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. 



TRANS LATORY 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. See IRRO- 

 TATIONAL WAVE 



TROPICAL CYCLONE - See HURRICANE 



TROPICAL STORM - A tropical cyclone with maximum winds less than 75 

 mph. 



TROUGH OF WAVE - The lowest part of a wave form between successive 



crests. Also that part of a wave below Stillwater level. (See 

 Figure A-3.3 



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

 as a volcanic eruption or earthquake. Commonly miscalled "tidal 



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. 



A-40 



