Glossary of Coastal Terminology: A - C

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ABRASION: Frictional EROSION by material transported by wind and WAVES.

ACCELEROMETER: A device used in WAVE buoys for measuring acceleration.

ACCRETION: The accumulation of (beach) SEDIMENT, deposited by natural fluid flow processes.

ACTIVE MARGIN: A margin consisting of a CONTINENTAL SHELF, a CONTINENTAL SLOPE, and an oceanic TRENCH.

AEOLIAN DEPOSITS: Wind-deposited SEDIMENTS, such as SAND DUNES. See Figure 8.

AGGRADATION: The geologic process by which various parts of the surface of the earth are raised in ELEVATION or built up by the deposition of material transported by water or wind.

ALLOCHTONOUS: A term applied to shelves that presently experience deposition of river-derived SEDIMENTS. See also DETRITUS.

ALONGSHORE: Parallel to and near the SHORELINE; same as LONGSHORE.

ALLUVIAL DEPOSITS: Detrital material which is transported by a RIVER and deposited - usually temporarily - at points along the FLOODPLAIN of a RIVER. Commonly composed of SANDS and GRAVELS.

ALTIMETER: An instrument that determines its distance above a particular surface.

ALTIMETER, LASER: An instrument that determines altitude by measuring the length of time needed for a pulse of coherent light to travel from the instrument to the surface and back, and multiplies half this time by the speed of light to get the straight-line distance to the surface.


AMPLITUDE: Half of the peak-to-trough range (or height) of a WAVE. See Figure 13.

ANGLE OF REPOSE: The maximum SLOPE (measured from the HORIZON) at which SOILS and loose materials on the banks of CANALS, RIVERS, or EMBANKMENTS stay stable.

AQUIFER: A geologic formation that is water-bearing, and which transmits water from one point to another.

ASEISMIC RIDGE: A submarine ridge with which no earthquakes are associated.

ASTRONOMICAL TIDE: The tidal levels and character which would result from gravitational effects, e.g. of the Earth, Sun, and Moon, without any atmospheric influences.

ATTENUATION: The loss or dissipation of WAVE energy, resulting in a reduction of WAVE HEIGHT (AMPLITUDE).

AUTOCHTHONOUS: A term applied to shelves on which older shelf sediments are primarily being reworked by modern shelf processes.

AUTOMATIC TIDE GAGE: An instrument that automatically registers the rise and fall of the TIDE. In some instruments, the registration is accomplished by printing the heights at regular intervals, in others by a continuous graph in which the height of the TIDE is represented by the ordinates of the curve and the corresponding time by the abscissae.

AVULSION: (1) Rapid EROSION of the shoreland by WAVES during a storm. (2) A sudden cutting off of land by flood, currents, or change in course of a body of water.

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BACKSHORE: (1) The upper part of the active BEACH above the normal REACH of the TIDES (high water), but affected by large WAVES occurring during a high. (2) (SMP) The accretion or erosion zone, located landward of ordinary high tide, which is normally wetted only by storm tides.

BACKWASH: (1) The seaward return of the water following the UPRUSH of the WAVES. Also called backrush or run down. (2) Water of WAVES thrown back by an obstruction such as a ship, BREAKWATER, CLIFF, etc.

BACKWASH RIPPLES: Low amplitude RIPPLE MARKS formed on fine SAND beaches by the BACKWASH of the WAVES.

BANK: The rising ground bordering a lake, RIVER or SEA.

BAR: An OFFSHORE ridge or mound of SAND, GRAVEL, or other UNCONSOLIDATED material which is submerged (at least at high tide), especially at the mouth of a RIVER or ESTUARY, or lying parallel to, and a short distance from, the BEACH. See Figure 2.

BARRIER BEACH: A BAR essentially parallel to the SHORE, which has been built up so that its crest rises above the normal HIGH WATER level. Also called BARRIER ISLAND and offshore barrier.

BARRIER ISLAND: A detached portion of a BARRIER BEACH between two INLETS. See Figure 6.

BARRIER SPIT: Similar to a BARRIER ISLAND, only connected to the mainland.

BASIN: A large submarine DEPRESSION of a generally circular, elliptical or oval shape.

BATHYMETRY: The measurement of DEPTHS of water in OCEANS, SEAS and lakes; also the information derived from such measurements.

BAY: A recess or INLET in the SHORE of a SEA or lake between two capes or HEADLANDS, not as large as a GULF but larger than a COVE. See also BIGHT, EMBAYMENT. See Figure 5.

BAYMOUTH BAR: A BAR extending partly or entirely across the mouth of a bay.

BEACH: (1) A deposit of non-cohesive material (e.g. SAND, GRAVEL) situated on the interface between dry land and the SEA (or other large expanse of water) and actively "worked" by present-day hydrodynamics processes (i.e. WAVES, TIDES and CURRENTS) and sometimes by winds. (2) The zone of UNCONSOLIDATED material that extends landward from the LOW WATER LINE to the place where there is marked change in material or physiographic form, or to the line of permanent vegetation. The seaward limit of a BEACH - unless otherwise specified - is the MEAN LOW WATER line. A BEACH includes FORESHORE and BACKSHORE. (3) (SMP) The zone of unconsolidated material that is moved by WAVES, wind and TIDAL CURRENTS, extending landward to the COASTLINE.

BEACH CREST: The point representing the limit of high tide storm WAVE RUN-UP.

BEACH EROSION: The carrying away of beach materials by WAVE action, TIDAL CURRENTS, LITTORAL CURRENTS or wind.

BEACH FACE: The section of the BEACH normally exposed to the action of WAVE UPRUSH. The FORESHORE of the BEACH.

BEACH HEAD: The CLIFF, dune or sea wall looming the landward limit of the active BEACH.

BEACH NOURISHMENT: The process of replenishing a BEACH by artificial means; e.g., by the deposition of dredged materials, also called beach replenishment or beach feeding.

BEACH PROFILE: A cross-section taken perpendicular to a given beach contour; the profile may include the face of a dune or sea wall, extend over the BACKSHORE, across the foreshore, and seaward underwater into the NEARSHORE zone.

BEACH RIDGE: A low extensive ridge of beach material piled up by storm waves landward of the BERM. Usually consists of very coarse SAND, GRAVEL or shells. Occurs singly or as a series of more or less parallel ridges.

BEACH SCARP: (1) An almost perpendicular SLOPE along the beach FORESHORE; an erosional feature due to WAVE action, it may vary in height from a few centimeters to several meters, depending on WAVE action and the nature and composition of the BEACH. See ESCARPMENT.  (2) (SMP) A steep slope produced by wave erosion.

BEACH WIDTH: The horizontal dimension of the BEACH measured normal to the SHORELINE.

BEAUFORT SCALE: The relationship between sea state and wind speed. The Beaufort Scale can be used to estimate wind speed at SEA, but is valid only for WAVES generated within the local weather system, and assumes that there has been sufficient time for a fully developed SEA to have become established.

BED: The bottom of a watercourse, or any body of water.

BEDDING PLANE: A surface parallel to the surface of deposition, which may or may not have a physical expression. The original attitude of a bedding plane should not be assumed to have been horizontal. See also CROSS-BEDDING.

BED LOAD: Heavy or large SEDIMENT particles that travel near or on the BED.

: (1) A level or gently sloping erosion plane inclined seaward. (2) A nearly horizontal area at about the level of maximum HIGH WATER on the sea side of a DIKE.

BENCH MARK: A mark affixed to a permanent object in tidal observations, or in a survey, to furnish a DATUM level.

BENCH MARK, TIDAL: A BENCH MARK whose ELEVATION has been determined with respect to MEAN SEA LEVEL at a nearby tide gauge; the tidal bench mark is used as reference for that tide gauge.

BENEFITS: The economic value of a scheme, usually measured in terms of the cost of damages avoided by the scheme, or the valuation of perceived amenity or environmental improvements.

BENTHOS: Those animals who live on the SEDIMENTS of the sea floor, including both mobile and non-mobile forms.

BENTHIC: Pertaining to the sub-aquatic bottom.

BERM: (1) On a BEACH: a nearly horizontal PLATEAU on the BEACH FACE or BACKSHORE, formed by the deposition of beach material by WAVE action or by means of a mechanical plant as part of a beach RECHARGE scheme. (2) On a structure: a nearly horizontal area, often built to support or key-in an armour layer. (3) (SMP) A linear mound or series of mounds of SAND and/or GRAVEL generally paralleling the water at or landward of the line of ordinary high tide. See Figure 2.

BERM BREAKWATER: Rubble mound with horizontal BERM of armour STONES at about sea-side WATER LEVEL, which is allowed to be (re)shaped by the WAVES.

BERM CREST: The seaward limit of the BERM, or the minimum DEPTH of a submerged BERM; also called berm edge.

BIFURCATION: Location where a RIVER separates in two or more reaches or branches (the opposite of a CONFLUENCE).

BIGHT: A slight indentation in a COAST forming an open BAY, usually crescent shaped.

BLOWOUT: A DEPRESSION on the land surface caused by wind EROSION.

BLUFF: A high, steep BANK or CLIFF.

BOG: (SMP) A wet, spongy, poorly drained area which is usually rich in very specialized plants, contains a high percentage of organic remnants and residues and frequently is associated with a spring, seepage area, or other subsurface water source. A bog sometimes represents the final stage of the natural processes of eutrophication by which lakes and other bodies of water are very slowly transformed into land areas.

BOIL: An upward flow of water in a sandy formation due to an unbalanced hydrostatic pressure resulting from a rise in a nearby STREAM, or from removing the overburden in making excavations.

BOTTOM BOUNDARY LAYER: The lower portion of the water flow that experiences frictional retardation based on its proximity to the BED. See also VELOCITY PROFILE.

BOULDER: A rounded rock on a BEACH, greater than 256 mm in diameter, larger than a cobble. See also GRAVEL, SHINGLE.

BOX GAGE: A TIDE GAGE that is operated by a float in a long vertical box to which the TIDE is admitted through an opening in the bottom. In the original type of box gage the float supported a graduated rod which rose and fell with the TIDE.

BREACHING: Failure of the BEACH HEAD or a DIKE allowing flooding by tidal action.

BREAKER: A WAVE that has become so steep that the crest of the WAVE topples forward, moving faster than the main body of the WAVE. Breakers may be roughly classified into four kinds, although there is much overlap (see Figure 2):

  • Spilling - bubbles and turbulent water spill down the front face of WAVE. The upper 25 percent of the front face may become vertical before breaking. Breaking generally across over quite a distance.
  • Plunging - a crest curls over air pocket; breaking is usually with a crash. Smooth splash-up usually follows.
  • Collapsing - breaking occurs over lower half of WAVE. Minimal air pocket and usually no splash-up. Bubbles and foam present.
  • Surging - WAVE peaks up, but bottom rushes forward from under WAVE, and WAVE slides up BEACH FACE with little or no bubble production. Water surface remains almost plane except where RIPPLES may be produced on the BEACH FACE during BACKWASH.

BREAKER INDEX: Maximum ratio of WAVE HEIGHT to WATER DEPTH in the SURF ZONE, typically 0.78 for spilling waves, ranging from about 0.6 to 1.5.

BREAKER ZONE: The zone within which WAVES approaching the COASTLINE commence breaking, typically in WATER DEPTHS of between 5 m and 10 m.

BREAKING DEPTH: The still-water DEPTH at the point where the WAVE breaks.

BREAKWATER: (1) A structure protecting a HARBOR, anchorage, or BASIN from WAVES. (2) (SMP) Offshore structure aligned parallel to the SHORE, sometimes shore-connected, that provides protection from WAVES.

BUFFER AREA: A parcel or strip of land that is designed and designated to permanently remain vegetated in an undisturbed and natural condition to protect an adjacent aquatic or wetland site from upland impacts, to provide habitat for wildlife and to afford limited public access.

BULKHEAD: (1) A structure separating land and water areas, primarily designed to resist earth pressures. (2) A structure or partition to retain or prevent sliding of the land. A secondary purpose is to protect the upland against damage from WAVE action.

BUOYANCY: The resultant upward forces, exerted by the water on a submerged or floating body, equal to the weight of the water displaced by this body.

BYPASSING, SAND: Hydraulic or mechanical movement of SAND from the accreting UPDRIFT side to the eroding DOWNDRIFT side of an INLET or HARBOR ENTRANCE. The hydraulic movement may include natural as well as movement caused by man.

BUOY: A float; especially a floating object moored to the bottom, to mark a CHANNEL, anchor, SHOAL, ROCK, etc. Some common types include: a nun or nut buoy is conical in shape; a can buoy is squat and cylindrical above water and conical below water; a spar buoy is a vertical, slender spar anchored at one end; a bell buoy, bearing a bell, runs mechanically or by the action of WAVES, usually marks SHOALS or ROCKS; a whistling buoy, similarly operated, marks SHOALS or channel entrances; a dan buoy carries a pole with a flag or light on it.

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CALIFORNIA CURRENT: A deep-ocean boundary current that flows south-southeasterly along the U.S. west coast. The current is shallow, broad and slow moving carrying cold, nutrient poor waters toward the equator.

CALM: The condition of the water surface when there is no WIND WAVES or SWELL.

CAMERA, AERIAL: A camera especially designed for photographing the Earth's surface from above the ground; usually carried in aircraft and Earth-orbiting satellites.

CAMERA, METRIC: A camera designed particularly for PHOTOGRAMMETRY, constructed so that the image is distorted geometrically as little as possible and the camera characteristics do not change from photograph to photograph.

CANAL: An artificial watercourse cut through a land area for such uses as navigation and irrigation.

CAPE: A relatively extensive land area jutting seaward from a continent or large island which prominently marks a change in, or interrupts notably, the coastal trend; a prominent feature.

CAPILLARY WAVE: A WAVE whose velocity or propagation is controlled primarily by the surface tension of the liquid in which the WAVE is travelling. A water WAVE in which the WAVE LENGTH is less than 2.5 cm is considered to be a capillary wave, while WAVES longer than 2.5 cm and shorter than 5cm are in an indeterminate zone between CAPILLARY and GRAVITY WAVES. See also RIPPLE. See Figure 10.

CARRYING CAPACITY: The maximum number of species that any particular area can support over an extended period of time.

CARTOGRAPHY: The science and art of making maps.


CHANGE OF TIDE: The change of one TIDE condition (rising or falling) for the other (falling or rising), or of one TIDAL CURRENT direction flow for the other.

CHANNEL: (1) A natural or artificial waterway of perceptible extent which either periodically or continuously contains moving water, or which forms a connecting link between two bodies of water. (2) The part of a body of water deep enough to be used for navigation through an area otherwise too shallow for navigation. (3) The deepest portion of a STREAM, BAY, or STRAIT through which the main volume of CURRENT of water flows. (4) (SMP) An open conduit for water either naturally or artificially created, but does not include artificially created irrigation, return flow or stockwatering channels (WAC 173-14-030 (8b)).

CHART DATUM: The plane or level to which SOUNDINGS, tidal levels or WATER DEPTHS are referenced, usually low water datum. See also DATUM PLANE and REFERENCE PLANE.

CHOPPY SEA: Short, rough WAVES tumbling with a short and quick motion. SHORT- CRESTED WAVES that may spring up quickly in a moderate breeze, and break easily at the crest.

CLASTIC ROCKS: ROCKS built up of fragments which have been produced by the processes of weathering and EROSION, and in general transported to a point of deposition.

CLAY: A fine grained SEDIMENT with a typical grain size less than 0.004 mm. Possesses electromagnetic properties which bind the grains together to give a bulk strength or cohesion.

CLIFF: A high steep face of rock.

CLIMATE CHANGE: Refers to any long-term trend in MEAN SEA LEVEL, WAVE HEIGHT, wind speed, drift rate etc.

COAST: A strip of land of indefinite length and width (may be tens of kilometers) that extends from the SEASHORE inland to the first major change in terrain features.

COASTAL CURRENTS: (1) Those CURRENTS which flow roughly parallel to the SHORE and constitute a relatively uniform drift in the deeper water adjacent to the SURF ZONE. These currents may be TIDAL CURRENTS, transient, wind-driven currents, or currents associated with the distribution of mass in local waters. (2) For navigational purposes, the term is used to designate a current in coastwise shipping lanes where the TIDAL CURRENT is frequently rotary.

COASTAL DEFENSE: General term used to encompass both coast protection against EROSION and sea defense against flooding.

COASTAL FORCING: The natural processes that drive coastal hydro- and morphodynamics (e.g. winds, WAVES, TIDES, etc).

COASTAL MANAGEMENT: The development of a strategic, long-term and sustainable land use policy, sometimes also called SHORELINE MANAGEMENT.

COASTAL PLAIN: The plain composed of horizontal or gently sloping strata of CLASTIC material fronting the COAST and generally representing a strip of recently emerged sea bottom that has emerged from the SEA in RECENT geologic times. Also formed by AGGRADATION.

COASTAL PROCESSES: Collective term covering the action of natural forces on the SHORELINE, and the NEARSHORE seabed.

COASTAL ZONE: The land-sea-air interface zone around continents and islands extending from the landward edge of a BARRIER BEACH or SHORELINE of coastal bay to the outer extent of the CONTINENTAL SHELF.

COASTLINE: (1) Technically, the line that forms the boundary between the COAST and the SHORE. (2) Commonly, the line that forms the boundary between land and the water. (3) (SMP) The line where terrestrial processes give way to marine processes, TIDAL CURRENTS, wind waves, etc.

COBBLE: Rounded ROCKS ranging in diameter from approximately 64 to 256 mm.

COLLOID: As a size term refers to particles smaller than 0.00024 mm, smaller than CLAY size.

COMBER: (1) A deepwater WAVE whose crest is pushed forward by a strong wind; much larger than a WHITECAP. (2) A long-period BREAKER.

COMPASS, SURVEYOR'S: A compass for determining the magnetic azimuth of a line of sight by means of a sighting device, a graduated horizontal circle, and a pivoted magnetic needle.

CONFLUENCE: The junction of two or more RIVER reaches or branches (the opposite of a BIFURCATION).

CONSERVATION: The protection of an area, or particular element within an area, accepting the dynamic nature of the environment and therefore allowing change.

CONTINENTAL SHELF: (1) The zone bordering a continent extending from the line of permanent immersion to the DEPTH, usually about 100 m to 200 m, where there is a marked or rather steep descent toward the great depths. (2) The area under active LITTORAL processes during the Holocene period. (3) The region of the oceanic bottom that extends outward from the SHORELINE with an average SLOPE of less than 1:100, to a line where the GRADIENT begins to exceed 1:40 (the CONTINENTAL SLOPE).

CONTINENTAL SLOPE: The declivity from the OFFSHORE border of the CONTINENTAL SHELF to oceanic depths. It is characterized by a marked increase in SLOPE.

CONTOUR CURRENT: A bottom current that flows parallel to the slopes of the continental margin (along the contour rather than down the SLOPE).

CONTOUR LINE: A line connecting points, on a land surface or sea bottom, which have equal ELEVATION. It is called an ISOBATH when connecting points of equal DEPTH below a DATUM.

CONTROLLING DEPTH: The least DEPTH in the navigable parts of a waterway, governing the maximum draft of vessels that can enter.

CONTROL NETWORK: Geodetic control together with the measured or adjusted values of the distances, angels, directions, or heights used in determining the coordinates of the control.

CONTROL, GEODETIC: A set of control stations established by geodetic methods.

CONTROL, GROUND: A point or set of points, the coordinates of which have been determined by survey, used for fixing the scale and position of a photogrammetrically determined NETWORK.

CONTROL, HORIZONTAL: The geometric data relating to the horizontal coordinates of a control station.

CONTROL, PHOTOGRAMMETRIC: Geodetic or other control established to provide scale, location, and orientation for photogrammetric NETWORK.

CONTROL, VERTICAL: The ELEVATIONS (or approximations thereto) associated with control points.

COORDINATE SYSTEM: A set of rules for specifying how coordinates are to be assigned to points.

CORE: (1) A cylindrical sample extracted from a BEACH or seabed to investigate the types and DEPTHS of SEDIMENT layers. (2) An inner, often much less permeable portion of a BREAKWATER, or BARRIER BEACH.

CORIOLIS EFFECT: Force due to the Earth's rotation, capable of generating currents. It causes moving bodies to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The "force" is proportional to the speed and latitude of the moving object. It is zero at the equator and maximum at the poles.

COSET: A group of units of CROSS-BEDDING which shows a uniform direction of current flow.

CO-TIDAL LINES: Lines which link all the points where the TIDE is at the same stage (or phase) of its cycle.

COUNTERCURRENT: A secondary current usually setting in a direction opposite to that of a main current.

COVE: A small sheltered recess in a SHORE or COAST, generally inside a larger EMBAYMENT.

CREEK: (1) A STREAM, less predominant than a RIVER, and generally tributary to a RIVER. (2) A small tidal CHANNEL through a coastal MARSH.

CREEP: Very slow, continuous downslope movement of SOIL or debris.

CRENULATE: An indented or wavy SHORELINE beach form, with the regular seaward- pointing parts rounded rather than sharp, as in the CUSPATE type.

CROSS-BEDDING: An arrangement of relatively thin layers of rock inclined at an angle to the more nearly horizontal BEDDING PLANES of the larger rock unit. Also referred to as cross-stratification.

CROSS SEA: Confused, irregular state of the SEA due to different groups of WAVES from different directions raised by local winds.

CROSS-SHORE: Perpendicular to the SHORELINE.

CURRENT: (1) The flowing of water, or other liquid or gas. (2) That portion of a STREAM of water which is moving with a velocity much greater than the average or in which the progress of the water is principally concentrated. (3) OCEAN CURRENTS can be classified in a number of different ways. Some important types include the following:

CURRENT METER: An instrument for measuring the velocity of a CURRENT. It is traditionally operated by a wheel equipped with vanes of cups which is rotated by the action of the impinging CURRENT. A recording device is provided to indicate the speed of rotation which is correlated with the velocity of the CURRENT.

CUSP: One of a series of short ridges on the FORESHORE separated by crescent-shaped TROUGHS spaced at more or less regular intervals. Between these cusps are hollows. The cusps are spaced at somewhat uniform distances along beaches. They represent a combination of constructive and destructive processes.

CUSPATE: Form of SHORELINE involving sharp seaward-pointing CUSPS (normally at regular intervals) between which the SHORELINE follows a smooth arc.

CUSPATE FORELAND: A large, sandy cusp-shaped projection of the COAST. See Figure 5.

CUSPATE SANDKEY: A cusp-shaped SAND island.

CUSPATE SPIT: A sandy cusp-shaped projection of the SHORELINE, found on both sides of some LAGOONS.

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Ecology - SEA Program | USGS - Coastal & Marine Geology

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Maintained by CMAP, Washington Department of Ecology
Address questions and comments to George Kaminsky
Modified 22 Mar 2012