EM 1110-2-1100 (Change 1)
31 Jul 03
SEICHE
(1) A standing wave oscillation of an enclosed waterbody that continues, pendulum fashion, after the cessation of
the originating force, which may have been either seismic or atmospheric. (2) An oscillation of a fluid body in response to a
disturbing force having the same frequency as the natural frequency of the fluid system. Tides are now considered to be
seiches induced primarily by the periodic forces caused by the Sun and Moon. (3) In the Great Lakes area, any sudden rise in
the water of a harbor or a lake whether or not it is oscillatory (although inaccurate in a strict sense, this usage is well
established in the Great Lakes area).
SEISMIC REFLECTION
The return of part of the energy of seismic waves to the earth's surface after the waves bounce off an acoustic
boundary (typically rock or material of different density).
SEISMIC REFRACTION
The bending of seismic waves as they pass from one material to another.
SEISMIC SEA WAVE
See TSUNAMI.
SELECTIVE SORTING
A process occurring during sediment transport that tends to separate particles according to their size, density, and
shape. A well-sorted distribution contains a limited range of grain sizes and usually indicates that the depositional
environment contains a narrow range of sediment sizes or a narrow band of depositional energy. A poorly-sorted distribution
contains a wide range of grain sizes indicating multiple sources of sediment or a wide range of deposition energies.
SELF-SUSTAINING BEACH
A BEACH that has either natural or engineered sand retention and that can be stable through the continued supply
of natural sediment sources, without any mechanical nourishment over a long period. Subsets include:
Natural or Geomorphically Self-sustaining Beaches: self-sustaining naturally without the construction of retaining
structures and with no continued mechanical sand nourishment.
Anthropogenically Self-sustaining Beaches: self-sustaining by the construction of retaining structure(s) with or
without initial beach fill but with no continued mechanical sand nourishment.
SEMIDIURNAL
Having a period or cycle of approximately one-half of a tidal day (12.4 hours). The predominating type of tide
throughout the world is semidiurnal, with two high waters and two low waters each tidal day. The tidal current is said to be
semidiurnal when there are two flood and two ebb periods each day.
SENSING, REMOTE
The response of an instrument or organism to stimuli from a distant source.
SETBACK
A required open space, specified in shoreline master programs, measured horizontally upland from an perpendicular
to the ordinary high water mark.
SETUP, WAVE
Superelevation of the water surface over normal surge elevation due to onshore mass transport of the water by wave
action alone.
SETUP, WIND
See WIND SETUP.
A-70
Appendix A Glossary of Coastal Terminology
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