DIVERGENCE - (1) In refraction phenomena, the increasing of distance 

 between orthogonals in the direction of wave travel. Denotes an 

 area of decreasing wave height and energy concentration. (2] In 

 wind-setup phenomena, the decrease in setup observed under that 

 which would occur in an equivalent rectangular basin of uniform 

 depth, caused by changes in planform or depth. Also the increase 

 in basin width or depth causing such decrease in setup. 



DOLPHIN - A cluster of piles. 



DOWNCOAST - In United States usage, the coastal direction generally 

 trending toward the south. 



DOWNDRIFT - The direction of predominant movement of littoral materials. 



DRIFT (noun) - (1) Sometimes used as a short form for LITTORAL DRIFT 



(2) The speed at which a current runs. (3) Also floating material 

 deposited on a beach (driftwood). (4) A deposit of a continental 

 ice sheet, as a drumlin. 



DRIFT CURRENT - A broad, shallow, slow-moving ocean or lake current. 



DUNES - (1) Ridges or mounds of loose, wind-blown material, usually 

 sand. (See Figure A- 7.) (2) BED FORMS smaller than bars but 

 larger than ripples that are out of phase with any water-surface 

 gravity waves associated with them. 



DURATION - In wave forecasting, the length of time the wind blows in 

 nearly the same direction over the FETCH (generating area). 



DURATION, MINIMUM - The time necessary for steady-state wave conditions 

 to develop for a given wind velocity over a given fetch length. 



EAGER - See BORE. 



EBB CURRENT - Tlie tidal current away from shore or down a tidal stream; 

 usually associated with the decrease in the height of the tide. 



EBB TIDE - Tlie period of tide between high water and the succeeding low 

 water; a falling tide. (See Figure A- 10.) 



ECHO SOUNDER - An electronic instrument used to determine the depth of 

 water by measuring the time interval between emission of a sonic or 

 ultrasonic signal and the return of its echo from the bottom. 



EDDY - A circular movement of water formed on the side of a main current. 

 Eddies may be created at points where the main stream passes pro- 

 jecting obstructions or where two adjacent currents flow counter 

 to each other. 



A-l 



