EM 1110-2-1100 (Change 1)
31 Jul 03
DEEP WATER WAVES
A wave in water the depth of which is greater than one-half the WAVE LENGTH.
DEFLATION
The removal of loose material from a beach or other land surface by wind action.
DEGRADATION
The geologic process by means of which various parts of the surface of the earth are worn away and their general
level lowered, by the action of wind and water.
DELTA
(1) An ALLUVIAL DEPOSIT, usually triangular or semi-circular, at the mouth of a river or stream. The delta is
normally built up only where there is no tidal or current action capable of removing the sediment at the same rate as it is
deposited, and hence the delta builds forward from the coastline. (2) A TIDAL DELTA is a similar deposit at the mouth of a
tidal INLET, the result of TIDAL CURRENTS that flow in and out of the inlet.
DELTA PLAIN
The nearly-level surface composing the landward portion of a large DELTA.
DENSITY
Mass (in kg) per unit of volume of a substance; kg/m3. For pure water, the density is 1000 kg/m3, for seawater the
density is usually more. Density increases with increasing salinity, and decreases with increasing temperature. More
information can be found in "properties of seawater". For stone and sand, usually a density of 2600 kg/m3 is assumed.
Concrete is less dense, in the order of 2400 kg/m3. Some types of basalt may reach 2800 kg/m3.
For sand, including the voids, one may use 1600 kg/m3, while mud often has a density of 1100 - 1200 kg/m3.
DENSITY CURRENT
Phenomenon of relative flow within water due to difference in density. For example, the salt-water wedge is a
density current, as is a volcanic nue ardente.
DENSITY STRATIFICATION
The lateral expansion of a sediment plume as it moves out of the distributary mouth, where salt and fresh water mix.
This is most likely to occur where the speed of the river flow is moderate to low and the distributary mouth is relatively deep.
DENSITY-DRIVEN CIRCULATION
Variations in salinity create variations in density in estuaries. These variations in density create horizontal pressure
gradients, which drive estuarine circulation.
DEPRESSION
A general term signifying any depressed or lower area in the ocean floor.
DEPTH
The vertical distance from a specified datum to the sea floor.
DEPTH CONTOUR
See CONTOUR, also ISOBATH.
DEPTH, CONTROLLING
See CONTROLLING DEPTH.
DEPTH FACTOR
See SHOALING COEFFICIENT.
A-22
Appendix A Glossary of Coastal Terminology
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