Mean Higher High Water (MHHW) - Average height of the daily higher high waters over a 19-year period. Only
the higher high water of each pair of high waters of a tidal day is included in the mean.
Mean High Water (MHW) - Average height of the daily high waters over a 19-year period. For semidiurnal or
mixed tides, the two high waters of each tidal day are included in the mean. For diurnal tides, the single daily
high water is used to compute the mean.
Mean Lower Low Water (MLLW) - Average height of the daily lower-low waters of a 19-year period. Only the
lower low water of each pair of low waters of a tidal day is included in the mean. Long used as the datum for
Pacific coast navigation charts, it is now gradually being adopted for use across the United States.
Mean Low Water (MLW) - Average height of the low waters over a 19-year period. For semidiurnal and mixed
tides, the two low waters of each
tidal day are included in the mean. For a diurnal tide, the one low water
of each tidal day is used in the mean. Mean Low Water has been used as datum for many navigation charts
published by the National Ocean Survey, but it is being phased out in favor of Mean Lower Low Water for all
areas of the United States.
Mean Sea Level - Average height of the sea surface over a 19-year period. Not necessarily equal to MEAN TIDE
LEVEL.
Mean Tide Level - Plane midway between MEAN HIGH WATER and MEAN LOW WATER. Not necessarily
equal to MEAN SEA LEVEL. Also called half-tide level.
Mixed Tide - A tide in which there is a distinct difference in height between successive high and successive low
waters. For mixed tides there are generally two high and two low waters each tidal day. Mixed tides may be
described as intermediate between semidiurnal and diurnal tides.
Module - A structural component, a number of which are joined to make a whole.
Neap Tides - Tides with decreased ranges that occur when the moon is at first or last-quarter- ;4nl in opposition
to each other. The neap range is smaller than the mean range for semidiurnal and mixed tides.
Nearshore - In beach terminology, an indefinite zone extending seaward from the shoreline well beyond the
breaker zone
Nourishment - Process of replenishing a beach either naturally by longshore transport or artificially by delivery
of materials dredged or excavated elsewhere.
Offshore - (1) (Noun) In beach terminology, comparatively flat zone of variable width extending from the breaker
zone to the seaward edge of the Continental Shelf. (2) (Adjective) Direction seaward from the shore.
Overtopping - Passing of water over a structure from wave runup or surge action.
Peat - Residual product produced by partial decomposition of organic matter in marshes and bogs.
Peat Pot (vegetation) - Pot formed from compressed peat and filled either with soil or peat moss in which a plant
or plants, grown from seed, are transplanted without being removed from the pot.
Perched Beach - Beach or fillet of sand retained above the otherwise normal profile level by a submerged dike or
sill.
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