Terms of Hydrology (T)

tailrace :

Channel which conducts water away from a water-wheel or turbine.

tailwater :

Water located just downstream from a hydraulic structure on a stream.

telemetering :

Recording at a distance of indications from instruments.

temperature lapse rate :

Decrease of the air temperature in degrees Celsius per 100 m of altitude in ...

tensiometer :

Instrument that consists essentially of a porous cup inserted in a soil and ...

thalweg :

Line following the deepest part of a streambed or channel or of a valley.

thaw :

Melting of snow and ice at the earth's surface, following a temperature ris ...

thermal infrared :

Preferred term for the middle wavelength ranges of the infrared region, ext ...

thermal load :

(1) Amount of heat transported by a river or canal per unit of time (joules ...

thermal spring :

Spring, the temperature of which is above the mean annual temperature of th ...

thermocline :

Layer in thermally stratified body of water in which the temperature gradie ...

thermo-mineral spring :

Thermal spring of a high mineral content.

thermo-osmosis :

Flow through porous media caused by differences of temperature.

Thiessen polygon :

Polygons formed by the perpendicular bisectors of the straight lines joinin ...

thixotropic :

Description of a substance that acts like a gel when stationary but like a ...

throat :

Minimum cross-sectional area within a flume. It may have any shape, e.g. re ...

throughfall :

Part of rainfall that reaches the ground directly through the vegetative ca ...

tidal piezometric efficiency :

Ratio of the range of the fluctuations of the piezometric level in a well t ...

tidal prism :

Volume of water that flows with the movement of the tide into a tidal chann ...

tidal range :

Difference in height between high tide and a consecutive low tide.

tidal river :

River in which the flow and water-level are affected by tides.

tide :

Periodic rise and fall of water in the seas or in large lakes due to the gr ...

time of concentration :

Period of time required for storm runoff to flow to the outlet from the poi ...

time series :

Set of observations, in order, taken at successive points of time, commonly ...

toe of interface :

Line of intersection between the bottom of an estuary or a coastal aquifer ...

tolerance :

Permissible variation of the specified value of a quantity. (TR)

tolerance limit :

Limiting lower or upper value specified for a quantitative characteristic.

torrent :

Watercourse having a steep slope, flowing in general with great velocity an ...

tortuosity :

(1) Ratio of the actual length of a stream channel measured between two poi ...

total acidity :

Amount of both weak and strong acids in water, usually expressed as millieq ...

total dissolved solids (tds) :

Total weight of dissolved mineral constituents in water per unit volume (or ...

total head :

Sum of the elevation of the free surface of a stream above a horizontal dat ...

total storage :

Volume of a reservoir including dead storage below the maximum controllable ...

trace element :

Chemical element present in a minor amount in water.

tracer :

Easily detectable material which may be added in small quantities to flowin ...

tractive force :

Force parallel to the bed exerted by flowing water on a sediment particle a ...

translatory wave :

Gravity wave that propagates in an open channel in a direction parallel to ...

transmissivity :

Rate at which water is transferred through a unit width of an aquifer under ...

transpiration :

Process by which water from vegetation is transferred into the atmosphere i ...

trap efficiency :

Ability of a reservoir to trap and retain sediment, expressed as a percent ...

travel time :

Time elapsing between the passage of a water parcel or packet between a giv ...

trend :

Long-term smooth movement in a time series.

triangular-profile weir :

Long-base weir having a longitudinal triangular profile. (ISO/772)

tributary :

Watercourse flowing into a larger watercourse or into a lake.

tritium unit (T.U.) :

Unit used to express tritium concentrations. One tritium unit is a concentr ...

tropical cyclone :

Cyclone of tropical origin of small diameter (some hundreds of kilometres) ...

true value :

Value which characterizes a quantity in the conditions which exist at the m ...

tsunami :

Great sea wave produced by a submarine earthquake or volcanic eruption.

Turbidity :

Condition of a liquid due to fine, visible material in suspension, which im ...

turbulent flow :

Flow with turbulence. In channel flow, it occurs at Reynolds number larger ...

Turnover :

(1) Action of turning over of a water body, e.g. a lake, whether or not str ...

turnover rate :

Ratio of the annual average groundwater recharge, expressed in volume, to t ...

turnover time :

Time required for supplying a volume equal to the total water reserve in a ...

twin-gauge station; twin-gage station (A) :

Gauging station at which two water level gauges define a reach for measurem ...