Glossary and Abbreviations
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
Algae
Simple aquatic plants that may be attached or free floating (planktonic) and
occur as single cells, colonies, branched or unbranched filaments.
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Algal bloom
Dense growth of planktonic algae or most commonly cyanobacteria (blue-green
bacteria formerly classified as algae) in nutrient enriched surface water bodies
causing discolouration of water.
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Amenity
A (SUDS) feature that increases aesthetic attractiveness or provides social
or environmental value, of a geographic location
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Antecedent conditions
The condition of a catchment before a rainfall event.
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Antecedent precipitation
The relevant rainfall that takes place prior to the point in time of interest.
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Aquatic bench
A shallow horizontal strip just beneath the water surface around the perimeter
of a pond on which aquatic planting is established
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Aquifer
A sub-surface zone or formation of rock or soil containing groundwater.
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Attenuation (of flow)
Reduction of peak flow and increased duration of flow.
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Attenuation storage
A storage unit designed to attenuate flows by limiting flow rates out of it
and storing the difference between the in-flow and out-flow temporarily, and
releasing it as in-flows reduce/ cease.
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Baffle
A device designed to encourage mixing of flows to prevent short-circuiting through
a pond. Also, a device designed to prevent floating solids or liquids from passing
forwards from their current location.
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Base flow
Dry-weather flows not directly generated by rainfall. It commonly constitutes
flows generated by domestic and industrial discharges but can also be associated
with long term infiltration or groundwater discharge.
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Basin
A depression acting as a storage unit to control stormwater flow during rainfall,
but is dry at other times.
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Best Management Practices
A range of measures designed to reduce the rate and quantity of surface runoff
from developed areas and to improve runoff water quality. Effectively the same
definition as SUDS used in countries other than UK and Ireland, though with
some difference in emphasis on certain aspects, for example Amenity.
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Biochemical oxygen demand (BOD)
The measure of the concentration of biodegradable organic carbon compounds in
solution. Used as a water quality indicator.
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Biodegradation
Decomposition of organic matter by micro-organisms and other living things.
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Biodiversity
A measure of the diversity of plant and animal life in a particular habitat
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Bioretention
A drainage practice that utilizes landscaping and soils to treat urban stormwater
runoff, filtering it through a designed planting soil media and collecting the
flow through perforated under-drainage pipework.
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Block paving
Pre-cast concrete blocks used to construct a flexible modular paving system.
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Brownfield (site)
Land which has already been built on in the past. Often, but necessarily, associated
with land that is contaminated.
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Bund
A barrier, dam, or mound usually formed from earthworks material and used to
contain or exclude water (or other liquids).
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Catchment
A defined area, often determined by topographic features or land use, from which
rain will contribute to runoff to a particular point.
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Catchpit
A small chamber incorporating to trap sediment and other debris through which
runoff passes.
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Chemical oxygen demand (COD)
The measure of the amount of oxygen taken up by chemical oxidation of all oxidisable
substances in the liquid sample. Used as a water quality indicator.
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Climate change
Changes in meteorological conditions caused by the enhanced Greenhouse Effect,
which is predicted to result in, amongst others, sea level rise and increased
rainfall intensities.
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Coliform
Bacteria found in the intestines, faeces, nutrient rich waters, soil, and decaying
plant matter. Commonly used as an indicator for the existence of pathogens.
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Computer model
A series of mathematical equations in a computer developed and used with the
aim of replicating the behaviour of a system to enable prediction of the system
performance for a range of conditions.
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Consent
Permission (usually conditional) granted by the appropriate public authority;
usually associated with the discharge of flow, or potentially polluting flow,
to a watercourse or into the ground.
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Contaminated ground
Ground that has the presence of such substances, which are present in sufficient
concentrations, are likely to have detrimental effects if mobilised by the use
of infiltration or other activity which disturbs their current state.
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Contributing area
The area that contributes storm runoff or other output to the receiving system.
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Control structure
Structure to control the volume or rate of flow of water through or over it.
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Controlled waters
Waters defined and protected under the Water Resources Act 1991. Any relevant
territorial waters that extend seaward for three miles from the baselines, any
coastal waters which extend inland from those baselines to the limit of the
highest tide or the freshwater limit of any river or watercourse, any enclosed
dock which adjoins coastal waters, inland freshwaters, including rivers, watercourses,
and ponds and lakes with discharges and ground waters (waters contained in underground
strata). For the full definition refer to the Water Resources Act 1991.
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Conventional drainage
The traditional method of draining surface water using open channels, subsurface
pipes and storage tanks
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Conveyance
The ability of a drainage feature to pass water from one location to another
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Critical duration event
The duration of rainfall event likely to cause the highest peak flow, or largest
volume, or cause the highest water level at a particular location, for a specified
return period event
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Curtilage
Land area within property boundaries
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Degradation
The process of breaking down matter to a less complex state, usually by biological
processes
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Deposition
Laying down of matter via a natural gravitational process
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Design criteria
A set of standards agreed by the developer, planners, and regulators a the proposed
system should satisfy.
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Design storm
A synthetic rainfall event of a specific profile, intensity and duration for
a given duration and return period; derived by statistically analysis of a recorded
historical series of rainfall events for a specific location.
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Detention basin
A vegetated depression, normally dry, constructed to store surface water temporarily
during periods of rainfall to attenuate flows and provide some treatment and
possibly infiltration.
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Detention pond
Ponds similar to Retention ponds, but specifically distinguished (in Scotland)
to have a smaller permanent pool volume which is sized to provide a treatment
volume of 1 times Vt. Used where the risk of serious polluting incidents is
considered to be low
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Development
The site area which is being considered for construction including drainage
design.
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Diffuse pollution
Pollution arising from land-use activities (urban and rural) that is spread
widely across a catchment. Although surface runoff is discharged at discrete
points, this is generally associated with diffuse pollution.
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Discharge
The flow rate of liquid passing through a conduit.
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Discharge consent
Permission to discharge surface water or effluent, subject to conditions laid
down by a Regulator.
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Dissolved oxygen (DO)
The amount of oxygen dissolved in water, used as an indicator of the health
of a body of water for supporting the ecosystem.
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Down pipes
Pipes leading down from roof guttering to the ground.
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Drainage
A collection of conveyance and storage components, including pipes, channels
and other engineered works (SUDS) designed to cater stormwater in a built-up
environment.
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Duration
The time period over which an event occurs or has an impact.
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Ecological status(1)
The quality of the structure and functioning of aquatic ecosystems associated
with surface waters, classified in accordance with Annex V (WFD).
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Ecology
All living things, such as trees, flowering plants, insects, birds and mammals,
and the habitats in which they live.
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Ecology
The relationship of all organisms with each other and their environment.
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Ecosystem
A biological community of interacting organisms and their physical environment.
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Environment
All physical and biological components (air, land, water resources, plant, and
animal life) and their interaction of an area at any scale.
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Environmental Impact
An assessment on the (potential) impacts of an activity or development, plan
or policy. Normally associated with consideration of assessment of measures
to mitigate the impacts; usually presented as an Environmental Impact Statement.
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Erosion
The natural processes of weathering, dissolution, abrasion, corrosion, and transportation,
by which solid material is worn away at a location and deposited elsewhere,
usually by wind or water.
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Estuary
A semi-enclosed body of water, usually the mouth of a river, in which seawater
is substantially diluted with freshwater and where water levels are a function
of both river flows and tidal influence.
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Eutrophication
Water pollution caused by excessive nutrients and plant growth which results
in reduced oxygen levels. Eutrophication can result in mass fish kill.
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Evapotranspiration
The process by which soil loses moisture by evaporation and by uptake and then
transpiration from plants.
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Event (rainfall)
Single occurrence of a rainfall period before and after which there is a sufficient
dry period for runoff and discharge from the drainage system to cease.
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Extended Detention Basin
A detention basin where the runoff is stored beyond the time required for attenuation
of flow (flood control). The extra time allows greater removal of pollutants
in the water. Extended detention basins still aim to drain down within 24 to
48 hours. Issues of vegetation health in the bed of the basin which is saturated
for long periods needs to be considered. Practicalities associated with robust
performance of the hydraulic control structure may be a limiting aspect.
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Extreme event
Single occurrence of an event that is likely to occur very infrequently (e.g.
long drought or big storm).
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Fauna
The animals found in a particular physical environment.
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Filter drain
A linear drain consisting of a trench filled with a permeable material, usually
gravel, often with a perforated pipe in the base of the trench to assist drainage.
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Filter strip
Gentle uniformly sloping vegetated area designed to drain surface runoff as
sheet flow from impermeable surfaces and remove sediment.
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Filtration
In storm water treatment; a common process that removes particulate matter by
separating water from solid material usually by passing it through media such
as sand, gravel or dense vegetation.
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Fines
Small soil particles less than 63 micron in size.
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First flush
The initial discharge of surface water in which sediments and pollutants is
of a higher concentration than average.
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Flood frequency
The probability of a flow rate being exceeded in any year.
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Flood Risk Assessment
Technical review of the risk of flooding, to or on a development, and on adjacent
sites upstream and downstream.
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Flood routeing
Consideration of ground level topography that act as pathways to minimise the
adverse effect of flooding when the design capacity of the drainage system has
been exceeded or has failed.
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Flood Studies Report
Landmark report for catchment Hydrology – NERC/Institute of Hydrology 1975.
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Floodplain
Land adjacent to a watercourse that is subject to frequent flooding under natural
conditions due to periods of extreme rainfall. Flooding may be prevented due
to intervention (constructed embankments), but the area so protected is still
referred to as the floodplain.
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Flora
The plants found in a particular environment.
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Flow control device
A device used for the control of surface water, e.g. a weir.
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Flow regime
The variation of discharge of a waterway usually over an annual or seasonal
period.
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Fluvial flooding
Flooding from rivers.
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Forebay
Entry area for inlets of a basin or pond that is specifically designed to trap
incoming coarse sediments to facilitate the operational management of the whole
system.
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Foul drainage
The infrastructure that drains domestic and commercial effluent.
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Freeboard
Distance between the design top water level and the top of a structure; provided
as a precautionary safety measure against system failure and to cater for wave
effects.
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Frequency
The number of occurrences of a certain phenomenon per unit time.
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Geocellular structure
A plastic box structure used in the ground, often to attenuate runoff.
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Geogrid
Plastic grid structure used to increase the bearing strength of soils or aggregates.
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Geomembrane
An impermeable plastic sheet, typically manufactured from polypropylene, high
density polyethylene or other geosynthetic material.
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Geotextile
A plastic fabric that is permeable.
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Good ecological potential
The status of a heavily modified or artificial body of waters as classified
in Annex V of the WFD.
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Good ecological status(1)
The values of the biological quality elements for the surface water body type
show low levels of distortion resulting from human activity, but deviate only
slightly from those normally associated with the surface water body type under
undisturbed conditions. The classification of ecological status of surface waters
is based on indicators chosen from the main biological groupings within an eco-system:
aquatic flora, macro-invertebrate fauna and fish fauna. Taken together with
hydromorphological and physico-chemical parameters, the overall ecological status
of the river, lake, estuary or coastal water would be defined.
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Good groundwater status(1)
The status achieved by a groundwater body when both its quantitative status
and its chemical status are at least "good".
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Good surface water status(1)
The status achieved by a surface water body when both its ecological and chemical
status are at least ‘good’. It is based on biological, hydro-morphological
and physiochemical elements.
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Gradient
The angle of inclination of conduit or ground topography; influences flow velocity
and system capacity.
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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.
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Greenfield
Land that has never been developed, other than for agricultural or recreational
use.
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Greenfield runoff
The runoff rate and volume from a site prior to development.
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Greenfield Site
New development on land which has not been previously developed, usually at
the periphery of existing urban areas. This creates increased rainfall-runoff
and has a hydraulic impact on watercourses.
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Greywater
Waste water from baths, showers, sinks (kitchen sinks are excluded due to nutrient
rich effluent), and domestic appliances before it reaches the sewer.
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Groundwater protection zone
Areas that influence water supply boreholes where groundwater must be protected
from pollution. These are defined by reference to travel times of pollutants
within the groundwater.
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Groundwater(1)
All water which is below the surface of the ground in the saturation zone and
in direct contact with the ground or subsoil, i.e. below the water table.
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Gully
A structure, usually associated with roads, to permit the entry of surface runoff
into the drainage system. It is usually fitted with a grating and a grit trap.
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Habitat
The area or environment where the particular conditions are suited to the existence
of an organism or ecological community
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Head-discharge
The relationship between a discharge rate and the water level causing that discharge.
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Heavy metal
A general term for metals with a high atomic mass (sometimes given as metals
with an atomic mass greater than that of calcium; Manhattan, 1990), often used
in discussion of metal toxicity. No definitive list of heavy metal exists, but
they generally include cadmium, zinc, mercury, chromium, lead, nickel, thallium,
and silver. Some metalloids, e.g. arsenic and antimony, are classified as heavy
metals for discussion of their toxicity.
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Highest Astronomical Tide
The highest level predicted to occur under average meteorological conditions
and any combination of astronomical conditions. HAT levels will not be reached
every year, but nor are they the most extreme level which can be reached, as
storm surges may cause considerably higher levels to occur.
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Hydraulic Control Unit
A hydraulic device to control the rate of the flow.
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Hydraulics
Hydraulics is another term for fluid mechanics used in the context of water
engineering, and is the study of flows. In the context of SUDS, hydraulics covers
the storage, conveyance and control of flows by the drainage network.
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Hydrogeology
Hydrogeology is the study of water below the ground surface and geological aspects
of surface water.
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Hydrograph
A graph showing, for a given point on a stream or conduit, the discharge, stage,
velocity, available power, or other property of water with respect to time.
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Hydrological regime
The quantity and dynamics of flow, and the connection to groundwaters.
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Hydrology
The study of water, its properties, distribution and utilisation, from when
it rains until it returns to the sea.
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Hydromorphological(1)
Hydromorphological elements relate to both the hydrological regime and the morphological
conditions for a water body, be it a river, transitional water, coastal water,
lake or heavily modified or artificial waterbody.
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Hyetograph
Temporal intensity profile of a rainfall event.
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Impermeable surface
Surface which resists the passage or infiltration of water.
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Impervious surface
Surface which resists the passage or infiltration of water or any object or
material
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Industrial hot spot
Often used to denote an area where land use or activities have generated or
generates pollutants which cause the runoff to be highly contaminated.
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Infiltration
(a) The unintended ingress of groundwater into a (piped) drainage system.
(b) The process of rainwater runoff passing into the ground.
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Infiltration basin
A basin, which is normally dry, that is designed to store and infiltrate surface
runoff into the ground. In order that Infiltration basins work correctly, the
ground should comprise fairly pervious soils and management of the basin usually
requires scarifying to maintain reasonable infiltration rates. Consideration
of the sediment concentration of the influent is important.
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Infiltration trench
A trench, usually filled with permeable granular material, designed to promote
infiltration of surface water to the ground.
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Initial rainfall loss
In hydrology, the rainfall needed to “wet” the catchment prior to
surface runoff taking place. It includes interception, surface wetting, and
filling of depressions.
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In-property storage
Storage of rainfall within the curtilage of the property, e.g. in the gutter,
roof space or chamber.
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Intensity-duration-frequency
The relationship between rainfall intensity (amount per unit of time), rainfall
duration (total time over which rainfall occurs) and frequency (return interval)
at which the specific intensity-duration relationship is expected to recur.
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Interception
The process by which rainfall may be prevented from reaching the ground or the
drainage system, for example vegetation.
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Interception storage
Provision of storage to prevent runoff from the site from small rainfall events,
in order to replicate the site response to greenfield conditions.
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Interflow
The horizontal passage of water through the soil, from where it may infiltrate
vertically to an aquifer, move horizontally to a watercourse, or be evaporated.
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Interim Code of Practice (SUDS)
An agreed interim position statement between various the UK stakeholders involved
with drainage on the status and application of SUDS. (see References or CIRIA
web site link)
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Joint probability
The probability of an outcome occurring due to the combined influence of two
hydrological phenomena. The two phenomena may have some degree of dependency.
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Land use
Catchments or development areas zoned based on economic, geographic or demographic
use of land, such as residential, industrial, farm, commercial.
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Level of Service
The design or actual performance of a system e.g. drainage network or flood
defence, normally expressed in terms of the frequency of flooding experienced.
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Linear ponds
An alternative to swales in serving runoff from roadways and hard standings.
They are vegetated open channels that provide storage, conveyance and some treatment.
They are particularly useful in flat terrain due to their hydraulic conveyance
capability.
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List I substance
A controlled substance as defined under the Groundwater Regulations 1998 and
the Dangerous Substances Directive (76/464/EEC). List I substances are considered
the most dangerous in terms of toxicity, bio-accumulation and persistence. These
substances should be prevented from entering the drainage system or discharging
to the environment.
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List II substance
A controlled substance as defined under the Groundwater Regulations 1998 and
the Dangerous Substances Directive (76/464/EEC). They are less toxic than List
I substances, but are still capable of harm, hence their discharge to the environment
is strictly limited.
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Long Term Storage
Storage of stormwater which is normally drained by infiltration that specifically
addresses the additional volume of runoff caused by the development compared
to greenfield runoff. The objective is to minimise any increase in flooding
in the river downstream.
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Management train
The management of runoff through the site using a range of SUDS techniques to
maximise the hydraulic and water quality treatment benefits.
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Mean High Water
The average tidal level of all high waters observed over a long period.
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Mean High Water Springs
(Also known as Spring High Water) The average height of the high waters of the
spring tides. Spring tides are those tides of increased range occurring bi-monthly
as the result of the gravitational effect of the moon.
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Mean Sea Level
The average level of the sea over a long period, or the level which would exist
in the absence of tides.
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Micropool
Pool at the inlet or outlet to a pond or wetland that is permanently wet and
improves the pollutant removal effectiveness of the system.
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Mini Swale
Small, grass-lined, channels designed to store and treat runoff from small rainfall
events and, when larger events occur, discharge excess water directly into a
supporting pipe drainage network.
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Morphology
The hydrological and physical characteristics of a river.
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Network
The whole (drainage) system of inter-connecting conveyance and storage structures,
usually the term used in the context of a computer model of the system
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Non-return valve
A pipe fitting that allows flow in one direction only.
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Numerical Modelling
The use of computer models to replicate the behaviour of natural and manmade
systems to assist in assessing their performance under a range of possible conditions.
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Nutrient
A substance providing nourishment for living organisms (such as nitrogen and
phosphorus).
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Off-line
A structure is said to be off-line when it comes into operation only once the
maximum “load” in the normal operational state of the system at a
location is exceeded.
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On-line
A structure is said to be on-line when it is in operation at all times under
all “loads”.
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Open Water
Clear water surface ie free from submerged or floating aquatic vegetation.
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Organic
Naturally occurring compounds of carbon combined with one or more other elements,
most often hydrogen, oxygen, nitrogen, sulphur and halogens such as phosphorous,
fluorine and bromine.
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Organic pollution
A general term describing the type pollution that is biodegradeable. The effects
of organic pollution are described by the levels of bio-chemical oxygen demand,
ammonia, and dissolved oxygen found in a waterbody.
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Orifice
A hole, usually round and specifically sized, often used to control the rate
of flow.
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Outfall
The point, location or structure where wastewater or drainage discharges from
a pipe, channel, sewer, drain, or other conduit.
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Overflow
The flow of excess water from a structure when the capacity of that structure
is exceeded.
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Overland flow
The flow of water over the surface from rainfall runoff before it enters some
defined channel or inlet, or from excess flow passing out of a drainage structure
that is full.
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Pathogen
An organism that causes disease.
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Pathway
The route taken by overland flow or other object in transit.
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Pavement
Technical name for the road or car park surface and underlying structure, usually
asphalt, concrete, or blockpaving. Note the path next to the road for pedestrians
(colloquial term of pavement) is the footway.
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Peak discharge
The maximum flow rate at a point in time at a specific location resulting from
a given storm condition.
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Penstock
A sliding plate which moves vertically to vary the size of an aperture (or close
it completely).
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Percentage runoff
The percentage of the rainfall falling on a specified area which provides runoff
(which enters the stormwater drainage system).
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Percolation
The process of water passing (or other liquid) through a porous substance (eg
soil or geotextile fabric).
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Permeability
A measure of the ease with which a fluid can flow through a permeable medium.
It depends on the physical properties of the medium, for example grain size,
porosity, and pore shape.
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Permeable pavement
A permeable surface that is paved and drains through voids between solid parts
of the pavement into a permeable sub-base.
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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 inter-connecting voids.
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Pervious pavement
Another term for permeable pavement. A permeable hardstanding designed to promote
infiltration of surface runoff into a permeable sub-base.
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Pervious surface
A surface that allows inflow of rainwater into the underlying construction or
soil.
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Pesticide
A general term for any chemical agent used in order to kill unwanted plants
(weeds), animal pests or disease causing fungi.
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Phreatic surface
Groundwater surface
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Piped system
Conduits, usually round, generally located below ground to conduct effluent
or other liquids to a suitable location for treatment and/or disposal.
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Point source pollution
Pollution that arises from an easily identifiable source, e.g. a WwTW outfall.
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Pollutant
A contaminant whose concentration has increased to an objectionable level and
which may cause harm to flora or fauna.
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Pollution
The addition of a pollutant to the environment (a natural body of water) which
diminishes the physical, chemical, radiological, or biological quality of a
resource (air, water or land) and may have a negative impact on flora and fauna.
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Pond
Depression of any size with a permanent pool of water, usually with ecological
value.
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Poor status(1)
Waters which show evidence of major alterations to the values of the biological
quality elements for the surface water body type and in which the relevant biological
communities deviate substantially from those normally associated with the surface
water body type under undisturbed conditions.
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Porosity
The percentage of the bulk volume of a rock or soil that is occupied by voids,
whether isolated or connected.
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Porous asphalt
An asphalt material used to make pavement layers pervious, with open voids to
allow water to pass through (previously known as pervious macadam).
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Porous paving
A permeable surface that drains through voids that are integral to the pavement.
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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.
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Priority substances
Key substances, usually pollutants, identified by legislation as being critical
to control from causing an impact on the environment.
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Probability
The estimated likelihood of a storm event e.g. a 1 in 100 year flood event is
one that is expected to be equalled or exceeded once every 100 years; it also
has a 1% chance of occurring in any one year.
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Public sewer
A sewer that is vested and maintained by the responsible public authority.
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Rainfall event
A single occurrence of rainfall before and after which there is a dry period
that is sufficient to allow the drainage system to return to, or near to, its
steady state.
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Rainfall intensity
Amount of rainfall occurring in a (short) period of time, generally expressed
in mm/hr.
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Rainfall ratio “r”
The ratio of depths for a 5 year return period event of 60 minute duration and
a 5 year return period event of 2 days duration.
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Rainwater butt
Small scale garden water storage device which collects rainwater from the roof
via the down-pipe.
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Rainwater harvesting or rainwater use system
A system that collects rainwater locally (usually from roofs, but occasionally
from hard standings) rather than allowing it pass to the drainage system.
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Rational Method
A simple drainage analysis method, used throughout the world, for calculating
the peak discharge in a drainage system for pipe sizing.
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Receiving waters
Water body (river or lake) which receives flow from point or non-point sources.
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Recharge
The addition of water to the groundwater system by natural or artificial processes.
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Reed bed
Area of grass-like marsh plants, in or adjacent to water bodies. Artificially
constructed reed beds are used to treat small volumes of the liquid component
of sewage effluent.
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Regulator
An organisation, usually government body, with the authority to stipulate requirements
such as consents for discharges to receiving waters.
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Residential access roads
These roads link dwellings and their associated parking areas and common open
spaces to distributor roads.
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Retention Pond
A SUDS pond consisting of a significant sized permanent pool of water (up to
4 times Vt) designed to treat surface runoff by detaining the water to provide
settling of sediments, and chemical and biological processing as well as provide
attenuation. Often used to provide high amenity value.
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Return period
The reciprocal of the average annual probability of exceedence of a specific
flow value or event.
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Risk
Risk is a measure of the combination of the likelihood of an event (hazard probability)
and the severity of the outcome (consequence).
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Risk assessment
An evaluation of all the relevant risks (hazards and consequences) to enable
appropriate actions or mitigating solutions to be devised.
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River Basin
The area of land from which all surface run-off flows through a sequence of
streams, rivers and, possibly, lakes into the sea at a single river mouth, estuary
or delta.
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Runoff
Water from precipitation which flows over surfaces and contributes to flows
in a drain, sewer or receiving water.
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Runoff coefficient
The proportion of total rainfall that appears as total runoff volume after subtracting
losses, such as depression storage, infiltration and interception.
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Salmonid Waters
High quality waters suitable for self sustaining populations of wild salmon
and trout.
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Scour
Localised erosion.
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Sediment
Organic or inorganic material that has been transported by water, which has
been deposited.
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Separate sewer
A sewer for surface water or foul sewage, but not a combination of both.
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Separate Sewer System
System whereby, foul sewage and stormwater run-off are kept separate and confined
to individual designated sewer systems: one for foul sewage which is conveyed
to treatment; and one for stormwater run-off which is discharged to water courses.
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Sewer
A pipe or channel taking domestic foul and/or surface water from buildings and
associated paths and hard-standings from two or more curtilages and having a
proper outfall.
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Sewerage
System of pipes (sewers) to transport sewage.
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Silt
The generic term for waterborne particles with a grain size of 4-63 mm, i.e.
between clay and sand.
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Simulation
The representation of specific conditions during a specific period in a sewerage
system, treatment works, river, etc., by means of a computer model.
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Single size grading (single size material)
Where the majority of the soil or aggregate material is of one nominal size,
although there may be small proportions of other sizes.
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Site Control
A term used in SUDS to denote drainage elements that are suitable for use in
storm water management to maximise quality and quantity benefits for a small
development or site.
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Soakaway
A pit, usually filled by single sized aggregate, into which surface water is
drained to infiltrate into the ground.
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Soil
The terrestrial medium on which many organisms depend, which is a mixture of
minerals (produced by chemical, physical and biological weathering of rocks),
organic matter, and water. It often has high populations of bacteria, fungi,
and animals such as earthworms.
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Soil Moisture Deficit (SMD)
A measure of soil wetness, calculated by the Meteorological Office in the UK,
to indicate the capacity of the soil to absorb rainfall.
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Source control
Practices which manage runoff at or near its source.
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Source-Pathway-Receptor Model
A method for establishing, assessing and communicating risk relationships.
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Standard Swale
A grass-lined channel designed to convey surface water, as well as controlling
and treating the flow.
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Storage
The impounding of water, either on the surface or in underground chambers.
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Storm
A natural occurrence which normally includes precipitation such as rainfall,
snow, or hail.
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Stormwater
The product of a meteorological event, often of rainfall, snow or hail, which
forms runoff from surfaces which have an inability to infiltrate.
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Sub-catchment
A division of a catchment, either for reasons of different land use, or for
defining the extent of the contributing area to a drainage location.
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Sustainable (Urban) Drainage Systems (SUDS)
Sustainable drainage systems: a sequence of conveyance systems and control structures
designed to manage the drainage of surface water more sustainably than conventional
techniques by providing treatment and reducing flow rates and volumes.
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Sump
A pit that may be lined or unlined and is used to collect water and sediments
before being pumped out.
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Surface water
Water from precipitation which has not seeped into the ground and which is discharged
to the drainage system.
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Surface Water Status(1)
The general expression of the status of a body of surface water, determined
by the poorer of its ecological and it chemical status.
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Suspended solids
Small particles that are carried in suspension in the water column and create
turbid, or cloudy conditions. Often used as a simple indicator of the water
quality of the water and also closely correlated with concentrations of some
other relevant pollutants.
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Swale
The term given to a grass channel for stormwater collection with shallow side
slopes and gradients to allow ease of maintenance and which is normally dry
except during rainfall. The design of the soil and vegetation is important to
maximise its operational effectiveness, both hydraulically and for treatment.
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Temporary storage
Storage of the excess water for high intensity events, where the drainage system
is temporarily overloaded.
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Time of entry
Time taken for rainwater to reach an inlet into the drainage system after hitting
the ground. Often used in conjunction with design using the Rational Method.
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Time series rainfall
A continuous or discontinuous record of individual events generated artificially
(stochastically) or selected from real historical events which is representative
of the rainfall in that area.
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Toxic material
Capable of producing an adverse effect in a biological system causing serious
injury or causing death. e.g. pesticides and heavy metals.
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Trash rack
Rack of bars installed to trap litter or debris to collect or to minimise risk
of blockage in the system downstream.
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Treatment
Improving the quality of water by physical, chemical and/or biological means.
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Treatment storage
Storage provided to provide partial water quality treatment to surface water,
primarily through sedimentation.
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Treatment train
A series of SUDS components, each designated to treat a different aspect of
runoff that are implemented together to maximise their effectiveness.
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Treatment Volume
The volume of water provided in a pond to provide dilution and detention to
inflowing surface runoff to provide partial treatment.
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Turbidity
Reduced transparency of a liquid caused by the presence of un-dissolved matter.
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Unconfined aquifer
An aquifer which is not overlain by an impermeable stratum.
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Under-drained Swale
A swale where water percolates down through the base of the swale into a perforated
pipe that collects and then discharges the flow to another part of the drainage
system or the receiving waters. The swale may be a conveyance unit (where the
under-drainage is aimed at ensuring well drained conditions in the bottom of
the swale), or be designed only to provide temporary storage for the percolation
process.
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Underground storage
Underground structure, often constructed using concrete, grp, steel tanks or
plastic void formers. They provide hydraulic attenuation, but do not treat the
runoff.
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Urban drainage
Drainage conveyance, storage elements and ancillary structures (pumping stations
etc) to serve the urban environment.
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Void ratio
The ratio of open air space to solid particles in a soil or aggregate structure.
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Vortex flow control
The induction of a spiral/vortex flow of water in a chamber used to control
or restrict flow.
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Wallingford Procedure
A design and analysis procedure for urban drainage networks. Produced by HR
Wallingford and the Institute of Hydrology in 1981. Funded by DoE.
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Wash off (of pollutants)
The transport of pollutant mass from a surface during a rainfall event.
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Waste
Any substance or object that the holder discards, intends to discard, or is
required to discard. Disposal of waste, particularly Hazardous waste, is controlled
by legislation.
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Water butt
Small tank, usually covered and placed at ground level, connected to a down-pipe,
to provide storage of water of runoff from roofs.
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Water quality
The chemical and biological content of water, usually compared to defined standards,
set by the national legislation or European Community Directives and enforced
by regulatory authorities in member states.
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Water Quality Treatment volume
The volume of water provided in a pond to provide dilution and detention to
inflowing surface runoff to provide partial treatment.
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Water table
The level where the surface of groundwater of an unconfined aquifer can be detected.
The water table level fluctuates with the seasons and the annual rainfall and
the demand on it made by man.
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Watercourse
A natural or artificial channel (rivers, streams, ditches) for conveying water
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Weir
A hydraulic structure, usually horizontal, of a predetermined height and length
to control the flow of water.
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Wetland
A continuously wet area in which the water is shallow enough to enable the growth
of bottom-rooted plants. It has a requirement for a continuous base flow to
maintain healthy vegetation. Treatment of stormwater can be very effective,
but if used for attenuation, consideration needs to be given to the effect of
fluctuating water levels on plant life.
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Whole life cost
The present day value of total costs of a structure throughout its likely operating
life (construction, operation, decommissioning).
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(1) As defined in the Water Framework Directive (2000/60/EC)
