EM 1110-2-1100 (Change 1)
31 Jul 03
PERMEABILITY
The property of bulk material (sand, crushed rock, soft rock in situ) which permit movement of water through its
pores.
PERMEABLE GROIN
A GROIN with openings or voids large enough to permit passage of appreciable quantities of LITTORAL DRIFT
through the structure.
PETROGRAPHY
The systematic description and classification of rocks.
PETROLOGY
That branch of geology which treats the scientific study of rocks.
PHASE
In surface wave motion, a point in the period to which the wave motion has advanced with respect to a given initial
reference point.
PHASE INEQUALITY
Variations in the tides or tidal currents associated with changes in the phase of the Moon in relation to the Sun.
PHASE VELOCITY
Propagation velocity of an individual wave as opposed to the velocity of a wave group.
PHI GRADE SCALE
A logarithmic transformation of the Wentworth grade scale for size classifications of sediment grains based on the
negative logarithm to the base 2 of the particle diameter: = -log2d. See SOIL CLASSIFICATION.
PHOTIC ZONE
The zone extending downward from the ocean surface within which the light is sufficient to sustain photosynthesis.
The depth of this layer varies with water clarity, time of year and cloud cover, but is about 100 m in the open ocean. It may
be considered the Depth to which all light is filtered out except for about one percent and may be calculated as about two and
one-half times the depth of a SECCHI DISK reading.
PHOTOGRAMMETRY
The science of deducing the physical dimensions of objects from measurements on images (usually photographs) of
the objects.
PHOTOMOSAIC
An assemblage of photographs, each of which shows part of a region, put together in such a way that each point in
the region appears once and only once in the assemblage, and scale variation is minimized.
PHREATIC LEVEL
Upper surface of an unconfined aquifer (e.g. the top sand layer in a dike) at which the pressure in the groundwater is
equal to atmospheric pressure.
PHYSICAL GEOLOGY
A large division of Geology concerned with earth materials, changes of the surface and interior of the earth, and the
forces that cause those changes.
PHYSICAL MODELING
Refers to the investigation of coastal or riverine processes using a scaled model.
Appendix A Glossary of Coastal Terminology
A-57
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