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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. (See also NODE.) 



LOWER HIGH WATER (LHW) - Tlie lower of the two high waters of any tidal 

 day. (See Figure A- 10.) 



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 A- 10.) 



LOW TIDE (LOW WATER, LW) - The minimum elevation reached by each falling 

 tide. See TIDE. (See Figure A-10.) 



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 intersection of any standard low tide datum plane 

 with the shore. 



LOW WATER OF ORDINARY SPRING TIDES (LWOST) - A tidal datum appearing in 

 some British publications, based on low water of ordinary spring 

 tides , 



MANGROVE - A tropical tree with interlacing prop roots, confined to low- 

 lying brackish areas. 



MARIGRAM - A graphic record of the rise and fall of the tide, 



MARSH - An area of soft, wet, or periodically inundated land, generally 

 treeless and usually characterized by grasses and other low growth, 



MARSH, SALT - A marsh periodically flooded by salt water. 



MASS TRANSPORT - The net transfer of water by wave action in the direction 

 of wave travel. See ORBIT. 



MEAN DIAMETER, GEOMETRIC - See GEOMETRIC MEAN DIAMETER. 



MEAN HIGHER HIGH WATER (MHHW) - The average height of the higher high 

 waters over a 19-year period. For shorter periods of observation, 

 corrections are applied to eliminate known variations and reduce 

 the result to the equivalent of a mean 19-year value. 



MEAN HIGH WATER (MHW) - The average height of the high waters over a 

 19-year period. For shorter periods of observations, corrections 

 are applied to eliminate known variations and reduce the results to 

 the equivalent of a mean 19-year value. All high water heights are 

 included in the average where the type of tide is either semidiurnal 

 or mixed. Only the higher high water heights are included in the 

 average where the type of tide is diurnal. So determined, mean high 

 water in the latter case is the same as mean higher high water. 



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