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Glossary

Term Description
Tsig Significant period = average period of the waves used to define Hsig.
TBT Tributyltin
Temporal Variability with time
Terrestrial Of land
Threshold of motion The point at which the forces imposed on a sediment particle overcome its inertia and it starts to move.
Tidal bore A tidal wave that propagates up a relatively shallow and sloping estuary or river in a solitary wave form.
Tidal characteristics Those features relating to the time, range, and type of tide.
Tidal constants Tidal relations that remain practically constant for any particular locality. Tidal constants are classified as harmonic and non harmonic. The harmonic constants consist of the amplitudes and epochs of the harmonic constituents, and the non harmonic constants include the ranges and intervals derived directly from the high and low water observations.
Tidal current The lateral movement of water associated with the rise and fall of the tides.
Tidal cycle The period when the seawater level rises and falls once
Tidal difference Difference in time or height between a high or low water at a subordinate station and a reference station for which predictions are given in the Tide Tables.
Tidal limit The point to which the tide reaches in an estuary, the end of the saltwater intrusion.
Tidal prism Volume of water entering and leaving an estuary during each tide, i.e. the difference between low water volume and high water volume.
Tidal range Vertical difference in high and low water level.
Tidal wave The rise and fall in water level due to the passage of the tide.
Tide The periodic rise and fall of the water resulting from gravitational interactions between Sun, Moon, and Earth (see also tidal current).
Tide (water level) gauge An instrument for measuring the rise and fall of the tide (water level).
Tide curve A graphical representation of the tidal height over a tidal cycle.
Tide levels (1) High astronomical tide (HAT), lowest astronomical tide (LAT): the highest and lowest tidal levels, respectively, which can be predicted to occur under average meteorological conditions.

(2) Mean high water springs (MHWS): the height of mean high water springs is the average throughout a year of the heights of two successive high waters during those periods of 24 hours (approximately once a fortnight) when the range of the tide is greatest.

(3) Mean low water springs (MLWS): the height of mean low water springs is the average height obtained by the two successive low waters during the same periods.

(4) Mean high water neaps (MHWN): the height of mean high water neaps is the average of the heights throughout the year of two successive high waters during those periods of 24 hours (approximately once a fortnight) when the range of the tide is least.

(5) Mean low water neaps (MLWN): the height of mean low water neaps is the average height obtained by the two successive low waters during the same periods.

(6) Mean high water (MHW), mean low water (MLW): mean high/low water, as shown on Ordnance Survey Maps, is defined as the arithmetic mean of the published values of mean high/low water springs and mean high/low water neaps.
Tide Tables Tables which give daily predictions of the times and heights of high and low waters.
Tide-producing force That part of the gravitational attraction of the Moon and Sun which is effective in producing the tides on the Earth.
Tombolo A narrow sand or shingle bar linking a small island with another island or the mainland.
Topographic Delineation of the natural and artificial features of an area.
TraC Transitional and coastal
Transgression The invasion of large area of land by the sea in a relatively short period of time (geologically).
Tsunami Long period ocean waves generated by geological and tectonic disturbances below sea level.
Turbidity A measure of light obscuration by water. Turbidity increases as the amount of suspended sediments in the water column increase.
TW Transitional Waters

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Last Modified on: 19 June 2011
Printed from the Estuary Guide on 26/08/2019 03:32:17