QUICKSAND. Loose, yielding, wet sand which offers no support to heavy 

 objects. The upward flow of the water has a velocity that eliminates 

 contact pressures between the sand grains and causes the sand-water mass 

 to behave like a fluid. 



RADIUS OF MAXIMUM WINDS. Distance from the eye of a hurricane, where surface 

 and wind velocities are zero, to the place where surface windspeeds are 

 maximum . 



RAY, WAVE. See ORTHOGONAL. 



RECESSION (of a beach). (1) A continuing landward movement of the shore- 

 line. (2) A net landward movement of the shoreline over a specified 

 time. Also RETROGRESSION. 



REEF. An offshore consolidated rock hazard to navigation, with a least depth 

 of about 20 meters (10 fathoms) or less. 



REEF, ATOLL. See ATOLL. 



REEF, BARRIER. See BARRIER REEF. 



REEF, FRINGING. See FRINGING REEF. 



REEF, SAND. BAR. 



REFERENCE PLANE. See DATUM PLANE. 



REFERENCE STATION. A place for which tidal constants have previously been 

 determined and which is used as a standard for the comparison of 

 simultaneous observations at a second station. Also, a station for which 

 independent daily predictions are given in the tide or current tables from 

 which corresponding predictions are obtained for other stations by means 

 of differences or factors. 



REFLECTED WAVE. That part of an incident wave that is returned seaward when a 

 wave impinges on a steep beach, barrier, or other reflecting surface. 



REFRACTION (of water waves). (1) The process by which the direction of a wave 

 moving in shallow water at an angle to the contours is changed: the part 

 of the wave advancing in shallower water moves more slowly than that part 

 still advancing in deeper water, causing the wave crest to bend toward 

 alinement with the underwater contours. (2) The bending of wave crests by 

 currents. (See Figure A-5.) 



REFRACTION COEFFICIENT. The square root of the ratio of the distance between 

 adjacent orthogonals in deep water to their distance apart in shallow 

 water at a selected point. When multiplied by the SHOALING FACTOR and a 

 factor for friction and percolation, this becomes the WAVE HEIGHT 

 COEFFICIENT or the ratio of the refracted wave height at any point to the 

 deepwater wave height. Also, the square root of the ENERGY COEFFICIENT. 



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