DECAY DISTANCE - The distance waves travel after leaving the generating 

 area (FETCH). 



DECAY OF WAVES - The change waves undergo after they leave a generating 

 area (FETCH) and pass through a calm, or region of lighter winds. 

 In the process of decay, the significant wave height decreases and 

 the significant wavelength increases. 



DEEP WATER - Water so deep that surface waves are little affected by the 

 ocean bottom. Generally, water deeper than one-half the surface 

 wavelength is considered deep water. 



DEFLATION - The removal of loose material from a beach or other land 

 surface by wind action. 



DELTA - An alluvial deposit, roughly triangular or digitate in shape, 

 formed at a river mouth. 



DEPTH - The vertical distance from a specified tidal datum to the sea 

 floor. 



DEPTH OF BREAKING - The Stillwater depth at the point where the wave 

 breaks. Also BREAKER DEPTH (See Figure A-2.) 



DEPTH CONTOUR - See CONTOUR. 



DEPTH, CONTROLLING - See CONTROLLING DEPTH. 



DEPTH FACTOR - See SHOALING COEFFICIENT. 



DERRICK STONE - S-e STONE, DERRICK. 



DESIGN HURRICANE - See HYPOTHETICAL HURRICANE. 



DIFFRACTION (of water waves) - Tlie phenomenon by which energy is trans- 

 mitted laterally along a wave crest. When a part of a train of waves 

 is interrupted by a barrier, such as a breakwater, the effect of 

 diffraction is manifested by propagation of waves into the sheltered 

 region within the barrier's geometric shadow. 



DIKE (DYKE) - A wall or mound built around a low-lying area to prevent 

 flooding. 



DIURNAL - Having a period or cycle of approximately one TIDAL DAY. 



DIURNAL TIDE - A tide with one high water and one low water in a tidal 

 day. (See Figure A- 10.) 



t 



A-IO 



