UPLIFT. The upward water pressure on the base of a structure or pavement. 



UPRUSH. The rush of water up onto the beach following the breaking of a 

 wave. Also SWASH, RUNUP. (See Figure A-2.) 



VALLEY, SEA. A submarine depression of broad valley form without the steep 

 side slopes which characterize a canyon. 



VALLEY, SUBMARINE. A prolongation of a land valley into or across a 

 continental or insular shelf, which generally gives evidence of having 

 been formed by stream erosion. 



VARIABILITY OF WAVES. (1) The variation of heights and periods between 

 individual waves within a WAVE TRAIN. (Wave trains are not composed of 

 waves of equal height and period, but rather of heights and periods which 

 vary in a statistical manner.) (2) The variation in direction of 

 propagation of waves leaving the generating area. (3) The variation in 

 height along the crest, usually called "variation along the wave." 



VERY SHALLOW WATER. See SHALLOW WATER. 



VELOCITY OF WAVES. The speed at which an individual wave advances. See WAVE 

 CELERITY. 



VISCOSITY (or internal friction) . That molecular property of a fluid that 

 enables it to support tangential stresses for a finite time and thus to 

 resist deformation. 



WATERLINE. A juncture of land and sea. This line migrates, changing with the 

 tide or other fluctuation in the water level. Where waves are present on 

 the beach, this line is also known as the limit of backrush. 

 (Approximately, the intersection of the land with the still-water level.) 



WAVE. A ridge, deformation, or undulation of the surface of a liquid. 



WAVE AGE. The ratio of wave speed to wind speed. 



WAVE, CAPILLARY. See CAPILLARY WAVE. 



WAVE CELERITY. Wave speed. 



WAVE CREST. See CREST OF WAVE. 



WAVE CREST LENGTH. See CREST LENGTH, WAVE. 



WAVE, CYCLOIDAL. See CYCLOIDAL WAVE. 



WAVE DECAY. See DECAY OF WAVES. 



WAVE DIRECTION. The direction from which a wave approaches. 



WAVE FORECASTING. The theoretical determination of future wave character- 

 istics, usually from observed or predicted meteorological phenomena. 



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