Annex 1. Glossary1

¹ The definitions given here are for use solely with this publication and may not be applicable in other contexts. Terms in italics in the definitions are also defined in this glossary.

alluvial	Deposited by a river, normally on a flood plain near the river's mouth
baffle	Slab or board partly closing a drainage channel to divert or slow down the flow of water
bedding	Sand or gravel placed beneath a drainage pipe or channel element to support it evenly
by-laws catchment area	Laws made at local level Area of ground from which rainwater will flow to a single point
checkwall	Wall placed across a drainage channel to prevent scouring
concentration time	Time required for rainwater from all over a catchment area to flow to a single point
crown	The highest point in the cross-section of a pipe
culvert	Drain for carrying water underneath a road or pathway
curing	Treatment of concrete by keeping its surface damp for the first seven days after placing, to ensure it develops its full strength
dissipator	Checkwall built of loose boulders which allows water to pass through the boulders but slows it down, dissipating its energy
element	Precast section of drainage channel lining or pipe
erosion	Removal of soil by the action of water
gabion	Bundle or bale of stones bound in wire or other mesh
grader	Machine used for road construction and maintenance, with a blade fixed between its front and rear wheels
groundwater	Water located beneath the ground surface
gully pot	Basin incorporated into the inlets of some closed drainage systems to collect sediment, which must be removed from it regularly
impermeable	Describes a material through which water cannot pass
in situ concrete	Concrete placed and allowed to set in the position where it will remain
infiltrate	(of a fluid) To pass into the pores or small spaces in a solid, e.g., soil
infrastructure	Permanent facilities for the common use of a community
invert	The lowest point in the cross-section of a pipe
landfill	Earth or rubble spread over the ground to raise the level
manhole	Underground chamber of brick or concrete, permitting entry to closed drains and sewers
masonry	Construction of brick or stones held together with mortar
mortar	Mixture of cement, sand and water
municipality	Organ of local government in a city or urban district
parasite	An organism that lives on or in another living organism and draws nourishment from it
pantograph	Instrument for mechanical copying of drawings or plans on the same or a different scale
planimeter	Instrument for measuring areas on paper
polder	Low-lying area of land protected from flooding by an embankment
primary drainage system	System of large drains, each serving a wide area of a city
receiving water body	Body of water into which water flows from a drainage system
refuse	Rubbish, garbage
return period	Average interval between storms or floods of a given severity
runoff	Water from rainfall, flowing over the ground and into drains and streams
runoff coefficient	Proportion of rainwater that flows over the ground and is thus likely to enter a drainage system
scouring	Washing away of soil (erosion) around, beneath or in the bed of a drain
secondary drainage system	Network of small drains within a neighbourhood serving a small catchment area and discharging into the primary drainage system
self-cleansing speed of flow	Speed of flow in a drain or sewer sufficient to prevent the accumulation of sediment
sewage	Human excreta and wastewater, flushed along a sewer
sewer	A pipe containing wastewater or sewage
slope	Gradient; inclination to the horizontal
sludge	Mixture of solids and water deposited on the bottom of drains, septic tanks, etc.
sluice gate	Structure that can be opened or closed to control the passage of water
stormwater	Water from rainfall flowing in a drain or sewer
topography	Shape of the ground surface, including the position of natural and manmade features
trapezoidal	Describes a drainage channel with sloping sides and a flat bottom
turnout	Drain taking water away from the side of a road
weephole	Small hole in a drainage channel lining through which water can flow, to relieve groundwater pressure