EM 1110-2-1100 (Change 1)
31 Jul 03
DEPTH OF BREAKING
The still-water depth at the point where the wave breaks. Also BREAKER DEPTH.
DERRICK STONE
See STONE, DERRICK.
DESIGN HURRICANE
See HYPOTHETICAL HURRICANE.
DESIGN STORM
A hypothetical extreme storm whose waves coastal protection structures will often be designed to withstand. The
severity of the storm (i.e. return period) is chosen in view of the acceptable level of risk of damage or failure. A DESIGN
STORM consists of a DESIGN WAVE condition, a design water level and a duration.
DESIGN WAVE
In the design of HARBORS, harbor works, etc., the type or types of waves selected as having the characteristics
against which protection is desired.
DESIGN WAVE CONDITION
Usually an extreme wave condition with a specified return period used in the design of coastal works.
DETACHED BREAKWATER
A BREAKWATER without any SUBAERIAL connection to the shore.
DETRITUS
Small fragments of rock which have been worn or broken away from a mass by the action of water or waves.
DIFFERENTIAL EROSION / WEATHERING
These features develop in rocks which have varying resistance to the agencies of erosion and/or weathering so that
parts of the rock are removed at greater rates than others. A typical example is the removal of soft beds from between harder
beds in a series of sedimentary rocks. The term may be applied to any size of feature, from small-scale `etching' to the
regional development of hills and valleys controlled by hard and soft rocks.
DIFFRACTION (of water waves)
The phenomenon by which energy is transmitted 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. (See Figure II-7-2)
DIFFRACTION COEFFICIENT
Ratio of diffracted wave height to DEEPWATER wave height.
DIFFUSION
The distributing or spreading-out of molecules, atoms, or substances into a vacuum, fluid, or porous medium so that
the concentration equalizes in all parts of the system
DIKE
Earth structure along sea or river in order to protect low lands from flooding by high water; dikes along rivers are
sometimes called LEVEES. Sometimes written as DYKE
DISCHARGE
The volume of water per unit of time flowing along a pipe or channel.
Appendix A Glossary of Coastal Terminology
A-23
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