EM 1110-2-1100 (Change 1)
31 Jul 03
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PARAPET
A low wall built along the edge of a structure such as a SEAWALL or QUAY.
PARTICLE VELOCITY
The velocity induced by wave motion with which a specific water particle moves within a wave.
PATCH REEF
A moundlike or flat-topped organic REEF, generally less than 1 km across, frequently forming part of a larger reef
complex.
PASS
In hydrographic usage, a navigable channel through a bar, REEF, or shoal, or between closely adjacent islands. On
the Gulf of Mexico coast, inlets are often known as passes (e.g., Sabine Pass).
PEAK PERIOD
The wave period determined by the inverse of the frequency at which the wave energy spectrum reaches its
maximum.
PEBBLES
Beach material usually well-rounded and between about 4 mm to 64 mm diameter. See SOIL CLASSIFICATION.
PENINSULA
An elongated body of land nearly surrounded by water and connected to a larger body of land by a neck or isthmus.
PERCHED BEACH
A beach or fillet of sand retained above the otherwise normal profile level by a submerged dike.
PERCOLATION
The process by which water flows through the interstices of a sediment. Specifically, in wave phenomena, the
process by which wave action forces water through the interstices of the bottom sediment and which tends to reduce wave
heights.
PERIGEAN RANGE
The average semidiurnal range occurring at the time of the PERIGEAN TIDES and most conveniently computed
from the harmonic constants. It is larger than the mean range where the type of tide is either semidiurnal or mixed and is of no
practical significance where the type of tide is diurnal.
PERIGEAN TIDAL CURRENTS
Tidal currents of increased velocity occurring monthly as the result of the moon being in perigee (i.e., at the point in
its orbit nearest the Earth).
PERIGEAN TIDES
Tides of increased range occurring monthly as the result of the moon being in perigee.
PERIODIC CURRENT
A current caused by the tide-producing forces of the moon and the sun; a part of the same general movement of the
sea that is manifested in the vertical rise and fall of the tides. See also CURRENT, FLOOD and CURRENT, EBB.
PERMANENT CURRENT
A current that runs continuously, independent of the tides and temporary causes. Permanent currents include the
freshwater discharge of a river and the currents that form the general circulatory systems of the oceans.
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Appendix A Glossary of Coastal Terminology
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