EM 1110-2-1100 (Change 1)
31 Jul 03
RECURVED SPIT
A spit whose outer end in turned landward by current deflection, by the opposing action of two or more currents, or
by WAVE REFRACTION; a HOOK.
RED TIDE
Discoloration of surface waters, most frequently in COASTAL ZONES, caused by large concentrations of
microorganisms.
REEF
An offshore consolidated rock hazard to navigation, with a least depth of about 20 meters (10 fathoms) or less.
Often refers to coral FRINGING REEFS in tropical waters.
REEF, ATOLL
See ATOLL.
REEF, BARRIER
See BARRIER REEF.
REEF BREAKWATER
Rubble mound of single-sized stones with a crest at or below sea level which is allowed to be (re)shaped by the
waves.
REEF, FRINGING
See FRINGING REEF.
REFERENCE PLANE
The plane to which sounding and tidal data are referred. See DATUM PLANE.
REFERENCE POINT
(1) A specified location (in plan elevation) to which measurements are referred. (2) In beach material studies, a
specified point within the REFERENCE ZONE.
REFERENCE STATION
A place for which tidal constants have previously been determined and which is used as a standard for the
comparison of simultaneous observations at a second station. Also, a station for which independent daily predictions are
given in the tide or current tables from which corresponding predictions are obtained for other stations by means of
differences or factors.
REFERENCE ZONE
In regard to beach measuring procedure, the part of the FORESHORE subject to wave action (between the Limit of
UPRUSH and the Limit of BACKWASH) at mid-tide stage. In areas of great tidal range a more complex definition is
needed.
REFLECTED WAVE
That part of an incident wave that is returned seaward when a wave impinges on a steep beach, barrier, or other
reflecting surface.
The process by which the energy of the wave is returned seaward.
REFRACTION (of water waves)
(1) The process by which the direction of a wave moving in shallow water at an angle to the contours is changed:
the part of the wave advancing in shallower water moves more slowly than that part still advancing in deeper water, causing
the wave crest to bend toward alinement with the underwater contours. (2) The bending of wave crests by currents. (See
Figure II-6-11.)
Appendix A Glossary of Coastal Terminology
A-63
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