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. 



PERMEABLE GROIN. A groin with openings large enough to permit passage of 

 appreciable quantities of LITTORAL DRIFT. 



PETROGRAPHY. The systematic description and classification 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: <1> = -log2d . See SOIL 

 CLASSIFICATION. 



PIER. A structure, usually of open construction, extending out into the water 



from the shore, to serve as a landing place, recreational facility, etc., 



rather than to afford coastal protection. In the Great Lakes, a term 

 sometimes improperly applied to jetties. 



PILE. A long, heavy timber or section of concrete or metal to be driven or 

 jetted into the earth or seabed to serve as a support or protection. 



PILE, SHEET. A pile with a generally slender flat cross section to be driven 

 into the ground or seabed and meshed or interlocked with like members to 

 form a diaphragm, wall, or bulkhead. 



PILING. A group of piles. 



PLAIN, COASTAL. See COASTAL PLAIN. 



PLANFORM. The outline or shape of a body of water as determined by the still- 

 water line. 



PLATEAU. A land area (usually extensive) having a relatively level surface 

 raised sharply above adjacent land on at least one side; table land. A 

 similar undersea feature. 



PLUNGE POINT. (1) For a plunging wave, the point at which the wave curls over 

 and falls. (2) The final breaking point of the waves just before they 

 rush up on the beach. (See Figure A-1.) 



PLUNGING BREAKER. See BREAKER. 



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