ORBITAL CURRENT. The flow of water accompanying the orbital movement of the 

 water particles in a wave. Not to be confused with wave-generated 

 LITTORAL CURRENTS. (See Figure A-3.) 



ORTHOGONAL. On a wave-refraction diagram, a line drawn perpendicularly to the 

 wave crests. WAVE RAY. (See Figure A-6.) 



OSCILLATION. (1) A periodic motion backward and forward. (2) Vibration or 

 variance above and below a mean value. 



OSCILLATORY WAVE. A wave in which each individual particle oscillates about a 

 point with little or no permanent change in mean position. The term is 

 commonly applied to progressive oscillatory waves in which only the form 

 advances, the individual particles moving in closed or nearly closed 

 orbits. Compare WAVE OF TRANSLATION. See also ORBIT. 



OUTFALL. A structure extending into a body of water for the purpose of 

 discharging sewage, storm runoff, or cooling water. 



OVERTOPPING. Passing of water over the top of a structure as a result of wave 

 runup or surge action. 



OVERWASH. That portion of the uprush that carries over the crest of a berm or 

 of a structure. 



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. 



PASS. In hydrographic usage, a navigable channel through a bar, reef, or 

 shoal, or between closely adjacent islands. 



PEBBLES. See SOIL CLASSIFICATION. 



PENINSULA. An elongated body of land nearly surrounded by water and connected 

 to a larger body of land. 



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. 



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. 



A-24 



