Glossary of Coastal Terminology: H - M
HABITAT: The place where an organism lives.
HEAD: (1) A comparatively high PROMONTORY with either a CLIFF or steep face. It extends into a large body of water, such as a SEA or lake. An unnamed HEAD is usually called a headland. (2) The section of RIP CURRENT which has widened out seaward of the BREAKERS, also called head of rip.
HEAVE: (1) The vertical rise or fall of the WAVES or the SEA. (2) The translational movement of a craft parallel to its vertical axis. (3) The net transport of a floating body resulting from WAVE action.
HIGHER HIGH WATER (HHW): The higher of the two high waters of any TIDAL DAY. The single HIGH WATER occurring daily during periods when the TIDE is DIURNAL is considered to be HIGHER HIGH WATER. See Figure 11.
HIGH SEAS: This term, in municipal and international law, denotes all that continuous body of salt water in the world that is navigable in its character and that lies outside territorial waters and maritime belts of the various countries, also called OPEN SEA.
HIGH WATER (HW): Maximum height reached by a rising TIDE. The height may be solely due to the periodic tidal forces or it may have superimposed upon it the effects of prevailing meteorological conditions. Nontechnically, also called the high tide.
HIGH WATER LINE: The intersection of MEAN HIGH WATER with the SHORE. The SHORELINE delineated on the nautical charts of the U.S. Coast and Geodetic Survey is an approximation of the mean high water line.
HORIZON: (1) The line or circle which forms the apparent boundary between Earth and sky. (2) (Geological) A plane in rock strata characterized by particular features, as occurrence of distinctive fossil species. One of the series of distinctive layers found in a vertical cross-section of any well-developed SOIL.
HURRICANE: A cyclonic storm, usually of tropic origin, covering an extensive area, and containing winds in excess of 75 miles per hour.
HYDROGRAPHY: (1) The description and study of SEAS, lakes, RIVERS and other waters. (2) The science of locating aids and dangers to navigation. (3) The description of physical properties of the waters of a region.
INLET: (1) A narrow strip of water running into the land or between islands. (2) An arm of the SEA (or other body of water) that is long compared to its width, and that may extend a considerable distance inland.
ISOSTASY: The tendency of the Earth's crust to maintain a state of near equilibrium, i.e., if anything occurs to modify the existing state, a compensation change will occur to maintain a balance.
ISOTOPE: An atom with a specified number of protons and a specified number of neutrons.
JETTY: (1) On open SEACOASTS, a structure extending into a body of water to direct and confine the STREAM or tidal flow to a selected CHANNEL, or to prevent shoaling. Jetties are built at the mouth of a RIVER or ENTRANCE to a BAY to help deepen and stabilize a CHANNEL and facilitate navigation. (2) (SMP) A structure usually projecting out into the SEA at the mouth of a RIVER for the purpose of protecting a navigational CHANNEL, a harbor or to influence water currents.
LAMINAR FLOW: Slow, smooth flow, with each drop of water traveling a smooth path parallel to its neighboring drops. Laminar flow is characteristic of low velocities, and particles of SEDIMENT in the flow zones are moved by rolling or SALTATION.
LANDMARK: A conspicious object, natural or man-made, located near or on land, which aids in fixing the position of an observer.
LITTORAL DRIFT: (1) The sedimentary material moved in the LITTORAL ZONE under the influence of WAVES and currents. (2) (SMP) The mud, SAND, or GRAVEL material moved parallel to the SHORELINE in the NEARSHORE ZONE by WAVES and CURRENTS.
LITTORAL TRANSPORT: The movement of LITTORAL DRIFT in the LITTORAL ZONE by WAVES and CURRENTS. Includes movement parallel (long shore drift) and sometimes also perpendicular (CROSS-SHORE transport) to the SHORE.
LITTORAL TRANSPORT RATE: The rate of transport of sedimentary material parallel to or perpendicular to the SHORE in the LITTORAL ZONE. Usually expressed in cubic meters (yards) per year. Commonly used as synonymous with LONGSHORE TRANSPORT RATE.
LONGSHORE CURRENT: A current located in the SURF ZONE, moving generally parallel to the SHORELINE, generated by WAVES breaking at an angle with the SHORELINE, also called the ALONGSHORE CURRENT. See also NEARSHORE CURRENT SYSTEM). See Figure 6.
LONGSHORE TRANSPORT RATE: Rate of transport of sedimentary material parallel to the SHORE. Usually expressed in cubic meters (yards) per year. Commonly used as synonymous with LITTORAL TRANSPORT RATE.
LOWER LOW WATER DATUM: An approximation to the plane of MEAN LOWER LOW WATER that has been adopted as a standard REFERENCE PLANE for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better determination of MEAN LOWER LOW WATER from a subsequent series of observations. See Figure 11.
LUNAR DAY: The time of rotation of the Earth with respect to the moon, or the interval between two successive upper transits of the moon over the meridian of a place. The mean lunar day is approximately 24.84 solar hours in length, or 1.035 times as great as the mean solar day. Also called TIDAL DAY.
MANAGED RETREAT: The deliberate setting back of the existing line of defense in order to obtain engineering and/or environmental advantages.
MARGIN, CONTINENTAL: A zone separating a continent from the deep-sea bottom.
MARKER, SURVEY: An object placed at the site of a station to identify the surveyed location of that station.
MARKER, REFERENCE: A mark of permanent character close to a survey station, to which it is related by an accurately measured distance and azimuth (or bearing).
MARSH: (1) A tract of soft, wet land, usually vegetated by reeds, grasses and occasionally small shrubs. (2) (SMP) Soft, wet area periodically or continuously flooded to a shallow depth, usually characterized by a particular subclass of grasses, cattails and other low plants.
MASS TRANSPORT, SHOREWARD: The movement of water due to WAVE motion, which carries water through the BREAKER ZONE in the direction of WAVE PROPAGATION. Part of the NEARSHORE CURRENT SYSTEM. See Figure 7.
MEAN HIGHER HIGH WATER (MHHW): The arithmetic average of the elevations of the HIGHER HIGH WATERS of a MIXED TIDE over a specific 19-year period. For shorter periods of observation, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year interval.
MEAN HIGH WATER (MHW): The average ELEVATION of all high waters recorded at a particular point or station over a considerable period of time, usually 19 years. For shorter periods of observation, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value. All HIGH WATER heights are included in the average where the type of TIDE is either SEMIDIURNAL or MIXED. Only the HIGHER HIGH WATER heights are included in the average where the type of TIDE is DIURNAL. So determined, mean high water in the latter case is the same as MEAN HIGHER HIGH WATER.
MEAN LOWER LOW WATER (MLLW): The average height of the lower low waters over a 19-year period. For shorter periods of observation, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value.
MEAN LOW WATER (MLW): The average height of the low waters over a 19-year period. For shorter periods of observation, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value.
MEAN WATER LEVEL: The mean surface level as determined by averaging the heights of the water at equal intervals of time, usually at hourly intervals.
METEOROLOGICAL TIDES: Tidal constituents having their origin in the daily or seasonal variation in weather conditions which may occur with some degree of periodicity.
MINERAL: A naturally occurring, inorganic, crystalline solid that has a definite chemical composition and possesses characteristic physical properties.
MIXED TIDE: Type of TIDE which the presence of a diurnal wave is conspicious by a large inequality in either the high or LOW WATER heights with two high waters and two low waters usually occurring each TIDAL DAY. In strictness, all TIDES are mixed, but the name is usually applied without definite limits to the TIDE intermediate to those predominantly SEMIDIURNAL and those predominantly DIURNAL.
MORPHODYNAMICS: (1) The mutual interaction and adjustment of the seafloor topography and fluid dynamics involving the motion of SEDIMENT. (2) The coupled suite of mutually interdependent hydrodynamic processes, seafloor morphologies and sequences of change.