bluuebunny/crossref_metadata_2025 huggingface dataset:
CAPE HATTERAS BEACH NOURISHMENT
Authors: Fisher John S. , Felder Wilson N.
Published: June 2019

The 1973 beach nourishment at Cape Hatteras placed approximately 465,000 m on the subaerial beach. Eighteen months later, about 51 percent of this material remained on the beach. During this period there were relatively few major storms, and this mild wave climate is largely responsible for this high retention. At the end of this monitoring period the beach was stable and fully capable of providing shoreline protection and recreation. A correlation is presented relating storm erosion with the complete storm wave climate, including a post-storm period. A new parameter is defined which includes a measure of wave steepness and longshore current velocity.
PREDICTION OF WAVE-INDUCED SEAFLOOR MOVEMENTS
Authors: Kraft Leland Milo , Watkins David James
Published: June 2019

Foundation design for offshore structures in areas where wave-induced bottom pressures cause submarine mud slides requires a knowledge of the potential depth of slide and of the magnitude and distribution of soil movements below the slide. Several methods have been developed to evaluate the stability of the seafloor due to wave-induced bottom pressures. These methods are reviewed and an improved procedure is presented. This procedure makes use of finite element analysis and combines in a rational manner oceanographic information on wave statistics with stress-strain behavior of soils under cyclic load conditions in order to evaluate the effects of a given storm history on the behavior of submarine sediments.
SCOUR AROUND MODEL PIPELINES DUE TO WAVE ACTION
Authors: Herbich John B.
Published: June 2019

The size, number and application of offshore pipelines are steadily increasing. At the same time, the incidence of reported pipeline failures is also increasing. There appear to be several reasons for these failures, and they can be placed in two basic categories: 1. inadequate cover, and 2. low "specific gravity" of the pipeline. Under the first category the depth of burial may be insufficient, the type of burial material may be inferior to the material alongside the trench, or the compaction of cover material may be inadequate. Under the second category the pipe may actually float up to the surface from the ocean bottom as material around the buried pipe liquifies. An extensive literature search revealed that many studies were conducted by Meyers (1936), Waters (1939), Johnson (1940), W.E.S. (1940), Rector (1954), Wiegel, et al (1954), Saville (1957), Iwagaki and Noda (1962), Nayak (1972), Noda (1972), and Earattupuzha (1974). In general, two types of "equilibrium profiles" were developed in the laboratory flumes, the "ordinary" and the "storm" (sometimes referred to as summer and winter profiles). Despite numerous previous investigations, knowledge of the "scale effects" involved in equilibrium beach profiles is inadequate. Many authors have analyzed model data without stating the relation between model and prototype dimensions. In addition, many have claimed certain phenomena observed in the model to be independent of initial slope. An extensive laboratory study was conducted to evaluate the development of underwater bars and scour patterns with the pipeline buried at various depths below the ocean bottom. Pictures of the beach profile were taken at specific time intervals through the glass wall of the wave tank. Attempts were made to correlate equilibrium profile geometric quantities, such as depth of offshore bar, scour depth and berm height with the wave characteristics. Qualitative agreement between laboratory and natural beach profiles were demonstrated by trial and error fitting of one to the other.
FIELD EXPERIMENT ON BEACH GRAVEL TRANSPORT
Authors: Hattori Masataro , Suzuki Takasuke
Published: June 2019

To examine the longshore transport processes of beach gravels under wave action, a field experiment was performed by tracing the dacite blocks injected on Fuji Coast, Shizuoka Prefecture, Central Japan. The mean dislocating velocity of the tracer was 2 to 3 m/day under normal sea conditions, while under storm conditions it reached about 400 m/day. This -velocity was fairly proportional to the longshore component of incident wave energy flux. The longshore variations of the size and shape of beach gravels were mainly resulted from the progressive attrition and impact breakage of beach gravels rather than from the selective transport.
SLED SYSTEM FOR PROFILING SUSPENDED LITTORAL DRIFT
Authors: Coakley J.P. , Savile H.A. , Pedrosa M. , Larocque M.
Published: June 2019

There are many factors which suggest that littoral zone processes in the Great Lakes differ substantially from those of the marine coasts described in the existing coastal research literature. Among these factors are the lack of an appreciable tidal cycle; the predominance of relatively short, steep, waves; the virtual absence of swell waves; and the presence of shore fast ice in winter. As a result, many of the empirical relationships derived for marine coasts might be of questionable applicability to Great Lakes coasts. The present study, which represents only one phase of a long-term project designed to develop more specific littoral transport relationships, is aimed at obtaining accurate, direct estimates of the actual littoral transport at an experimental site located at the western end of Lake Ontario. This paper will describe a mechanical system designed to collect a series of time-averaged samples of suspended sediment for concentration determinations as well as flow velocity and water depth at locations across the surf zone. Some preliminary results of the field program using the system will also be presented and discussed.
THE OBSERVED JOINT DISTRIBUTION OF PERIODS AND HEIGHTS OF SEA WAVES
Authors: Goda Yoshimi
Published: June 2019

Analysis is made of 89 records of surface waves for the joint distribution of the heights and periods of zero up-crossing waves. Records are classified into five groups according to the rank of the correlation coefficient between individual wave heights and periods, and the data of the joint distribution are presented for five groups separately. In comparison with the present data, the theory of Longuet-Higgins for a narrow band spectrum can describe the joint distribution in its upper portion with high waves when the spectral width parameter is fitted to the marginal distribution for wave periods, although the joint distribution in the lower portion with low waves shows deviation from the theory. Another theory by a group of C.N.E.X.O. based on the distribution of positive maxima can describe the general pattern of observed distribution better than the former theory, but the agreement remains qualitative. The present data also suggests that the joint distribution of wave periods and heights may be parameterized with the correlation coefficient between wave heights and periods.
PREDICTION OF BEACH PLANFORMS WITH LITTORAL CONTROLS
Authors: Perlin Marc , Dean R.G.
Published: June 2019

Three numerical models representing shoreline response are desscribed and applied to a number of problems of coastal engineering interest. Included are: (1) a one-line explict model, (2) a one-line implicit model, and (3) a two-line explicit model. Simplified refraction and diffraction schemes are incorporated into the models. The models allow grid elements to be activated and deactivated as sand is initially deposited in or the last sand removed from a grid at a jetty inclined to the shoreline. The one-line explicit model and twoline explicit model are similar to those described by Bakker, Breteler and Roos'3'. The one-line implicit model offers the advantage of stable computations for much longer time steps. Example applications of shoreline response are presented to illustrate the utility of the model including: permeable versus impermeable jetties, shoreline perturbations caused by jetties which are aligned with the incoming waves versus jetties perpendicular to shore, shoreline response inside a groin compartment and the effect of a littoral barrier. In addition, the one-line implicit model is applied to predict the shoreline response in the vicinity of an offshore breakwater at Channel Islands Harbor, California where sediment is accumulated and dredged periodically. In this case, excellent shoreline response data are available from the prototype; however, only visual wave observations were available for this comparison and it was found necessary to increase the sediment transport relationship fourfold to achieve even approximate correspondence. Numerical models offer a powerful means which, when combined with good judgement, should strengthen the coastal engineer's ability to predict the effects of a coastal engineering design. The research needs to improve numerical modeling capabilities are presented.
IMPORTANCE OF HANDLING LOSSES TO BEACH FILL DESIGN
Authors: Hobson R.D. , James W.R.
Published: June 2019

Beach nourishment models commonly employed by the U.S. Army Corps of Engineers compare textural properties of native beach and dissimilar borrow sediments to determine overfill and renourishment requirements for beach fill projects. It is assumed for these comparisons that the texture of borrow sediments is unchanged by dredging and handling operations but investigations have shown that significant handling losses do, in fact, occur. This paper presents results from four field studies that document textural changes caused by dredging and sediment handling at Rockaway Beach, NY, and at New River Inlet, NC. Errors associated with calculating volumes of sediment dredged and lost using standard surveying and production methods are discussed and an alternate method is presented as a handling-loss model that compares bottom and dredged sediment texture to determine volumes lost. The results of the studies presented are that handling operations do create significant changes in bottom sediment texture which, in turn, do affect beach fill model calculations by generally improving the predicted performance of these sediments as fill. The proposed handling-loss model predicts volumetric losses that greatly exceed losses generally anticipated during project construction. Discrepancies between loss estimates are discussed in terms of possible inadequacies of the model and of mechanisms that might consistently minimize losses using the standard methods for determining dredged sediment volumes.
SOME FACTS AND FANCIES ABOUT BEACH EROSION
Authors: Silvester Richard
Published: June 2019

Coastal defense up to the present has employed seawalls, groynes and renourishment, all of which do not tackle the basic problem of lack in sediment supply from upcoast. The need is for sufficient sand to be continually available for the formation of the defensive offshore bar. If means are provided for this material to be returned directly on shore by subsequent swell, a stable situation 'ensues. Such normal re-deposition occurs within bays formed between headlands which have reached equilibrium shape or nearly so. Comparisons are made between various stabilization procedures. The influence of sand characteristics in renourishment is discussed. Stabilization of coasts has been carried out over many decades. The remedies have taken three major forms, namely, seawalls, groynes, and in more recent times sand renourishment. Whilst shapes and orientation of these structures have been varied in order to optimise protection, engineers in the main have relied upon bigness for greater reliability. Investment in dredging to supply sediment "temporarily" to beaches is growing prodigiously. It is now time to sit back and reassess the situation, so as to determine a change of outlook, be it only slight, that may effect greater long term economies.
FACTORS GOVERNING THE DISTRIBUTION OF DREDGE-RESUSPENDED SEDIMENTS
Authors: Bohlen W. Frank
Published: June 2019

Field observations are analyzed to determine the primary factors governing the distribution of sediments suspended by clam-shell bucket dredge operations. These data show the plumes produced under typical estuarine conditions to be relatively small scale features having maximum longstream dimensions of approximately 700 m. Plumes can be considered to consist of three contiguous zones: an initial mixing zone, a secondary zone and a final mixing zone. The initial mixing zone immediately adjacent to the dredge has dimensions governed by bucket induced mixing and suspended material concentrations determined by dredge efficiency. Observations indicate that dimensions can be reasonably estimated using wake theory and that efficiencies result in the introduction of 2-4% of the sediment mass contained in each bucket load. Resultant concentrations range between 200 and 400 mg/x,. Progressing downstream into the secondary mixing zone concentrations decay rapidly due primarily to gravitational settling. The observed decay rates indicate an average settling velocity of 4.7cm/sec well in excess of values based on the grain size characteristics of the dredged sediment. The behavior suggests significant particle agglomeration within this area. At the downstream limit of this zone distributions become essentially exponential in character and remain so through the final mixing zone. In this area concentrations progressively approach the upstream background levels and variations are governed primarily by diffusion. In each of these zones the observed distributions appear amenable to relatively straightforward modeling.
MOVABLE BED MODEL TESTS ON DUNE EROSION
Authors: Vellinga P.
Published: June 2019

The primary sea defence system of the Netherlands consists for a large part of sandy beaches and dunes. The row of dunes, however, is rather narrow in some places, due to long-term erosion, and reinforcement has become necessary (Figure 1 and 2). In this connection a special governmental committee requested the co-operation of the Delft Hydraulics Laboratory to developed a design criterion for a dune sea defence system that could withstand a storm surge with a frequency of occurrence of once in 10,000 years (Figure 3). For that purpose all available field observations on dune erosion were analysed and a provisional, empirical, guide-line was developed in 1972 \_\J , but because of the limited amount of field data and the complexity of a theoretical approach it was decided to check the validity of this guide-line by means of a model investigation. As no adequate scaling relationships are available for movable bed models with waves, the tests were set up in the form of a scale series. A large number of two-dimensional tests with various geometric scales using two types of sand (D50 = 225 um and D50 = 150 urn) was carried out in 1975.
WAVE TRANSMISSION THROUGH TRAPEZOIDAL BREAKWATERS
Authors: Madsen Ole Secher , Shusang Paisal , Hanson Sue Ann
Published: June 2019

In a previous paper Madsen and White (1977) developed an approximate method for the determination of reflection and transmission characteristics of multi-layered, porous rubble-mound breakwaters of trapezoidal cross-section. This approximate method was based on the assumption that the energy dissipation associated with the wave-structure interaction could be considered as two separate mechanisms: (1) an external, frictional dissipation on the seaward slope; (2) an internal dissipation within the porous structure. The external dissipation on the seaward slope was evaluated from the semi-theoretical analysis of energy dissipation on rough, impermeable slopes developed by Madsen and White (1975). The remaining wave energy was represented by an equivalent wave incident on a hydraulically equivalent porous breakwater of rectangular cross-section. The partitioning of the remaining wave energy among reflected, transmitted and internally dissipated energy was evaluated as described by Madsen (1974), leading to a determination of the reflection and transmission coefficients of the structure. The advantage of this previous approximate method was its ease of use. Input data requirements were limited to quantities which would either be known (water depth, wave characteristics, breakwater geometry, and stone sizes) or could be estimated (porosity) by the design engineer. This feature was achieved by the employment of empirical relationships for the parameterization of the external and internal energy dissipation mechanisms. General solutions were presented in graphical form so that calculations could proceed using no more sophisticated equipment than a hand calculator (or a slide rule). This simple method gave estimates of transmission coefficients in excellent agreement with laboratory measurements whereas its ability to predict reflection coefficients left a lot to be desired.
COMBINATION EFFECT OF PNEUMATIC BREAKWATER AND OTHER TYPE BREAKWATER ON WAVE DAMPING
Authors: Iwagaki Yuichi , Asano Toshiyuki , Honda Tsutomu
Published: June 2019

This paper deals experimentally with combinations of the pneumatic breakwater and other type breakwaters in order to increase the effectiveness of wave damping. Firstly, a submerged breakwater is picked up, and the wave damping effect of this combined type breakwater is examined. Results obtained in this experiment show that some improvements on the wave damping are found for low frequency waves that cannot be damped by the pneumatic breakwater only. The reason of appearence of the combination effect is explained that a part of energy of the transmitted waves over the submerged breakwater transfers to shorter period waves. Secondly, a floating breakwater is combined with the pneumatic breakwater. Experiments show that the transmission factor for high frequency waves becomes smaller than that of the pneumatic breakwater only, while there is not so much wave damping effect for low frequency waves even when the floating breakwater is combined. In addition, a guide plate is set below the bottom of the floating breakwater in order to increase the horizontal flow velocity for a given air discharge. It is found that the velocity of horizontal surface flow by using the guide plate increases as much as about 1.3 times that in the case of the pneumatic breakwater only. As a result, a little improvement on the wave damping due to the guide plate is also found.
NON-CONSERVATIVE WAVE INTERACTION WITH FIXED SEMI-IMMERSED RECTANGULAR STRUCTURES
Authors: Steimer Robert B. , Sollitt Charles K.
Published: June 2019

Previous attempts to analytically describe wave reflection and transmission at surface penetrating structures have neglected losses due to flow expansion, contraction, and skin drag along the structure boundaries (Black and Mei, 1970; Ijima, et al., 1972). The model described in this study includes these effects and allows for the inclusion of a dissipative medium such as rubble or closely spaced piles in the region beneath the structure. The problem of a fixed, two-dimensional structure in a train of monochromatic incident waves is modeled, as shown in Figure 1. The solution allows for 1) variable structure length and draft, 2) different depths in the regions fore, aft, and beneath the structure, 3) variable wave amplitude and period, and 4) turbulent and inertial damping in the region beneath the structure. An equivalent work technique is applied to linearize the damping beneath the structure, yielding a potential flow problem in all three regions. Amplitudes for the resulting series of eigenfunctions in each region are determined by matching pressure and horizontal mass flux at the region interfaces, orthogonalizing these expressions over the depth, and simultaneously solving the resulting equations to yield complex reflection and transmission coefficients. Complex horizontal and vertical force coefficients for the structure are also determined from the integrated Bernoulli equation. The solution technique is computationally efficient. In general, five modes in the eigen series provide satisfactory convergence for the various hydrodynamic parameters. Approximately six-tenths of a computer system second are required to solve for a single wave-structure condition. The results compare favorably with variational methods used by others.
EFFECTS OF WAVE GROUPING ON BREAKWATER STABILITY
Authors: Johnson R.R. , Mansard E.P.D. , Ploeg J.
Published: June 2019

It has been found that certain sequences of waves, such as occurring within well defined wave groups, can cause greater damage to rubble mound structures, than equally high individual waves dispersed throughout a wave train. It has therefore been necessary to develop a new wave synthesizing technique, which allows control of the phasing of the wave frequencies, so that a similar degree of wave grouping can be produced in the laboratory as is expected to occur at a particular location in the prototype. Also, during the course of this investigation, an attempt was made to simulate the strength of concrete armour units to the correct model scale. The breaking of armour units, due to their rocking or being displaced, resulted in a much higher percentage of damage, than would have been possible to predict from tests with commonly used model armour units.
DOLOS-ARMORED BREAKWATERS: SPECIAL CONSIDERATIONS
Authors: Carver Robert D. , Davidson D. Donald
Published: June 2019

Rubble-mound breakwaters are used extensively throughout the world to provide protection from the destructive forces of storm waves for harbor and port facilities. In some locations, a proposed rubble-mound breakwater may be subject to attack by waves of such magnitude that quarrystone of adequate size to provide economic construction of a stable breakwater is not available. Under these circumstances, it is required that the protective cover layer consist of specially shaped concrete armor units. In 1966, Merrifield and Zwamborn (1) introduced a new shape of armor unit, the dolos (Figure 1) which was acclaimed to have much higher stability characteristics than any existing armor unit. Site-specific model tests conducted at the U. S. Army Engineer Waterways Experiment Station (WES) by Davidson (2); Carver (3); Bottin, Chatham, and Carver (4): and Carver and Davidson (5) have shown dolos to exhibit an excellent stability response when exposed to breaking wave conditions. Comprehensive stability tests of dolos also have been conducted at WES by Carver and Davidson (6) for a wide range of nonbreaking wave conditions. These tests used randomly placed dolosse with a first underlayer stone weight of W /5 and a density of units per given area (N/A) equal to 0.83 V~2'3, i!e., n=2, k =0.94, and P=56 percent. It was concluded from this study that the stability response of dolos can be adequately predicted by the Hudson Stability Equation for the range of wave conditions investigated. Their data indicated an average stability coefficient (K) of 33 for dolosse use in a nonbreaking nonovertopping wave environment. Based on the lower limit scatter of their data, a K of 31 was approved for design.
PERFORMANCE OF DOLOS BLOCKS IN AN OPEN CHANNEL SITUATION
Authors: Brebner Arthur
Published: June 2019

Tests on 100 gm model dolos units on the bed of an open-channel under steady state turbulent flow reveal that the dolos unit has no inherent interlocking property that would make it preferable to ordinary armour stone of the same weight in resisting movement. However interlocking can occur when dolos units are placed on a slope since the natural angle of repose of dolos units is much greater than that of ordinary armour stone, thus accounting for the enhanced Kp of dolosse in a breakwater situation.
WAVE FORCES ON A ROW OF CYLINDRICAL PILES OF LARGE DIAMETER
Authors: Berkhoff J.C.W. , V.d. Weide J.
Published: June 2019

In order to determine wave forces on a row of three cylindrical piles (Figure 2), a numerical computation procedure was applied using a solution of the Helmholz equation, in which the scattered wave field is described as the result of a series of singular sources located along the circumference of the pile [^Berkhoff, 1976, reference lj . Results of the computations were verified by means of model experiments, using both regular and irregular waves. It is shown that for the two pile geometries, included in the study, strong mutual interference will occur, resulting in transverse forces which are much higher than those found for single piles.
CHANGES IN HEIGHT OP SHORT WAVES ON LONG WAVES
Authors: Sato Michio , Nakamura Kazuo
Published: June 2019

In this paper we describe an experimental study on changes in height of short gravity waves on long waves. Experiments were conducted by making mechanically generated long waves superpose on mechanically generated short waves in a wave flume of 30m long and lm wide. Exact solution by Longuet-Higgins and Stewart explained our experimental results, but approximate expression a'= a,(l+P) which is widely accepted seemed to be inadequate to explain our results.
VOCOIDAL THEORY FOR ALL NON-BREAKING WAVES
Authors: Swart D.H. , Loubser C.C.
Published: June 2019

The ideal theory for the prediction of wave-induced phenomena should be sufficiently accurate in all relative water depths, easy to apply and extensively tabulated. No available theory meets all these requirements. Vocoidal theory has been developed for application in all water depths. An extensive evaluation against experimental data proves that this theory meets the above requirements.
PROBABILITY DENSITY FUNCTIONS OF BREAKING WAVES
Authors: Thornton Edward B. , Schaeffer George
Published: June 2019

Waves in the surf zone are a highly nonlinear process which is evident by the appearance of secondary waves. The secondary waves appear as strong peaks in the period PDFs corresponding to the first harmonic of the peak of the wave spectrum. The strong first harmonic period peak is also reflected in the highly correlated height and velocity PDFs. Due to the high probability of the secondary waves, the mean wave period for breakers is a poor descriptor of the average period of the offshore incident waves. The joint probability density functions for periods and heights of the breaking waves show high correlation (0.60-0.80) which says that greater wave periods are associated with larger breaker heights. The joint PDFs of period and particle velocity, and velocity and height, suggest that the maximum onshore particle velocities are correlated with both the wave periods and wave heights.
ESTIMATION OF WATER PARTICLE VELOCITY OF BREAKING WAVE
Authors: Sakai Tetsuo , Iwagaki Yuichi
Published: June 2019

A possibility to estimate the water particle velocity of breaking wave on beaches by giving only the values of the beach slope i and the deep-water wave steepness H0/Lo is investigated. The data of the water particle velocity and profile of breaking wave on the beaches measured by Iwagaki, Sakai, Tsukioka and Sawai(1974) are used for this purpose. A method of using empirical curves relating the coefficients of Dean's stream function to i and H0/L0 does not give good results. The relations between the asymmetric breaking wave profile, i and Ho/L0 are examined. As well as the front face of the profile, the slope behind the crest above some level is found to become steep when H0/L0 becomes small. The breaking wave profiles are reproduced by using the empirical curves relating the parameters characterizing the breaking wave profile to i and Ho/L0. The velocity of Dean's stream function calculated from the reproduced profile explains the measured velocity better than that of Stokes waves. It is therefore possible to estimate the water particle velocity of breaking wave on beaches by giving only the values of i and Ho/Lo.
INFLUENCE OF BREAKWATER-REFLECTION ON DIFFRACTION
Authors: Daemrich Karl-Friedrich , Kohlhase Soren
Published: June 2019

Diffraction calculations for breakwaters are often based on SOMMERFELDs solution, which is mathematically exact for thin full-reflecting walls. For breakwaters with low reflecting frontsides, and if guidewalls are used, commonly a modified solution is applied, reducing the second term of the solution- formula proportional to the degree of reflection. It could be shown that this approach is not sufficient in the region just behind the breakwater, especially for small angles of wave attack. Regarding the exact solution for wedges it was possible to determine a special weighing factor for the second term of the SOMMERFELD solution, dependent on the degree of reflection and the wave direction, which leads to a better agreement between model tests and theoretical results.
A NUMERICAL APPROACH FOR THE DETERMINATION OF THE WAVE HEIGHT DISTRIBUTION IN A HARBOUR
Authors: Kohlhase S. , Daemrich K.F. , Berger U. , Tautenhain E. , Burkhardt O.
Published: June 2019

The paper deals with a mathematical method to calculate wave heights in harbours caused by diffraction and reflection. Using the complete SOMMERFELD-solution for a semi-infinite breakwater, a linear superposition method is applied. The reflections of the harbour boundary are taken into account using a geometric mirroring principle. The computer-programme allows the phase-correct superposition of any number of wave systems and, therefore, also the consideration of re-reflections which can be important in the presence of vertical walls. For the presentation of results (K'-lines) an interpolation-plot-programme is used. The computer-programme has been applied to the harbour Greenville extension (Liberia) (BURKHARDT, 1977). Hydraulic model tests were performed to check the programmes, especially with respect to the influence of harbour reflections and the layout of the breakwater head.
WAVE HEIGHT DISTRIBUTION AROUND PERMEABLE BREAKWATERS
Authors: Hotta Shintaro
Published: June 2019

By superimposing solutions due to Sommerfeld, a calculation was made to obtain the wave height distribution around permeable breakwaters in a constant water depth. The cases dealt with were a semi-infinite breakwater, a single relatively large gap in a long breakwater and a single detached breakwater all with incident waves normal to the breakwater. Some cases were verified through experiments in a shallow water basin.
A COMBINED FE-BIE METHOD FOR WATER WAVES
Authors: Hauguel A.
Published: June 2019

The finite element method and boundary integral equation method are general approximation processes applicable to a wide variety of engineering problems. After a brief description of the combined method, several examples are given for water waves problems : tides, harbour oscillations and waves diffraction and refraction.
WAVE REFRACTION ACROSS A SHEARING CURRENT
Authors: Jonsson Ivar G. , Skovgaard Ove
Published: June 2019

Conservation of wave crests and wave action is introduced to yield the new wave length L2 and new wave height H2 as a wave train of plane incidence crosses a shearing current; refraction angle a is determined by Snell's law. Input parameters are water depth h (assumed constant), absolute wave period Ta, angle of incidence aj, current velocities U> and U (see Fig 1), and initial wave height H . Solution domains are also given, analytically and graphically. The numerical results for L., L,, a,, and H2 are presented non-dimensionally in a number of figures, with dimensionless input parameters. As a direct illustration of the effect of the shearing current, a sequence of graphs are presented, showing in dimensional form the variation of L2 , a2 , H2, and steepness S2 = H 2/L2 with U2 for fixed values of h, ctj, U^, Ta, and Hj. Large positive and negative currents can increase the steepness significantly. The variation of S2/Sj with Ta and h is finally depicted, demonstrating the "filtering" effect of a shearing current on waves. A numerical example shows how simple it is to calculate accurately quantities Lj, L2, a2, and H2.
WAVE CLIMATE IN SOME ZONES OFF THE BRAZILIAN COAST
Authors: Homsi Alberto
Published: June 2019

METEOROLOGICAL FEATURES - The Brazilian coast could be considered a calm area not affected by violent tropical storms. The major meteorological factor in Brazil is the South Atlantic anticyclone, almost permanent, which causes periodical northward heading of cold fronts. A slightly reduced energy and frequency of storms could be observed going up from South coast toward North and could reach the major part of Northeast region. As a general condition the average monthly frequency of cold fronts passing along the Brazilian coast is higher during the winter - five per month with an average duration of 3 days, decreasing to 2 per month during summer with an average duration of 5 days. During winter high waves could occur between Santos and Macae caused by a depression near the Rio de Janeiro as the cold front stays at North, before the cold front goes down to South. Fig. l shows the average flow pattern across Brazil for summer and winter periods and a six days cold front advancing toward North, going into as far as to tropical latitudes during winter time. The daily tracks of the winter cyclones appear on this figure; they do not get beyond latitudes of 40 South.
NEAR-BOTTOM CURRENT MEASURED BY ACOUSTIC SENSORS
Authors: Selanger K.A. , Carstens T.
Published: June 2019

A vertical current profile has been measured with three acoustic meters 60 cm, 100 cm and 200 cm from the sea bottom. The depth at the measuring site was 84 metres. The profile is found to depend on the time scale of the water particle motion. An Ekman-like turning of the current is also observed, and the thickness of friction layers is estimated. Comparison of the current data with wave measurements indicates that the vertical transfer of surface wave energy is 30-50 per cent less than first order wave theory prescribes.
OSCILLATORY LAMINAR FLOW ABOVE A ROUGH BED
Authors: George C.B. , Sleath J.F.A.
Published: June 2019

Measurements are reported of the velocity distribution in the laminar boundary layer above a rough bed oscillating in its own plane in still air. The measurements were made with a hot-wire anemometer and the beds consisted of spheres packed closely together on flat plates. Particular attention was paid to the jets of fluid associated with individual roughness elements reported by Keiller & Sleath (1976). The probe used by Keiller & Sleath could be traversed vertically but not parallel to the bed. Consequently it is not known whether or not the velocities which they measured represent the maximum jet velocity at a given height since the probe was not necessarily in the vicinity of the jet at the moment at which it was maximum. In these new tests the probe could be traversed horizontally as well as vertically. It is found that one jet is formed by each roughness element during each half cycle. This jet is directed upwards from the bed. Its intensity shows relatively little variation with Reynolds number for the range of conditions investigated but increases significantly with the relative roughness parameter BD. The moment in the half cycle at which the jet is formed and the location of its axis appear to vary with both gD and Reynolds number. Visual observations suggest that the jet is associated with incipient vortex formation. The variation in velocity with height in the jets of fluid is significantly different from that given by Stokes' theoretical solution for a flat bed. Except in the immediate vicinity of the bed, the jet velocity predominates over that during the rest of the cycle.
FREQUENCIES AND PROBABILITIES OF EXTREME STORM SURGES
Authors: Bohrbuter Alfred
Published: June 2019

The North Sea as a very shallow sea with high wind set-up effects is acting highly as extremely sensitive measuring equipment for climatic changes, especially for surge producing weather conditions. The flood disaster in the Netherlands 1953, in Germany 1962, the Adolph-Bermpohl-Orkan (1967), with mean wind speed of 37 ra/sec. over 5 hours, the strong continental storm with high damages in the forests from France till Poland in November 1972, a series of 6 heavy floods in November/ December 1973 and two extreme floods in January 1976 with the highest water levels ever registrated in the German bight are indications for some changes in meteorological conditions. In this paper some hypothetical models shall be introduced which are able to show how extreme storm surge frequencies and probabilities are changing with time.
STORM SURGE PREDICTION BY COMBINED WIND AND TIDE DATA
Authors: Christiansen Herman , Siefert Winfried
Published: June 2019

The authors suggest a storm tide forecasting method that allows high water predictions for a coastline 3 to 4 hours in advance with an accuracy of ± 30 min in time and ± 20 to 30 cm in height. It is based on actual (not on predicted) data, i.e. exact wind velocity and direction data from a reference station and tide data from two gauges. The method was developed by analysing storm surge curves and wind data of those 50 storm tides that occurred since 1965 in the German Bight. Another 50 storm tides back to the year of 1930 were taken into account, though without exact wind data. The method was proved at all storm tides since 1965 and applied with good success to the events during fall and winter 1977/78 for the coastline off Cuxhaven.
STORM SURGE FORECASTING METHODS IN ENCLOSED SEAS
Authors: Hamblin P.F.
Published: June 2019

Storm surges in enclosed seas although generally not as large in amplitude as their oceanic counterparts are nonetheless of considerable importance when low lying shoreline profiles, shallow water depth, and favourable geographical orientation to storm winds occur together. High water may result in shoreline innundation and in enhanced shoreline erosion. Conversely low water levels are hazardous to navigation. The purpose of this paper is to discuss the problem of storm surge forecasting in enclosed basins with emphasis on automated operational procedures. In general, operational forecasting methods must be based on standard forecast parameters, require a minimum of computational effort in the preparation of the forecast, must be applicable to lakes of different geometry and to any point on the shore, and to be able to resolve water level changes on an hourly basis to 10 cm in the case of high water level excursions associated with large lakes and less than that for smaller lakes. Particular physical effects arising in lakes which make these constraints difficult to fulfill are the reflections of resurgences of water levels arising from lateral boundaries, the stability of the atmospheric boundary layer and the presence of such subsynoptic disturbances as squall lines and travelling pressure jumps.
WAVE SET-UP IN THE SURF ZONE
Authors: Hansen Uwe A.
Published: June 2019

In designing coastal protective structures the knowledge of the static load due to the water level elevation is as important as that of the dynamic load due to the waves. The structure, designed at sandy coasts with well formed surf zones on the beach - these areas are the basis of this examination - has to stand against both, the superposition of the static and dynamic load, which are dependent on each other. Undoubtedly a rise in the design water level (a summation of different influences - see figure 1) will cause an increase in the wave heights and the reverse will happen, when the design water level decreases.
MATHEMATICAL MODELING OF SHORELINE EVOLUTION
Authors: Le Mahaute Bernard , Soldate Mills
Published: June 2019

A mathematical model for long term shoreline evolution is developed. The combined effects of variations of sea level, wave refraction, wave diffraction, loss of sand by density currents during storms, by rip currents and by wind, bluff erosion and berm accretion as well as effects of man-made structures such as long groin or navigational structures and beach nourishment are all taken into account. A computer program is devloped with various subroutines which permit modification as the state-of-the-art progresses. The program is applied to a test case at Holland Harbor, Michigan.
MORPHODYNAMIC VARtABILITY OF HIGH-ENERGY BEACHES
Authors: Wright L.D. , Thom B.G. , Chappell J.
Published: June 2019

Field observations of beach and inshore morphology and of surf and inshore current spectra using an array of pressure transducers and low-inertia bidirectional flow meters interfaced with an in-field mini-computer/logging system have been replicated on several beaches in southeastern Australia under a range of energy conditions. Two broad extremes of beach conditions are distinguished spatially and temporally: (1) reflective systems In which much of the incident wave energy Is reflected from the beach face; and (2) dissipative systems with wide surf zones and high turbulent viscosity. Reflectivity increases as the ratio of wave steepness to beach (or bed) steepness decreases. Compared to steep, unbarred reflective beaches which are common in deeply indented or partially protected compart-, ments, the topography of exposed dissipative systems is more complex and varied: six time-and-environment-dependent morphologic types with different bar patterns and bar-beach relationships are recognized. The greatest total dissipation prevails In regions of most abundant inshore sediments or during and immediately after severe storms. Between the reflective and dissipative extremes there is a hierarchy of observed resonant frequencies with the highest frequency resonance occurring in the most reflective cases. Results indicate that near the beach face, motions associated with resonance at periods greater than incident wave periods exhibit strong net seaward resultants and are probably important sources of beach erosion. Reflective beaches are sensitive to resonant excitations over a wider range of frequencies and under lower energy conditions than are dissipative beaches. Hence, although reflective beaches represent the accretive end point of a "beach cycle" they are also more delicately poised with a higher potential for erosion.
PROCESS-RESPONSE MODELS FOR DEPOSITIONAL SHORELINES: THE GERMAN AND THE GEORGIA BIGHTS
Authors: Nummedal Dag , Fischer Ian A.
Published: June 2019

Sediment dispersal patterns in tidal inlets within the German and the Georgia Bights are found to be controlled by three major environmental factors: (1) the tide range, (2) the nearshore wave energy, and (3) the geometry of the backbarrier bay. Both embayments chosen for study are characterized by high wave energies and low tide ranges on their flanks, and low wave energies and high tide ranges in their centers. The spatial variability in inlet morphology, therefore, contains information on the relative role of tides and waves in inlet sediment dispersal. The paper concludes by proposing a simple model for inlet morphologies for successively greater relative role of tidal currents in the sediment dispersal.
PERIODIC FLOWS FROM TIDAL INLETS
Authors: Wilkinson D.L.
Published: June 2019

A study was undertaken of the flow produced in the offshore region by tidal currents at the entrance of a coastal inlet. The gross features of the offshore flow structure were examined in an idealised two dimensional model in which a sinusoidally reversing flow was discharged from an open channel into a large stagnant basin. During each period of ebb flow, the discharge from the simulated inlet developed a structure very similar to that of a starting jet, and a vortex pair was observed to form and ultimately became the dominant feature of the flow. Although variable bottom topography and long shore currents will distort the flow pattern, the rotational motions observed in these experiments would be expected to persist. The study was restricted to coastal inlets in which the sectional area of the entrance channel is several orders of magnitude smaller the area of water surface inside the inlet.
NEAR-BOTTOM VELOCITIES IN WAVES WITH A CURRENT
Authors: Bakker W.T. , Van Doorn Th.
Published: June 2019

Bakker (1974) developed a mathematical model concerning the sand concentration and velocity distribution in an oscillatory turbulent flow, with or without resultant current. The flow is assumed to be uniform in horizontal direction. The present paper reports on an experimental verification of this theory. Furthermore, the numerical accuracy of the model has been investigated and diagrams are presented which enable the computation by hand of global velocity profiles.
UNDULATED BOTTOM PROFILES AND ONSHORE-OFFSHORE TRANSPORT
Authors: Manhohar Madhav
Published: June 2019

Underwater bars, the characteristic features of oceans and lakes occur singly or in a series along the coast. Nearest bar to the shore, namely the break-point bar moves shoreward in summer, joins the coast and is replaced by another bar in its original place. The other seaward bars are storm bars, more or less permanent though they may shift slightly in orientation, position and shape depending upon the wave climate and state of the coastal processes. With the sediment and bottom profiles changing constantly with differing wave characteristics and beach exposure, a rigorous mathematical analysis for long range variability of profiles and therefore coastal processes in not possible. Therefore, the concept of medium depth and steepness characteristics is introduced to distinguish the profiles and their major dimensions. Onshore-offshore sediment motion is sometimes far in excess of longshore transport mostly confined in the breaker zone. When submarine bars are present, such motion is considerable mainly as a result of the hydrodynamic reaction between the rotating eddies generated over the bars and the bar surface. By means of dimensional analysis, it is possible to relate the quantity of onshore-offshore motion to the bar dimensions, wave period, water depth and transport direction by profile steepness characteristics. The above two concepts are then applied to the Nile Delta coastal processes with satisfactory results.
USES FOR A CALCULATED LIMIT DEPTH TO BEACH EROSION
Authors: Hallermeier Robert J.
Published: June 2019

A sediment entrainment parameter is used to calculate maximum water depth for intense bed agitation by shoaling linear waves of given height and period. Calculated limit depths agree with available laboratory measurements of water depth at an erosive wave cut into slopes of quartz and other fine sediments. Ignored variables have small effects on the agreement between calculations and laboratory measurements. On natural seasonal beaches, available measurements of seaward limit to appreciable sand level changes agree with limit depths calculated for extremely high waves expected 12 hours per year. The apparent accuracy and lack of scale effect in the calculated limit depth justify several applications in field and laboratory projects.