevent backflow from a sewer towards a property or a group of properties.
- areal reduction factor
A factor applied to point rainfall depths or intensities to generate values applicable to an area.
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.
- base flow
Sustained or dry weather flows not directly generated by rainfall. It commonly constitutes flows generated by domestic and industrial discharge and also infiltration.
- best management practices
Structural and non-structural measures used to store or treat urban surface water runoff to reduce flooding, remove pollution and provide other amenities.
- brownfield site
Redevelopment of a site often associated with pollution issues.
The area contributing surface water to a point on a drainage or river system, which may be divided in to sub-catchments.
The process of implosion of air in water that is a function of high velocities, which cause damage.
- Colebrook-White equation
An empirical equation relating flow to roughness and gradient of a conduit and the viscosity of the fluid.
- collection system
In wastewater, a system of conduits, generally underground pipes, which receive and convey sanitary wastewater (domestic and/or industrial) and/or stormwater.
- combined network
A sewer network that collects rainfall from impervious surfaces and foul water from domestic and industrial sources.
- combined sewage
Foul sewage mixed with surface water, also known as storm sewage.
- combined sewer
A sewer design to carry surface water and foul sewage within the same pipe.
- contributing area
The area of the catchment that contributes storm runoff directly to a sewerage system.
- control structure
A hydraulic device to limit the rate of flow.
- CSO (combined sewer overflow)
An outfall from a combined sewer designed to prevent the capacity of the sewer or a sewage treatment works from being exceeded under storm flow conditions by allowing the discharge of excess diluted sewage to another sewer, tank, watercourse or some other disposal point.
A covered channel or pipeline (defined by the Highway Agency as wider than 900mm)
- depression storage
Natural depression on the surface of the ground that need to be filled by rainfall before runoff can take place.
- design criteria
A set of standards agreed by the developer, planners and regulators that the proposed system should satisfy.
- design storm
A synthetic rainfall event of a given duration and return period, which is derived by statistically analysing an historical series of rainfall events for a specific location.
- detention basin
A vegetated depression which is normally dry, excepting post storm events, constructed to store water temporarily to attenuate flows. May allow infiltration of water in to the ground.
- detention tanks (balancing tanks)
Tanks constructed in a sewerage system to store a volume of water temporarily during peak flows (see off-line and on-line tanks).
The volume of liquid flowing through a cross-section of conduit per unit of time.
- discharge coefficient
A coefficient, derived by experiment, applied in a formula, by which the theoretical discharge of a fluid through an oriface, weir or nozzle, can be correctly calculated.
- domestic (foul) wastewater
Wastewater from household services including overflows from sinks, toilets, washing machines, etc.