TIDE, STORM. See STORM SURGE. 



TOMBOLO. A bar or spit that connects or "ties" an island to the mainland or 

 to another island. See CUSPATE SPIT. (See Figure A-9.) 



TOPOGRAPHY. The configuration of a surface, including its relief and the 

 positions of its streams, roads, building, etc. 



TRAINING WALL. A wall or jetty to direct current flow. 



TRANSITIONAL ZONE (TRANSITIONAL WATER). In regard to progressive gravity 

 waves, water whose depth is less than 1/2 but more than 1/25 the 

 wavelength. Often called SHALLOW WATER. 



TRANSLATORY WAVE. See WAVE OF TRANSLATION. 



TRANSPOSED HURRICANE. See HYPOTHETICAL HURRICANE. 



TROCHOIDAL WAVE. A theoretical, progressive oscillatory wave first proposed 

 by Gerstner in 1802 to describe the surface profile and particle orbits of 

 finite amplitude, nonsinusoidal waves. The wave form is that of a prolate 

 cycloid or trochoid, and the fluid particle motion is rotational as 

 opposed to the usual irrotational particle motion for waves generated by 

 normal forces. Compare IRROTATIONAL WAVE 



TROPICAL CYCLONE. See HURRICANE 



TROPICAL STORM. A tropical cyclone with maximum winds less than 34 meters per 

 second (75 mile per hour). Compare HURRICANE. 



TROUGH OF WAVE. The lowest part of a waveform between successive crests. 

 Also, that part of a wave below still-water level. (See Figure A-3.) 



TSUNAMI. A long-period wave caused by an underwater disturbance such as a 

 volcanic eruption or earthquake. Also SEISMIC SEA WAVE. Commonly 

 miscalled "tidal wave." 



TYPHOON. See HURRICANE. 



UNDERTOW. A seaward current near the bottom on a sloping inshore zone. It is 

 caused by the return, under the action of gravity, of the water carried up 

 on the shore by waves. Often a misnomer for RIP CURRENT. 



UNDERWATER GRADIENT. The slope of the sea bottom. See also SLOPE. 



UNDULATION. A continuously propagated motion to and fro, in any fluid or 

 elastic medium, with no permanent translation of the particles themselves. 



UPCOAST. In United States usage, the coastal direction generally trending 

 toward the north. 



UPDRIFT. The direction opposite that of the predominant movement of littoral 

 materials. 



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