Coastal Structures 2003

The previous numerical simulation of the performance of rubble mound structures under sequences of hurricanes is extended to compute the reduction of the minimum cover depth of the armor stone layer under sequences of storms. The computed cover depth is reduced episodically by several major storms but the reduction rate decreases as the damaged armor layer ages. The performance is compared for the two-layer thick armor layers with the high and low nominal stone diameters whose ratio is 1.5. The reduction and variability of the normalized cover depth is much smaller for the high nominal diameter D_n50. The quality of armor stone placement is less important than the difference between the high and low D_n50. To compare the performance of the high and low D_n50 for the same layer thickness, computation is also made for the performance of the three-layer thick armor layer with the low D_n50. The increase of the initial layer thickness for the low D_n50 does not reduce the damage and variability of the cover depth but increases the remaining capacity of the damaged armor layer for protecting the underlayer to the level of the two-layer thick armor layer with the high D_n50 if the three-layer thick stone layer is constructed well.

This paper discusses performance design as an advanced design methodology for maritime structures, focusing on deformation-based reliability design of armor stones and blocks of breakwaters. The stability performance of breakwater armors is specifically considered by describing the design criteria (allowable limits) of damage level with respect to different design levels including probabilistic aspects. The accumulated damage during a lifetime is also discussed.

This paper presents a simulation system for the probabilistic optimization of rubble mound and vertical structures. System development extends previous work by the authors on deterministic optimal design procedures to include probabilistic principles. Traditional optimization analysis considers the balance between initial construction costs and long-term maintenance costs and provides a means for selecting the structure design that corresponds to the least total cost. The probabilistic optimization method presented in this paper introduces probability distributions for critical parameters including wave conditions, costs, and structural performance measures. The analysis produces statistical estimates of optimal design values rather than a single deterministic value. The utility of probabilistic optimization is relevant where there is considerable uncertainty regarding hydraulic/foundation conditions and costs for breakwater construction. This is often the case during planning or in remote locations. The paper presents an example application of the probabilistic simulation system for the design of artificial islands in New York Harbor.

A new parameter representing the maximum depth-integrated wave momentum flux occurring in a wave is proposed for characterizing wave processes at coastal structures. This parameter is a physically relevant descriptor of wave forcing; and having units of force, it is useful for developing meaningful physical formulations between the waves and the process occurring at the structure. This paper overviews the development of the wave momentum flux parameter, and it presents an empirical formula was estimating the parameter for nonlinear steady waves of permanent form. New formulas for irregular wave runup on plane, impermeable slopes are given in terms of the wave momentum flux parameter as an example application.

In this paper, new generalized breakwater armor stone stability equations are derived based on the assumption that the maximum wave momentum flux is proportional to the maximum wave forces on armor units. Stability equations are derived for uplift, sliding, and rolling incipient motion. A generalized empirical stability equation is proposed that characterizes these three cases of instability. This equation is fit to small-scale laboratory data yielding two stability equations distinguished by whether the waves are surging or plunging on the structure. In the new stability relations, wave-structure interaction and nearshore nonlinear wave transformation are separate, overcoming a major limitation of previous stability relations. The new relations clearly illustrate the influence of water depth and wave period on stability. The momentum-based approach illustrates why minimum stability is observed for steep plunging breakers in shallow water.

The paper presents the results of a hydraulic model test study of the influence of concrete mass density and placement method on the stability of cube armour in a 1:2 slope cone shaped roundhead exposed to short — crested seas. Location and development of armour displacements were studied for concrete cubes with mass density of 2.4 t/m³ and 2.8 t/m³ in random and regular placement. Significant increase in stability for the higher mass density cubes was found showing that the same dimension cubes can be used in roundhead and trunk, if for the top layer of the most exposed part of the roundhead are used cubes with concrete mass density 2.8 t/m³ instead of 2.4 t/m³. Significant smaller crane capacity is needed compared to the conventional solution of unchanged mass density which implies approximately a doubling the mass of the roundhead armour units.

The objective of this paper is to bring some international perspectives on the policy, design, construction, and monitoring aspects of Coastal Structures in general, and whenever possible, to present some comparison between the experiences of various countries.

In this paper it is shown that by (1) an adequate control of the testing procedure and (2) evaluating the influence of the wave reflection on the main layer stability, a significant reduction of the experimental scatter is obtained and a coherent explanation of the evolution, during the experiment, of the number of the displaced units can be given. This work may help to reduce: (1) the design uncertainty and (2) the construction and maintenance breakwater costs.

The stability of rock slopes under wave attack is addressed in this paper. Physical model tests have been conducted and analysed to obtain information on how to apply design formulae for conditions including situations in which wave breaking occurs on shallow foreshores. The analysis is based on tests on structures with a 1:100 foreshore and a 1:30 foreshore. It has been found that especially for applications with shallow foreshores the formulae by Van der Meer can better be applied a) by using the spectral wave period T_m–1,0 instead of the mean wave period T_m from time-domain analysis, b) by re-calibrating the coefficients, and c) by adapting the confidence levels. In addition, an alternative formula has been developed that, although it is simple, leads to the same accuracy for the more than 200 test conditions studied here.

The influences of wave groups and spectral shape on the stability of rubble mound breakwaters have been investigated by several researchers up to now. But, results were not conclusive in these researches, where different wave grouping and spectral shape parameters were used. This study aims to find an answer to that question by means of hydraulic model experiment. According to the result of the experiments, the damage to breakwater armour layer is almost same for different spectrum shapes and pronounced wave grouping, under the condition of similar wave statistics. Experiments also indicate that the wave trains with same significant wave height, H_1/3, but with different extreme waves whose heights are higher than H_1/3 cause different damage levels. The higher the extreme waves are, the more destructive the wave train is. Therefore it is concluded that occurrence of high extreme waves in a wave train is more important point than grouping and spectral shape in the stability of rubble mound breakwaters. It is also noted that the spectral shape indirectly affects the stability not due to the wave grouping but due to the extreme waves in a wave train since the occurrence probability of the high extreme waves becomes higher as the spectral shape becomes narrower under same significant wave height condition.

Horizontally composite breakwaters covered fully with wave-dissipating concrete blocks have been widely employed in Japan because of the efficiency in rapid construction. However, in recent years, due to economical advantage, layered covered types having the core material beneath the primary cover layer have increasingly been constructed. Hudson and Van der Meer pointed out the influence of layer thickness and permeability of core material on the stability of armor units used for rubble mound breakwaters. Although these factors also affect the stability of armor blocks in horizontally composite breakwaters, such influences have not yet been evaluated quantitatively. In this paper, the results of a series of hydraulic model experiments are described. First, stability tests were conducted under several combinations of layer thickness and core material. Second, the velocity fields on the breakwater were measured to correlate the wave force with the stability test results. Finally, an assessment methodology of the interlocking force in the armor layer based on possible displacement length is proposed and applied to dolos armor layer.

The paper presents results of 3D laboratory experiments on low-crested breakwaters. Two typical structural layouts were tested at model scale in a wave basin at Aalborg University, Denmark, to identify and quantify the influence of various hydrodynamic conditions (obliquity of short crested waves, wave height and wave steepness) and structural geometries (crest width and freeboard) on the stability of low-crested breakwaters. Results are given in terms of recommendations for design guidelines for structure stability. Damage parameters for the trunk and the roundhead are proposed based on analysis of observed damage. Results for initiation of damage are compared to existing data and a good agreement is found.

The quality of materials used in coastal and river structures is of primary importance for protection against the hydraulic action of waves and currents. The ability of natural armourstone blocks not to display significant breakage along weakness planes and cracks is defined as integrity. In an initial research survey designed to address materials quality issues, where professionals identified integrity essential. However, it remains poorly understood. Methods for assessing block integrity have been documented and this research focuses on full-scale destructive tests. A preliminary field study established experimentally that the documented methods display poor repeatability and limited correlations with each other. In addition, full-scale impact testing displays a significant variability due to limited control of the test conditions. Consequently, a full-scale splitting test was developed to provide a better control of test conditions. To evaluate its ability (i) to differentiate different types of discontinuities affecting the sample and (ii) to offer a correlation with effective loads, a field study was set up, which is currently under progress. The results were studied by plotting the changes in the mass distribution. The form of the mass distribution before and after energy is applied and the shift to smaller sizes provides a powerful analytical tool to study the breakage processes. Comparing the mass reduction results of the full-scale splitting test and the mass reduction results of routine handling in the quarry provides a means of relating breakage in a standardized test to potential breakage in handling operations and in long-term service. Such a calibration process has the potential to authenticate a test method whose results can subsequently be used to predict the performance of this important class of construction materials.

This paper discusses the need for further guidance on the packing and stability of armour layers made up of individually placed rocks. It uses the results from full-scale revetments and their laboratory replica models to demonstrate the need for the blockiness parameter in armour shape classification if physical models are to be representative. With both blockiness and aspect ratio of an armourstone source characterised, it is possible to predict porosity and layer thickness with accuracies not previously reported and these are presented in simple formulae. Both single and double layer models were tested to examine the ability of such layers to resist damage from wave attack. Performance of the structures is compared with the predictions of Van der Meer's stability formulae. Results are discussed in the light of limited full-scale armour layer porosity data from UK structures and research panels. It is suggested that the individual placement of blocky shaped rock armour tends to produce low armour layer porosities, which in turn, confers considerable reserve stability for such structures designed with Van der Meer's formulae.

This paper describes a simple method to estimate storm wave conditions that caused damage to rubble mound breakwaters and revetments when no site wave measurements or wave information are available. The method consists of performing back analysis of armorstone cross-section design for breakwaters and/or revetments based on sustained damages occurring after storm wave action. The method utilizes construction record drawings, topographic survey data of damaged areas and van der Meer (1988) armorstone formula. Examples of back analysis calculations are shown, using information from physical model studies and from field coastal structures in Rio Grande do Sul, Brazil, and Port aux Basques, Newfoundland, Canada.

The assessment of armor damage on rubble mound structures can be carried out with different methodologies that need to be properly calibrated to guarantee the reliability of the results. The most commonly used parameter for the assessment of damage is the so called damage parameter. For prototypes, the averaged eroded area can be calculated if the geometry of the structure is measured before and after the damage. In the laboratory, profiling is the most common method used to assess the damage, but there are two other methods that can be applied.

In this paper, a small-scale experiment measuring damage development on rubble mound jetties is discussed. The jetties were arranged in a parallel configuration to form an inlet and were exposed to four long-term storm series composed of waves only and waves on a steady ebb current. In this paper, only tests with waves head-on to the jetties are discussed. The experiment yielded unique topographic data of one structure acquired throughout each storm using a precision laser profiler. The data show that previously developed equations for predicting damage development on breakwaters can predict damage on jetties; but the empirical calibration coefficients are shown to be variable between test series. Damage development for jetties with wave crests perpendicular to structure alignment appears to be similar to that of breakwater cross sections where wave crests are parallel to structure alignment.

Medium height breakwaters are subjected to a considerable amount of overtopping. This implies the armour on the inner slope has to stable against overtopping waves. Existing equations do lack some basic understanding of the process of starting up movement of rock on the inner slopes. In order to get more insight into this phenomenon a special device has been constructed in the laboratory. In this device it is possible to generate one single, overtopping wave. So with this piece of equipment overtopping of single waves can be repeated several times and a relation can be looked for between the individual plunge and the stability of the individual blocks. In an other research program the relation between the random waves and the individual plunges is investigated. As a follow up the results of damage by individual waves will be combined with the distribution of overtopping water over a breakwater. This combination will result in a damage distribution due to random overtopping. It has been found from the first test series that stability of the blocks can be described as a function of the maximum water velocity on the crest, combined with some geometrical parameters of the inner slope. From this research followed that the crest height and inner slope also had an effect on stability.

In order to construct an economical and reasonable structure, design methods, which can take economical efficiency into consideration, is necessary. The performance based design that specifies the performance of a structure is one of the economical design methods. An economical design would be established by allowing deformation of a structure within limits which satisfy the performance demanded. Therefore, the deformation of a structure should be estimated quantitatively. A probability which the deformation occurs should be evaluated, too. Conventionally, this is done by hydraulic model tests. The model tests, however, have scale effects, and they might be expensive. Accordingly, the development of the numerical computation method for the deformation is useful for the performance based design. One of coastal and maritime structures with the higher applicability for the performance based design might be a rubble mound structures, such as a sloping breakwater, an artificial leaf, or a rubble submerged breakwater. Two prediction methods of deformation for rubble mound structures were developed in this study. One is a deterministic method, and the other is a stochastic method. A deterministic method is consisted of fluid analysis and distinct element analysis. The stochastic method is an approximately method which expanded the deterministic method based on the reliability theory.

Two methods are compared to estimate the rubble-mound breakwater armor damage evolution in nonstationary wave conditions. The first method is based on the exponential model on individual waves proposed by Medina. The second method is based on Neural Networks pruned using Evolutionary Strategies. Both methods give reasonably good agreement with laboratory observations.

In Portugal rubble-mound breakwaters are the most common harbour protection structure. Since 1985, the Portuguese Civil Engineering Laboratory is in charge of the periodic visual inspection of most of these structures. This paper describes the procedures and the results of this work as well as the methodology that is being developed to combine the information from those inspections with that from the surveys of both the above water and submerged parts of the breakwaters in order to get better diagnoses for this kind of structures.

Puertos del Estado (the State Ports of Spain), the seven Spanish maritime engineering laboratories (Universities of La Coruña and Cantabria, Polytechnic Universities of Valencia, Barcelona and Madrid, and the laboratories CEDEX and INHA) and the University of Granada have been working together on the influence of wave reflection on the stability of rubble-mound breakwaters. With several laboratories working together, it is of great importance to ensure that their results are fully comparable. With this in view, and prior to performing the tests, all factors that could have a bearing on the experimental results were analyzed. This has resulted in a standard methodology for running the tests, which is the object of this paper.

Significant developments in the UK and Europe over the last decade in the use of waste materials in coastal structures are explained. The requirements for such materials given their likely context of use are set out. Specific information is given on the application of recycled timber and secondary and recycled aggregates and the paper concludes with a more detailed case study based around the re-use of tyres.

In this new study, the sliding performances of vertical caisson type breakwaters are discussed using the Monte Carlo simulation technique for detail in various conditions, such as, wave characteristics (breaking or non-breaking), caisson type, etc. Horizontally composite breakwaters are also analyzed from the viewpoint of sliding performance of the caisson incorporating wave pressure increase caused by damage to wave-dissipating concrete blocks.

A goal reflection coefficient is chosen to be K_R=0.4 and a design method for double slit-wall breakwaters with double slitted front walls, which has optimum dimension from a viewpoint of low wave reflection in wider frequency range, is proposed in the present study. The procedure of the design method is based on a numerical calculation with the Boundary Integral Method developed by the authors. In the procedure, important parameters affecting the goal reflection coefficient from the viewpoints of construction coasts are introduced explicitly.

The objectives of the present paper are classified into two items: One is to compare simulation results of the expected sliding distance for various existing parameter values of uncertain factors (e.g., estimation errors of deepwater wave height, calculation errors of wave transformation, wave period and wave force, uncertainties of friction factor), which is considered in reliability design procedures of caisson-type breakwaters, and the other is to propose an alternative for improved evaluation of the expected sliding distance in the reliability calculations. A doubly-truncated normal distribution is employed as the alternative.

A new estimation method for cumulative damage of armor stones covering a rubble mound foundation of a composite breakwater is proposed. The method is based on a wave induced flow field near the breakwater mound, which is calculated by a numerical wave flume CADMAS-SURF, and successive Monte Carlo simulation. Trial computations and comparisons with experimental results demonstrate the validity and usefulness of the proposed method.

The composite breakwater is one of the typical structures of breakwaters. In composite breakwaters, the stability of the rubble mound foundation plays quite an important role as well as that of a caisson. The rubble mound is usually protected by armor units, large stones or concrete blocks. This is to prevent dispersion of the rubble stones and deformation of the mound due to the action of the waves. The stable mass of the rubble mound armor units of composite breakwaters is generally calculated using the stability formula based on Ns. As to the stability number Ns, Tanimoto et al. proposed a formula for the stability of rubble mound armor units based on the standing wave theory and Kimura et al. modified Tanimoto's formula especially for concrete armor units. In recent years, there is more attention paid to maritime structures with high rubble mounds from the viewpoint of harmony with the sea environment. In high rubble mounds, there is a high possibility that impact breaking wave action occurs on the mound. Tanimoto's formula can not be applied in this case because it is based on cases where the water depth on the mound is comparatively large. Although Kimura's formula covers a high rubble mound, it does not take impact breaking waves into consideration. In our study, the stability of concrete armor blocks covering the rubble mound was carefully examined in a two-dimensional model test. From these results, a method to calculate the necessary mass of armor blocks for composite breakwaters is newly proposed, in which the impact breaking waves is taken into account.

An extensive programme of ongoing field, laboratory and numerical investigations into the characteristics of wave impacts is described and early results presented. Shock pressures are found to be highly localised, both spatially and temporally, able to propagate into cracks and, in freshwater at least, capable of reaching surprising intensities. Conventional scaling of 1:4 hydraulic model data implies that ocean waves ∼4m high could generate heads in excess of 1000m. Attention is drawn to the possibility that, in practice, such extreme pressures may be constrained by the acoustic (water hammer) limit. The parameter map used for predicting impacts is shown not to be entirely reliable and preliminary results of the numerical models are discussed.

It is accepted that dynamic loads and structural responses must be analysed in design of large offshore structures. Recent studies in Europe and Japan have shown that it is unsafe to ignore high intensity short duration loads in design of caisson breakwaters and related harbour structures. Dynamic effects of wave loads are however seldom included in structural analysis of coastal structures, leading to designers ignoring short-duration wave loads, perhaps contributing to damage to a range of breakwaters, seawalls or suspended decks. This paper reports recent advances in knowledge on impulsive wave loads, describes analysis for dynamic responses, and illustrates a range of prediction methods to include these important effects in design. It compares measurements of impulsive and pulsating loads from physical models of coastal structures, to quantify their magnitude and relative importance.

Increasing sea water levels and storminess has intensified the need for structural measures to reduce wave overtopping without significantly raising the height of the wall. The use of recurves / wave return walls / parapets on vertical walls has been shown capable of significantly reducing wave overtopping, but may increase wave loading. Many parapet / recurve solutions have been used in practice, but no general guidance on their design are yet available. In this paper a significant amount of data have been gathered together under the EC CLASH project (EU project no. EVK3-CT-2001-00058) and studied more systematically for the first time. The paper discusses problems with systematic approaches to both overtopping and wave loading. It concludes with a simple reduction factor for wave overtopping depending on geometrical dimensions of the parapets and some guidance on wave loading for these cases.

Within a research project on Exposed Jetties, a series of physical model studies has measured wave-induced loading on a model of an open-piled jetty structure. These measurements gave a series of force and pressure data on selected structural elements of the model jetty, covering a wide range of wave conditions and deck geometries. Initial analysis of these new data revealed inconsistencies and gaps in methods previously used to predict wave-induced loading on jetty structures and provided the basis for new guidance for their hydraulic design. A series of dimensionless variables has been found for horizontal and vertical forces (and pressures) on beam elements and deck slabs. Dimensionless relationships are presented for selected configurations and structure elements to provide consistent engineering guidance for wave loading on exposed (open piled) jetties.

Stability of a tube element for the Naha Immersed Tunnel is experimentally and numerically investigated under various wave conditions. The construction site of the tunnel is located in Okinawa Island that suffered from frequent raids of typhoon. It is found through the investigation that weight control is not enough to stabilize the element during construction stage, and that backfilling on the sidewall of the element is inevitable. A rapid emplacement method is developed to construct the tunnel safely. No. 1 element was successfully placed with this method.

In the caisson-type bulkhead sitting on the rubble mound with a waterproof structure using a waterproof sheet, the wave pressure transmitted through the mound, the backfill and the seabed will always act on the waterproof sheet. In order to prevent the sheet from being lifted up and ruptured by the pressure, weighting materials are usually placed on the waterproof sheet as a weight. When we design the cross section of weighting materials, it is important to appropriately evaluate the wave pressure acting on the waterproof sheet as an external force. However, few studies have been conducted on wave pressure characteristics, and there are many unknowns. Therefore, in this study, we performed a hydraulic model experiment. We analyzed this numerically, using the numerical wave flume to clarify the characteristics of the wave pressure acting on the waterproof sheet. Through this study, we propose a simple method to calculate wave pressures.

The EU project CLASH, stands for `Crest Level Assessment of coastal Structures by full scale monitoring, neural network prediction and Hazard analysis on permissible wave overtopping'. One of the objectives of CLASH is to produce a generally applicable prediction method for wave overtopping at coastal structures based on permissible wave overtopping and hazard analysis. The set up of a homogeneous database on wave overtopping is one of the main tasks within the framework of CLASH and is the main subject of this paper. On the one hand, the database gives a detailed inventory of overtopping tests which have been performed and on the other hand, the database serves as the starting point for a neural network prediction method.

Wave overtopping has been responsible for many dike failures, dike breaches and severe floodings in the past. An example of dike failures due to wave overtopping is given. At first, it seems to be astonishing that dike failures are initiated on the landward slope since the incoming waves are hitting the seaward slope. Three aspects are responsible for this misinterpretation. First, wave overtopping has been often neglected for the design of seadikes because a no overtopping criteria was assumed. Second, landward slopes of seadikes are often steeper and the cover (mostly clay) of the landward slope is thinner than the cover of the seaward slope. Third, the landward slope has been designed based on experience and no physically based design methods are available at present. In the future, the necessity of a well designed landward slope is increasing due to the uncertainties concerning sea level rise and the increasing frequencies and intensities of storm surges worldwide. Present formulas for wave overtopping consider average overtopping rates. Average overtopping rates are required to design the drainage of the hinterland of seadikes but not for the stability of the landward slope. The stability of the landward slope depends, besides geotechnical aspects, on the instantaneous loads due to wave overtopping, which can be described by layer thicknesses and overtopping velocities.

The main objectives of the project were firstly to investigate the influence of rock density on the armour layer stability and secondly to collect large scale data on wave run-up and wave overtopping. By using high density rock for coastal protection measures, the required size and volume of rock can be reduced. The filter layer also benefits from this reduction and sections of a breakwater suffering severe wave attack can be protected more effectively with high density rock without changing the rock size used in other sections. The disadvantage of using high density rock is believed to be higher wave run-up and increased wave overtopping discharges.

Hydraulic model tests were performed within the European CLASH project at two different sites in Europe to hindcast measured overtopping rates during storm events from prototype measurements at the Zeebrugge rubble mound breakwater. The paper describes the general methodology behind this comparison and results regarding uncertainties in measurements of both waves and mean overtopping rates. Quantification of uncertainties is shown to be the first step in being able to quantify model and scale effects and therefore need to be properly assessed. First plots of available model tests showing considerable scatter in wave overtopping results are also given together with initial data points from prototype measurements.

As part of a major European research project into wave overtopping at coastal structures, overtopping discharges have been measured at full-scale on a vertical seawall in Southeast England. The measurement site, Samphire Hoe, is an area of reclaimed land just west of Dover on the English channel coast, and is an ideal location for monitoring overtopping. The site is described in detail, and the design and operation of the measurement equipment are also outlined. Overtopping was measured on three occasions and the storms and their results are discussed. It is shown that the field measurements compare well with empirical prediction methods by Besley and Bruce et al. Additional discussion interprets the hazardous nature of each of the storms.

The objective of this paper is to describe the recently installed full scale measurement infrastructure to quantify hazards resulting from wave overtopping at the Zeebrugge rubble mound breakwater. First the measurement site and the specific set-up used for wave overtopping measurements is briefly described followed by the description and design of the instrumentation to quantify hazards. Finally, preliminary conclusions are drawn.

Rubble mound breakwaters are designed for allowable wave overtopping conditions by either physical modelling or numerical modelling or a combination of both. These models need to be calibrated and model results need to be verified against reality. One of the main outcomes of the EC OPTICREST project was that wave run-up on a rubble mound breakwater is underestimated in small scale models compared to full scale (De Rouck et al. (2001)). As wave run-up is closely related to wave overtopping, small scale model tests might underestimate wave overtopping as well. The link between full scale and laboratory wave overtopping measurements has not been made in a systematic way yet. One of the main objectives of the research project CLASH (Crest Level Assessment of coastal Structures by full scale monitoring, neural network prediction and Hazard analysis on permissible wave overtopping, 2002–2004), funded by the European Commission under contract n^o EVK3-CT-2001-00058 is to solve the problem of suspected scale and / or model effects for wave overtopping. To accomplish this objective, field measurements on wave overtopping are carried out at three different locations in Europe: a vertical seawall with rubble mound toe protection at Samphire Hoe, United Kingdom (Pullen et al., 2003), a rock armoured rubble mound breakwater in shallow water at Ostia, Italy (Franco et al., 2003) and a rubble mound breakwater armoured with flattened Antifer cubes at Zeebrugge, Belgium. All prototype sites will be modelled in two different laboratories and laboratory results will be compared to prototype results. The objective of this paper is to describe the full scale infrastructure to measure wave overtopping at the Zeebrugge rubble mound breakwater.

This paper describes new wave overtopping field measurements at Ostia yacht harbour breakwater (Rome, Italy). The structure, the measurement strategy and the equipment are described in some details. Preliminary results of a recently measured overtopping storm (Oct 2003) are presented. The activities are carried out within the framework of the European Union research project CLASH, aimed at studying model scale effects in overtopping studies and at providing scientific and professional communities with reliable crest level design criteria for coastal structures.

To conduct risk assessment of storm surge floods for hazard maps, a definitive method of setting up tide levels and wave overtopping rates should be established for inundation simulation. In this study, extreme statistics analysis of tide levels, waves, and wave overtopping rates was conducted by using results of a Monte Carlo simulation for 2,000 years with a stochastic typhoon model based on observed past typhoons.

Most prediction methods for wave overtopping are based on physical model tests under simple 2-D conditions. This paper describes experiments to measure mean and wave-by-wave overtopping discharge under oblique wave attack. Results suggest that overtopping discharges reduce significantly only for angles of wave attack > 30°. With increasing obliquity, impulsive events transform to "impact-like" events (0° < β ≤ 30°) and then eventually to reflecting waves (60°). Tentative guidance is given for appropriate formulae for each obliquity.

This paper revisits 2-D physical model wave-overtopping results for unique, steel sheet pile vertical walled and concrete-stepped revetments along the Chicago, Illinois, USA shoreline. To provide design guidance, the U.S. Army Engineering Research and Development Center's Coastal and Hydraulic Laboratory, performers of the physical model studies, developed a predictive formula applying multiple regression analysis. This formula lacks separation of some key parameters including revetment width and toe berm effects. Therefore, this paper applies dimensional analysis to the existing site-specific physical model data in an attempt to improve the predictive formula.

The paper aims to improve the prediction of wave transmission behind low-crested rubble mound breakwaters by employing artificial neural networks. Data from physical experiments on rubble mound low-crested structures have been gathered within the European research program DELOS and this dataset has been used. The present work demonstrates that the neural network approach is able to improve the results compared to classical formulations in the prediction of the wave transmission coefficient as a function of both hydraulic and structural parameters.

Wave transmission over low-crested structures has often been subject for research, as the wave field behind these structures determines what will happen in this area. Detached low-crested structures are often parallel to the coastline and in most cases wave attack will be perpendicular to this coastline and therefore, perpendicular to the structure. This situation can be simulated by small scale physical modeling in a wave flume. Results have been given by Van der Meer and Daemen (1994) and d'Angremond, van der Meer and de Jong (1996). Recent research, including all data of the above given references and new extensive data sets, has enlarged the insight on the topic, see Briganti et al. (2003). The results from 2D tests are: 1) prediction formulae for the wave transmission coefficient K_t and 2) description of change of spectral shape due to wave transmission. In quite some situations low-crested structures are not parallel to the coast. T-shaped groynes are an example, but also breakwaters for a harbour where only under very extreme storm surge the structure can be considered as low-crested. In these situations wave attack is very often not perpendicular, to. the alignment of the structure and in many situations even quite oblique wave attack and transmission occurs. But what will be the difference with perpendicular attack? More in detail: 1) Are the prediction formulae for K_t still valid? 2) Is the spectral change (more energy to high frequencies) similar to perpendicular wave attack? 3) Is there any influence of short-crestedness of waves? and 4) Are wave directions similar in front of the structure and after transmission? Only a three dimensional investigation in a short-crested wave basin can give answer to these questions. Within the EU-project DELOS these tests have been performed and are the subject of this paper.

Within the European Union funded research project DELOS, a wide database containing more than 2000 2D laboratory tests on wave transmission behind low crested structures has been collected. The data has been reanalysed in order to test and improve the reliability of the existing design formulae by improving the description of the dependency of wave transmission on structural and hydraulic parameters. Also the change of wave energy spectra has been analysed and related to governing parametetrs.

Wave transmission is a leading parameter determining the response of the shoreline to a detached breakwater. Wave transmission properties can vary significantly depending on structure configuration and composition, and they can also vary over different time scales as controlled by tidal variations or changes in incident wave conditions. Therefore, the capability to predict shoreline response to detached breakwaters for a wide range of engineering conditions requires an expression for the wave transmission coefficient that is valid over a broad range of environmental forcing and breakwater designs. To improve the predictive capability of the GENESIS shoreline response numerical model, several published empirical formulas for the wave transmission coefficient were evaluated. A dominant mode approach introduced by Ahrens provided the most appropriate general predictive procedure suitable for shoreline response modeling. The application of an artificial neural network for predicting wave transmission was also evaluated and found to be a suitable general predictive procedure.

The 2D numerical wave flume based on VOF method, called CADMAS-SURF, was applied the hydraulic pressures acting on the structures due to the flooded water. The validity of this model verified due to comparison with experimental data. Then the numerical simulation of the hydraulic pressures was carried out. The numerical results suggested the importance of detached breakwaters to decrease the amount of flooded water and hydraulic pressures.

Well-verified guidance exists for the prediction of wave overtopping over vertical walls, including breaking / impulsive and non-breaking / pulsating wave attack. For broken waves, only Goda's design charts give guidance, and only for sea steepnesses s_op < 0.036. This paper presents results of tests to quantify overtopping of vertical walls under predominantly broken wave attack. Tentative guidance is suggested. For cases where the toe of the wall is submerged, an adjustment to the method of Besley is suggested. For cases where the water level falls below the toe of the wall, adjustment to the method for sloping structures of van der Meer and Janssen is suggested.

Storm waves breaking in the surf zone and crashing over seawalls are a violent natural phenomenon with the potential to cause enormous damage. Much of the existing design guidance for seawalls considers the mean overtopping discharge on the structure. Under impacting conditions, however, the overtopping volumes associated with individual events can be significant. Under the UK Engineering and Physical Sciences Research Council (EPSRC) funded VOWS project and the European Commission funded CLASH project work has been undertaken using both laboratory investigation and computer simulation to quantify these wave by wave overtopping volumes. This paper discusses the application of the AMAZON-SC multiphase numerical wave flume developed by Manchester Metropolitan University to simulate experiments of violent wave overtopping conducted in the Edinburgh University 20m wave flume.

In this paper, an extended version of the model of Lin and Liu is applied to study the cases of small negative freeboard wave overtopping and overflow of seawalls. The model computes a finite difference solution to the incompressible Reynolds equations for the mean flow field and the k - ε equations for the turbulent field are obtained on a non-uniform mesh. The free surface locations are presented by the volume of fluid (VOF) data on the mesh. The extended model includes the capability of simulating flows in porous media, which use the resultant spatially averaged equations to describe the mean motion of flow, and also uses an internal source function to generate waves. The model performance is being compared against laboratory models and other numerical models. The model reproduces the results of the well-known weir equation very well and is then used to investigate combined discharge due to overflow and wave overtopping of impermeable seawalls for increasing wave activity for a range of negative level freeboard values. Results for irregular wave attack are presented together with suggested extensions of design formulae.

In Port of Kushiro, a breakwater with an artificial shallow reef is now being constructed. This shallow reef will be used for fish and seaweed firm. The reef is filled with loosely deposited dredged sand and covered with armor blocks to prevent scouring by overtopping waves. Because of the strong wave overtopping, the sandbed will be suffered from liquefaction. Suzuki et al. conducted a series of experiments to examine wave-induced liquefaction in a loosely packed fine sandbed. Liquefaction with residual pore pressure occurs due to wave driven shear stress in the sandbed. The compaction of a liquefied sandbed in response to cyclic wave loading was also observed. In a usual seabed, liquefaction with residual pore pressure does not occur because cyclic wave loads compact the sand. On the other hand, the loosely deposited sandbed behind the breakwater is likely liquefied due to wave overtopping after the construction. In order to avoid devastating liquefaction, we conducted a series of experiments in a wave flume. FEM simulation was also conducted in order to evaluate the liquefaction limit.

An extensive program of field measurements of currents around a beach defence system is described and results are shown. The monitoring program was carried out in the last three years around a semi-submerged breakwater built in Lido di Dante, Italy to protect a beach nourishment and prevent erosion. The monitoring aims to study the complex hydrodynamics of Low-Crested Structures (LCS). Drifter tracks surveyed in the study area together with current and wave measurements through an ADCP provide a better comprehension of the hydrodynamics during typical wave storms and a tool for the calibration of numerical models.

An 8.5 hectare (21 acre) sediment cap was designed for remediation of contaminated sediments at the McCormick & Baxter Creosoting Company Superfund Site in Portland, Oregon. The sediment cap was designed to provide physical and chemical isolation of the underlying contaminated sediment in addition to physical stability of the cap itself. Contaminants of concern at the site include Arsenic, Pentachlorophenol, Carcinogenic Polynuclear Aromatic Hydrocarbons (cPAH) and Dioxins/Furans. Hydraulic analyses conducted for the project included vessel wake, wind waves, wave transformations across complex bathymetry, flood induced currents and propeller induced currents. The design incorporates several features to enhance both terrestrial and aquatic habitat at the site that is a migration route for endangered species of anadromous fish.

In March of 2001, The Hydrographic and Oceanographic Service of the Chilean Navy (SHOA — Servicio Hidrográfico y Oceanográfico de La Armada de Chile) embarked on a comprehensive wave modelling programme with the objective of developing a 40 year deepwater wave database over the entire Chilean coastline. It was recognized that the institutionalization of a high quality reliable deepwater wave database will result in improved engineering and lower investment costs of coastal and marine infrastructure. This paper and presentation will provide a detailed description of this comprehensive coastal engineering initiative known as "Olas Chile". A focal point of the paper will be the development of a long-term hindcast of Pacific Ocean wave conditions for the entire coastline of Chile using the 2^nd generation wave model known as WAVAD. Emphasis will be placed on the bi-modal nature of the wave climate in the South Pacific due to the presence of both northern and southern hemisphere swells, the resulting importance of an accurate development of the bi-dimensional (2D) wave energy spectrum (or directional spectrum) in deepwater required to adequately describe the directional characteristics of the operational wave climate, and the necessity to spectrally transfer the 2D spectra using a frequency-direction transfer function.

A natural or dredged channel extending outwards an harbor entrance may strongly influence wave penetration into the harbor itself. Bottom refraction and diffraction induced by the channel boundary slopes can actually cause either concentration or dispersion of wave energy at the harbor entrances, depending on the direction of incoming waves. Wave penetration may therefore depend on directional spreading of incoming wave energy more than on its frequency spreading. The present paper illustrates the results of an investigation carried out on the Malamocco inlet of the Venice lagoon - Italy - by means of a 2D fully elliptic mild-slope equation FEM model, alongside a study intended to support a barrier-system design aimed at protecting Venice from storm-surge flooding. Being characterized by a natural channel extending outwards its entrance actually makes this inlet a particularly suitable case of study. Both frequency and directional spreading have been simulated by means of the superposition principle, either taking into account or not taking into account wave breaking. The results confirm the smoothing effect on both wave concentration and attenuation due to the directional spreading, and show that wave attenuation is to be expected for waves traveling along direction nearly parallel to the channel axis (0°–10° to the channel axis), whilst wave concentration arises when the wave direction is about 20°–30° to the channel axis.

Velocity profiles at the swash zone have been sampled with an ADVP during a large scale experiment on a fixed bed beach. The unique set of data permits to observe the time variation of the velocity distributions and to contribute to the debate concerning the variation of the friction factor, f, in a swash cycle. The analyses of the velocity data with the ballistic model and with the Law of the Wall have given opposite results. It is shown that if the pressure gradient is considered, the friction factor is expected to be larger at uprush than at downrush. Finally, for the adopted beach characteristics and at transects above the still water level shoreline, it is assumed f =0.016 at the uprush, and f = 0.009 at the downrush.

A numerical model, solving the Navier-Stokes equations with a Volume-of-Fluid (VOF) method has been used to simulate wave breaking on an impermeable slope. The VOF-method applied in the present study has been improved and applied to compute pressures on a slope caused by breaking waves. The comparison of the computational results with results from physical model tests demonstrates a good performance of the model. A qualitative comparison shows that the wave pattern is simulated realistically. Both the overturning of the waves and the bouncing of the wave tongue after hitting the slope are present in the numerical model results. Comparison of the measured and the computed pressure signals shows that the model provides reasonable results for conditions with non-overtopping waves and for some cases with overtopping waves.

This paper presents results of surface elevation and kinematics measurements made in the UK Coastal Research Facility (UKCRF). Investigations were made into the behaviour of focused wave groups as they ran up and overtopped a plane beach and a sea wall. Measurements of the kinematics of focused wave groups were made using an acoustic Doppler velocimeter (ADV) and a laser Doppler anemometer (LDA). Kinematics results from the LDA alone are presented in this paper. Analysis of the data has revealed information about the harmonic structure of the wave group both for surface elevation and kinematics.

This paper presents the results of a numerical investigation on the flow fields around a cylinder exposed to oscillatory plus mean flow. The flow fields were simulated using the Navier-Stokes equations expressed in a generalized curvilinear coordinate system. Descriptions are given of the three-dimensional flow structures around the base of the cylinder and examinations are made on the effects of the coexisting current ratio, V_r, and the Keulegan-Carpenter number, KC, on the vortex motion. It is shown that the horseshoe vortex increases in both size and lifespan with V_r and KC. The results indicate that the streamwise extent of the horseshoe vortex can be correlated well with a single dimensionless parameter. The bed shear stress under the vortices is also investigated in detail. The amplification of the bed shear stress is heavily influenced by V_r and KC. The results show that the maximum shear stress beneath the horseshoe vortex is sufficiently larger than that of the pure oscillatory flow and the value is less than that of the pure current case.

The purpose of this study is to define the flow pattern of nearshore bottom currents driven by wave-current interaction and thus to confirm hydrodynamic mechanisms associated with morphological changes at open channel ocean outfalls at the shore. Use is made of an earlier study reported by the authors on the interaction of horizontal momentum jets and opposing shallow water waves at a shore, and of an unpublished later laboratory study. The turbulent jet discharge was shore-normal, directed offshore, and the incident wave direction was shore-normal, travelling toward shore. The waves approaching shore were refracted by the horizontal shear of the jet. Flow visualization was used to determine the flow pattern in the jet and the induced circulation on both sides of the jet, for a range of wave and jet characteristics. The experimental data showed several distinct flow pattern regimes. Theoretical analyses were conducted to yield quantitative design parameters to characterize various flow pattern regimes. The observed flow regimes were found to depend on the ratio of the wave momentum action on the jet to the jet initial momentum. Confirmation of the obtained design parameters was obtained by comparison with field data for the formation of accretion shoals and erosion spots near marine outfalls.

This paper considers effects of waves reflected from breakwaters on small vessels near or entering harbours. The implications for the safety of small vessels navigating in regions of crossing wave trains are discussed. Studies to examine the nature of the sea state in areas where such conditions are created by reflective breakwaters or other coastal structures are summarised. Recommendations are provided for considering the implications for vessel safety when small craft must traverse such areas.

This paper presents a new method to separate damped incident and reflected waves propagating over a muddy bottom and to estimate associated dissipation ratios from simultaneous recordings of wave profiles. On the basis of the resolution results, the reflection coefficient of the structure is estimated. The resolution technique is verified by an agreement with numerical experiments, and the technique is modified to improve the accuracy. Using recorded wave data, the analysis examined wave-damping ratios predicted by mud motion theory under regular waves. Thus, both numerical and laboratory experiments verify the resolution techniques.

This paper describes a recently developed numerical modelling system, which is capable of taking account of wave reflection from a group of nearshore breakwaters and the effect of the leakage through leaky nearshore structures. The model, which also includes other nearshore processes, such as wave-current interaction and wave breaking, was tested against the experimental data obtained from tests over a complex topography and a group of scaled-down breakwaters. Comparisons of the computed results of wave height and wave-induced current with measurements showed that the model performed well in reproducing nearshore hydrodynamics.

In this study, laboratory experiments were conducted in order to investigate mass transport velocities and turbulence flows around an artificial reef due to a new type wave front breaker over it. In addition to this, we examined a classification of an occurrence condition for the wave front breaker. Consequently, it was found that the occurrence condition of the wave front breaker was classified using the Ursell Parameter and relative crown depth, and an increase of mean water level behind the artificial reef did not affect the occurrence of the wave front breaker. Furthermore, reverse layers of mass transport velocities were found around the toe area of the artificial reef. The thickness of the reverse layers varied with the incident wave height and had its peak. Strong turbulence occurred during the wave run-down to the run-up phase at the breaking point. In addition, the time-averaged turbulence intensity maintained a large value not only beneath the jet mixing due to the wave breaking, but also near the bottom at the breaking point.

Distributions of wave heights around submerged, detached breakwaters with wide crests, or artificial reefs, are computed with a new numerical scheme using a gradational wave breaking process based on parabolic equation for directional random waves. Applicability of the numerical scheme has been verified with laboratory and field data. The governing factors for the wave transmission coefficient are identified and several design diagrams are presented. Artificial reefs with their longitudinal axes perpendicular to the shoreline are demonstrated to perform better than shore-parallel artificial reefs.

A general form of high-order Boussinesq equations is newly derived. The dispersion characteristics are further improved by partially replacing the dispersion terms. Compared with the previous models, the linear dispersion property of the present model is significantly improved. For group velocity, the 5th and 3rd order models give excellent agreement with the theory in the range of kh < 50 and 10, respectively. In addition, a practical numerical model based on the 3rd order equations is developed. The model is applied to the study of wave deformation around an artificial reef placed on a sloping beach. Systematic computations and hydraulic experiments are carried out under severe conditions of small water depth above the reef. The comparison between experiments and numerical predictions shows that the present model can reproduce the complicated wave fields including reflection, breaking, disintegration, re-generation very well.

Within the EU-funded project DELOS, 3D tests were performed in the 12.5 m x 9.7 m wave basin at Aalborg University, DK, with the aim of analysing waves and currents around low-crested structures. The paper presents some experimental results on overtopping of low-crested structures both in a symmetrical layout, composed by two detached breakwaters with a gap in between, and in a oblique layout, composed by a single breakwater oblique to the beach. An original scheme for evaluating overtopping processes with varying structure submergence and wave attacks is provided and discussed in comparison with experimental mass balance.

An analysis of the near-fiel flow at porous low-crested structures under breaking conditions is conducted, using a VOF-type numerical model based on the Reynolds-Averaged Navier Stokes (RANS) equations and including a k-ε model. Results of numerical simulations of small-scale laboratory experiments on rubble-mound submerged breakwaters are presented, with emphasis on the influence of the crest width on the flow conditions. Both experimental and numerical wave flumes include a system of flow recirculation aimed to prevent the usual excessive set-up leeward of overtopped structures in 2DV configurations. The numerical model is proven to reproduce with a high degree of agreement the different phenomena of wave interaction with low-crested structures and can be used as a valuable tool for functional and structural design.

Laboratory measurements of waves and currents collected around low-crested structures tested in a three-dimensional wave basin are used to calibrate and/or validate numerical models of varying complexity. Waves generated in the basin included regular as well as irregular, directional waves. Numerical models applied in the analysis were both of the phase-averaged and depth-integrated two-dimensional (in the horizontal) type, as well as a fully three-dimensional Navier-Stokes solver. The results obtained from the comparison of model results to measurements are presented and discussed.

A statistical comparison is presented between measured and computed cumulative distribution functions of wave height, pressure and velocity around and inside rubble mounds for submarine outfalls. The data set is obtained from laboratory and prototype experiments, originally designed to determine the stability of the stones protecting the pipeline. From the experiments, it was found that the peak horizontal velocity at the crest of the structure is continuously underestimated during the design stages. Generally speaking, although all cumulative distribution functions follow reasonably well the Rayleigh distribution, the largest waves deviates, yielding an increased maximum value for pressures and velocities. Since the stability of the stones is directly linked with this velocity, an enhanced formulation to assess it has been tested successfully, although the performance of the model has to be improved.

The stability of coastal lagoons is often precarious. Their ecological balance is easily altered by changes in the surrounding environment, particularly those of nearby urban developments. Common problems include pollution and eutrophication. Since these lagoons are generally connected to the sea by either natural or artificial channels, one way to improve water quality in the lagoon is to increase the input of seawater through these channels, thus flushing out the pollutants and thereby controlling eutrophication. One of the main advantages of the flushing system presented in this paper is that virtually no maintenance is required. From the experiments carried out in the laboratory and on the coast an analytical model was developed to assist in the design of a wave amplifier. The analytical model is in agreement with the results obtained with monochromatic waves in the laboratory. The seawater obtained by such a method could be injected into a coastal lagoon to flush out pollutants and improve water quality. A wave amplifier of this type could also be used to clean out tanks at aquaculture farms on the coast.

Oregon State is upgrading its multidirectional wave basin under the National Science Foundation Network for Earthquake Engineering Simulation (NEES) program to create a next-generation experimental testing facility for research and practicing engineers. The new facility addresses the unique requirements posed by tsunami researchers, with basin dimensions and wave generation capabilities closely matching the community's vision of the "ideal basin". When completed in 2004, the basin will support high resolution, unprecedented-scale experiments with very dense instrumentation. Researchers will be able to test and validate advanced analytical and numerical models of general environmental fluid mechanics issues in coastal science and engineering including tsunami phenomena induced by sub-sea earthquakes, spanning a full range of ocean, coastal, and harbor studies. An integral part of the upgraded facility is the exploitation of advanced network technologies to allow researchers located at distant sites to play active roles in experiments at the facility, viewing data and images in real time and participating in decision-making. The broader research community will benefit from this large long-wave experiment facility, a comprehensive experiment databank, with specialized interfaces for experiment re-play, searching and browsing archives of past experiments, extraction of experimental data for use in validating numerical models, and a community repository for numerical simulation codes. A summary of the progress on basin building, wave generator and network system design, construction, installation and planned research will be presented.

In engineering practice submerged soils are commonly considered to be saturated and consequently the pore fluid may be regarded as incompressible. At shallow water depths this two-phase model is not in accordance with natural conditions. Even small quantities of gas bubbles change the stiffness properties of the pore fluid dramatically. In response to external fluctuating pressures, the gas bubbles in the pores experience a volume change, thus causing local transient flow. The latter must be consistent with the permeability law of the soil. Based on Biot's consolidation equation, both uncoupled and coupled numerical simulations and analytical estimates have been employed, demonstrating that time-varying pressure loading contributes to soil deformation, fluidization and hydraulic failure. A variety of geotechnical situations is reviewed. These include rapid draw-down, wave loading and turbulent water current acting on both a protected or unprotected sandy soil bed in shallow water. The actual pore pressure response of the submerged subsoil has been calculated. It is demonstrated that this loading contributes to sand bed deformation, fluidization and associated failure. The vulnerability to erosion and scouring is emphasised.

Groin notching has been used in the Spring Lake, New Jersey section of the Sea Bright to Manasquan, New Jersey Beach Erosion Control Project, to allow increased post-nourishment littoral transport through an extensive groin field. Construction procedures for the groin notching illuminated various difficulties of working in the surf zone. Through monitoring and analysis of beachfill performance data, trends regarding groin notch location were developed, and an erosional "Hot Spot" was identified and improved through a subsequent groin notching and beachfill renourishment.

This study involved the design of beach diamond mining between Alexander Bay Harbour and the mouth of the Orange River on the west coast of South Africa. To mine this area entailed creating artificial sand beaches overlying rocky areas. Numerical modelling was conducted to predict the shoreline evolution resulting from sand feeding. The effectiveness of groynes to trap the limited natural longshore drift and sand dumped updrift of the groynes, was also considered. In addition, the structural design of these temporary groynes was carried out. Rock, concrete cubes and geotextile structures were investigated. The effects of different sand feeding rates and discharge locations in conjunction with varying groyne lengths and locations were simulated. Time-varying mineable areas were predicted. A temporary sand dike was designed to protect the mining activities from the sea. The potential physical impacts on the Alexander Bay Harbour and on the mouth of the Orange River were also investigated, as the high sand feeding rates advantageous to mining could potentially severely affect the harbour and river mouth.

The performance and durability of timber groynes (or `groins') is highly dependent on the design and detailing of the structure. Using knowledge and experience developed over generations an effective functional design can be achieved, which may ultimately result in lower whole life costs and provide environmental advantages over alternative materials.

Rock groynes (or groins) are regularly used in coastal engineering to control the morphological development of beaches and to provide protection against coastal erosion. Established design guidance provides a good degree of confidence in predictions of performance of many coastal structures, but it is widely perceived that simple design rules can be overly prescriptive, particularly for nearshore structures in shallow water depths. Strict adherence to design guidance has required many structures to be built using multiple rock sizes, imported rock and carefully prepared foundations. Some innovative groyne schemes within the UK have, however, used locally available rock with simplified cross-sections placed on unprepared foundations, apparently without significant reduction to the overall performance of the scheme. This paper presents findings from a short research project, relating to the design and assessment of low cost rock structures for beach control and coast protection. Practical experience from structures around the UK was reviewed, with particular emphasis on those that depart from conventional design rules. The paper demonstrates that lower cost rock groynes provide opportunities for reduced lifecycle costs and may be particularly appropriate in situations where conventional structures would be uneconomic.

A numerical model based on finite-amplitude, shallow-water wave theory is developed to predict irregular wave breaking and transmission as well as wave force on an innovative Shore-RIB structure that consists of one or two tubes held by an anchored fabric shroud. The numerical model slightly underpredicts the measured transmission coefficient which decreased linearly with the increase of the ratio between the crest elevation of the structure and the incident spectral significant wave height. The maximum fabric tension predicted using the computed wave force is in fair agreement with the measured tension. The difficulties in predicting the temporal variations of the fabric tension due to intermittent tube oscillations are discussed using the measured and predicted results.

Geotextile tubes (GTs) have become increasingly popular in recent years for coastal engineering applications due in large part to their relatively low cost. However, depending on the application, GTs may require significantly more maintenance than alternative structural approaches such as articulating block mats, graded riprap, and sheet piling. GT applications are very specialized, and unique considerations are needed in design, construction, and maintenance. Although the basic concept appears simple, it is essential that a GT application be designed and constructed by qualified individuals with hands-on experience to achieve a successful installation. To date, much of what has been learned regarding GTs comes from unexpected installation and/or performance problems and the resulting corrective actions, as opposed to laboratory testing or numerical analysis. This is especially true with repair and maintenance of GTs. Some trial and error with prototype installations is necessary, since laboratory and numerical analyses involve idealized settings and do not include all the complex variables encountered during construction and in the dynamic coastal environment. Many of the problems encountered have been avoided in subsequent applications by continually enhancing technical specifications, so as not to repeat deficiencies in both design and construction.

The Samoa Stone^TM is a new, unique, patented, aesthetic, interlocking concrete armor unit. It is versatile and can be used to protect shorelines, waterways, coastal structures, and hydraulic control structures from erosion by waves and steady currents. This paper discusses historical development, unit geometry, and armor layer characteristics. A physical model study investigating armor stability, wave runup, and wave transmission is summarized. Design recommendations and potential uses of Samoa Stone are discussed.

The US Army Corps of Engineers (USACE) has undertaken a thorough study of coastal processes in and around the entrance to Grays Harbor, WA, in order to optimize the performance of the North Jetty. As part of this study, detailed numerical modeling of 2D nearshore circulation and sediment transport was conducted to evaluate the impacts of a number of structural alternatives on waves, water levels, nearshore circulation and the resulting sediment transport relative to existing conditions (MacDonald et al., 2003). This work was done to examine the sensitivity of these impacts to variations in nearshore bathymetry. This paper summarizes the approach and findings of this fine-scale nearshore modeling work. Five structural alternatives were investigated along with two sets of bathymetric conditions in order to account for the year-to-year variability in nearshore morphology. Several numerical models were used to study the waves, circulation patterns, sediment transport potential and sediment bypassing. Ninety-six simulations were performed for each structure-bathymetry combination to represent the local tide and wave climate. A novel approach of this work was the analysis of the results in terms of an annualized climate. The results of this fine-scale nearshore modeling work showed that all alternatives were successful, to varying degrees, in promoting sediment retention on the adjacent beach and in reducing sediment bypassing into the inlet.

This paper presents an update on the National Shoreline Erosion Control Development and Demonstration Program (Section 227 Program). The primary purpose of this U.S. Army Corps of Engineers (USACE) research and development program is to evaluate innovative shoreline erosion abatement technologies demonstrated at prototype scale and assess value added relative to more traditional methods of shoreline erosion control and sediment management strategies. To date, 13 demonstration projects are included in the program.

Erosion in Cape Lookout State Park on the Oregon coast removed a line of high dunes that had existed between the ocean beach and park facilities, so winter storms were able to flood the park grounds. Shore protection was needed, but it was decided that a conventional quarry-stone revetment or seawall would not be used in this park setting. Instead, the decision was made to construct a dynamic revetment, designed to be similar to a natural cobble beach, backed by an artificial dune reinforced with a core of sand-filled geotextile bags. Since their construction in 2000, we have monitored the structures in a program of periodic surveys, measurements of cobble mobility through tagging, and analyses of tides and wave runup compared with structure elevations. To date the structures have survived three winters, including major storms that resulted in some overtopping. Thus far this natural form of shore defense has proved to be successful in protecting the State park from significant storm damage, but their long-term stability remains uncertain.

A demonstration project was installed at Cape May Point, New Jersey as part of the US Army Corps of Engineers National Shoreline Erosion Control Development and Demonstration Program. The purpose of the demonstration program is to evaluate prototype-scale innovative or non-traditional shoreline erosion control methods. The Cape May Point, N.J. project consisted of installing a linear prefabricated concrete submerged breakwater called the Beachsaver Reef^TM and a linear prefabricated concrete sill called a Double-T across the seaward end of two adjacent groin compartments to abate shoreline erosion. This area is subject to both strong tidal currents and wave action and has a history of beach erosion. A monitoring plan has been implemented to evaluate the effectiveness of these two structures in retaining sand within the groin compartments, as well as retaining new beach fill sand that is to be placed in 2004. Project monitoring includes cross-shore beach profiles to document shoreline change and beach volume retention, scour and settlement measurements to assess structural stability, sediment samples to assess grains size changes, wave and current monitoring to measure wave/current modifications and aerial photography to document regional scale sediment, shoreline and duneline movements within the eight groin compartments that compose the Cape May Point oceanfront.

A sliding stability analysis was conducted for a pre-cast concrete double-T to be used as an innovative type of shore protection at Cape May Point, New Jersey. Three analytical methods were used to find the dynamic wave-induced force: (1) drag force using linear theory, (2) drag force using stream function theory, and (3) wave force assuming linear, long waves. Sliding stability was checked as both a stand-alone structure and in the presence of a perched beach. It was found that the structure was safe against sliding for all the wave events considered.

The Section 227 National Shoreline Erosion Control and Demonstration Program provides authorization by which innovative shore protection devices, designs, and methods can be constructed, monitored and evaluated for functional performance and structural integrity. The objectives of the program are to: a) assess and advance the state of the art of shoreline control technology, b) develop and encourage the development of innovative solutions to shoreline erosion, and c) communicate findings to the public, state, and local officials in order to develop means for advancing the use of well-engineered alternative approaches to shoreline erosion control. The project site is located in Jefferson County southwest of the Sabine Pass and northeast of High Island, Texas in an area of actively eroding shoreline. The site area is completely undeveloped and is characterized by a broad salt marsh having a muddy substrate. Beaches are narrow and steep and are composed of mud or a thin veneer of sand and shell over mud. Sediment supply is negligible and the shoreline is actively eroding at rates between 1.5 m/y and 3.0m/y. Tides are mixed diurnal and semi-diurnal and tidal ranges are mostly limited to one to two feet. Wave heights average less than three feet although storm waves regularly flood the adjacent land and deposit washover terraces of sand and shell. Frequent flooding and long-term shoreline retreat have destroyed much of State Highway 87 adjacent to the McFaddin National Wildlife Refuge.

Completed in May 1999, the second beach renourishment of the Ft. Pierce Federal Shore Protection Project extended south approximately 1.3 miles beginning immediately south of the Ft. Pierce Inlet south jetty. Confronted with the loss of the design beach in less than two years following the 1999 project, the U.S. Army Corps of Engineers (USACE), Jacksonville District, tasked Taylor Engineering (2002) to conduct an engineering and least-cost analysis to improve the project performance in the northern 2,200-ft project segment between R-34 and R-36. The evaluation considered several combinations of alternatives, including reducing the renourishment interval, placing additional feeder beach fill, and/or constructing shore protection structures, to maintain the design beach until the end of the authorized life (2020). The final recommended design featured six T-head groins and a nearshore breakwater to stabilize the northernmost 2,200-ft project segment, in combination with the beach renourishment every four years along the entire project beach. This paper summarizes the design methodology with specific attention to T-head groins.

Beach restoration with periodic renourishment has proven to be an effective solution in some locations. However, considering project size, location, erosion rates and the availability of a suitable sand source, some erosion problems may be more cost effectively addressed with erosion control structures. Additionally, depletion of sand resources for nourishment has resulted in an increased level of interest in structural erosion control alternatives. The most difficult aspect of erosion control structure design is avoiding downdrift impacts. Conceptually, an optimum solution might consist of a low maintenance erosion control structure, which interacts with the littoral system to perch a stabilized beach and maintain longshore sediment transport. Such a design has been applied since 1997 at four locations along the southwest coast of Florida. The composite T-groin design developed by Humiston and Moore Engineers uses the combined function of a nearshore breakwater and a low profile shore-perpendicular groin. Sheetpile are utilized in the core of the structure to establish a barrier to control sand losses through the breakwater segment, with a precise crest elevation to allow a desired level of overtopping. This establishes the shape of the salient formation. Weir sections are included in the design to limit the extent of the salient formation and promote lateral sand bypassing in the lee of the breakwater, or T-head, segment. Two permanent installations have been completed and monitored for over three years in southwest Florida. One of the most important documented findings of the monitoring collected thus far is that the design allows for sand bypassing to eliminate adverse downdrift impacts. Additionally, post storm surveys have shown that storm waves overtopping the low profile structures redistribute sand from the salients to adjacent beaches. This appears to be beneficial to adjacent beaches by increasing the sand supply under conditions which are otherwise conducive to erosion.

The Prefabricated Erosion Prevention (P.E.P) Reef was deployed in 1996 and was monitored on a quarterly basis until June 2000. This paper summarizes the performance of the Vero Beach, Florida installation of the P.E.P. Reef. A three-year monitoring program was conducted to provide an evaluation of the effectiveness of the P.E.P. Reef system. This monitoring program included quarterly beach profile surveys, multiple wave gage deployments, breakwater settlement monitoring, and scour rod measurements, as well as an analysis of pre-project historical shoreline change. The purpose of the monitoring program was to: 1) determine changes in the shoreline response to the P.E.P Reef relative to control locations along the adjacent shoreline, 2) changes in bathymetry of the study area to identify patterns of erosion and accretion, 3) changes in beach profile and resulting sediment volume to identify impacts of natural hardbottom, seawalls and the P.E.P. Reef on coastal processes, 4) wave transmission effects, 5) modifications to wave induced currents, 6) scour around the reef segments, and 7) settlement of the reef units over time. The results of each of these objectives are given herein.

The breakwater field in Holly Beach Louisiana was constructed in the early 1990's by the Louisiana Department of Transportation and Development (LADOTD) in response to continued erosion of the shoreline and damage to Highway LA 82. Subsequent to the installation of the breakwater field, the beach continued to erode throughout the majority of the breakwater field. The continued erosion prompted the Louisiana Department of Natural Resources (LADNR) to undertake a sand management study to better understand the erosion and to protect the road and environmentally sensitive marshes. The management plan recommendations included a beach nourishment project and structural rehabilitation of some of the breakwaters. These works were constructed in 2002–2003. This paper describes the improvements to the breakwater units.

Portions of the Chenier Plain coastline of Southwestern Louisiana are receding at an average rate in excess of 12 meters per year, resulting in the loss of a significant amount of coastal wetlands. The shoreline between Joseph Harbor and Beach Prong, approximately 15 kilometers, in the Louisiana Department of Wildlife and Fisheries Rockefeller Wildlife Refuge has some of the highest erosion rates in the region. The coast consists of shell hash and sand beaches perched on under-consolidated, clayey marsh deposits that erode rapidly in response to normal wave conditions and episodic storm events. The National Marine Fisheries Service and the Louisiana Department of Natural Resources funded a feasibility study and alternatives analysis under the Federal Coastal Wetlands Planning, Protection, and Restoration Act. The project has a stated goal of halting net shoreline erosion which would result in the protection of approximately 350 hectares of wetlands. Proposed alternatives included offshore breakwaters, sand placement, revetments, and geotextile structures. The structural, geotechnical, and environmental feasibility of each alternative was considered along with a constructability analysis. These criteria were used to select alternatives for further analysis; a conceptual design for selected alternatives was prepared. Poor soil conditions played a major role in the feasibility analysis and conceptual design for each alternative.

This paper presents the use of artificial reef structures as submerged breakwaters, providing both wave attenuation for shoreline stabilization, and habitat for biological and environmental enhancement. The interactions between the coastal process and the reefs and submerged breakwaters are discussed, and examples of natural reefs and man-made submerged breakwaters are shown.

The aggregation effect of the artificial fish reef was investigated through numerical simulation and experiments in the field and the laboratory. When compared with the measured probability of existence of young red seabream and black seabream around the model fish reef in the laboratory with the calculated flow pattern, it is found that the provability of existence of black seabream in the upstream side is higher than that of red sea bream. This comes from the difference in the swimming ability of both fishes. Around the artificial fish reef in the field, it was observed various fishes of all types more than 25 species. Each species exists in a specific region of the reef that toughly corresponds to the calculated flow velocity.

Complex principal component analysis (CPCA) is applied to examine medium-term geomorphological behavior of an exposed sandy beach adjacent to a gigantic breakwater of the Port of Sendai located near a river mouth in the Sendai Coast, Japan, using a 12-year series of bathymetry survey data. The results of CPCA and conventional real-PCA demonstrate that erosion and subsequent accretion of the submerged terrace formed in front of the river mouth appear in the first mode of CPCA and have the most significant influence on the medium-term geomorphology of the study area. The first mode is mostly caused by northward alongshore sediment transport driven by wave energy flux, explained from the observed wave data. The second mode of CPCA demonstrates that the sediments previously discharged from the river return again into the nearshore region, and furthermore, the topography changes due to cross-shore sediment transport emerge in the third mode of CPCA.

Lake Michigan is one of the main sources for water supply of the Chicago Metropolitan area. In 1885, the City of Chicago has experienced a severe typhoid epidemic as result of contaminated water from the river into the lake. In order to prevent further contamination, the city engineers have designed in 1900 a timber cribbing wall that separates the Lake and the river, and a series of locks along the Chicago River that reversed the flow of the river away from the Lake Michigan. Over time, the wall started to deteriorate this having as result an uncontrolled leakage of water from the Lake into the river. As part of the Great Lakes system, the water quality and quantity of Lake Michigan is carefully monitored by the local, state and interstate agencies. In order to stop and control the amount of water taken from the Lake Michigan to the Chicago River, a new cutoff wall, a pump station and four sluice gates were designed by Consoer Townsend Envirodyne Engineers, Inc. (CTE-Engineers), for the Illinois Department of Natural Resources — Office of Water Resources. The project location is known as Chicago River Turning Basin, since it was used in the past for vessel maneuvers.

The proposed prototype repair section can be thought of as an integration of two drastically different rubblemound design concepts. The crest area of the repair is composed of parallelepiped stone placed in a highly controlled laid-up manner. The anticipated high stability of the crest is achieved from the tight interlocking of all armor units: If one armor unit is displaced from the crest, the neighboring armor units may unravel and the stability of the entire crest section may be jeopardized. To buttress the crest area of the repair (both during and after construction), a toe berm was incorporated into the design. The toe berm was constructed using irregular shaped (but not slabby) stone carefully placed to minimize voids and provide maximum stone-to-stone contact (interlocking). The anticipated stability of each armor stone used in the toe berm is achieved independently. If one or several armor units are displaced from the toe berm, the overall stability of the toe berm is not compromised. The toe berm is also expected to act as an energy dissipater for waves (before waves impact the crest section) and as a bench on which displaced armor stone comes to rest (maintains a functional cross-section, rather than allowing displaced stone to fall down slope).

Sirevåg harbour is located in a narrow bay on the west coast of Norway approximately 50 km south of the city of Stavanger. The area outside the harbour is an open coast with no reefs or shoals that give shelter from the waves. The wave height reducing effects are refraction and in shallow water also wave breaking. A new breakwater was constructed in Sirevåg, starting in January 2000 and completing in July 2001. The primary reason for the new breakwater was to give better protection of the harbour and to improve the sailing conditions in and out of the harbour. The breakwater was designed and constructed as a statically stable Icelandic type berm breakwater for a wave height with a 100-year return period. The design 100-year recurrence wave height at the location of the breakwater was established as H_s,100 = 7.0 m. During the first winter in service the breakwater experienced a storm reaching the design level. The breakwater survived the storm without any reshaping. However stability model tests showed that there should have been a marked recession of the berm. The apparent discrepancy between the model test results and the field behaviour of the Sirevåg berm breakwater is discussed in this paper. The construction cost for the Sirevåg berm breakwater proved to be considerably lower than reported from other projects. This is partly due to the availability of a suitable armourstone quarry and also to the maximisation of the quarry yield and the utilisation of all size grades from the quarry to the benefit the integity of the structure.

In 2000 a vertical breakwater was completed to shelter the small army harbour on the Isle of Alborán, a small island in the Sea of the same name, halfway between Southeastern Spain and Morocco. In November 2001, a severe storm swept the Alborán Sea. This paper deals with the effects of the storm, the behavior of the vertical breakwater, the damage to the parapet, and the proposed solutions

PB Ports & Marine, Inc., a subsidiary of Parsons Brinckerhoff Quade & Douglas, Inc. (PB), was commissioned by the United States Army Corps of Engineers, New York District (USACE), to perform a condition survey of two existing historical breakwaters located on Lake Champlain; one in Burlington, Vermont and the other in Plattsburgh, New York. Both breakwaters are oriented roughly parallel to the shoreline, approximately 300 meters from the shore and protect public harbors serving recreational boats. The Burlington Harbor is located on the Eastern Shore of Lake Champlain, about 65 kilometers south of the Canadian Border. The Plattsburgh Harbor is located on the Western Shore of Lake Champlain, about 40 kilometers south of the Canadian Border. The crest elevation of the existing breakwaters varies from 0.9 meters to 1.8 meters above the Mean Lake Level (MLL) at Burlington. Therefore, the breakwaters occasionally become submerged and often experience wave overtopping during high water periods. On average, Lake Champlain freezes on February 11 and opens to navigation on April 8. The ice is usually thicker on the harbor side due to the combined effects of weaker wave action, relatively shallow water in the harbor and trapping of ice by the breakwater. There are times when the harbor side is frozen while there is no ice on the lakeside of the breakwaters. Both breakwaters, built at the end of the 19^th century, are comprised of timber cribs filled with stone. Concrete superstructures built at the breakwater ends support beacon lights. Presently, the original cribs of both breakwaters are severely deteriorated. Several repairs have been performed during the 19^th and 20^th centuries to keep the breakwaters functional. Those repairs consisted of the replacement of deteriorated crib portions and placement of riprap and heavy armor stone on the lakeside of the breakwaters. However, deterioration of the timber on the harbor side is continuing. In some places, the crib walls have collapsed, causing the release of stone fill.

In 1948, the Port of Newport sank two flat-bottom concrete ships in Yaquina Bay, Oregon, to serve as wharves for cargo handling. Port of Newport records indicate that over the past 30 years, the westernmost hull has moved episodically about 3 ft southward toward the bay, resulting in settlement of the dredged sand backfill, damage to the laydown area pavements, structural damage to the hull, and considerable maintenance expenditures. The easternmost hull has reportedly been stable. In 2000, a geotechnical investigation was undertaken to identify the conditions causing movement of the hull and determine whether the movement was occurring at the subgrade-ship interface or whether there was a deep-seated failure occurring in the marine sedimentary rock. The investigation included a site reconnaissance, exploratory borings, installation and monitoring of instrumentation, laboratory testing of soil samples, and engineering analyses. The instrumentation data indicated the hull was sliding on its base and rotating very slowly toward the bay, and a deep-seated failure was not occurring. The field data was used to develop and calibrate a stability model for various boundary pore pressure conditions and failure mechanisms (sliding and rocking). The model indicates a state of incipient failure for critical tide and groundwater conditions.

As part of development programs at the Port of Los Angeles (POLA), channel and basin dredging, and berth improvements are planned. Beneficial use of the dredge spoils is planned for use in construction of the 16.2-hectare (40-acre) Pier 300 extension terminal, among other projects. This paper discusses data management and material characterization for the Channel Deepening, as well as engineering analyses related to the design and construction of the Pier 300 extension terminal.

The north and south jetties at the entrance to Tillamook Bay, Oregon have experienced damage to both jetty heads as well as areas along the trunks. The deterioration of the jetties has been more pronounced in the last 7 years. There is concern that the receding jetty heads will contribute to already hazardous navigation conditions over the ebb tidal shoal and within the navigation channel. Navigating the channel becomes even more dangerous because of remnant jetty stone that lies under water just seaward of the exposed end of the south jetty. Erosion of the shoreline along the north jetty is a major concern in terms of a potential breach at the jetty root. A recent apparent increase in the Pacific Ocean wave climate has exposed both jetties to more extreme storm waves, especially the south jetty which is more exposed to southwesterly storm events. Increasing wave heights and aging structures has led to a need for major repairs to these and other jetties along the Oregon coast. This paper will look at the issues that are dealt with when evaluating jetties for repair.

The main purpose of this paper is to discuss geologic hazards that affect the vulnerability of the Columbia River waterway and to better understand the complex relations among geologic hazards, transportation and their influence on the community. For this project, we considered engineered systems, geohazards and limited economic data to determine the overall vulnerability in our community.

This paper presents a framework for reducing lifecycle costs of maintaining the engineered navigation entrance at the mouth of the Columbia River (MCR), an ocean entrance located on the Pacific Northwest coast of the United States. At MCR, three jetties with a total length of 15.7 km were constructed on massive tidal shoals during 1885–1939, and the morphology of the inlet has been changing ever since. The jetties have experienced significant deterioration since construction, mainly due foundation instability associated with the erosion of tidal shoals on which the jetties were built. A jetty breach at MCR would result in rapid in-filling of the 17 meter deep navigation channel. Considerable effort has been expended to rehabilitate the MCR jetties and more is needed to prevent a catastrophic breach. Is placing more stone on the jetties the best way to sustain navigation through the MCR? A holistic approach is used to rationally examine the functional performance of the jetties, optimal repair strategy (which structures to repair first and where); and maximize the utilization of dredged sand as a resource. Elements of this paper also include: A) Development of a digital elevation model (DEM) to analyze the MCR jetties and adjacent morphology. B) Application of a 2-D hydrodynamic model to investigate the impact of present/future jetty deterioration (and reconstruction) upon the morphology and sediment budget at MCR. This paper concludes that a targeted placement of dredged sand can reduce erosion of the sand shoals, mitigate deterioration of jetty foundation, and prevent the need for future jetty repair. The framework discussed in this paper, which deals in part with employing regional sediment management, can be readily applied to similar ocean inlets where jetties are used to control sand shoal migration and retain a viable navigation channel.

The jetties and surrounding dynamics at the entrance of Coos Bay, Oregon form a unique and complex system that requires a systematic and comprehensive approach to its management. The deterioration of the north and south jetties due to channel deepening and movement, erosion of shoal foundations, lack of maintenance, and an increase in wave climate caused a breach of the north jetty at its root in November 2002. The emergency repair of the north jetty that followed provides an example of how the features and individual processes at work in an area can and must be incorporated into the successful design and maintenance of its structures. The evolution of the breach at Coos Bay can be used as a learning tool to show that it is imperative to understand the sediment pathways and their effect on navigation structures in order to maximize the efficiency and durability of a jettied entrance. This paper will review the conditions that led to the jetty breach, the emergency repair methods used at the north jetty, and the issues and concerns that will influence the decisions made about the future maintenance of the navigation entrance at Coos Bay.

The New York District Corps of Engineers has embarked on a major, and ongoing effort to renourish the beaches of northern New Jersey as a cost-effective means of controlling shoreline damage. However numerous existing shoreline structures bisect the nourishment project, inhibiting the natural migration and restoration of the beach back to a continuous, straight shoreline. Various strategies have been applied to compensate for these structures including burial, notching, shortening, and even lengthening. One particular structure is uniquely challenging in that not only does it drain an upland lake, but it also is a migratory path for fish. The Deal Lake outfall is the only pathway for herring to return from the sea to spawn in the lake. To develop a solution for this structure that could bypass sediment to maintain a straight shoreline, yet also create and sustain an open migratory path for fish back up the outfall, a Value Engineering study was initiated at the concept level. The study addressed geometric effects of structure shape on sand bypassing, fish swimming and maneuvering capabilities, and public recreation and interest considerations. Various concepts ranged from systems of fish ladders, to fully submerged outfalls with lighting to orient fish, to jetties spurs, and scour inducing groin heads. A preliminary design concept was constituted from the Value Engineering recommendations and extensively tested in a movable bed physical model. Behavior of the outfall system to bypass sediment under wave loadings from various directions was monitored. The ability for the outfall to remain clear of sediment was enhanced using a concept of reflected wave action to promote sediment agitation. A final design was developed which employed a notch to an existing groin, a downstream spur situated just landward of the notch, and a self-scouring outfall pipe issuing from the spur.

This paper describes a dynamic analysis of a floating bridge across Lake Okanagan at Kelowna, British Columbia, Canada. The structure is a replacement for an existing floating bridge that was opened to traffic in 1958. The floating section of the proposed new bridge consists of continuous concrete pontoons with a total length of 697 m. Due to the exposure of the bridge to wind generated waves and the large horizontal dimensions of the structure, a short-crested wave field was used to model the correlation of wave forces along the structure length. Numerical wave hindcasting was conducted to determine the design wave conditions, including the effects of directional spreading. A two-dimensional wave diffraction numerical model was used to calculate the frequency dependent hydrodynamic coefficients (added masses, damping and exciting forces) used in the dynamic analysis. The response of the bridge to wind and wave loads was evaluated in the frequency domain using a commercial finite element structural model. The response parameters of interest included the motions of the bridge, the anchor cable tensions and the six sectional forces in the pontoons (two bending moments, torque, two shears and an axial load).