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 set-up. 



DOWNCOAST - In United States usage, the coastal direction generally- 

 trending towards the south. 



DOWNDRIFT - The direction of predominant movement of littoral materials, 



DRIFT (noun) - (l) The speed at which a current runs; (2) Also, float- 

 ing material deposited on a beach (driftwood); (3) A deposit of a 

 continental ice sheet, as a DRUMLIN; (U) Sometimes used as an 

 abbreviation of LITTORAL DRIFT. 



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



DUKW - (pronounced duck) Amphibian Truck, 2^ ton, 6x6. 



DUNES - Ridges or mounds of loose, wind-blown material, usually sand. 

 (See Figure A-T) 



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

 essentially 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 - The movement of the tidal current away from shore or 

 down a tidal stream, 



EBB TIDE - A non-technical terra referring to that period of tide between 

 a high water and the succeeding low water; falling tide. 

 (See Figure A-IO) 



ECHO SOUNDER - A survey instrument that determines the depth of water 

 by measuring the time required for a sound signal to travel to the 

 bottom and return. It may be either "sonic" or "supersonic" de- 

 pending on the frequency of sound wave, the "sonic" being generally 

 within the audible ranges (\inder 15,000 cycles per sec). 



EDDY - A circ\ilar 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. 



EDDY CURRENT - See EDDY. 



EELGRASS - A submerged marine plant with very long, narrow leaves, 



abundant along the North Atlantic Coast. See also KELP and SEA- 

 WEED. 



A-11 



