Glossary

This glossary of terms is intended primarily to help explain some of the technical vocabulary used in the Gauging Station and Catchment descriptions. Where possible, the definitions given below are based upon those developed by the International Standards Organisation1.

Surface Water

Afflux The rise in water level immediately upstream of, and due to, an obstruction.
Backwater (curve) The profile of the water surface upstream when its surface slope is generally less than the bed slope. The backwater curve generally occurs upstream of an obstruction or confluence.
Broad-crested A weir of sufficient breadth (in the direction of the flow) such that critical flow occurs on the crest of the weir. The term long-crested is sometimes also applied to such structures.
Cableway An assembly of winches and ropes and a carrier for placing the current meter at any desired point in the cross section.
Calibration The establishment of a discharge relationship (or rating) with the measured stage values. Sometimes used as a synonym for the stage-discharge relation.
Compensation A minimum flow which a water authority is under an obligation to discharge into a watercourse as a condition of carrying out their undertaking. Commonly the obligation relates to the maintenance of a discharge rate below a reservoir. The term 'residual flow' is preferred by some authorities.
Compound weir A weir containing two or more sections, which may be of different types, each section normally having a different height.
Control The physical properties of a channel, natural or artificial, which determine the relationship between stage and discharge at a location in the channel.
Crest-tapping A means of measuring the pressure head near to the crest of a weir - the ratio of this head to the upstream measured head can be used to determine the reduction factor necessary when flows are non-modular.
Critical flow The flow in which the total energy head* is a minimum for a given discharge; critical flow conditions are created by the installation of most standard weirs and flumes (as well as by natural obstructions and constrictions).
Depth of approach The depth of the upstream bed at the tapping point below the lowest point of a weir crest.
Drawdown curve The profile of the water surface where its surface slope exceeds the bed slope, for instance, immediately upstream of a weir or flume.
Drowned (or submerged) A weir in which the upstream level is affected by the downstream water level (and the 'modular' stage-discharge relation no longer applies).
Flume An artificial channel with clearly specified shape and dimensions which may be used for the measurement of flow. A standing-wave flume, for instance, contains a constriction which causes the flow to change from sub-critical* to super- critical* and in which the measurement of upstream water level (alone) allows the discharge to be computed.
Freshets The periodical release of discharge rates over and above the basic compensation flow. These artificial floods are intended to benefit the aquatic environment, particularly fisheries.
Gaugeboard A device with a graduated scale installed at a gauging station for measuring the level of water relative to a datum. Gaugeboards can be either vertical or inclined.
Hydraulic jump The sudden change of flow from super-critical flow to sub-critical flow. The transition is marked by a standing-wave.
Hysteresis The effect on the stage-discharge relation at a gauging station subject to variable water surface slope where, for the same gauge height, the discharge on a rising stage differs from that on a falling stage.
Influent stream One which flows above the water-table and contributes to it by natural leakage through the bed of the channel (sometimes termed a 'losing' stream; conversely a 'gaining' stream has its flow naturally augmented by inflow through the bed or banks).
Invert The lowest part of the cross-section of a natural or artificial channel.
Modular limit The submergence ratio when the flow just begins to be affected by the downstream level.
Nappe The jet formed by the flow over a weir. A clinging nappe is one held in contact with the downstream face of a weir.
Rhymer weir A simple form of variable geometry weir consisting of fixed horizontal beams which support vertical timber posts to form a series of rectangular openings ? these may be closed by means of timber gates.
Stage The elevation of the free surface of a stream relative to a datum; sometimes also referred to as the gauge height.
Stage-discharge An equation, table or formula which expresses the relation between the stage relation and the discharge in an open channel at a given cross-section.
Stilling well A well connected with the main stream in such a way as to permit the measurement of stage in relatively still liquid.
Submergence The ratio of the downstream total head (measured head plus velocity head) to the upstream total head over a weir.
Suppressed weir A weir whose sides are in the same plane as the open channel thus eliminating (suppressing) side contractions of the stream.
Thin-plate weir A weir constructed of a vertical thin plate with a thin crest shaped in such a manner that the nappe springs clear of the crest.
Triangular- A weir having a triangular profile in a vertical profile weir direction in the direction of flow. The 'Crump' and 'Flat V' weirs are examples of such structures.
Unstable channel Channel in which there are frequent and significant changes in control.
Velocity of The mean velocity in an open channel at a specified approach distance upstream of a measuring device.
Velocity head The head obtained by dividing the square of the mean velocity (in the measuring section) by twice the acceleration due to gravity.

Ground Water

Aquifer A rock formation containing groundwater that can be abstracted economically in useful quantities.
Artesian well A shaft, or more commonly a borehole, within which, when the aquifer is penetrated, water rises within the well to a level above the top of the aquifer, i.e. above the base of a confining layer. The term is usually reserved for wells that naturally overflow at the ground surface; where the water level rises, but does not reach the ground surface, the term sub-artesian is sometimes used.
Borehole A well constructed by machinery, usually less than one metre in diameter. Usually constructed vertically, but inclined boreholes are occasionally constructed.
Confined aquifer An aquifer in which groundwater is held under pressure by a confining layer (see also artesian well).
Confining layer An impermeable rock formation that immediately overlies an aquifer, and which may contain water in the latter under pressure.
Groundwater Sub-surface water contained within the saturated zone.
Observation well A shaft or borehole used for observing groundwater head or quality.
Permeability The ability of a material to allow the passage of a fluid.
Piezometric The surface that represents the static head of the groundwater surface in a confined aquifer; in practice, the static head is taken to be the water level measured in a well penetrating a confined aquifer.
Potentiometric The surface that represents the static head of the groundwater surface in both confined aquifers and water-table aquifers (i.e. where the water or pressure surface is at atmospheric pressure). This term includes piezometric surface and water-table.
Rising A term used particularly in South West England for a continuous outflow of subterranean water of such dimensions as to be regarded as the emergence of a stream rather than a spring; characteristic of Karstic aquifers such as the Carboniferous Limestone in the Mendip Hills.
Saturated zone That part of an aquifer, normally beneath the deepest water-table, in which ideally all voids are filled with water under pressure greater than atmospheric.
Shaft A well constructed by hand and generally greater than one metre in diameter.
Unsaturated zone That part of an aquifer between the ground surface and the water-table.
Water level In this context, the altitude (or depth) of the water surface as measured in a well.
Water-table The surface of a groundwater body at which the water pressure is atmospheric. Unless the water-table is coincident with the ground surface, an unsaturated zone will be present.
Well A term used to include both shafts and boreholes although occasionally used for shafts only.

Abbreviations

Note: The following abbreviations do not purport to represent any standardised usage; they have been developed for use in the Hydrological data UK series of publications only. Where space constraints have required alternative forms of these conventional abbreviations to be used, the meaning should be evident from the context.
Adf Average daily flow
ALF Alleviation of Low Flows
AOD Above Ordnance Datum
B-c Broad-crested
Bk Beck
Blk Black
Br Bridge
Brk or B Brook
Brn Burn
BNFL British Nuclear Fuels Ltd
BS British Standards
Ch Channel
C/m Current meter(ing)
Com Common
Dk Dike
Dmfs Daily mean flows
Dr or D Drain
D/s Downstream
E East
EM Electromagnetic gauging station
F&M Foot and Mouth disease
Frm Farm
G/s Gauging station
Gw Groundwater
HEP Hydro-electric power
Hifs Highest instantaneous flows
Ho House
Hosp Hospital
IH Institute of Hydrology
L Loch or lake
Lb Left hand river bank (looking downstream)
Ln Lane
L'st Limestone
Ltl Little
MAF Mean annual flood
Mkt Market
Ml/d Megalitres per day
Mnr Manor
N North
NERPB North East River Purification Board
NSHEB North of Scotland Hydro- Electric Board
Ntch Notch
NW North West
OD Ordnance Datum
O/f Outfall or outflow
ORS Old Red Sandstone
Pk Park
Pop Population
POR Period of record
PS Pumping station
Pt Point
PT Permo-Triassic (sandstones)
PWS Public water supply
Q95 The flow exceeded 95% of the time
QMED Median annual flood
Rb Right hand river bank (looking downstream)
R/c Racecourse
RCS Regional communications system
Rd Road
Res Reservoir
Rh Right hand
RPB River Purification Board
S South
S'st Sandstone
Sch School
S-D Stage-discharge relation
SDD Scottish Development Department (now SOE)
SE South East
SOE Scottish Office Environment Department
Sl Sluice
Sp Spring
St Stream
STW Sewage Treatment Works
SW South West
TS Transfer scheme
US Ultrasonic gauging station
U/s Upstream
VA Velocity-area gauging station/method
W West
W'course Watercourse
WBGS West Berkshire Groundwater Scheme
Wd Wood
Wr Weir
WRW Water reclamation works
Wtr Water
WTW Water treatment works

Reference

1. International Standards Organisation, 1978. Liquid flow measurement in open channels. Vocabulary and symbols, ISO 772,1978.