2005-08-09T11:27:21 Coastal Data Information Program (CDIP) Julie Thomas More information: http://cdip.ucsd.eduhttp://cdip.ucsd.edu Waves measurement and models Shoreline protection manual ARMI CORPS of Eng. Luis Bermudez MMI Julie Thomas Term A device used in wave buoys for measuring acceleration and buoy movement. ACCELEROMETER SURGE (1) The name applied to wave motion with a period intermediate between that of the ordinary wind wave and that of the tide, say from 2 to 60 min. It is low height, usually less than 0.9 m (3 ft). See also SEICHE. (2) see STORM SURGE. SURGE SEA, SEAS Waves caused by wind at the place and time of observation. SEA, SEAS SST See SEA SURFACE TEMPERATURE. SST Waves with a single height, period, and direction. REGULAR WAVES REGULAR WAVES DEEP WATER Water so deep that surface waves are little affected by the ocean bottom. Generally, water deeper than one-half the surface wavelength is considered deep water. Compare SHALLOW WATER. DEEP WATER SEA STATE SEA STATE Description of the sea surface with regard to wave action. NAUTICAL MILE The length of a minute of arc, 1/21,600 of an average great circle of the Earth. Generally one minute of latitude is considered equal to one nautical mile. The accepted United States value as of 1 July 1959 is 1,852 meters (6,076.115 feet), approximately 1.15 times as long as the U.S. statute mile of 5,280 feet. NAUTICAL MILE D<SUB>P</SUB> See PEAK DIRECTION. D<SUB>P</SUB> WAVE FREQUENCY The inverse of wave period. WAVE FREQUENCY A series of waves from the same direction. WAVE TRAIN WAVE TRAIN MEAN SEA LEVEL MEAN SEA LEVEL The average height of the surface of the sea for all stages of the tide over a 19-year period, usually determined from hourly height readings. BASIN SURGE, ENERGY BASIN SURGE that occurs within a partially enclosed area such as a man-made harbour or marina. BASIN SURGE, ENERGY BASIN The WAVE PERIOD determined by the inverse of the frequency at which a wave energy spectrum (WAVE SPECTRUM) reaches its maximum. PEAK PERIOD PEAK PERIOD FULLY-DEVELOPED SEA The waves that form when wind blows for a sufficient period of time across the open ocean. The waves of a fully developed sea have the maximum height possible for a given wind speed, FETCH and duration of wind. FULLY-DEVELOPED SEA SWASH The rush of water up onto the beach face following the breaking of a wave. SWASH 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. ASTRONOMICAL TIDE SETUP, WAVE Superelevation of the water surface over normal surge elevation due to onshore mass transport of the water by wave action alone. SETUP, WAVE The lowest part of a waveform between successive crests. Also, that part of a wave below still-water level. TROUGH OF WAVE TROUGH OF WAVE LONGSHORE BAR LONGSHORE BAR A sand ridge or ridges, runing roughly parallel to the shoreline and extending along the shore outside the trough, that may be exposed at low tide or may occur below the water level in the offshore. SHALLOW WATER SHALLOW WATER (1) Commonly, water of such a depth that surface waves are noticeably affected by bottom topography. It is customary to consider water of depths less than one-half the surface wavelength as shallow water. (2) More strictly, in hydrodynamics with regard to progressive gravity waves, water in which the depth is less than 1/25 the wavelength. Diagram showing the long-term distribution of wind speed and direction. WIND ROSE WIND ROSE The short-crested waves that may spring up quickly in a moderate breeze, and which break easily at the crest. Also known as WIND CHOP. CHOP CHOP HEAVE 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. WIND SEA Wave conditions directly attributable to recent winds, as opposed to swell. WIND SEA FOAM LINE FOAM LINE (1) The front of a wave as it advances shoreward, after it has broken. (2) Lines of foam such as those which move around the head of a rip current. DIFFRACTION OF WAVES DIFFRACTION OF WAVES The phenomenon by which energy is transmitted laterally along a wave crest. When a part of a train of waves is interrupted by a barrier, such as a breakwater, the effect of diffraction is manifested by propagation of waves into the sheltered region within the barrier's geometric shadow. Parallel to and near the shoreline. LONGSHORE LONGSHORE (1) In beach terminology an indefinite zone extending seaward from the shoreline well beyond the breaker or surf zone. (2) The zone which extends from the SWASH zone to the position marking the start of the offshore zone, typically at water depths of the order of 20 m. NEARSHORE NEARSHORE SURF (1) Breaking waves near the shore. (2) The wave activity in the area between the shoreline and the outermost limit of breakers. SURF EL NINO Warm equatorial water which flows southward along the coast of Peru and Ecuador during February and March of certain years. It is caused by poleward motions of air and unusual water temperature patterns in the Pacific Ocean, which cause coastal downwelling, leading to the reversal in the normal north-flowing cold coastal currents. During many El Nino years, storms, rainfall, and other meteorological phenomena in the Western Hemisphere are measurably different than during non-El Nino years. EL NINO WAVE HEIGHT WAVE HEIGHT The vertical distance between a crest and the preceding trough. See also SIGNIFICANT WAVE HEIGHT. MEAN LOWER LOW WATER (MLLW) The average height of the lower low waters over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. Frequently abbreviated to LOWER LOW WATER. MEAN LOWER LOW WATER (MLLW) PEAK DIRECTION PEAK DIRECTION The WAVE DIRECTION at the frequency at which a wave energy spectrum (WAVE SPECTRUM) reaches its maximum. Wave moving landward. INCIDENT WAVE INCIDENT WAVE Diagram showing the long-term distribution of wave height and direction. WAVE ROSE WAVE ROSE 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. Experience indicates that a careful observer who attempts to establish the character of the waves will record values which approximately fit the definition of the significant wave. SIGNIFICANT WAVE SIGNIFICANT WAVE DEEP WATER WAVES DEEP WATER WAVES A wave in water the depth of which is greater than one-half the WAVELENGTH. A series of waves generated in a laboratory, each of which has the same length and period. MONOCHROMATIC WAVES MONOCHROMATIC WAVES SIGNIFICANT WAVE HEIGHT The average height of the one-third highest waves of a given wave group or sample. In spectral analyses (like those applied by CDIP), significant wave height is often estimated as Hmo, 4 times the square root of the total energy ( Hm0 = 4(m0)^.5 ). SIGNIFICANT WAVE HEIGHT DEPTH The vertical distance from a specified datum to the sea floor. DEPTH SHORE NORMAL A line at right-angles to the bottom contours in the surf zone. SHORE NORMAL H<SUB>S</SUB> See SIGNIFICANT WAVE HEIGHT. H<SUB>S</SUB> SEA SURFACE TEMPERATURE SEA SURFACE TEMPERATURE The temperature of water at or near the surface of the sea. The seasonal and anual distribution of wave height, period and direction. WAVE CLIMATE WAVE CLIMATE SWELL SWELL Wind-generated waves that have traveled out of their generating area. Swell characteristically exhibits a more regular and longer period and has flatter crests than waves within their fetch (SEAS). The theoretical determination of future wave characteristics, usually from observed or predicted meteorological phenomena. FORECASTING OF WAVES FORECASTING OF WAVES The laboratory simulation of irregular sea states that occur in nature. RANDOM WAVES RANDOM WAVES A wave whose velocity of propagation is controlled primarily by the surface tension of the liquid in which the wave is traveling. Water waves of length less than about 2.5 cm are considered capillary waves. Waves longer than 2.5 cm and shorter than 5 cm are in an indeterminate zone between capillary and gravity waves. CAPILLARY WAVE CAPILLARY WAVE BASIN, BOAT A naturally or artificially enclosed or nearly enclosed harbor area for small craft. BASIN, BOAT The change waves undergo after they leave a generating area (FETCH) and pass through a calm, or region of lighter winds. In the process of decay, the significant wave height decreases and the significant wavelength increases. DECAY OF WAVES DECAY OF WAVES LOW TIDE (LOW WATER, LW) The minimum elevation reached by each falling tide. See TIDE. LOW TIDE (LOW WATER, LW) PIER A structure, usually of open construction, extending out into the water from the shore, to serve as a landing place, recreational facility, etc., rather than to afford coastal protection. In the Great Lakes, a term sometimes improperly applied to jetties. PIER CURRENT, LONGSHORE CURRENT, LONGSHORE The littoral current in the breaker zone moving essentially parallel to the shore, usually generated by waves breaking at an angle to the shoreline. (1) the highest part of a wave. (2) That part of the wave above still-water level. CREST OF WAVE CREST OF WAVE IRREGULAR WAVES Waves with random wave periods (and in practice, also heights), which are typical for natural wind-induced waves. IRREGULAR WAVES (1) Waves being locally formed and built up by the wind; SEAS. (2) Loosely, any wave generated by wind. WIND WAVES WIND WAVES The time for a wave crest to traverse a distance equal to one wavelength. The time for two successive wave crests to pass a fixed point. WAVE PERIOD WAVE PERIOD T<SUB>P</SUB> See PEAK PERIOD. T<SUB>P</SUB> GLOBAL POSITIONING SYSTEM (GPS) GLOBAL POSITIONING SYSTEM (GPS) A navigational and positioning system developed by the U.S. Department of Defense, by which the location of a position on or above the Earth can be determined by a special receiver at that point interpreting signals received simultaneously from several of a constellation of special satellites. The nontidal vertical water movement in a harbor or bay. Usually the vertical motions are low; but when oscillations are excited by a tsunami or storm surge, they may be quite large. Variable winds, air oscillations, or SURF BEAT also may cause oscillations. See SEICHE. HARBOR OSCILLATION (HARBOR SURGING) HARBOR OSCILLATION (HARBOR SURGING) WATER DEPTH WATER DEPTH Distance between the seabed and the still water level. A float; especially a floating object moored to the bottom. CDIP's buoys are equipped with sensors so that, in addition to floating, they can measure climatological variables such as wave height and water temperature. BUOY BUOY JETTY On open seacoasts, a structure extending into a body of water, which is designed to prevent shoaling of a chanel by littoral materials and to direct and confine the stream or tidal flow. Jetties are built at the mouths of rivers or tidal inlets to help deepen and stabilize a chanel. JETTY TSUNAMI A long-period wave caused by an underwater disturbance such as a volcanic eruption or earthquake. Also SEISMIC SEA WAVE. Commonly miscalled "tidal wave." TSUNAMI ATTENUATION 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. HINDCASTING In wave prediction, the retrospective forecasting of waves using measured wind information. HINDCASTING SEICHE SEICHE (1) A standing wave oscillation of an enclosed waterbody that continues, pendulum fashion, after the cessation of the originating force, which may have been either seismic or atmospheric. (2) An oscillation of a fluid body in response to a disturbing force having the same frequency as the natural frequency of the fluid system. Tides are now considered to be seiches induced primarily by the periodic forces caused by the Sun and Moon. (3) In the Great Lakes area, any sudden rise in the water of a harbor or a lake whether or not it is oscillatory (although inaccurate in a strict sense, this usage is well established in the Great Lakes area). The speed at which an individual wave advances. VELOCITY OF WAVES VELOCITY OF WAVES WAVE DIRECTION The direction from which a wave approaches. WAVE DIRECTION SURF BEAT Irregular oscillations of the nearshore water level with periods on the order of several minutes. SURF BEAT The transmission of waves through water. PROPAGATION OF WAVES PROPAGATION OF WAVES (1) The term which applies to the WIND WAVES and SWELL of lakes and oceans, also called a 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 velocity depends only upon the wavelength. SURFACE GRAVITY WAVE (PROGRESSIVE) SURFACE GRAVITY WAVE (PROGRESSIVE) The process by which the energy of the wave is returned seaward. REFLECTION REFLECTION 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. AMPLITUDE, WAVE AMPLITUDE, WAVE A rise above normal water level on the open coast due to the action of wind stress on the water surface. Storm surge resulting from a hurricane also includes that rise in level due to atmospheric pressure reduction as well as that due to wind stress. STORM SURGE STORM SURGE BIGHT BIGHT A bend in a coastline forming an open bay. A bay formed by such a bend. GRAVITY WAVE A wave whose velocity of propagation is controlled primarily by gravity. Water waves more than 5 cm long are considered gravity waves. Waves longer than 2.5 cm and shorter than 5 cm are in an indeterminate zone between CAPILLARY and GRAVITY WAVES. GRAVITY WAVE WAVE STEEPNESS The ratio or wave height to wavelength also known as sea steepness. WAVE STEEPNESS WAVE A ridge, deformation, or undulation of the surface of a liquid. WAVE GAUGE (GAGE) GAUGE (GAGE) Instrument for measuring the water level relative to a datum. UPWELLING The process by which water rises from a deeper to a shallower depth, usually as a result of offshore surface water flow. It is most prominent where persistent wind blows parallel to a coastline so that the resultant Ekman transport moves surface water away from the coast. UPWELLING MEAN WAVE HEIGHT MEAN WAVE HEIGHT The mean of all individual waves in an observation interval of approximately half an hour. In case of a Rayleigh-distribution 63% of the SIGNIFICANT WAVE HEIGHT. SURF ZONE SURF ZONE The zone of wave action extending from the water line (which varies with tide, surge, 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 to 10 meters. 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 TIDE, HIGH WATER (HW) HIGH TIDE, HIGH WATER (HW) WAVELENGTH The horizontal distance between similar points on two successive waves measured perpendicular to the crest. WAVELENGTH The periodic rising and falling of the water that results from gravitational attraction of the Moon and Sun and other astronomical bodies 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. TIDE TIDE BAR 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. The area in which SEAS are generated by a wind having a fairly constant direction and speed. FETCH FETCH INFRAGRAVITY WAVE, LONG WAVES INFRAGRAVITY WAVE, LONG WAVES Long waves with periods of 30 seconds to several minutes. REFRACTION OF WAVES (1) The process by which the direction of a wave moving in shallow water at an angle to the contours is changed: the part of the wave advancing in shallower water moves more slowly than that part still advancing in deeper water, causing the wave crest to bend toward alinement with the underwater contours. (2) The bending of wave crests by currents. REFRACTION OF WAVES BATHYMETRY BATHYMETRY The measurement of depths of water in oceans, seas, and lakes; also information derived from such measurements. WAVE SPECTRUM WAVE SPECTRUM In ocean wave studies, a graph, table, or mathematical equation showing the distribution of wave energy as a function of wave frequency. The spectrum may be based on observations or theoretical considerations. Several forms of graphical display are widely used. That part of an incident wave that is returned seaward when a wave impinges on a steep beach, barrier, or other reflecting surface. REFLECTED WAVE REFLECTED WAVE OCEANOGRAPHY OCEANOGRAPHY The study of the sea, embracing and indicating all knowledge pertaining to the sea's physical boundaries, the chemistry and physics of seawater, marine biology, and marine geology.