Glossary of Coastal Terminology: S - T

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SALIENT: Coastal formation of beach material developed by wave REFRACTION and DIFFRACTION and LONGSHORE DRIFT comprising of a bulge in the COASTLINE towards an OFFSHORE island or BREAKWATER, but not connected to it as in the case of a TOMBOLO. See also NESS, CUSP.

SALINITY: Number of grams of salt per thousand grams of sea water, usually expressed in parts per thousand.

SALINITY GRADIENT: Change in SALINITY with DEPTH, expressed in parts per thousand per foot.

SALTATION: A term used to describe the movement of a particle being transported by wind or water which is too heavy to remain in suspension. The particle is rolled forward by the current, generates lift and rises, loses the forward momentum supplying the lift and settles to the floor, where the process is repeated. The size of the particles which can be saltated depends upon the velocity of the current and its density, e.g., water will saltate larger particles than air at the same velocity.

SALT-WEDGE ESTUARY: In this circulation type, the density-driven component dominates and two well-mixed layers are separated by a sharp HALOCLINE. The seawater entering the CHANNEL appears as a TONGUE or wedge.

SAND: An UNCONSOLIDATED (geologically) mixture of inorganic SOIL (that may include disintegrated shells and coral) consisting of small but easily distinguishable grains ranging in size from about .062 mm to 2.0 mm.

SAND BAR: (1) See BAR. (2) In a RIVER, a ridge of SAND built to or near the surface by RIVER CURRENTS.

SAND DUNE: A DUNE formed of SAND.

SAND SPIT: A narrow SAND EMBANKMENT, created by an excess of deposition at its seaward terminus, with its distal end (the end away from the point of origin) terminating in open water.

SAND WAVES: (1) LONGSHORE sand waves are large-scale features that maintain form while migrating along the shore with speeds on the order of kilometers per year. (2) Large-scale asymmetrical bedforms in sandy RIVER beds having high length to height ratios and continuous crestlines.

SCARP: See ESCARPMENT.

SCOUR PROTECTION: Protection against EROSION of the seabed in front of the TOE.

SEA: (1) See OCEAN. (2) A large body of salt water, second in rank to an OCEAN, more or less LANDLOCKED and generally part of, or connected with, an OCEAN or a larger sea. (3) WAVES caused by wind at the place and time of observation. (4) State of the OCEAN or lake surface, in regard to WAVES.

SEA BREEZE: A breeze that blows from the SEA toward the land caused by unequal heating of land and water masses.

SEA CLIFF: A CLIFF situated at the seaward edge of the coast. See Figure 2.

SEACOAST: The coast adjacent to the SEA or OCEAN.

SEA DEFENSES: Works to prevent or alleviate flooding by the SEA.

SEA GRASS: Members of marine seed plants that grow chiefly on SAND or sand-mud bottom. They are most abundant in water less than 9 m deep. The common types are: Eel grass (Zostera), Turtle grass (Thallasia) and Manatee grass (Syringodium).

SEA LEVEL RISE: The long-term trend in MEAN SEA LEVEL.

SEA PUSS: A dangerous LONGSHORE CURRENT; a RIP CURRENT caused by return flow; loosely, the submerged CHANNEL or INLET through a BAR caused by those CURRENTS.

SEAMOUNT: Conical mountain rising 1000 m or more above the sea floor.

SEASHORE: (1) (Law) All ground between the ordinary high-water and low-water mark. (2) The SHORE of the SEA or OCEAN.

SEAWALL: (1) A structure built along a portion of a coast primarily to prevent EROSION and other damage by WAVE action. It retains earth against its shoreward face. (2) (SMP) A structure separating land and water areas primarily to prevent EROSION and other damage by WAVE action. Generally more massive and capable of resisting greater wave forces than a BULKHEAD.

SECHHI DISK: Visibility disk used to measure the transparency of the water column.

SEDIMENT: (1) Loose, fragments of ROCKS, MINERALS or organic material which are transported from their source for varying distances and deposited by air, wind, ice and water. Other sediments are precipitated from the overlying water or form chemically, in place. Sediment includes all the UNCONSOLIDATED materials on the sea floor. (2) (SMP) The fine grained material deposited by water or wind.

SEDIMENT CELL: In the context of a strategic approach to COASTAL MANAGEMENT, a length of COASTLINE in which interruptions to the movement of SAND or SHINGLE along the beaches or NEARSHORE sea bed do not significantly affect beaches in the adjacent lengths of COASTLINE.

SEDIMENT SINK: A point or area at which beach material is irretrievably lost from a coastal cell, such as an ESTUARY, or a deep CHANNEL in the seabed. See Figure 8.

SEDIMENT SOURCE: A point or area on a COAST from which beach material arises, such as an eroding CLIFF, or RIVER mouth. See Figure 8.

SEDIMENT TRANSPORT: The main agencies by which sedimentary materials are moved are: gravity (gravity transport); running water (RIVERS and STREAMS); ice (glaciers); wind; the SEA (CURRENTS and LONGSHORE DRIFT). Running water and wind are the most widespread transporting agents. In both cases, three mechanisms operate, although the PARTICLE SIZE of the transported material involved is very different, owing to the differences in density and VISCOSITY of air and water. The three processes are: rolling or traction, in which the particle moves along the BED but is too heavy to be lifted from it; SALTATION; and suspension, in which particles remain permanently above the BED, sustained there by the TURBULENT FLOW of the air or water. See Figure 8.

SEDIMENT TRANSPORT PATHS: The routes along which net SEDIMENT movement occurs.

SEISMIC REFLECTION: The return of part of the energy of SEISMIC WAVES to the earth's surface after the WAVES bounce off a rock boundary.

SEISMIC REFRACTION: The bending of SEISMIC WAVES as they pass from one material to another.

SEISMIC WAVES: A long-period WAVE caused by an underwater seismic disturbance or volcanic eruption.

SEMIDIURNAL: Having a period or cycle of approximately one-half of a TIDAL DAY (12.4 hours). The predominating type of TIDE throughout the world is semidiurnal, with two high waters and two low waters each TIDAL DAY. The TIDAL CURRENT is said to be semidiurnal when there are two flood and two EBB periods each day. See Figure 11.

SEMIDIURNAL TIDE: TIDES occurring twice daily. There are two high and two lows per TIDAL DAY. See Figure 12.

SENSING, REMOTE: The response of an instrument or organism to stimuli from a distant source.

SET (OF CURRENT): The direction towards which a current flows.

SETBACK: (SMP) A required open space, specified in shoreline master programs, measured horizontally upland from an perpendicular to the ordinary high water mark.

SHALLOW WATER: Water of such DEPTH that surface WAVES are noticeably affected by bottom TOPOGRAPHY. Typically this implies a WATER DEPTH equivalent to less than half the WAVE LENGTH.

SHALLOW WATER WAVE: A PROGRESSIVE GRAVITY WAVE which is in water less than 1/25 the WAVE LENGTH in DEPTH.

SHEET EROSION: The removal of a thin layer of surface material, usually topsoil, by a flowing sheet of water.

SHEET FLOW: SEDIMENT grains under high sheer stress moving as a layer that extends from the BED surface to some distance below (on the order of a few cm). Grains are transported in the direction of fluid flow.

SHEET, SMOOTH: A sheet on which field control and hydrographic data such as SOUNDINGS, depth curves, and regions surveyed with a wire drag are finally plotted before being used in making a final chart.

SHELF, CONTINENTAL: See CONTINENTAL SHELF.

SHINGLE: A loose term for coarse beach material, a mixture of GRAVEL, PEBBLES and larger material, often well-rounded and of hard rock, e.g. chert, flint, etc.

SHOAL: (1) (noun) A detached area of any material except rock or coral. The DEPTHS over it are a danger to surface navigation. Similar continental or insular shelf features of greater DEPTHS are usually termed BANKS. (2) (verb) To become shallow gradually. (3) To cause to become shallow. (4) To proceed from a greater to a lesser DEPTH of water.

SHORE: That strip of ground bordering any body of water which is alternately exposed, or covered by TIDES and/or WAVES. A SHORE of UNCONSOLIDATED material is usually called a BEACH.

SHOREFACE: The narrow zone seaward from the low tide shoreline permanently covered by water, over which the BEACH SANDS and GRAVELS actively oscillate with changing WAVE conditions.

SHORELINE: (1) The intersection of a specified plane of water with the SHORE. (2) (SMP) All of the water areas of the state, including reservoirs and their associated uplands, together with the lands underlying them, except those areas excluded under RCW 90.58.030(2)(d).

SHORELINE MANAGEMENT: The development of strategic, long-term and sustainable COASTAL DEFENSE and land-use policy within a SEDIMENT CELL.

SHORT-CRESTED WAVE: A WAVE, the crest length of which is of the same order of magnitude as the WAVE LENGTH. A system of short-crested waves has the appearance of hills being separated by TROUGHS.

SHORE TERRACE: A TERRACE made along a COAST by the action of WAVES and shore currents; it may become land by the uplifting of the SHORE or the lowering of the water.

SIGNIFICANT WAVE: A statistical term relating to the one-third highest WAVES of a given WAVE GROUP and defined by the average of their heights and periods.

SIGNIFICANT WAVE HEIGHT: Average height of the highest one-third of the WAVES for a stated interval of time.

SIGNIFICANT WAVE PERIOD: Average period of the highest one-third of the WAVES for a stated interval of time.

SILT: SEDIMENT particles with a grain size between 0.004 mm and 0.062 mm, i.e. coarser than CLAY particles but finer than SAND.

SLACK WATER (SLACK TIDE): The state of a TIDAL CURRENT when its velocity is near zero, especially the moment when a reversing current changes its direction and its velocity is zero. The term is also applied to the entire period of low velocity near the time of turning of the current when it is too weak to be of any practical importance in navigation. The relation of the time of slack water to the tidal phases varies in different localities. In some places slack water occurs near the times of high and low water, while in other localities the slack water may occur midway between HIGH and LOW WATER.

SLIDE: In mass wasting, movement of a descending mass along a plane approximately parallel to the SLOPE of the surface.

SLIP FACE: The steep, downwind SLOPE of a DUNE; formed from loose, cascading SAND that generally keeps the SLOPE at the ANGLE OF REPOSE (about 34 degrees).

SLOPE: The degree of inclination to the horizontal. Usually expressed as a ratio, such as 1:25, indicating one unit rise in 25 units of horizontal distance; or in a decimal fraction (0.04). also called GRADIENT.

SLOUGH: A small muddy marshland or tidal waterway which usually connects other tidal areas.

SLUMP: In mass wasting, movement along a curved surface in which the upper part moves vertically downward while the lower part moves outward.

SMALL DIURNAL RANGE: Difference in height between MEAN LOWER LOW WATER (MLLW) and MEAN HIGHER HIGH WATER (MHHW). Applicable only when the type of TIDE is either SEMIDIURNAL or MIXED.

SOFT DEFENSES: Usually refers to beaches (natural or designed) but may also relate to energy-absorbing beach-control structures, including those constructed of rock, where these are used to control or redirect COASTAL PROCESSES rather than opposing or preventing them.

SOIL: A layer of weathered, UNCONSOLIDATED material on top of bed rock; often also defined as containing organic matter and being capable of supporting plant growth.

SOIL HORIZONS: Layers of SOIL that are distinguishable by characteristic physical or chemical properties.

SOLITARY WAVE: A WAVE consisting of a single ELEVATION (above the water surface) of height not necessarily small compared to the DEPTH, and neither followed or preceded by another ELEVATION or DEPRESSION of the water surface.

SORTING: Process of selection and separation of SEDIMENT grains according to their grain size (or grain shape or specific gravity).

SOUND: (1) (noun) a relatively long arm of the SEA or OCEAN forming a CHANNEL between an island and a mainland or connecting two larger bodies, as a SEA and the OCEAN, or two parts of the same body; usually wider and more extensive than a STRAIT. (2) (verb) To measure the DEPTH of the water.

SOUNDING: A measured DEPTH of water. On hydrographic charts the SOUNDINGS are adjusted to a specific plane of reference (SOUNDING DATUM).

SOUNDING DATUM: The plane to which SOUNDINGS are referred. See CHART DATUM.

SOUNDING LINE: A line, wire or cord used in SOUNDING. It is weighted at one end with a plummet.

SPIT: (1) A long narrow accumulation of SAND or SHINGLE, lying generally in line with the COAST, with one end attached to the land the other projecting into the SEA or across the mouth of an ESTUARY. See also NESS. (2) (SMP) An accretion shoreform which extends seaward from and parallel to the SHORELINE. See Figure 5.

SPRING RANGE: The average SEMIDIURNAL RANGE occurring at the time of SPRING TIDES and most conveniently computed from the harmonic constants. It is larger than the MEAN RANGE where the type of TIDE is either SEMIDIURNAL or MIXED, and is of no practical significance where the type of TIDE is DIURNAL.

SPRING TIDAL CURRENTS: TIDAL CURRENTS of increased velocity occurring semi-monthly as the result of the moon being new or full.

SPRING TIDE: A TIDE that occurs at or near the time of new or full moon, and which rises highest and falls lowest from the MEAN SEA LEVEL (MSL).

STAND OF TIDE: An interval at HIGH or LOW WATER when there is no discernable change in the height of the TIDE. The WATER LEVEL is stationary at HIGH and LOW WATER for only an instant, but the change in level near these times is so slow that it is not usually perceptible. See SLACK WATER.

STANDING WAVE: (1) A type of WAVE in which the surface of the water oscillates vertically between fixed nodes without progressing. (2) A WAVE of essentially stable form which does not move with respect to a selected REFERENCE POINT.

STATION, CONTROL: A point on the ground whose horizontal or vertical location is used as a basis for obtaining locations of other points.

STEP: The nearly horizontal section which more or less divides the BEACH from the SHOREFACE. See Figure 3.

STILLWATER LEVEL (SWL): The surface of the water if all WAVE and wind action were to cease. In DEEP WATER this level approximates the midpoint of the WAVE HEIGHT. In SHALLOW WATER it is nearer to the TROUGH than the CREST. Also called the UNDISTURBED WATER LEVEL.

STONE: Quarried or artificially broken rock for use in construction.

STORM SURGE: A rise or piling-up of water against SHORE, produced by strong winds blowing ONSHORE. A storm surge is most severe when it occurs in conjunction with a high TIDE. See Figure 10.

STRAIT: A relatively narrow waterway between two larger bodies of water. See SOUND.

STRAND: The SHORE or BEACH of the OCEAN or a large lake. The land bordering any large body of water, especially a SEA or an arm of the OCEAN.

STRAND LINE: An accumulation of debris (e.g. seaweed, driftwood and litter) cast up onto a BEACH, and lying along the limit of WAVE UPRUSH.

STRATIGRAPHY: (1) The study of stratified ROCKS (SEDIMENTS and volcanics) especially their sequence in time. (2) The character of the ROCKS and the correlation of beds in different localities.

STREAM: (1) Any flow of water; a current. (2) A course of water flowing along a BED in the earth.

STREAM CURRENT: A narrow, deep and swift OCEAN CURRENT, such as the Gulf Stream. Opposite of DRIFT CURRENT.

STRUCTURAL GEOLOGY: The branch of GEOLOGY concerned with the internal structure of bed rock and the shapes, arrangement, and interrelationships of rock units.

SUB-AERIAL BEACH: That part of the BEACH which is uncovered by water (e.g. at LOW TIDE sometimes referred to as DRYING BEACH).

SUBDUCTION ZONE: Elongate region in which the sea floor slides beneath a continent or island arc.

SUBMARINE CANYON: V-shaped VALLEYS that run across the CONTINENTAL SHELF and down the CONTINENTAL SLOPE. See Figure 8.

SUBMERGENT COAST: A COAST in which formerly dry land has been recently drowned, either by land SUBSIDENCE or a rise in seal level.

SUBORDINATE STATION: A TIDE or current station at which a short series of observations has been obtained, which is to be reduced by comparison with simultaneous observations at another station having well-determined tidal or current constants.

SUBSIDENCE: Sinking or downwarping of a part of the earth's surface.

SUB-TIDAL BEACH: The part or the BEACH (where it exists) which extends from LOW WATER out to the approximate limit of storm EROSION. The latter is typically located at a maximum WATER DEPTH of 8 to 10 m for moderate WAVE environments and is often identifiable on surveys by a break in the SLOPE of the BED.

SURF: (1) Collective term for BREAKERS. (2) The WAVE activity in the area between the SHORELINE and the outermost limit of BREAKERS. (3) The term surf in literature usually refers to the breaking WAVES on SHORE and on REEFS when accompanied by a roaring noise caused by the larger WAVES breaking.

SURF BEAT: irregular OSCILLATIONS of WATER LEVEL within the SURF ZONE with periods in the order of several minutes.

SURF ZONE: (1) The NEARSHORE zone along which the WAVES become BREAKERS as they approach the SHORE. (2) The zone of WAVE action extending from the WATER LINE (which varies with TIDE, SURGE, set-up, etc.) out to the most seaward point of the zone (BREAKER ZONE) at which WAVES approaching the COASTLINE commence breaking, typically in WATER DEPTHS of between 5 m and 10 m. See Figure 6.

SURFACE GRAVITY WAVE (PROGRESSIVE): (1) this is the term which applies to the WIND WAVES and SWELL of lakes and OCEANS, also called SURFACE WATER WAVE, SURFACE WAVE or DEEP WATER WAVE, (2) a PROGRESSIVE GRAVITY WAVE in which the disturbance is confined to the upper limits of a body of water. Strictly speaking this term applies to those PROGRESSIVE GRAVITY WAVES whose CELERITY depends only upon the WAVE LENGTH. See Figure 10.

SURFACE WATER WAVE: see SURFACE GRAVITY WAVE (PROGRESSIVE).

SURFACE WAVE: see SURFACE GRAVITY WAVE (PROGRESSIVE). See Figure 10.

SURGE: (1) Long-interval variations in velocity and pressure in fluid flow, not necessarily periodic, perhaps even transient in nature. (2) The name applied to WAVE motion with a period intermediate between that of an ordinary wind WAVE and that of the TIDE. (3) Changes in WATER LEVEL as a result of meteorological forcing (wind, high or low barometric pressure) causing a difference between the recorded WATER LEVEL and that predicted using harmonic analysis, may be positive or negative.

SURVEY, CONTROL: A survey that provides coordinates (horizontal or vertical) of points to which supplementary surveys are adjusted.

SURVEY, HYDROGRAPHIC: A survey that has as its principal purpose the determination of geometric and dynamic characteristics of bodies of water.

SURVEY, PHOTOGRAMMETRIC: A survey in which monuments are placed at points that have been determined photogrammetrically.

SURVEY, TOPOGRAPHIC: A survey which has, for its major purpose, the determination of the configuration (relief) of the surface of the land and the location of natural and artificial objects thereon.

SUSPENDED LOAD: The finest of the BEACH SEDIMENTS, light enough in weight to remain lifted indefinitely above the bottom by water turbulence.

SWASH: (1) Same as UPRUSH. (2) A body of dashing, splashing water. (3) A BAR over which the OCEAN washes.

SWASH BARS: Low broad sandy BARS formed by SEDIMENT in the surf and SWASH ZONES, separated by linear depressions, or RUNNELS, running parallel to the SHORE.

SWASH CHANNEL: A narrow SOUND or CHANNEL of water lying within a sandbank, or between a sandbank and a SHORE.

SWASH MARK: The thin wavy line of fine SAND left by the UPRUSH when it recedes from its upward limit of movement on the BEACH FACE.

SWASH ZONE: The zone of WAVE action on the BEACH, which moves as WATER LEVELS vary, extending from the limit of run-down to the limit of RUN-UP. See Figure 6.

SWELL: WAVES that have traveled a long distance from their GENERATING AREA and have been sorted out by travel into LONG WAVES of the same approximate period.


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T

TECTONIC FORCES: Forces generated from within the earth that result in uplift, movement, or deformation of part of the earth’s crust.

TECTONICS: The study of the major structural features of the Earth’s crust or the broad structure of a region.

TERRIGENOUS SEIDMENTS: Literally ‘land-formed’ sediment that has found its way to the sea floor. The term is applied (a) to sediments formed and deposited on land (e.g., soils, SAND DUNES) and (b) to material derived from the land when mixed in with purely marine material (e.g., SAND or CLAY in a shelly limestone).

TERRACE: A horizontal or nearly horizontal natural or artificial topographic feature interrupting a steeper SLOPE, sometimes occurring in a series.

THALWEG: The line down the center of the main CHANNEL of a stream.

THRESHOLD VELOCITY: The maximum orbital velocity at which the SEDIMENT on the BED begins to move as waves approach shallow water.

TIDAL CURRENT: The alternating horizontal movement of water associated with the rise and fall of the tide caused by ASTRONOMICAL TIDE-producing forces.

TIDAL DATUM: See REFERENCE PLANE.

TIDAL DAY: See LUNAR DAY.

TIDAL DELTA: See DELTA.

TIDAL FLATS: (1) Marshy or muddy areas covered and uncovered by the rise and fall of the tide. A TIDAL MARSH. (2) (SMP) Marshy or muddy areas of the seabed which are covered and uncovered by the rise and fall of tidal water.

TIDALLY DRIVEN CIRCULATION: The movement of fresh water and seawater that are mixed by the sloshing back and forth of the ESTUARY in response to ocean tides.

TIDAL MARSH: Same as TIDAL FLATS.

TIDAL PERIOD: The interval of time between two consecutive like phases of the tide or TIDAL CURRENT. See Figure 11.

TIDAL POOL: A pool of water remaining on a BEACH or REEF after recession of the tide.

TIDAL PRISM: (1) The total amount of water that flows into a HARBOR or out again with movement of the tide, excluding any fresh water flow. (2) (SMP) The volume of water present between mean low and mean high tide.

TIDAL RANGE: See RANGE OF TIDE.

TIDAL RISE: The height of tide as referred to the DATUM of a chart. See Figure 11.

TIDAL STAND: An interval at HIGH or LOW WATER when there is no observable change in the height of the tide. The water level is stationary at HIGH and LOW WATER for only an instant, but the change in level near these times is so slow that it is not usually perceptible.

TIDAL WAVE: (1) A wave, in the oceans and seas, produced by tides and TIDAL CURRENTS. (2) Non-technical term in popular usage for an unusually high and destructive water level along a shore. It usually refers to STORM SURGE or TSUNAMI.

TIDE: The periodic rising and falling of the water that results from gravitational attraction of the moon and sun acting upon the rotating earth. Although the accompanying horizontal movement of the water resulting from the same cause is also sometimes called the tide, it is preferable to designate the latter as TIDAL CURRENT, reserving the name tide for the vertical movement. See Figure 11.

TIDE, ASTRONOMIC: The periodic change in magnitude and direction of gravity as caused by attraction of the Sun, Moon, and other members of the Solar system.

TIDE, DIURNAL: See DIURNAL.

TIDE, EBB: See EBB TIDE.

TIDE, FLOOD: See FLOOD TIDE.

TIDE GAGE: A device for measuring the rise and fall, and the current height of the tide.

TIDE LEVEL: The height of the tide above a specified level.

TIDE, MIXED: See MIXED TIDES.

TIDE, NEAP: See NEAP TIDES.

TIDES, RIP: See RIP.

TIDE, SEMIDIURNAL: See SEMIDIURNAL, SEMIDIURNAL TIDE.

TIDE, SLACK: See SLACK WATER.

TIDE, SPRING: See SPRING TIDES.

TIDE STAFF: A tide gage consisting of a vertical graduated staff from which the height of the tide can be read directly. It is called a fixed staff when it is secured in place so that it cannot be easily removed. A portable staff is one that is designed for removal from the water when not in use.

TIDE STATION: The geographic location at which tidal observations are made. It is called a primary tide station when continuous observations are to be taken over a number of years to obtain basic tidal data for the locality. A secondary tide station is one operated over a short period of time to obtain data for a specific purpose.

TIDE TABLES: Tables which give daily predictions of the times and heights of the tide. These predictions are usually supplemented by tidal differences and constants by means of which additional predictions can be obtained for numerous other places.

TIDES, TYPES OF: The characteristic form of the tide with special reference to the relation of the DIURNAL and SEMIDIURNAL waves. Tides are sometimes classified as DIURNAL, SEMIDIURNAL and MIXED, but there are no sharply defined limits separating the groups. The tide is said to be DIURNAL when the diurnal wave predominated and only a single HIGH and single LOW WATER occur each day during the greater part of the month. The tide is SEMIDIURNAL when the semidiurnal wave predominates and two HIGH and two LOW WATERS occur each tidal day with a relatively small inequality in the HIGH and LOW WATER heights. In the MIXED type of tide the DIURNAL and SEMIDIURNAL waves are both important factors and the tide is characterized by large inequality in the HIGH or LOW WATER heights or in both. There will usually be two HIGH and two LOW WATERS each day, but occasionally the tide will become DIURNAL. See Figure 11.

TIDE, WIND: See WIND TIDE.

TOE: (1) Lowest part of sea- and portside breakwater SLOPE, generally forming the transition to the seabed. (2) The point of break in SLOPE between a dune and a beach face.

TOMBOLO: (1) Coastal formation of BEACH material developed by REFRACTION, DIFFRACTION and LONGSHORE DRIFT to form a 'NECK' connecting a COAST to an offshore island or BREAKWATER (see also SALIENT). (2) (SMP) A causeway-like ACCRETION SPIT that connects an offshore rock or island to the main shore, or to another island. See Figure 5.

TONGUE: A long narrow strip of land, projecting into a body of water.

TOPOGRAPHIC MAP: A map on which elevations are shown by means of CONTOUR LINES.

TOPOGRAPHY: The form of the features of the actual surface of the Earth in a particular region considered collectively.

TRAINING WALL: A wall or JETTY to direct current flow.

TRANSGRESSION, MARINE: The invasion of a large area of land by the sea in a relatively short space of time (geologically speaking). Although the observable result of a marine transgression may suggest an almost ‘instantaneous’ process, it is probable that the time taken is in reality to be measured in millions of years. The plane of marine transgression is a plane of UNCONFORMITY. The reverse of a transgression is a regression.

TRANSITIONAL WATER (ZONE): In regard to PROGRESSIVE GRAVITY WAVES, water whose DEPTH is less than one-half, but more than 1/25, the wave length, also called a SHALLOW WATER WAVE.

TRANSVERSE BAR: A BAR which extends approximately at right angles to the SHORELINE.

TRAVEL TIME: The time necessary for waves to travel a given distance from the GENERATING AREA.

TRENCH: A long narrow submarine DEPRESSION with relatively steep sides.

TROUGH: A long and broad submarine DEPRESSION with gently sloping sides.

TROUGH, WAVE: See WAVE TROUGH.

TRUNCATED LANDFORM: A landform cut off, especially by EROSION, and forming a steep side or CLIFF.

TSUNAMI: A large, high-velocity wave generated by displacement of the sea floor (such as sudden faulting, landsliding, or volcanic activity); also called seismic sea wave. Commonly misnamed TIDAL WAVE. See Figure 10.

TURBIDITY: (1) A condition of a liquid due to fine visible material in suspension, which may not be of sufficient size to be seen as individual particles by the naked eye but which prevents the passage of light through the liquid. (2) A measure of fine suspended matter in liquids.

TURBIDITY CURRENT: A flowing mass of sediment-laden water that is heavier than clear water and therefore flows downslope along the bottom of the sea or a lake.

TURBULENT FLOW: Any flow which is not LAMINAR, i.e., the stream lines of the fluid, instead of remaining parallel, become confused and intermingled.

TYPE OF TIDE: See TIDE, TYPE OF.


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