Lowest astronomical tide under any predictable astronomical or meteorological conditions.
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HALF-TIDE BASIN
A lock of very large size and usually of irregular shape, the gates of which are kept open for several hours after high tide so that vessels may enter as long as there is sufficient depth over the sill. Vessels remain in the half-tide basin until the ensuing flood tide before they may pass through the gate to the inner harbor. If entry to the inner harbor is required before this time, water must be admitted to the half-tide basin from some external source.
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HARMONIC FUNCTION
Any real function that satisfies a certain equation. In its simplest form, as used in tide and tidal current predictions, it is a quantity that varies as the cosine of an angle that increases uniformly with time
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HARMONIC CONSTANTS
The amplitudes and epochs of the harmonic constituents of the tide or tidal current at any place
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HIGH WATER
The maximum height reached by a rising tide. The height may be due solely to the periodic tidal forces or it may have super- imposed upon it the effects of prevailing meteorological condi- tions. Use of the synonymous term HIGH TIDE is discouraged.
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HALF-TIDE LEVEL
A tidal datum midway between mean high water and mean low water. Mean sea level may coincide with half-tide level, but seldom does; the variation is generally about 3 centimeters and rarely exceeds 6 centimeters. Also called MEAN TIDE LEVEL.
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HALF TIDE
The condition or time of the tide when midway between high and low
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HARMONIC PREDICTION
Method of predicting tides and tidal currents by combining the harmonic constituents into a single tide curve, usually performed by computer.
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HIGH WATER MARK
A line or mark left upon tide flats, beach, or alongshore objects indicating the elevation of the intrusion of high water. It should not be confused with the MEAN HIGH WATER LINE or MEAN HIGHER HIGH WATER LINE
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HARMONIC ANALYSIS
The process by which the observed tide or tidal current at any place is separated into basic harmonic constituents. Also called HARMONIC REDUCTION.
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NATIONAL TIDAL DATUM EPOCH
The specific 19-year cycle adopted by the National Ocean Survey as the official time segment over which tide observations are taken and reduced to obtain mean values(e.g., mean lower low water, etc.) for tidal datums. It is necessary for standardization because of apparent periodic and apparent secular trends in sea level. The present National Tidal Datum Epoch is 1960 through 1978.
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