EM 1110-2-1100 (Change 1)
31 Jul 03
O
OCEANOGRAPHY
The study of the sea, embracing and indicating all knowledge pertaining to the sea's physical boundaries, the
chemistry and physics of seawater, marine biology, and marine geology.
OFFSHORE
(1) In beach terminology, the comparatively flat zone of variable width, extending from the SHOREFACE to the
edge of the CONTINENTAL SHELF. It is continually submerged. (2) The direction seaward from the shore. (3) The zone
beyond the nearshore zone where sediment motion induced by waves alone effectively ceases and where the influence of the
sea bed on wave action is small in comparison with the effect of wind. (4) The breaker zone directly seaward of the low tide
line. (See Figure A-1)
OFFSHORE BARRIER
See BARRIER BEACH.
OFFSHORE BREAKWATER
A BREAKWATER built towards the seaward limit of the littoral zone, parallel (or nearly parallel) to the shore.
OFFSHORE CURRENT
(1) Any current in the offshore zone. (2) Any current flowing away from shore.
OFFSHORE WIND
A wind blowing seaward from the land in the coastal area.
ONSHORE
A direction landward from the sea.
ONSHORE WIND
A wind blowing landward from the sea in the coastal area.
OPPOSING WIND
In wave forecasting, a wind blowing in a direction opposite to the ocean-wave advance; generally, a headwind.
ORBIT
In water waves, the path of a water particle affected by the wave motion. In deepwater waves the orbit is nearly
circular, and in shallow-water waves the orbit is nearly elliptical. In general, the orbits are slightly open in the direction of
wave motion, giving rise to MASS TRANSPORT. (See Figure II-1-4.)
ORBITAL CURRENT
The flow of water accompanying the orbital movement of the water particles in a wave. Not to be confused with
wave-generated LITTORAL CURRENTS. (See Figure II-1-4.)
ORDINARY HIGH WATER MARK (OHWM)
That mark that will be found by examining the bed and banks and ascertaining where the presence and action of
waters are so common and usual, and so long continued in all ordinary years, as to mark upon the soil a character distinct
from that of the abutting upland, in respect to vegetation as that condition exists on June 1, 1971, as it may naturally change
thereafter, or as it may change thereafter in accordance with permits issued by a local government. Also defined as MEAN
HIGH WATER LINE (Shalowitz 1962).
ORDINARY TIDE
This expression is not used in a technical sense by the U.S. Coast and Geodetic Survey, but the word "ordinary"
when applied to tides, may be taken as the equivalent of the word "mean". Thus "ordinary HIGH WATER LINE" may be
assumed to be the same as "mean high water line".
A-54
Appendix A Glossary of Coastal Terminology
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