bluuebunny/crossref_metadata_2025 huggingface dataset:
OPERATIONAL PROCEDURES RICHARDS BAY HARBOUR
Authors: Zwamborn J.A. , Cox P.J.
Published: June 2019

The new port of Richards Bay on the east coast of South Africa (Figure 1), was officially opened in April 1976 and was mainly built for the export of bituminous coal. Exports increased from an initial 2,5 million tons per annum to 26,5 million tons per annum in 1981. Extensions are now under way to increase this further to 44 million tons per annum by 1987.
STUDY OF SHIP'S TRACK AND MOTIONS AT PORT TARANAKI
Authors: Greenstreet G.
Published: June 2019

This paper describes a study carried out at Port Taranaki, New Plymouth, New Zealand to determine ship's track and motions at the port entrance. The results of the study being used to establish the extent (plan area) and optimum depth of proposed capital dredging works. The time lapse photographic technique, incorporating reference levels and bearings in each frame, used to record vessels entering and leaving the port is described, Maximum increases in ship's draft due to sea conditions are given.
WAVE INDUCED VELOCITIES CLOSE TO A RIPPLED BED
Authors: Du Toit C.G.
Published: June 2019

The results are reported of velocity measurements in oscillatory flow over rippled beds. Velocities were measured with a laserdoppler anemometer in both an oscillating tray rig and an oscillatory flow U-tube. Both self-formed and artificial ripples were examined. The results obtained in the two test rigs were compared and it was concluded that the flow fields obtained in the two cases were dynamically similar. Measurements of the flow field clearly showed the formation, growth and ejection of vortices, as well as a strong surge of fluid over the ripples during and after flow reversal.
MASS TRANSPORT IN VOCOIDAL THEORY
Authors: Gonsalves J.W. , Swart D.H.
Published: June 2019

The concept of mass transport is theoretically discussed within the framework provided by Vocoidal theory. The Lagrangian mass transport is divided into two parts; firstly treating the fluid as being inviscid and secondly, incorporating viscosity by means of the free surface and bottom boundaries. Eulerian mass transport is defined and is shown to correspond, in deep water, to the net flow predicted by Stokes and others.
PROBABILITY DENSITY FUNCTION OF WAVE HEIGHTS OFF THE WESTERN COAST OF TAIWAN
Authors: Tang Frederick L.W. , Juang Jea-Tzyy
Published: June 2019

A new probability density function of wave heights off the western coast of Taiwan is submitted in this paper. According to the bathymetry of this area, waves from the central part of Taiwan Strait refract to the point of measurement and minor waves generated by local wind add the energy on the major ones; So an analytical solution is to be worked out by assuming that the wave energies are the linear sum of these two sources and convolution integral is adopted. The new model approaches reality better than Ray'leigh's.
WAVE ENERGY VARIATION NEAR CAPE TOWN, SOUTH AFRICA
Authors: Shillington F.A.
Published: June 2019

A three month time series of wave height measurements taken every six hours for twenty minutes duration at two sites (one in 24 m deep water and the other in 15 m deep water) off the South African coast have been used to examine wave energy dissipation. The rocky nature of the bottom has ruled out the possibility of dissipation due to sediment motion and percolation and only dissipation due to bottom friction has been considered. The theoretical work of Hasselmann and Collins 1968 has provided the basic technique. Average friction factors obtained have been in the range 0.17 to 0.50 but have very large scatter. Such large friction factors were not considered possible until recently (Grant and Madsen 1982) when it has been shown that if the hydraulic roughness is of the same order as the bottom orbital excursion, the friction factor tends to a value of 0.23. An attempt will be made in future work to reduce the scatter of the results by careful selection from a longer subsection of the original time series.
THE EFFECT OF BED SLOPE ON WAVE CHARACTERISTICS
Authors: Nelson R.C.
Published: June 2019

In all wave theories used in engineering applications it is assumed that the profile of the bed is horizontal which results in a symmetrical wave shape and velocity field, so that, strictly speaking, they can be applied only to this condition. Nearshore bottom profiles are, however, seldom horizontal, and a wave moving over a shoaling slope has an asymmetrical profile which is associated with an asymmetrical velocity field within the wave which, in turn, directly influences the movement of bed sediment. As a matter of necessity, but within reason, engineers have ignored the influence of bed slope on the wave theory used. This course of action was justifiable on many counts, not the least of which was that inaccuracies associated with the theories used were far greater than any inaccuracies introduced by ignoring bed slope parameters. However, wave theories developed in recent years have become increasingly accurate and reliable so that it may now be necessary to take account of bed slope parameters in applying these wave theories before further improvements can be made in the techniques used to predict wave-induced sediment transport.
SENSITIVITY OF PARAMETERS AND APPROXIMATIONS IN MODELS OF TIDAL PROPAGATION AND CIRCULATION
Authors: Leendertse Jan J. , Liu Shia-Kung
Published: June 2019

In the last ten years a system has been designed for the two-dimensional simulation of the hydrodynamics and water quality in well-mixed estuaries, coastal seas, harbors, and inland waters. The system called SIMSYS2D or WAQUA, can simulate the hydrodynamics in complicated geographical areas, and the model can determine the land/water boundary during simulation [1]. The system accounts for the sources of discharges, tidal flats, islands or dams, and time-varying or time-invarying flow restrictions such as generated by openings in dams, sluices, or storm-surge barriers. In the SIMSYS2D system numerous finite difference approximations of the vertically integrated hydrodynamic equations and their boundary conditions are available to the investigator, A large number of models and model experiments with two-dimensional models have been described in the literature. In many instances, authors have emphasized the advantages of the particular approximations they were using in their model and sometimes made comparisons with other approximations by use of hypothetical geographical areas. Generally, no comparisons are given of different computation methods applied to actual estuaries. Currently, no comprehensive overview of the comparative importance of the approximations of the terms of the hydrodynamic equations based on experiments of typical estuaries, is available. Nor has a practical assessment been made on the comparative importance of timestep size, grid size, depth accuracy, roughness estimates, and approximation of the closure term by viscosity or other expressions. To obtain an insight into the relative importance of computational and systems parameters, a large number of experiments were made with models of the Eastern Scheldt using the SIMSYS2D system in many of its modes. Some of the more important results of this extensive analysis will be presented in this paper.
NEARSHORE WAVE SPECTRA MEASURED DURING HURRICANE DAVID
Authors: Ochi Michel K. , Chiu Ming-Hsing
Published: June 2019

This paper presents the results of an analysis carried out on wave spectra measured at three nearshore sites along the United States Florida coast when Hurricane DAVID passed these sites in 1979. Included are (a) the variability of the shapes of wave spectra during the stages of growth and decay of the hurricane-generated seas, (b) the presentation of spectra according to various spectral formulations, and (c) a comparison between spectra measured at the coastal sites and those measured in deep water for the same severity (significant wave height) of hurricane-generated seas.
ARTIFICIAL MANIPULATION OF BEACH PROFILES
Authors: Kama Timothy W. , Svetlichny Michael
Published: June 2019

A field study was conducted at Myrtle Beach, South Carolina (U.S.A.), to determine the response of natural beaches to artificial manipulation by sand scraping. Between March 1981 and May 1982, a total of 100,000 m3 of sand was shifted from the lower beach to the backbeach on three occasions over a R-km length of shoreline. Fiftyfour profile stations were surveyed to the -1.0 meter contour as many as ten times during the study to determine the effect of scraping and fill along a stable-to-slightly erosional beach. The purpose of the scraping and fill was to provide temporary erosion relief, protect existing dunes and structures, and provide a wider recreational beach at high tide. It was found that scraping and fill had little adverse effect on the beach cycle in the northern zone of the project area, which is fronted by a natural dune system. Fill placed at a gentle slope along the seaward margin of the dunes remained in place for up to ten months before eroding to the prefill surface. In contrast, similar quantities of fill along shore protection structures in the southern zone eroded in several weeks to four months. The study found significant differences in the response of armored versus unarmored shorelines with higher erosion rates and slower recovery of the beach at armored stations.
MORPHOLOGY AND DYNAMICS OF CRESCENTIC BAR SYSTEMS
Authors: Goldsmith V. , Bowman D. , Kiley K. , Burdick B. , Mart Y. , Sofer S.
Published: June 2019

Aerial photograph and field studies in the southeastern Mediterranean, involving bathymetric mapping, and concurrent and antecedent wave measurements, have been used to delineate the sequential development of crescentic bars and associated dynamics. The bar sequence includes multiple parallel or wavy bars, ridge and runnels, oblique/transverse bars, single crescentic and double crescentic bars, and occurs during a calming down of wave activity from 2.5 to 0.5 m waves. The concomitant wave data, including wave directions, energy spectrum, significant wave height, and length of the calm period, showed strong correlation with the bar stages. An increase in total bar occurrence during summer is related to a major wave energy decrease in the spring, when significant wave heights (H ) < 1 m sharply increase to 70-85% in April-May. Inner single crescentic and initial double-crescentic bars are largely restricted to the calmest wave months of May/April to October/November, which reflects their sensitivity to wave energy. The aseasonal occurrence is best shown by the mature double crescentic type, which apparently is the final stage in the crescentic bar development sequence. Two bar developmental sequences were delineated: one shore-normal and the other initially oblique, but gradually rotating to shore-normal in the mature stage. Out of phase relationships between inner and outer bar systems resulted from the lag in response of the outer bars behind changes in wave direction. Among the inner crescentic bars and shore rhythms, phase-correlation was the rule. Crescentic bars are well developed on this coast because of the dissipative conditions and the distinct wave climate. High waves in the winter remove the existing bars, and extended calms allow the full development of the crescentic bar sequence. Similar bar types occur on different coasts in different sequences and in different proportions of time. Thus, it is suggested that these differences are attributable to global differences in the occurrences of threshold wave height conditions .
LITTORAL PROCESSES IN CAMPELLO COASTS
Authors: Diez J.J. , Arenillas M.
Published: June 2019

The coasts of Campello (fig. 1), just at the North of Alicante, have undergone important erosions in the last few years. A study has been developed for over one year to separate seasonal and permanent variations of the shoreline. The geomorphology and the recent generation of these coasts have "been established and the study and wind wave regimes have heen defined to evaluate the littoral transports, particularly the longshore ones. The seasonal transverse 1 profiling nay show the seasonal changes in the littoral zone and the sieve and mineralogical analysis of the different samples of +he beaches have completed the data for the discussion. Taking into account other studies of the authors in other parts of the East and Southeast coasts of Spain, an hypothesis on the littoral processes has been established, separating the seasonal and the permanent and degradative consequences. Some recommendations to keep at least the present situation of the beaches and to protect the other stretches of the shore are presented as final conclusions.
COMPUTATIONAL ALGORITHM FOR LONGSHORE ENERGY FLUX INCORPORATING FRICTION
Authors: Walton T.L. , Weggel J.R.
Published: June 2019

The calculation of longshore sand transport on "beaches is a significant coastal engineering problem with application to various areas of coastal structure design (i.e., jetties, groins, and offshore "breakwaters), and inlet navigation channel design (i.e., studies of required maintenance dredging). Longshore sand transport as a first approximation is linearly related to longshore energy flux (see Bruno, et al. (1981)), hence, this paper simply presents a method for computing longshore energy flux as a means of determining longshore sand transport. The approach used herein for calculating longshore energy flux includes an analytical method for incorporating frictional wave energy dissipation. The method is simple enough to program on a hand-held programmable calculator. It therefore provides a method hy which rapid calculations can he made for a site at which offshore wave data exist. If offshore directional random wave data are available (i.e. directional wave spectra) then more advanced techniques should he used (see Walton and Dean (1981)).
DESIGN AND CALIBRATION OF FALSE BAY SEDIMENT MODEL
Authors: Schoonees J.S. , Moller J.P.
Published: June 2019

False Bay is situated near Cape Town in the Republic of South Africa. The National Research Institute for Oceanology (NRIO) of the Council for Scientific and Industrial Research (CSIR) was commissioned to undertake studies on a recreational scheme in the Strandfontein area of False Bay. A tidal pool was built as phase 1 of this project. Phase 2 is a bathing improvement scheme (see Figures 1 and 2). The aim of the bathing improvement scheme which consists of a number of structures, is to provide bathing facilities for the Mitchell's Plain community. At present the major part of the coast is rather unsafe for bathing mainly because of very steep beach profiles. Conditions were laid down to ensure safe bathing, e.g. a uniform flat beach slope and the absence of rock and rip currents. Further requirements were that a safe bathing beach must be formed soon after completion of the structures and that the adjacent coastline must not be adversely affected in the long term. This paper deals with the design and calibration of a sediment model which was chosen to evaluate and optimise the design of the proposed T-groyne and the system of detached breakwaters shown in Figure 3.
HYDKOSEDIMENTOLOGICAL STUDIES IN BAHIA BLANCA
Authors: Petroni R.V. , Serman D.D. , Escalante R.S.
Published: June 2019

The increasing international grain trade make it necessary to have more deep facilities for large draught ships. Within the areas of major agriculture developments, Bahia BIan ca harbour complex, is one of the most important and consequen (;ly also its improvement. In order to achieve this improvement a deeper and wider navigation channel has to be designed. The actual channel, 100 km. long is limited to bulk up to 37 ft. draught. It is developed along a sandy coast with large bars and islands. Bahia Blanca is the southwest of the Buenos Aires Province, within trapezoidal shape, where the mean tidal range chang m in the inner part to 1,8 m in the outer part. Try prove a so long channel in a complex sedimentologic imply a rather difficult task, which requires a ful gation programme to achieve an economical and techn tion. To this end, extensive field and desk studies ed out covering all the influence area and testing altematives . . carriers and silty located at a Bay of es from 3,5 ing to imal area . ly investiical so luwe re carri different One of the major problems to solve is the sedimentological sta bility of the channel due to the action of currents and waves. The use of mathematical models and of large and reliable field surveys, together with a pilot test dredging used as a one to one model for the calibration of the transport formulas, looks as the most suitable method to attack such problems. The results of this study are part of the navigation channel project carried out by the firm NEDECO-ARCONSULT for the Argen tine Government.
SECOND ORDER THEORY OF MANOMETER WAVE MEASUREMENT
Authors: Biesel F.
Published: June 2019

The paper refers to pressure gage wave measurements . First order transformation of the pressure spectrum into a surface level spectrum leads to hitherto unexplained discrepancies with prototype simultaneous pressure and level measurements . Use of second order gravity wave theory allows to draw the following conclusions » Second order effects appear to give a reasonable explanation of the observed discrepancies . A complete check would require specially made wave measurements and analyses . Second order corrections do not significantly affect mean values, such as significant height, if the manometer depth is not unduly large.
A PROCESS-RESPONSE MODEL FOR HURRICANE WASHOVERS
Authors: Suter John R. , Nummedal Dag , Maynard Amy K. , Kemp Paul
Published: June 2019

The passage of Hurricane Allen over Padre Island in August 1980 presented an excellent opportunity to study the effects and controls of coastal morphology on hurricane deposits. In the Caribbean Sea, Hurricane Allen achieved a central pressure of 899 mb, making it the second strongest Atlantic hurricane ever recorded. Once in the Gulf of Mexico, the storm approached the Texas coast from the east-southeast, building a significant storm surge. Near Brownsville, the storm stalled, spending much of its energy offshore before making landfall early on August 10th near Brazos Santiago Pass at the southern tip of Padre Island. Surge gauges show that peak recorded storm tides of about 3 m occurred at Port Mansfield, some 35 km north of landfall. Analysis of tide data indicates a time lag of some 14 hours on the rising storm tide between the Gulf and south Laguna Madre. This is due both to the limited tidal exchange across Padre Island and to set-down in the lagoon due to southward-directed cyclonic winds. By contrast, measurements taken in Corpus Christi Bay, some 180 km north of landfall, show that at that point Gulf and bay tides were in phase. The cross-barrier water level differential at South Padre Island (up to 1.5 m) greatly facilitated hurricane breaching of the island. Oblique and vertical aerial photography show that Padre Island was breached in many places, with about 40 major hurricane channels still open several days after the storm. Surge heights were sufficient to inundate all of South Padre Island except for isolated "dune islands" resulting in broad and often coalescing washover deposits. The more continuous dune ridge on North Padre Island resulted in smaller, discrete washovers. Intensity, distribution, and morphology of washovers are functions of storm tide elevation, its phase relationships, island topography, and lagoonal water depth. The relationship is complex, yet precise enough to permit prediction of the island's response to the impact of a given storm.
SCOUR BEHIND CIRCULAR CYLINDERS IN DEEP WATER
Authors: Imberger Jorg , Alach Des , Schepis John
Published: June 2019

Flume test data is presented for the depth of scour in deep water near a vertical cylinder placed in a uniform sand and a fine calcareous ocean sediment. The ratio of the depth of scour to the cylinder diameter at equilibrium is shown to depend only on the ratio of the shear velocity to the critical shear velocity at which bed motion is initiated. Protection against scour by placing collars around the cylinder is shown to be of marginal value.
FIELD INVESTIGATION OF LONGSHORE TRANSPORT DISTRIBUTION
Authors: Berek E.P. , Dean R.G.
Published: June 2019

Following a change in wave direction, the active contours in an idealized pocket beach respond by rotating such that they approach a perpendicular orientation relative to the incoming wave rays. Assuming that cross-shore sediment transport does not contribute to this contour rotation, and that the contours are in the early stages of this equilibration process, the amount of contour rotation can be interpreted as the cross-shore distribution of the longshore sediment transport. As part of the Nearshore Sediment Transport Study, detailed nearshore profile measurements were conducted at Santa Barbara, California. Twenty-two of these profile lines were located on Leadbetter Beach, which is a quasi-pocket beach. To explore the concept described above, two of the nine intersurvey periods were selected due to their strong indications of wave direction change. Analysis of these data sets yielded two estimates of cross-shore distribution of longshore sediment transport which were compared with those presented by Komar, Fulford and Tsuchiya. Although these three distributions differ significantly, the effect of the tidal variations is to "smear" the differences in the inferred distributions as evident in the contour displacements. It was found that none of the relationships for longshore transport distribution predicted the amount of transport inferred in water depths greater than one meter. It is possible, especially for one of the intersurvey periods that the changes in contour locations were so extreme that substantial crossshore sediment transport was induced and would be interpreted as longshore transport occurring in water depths greater than had actually occurred. The method introduced here should be useful in other field and laboratory programs to investigate the cross-shore distribution of longshore sediment transport.
Complete Proceedings - Single PDF Download
Authors: Edge Billy L.
Published: June 2019

These proceedings of the Eighteenth Coastal Engineering Conference held in Cape Town, Republic of South Africa, November 14-19, 1982 include the 167 papers presented at the conference. The proceedings are divided into 5 major subject areas. Part I, theoretical and observed wave characteristics, includes discussions on wave height distribution, waves in nearshore zones, tide predictions, wave energy conversion and wind effects. Part II, covers aspects of coastal sediment problems such as sediment transport, shore protection, beach profile changes, and beach erosion. Part III, coastal structures and related problems, covers construction, monitoring and performance of different coastal and offshore structures. Coastal, estuarine, and environmental problems are addressed in Part IV, including design of coastal water intakes, salinity intrusion, ocean outfalls, and environmental effects of construction. The final section covers ship motion response.
A RANKIN VORTEX NUMBER AS A GUIDE TO THE SELECTION OF A MODEL HURRICANE
Authors: Bretschneider Charles L. , Lo Jen-Men
Published: June 2019

A model hurricane is defined by a model pressure profile, which is the same in all radial directions from the center of the hurricane. The model describes concentric circles of constant pressure known as isobars. The slope of the pressure profile gives the pressure gradient used in the gradient wind equation, together with other considerations determines the time history moving hurricane wind and pressure fields. The appropriate model hurricane can then be coupled with various other models for the determination of design criteria such as wind, waves, currents, wave forces, storm surge, wave run-up, coastal flooding and inundation limits. Because of the many requirements for accurate output data, there have always been concerns of the proper use of and selection of the appropriate hurricane model for a particular task and location. The primary purpose of the paper is to begin to build a guide for determining the appropriate model to be used for a particular situation and criteria. When the data pressure profile is available, there is no need for a model since the slope of the data pressure profile gives the pressure gradient, which can be used directly in the gradient wind equation. The data pressure profile can also be fitted to the most appropriate model by various techniques of correlation.
AN ASSESSMENT OF BEACH NOURISHMENT SEDIMENT CHARACTERISTICS
Authors: Stauble D.K. , Hansen M. , Blake W.
Published: June 2019

An important component of beach nourishment design is to assess the compatibility of the borrow material with the native beach sediment. One avenue to judge the "success" of a project is the amount of fill retained over a specific period of time after fill placement. Presumably, if the fill material placed on the eroded beach is compatible with the energy of the coastal processes, it will be resorted along the profile but be retained within acceptable limits in the vicinity of the project area. At present the selection of suitable borrow material is based only on theoretical criterion. Specifically, the Fill Factor and Renourishment Factor are based on models developed by Krumbein (1956), Krumbein and James (1965), James (1974), Dean (1974), James (1975) and Hobson (1977). These methods of judging borrow area suitability have not been fully tested in the field and the Shore Protection Manual (U.S. Army, 1977) warns that they should only be used as a general indication of possible fill behavior. A review of monitoring reports on selected recent beach restoration and sand by-pass projects revealed a lack of standardization on data collection and analysis. Little evaluation of the actual behavior of fill material on the nourished beach had been carried out. To assess the suitability of the fill material, projects with adequate data were investigated and the short (one year) and long term (two to three years) behavior of actual fill data was described. Detailed collection of native sediment before nourishment, representative borrow material at time of placement and samples at specific times after fill placement were used to determine the redistribution of fill grain size characteristics and determine the accuracy of the present beach fill models. It was found that present models do not take into account non-normal grain size distributions found at the projects studied or CaCO,, shell material. A safety factor assuming loss of fine material from the borrow should be used with the Adjusted Shore Protection Manual Fill Factor Method to give more accurate results. The delta variable in the Renourishment Factor was found to vary between projects and should be calculated for each project. At the present time use of the entire grain size distribution is necessary to understand the sediment redistribution after fill placement.
METHOD FOR ASSESSING STORM DAMAGE TO BEACH HOUSES
Authors: Doyle Lynn C. , Fox William L.
Published: June 2019

Methods and procedures for the assignment of the pro rata share of damages caused by rising water and high winds arising from natural weather phenomena were virtually non-existent following Hurricane Frederic in 1979. Damages to beach front structures were often assumed to be caused by high water. Frederic marked the first natural weather disaster to strike a heavily populated area since the formation of the National Flood Insurance Program in 1970. The damages caused by the winds and rising water from Hurricane Frederic, therefore, created an economic incentive to attempt to distinguish between wind and rising water contributions. This paper presents a method and outlines procedures followed in damage assessments following Hurricane Frederic in an effort to minimize the difficulties insurance carriers and adjustors may have following future similar phenomena. It may, additionally, serve to promote improved design and/or building codes where such phenomena are probable.
BEACH AND DUNE RESPONSE TO SEVERE STORMS
Authors: Kriebel David L. , Dean Robert G.
Published: June 2019

A numerical model is developed and applied to estimate the frequency distribution of severe erosion events. The proposed method is an extension of existing Monte Carlo storm surge simulation models. Hurricane and tropical storm meteorological parameters are randomly selected to generate a series of synthetic storms; the storm surge for each storm is estimated using a Bathystrophic storm surge model. The storm surge hydrograph is then used as input to a numerical erosion simulation model which determines beach profile response for each storm based on wave energy dissipation per unit volume as a general erosion forcing mechanism. Five 100-year random simulations are performed from which the return periods of storm surge and erosion, i.e. volume eroded and dune recession, are estimated.
COASTAL CHANGES AT BETHANY BEACH, DELAWARE
Authors: Dick Jennifer E. , Dalrymple Robert A.
Published: June 2019

The coastal processes affecting Bethany Beach, Delaware were studied and the short-term and long-term trends in coastal changes were determined in order to develop recommendations for protecting Bethany against coastal erosion (Dick and Dalrymple, 1983). Bethany Beach is located on the Delaware Atlantic coastline which is a wide sandy baymouth barrier beach distinguished by highlands at Rehoboth Beach and Bethany Beach. The shoreline is straight, with only minor bulges and indentations (see Figure 1). Bethany Beach is a residential and resort community. Privatelyowned properties front the publicly-owned beach. Construction of new motels and summer homes is anticipated along with the continued growth of commercial activities to accommodate the increased number of visitors. Bethany is protected by a series of nine groins built between 1934 and 1945. Many of these groins have deteriorated, and are flanked at the landward end. Winter storms severely erode the beach and damage shorefront property. The beach is generally narrow (approximately 45 m wide), especially along the southern portion, and is backed by low dunes (about 15-45 m above NGVD). A timber bulkhead extends along most of the backshore.
PROCEDURE FOR DETERMINING DREDGING REQUIREMENTS IN COASTAL INLET CHANNELS
Authors: Forman James W. , Vallianos Limberios
Published: June 2019

In order to assess the technical feasibility of a long term maintenance dredging plan at Oregon Inlet, a simple procedure was devised to evaluate the capabilities of existing ocean going hopper dredges to maintain an ocean entrance channel in an inlet environment characterized by wave climate and resulting influx of littoral material as severe as any Atlantic coast location. The dredging analysis procedure described in this paper was used to evaluate dredge plant capabilities under the operational constraints imposed by depth limitations resulting from the continuous influx of sediment into the project channel, the wave climate, and dredging production capacity in terms of actual hopper capacity and cycle times for different disposal schemes. The shoaling and dredging simulation procedure is described in terms of its application to the proposed navigation project at Oregon Inlet, NC.
NUMERICAL SIMULATION ON THE CHANGE OF BOTTOM TOPOGRAPHY BY THE PRESENCE OF COASTAL STRUCTURES
Authors: Yamaguichi Masataka , Nishioka Yoichi
Published: June 2019

This paper presents a numerical model for predicting the change of bottom topography caused by coastal structures placed on a sandy beach. The model consists of three submodels of wave transformation by varying topography and coastal structures, nearshore current and change of bottom topography. The computation of nearshore current patterns induced by the presence of a detached breakwater shows qualitative agreement with the experiment. The effects of wave and structure characteristics on current pattern and topographical change are investigated by consideration of model computation with several configurations of coastal structures such as detached breakwaters or groins. The main conclusions are that the model produces the general features of erosion and deposition caused by coastal structures and that drastic change of current pattern and bottom topography occur when reflected waves from the structures cover a large area.
SUSPENDED SAND TRANSPORT ON A DISSIPATIVE BEACH
Authors: Downing John P.
Published: June 2019

Field studies were conducted in November 1979 to measure suspended sand transport on Twin Harbor Beach, Washington U.S.A. This beach has an average slope of 0.02 and is composed of well-sorted sand with a mean diameter of 0.21mm. The significant height of breaking swells approaching the beach at small angles can be estimated from variance spectra of water level by 4.36 0^. In the surf zone significant wave heights are linearly related to the local mean water depth by Y = H /h » 0.45. Variance, a \, in the gravity wave band (0.048 to 1.0 Hz) is proportional to water depth squared. Low-frequency variance (less than 0.048 Hz) although not systematically related to water depth, is usually largest in the inner surf zone where breakers are small. Sand suspension is correlated with strong offshore flows that recur at about one-fifth the incident wave frequency. Vertical mixing of sand in the water column by these water motions rather than turbulence generated by shear at the bed associated with individual wave oscillations is a key mechanism in sand transport on dissipative beaches. The largest sediment loads occur in the inner surf zone where lowfrequency motions dominate the breakers. Maximum longshore transport rates, however, were measured in the middle of the surf zone because of the higher longshore current speeds there. The suspended load probably accounts for as much as 45 percent of the litoral drift on a dissipative beach exposed to moderately-high swells approaching the shore at small angles.
SHORE APPROACH AT THE DANISH NORTH SEA COAST, MONITORING OF SEDIMENTATION IN A DREDGED TRENCH
Authors: Mangor Karsten , Sorensen Torben , Navntoft Erling
Published: June 2019

The Danish Natural Gas and Oil Transmission system included the landing of a 30' Gas pipeline and a 20' Oil pipeline in a common shore approach at the Danish North Sea Coast. The location of the site is shown in Figure 1.1.
OFFSHORE BREAKWATER, WHEATLY, ONTARIO
Authors: Beaulieu G.T. , Skafel M.G. , Baird W.F.
Published: June 2019

The safe entry during storms to the fishing harbour at Wheatley on Lake Erie was compromised by breaking waves at the harbour entrance. These waves approach the entrance from a narrow easterly sector due to storm tracks, fetch limitations, and refraction. Using a physical model, a small offshore breakwater was selected as the best solution to eliminate the breaking waves. During the six years since construction, the breakwater has performed satisfactorily and has had a negligible effect on the littoral processes as determined from regular bathymetric surveys.
DEVELOPMENT OP A SEDIMENT TRANSPORT MEASURING SYSTEM
Authors: Renger Eberhard
Published: June 2019

A new method for continuously recording sediment concert - trations with high accuracy has been developed. It is proposed to apply the method for In-situ measurements in connection with investigations of tidal control and sediment transport induced by shipping traffic. The operating principle is as follows: at the measurement location, sedime~nt laden water is continuously sucked-in by means of a pump and is forced under pressure into a hydrocyclone ( solid bowl centrifuge ) through a delivery pipe of varying length. Here the extracted sediment flux (particle size *> 5 nm) is delivered by the shortest route to a settling tank and continuously weighed under water (wet-weighing). Following calculation and appropriate adjustment to the sample discharge ( Q ) the weight increase for selected time intervals ( AG (At)) yields the mean concentration for the time interval ( c (At)) in weight / unit volume ( mg/1 ) (direct measurement, calibration not required ). Details and experiences of the 3 major development stages will be described. A fully-automatic instrument for continuously measuring nonsteady sediment movement is now available. The instrument may be installed above as well as below water as desired.
FREQUENCY OF OCCURRENCE OF STORM SURGES IN AN ESTUARY: A STOCHASTIC APPROACH
Authors: Sas Marc
Published: June 2019

This paper presents the results of a study on the frequency of occurrence of storm surge levels in the river Scheldt at Antwerp, related to the design of a storm surge barrier and the evaluation of the dike safety in the Scheldt basin. The basic principles of the extreme value distribution methods, the joint probability methods and simulation models are examined. A new technique, based upon the simulation of storms by variables characterizing the resulting surge is proposed. Results are compared with those of other methods.
BEACH FILL BY TURNING THE COURSE OF SANDBARS
Authors: Erchinger Heie Focken
Published: June 2019

The paper discribes the littoral drift along the Eastfrisian Islands. The inlets between the islands are crossed by offshore bars which migrate round the deep channel of the inlet northwards on a bow. Their point of approaching the next island scatters. That causes periods of accretion during the approach of the bars on the beach and of erosion in certain beach sections without bar approach and sand supply. When an offshore bar approaches a beach it moves a swash channel ahead as a rule. This causes a rising beach erosion by currents and wave wash and hinders the settling of the bar on that beach section. This paper reports a field study on influencing the migration of a bar by building a sand dam through such a swash channel. It was intended of feed the eroded section of the beach by the steered approach of the bar. The accretion by the desired approach of the bar on the eroded beach section was higher than expected and measured more than 270 m'/m.
BEACH AND SURF ZONE EQUILIBRIA AND RESPONSE TIMES
Authors: Wright L.D. , May S.K. , Short A.D. , Green M.O.
Published: June 2019

Analyses were performed on a 6% year time series of daily wave data, daily beach state data and monthly beach and surf zone profile data. Beach state changes, which involve the relatively rapid redistribution of sediment already stored locally, are predictable in terms of Dean's (3) simple parameter A - H, /(w T) where H, is breaker height, w is sediment fall velocity and T is wave period. Each of the six beach states has a different equilibrium range of S2 values and the direction of change (erosion or accretion) depends on the departure from the equilibrium association. Empirical eigenvector analyses performed on the profile data permitted separation of different response components. The lower order vectors expressing the grosser aspects of the profile features such as beach volume and surf zone gradient displayed maximum variance at periods in excess of 2 years whereas much shorter response times characterized the higher order components such as bar-trough shapes and asymmetries. We infer that the fast response, and more predictable, components of beach and surf zone change largely involve smaller scale sediment exchanges between the beach and surf zone whereas the slower responses are related to larger scale exchanges between the surf zone and the inner continental shelf.
MODELING OF NEARSHORE WAVE DRIVEN CURRENTS
Authors: Hubertz Jon M.
Published: June 2019

A nearshore current modeling system has been assembled which consists of a shallow water directional spectral wave model, an algorithm to convert directional spectral output from the wave model to radiation stress components and a current model to calculate nearshore wave-driven currents from the radiation stress field. Wave-driven longshore currents have been hindcast at a coastal site for two wave conditions during a northeaster type storm off Cape Hatteras in October 1982. For one event, when local winds were strong, the calculated longshore current is only a fraction of what was measured. This discrepancy is attributed to a non-wave-driven component of flow which was present but not represented in the model. During the other event, winds were low and long period swell was present. In this case, the calculated and measured longshore flow agree well. Both measured and calculated shore normal profiles of longshore current in each case show a generally uniform structure across the surf zone. This is in contrast to theoretical profiles based on monochromatic waves which show a maximum in longshore flow near the breaker line.
IMPROVED FORMULAS FOR ESTIMATING OFFSHORE WINDS
Authors: Hsu S.A.
Published: June 2019

Differences in onshore and offshore wind speeds have long been known to exist [see, e.g., (2), (15), (16)]. Marine meteorologists in the weather services are required to forecast offshore winds. Many studies related to coastal marine sciences and engineering require wind data or estimates for offshore regions. Yet in situ measurements over water are often lacking. Traditionally, wind measurements over land, preferably near coasts, have been used to estimate offshore winds. However, because simultaneous onshore and offshore observations do not always exist, systematic studies such as simple comparisons between these two environments are also lacking. Only recently the U.S. National Oceanic and Atmospheric Administration (NOAA) deployed a network of buoys for longer term measurements over the continental shelf as well as farther offshore. All of these buoys are located in or near U.S. coastal waters. However, there are still vast regions in other parts of the world where such a network does not exist.
STEADY FLOWS IN THE NEARSHORE ZONE
Authors: Haines John W.
Published: June 2019

Field measurements using electronmagnetic flowmeters on two natural beaches are presented. Mean flows are compared to theory. The horizontal and vertical structure are discussed.
VARIATION OF SEDIMENT SUSPENSION IN OSCILLATORY FLOW
Authors: Staub Carsten , Jonsson Ivar G. , Svendsen Ib A.
Published: June 2019

Different syphon type suspended load probes were used together with a newly developed 'carousel' sampler for measurements of the instantaneous sediment concentration in turbulent oscillatory flow over a sand bed. Shields parameters were well above the rippled/flat bed transition region, resulting in intense sediment transport over a flat bed. The measurements were performed at different levels in a large oscillating water tunnel. They showed some characteristic features of the temporal concentration variation and of the variation with height of the mean concentration. Also a pronounced effect of the orientation of the suction tube relative to the flow was observed.
SCALE EFFECTS IN LARGE COASTAL MOBILE BED MODELS
Authors: Kamphuis J.W. , Nairn R.B.
Published: June 2019

A series of mobile bed model tests of a prototype circular sand island was performed to determine scale effects. It was found that scale effect was largely a function of mobility number with some secondary effects of Reynolds number, bedform and critical profile depth. It was concluded that a model series using prototype sand grain size is necessary at this time to effect successful extrapolation to prototype.
BOTTOM TURBULENT BOUNDARY LAYER IN WAVE-CURRENT CO-EXISTING SYSTEMS
Authors: Asano Toshiuki , Iwagaki Yuichi
Published: June 2019

This study presents a new mathematical method calculating the water particle velocity in the wave-current co-existing systems. A boundary layer thickness 5,,, in the co-existing system is expected to be variable with the water particle velocity ratio of wave component to current component. In this method, the boundary layer equation is solved as a free boundary problem by treating 6,,, as an unknown boundary value. Several characteristics of the turbulent boundary layer such as the friction factor, friction velocity, boundary layer thickness, etc. are calculated by this method and the effect of the wave-current velocity ratio on them is discussed. Furthermore, the velocity reduction of the current due to wave superimposing is investigated. In addition, near-bottom velocities are measured by a laser-doppler velocimeter in the pure current, the pure wave and the wave-current co-existing fields. These results are compared with calculated ones by this mathematical method.
NUMERICAL SIMULATION OF SECONDARY CIRCULATION IN THE LEE OF HEADLANDS
Authors: Falconer Roger A. , Wolanski Eric , Mardapitta-Hadjipandeli Lida
Published: June 2019

The paper gives details of a study to refine and further develop a two-diirensional depth average numerical model to predict more accurately the eddy shedding features often observed in the lees of headlands. Details are given of the application of the model to Rattray Island, just east of Bowen, North Queensland, Australia, where the strong tidal currents flowing past the island give rise to separation and hydrodynamic circulation in the lee of the island. In the governing differential equations used to predict the secondary circulation, particular emphasis has been placed on the representation of the shear stresses associated with the free shear lateral mixing layer in the downstream wake of the headland. Use of an experimentally determined lateral velocity distribution in the shear layer, together with an eddy viscosity approach, have led to the use of a relatively simple turbulence model, including both free shear layer and bed generated turbulence. A comparison of the numerically predicted velocities with corresponding field measured results around Rattray Island has shown an encouraging agreement, although there were some differences. The main difference between both sets of results was that the vorticity strength of the secondary circulation predicted in the numerical model was noticeably less than that measured in the field.
SAFETY AND RELIABILITY OF BREAKWATERS
Authors: Mol A. , Groeneveld R.L. , Waanders A.J.
Published: June 2019

This paper discusses the need to incorporate a reliability analysis in the design procedures for rubble mound breakwaters. Such an analysis is defined and a suggested approach is outlined. Failure mechanisms are analysed and categorized in Damage Event Trees. The probability of failure is computed using a level III simulation method to include time and cumulative effects and to account for skewed probability distributions. Typical outputs of the computer program are shown and compared with results according to traditional design approaches. The paper concludes that there is a definite need to include reliability analysis in the design procedures for larger breakwaters and such an analysis must consider the accuracy of design parameters and methods.
REHABILITATION METHODS FOR DAMAGED BREAKWATERS
Authors: Croeneveld R.L. , Mol A. , Nieuwenhuys E.H.
Published: June 2019

A number of studies have been undertaken recently to select optimum methods for rehabilitating damaged breakwaters in the Mediterranean and in the Atlantic Ocean. This paper outlines the approach to these studies and discusses the relative merits of the various concepts considered for repairing the damaged structures. Based on case studies of two projects, the paper also shows how the principle concepts have been successfully applied.
STABILITY OF BREAKWATERS WITH VARIATIONS IN CORE PERMEABILITY
Authors: Timco G.W. , Mansard E.P.D. , Ploeg J.
Published: June 2019

In setting-up a breakwater test in a laboratory flume, the conventional practice is to scale geometrically the armour units, underlayer rocks and core material based on the Proude scaling criteria. However, because some of the properties of the water are not scaled for a model test, the Reynolds scaling law is violated. This can result in improper water flow distribution through the model breakwater. To investigate this problem, a series of tests were performed with a model breakwater in which the permeability (and porosity) of the core was varied over a wide range, and the hydraulic response and breakage of the armour units were measured. It was found that the overall stability of the breakwater could be drastically affected if the flow in the core is scaled incorrectly.