Glossary of Coastal Terminology: S - T
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.
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 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.
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 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).
SEAMOUNT: Conical mountain rising 1000 m or more above the sea floor.
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 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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
SUBDUCTION ZONE: Elongate region in which the sea floor slides beneath a continent or island arc.
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 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.
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.
TECTONIC FORCES: Forces generated from within the earth that result in uplift, movement, or deformation of part of the earths crust.
TECTONICS: The study of the major structural features of the Earths 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).
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.
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 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, 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.
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.
TOPOGRAPHY: The form of the features of the actual surface of the Earth in a particular region considered collectively.
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.
TROUGH, WAVE: See WAVE TROUGH.
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.
TYPE OF TIDE: See TIDE, TYPE OF.