EM 1110-2-1100 (Change 1)
31 Jul 03
LOOP
That part of a STANDING WAVE where the vertical motion is greatest and the horizontal velocities are least.
Loops (sometimes called ANTINODES) are associated with CLAPOTIS and with SEICHE action resulting from wave
reflections. Compare NODE.
LOW TIDE (LOW WATER, LW)
The minimum elevation reached by each falling tide. See TIDE. (See Figure II-5-16.)
LOW TIDE TERRACE
A flat zone of the beach near the low water level.
LOW WATER (LW)
The minimum height reached by each falling tide. Nontechnically, also called LOW TIDE.
LOW WATER DATUM
An approximation to the plane of mean low water that has been adopted as a standard reference plane. See also
DATUM, PLANE and CHART DATUM.
LOW WATER LINE
The line where the established LOW WATER DATUM intersects the shore. The plane of reference that constitutes
the LOW WATER DATUM differs in different regions.
LOW WATER OF ORDINARY SPRING TIDES (LWOST)
A tidal datum appearing in some British publications, based on low water of ordinary spring tides.
LOWER HIGH WATER (LHW)
The lower of the two high waters of any tidal day. (See Figure II-5-16.)
LOWER LOW WATER DATUM
An approximation to the plane of MEAN LOWER LOW WATER that has been adopted as a standard reference
plane for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better
determination of MEAN LOWER LOW WATER from a subsequent series of observations.
LOWER LOW WATER (LLW)
The lower of the two low waters of any tidal day. The single low water occurring daily during periods when the
tide is diurnal is considered to be a lower low water. (See Figure II-5-16.)
LOWEST ASTRONOMICAL TIDE (LAT)
The lowest tide level which can be predicted to occur under average meteorological conditions and any
combination of astronomical conditions. This level may not be reached every year.
LUNAR DAY
The time of rotation of the Earth with respect to the moon, or the interval between two successive upper transits of
the moon over the meridian of a place. The mean lunar day is approximately 24.84 solar hours in length, or 1.035 times as
great as the mean solar day. Also called TIDAL DAY.
LUNAR TIDE
The portion of the tide that can be attributed directly to attraction to the moon.
A-46
Appendix A Glossary of Coastal Terminology
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