EM 1110-2-1100 (Change 1)
31 Jul 03
ARMOR LAYER
Protective layer on a BREAKWATER or SEAWALL composed of armor units.
ARMOR UNIT or STONE
A relatively large quarrystone or concrete shape that is selected to fit specified geometric characteristics and
density. It is usually of nearly uniform size and usually large enough to require individual placement. In normal cases it is
used as primary wave protection and is placed in thicknesses of at least two units.
ARTIFICIAL NOURISHMENT
The process of replenishing a beach with material (usually sand) obtained from another location.
ASTRONOMICAL TIDE
The tidal levels and character which would result from gravitational effects, e.g. of the Earth, Sun and Moon,
without any atmospheric influences.
ATOLL
A ring-shaped coral REEF, often carrying low sand islands, enclosing a shallow LAGOON. The reef is surrounded
by deep water of the open sea.
(1) A lessening of the amplitude of a wave with distance from the origin. (2) The decrease of water-particle motion
with increasing depth. Particle motion resulting from surface oscillatory waves attenuates rapidly with depth, and practically
disappears at a depth equal to a surface wavelength.
AUTOCHTHONOUS
A term applied to shelves on which older shelf sediments are primarily being reworked by modern shelf processes.
AUTOMATIC TIDE GAGE
An instrument that automatically registers the rise and fall of the tide. In some instruments, the registration is
accomplished by printing the heights at regular intervals, in others by a continuous graph in which the height of the tide is
represented by the ordinates of the curve and the corresponding time by the abscissae.
AVULSION
(1) Rapid EROSION of the shore land by waves during a storm. (2) A sudden cutting off of land by flood, currents
or change in course of a body of water.
AWASH
Situated so that the top is intermittently washed by waves or tidal action. Condition of being exposed or just bare at
any stage of the tide between high water and chart datum.
Appendix A Glossary of Coastal Terminology
A-3
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