COASTAL ENGINEERING MANUAL

A

ABRASION

The mechanical wearing away by rock material transported by wind or water

ABRASION PLATFORM

A rock or clay platform which has been worn by the processes of abrasion.

ACCELEROMETER

A device used in wave buoys for measuring acceleration.

ACCRETION

May be either natural or artificial.  Natural accretion is the buildup of land, solely by the action of the forces of nature, on a beach by deposition of water- or airborne material.  Artificial accretion is a similar buildup of land by reason of an act of man, such as the accretion formed by a GROIN, BREAKWATER, or beach fill deposited by mechanical means.  Also AGGRADATION.

ACTIVE MARGIN

A margin of a continental plate consisting of a continental shelf and slope, and an oceanic trench or basin.

ADJUSTABLE GROIN

A GROIN whose permeability can be changed, usually with gates or removable sections.

ADVANCE (of a beach)

(1) A continuing seaward movement of the shoreline.  (2) A net seaward movement of the shoreline over a specified time.  Also PROGRESSION.

AEOLIAN

See EOLIAN.

AGE, WAVE

The ratio of wave velocity to wind velocity (in wave forecasting theory).

AGGRADATION

See ACCRETION.

ALIGNMENT

The course along which the center line of a channel, canal or drain is located.

ALLOCHTONOUS

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

ALLUVIAL DEPOSITS

Detrital material which is transported by a river and deposited B usually temporarily B at points along the flood plain of a river. Commonly composed of sands and gravels.

ALLUVIAL PLANE

A plain bordering a river, formed by the deposition of material eroded from areas of higher elevation.

ALLUVIUM

Soil (sand, mud, or similar detrital material) deposited by streams, or the deposits formed.

ALONGSHORE

Parallel to and near the shoreline;  LONGSHORE.

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.

ALTIMETER, LIDAR

See ALTIMETER, LASER.

AMPLITUDE, WAVE

(1) The magnitude of the displacement of a wave from a mean value.  An ocean wave has an amplitude equal to the vertical distance from still-water level to wave crest.  For a sinusoidal wave, the amplitude is one-half the wave height.  (2)  The semirange of a constituent tide.

ANCHOR ICE

Spongy underwater ice formed on a submerged object or attached to the bottom of a shallow body of water which is itself not frozen;  syn. bottom ice

ANGLE OF REPOSE

The maximum slope (measured from the horizontal) at which soils and loose materials on the banks of canals, rivers or embankments will stay stable.

ANISOTROPIC

 Having properties that change with changing directions.

ANOXIC

Refers to an environment that contain little or no dissolved oxygen and hence little or no benthic marine life. These conditions arise in some basins or fjords where physical circulation of seawater is limited.

ANTIDUNES

BED FORMS that occur in trains and are in phase with, and strongly interact with, gravity water-surface waves.

ANTINODE

See LOOP.

APRON

 Layer of stone, concrete or other material to protect the toe of a structure.

AQUIFER

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

ARCHIPELAGO

A sea that contains numerous islands;  also the island group itself.

ARMOR LAYER

Protective layer on a BREAKWATER or SEAWALL composed of armor units.

ARMOR UNIT

A relatively large quarrystone or concrete shape that is selected to fit specified geometric characteristics and density.  It is usually of nearly uniform size and usually large enough to require individual placement.  In normal cases it is used as primary wave protection and is placed in thicknesses of at least two units.

ARTIFICIAL NOURISHMENT

The process of replenishing a beach with material (usually sand) obtained from another location.

ASPERITIES

The three-dimensional irregularities forming the surface of an irregular stone (or rock) subject to wear and rounding during abrasion.

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.

ATOLL

A ring-shaped coral REEF, often carrying low sand islands, enclosing a shallow LAGOON.  The reef is surrounded by deep water of the open sea.

ATTENUATION

(1) A lessening of the amplitude of a wave with distance from the origin.  (2) The decrease of water-particle motion with increasing depth.  Particle motion resulting from surface oscillatory waves attenuates rapidly with depth, and practically disappears at a depth equal to a surface wavelength.

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 shore land by waves during a storm. (2) A sudden cutting off of land by flood, currents or change in course of a body of water.

AWASH

Situated so that the top is intermittently washed by waves or tidal action.  Condition of being exposed or just bare at any stage of the tide between high water and chart datum.

B

BACK BARRIER

Pertaining to the lagoon-marsh-tidal creek complex in the lee of a coastal barrier island, barrier spit, or baymouth barrier.

BACKBEACH

See BACKSHORE.

BACKRUSH

The seaward return of the water following the uprush of the waves.  For any given tide stage the point of farthest return seaward of the backrush is known as the Limit of backrush or limit backwash. 

BACKSHORE

That zone of the shore or beach lying between the foreshore and the coastline comprising the BERM or BERMS and acted upon by waves only during severe storms, especially when combined with exceptionally high water.  Also BACKBEACH.  (See Figure IV-1-2.)

BACKWASH

(1) See BACKRUSH.  (2)  Water or waves thrown back by an obstruction such as a ship, BREAKWATER, or cliff.

BACKWASH RIPPLES

 Low amplitude ripple marks formed on fine sand beaches by the Backwash of the waves.

BACKWATER CURVE

The longitudinal profile of the water surface in an open channel where the depth of flow has been increased by an obstruction as a weir or a dam across the channel, by increase in channel roughness, by decrease in channel width or by a decrease of the bed gradient

BANK

(1) The rising ground bordering a lake, river, or sea; or of a river or channel, for which it is designated as right or left as the observer is facing downstream.  (2) An elevation of the sea floor or large area, located on a continental (or island) shelf and over which the depth is relatively shallow but sufficient for safe surface navigation (e.g., Georges Bank);  a group of shoals.  (3) In its secondary sense, used only with a qualifying word such as "sandbank" or "gravelbank," a shallow area consisting of shifting forms of silt, sand, mud, and gravel.

BAR

A submerged or emerged embankment of sand, gravel, or other unconsoli­dated material built on the sea floor in shallow water by waves and currents.   See BAYMOUTH BAR, CUSPATE BAR. 

BARRIER BEACH

A bar essentially parallel to the shore, the crest of which is above normal high water level.  Also called offshore barrier and BARRIER ISLAND.

BARRIER FLAT

 The flat area, often marshy and populated with low vegetation, on the bay or lagoon side of a barrier island

BARRIER ISLAND

A detached portion of a barrier beach between two inlets.  It commonly had DUNES, vegetated areas, and swampy terranes (see BARRIER FLAT) extending from the beach into the lagoon.  Example: Outer Banks, North Carolina.

BARRIER LAGOON

A bay roughly parallel to the coast and separated from the open ocean by barrier islands.  Also, the body of water encircled by coral islands and REEFS, in which case it may be called an ATOLL lagoon.

BARRIER REEF

A coral REEF parallel to and separated from the coast by a lagoon that is too deep for coral growth.  Generally, barrier reefs follow the coasts for long distances and are cut through at irregular intervals by channels or passes.  Example:  Great Barrier Reef, Queensland, Australia.

BARRIER SPIT

 Similar to a barrier island, but connected to the mainland.

BASIN

A depressed area with no surface outlet, such as a lake basin or an enclosed sea.

BASIN, BOAT

A naturally or artificially enclosed or nearly enclosed harbor area for small craft.

BASTION

A massive groin, or projecting section of seawall normally constructed with its crest above water level.

BATHMETRIC CHART

A topographic map of the bed of the ocean, with depths indicated by contours (isobaths) drawn at regular intervals.

BATHYMETRY

The measurement of depths of water in oceans, seas, and lakes; also information derived from such measurements.

BAY

A recess in the shore or an inlet of a sea between two capes or head­lands, not so large as a gulf but larger than a cove.  See also BIGHT, EMBAYMENT.

BAYMOUTH BAR

A bar extending partly or entirely across the mouth of a bay .

BAYOU

A minor sluggish waterway or estuarial creek, tributary to, or connecting, other streams or bodies of water, whose course is usually through lowlands or swamps.  Sometimes called SLOUGH.  Term is commonly used in the southern United States.

BEACH

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 (usually the effective limit of storm waves).  The seaward limit of a beach--unless other­wise specified--is the mean low water line.  A beach includes fore­shore and backshore.  (See Figure IV-1-2.)  See also SHORE, SUSTAINABLE BEACH, AND SELF-SUSTAINING BEACH.

BEACH ACCRETION

See ACCRETION.

BEACH BERM

A nearly horizontal part of the beach or backshore formed by the deposit of material by wave action.  Some beaches have no berms, others have one or several.  (See Figure IV-1-2.)

BEACH CREST

The point representing the limit of normal high tide wave run-up (see BERM CREST)

BEACH CUSP

See CUSP.

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 the wave uprush.  The FORESHORE of a BEACH.  (Not synonymous with SHORE­FACE.)

BEACH FILL

Material placed on a beach to renourish eroding shores.

BEACH HEAD

The cliff, dune or sea wall looming above the land ward limit of the active beach

BEACH MATERIAL

Granular sediments, usually sand or shingle moved by the sea.

BEACH PLAN SHAPE

The shape of the beach in plan;  usually shown as a contour line, combination of contour lines or recognizable  features such as beach crest and/or the still water line

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

See RIDGE, BEACH.

BEACH SCARP

See SCARP, BEACH.

BEACH WIDTH

The horizontal dimension of the beach measured normal to the shoreline and landward of the higher-high tide line (on oceanic coasts) or from the still water level (on lake coasts)

BEAUFORT SCALE

Table A-1

Beaufort Wind Scale                                        

Beaufort Number                Wind Speed (knots)           WMO Description ¹           

0              < 1          Calm     

1              1 - 3        Light air

2              4 - 6        Light breeze         

3              7 - 10      Gentle breeze      

4              11 - 16   Moderate breeze 

5              17 - 21   Fresh breeze       

6              22 - 27   Strong breeze      

7              28 - 33   Near gale             

8              34 - 40   Gale      

9              41 - 47   Strong Gale         

10           48 - 55   Storm    

11           56 - 63   Violent storm       

12           $ 64        Hurricane             

¹ World Meteorological Organization, from http://www.crh.noaa.gov/lot/webpage/beaufort/ (28 Aug. 2001)                                    

Classification of the force of the winds in accordance with a scale established by Rear-Admiral, Sir Francis Beaufort in which the range of intensity varies from 0 to 12, of integers (0 to 12) with a description of the state and behavior of a "well-conditioned man-of-war."

BED

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

BED FORMS

Any deviation from a flat bed that is readily detectable by eye and higher than the largest sediment size present in the parent bed material;  generated on the bed of an alluvial channel by the flow.

BED LOAD

Sediment transport mode in which individual particles either roll or slide along the bed as a shallow, mobile layer a few particle diameters deep, the part of the load that is not continuously in suspension.

BED PROTECTION

A (rock) structure on the bed in order to protect the underlying bed against erosion due to current and/or wave action.

BED SHEAR STRESS

The way in which waves (or currents) transfer energy to the sea bed.

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.

BEDROCK

The solid rock that underlies gravel, soil, and other superficial material.  Bedrock may be exposed at the surface (an outcrop) or it may br buried under a few centimeters to thousands of meters of unconsolidated material.

BENCH

(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, 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.

BENCH MARK

A permanently fixed point of known elevation.  A primary bench mark is one close to a tide station to which the tide staff and tidal datum originally are referenced.

BENEFITS

The asset 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

BENTHIC

Pertaining to the sub-aquatic bottom.

BENTHOS

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

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 renourishment scheme.  Some natural beaches have no berm, others have several.  (2) On a structure:  a nearly horizontal area, often built to support or key-in an armor layer.

BERM, BEACH

See BEACH BERM.

BERM BREAKWATER

Rubble mound structure with horizontal berm of armor stones at about sea level, which is allowed to be (re)shaped by the waves.

BERM CREST

The seaward limit of a BERM.  Also called BERM EDGE.  (See Figure IV-1-2.)

BIFURCATION

Location where a river separates in two or more reaches or branches (the opposite of a confluence).

BIGHT

A bend in a coastline forming an open bay.  A bay formed by such a bend.

BIOTURBATION

The disturbance of sediment bedding by the activities of burrowing organisms.

BIRDFOOT DELTA

A river delta formed by many levee-bordered distributaries extending seaward and resembling in plan the outstretched claws of a bird.  Example:  Mississippi River delta.

BLANKET (FOUNDATION or BEDDING)

A layer or layers of graded fine stones underlying a BREAKWATER, GROIN or rock embankment to prevent the natural bed material from being washed away.

BLOWN SANDS  See EOLIAN SANDS.

BLOWOUT

A depression on the land surface caused by wind erosion.

BLUFF

A high, steep bank or cliff.

BOG

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.

BOLD COAST

A prominent landmass that rises steeply from the sea.

BORE

A very rapid rise of the tide in which the advancing water presents an abrupt front of considerable height.  In shallow estuaries where the range of tide is large, the high water is propagated inward faster than the low water because of the greater depth at high water.  If the high water over­takes the low water, an abrupt front is presented, with the high-water crest finally falling forward as the tide continues to advance.  Also EAGER.

BOTTOM (nature of)

The composition or character of the bed of an ocean or other body of water (e.g., clay, coral, gravel, mud, ooze, pebbles, rock, shell, shingle, hard, or soft). (See Figure IV-1-2.)

BOTTOM BOUNDARY LAYER

 The lower portion of the water flow that experiences frictional retardation based on its proximity to the bed.

BOTTOMSET

One of the horizontal or gently inclined sediment layers deposited in front of the advancing forest beds of a delta.

BOULDER

A rounded rock more than 256 mm (10 inch) in diameter; larger than a cobblestone.  See SOIL CLASSIFICATION.

BOUNDARY CONDITIONS

Environmental conditions, e.g. waves, currents, drifts, etc. used as boundary input to physical or numerical models

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.

BRAIDED RIVER

A river type with multiple channels separated by shoals, bars and islands

BREACHING

Failure of the beach head or a dike allowing flooding by tidal action

BREAKER

A wave breaking on a shore, over a REEF, etc.  Breakers may be classified into four types (See Figure II-4-1):

COLLAPSING--breaking occurs over lower half of wave, with minimal air pocket and usually no splash-up.  Bubbles and foam present.          PLUNGING--crest curls over air pocket; breaking is usually with a crash.  Smooth splash-up usually follows.

SPILLING--bubbles and turbulent water spill down front face of wave.  The upper 25 percent of the front face may become vertical before breaking.  Breaking generally occurs over quite a distance.