EM 1110-2-1100 (Change 1)
31 Jul 03
RISK ANALYSIS
Assessment of the total risk due to all possible environmental inputs and all possible mechanisms.
ROADSTEAD
An area of the sea used for anchorage of vessels and transhipment of cargo, usually without the protection from
weather associated with harbors.
ROCK WEATHERING
Physical and mineralogical decay processes in rock brought about by exposure to climatic conditions either at the
present time or in the geological past.
ROCK
(1) An aggregate of one or more minerals; or a body of undifferentiated mineral matter (e.g., obsidian). The three
classes of rocks are: (a) Igneous crystalline rocks formed from molten material. Examples are granite and basalt. (b)
Sedimentary resulting from the consolidation of loose sediment that has accumulated in layers. Examples are sandstone,
shale and limestone. (c) Metamorphic formed from preexisting rock as a result of burial, heat, and pressure. (2) A rocky
mass lying at or near the surface of the water or along a jagged coastline, especially where dangerous to shipping.
ROLLER
An indefinite term, sometimes considered to denote one of a series of long-crested, large waves which roll in on a
shore, as after a storm.
ROTARY CURRENT, TIDAL
A tidal current that flows continually with the direction of flow changing through all points of the compass during
the tidal period. Rotary currents are usually found offshore where the direction of flow is not restricted by any barriers. The
tendency for the rotation in direction has its origin in the deflecting force of the earth's rotation and, unless modified by local
conditions, the change is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The
velocity of the current usually varies throughout the tidal cycle, passing through two maxima in approximately opposite
directions and two minima with the direction of the current at approximately ninety degrees from the direction at the time of
maximum velocity.
RUBBLE
(1) Loose angular waterworn stones along a beach. (2) Rough, irregular fragments of broken rock.
RUBBLE-MOUND STRUCTURE
A mound of random-shaped and random-placed stones protected with a cover layer of selected stones or specially
shaped concrete armor units. (Armor units in a primary cover layer may be placed in an orderly manner or dumped at
random.)
RUNUP, RUNDOWN
The upper and lower levels reached by a wave on a beach or coastal structure, relative to still-water level.
RUNNEL
A corrugation or trough formed in the FORESHORE or in the bottom just offshore by waves or tidal currents (see
RIDGE and RUNNEL).
A-66
Appendix A Glossary of Coastal Terminology
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