EM 1110-2-1100 (Change 1)
31 Jul 03
REFRACTION COEFFICIENT
The square root of the ratio of the distance between adjacent orthogonals in deep water to their distance apart in
shallow water at a selected point. When multiplied by the SHOALING FACTOR and a factor for friction and percolation,
this becomes the WAVE HEIGHT COEFFICIENT or the ratio of the refracted wave height at any point to the deepwater
wave height. Also, the square root of the ENERGY COEFFICIENT.
REFRACTION DIAGRAM
A drawing showing positions of wave crests and/or orthogonals in a given area for a specific deepwater wave period
and direction. (See Figure II-6-11.)
REGULAR WAVES
Waves with a single height, period, and direction.
RESERVOIR
An artificial lake, basin or tank in which a large quantity of water can be stored.
RESIDUAL (WATER LEVEL)
The components of water level not attributable to astronomical effects.
The phenomenon of amplification of a free wave or oscillation of a system by a forced wave or oscillation of
exactly equal period. The forced wave may arise from an impressed force upon the system or from a boundary condition.
RETARDATION
The amount of time by which corresponding tidal phases grow later day by day (about 50 minutes).
RETROGRESSION (of a beach)
See RECESSION.
RETURN PERIOD
Average period of time between occurrences of a given event.
REVERSING TIDAL CURRENT
A tidal current that flows alternately in approximately opposite directions with a SLACK WATER at each reversal
of direction. Currents of this type usually occur in rivers and straits where the direction of flow is more or less restricted to
certain channels. When the movement is towards the shore, the current is said to be flooding, and when in the opposite
direction it is said to be ebbing.
REVETMENT
(1) A facing of stone, concrete, etc., to protect an EMBANKMENT, or shore structure, against erosion by wave
action or currents. (2) A retaining wall. (3) Facing of stone, concrete, etc., built to protect a SCARP, EMBANKMENT or
shore structure against erosion by waves of currents.
REYNOLDS NUMBER
The dimensionless ratio of the inertial force to the viscous force in fluid motion,
Re = LV
_
γ
where L is a characteristic length, γ the kinematic viscosity, and V a characteristic velocity. The Reynolds number is
of importance in the theory of hydrodynamic stability and the origin of turbulence.
RIA
A long, narrow inlet, with depth gradually diminishing inward. Shorter and shallower than a FJORD.
A-64
Appendix A Glossary of Coastal Terminology
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