Showing papers on "Waves and shallow water published in 1970"

Longshore currents generated by obliquely incident sea waves: 1

Abstract: By using known results on the radiation stress associated with gravity waves, the total lateral thrust exerted by incoming waves on the beach and in the nearshore zone is rigorously shown to equal (E0/4) sin 2θ0 per unit distance parallel to the coastline, where E0 denotes the energy density of the waves in deep water and θ0 denotes the waves' angle of incidence. The local stress exerted on the surf zone in steady conditions is shown to be given by (D/c) sin θ per unit area, where D is the local rate of energy dissipation and c is the phase velocity. These relations are independent of the manner of the energy dissipation, but, because breaker height is related to local depth in shallow water, it is argued that ordinarily most of the dissipation is due to wave breaking, not to bottom friction. Under these conditions the local mean longshore stress in the surf zone will be given by (5/4)ρumax2 s sin θ, where ρ is the density, umax is the maximum orbital velocity in the waves, s is the local beach slope, and θ is the angle of incidence. It is further shown that, if the friction coefficient C on the bottom is assumed constant and if horizontal mixing is neglected, the mean longshore component of velocity is given by (5π/8)(s/C) umax sin θ. This value is proportional to the longshore component of the orbital velocity. When the horizontal mixing is taken into account, the longshore currents observed in field observations and laboratory experiments are consistent with a friction coefficient of about 0.010.

Edge‐, bottom‐, and Rossby waves in a rotating stratified fluid

Abstract: It is found that in a rotating stratified fluid bounded by a single rigid wall, edge waves may occur at all frequencies less than or equal to N sin a (a is the angle of the wall from the horizontal and N the Brunt‐Vaisala frequency). These decay exponentially away from the boundary, in a distance of O(S) wavelengths, for α = O(1), or O(S ‐1) wavelengths, for αS ≤ O(1), where S is the ratio of N to the Coriolis parameter f, taken for illustration to be large. The phase and energy both move with a component to the left, facing shallow water. The waves could, for example, appear as an internal tide at the continental rise or as baroclinic meandering of currents over a slope. The low‐frequency limit, αS ≪ 1, is studied in detail. To allow for large scales of motion other rigid boundaries and variations in f are included. The edge (actually “bottom") waves then merge with topographic‐planetary waves as the wavelengths increase; the familiar depth‐independent mode is found to be possible in the sea for...

Shallow water waves on shear flows

Abstract: An equation for waves on the surface of a flow with shear is deduced and shown to reduce by suitable scaling to the classical equation of Korteweg & de Vries, which describes such motions on a stationary flow. For steady flows the corresponding theory of cnoidal waves is obtained and the results of Benjamin (1962) for a solitary wave recovered.

Sea level at -175 m off the Great Barrier Reef 13,600 to 17,000 year ago.

Abstract: THE shelf around Australia, like many other continental shelves1, has its edge chiefly2–5 at depths of 120 to 130 m and is marked locally by terraces and notches, which register low stands of the sea during the Quaternary. From radiometric dates of shallow water fossils recovered from terraces in different parts of the world the lowest eustatic level of the sea during the past 35,000 yr is estimated to be −130 m, 16,000 yr ago6. More recent information, principally from Australian waters, suggests that the sea level may have stood much lower during this period. Dill7 and Conolly4 found submerged terraces with shallow water fossils and sediments between depths of 175 to 238 m in 39 of 78 narrow beamed echo sounder profiles made all around Australia. The continuity and consistent depth of the terraces indicate that there has been little tectonic warping of the continental margin since the terraces were formed. Similar features are reported off southern and Baja California7, and a shallow water mollusc from a deep terrace off Baja California has a radiocarbon date of 14,380±190 yr BP. Another record of shallow water fossils of similar age and depth relates to the south-eastern Caribbean Sea8, where fragments of algae and hermatypical corals at a depth of 157 m (Station index 1,203) have radiocarbon dates of 13,590±270 and 13,800±330 yr BP, and algae at 187 m (Station index 1,202) a date of 14,220±350 yr BP. These organisms did not necessarily live at sea level6 but, being reef dwellers, probably indicate shallow water. To date, the evidence from Australia is only morphological. Here we describe the occurrence and radiometric dates of two shallow water specimens collected in situ from deep terraces off the Great Barrier Reef during descents by J. J. V. in the Japanese research submersible Yomiuri in February 1969.

Field Observations of Dendraster excentricus, a Sand Dollar of Western North America

Abstract: Observations were made on behavior, distribution, and biotic relationships of the sand dollar Dendraster excentricus along the Pacific coast of California and Baja California, Mexico. Populations occur on sandy bottom in bays, tidal channels, and along the outer coast. Orientation and feeding behavior, which are related to water movement, vary between populations in the different habitats. In sheltered bays, where there is relatively little water movement, sand dollars remain in shallow water, frequently move, and lie flat on the bottom where they feed on deposited material. In tidal channelsand protected areas of the outer coast, habitats with moderate water movement, adults are more stationary, usually are in an inclined position, and feed primarily on suspended material. Density estimates and aggregation values are greatest in these populations. In outer-coast areas consistently exposed to heavy seas, where water movement is greatest, sand dollars are usually buried, and presumably feed on deposited material. Two types of distribution patterns occur in populations along the protected outer coast. In one type, the populations run parallel to shore as dense bands, and maintain a characteristic pattern that is reformed when disrupted by occasional heavy seas. Usually juveniles are most abundant shoreward, and move seaward with age. The outer margin of these populations is well-defined in 4-12 m of water, and here the largest individuals and greatest densities occur. Most of our observations are of these populations. The other type of distribution is similar, except that it extends into deeper water, and below about 10-15 m; individuals become progressively smaller with depth. Various other organisms coexist with the sand dollars, many of them using the inclined sand dollars as shelter or a hard substrate. Known predators include fishes, crabs and sea stars. Fouling by the barnacle Balanus pacificus also may contribute to sand-dollar mortality. At present, separate taxa for the ecologically different populations of D. excentricus are not justified.

The Measurement of Water Depth by Remote Sensing Techniques

Abstract: : The study demonstrates successful remote determination of shallow water depth by measuring wave refraction changes and using the Fourier transform plane for wavelength measurements with data obtained at a Lake Michigan test site. The study shows that the technique is suitable for use from spacecraft altitudes, provided that water waves of suitable length occur in the region of interest.

Gravity wave refraction by islands

Abstract: The refractive influence on tsunami run-up of the offshore bottom topography of islands is analyzed. Shallow water theory is used to treat problems in which the geometry resembles that of individual Hawaiian islands and in which the incident wave is plane and monochromatic.Mathematically, the differential equation for long-wave propagation is converted into an integral equation to which numerical methods are applied. Results of practical importance include the run-up on island coastal areas. The results are used in conjunction with earlier one-dimensional analyses to estimate the total tsunami run-up.

Probabilities of breaking wave characteristics

Abstract: Utilizing the hydrodynamic relationships for shoaling and refraction of waves approaching a shoreline over parallel bottom contours a procedure is developed to transform an arbitrary probability density of wave characteristics in deep water into the corresponding breaking characteristics in shallow Water A number of probability distributions for breaking wave characteristics are derived m terms of assumed deep water probability densities of wave heights wave lengths and angles of approach Some probability densities for wave heights at specific locations in the surf zone are computed for a Rayleigh distribution in deep water The probability computations are used to derive the expectation of energy flux and its distribution.

Planktonic Foraminifera: Differential Production and Expatriation off Baja CALIFORNIA1

Abstract: The species composition, living : dead ratios, morphology, and size distribution of planktonic foraminifera were studied in 54 depth-controlled tow samples using a 333-p net (O3,000 m) from northwest of Guadalupe Island, Baja California, Paired sampling and replicate tows permitted the determination of confidence limits on concentration and percentage estimates. Average concentrations of living foraminifera range from about l/m’ in shallow water to less than l/1,000 ms at depth, Concentrations of empty shells are between 3 to lO/l,OOO m3 throughout. The depth of equal standing stock for live and empty individuals is between 5,000 and 10,000 m. The minimum replacement time for the living populations corresponds to the settling time through this column and is between 5 and 40 days. The apparent replacement times vary considerably between species and between sizes within species. The living assemblage consists of a mixture of northern, central, and southern species dominated by northern ones. Central water species are relatively abundant immediately below the surface water. The southern element has a maximum at about 1,000-m depth. This distribution is in agreement with physical measurements, suggesting shallow entrainment of central water into the California Current and indicating a countercurrent at depth. It is suggested that the fauna contained in the oxygen-poor intermediate water is expatriated and that its great proportion of specimens with small terminal chambers (“kummerforms”) is due to unfavorable living conditions during submergence. The notion that kummerform development indicates termination or slowing of growth is supported by a trend toward increase of kummerform proportions in living populations in large shell sizes and at subsurface depths and by the relatively high empty shell output of kummcrforms. Oceanic stability of past ages may be recognized in fossil foraminifcral deposits if oceanic mixing enhances kummerform development and if the effects of differential preservation can be accounted for.

The Shallow Water Anomuran Crab Fauna Of Southwestern Baja-California Mexico

Abstract: Thirty-five species of anomuran crabs are reported from the 1964 \"Mag Bay\" Expedition, 19 orv\\hich are new records for the outer coast of southern Baja California, Mexico. A checklist and keys are appended for the 52 species of Anomura nov\\ known to inhabit this area. RESUMEN.—Durante la Expedicion \"'Mag Bay\" en 1964, se observaron treinta y cinco especies de cangrejos anomuros, diez y nueve de ellas encontradas por primera vez, en las costas occidentales de la zona meridional de Baja California. Mexico. Se incluye una lista y las claves correspondientes para las 52 especies de Anomuros observados hasta la fecha en aquellas regiones. The purpose of the \"Mag Bay\" Expedition of 1964 was to study the maritime biota along the coast of Baja California, Mexico, from Punta San Eugenio (Punta Eugenia) to the lower entrance of Bahfa Magadalena (Figs. 1, 2). Dr. Carl L. Hubbs, Scripps Institution of Oceanography, was the originator and leader of the expedition, which was supported by the Office of Naval Research. The scientific party was divided into three teams: Team 1, aboard the R/V HORIZON, was responsible for sampling in deep water; Team 2, in small craft, worked in the mangrove-estuarine environment; Team 3, aboard the Scripps vessel T-441, was responsible for \"on site\" fish poisonings, invertebrate and algal collecting, and otter trawling along the 20and 40 m depth contours in the area of study. Two of the authors (TSH and TBS) were members of Team 2, where SCUBAwas used in depths of one to 30 meters. A concerted effort was made to collect decapod crustaceans and echinoderms, as well as fish. The specimens were returned to the T-441, where they were kept alive until color notes and tentative identifications could be recorded. At the conclusion of the cruise, the anomuran crabs were forwarded to the Allan Hancock Foundation for study by the senior author (JH). Thirty-five species of Anomura were collected, of which 19 constitute new records for the outer coast of southern Baja California (Punta San Eugenio and southward) within the 40 m contour. A checklist and keys to all species known to fall within these geographical and bathymetrical limits are appended. This report is a Contribution from the Allan Hancock Foundation, no. 339 , supported by NSF Grant GB-2039, and a Contribution from the Scripps Institution of Oceanography, supported by NSFGrant GB2312 (to D. L. Fox). HISTORICAL RESUME The following anomuran crabs are presently known from the region under consideration: Miinida mexicana (Benedict, 1902), Dardaniis sinistripes (Rathbun, 1910), Pleuroncodes planipes, and Emerita analoga (Schmitt, 1921). In addition, Glassell (1936) reported on several porcellanids which he collected at Bahfa Magdalena. These included Petrolisthes hirtipes (Lockington), and the new species Orthochela pumila. Pisosoma erosa { = Megalobrachium erosum), and Porcellana magdalenensis ( = Pisidia magdalenensis). He also treated the porcellanid and hermit crabs from the Templeton Crocker Expedition of SAN DIEGO SOC. NAT. HIST.. TRANS. 16 (2): 13-32, 4 JUNE 1970 14 SAN DIEGO SOCIETY OF NATURALHISTORY VOL. 16 Figure 1. Map of Baja California, Mexico. Area delimited by the box on the western side of the peninsula is shown enlarged in figure 2. 1936 (Glassell, 1937a, 1937b). However, only one species comes within the scope of the present work, Paguristes bakeri Holmes, which was collected otT Isla Cedros (Glassell, 1937b.) Schmitt (1939) listed \"Paguristes species'' from Bahfa Magdalena, a form still awaiting description. To the known fauna Haig (1960) added 16 species of Porcellanidae. 1970 HAIG, HOPKINSANDSCANLAND:ANOMURANCRABS Figure 2. Map of Bahia Magdalena region, Baja California, Mexico. The presence of 19 additional species in this fauna, and the larger number of new records, attests to the effectiveness of SCUBAin an area already well surveyed by dredging and intertidal collecting. ANNOTATEDSPECIES LIST Family COENOBITIDAE Coenobita compressus H. Milne Edwards Cenobita compressa H. Milne Edwards, 1837: 241. Coenobita compressus -.Boone, 1931: 145, text-fig. 3; Holthuis, 1954: 16, text-figs. 4a-b. Recorded Range. —Santa Rosalfa, Golfo de California, to Estrecho de Magallanes. Islas Revillagigedo; Isla del Coco; Archipielago de Galapagos. Material. —Punta Belcher; above high tide at night; 2 Feb. 1964; Id', 2 9. Remarks. —Glassell (1937b: 242-243) stated: \"For the most part these terrestrial hermit crabs inhabit the land bordering on the sea. They select heavy shells for their abode. They are, in the main, vegetarians, though they do not limit their diet and may at times act as scavengers, or become carnivorous ... In addition they are good tree climbers.\" 16 SAN DIEGO SOCIETY OF NATURALHISTORY VOL.16 On Punta Belcher we observed that these animals are nocturnal. A search for their homesites was fruitless, although the crabs \"appeared\" within 17m of the camp just after dark, and could not be found after daybreak. Probably they had remained inactive in their shells along the upper tide marks during the day, and thus went unnoticed. Six to 10 individuals were observed feeding on dead or molted Pleuroncodes planipes which formed windrows on the beach. The range of this species is extended to the outer Baja California coast, and 300 km north along the outer coast. Family DIOGENIDAE Dardanus sinistripes (Stimpson) Pagurus sinistripes Stimpson, 1858: 22i (nom. nud): \\S59: S2. Dardanus sinistripes: Glassell, 1937b: 251. Recorded Range. —Bahfa Magdalena (Rathbun, 1910) and Isla Tiburon, Golfo de California, to Bahfa de Sechura, Peru. Material. —Off Boca de Santo Domingo; otter trawl; 40 m; 27 Jan. 1964; 1 ? . Laguna de Santa Maria: 1.2 m; 29 Jan. 1964; Id\". Color. —\"In alcohol, the carapace is buff with red markings. The chelipeds, purple and red, with the interior margins of the meri white; the teeth of the fingers white, bordered with yellow. The ambulatory legs are purple, their dactyli with dark brown setae, their meri and carpi blotched on a light ground with red\" (Glassell, 1937b). There are two narrow, dark bands, one median and the other proximal, on the eyestalk. Calcinus californiensis Bouvier Calcinus californiensis Bouvier, 1898: 380; Glassell, 1937b: 252. Calcinus californiensis: Chace, 1962: 627, text-figs. 5-6. Recorded Range. —Isla San Jose, Golfo de California, to Acapulco, Me'xico. Isla Clipperton. Material. —Punta Cala; 3 m; 31 Jan. 1964; Id, 1 ?. Roca de la Vela;6 m; 1 Feb. 1964; 2$. Inside Punta Tosca, in lagoon; 5 m; 4 Feb. 1964; 5c^, 2 9. Color. —The coloration of this and allied species, in both live and preserved material, was discussed in some detail by Chace (1962: 628). A broad white band at the base of the cornea and the solid dark color of the dactyls of the walking legs unmistakably identify the above specimens as Calcinus californiensis. Remarks. —The range of this species is extended to the outer Baja California coast, and 300 km north. Aniculus elegans Stimpson Aniculus elegans Stimpson, 1858: 234 («om. nud.): 1859: 83; Boone, 1931: 140, text-fig. 1. Recorded Range. —Golfo de California (exact locality not stated) to Cabo de San Francisco, Ecuador. Material. -Outside Bahfa Magdalena; 18 m; 1 Feb. 1964; 1 juv. Inside Punta Tosca, in lagoon; 5 m; 4 Feb. 1964; 1 ?. Off Punta Redonda; 15 m; 5 Feb. 1964; 6d\", 5?. Color. —Carapace red, with a pink area on the posterior part of the shield. Eyestalks tan. Chelipeds pink, with red on the fingers and on the distal half of the chelae. Dactyls of walking legs darkred; other segments pink. A broad, submedian red band on the propodus, a submedian red blotch on the anterior margin of the carpus, and a smaller median blotch on the anterior margin of the merus. Remarks. —Off Punta Redonda these hermits occurred under rocks in aggregates of 1970 HAIG, HOPKINSANDSCANLAND:ANOMURANCRABS 17 five or more. Porcellana paguriconviva Glassell were found in the shells of specimens collected at the same locality, an association that has not been recorded previously. The range of this species is extended to the outer Baja California coast, and 300 km north. Trizopagurus magnificus (Bouvier) Clibanarius magnificus Bouvier, 1898: 378. Clibanarius chetyrkini Boone, 1932: 29, text-fig. 8. Trizopagurus magnificus: Forest, 1952: 4, 12, text-figs. 2, 11, 18. Recorded Range. —Golfo de California (exact locality not stated) to Isla de la Plata, Ecuador. Archipielago de Galapagos. Material. —Roca de la Vela; 6 m; 1 Feb. 1964; 1 ?. Off Punta Redonda; 15 m; 5 Feb. 1964; 15. Color. —The species may be readily identified by the large, irregular pale blotches on a dark background which cover the carapace shield, eyestalks, chelipeds, and walking legs. Remarks. —The range of this species is extended to the outer Baja California coast, and 300 km north. Clibanarius panamensis Stimpson Clibanarius panamensis Stimpson, 1858:235 (nom nud.): 1859: 84; Holthuis, 1954: 23, text-figs. 7-8. Recorded Range. —Santa Rosalfa, Golfo de California, to Isla de la Correa, Peru. Material. —Laguna de Santa Marfa; in +1 mand out of water; 29 Jan. 1964; 8c?, 1 ?. Color. —Hermits of this species may be recognized immediately by the color pattern of the walking legs, which consists of longitudinal dark and light stripes, subequal in width, on each segment. Remarks. —The range of this species is extended to the outer Baja California coast, and 300 km north. Isocheles pilosus (Holmes) Hoiopagurus pilosus Holmes, 1900: 154;Schmitt, 1921: 127, pi. 17 fig. 2; Ricketts and Calvin, 1939: 189, pi. 39 fig. 2. Isocheles pilosus: Forest, 1964: 294. Recorded Range. —Off San Francisco Bay, California, to Estero de Punta Banda, outer Baja California. Material. —Punta Abreojos, Bahfa de Ballenas; +.7 m while wading; 29 Jan. 1964; 1 . 2.5 miles west of Boca de Santo Domingo; 16' otter trawl; 14-20 m; 26 Jan. 1964; Id\". Outside Punta Hughes; 20 m; 30 Jan. 1964; 1 2 (juv.). Punta Pequena, Bahfa de San Juanico; 3 m; 8 Feb. 1964; Id\", 1 juv. Rem

The Wave Resistance of an Air-Cushion Vehicle in Accelerated Motion

Abstract: The report is concerned with the theoretical wave resistance of an air cushion vehicle (ACV) traveling over water of uniform finite or infinite depth, in steady or unsteady motion. Referring first to steady motion, it is shown that the unrealistic oscillations in the wave resistance curve at low Froude numbers found by previous workers can be eliminated by using a smoothed out pressure distribution rather than one with sharp edges studied exclusively in the past. The main result of unsteady motion calculations is that the peak wave resistance in shallow water, even in moderately accelerated motion, is appreciably less than the corresponding steady-state value. One feature of unsteady motion is that besides wave resistance there is another mechanism transferring energy to the free surface which is called the dynamic extention power. Contrary to intuition, the wave resistance in unsteady motion over finite depth sometimes becomes negative at supercritical Froude numbers before finally approaching zero at infinite speed. (Author)

The shallow water equations

Abstract: In this paper a set of exact nonlinear equations is derived for gravity flows. By assuming the flow to be shallow and assuming the vertical acceleration to be small these equations reduce to the classical equations for long waves in shallow water. If only shallowness is assumed a set of equations results, which admits in the steady case periodic solutions for Froude numbers smaller than 1 and laminar jumps for Froude numbers larger than 1. In the last section potential flows are discussed.

Bathymetry and Bottom Structure of Zones Near the Island of Elba Used for Acoustical Trials in Shallow Water

Abstract: : Two shallow-water zones situated north and south-east of the Island of Elba have been surveyed to obtain information about the bottom conditions. The area to the north of the island has a depth of 100 m to 130 m and a very flat bottom covered with clay and sand-clay sediments. The area to the south- east of the island is of the same depth and has a flat bottom covered with clay sediments. In this area a very strong acoustic reflector exists under the sedimentary layer.

The theory of wave refraction in shoaling water, including the effects of caustics and the spherical earth,

Abstract: : The existing wave refraction theory for surface water waves fails to predict wave behavior at and near a caustic. It is also inadequate for computing ray paths and refraction coefficients for waves traveling over large expanses of shoaling water. In the vicinity of a caustic, ray crossings occur, and the wave amplitude, according to existing theory, becomes infinite. This is, of course, devoid of physical meaning. The conventional equations for the ray path and ray separation are derived in Cartesian coordinates and therefore are valid only for a relatively small area of the ocean that can be considered as a plane surface. It is expected that considerable error in the ray patterns will occur if these equations are used for larger areas in which the curvature of the earth plays an important role. In order to overcome the first difficulty, the linearized wave equations were first modified in such a way that the bottom slope was taken into account. To solve the second problem, Fermat's principle was applied directly to the spherical polar coordinate system and the equations for the ray path and ray separation were derived in terms of latitude and longitude.

An Echo-Sounding Record and a Sound Transmission Record Showing Internal Waves.

Abstract: : An echo-sounding record taken from R.V. CLIONE in shallow coastal water showed a strong return from a 'cloud' in the lower half of the water column, the cloud apparently consisting of zooplankton and larval fish. Its upper surface varied sinusoidally in depth with amplitude about 10 m and period about 7 min. Two hours earlier the level of 2 kHz sound, received on CLIONE from a bottom-laid source 2 km distant, varied through several dB with period about 5 1/2 min. The regularity of the records, together with other evidence, suggests internal waves controlled by the varying temperature structure and current flow through the tidal cycle. The apparent wavelength reduces with time from about 100 m to about 40 m, and perhaps less. The measured shear flow in the tidal stream is of the right order to affect the stability of the water column, but very extensive measurements would be needed for a detailed check with theory. (Author)

An Experimental Study of Gravity Wave Behavior Near a Straight Caustic

Abstract: : An experimental study of gravity wave behavior near a straight caustic generated on a uniformly sloping bottom was carried out in a 4.26 meters (14 feet) square and 30.48 centimeters (1 foot) deep wave tank. Gravity waves were generated in shallow water of constant depth and propagated toward a portion of the tank where the depth increased linearly to a value equivalent to deep water. The straight line which the depth started to increase was 50 degrees to the wave crests at the generation source. The waves propagated up to this line, then refracted, totally reflected, and turned back toward the shallow water. The results of the experiment show that the experimental model not only successfully produces a caustic but also verifies the theoretical results near the caustic derived recently by Chao (1970) within a linear theory. When waves approach the caustic their amplitudes increase monotonically and attain maximum values within the caustic boundary that are about two times the amplitude in the source region. Near the caustic in the shadow region, the amplitudes decrease exponentially. (Author)

Adaptive Moving Grid Solutions of a Shallow- water Transport Model with Steep Vertical Gradients

Abstract: We investigate the use of a boundary-fitted moving adaptive grid technique in vertical direction for the numerical modeling of transport in multi-dimensional shallow-water applications. The difficulty with such modeling is that both the non-horizontal bottom and the free water surface, as well as nearly-horizontal regions of high gradient are to be represented accurately. The results that we present show that by using a moving grid that adapts automatically to the solution and is fitted to both the bottom and the free surface, it is possible in principle to model all relevant transport processes.

Effect of Viscosity on Long Waves in Shallow Water

Abstract: A linearized theory is used to investigate the effect of viscosity on long gravity waves in shallow water. The propagation of an initial disturbance to the surface is considered and an asymptotic solution to this problem is obtained.

Deformation of rotational tidal currents in shallow coastal water

Abstract: Along gently sloping coasts of seas having rotary tidal currents, the symmetry of the rotary current is interrupted where the water is shallow As a result, residual counter currents are formed The dynamics of such a current system are described based on current measurements in the Elbe Estuary (southeastern North Sea) The residual currents of this area result in the movement of bottom sediment and are most likely responsible for a series of similar appearing morphologic features.

An Investigation Of The Shoaling Of Large Amplitude Internal Waves UsingComputational Fluid Dynamics

Abstract: The transformation of internal waves in shallow water is important for stuhes of energy dissipation and for enhanced mixing of nutrients and pollutants in the ocean. The wave transformations are also important because they affect the propagation of sound in the upper surface layers of the ocean and the flows induced by the waves may affect moored oil platforms and submersibles. In this paper attention is focussed on the behaviour of a typical large amplitude internal wave passing into shallow water. A Computational Fluid Dynamics (CFD) code is used to solve the 111, two-dimensional time dependent conservation equations for the fluid. Turbulence is modelled using a two equation turbulence model with account taken of the effects of stratification on turbulence. The CFD sirnulations predict the wave transformations occurring as the primary wave propagates on-shelf and the velocity distributions, turbulence production and fluid transport induced by passage of the waves.

Numerical Simulation Of Middle-AmericaTrench Generated Tsunamis, Their CoastalArrival And Inundation Patterns In Mexico

Abstract: To assess the extent and consequences of Middle America Trench generated tsunami impact to Eastern Pacific coastal communities of Mexico, computer simulations are performed. The tsunami source is described as an ocean water disturbance generated by an earthquake sea-floor deformation, assumed as a mirror sea-surface motion image. Deep water linear wave theory for the generation and far ocean propagation, and shallow water non-linear wave theory close to the shore are considered. Nonlinear discharge-depth relationships conditioned to the state of the water level at the boundaries, are used to model the flooding and recession at the coast. The computations are carried out through an explicit finite-difference numerical integration algorithm for interconnected discrete grids of different sizes. One of the most recent and well documented tsunamis in Mexico, considered as representatives of highly probable average cases, is satisfactorily modeled. Source parameters from large tsunamigenic past-earthquakes at seismic gaps off the Middle America Trench are used to simulate extreme future tsunamis. Inundation maps showing water runup and extension of flooding for some densely populated coastal areas and major industrially developed ports of the Eastern Pacific coast of Mexico, are produced for civil protection purposes.

Wave investigations in shallow water

Abstract: Examination of the significant heights of zero-crossing waves in the Elbe Estuary has yielded two noteworthy results: 1 In the deeper water of the estuary, the value of the quotient relating the significant and the mean wave heights is larger than on the bordering tidal flat. 2. The value of this function is dependent on the height of the waves; on the tidal flat this dependency is considerably more sensitive than in deeper water. With increasing wave height the value of significant wave height divided by mean height becomes smaller The propagation direction of waves moving onto the tidal flat is contingent upon the position of intertidal channels Such channels sharply reduce the possible propagation directions The waves nearly always move up-channel regardless of the wind direction It is possible to derive special wave period and wave height distributions representing the conditions m very shallow water.

Water waves produced by cratering explosions in shallow water.

Abstract: : In the course of developing the capability of predicting the characteristics of water waves generated by explosions detonated in shallow water beneath the ocean floor, the pertinent data from past experiments were analysed using dimensional analysis as a framework. Data were examined from one series of high explosive cratering experiments detonated beneath the floor in shallow water, and from two series of high explosive experiments and one nuclear explosive experiment detonated above the floor in shallow water. The data indicate that the maximum radius of the water column produced by the explosion is proportional to the cube root of the ratio of explosive yield to ambient pressure at the point of detonation. Further, the data show that the maximum radius of the column of water is proportional to the square root of the product of wave height and distance from the source. The conclusions of this scheme of analysis are being tested with hydrodynamic computer code calculations.

A Parametric Study Of Wind Wave SpectrumRepresentations For Shallow Water

Abstract: Different wind wave spectrum representations for shallow water are compared from a parametric point of view, including formulations with both constant (TMA and FRF spectra) and variable (Wallops-SW and GLERL spectra) frequency exponents. The results of the research clearly show the necessity of at least four parameters in order to achieve an adequate representation of the full range of the spectrum in non-saturated or decaying seas propagating in shallow water. Furthermore, when the modelling of the high frequency range is not of special interest, the total number of independent parameters could be reduced to only three without considerable loss of accuracy. Comparisons of theoretical shallow water spectral forms with spectra calculated from actual field measurements do not show any definite tendency in performance, being possible to obtain good results with any of the studied spectra. So, the selection of which spectrum to use in a particular application is still a quite subjective decision, being of importance the availability of input parameters needed for each model.