Drainage Terms A-Z
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rainfall intensity
Amount of rainfall occurring in a unit of time, generally expressed in millimetres per hour (mm/h).
rainfall profile
A series of values of rainfall intensity varying with time; a rainfall event is referred to as a hyetograph.
raingauge
An instrument used to measure and record the amount of rainfall at an allocated location.
rational method
A simple method, used throughout the world, for calculating the peak discharge in a drainage system for pipe sizing.
reach (river)
A stretch of river between two points, often used where the river characteristics are similar.
receiving waters
Water body (river or lake) that receives flow from point or non-point sources such as combined sewer overflows.
regulator
(1) A structure installed in a sewer, conduit or channel to control the flow of water or wastewater at an intake, or overflow or t control the water level along a canal, channel or treatment unit.
(2) The term used in the UK to refer to the Environment Agency and OFWAT due to their legal involvement in controlling water companies.
reservoir storage
The phenomenon by which a volume of flow is stored temporarily on a surface or in a length of pipe or channel as the depth and rate of flow increase; the storage is depleted after the peak of the storm passes.
retention pond
A pond constructed for the temporary storage of surface water runoff, which releases the stored water at controlled rates.
return period
The reciprocal of the average annual probability of exceedence of a specific flow value or event.
runoff
Water from precipitation that flows off a surface to reach a drain, sewer or receiving water.
runoff coefficient
The proportion of total rainfall that appears as total runoff volume after subtracting depression storage, infiltration and interception. |
