MANGROVE - A particular kind of tropical tree or shrub with thickly 

 matted roots, confined to low-lying brackish areas, 



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



MARSH - A tract 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 under ORBIT. 



MEAN DIAMETER, GEOMETRIC - The diameter equivalent of the arthmetic 



mean of the logarithmic frequency distribution. In the analysis 

 of beach s ands it is taken as that grain diameter determined graph- 

 ically by the intersection of a straight line through selected 

 boundary sizes (generally points on the distribution curve where 

 16 and 8h percent of the sample by weight is coarser) and a 

 vertical line through the median diameter of the sample. 



MEAN HIGHER HIGH WATER (MHHl'^) - 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. 



I'ffiAN HIGH WATER (i'iHl^J) - 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 result 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, 



MEAN HIGH WATER SPRINGS - The average height of the high waters occurring 

 at the time of spring tide. Frequently abbreviated to High Water 

 Springs, 



MEAN LOWER LOW ViATER (tlLLW) - Frequently abbreviated lower low water. 

 The average height of the lower low waters over a 19-year period. 

 For shorter periods of observations, corrections a re applied to 

 eliminate known variations and reduce the result to the equi-a;alent 

 of a mean 19-year value » 



A-19 



