EM 1110-2-1100 (Change 1)
31 Jul 03
SILL
(1) A submerged structure across a river to control the water level upstream. (2) The crest of a spillway.
SILT
Sediment particles with a grain size between 0.004 mm and 0.062 mm, i.e. coarser than clay particles but finer than
sand. See SOIL CLASSIFICATION.
SINUSOIDAL WAVE
An oscillatory wave having the form of a sinusoid.
SLACK TIDE (SLACK WATER)
The state of a tidal current when its velocity is near zero, especially the moment when a reversing current changes
direction and its velocity is zero. Sometimes considered the intermediate period between ebb and flood currents during which
the velocity of the currents is less than 0.05 meter per second (0.1 knot). See STAND OF TIDE.
SLIDE
In mass wasting, movement of a descending mass along a plane approximately parallel to the slope of the surface.
SLIP
A berthing space between two piers.
SLIP FACE
The steep, downwind slope of a DUNE; formed from loose, cascading sand that generally keeps the slope at the
ANGLE OF REPOSE (about 34 deg.).
SLOPE
The degree of inclination to the horizontal. Usually expressed as a ratio, such as 1:25, indicating one unit rise in 25
units of horizontal distance; or in a decimal fraction (0.04). Also called GRADIENT.
SLOUGH
A small muddy marshland or tidal waterway which usually connects other tidal areas. See BAYOU.
SLUICE
A structure containing a gate to control the flow of water from one area to another.
SLUMP
In mass wasting, movement along a curved surface in which the upper part moves vertically downward while the
lower part moves outward.
SOFT DEFENSES
Usually refers to beaches (natural or designed) but may also relate to energy-absorbing beach-control structures,
including those constructed of rock, where these are used to control or redirect coastal processes rather than opposing or
preventing them.
SOIL
A layer of weathered, unconsolidated material on top of bed rock; in geologic usage, usually defined as containing
organic matter and being capable of supporting plant growth.
SOIL CLASSIFICATION (size)
An arbitrary division of a continuous scale of grain sizes such that each scale unit or grade may serve as a
convenient class interval for conducting the analysis or for expressing the results of an analysis. There are many
classifications used (see Table III-1-2).
Appendix A Glossary of Coastal Terminology
A-73
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