ONSHORE WIND - A wind blowing landward from the sea in the coastal area. 



OPPOSING WIND - In wave forecasting, a wind blowing in the opposite 

 direction to that in which the waves are travelling. 



ORBIT - In water haves, the path of a water particle affected by the • 

 wave motion. In deep water waves the orbit is nearly circular 

 and in shalloirj water waves the orbit is nearly elliptical. In 

 general, the orbits are slightly open in the direction of wave 

 motion giving rise to MSS TRANSPORT. (See Figure A-3) 



ORBITAI. CURR?JNT - The flow of water accompanying the orbital movement 

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

 generated LITTORAL, CURRENTS. (SeeFigure A-3) 



ORTHOGONAL - On a refraction diagram, a line drawn perpendicular to the 

 wave crests. (See Fignire A-6) , 



OSCILIATION - A periodic motion to and fro, or up and dovm. 



OSCIILATORy WAVE - A wave in which each individual particle oscillates 

 about a point with little or no permanent change in 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. Distinguished from a WAVE of 

 TRAI^SLATION , See Also ORBIT. 



OUTFALL - (1) The vent of a river, drain, etc. (2) A structure ex- 

 tending into a body of water for the purpose of discharging sewage, 

 storm runoff, or cooling water. 



OVERWASH - That portion of the uprush that carries over the crest 

 of a berm or of a structure. 



PARAPET - A low wal] built along the edge of a structure as on a seawall 

 or quay. 



PASS - In hydrographic usage a navigable channel, through a bar, reef, 

 or shoal, or between closely adjacent islands. 



PARTICLE 7EIGCITY - For waves, the velocity induced by wave motion with 

 which a specific water particle moves. 



PEBBLES - See SOIL CLASSIFICATION. 



PENINSULA - An elongated portion of land nearly surrounded by water, and 

 connected to a larger body of land. 



PERIODIC CURRE:NT - 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-22 



