Coastal Dynamics 2005: State of the Practice

The results from an investigation of the variability of beach profiles using a wavelet transform are presented and compared with the results from an empirical orthogonal function (EOF) analysis. The field data come from the Field Research Facility (FRF) at Duck, North Carolina USA, which is unparalleled with respect to high spatial and temporal resolution of the profile evolution over 22 years from July 1981 to September 2003. It is confirmed that the results from the wavelet analysis are comparable with those from EOF analysis. As EOF analysis does, wavelet analysis can characterize the basic patterns of beach profile changes. Moreover, by wavelet analysis the basic patterns of the variability of beach profiles can be specified to quantitative spatial scales at particular offshore locations. Wavelet analysis can show the relationship between successive surveyed beach profiles at several spatial scales, and the relationship between successive points along offshore at different scales can be seen different without assuming statistical stationary.

Victoria beach (SW Spain) has a rocky flat at the northernmost zone. This has allowed to choose one profile and monitoring the changes induced by a single day storm. Topographic data taken during 21 days and different tendencies of the beach profile, as the accretion rate, were identified. The analysis is carried out by means of Empirical Orthogonal Function (EOF) techniques, in order to separate the spatial from the temporal variability of the beach profile data. Among the conclusions, it should be highlighted that a swing or oscillation point of the profile was found around the intertidal zone. Furthermore, the erosion has been irreversible in a short term, and the recuperation consisted only in a modification of the slopes of the emerged part, trying to assimilate them to the ones before the storm.

A formulation to determine the equilibrium beach profile for refraction-diffraction areas is proposed. An analytical expression for the wave energy flux for refraction-diffraction areas is derived from the "mild slope equation". Assuming uniform wave energy dissipation per unit water volume, it is established that the total shape parameter for the equilibrium beach profile for refraction-diffraction areas is composed of a sediment grain size shape parameter (Dean's parameter) and a refraction-diffraction shape parameter (ref-dif shape parameter). An expression to calculate this latter parameter is determined analytically and empirically based on field data. The proposed formulation is used for beaches where the sediment grain size is uniform alongshore and for beaches where the sediment grain size is not uniform alongshore, being observed two different behaviours.

This contribution presents the results of intensive field surveys executed during late spring and summer 2004 along two pocket beaches located in the northwestern and eastern coast of the Faial island (Azores archipelago, Portugal). The main purpose of this study was to characterize the morphodynamics of these two beaches by associating the short-term evolution of a couple of beach profiles, monitored on a fortnight basis, with the wave climate and wave refraction model output. Study shows that both these beaches are undergoing rapid and significant phases of accretion/erosion during summer time in relation with growing sea state. Also, fast beach rotation has been noted. Although these two beaches are located to the west and to the east of the island and despite the prominence of westward waves and winds, their evolution appears simultaneous. This manuscript constitutes the first step towards achieving a comprehensive understanding of beach morphodynamics in the Azores.

Sand grains, bedforms and the wave boundary layer cause roughness for tidal currents. This paper reports roughness determined from flow velocity measurements in calm weather and storms derived from 1900 hours of detailed flow measurements on a sandy shoreface, 2 km off Noordwijk, The Netherlands. The roughness was determined by fitting logarithmical velocity profiles to data of 3 sensors. The results are compared to observed bedform dimensions and wave conditions. The roughness decreases for increasing current velocity in Hm0 waves <2 m, but increases for larger waves which indicates that apparent wave roughness dominates during storms. Waves opposing the current cause a larger apparent roughness. Individual events show contrasting trends that are probably related to development of current ripples, wave ripples and hummocks.

The sea floor of the North Sea is covered by periodic bedforms of different scales. The superposition of bedforms causes difficulties for determining individual bedform parameters. In this article we compare two new methods for separating the sand wave component from the mega ripple component in Multibeam Echo Sounding measurements (MBES). One method determines a Fourier decomposition of the MBES signal, the other method uses geostatistical filtering. Both methods are described and tested on two MBES data sets of the North Sea bed. The test results correspond well. As a first application of the separation methods we determine individual bedform parameters of the separated bedforms, more particularly their wavelength and waveheight.

The objective of this study was to develop a reliable and general formula for the prediction of bed-load transport under a wide range of conditions. More than 1000 steady and 500 oscillatory flow cases compiled from the literature were used in the study. The relationship between the bed-load transport and the total Shields parameter to the power 1.5 was first confirmed for steady flow with an exponential factor to take into account the effect of the critical Shields parameter. The proposed formula for the steady current was then expanded and generalized to take into account the effects of oscillatory flow as well as oscillatory flow with a superimposed current at an arbitrary angle. Particular attention was paid to phase-lag effects in the sheet-flow regime by introducing an additional parameter.

Short-term dynamics of the sandy Kwinte bank is examined in terms of water circulation, sediment transport and bedforms mobility during a tidal cycle using a hull-mounted ADCP and towed side-scan sonar, along a profile across the bank. Tidal rectification of the flow over the bank has been observed, together with clockwise rotation of the tidally-averaged currents. The computed net sediment transport, from a 1D sediment transport model, is generally in the direction of the ebb currents, towards the SW. In details, a convergence of the sand transport is predicted towards the top of the west flank. SSS images reveal reversal of megaripples asymmetry during the tide. These results match with the stability model for sand banks formation and maintenance, and suggest that bank dynamics have to be studied as a whole system which includes the adjacent swales and banks.

The 1DV two-layer model of oscillatory sheet flow of Malarkey et al. which was developed for a single grain size has been modified to include grain fractions. The model includes a suspension layer above a sheet-flow layer consisting of prescribed profiles of concentration and velocity. Since this model keeps track of the total sediment in the water column through the wave cycle it is ideally suited for representing graded sediments. The modified model has been compared with the graded sediment data of Hassan et al. The results show that the model can reproduce the statistical characteristics of the sediment in suspension and produces fractional transport rates that are consistent with the experiments. However, it also demonstrates that a sediment weighting function limited by the amount of sediment in suspension is not sufficient to give rise to the apparent effects of hiding and exposure seen in the data.

A model of the coastal wave and current boundary layer structure is developed by the use of the k – ε turbulent closure model. The finite difference method is used to solve the governing equations. Vertical logarithmic grids and equal time steps are adopted. The following modeled results are obtained: 1) vertical profiles of wave velocity amplitude, eddy viscosity coefficient and turbulent kinetic energy with waves only; 2) vertical profiles of wave velocity amplitude, mean current velocity, eddy viscosity coefficient and turbulent kinetic energy with waves having a following current. To test the validity and the rationality of the present model, vertical profiles of modeled wave velocity amplitude and mean velocity are compared with those corresponding experimental results of Jensen, Jonsson and Carlsen, and van Doorn, respectively.

In this work, numerical simulations of the oscillatory boundary layer induced by an oscillatory-ripple-covered bed in a fluid otherwise at rest and in the presence of superimposed weak currents are presented. The simulations are performed using a rather new promising numerical technique named the Lattice Boltzmann Method and a brief description of the method is given. The dynamics of coherent structures in the boundary layer are presented. The results show a cycling repetition of jet of vortices from the boundary. Their interaction lead to a momentum transportation at a distance from the boundary that decreases for increasing value of the tested superimposed currents. For the lowest values of the superimposed currents, time-averaged velocity fields as well as time-space-averaged velocity profiles show the formation of a streak of fluid, close to the ripple crest level where the velocity is against the current.

This study documents the development of a beach berm and the associated closure of an intermittently open coastal lagoon on a gently sloping beach on the east coast of Australia. The berm grew 1.17 m in elevation over 11 days, and essentially closed the lagoon except at high tide within 4 days after opening. Berm growth was vertical with no notable horizontal accretion in the shore normal direction. Wave runup and overtopping were also measured and overtopping into the lagoon channel was found to be dominated by long waves. Berm development is found to be largely dependant upon swash and overtopping potential. Large overtopping potential at the start of the experiment resulted in substantial sediment transport, deposition and rapid berm growth. With berm growth, overtopping potential ultimately become restricted, reducing the sediment volumes deposited and consequently limiting further berm growth.

By adding a simple fixed-point sediment source to a numerical one-contour-line coastal evolution model, we investigate how the distribution of wave approach angles affects the evolution of wave-dominated deltas. These experiments are motivated by recent findings that shoreline evolution is strongly dependant on wave approach angle, and that the ability for alongshore sediment transport to flatten a bump along a sandy coast decreases as deep-water waves approach from more oblique angles. Waves approaching from sufficiently oblique angles (high-angle waves) result in a shoreline instability. Simulations using the one-line numerical model, which includes a simple parameterization of barrier overwash, show that, for the same sediment supply and wave energy, deltas prograde faster and with a more pronounced aspect ratio if the proportion of high-angle waves is increased. An asymmetry in the wave climate increases the tendency towards shoreline instability on the downdrift delta wing; simulations exhibit overwashing spits that extend from the river mouth. This asymmetrical delta evolution is reminiscent of Sf. Gheorghe (St. George) lobe of the Danube Delta, Romania. Other simulations with an initially high then later reduced sediment input rate resemble the basic form of the Ebro Delta, Spain, with lobes recurving towards the mainland extending from both sides of the river mouth. These preliminary investigations demonstrate that reshaping of deltas by waves and subsequent overwash can give rise to surprisingly complex shapes and behaviors.

The majority of barrier beaches and spits along the south coast of England are in the ultimate phase of barrier breakdown. This is due to an imbalance between their forcing hydrodynamic and resisting morphodynamic factors. The Holocene sediment supply that once fed these dynamic systems is no longer readily available because of natural and anthropogenic causes. Management in the form of "hard" and "soft" engineering is required therefore, to maintain stability as flood defences in their present positions. Current management practices are often not economically viable or sustainable solutions in the long term. With greater risks predicted, arising from sea level rise and increased storm surges, significant management decisions must be made with a limited understanding of the way that these beaches perform under storm attack. Findings from application of Bradbury's overwashing model at the Medmerry barrier, West Sussex are presented.

The threshold of motion of coarse particles under regular shoaling waves is studied. Experiments are performed to investigate the effects of bed fluid acceleration on coarse particle stability. By varying wave height, wave period and water depth, combinations of similar peak orbital velocities and weak to strong intra-wave accelerations were created. Qualitatively we found that initiation of motion occurs at or is very close to the maximum shear stress due to the combined effects of drag/lift and acceleration as introduced by Nielsen and Callaghan. However, quantitatively their formulation does not lead to convincing discrimination between motion and no motion. We expect this to be due to the assumption that the coefficients for drag/lift and acceleration in their formulation are taken equal and constant. From literature and from plotting our data against the Keulegan-Carpenter number we expect that these coefficients strongly vary due to flow separation effects.

This paper investigates cross-shore profile changes of coarse-grained beaches, with particular regard to discussing the tendency for onshore transport and profile steepening in the swash zone. The discussion includes observed morphological changes on a gravel beach from experimental investigations at the Large Wave Flume (GWK) in Hanover, Germany. We investigate the profile evolution evaluating the transport rates from a bed-load sediment transport formulation coupled with velocities calculated from a set of Boussinesq equations. We discuss the influence of bottom friction on the predicted profiles and the use of non-symmetric C-values for the swash phase in the sediment transport equation. This is done to elucidate the processes that are involved in the morphological response of these beaches. Physical mechanisms believed to be important are: infiltration effects on the flow above the beachface, the more accelerated flow in the uprush and the bore collapse from a plunging breaker.

Spatial patterns of surface sediment distributions on a mixed beach are measured using a new survey methodology, across three beach sections at Pevensey Bay, south east England. Spatial patterns in distribution and composition are related to antecedent hydrodynamic conditions and beach topography. Results indicate that higher energy waves produce a beach surface with a more homogenous grain size distribution, in contrast lower energy waves produce surfaces that are more mixed. In addition under storm conditions, a ‘type' beach response was observed, consisting of a fine upper and coarse lower beach face. The high tide berm is shown to be composed of finer material than the beach material below. The survey method described is considered appropriate to measure surface sediment distribution patterns on mixed beaches, over large areas, on a tidal time-scale.

Within the surf zone, the energy expended by wave breaking is strongly influenced by nearshore bathymetry, which is often linked to the character and abundance of local sediments. Based upon a continuous, two year record of Argus Beach Monitoring System (ABMS) data on the north shore of Kachemak Bay in southcentral Alaska, we model the enhancement of wave energy dissipation by the presence of intertidal sand waves. Comparison of model results from simulations in the presence and absence of sand waves illustrates that these ephemeral morphological features can offer significant protection to the backing beach and sea cliff through two mechanisms: (1) by moving the locus of wave breaking seaward and (2) by increasing energy expenditure associated with the turbulence of wave breaking.

Recent studies have indicated that extreme storm events along the Dutch coast are more severe than previously assumed. Particularly for the wave period significantly larger values may occur. Therefore, the safety assessment tools presently used for the dunes along the Dutch coast need to be reviewed. However, insight in the effect of the wave period on dune erosion is very limited, thus needs to be investigated. This is done first by carrying out small-scale 2D physical model tests. The results of a preliminary analysis show an increase of dune erosion of 25–35% for an increase in wave period of T_p = 12 s to T_p = 18.4 s. Next to the tests, a preliminary evaluation of the performance of two numerical models for dune erosion was carried out with the results of the tests. In the near future, the investigations will be continued with large-scale 2D physical model tests.

A research version of Delft 3D is used to simulate dune erosion by wave group forcing. The first three hours of a dune erosion experiment in the Delta flume are simulated and compared with measured data from this experiment. The effect of wave groupiness on dune erosion is studied by comparing model results including wave group forcing with model results using a time-invariant wave forcing.

An analytical model of dune erosion was developed based on impact theory, where the weight of eroded material is assumed proportional to the impact force from waves hitting the dune. The model was validated with data from several laboratory and field studies on dune erosion covering a wide range of hydrodynamic, sediment, and geometric conditions. Overwash was then included in the model and the evolution of a rectangular-shaped dune subject to both wave impact and overwash was investigated. Finally, an analytical solution for the case of a schematized barrier islands exposed to overwash was developed. Analytical models are useful in the initial stage of a project when approximate estimates are required.

In Galicia, the northwest of Spain, there is a big bay called Ría de Ares and is more than 5 kilometres long. At the end of the Ría de Ares the Eume river conform an estuary where Ponteudeume port is located, a harbour for fishermen and sport boats. The tidal inlet is surrounding by natural rocks on one side and a jetty built in 1985 that sustain Cabanas beach on the other side, converting it into a pocket beach. The environmental administration was worried about three items: The lack of dry sand in the north part of Cabanas beach, the lack of draught in the navigation channel and the visual impact of the jetty. This study embraces the analysis of historical data, a short term study that includes the wave propagation from deep to shallow water, the study of the wave currents and an inlet circulation analysis, where the current are forced by the tides and the river inflow. A long term evolution model is also applied to the Eume tidal inlet and Cabanas beach founded in the formulation of a sediment budget to establish the optimum maintenance dredging strategy.

The purpose of this paper is to describe the morphology and attempt to understand the morphodynamics of bars located on an ebb delta close to an inlet mouth in a megatidal context. Although there have been numerous studies on the morphology and physical processes affecting such bars, these concern only microtidal and mesotidal settings. The west Cotentin coast (Normandy, France) is a fine example of a megatidal coast with one of the largest tidal ranges in the world. The mean spring tidal range is up to 10 m. Fieldwork was undertaken during one month and involved the deployment of an electromagnetic current meter, a pressure sensor and DGPS surveys to measure topographic changes every 2 days. Along the western coast of Cotentin, in spite of the very large tidal inlet, bars are generally small (2 m high and 250 m long) compared with other tidal environments. During the campaign, the bar migrated exclusively landward over a distance of 4 m. Its volume did not change significantly. This slow migration rate is attributed to the large tidal range. In the megatidal setting, the tidal water level fluctuations control the duration of the emergence and flooding periods, as well as the translation rate of different hydrodynamic zones across the ebb delta surface. Field observations showed that bar migration and the shoal volume variation patterns during the experiment may be divided as a function of hydrodynamical conditions. These results clearly indicate a morphodynamic behaviour pattern strongly hinged on the specific local megatidal hydrodynamic conditions.

A laboratory study of the effect of wave action on turbulent gravity currents generated by an instantaneous release of dense fluid is described. Dense fluid is released in the centre of the flume, generating a gravity current propagating horizontally with two fronts. This gravity current type, in the absence of waves, spreads symmetrically and propagating with the length scales according to the standard box models. In the presence of gravity waves the length of the gravity current is, to leading order unchanged, but the centre is advected in the direction of the wave motion. The shear of the mean flow generated by the oscillatory wave motion modifies the shape of the gravity current, inducing an asymmetry in the current height.

Despite comprehensive studies being made on the hydro-ecological environments of tidal flats, the geo-environments inside tidal flat soils remain poorly explored. The paper presents the results from recent field observations targeting the dynamics of suction which represents soil moisture tension and the associated geo-environments in an intertidal sandy flat of an estuary. The mechanism of water retention of the soil surface layer involving the simultaneous processes of evaporation, upward moisture movement and salinity accumulation is particularly noteworthy. Furthermore, the internal geo-structures of the sandy flat as obtained from shallow seismic survey are illustrated and discussed as a consequence of such geo-environmental dynamics.

Two field experiments were conducted in spring 2004 on Porsmilin and Blancs Sablons macrotidal beaches in the Iroise Sea (west Brittany, France). Aims were to qualify beach agitation and understand physical processes control on beach morphology. Hydrodynamic forcing was very variable during the experiment with successive storm events (Hs approx. 1.5 m) and post-storm calm conditions during which a recurrent low amplitude sand bar formed on spring low tide levels at Porsmilin. 2DH flow structure was mainly characterized by a strong undertow in Porsmilin surf zone during storm events while Blancs Sablons currents were highly modulated by semi-diurnal and spring/neap tidal range in the shoaling zone. Morphological change at Porsmilin is expected to be related to infragravity wave energy : (1) spring low tide level swash bar enhanced by low frequency waves in shallow water depth during low energy conditions, and (2) occurrence of ponctual stationnary long waves (0.008 hz) at low and high tide levels after storm peak that could be involved in cusp morphology.

Meteorological data at Dunkirk between 1956 and 2001, show two periods of higher storminess between 1956 and 1962 and between 1972 to 1977. Tide-gauge records from Dunkirk harbor show similar results, the frequency of high magnitude storm surges (≥100 cm) being higher during the 1960's and the second half of the 1970's. The assessment of the impacts of storm surges on coastal erosion was carried out through the use of a storm erosion susceptibility index (SESI) which integrates the magnitude of the storm surge, duration of the event, and wave height. At a medium time-scale (decades), no direct relationship was observed between the SESI and coastline evolution because potential impacts of storm surges highly depend on the upper beach morphology at the time of the event. At a short time scale, however, the use of the SESI appears to be useful for evaluating the potential effects of storms on shorelines.

An X-band marine radar system was employed in the vicinity of Hazaki Oceanographical Research Station (HORS) located at Ibaraki prefecture of Japan. The nearshore region around HORS exhibited a complicated morphological feature represented by a barred beach as a result of frequent exposure to large storm events. The radar system provides subsequent wave images having a clear variation of wave pattern during a storm event. These images were analyzed with an improved approach based on spectra analysis and PIV technique. Both wave period and spatial distribution of wave celerity vectors were determined based on a refined approach to Bell. A linear bathymetric inversion algorithm was initially examined and then applied to derive the nearshore bathymetry around HORS. The computed beach profile showed an appropriate agreement with the measured ones. However, there is a discrepancy existed due to ignorance of nearshore currents.

A cross-correlation particle image velocimetry (PIV) method has been used to obtain detailed velocity measurements of flow over ripples in the Aberdeen Oscillatory Flow Tunnel. The new data is distinguished from previous work of this kind in that the measurements were made over full-scale, mobile ripples. A total of 14 velocity measurement experiments were carried out, covering a wide range of flow and mobility conditions and ripples with dimensions in the range 2.5 < η < 10 cm and 18.5 < λ < 55 cm. The paper presents example results from the measurements, illustrating the quality of the data and some important features of the flow behaviour. Attention is given to velocities near the ripple crest, velocities near the ripple surface, the time-averaged velocity field and the time- and horizontally-averaged velocity profiles.

Wave setup and longshore currents on planar beaches induced by directional spectral waves have been computed for beach slopes ranging from 1/100 to 1/10, waves with deepwater wave steepness from 0.005 to 0.08 and offshore incident angles from 1° to 70°. The author's random wave breaking model PEGBIS (parabolic equation with gradational breaker index for spectral waves) is employed for evaluation of wave attenuation by breaking. Empirical formulas are derived for estimation of the wave setup at the shoreline and cross-shore distribution of longshore currents. Effects of spectral shape, surface roller, and kinematic viscosity on wave setup and longshore currents are examined.

The characteristic wave period (or frequency) is a key parameter in most of hydrodynamic models and paradoxically its determination is not easy, particularly in presence of wind sea conditions or in the nearshore zone. In this paper, we propose to show why it is complex to clearly define this parameter and the implication that it can induce in the determination of wave energy decay parameterization. In particular we will focus on one example, which concerns the parameterization of the γ parameter (the ratio of significant wave height to local water depth) in the surf zone. We will show that the discrepancy previously observed between two parameterizations can be partially explained by the determination of the characteristic wave period (or frequency).

Large scale laboratory experiments concerning breaking wave propagation over a fixed-bed, barred beach were performed. The primary observations of interest were video intensity time series obtained from a set of high-resolution video cameras in order to study the onset of wave breaking in shallow water and wave roller transformation in the surf zone. The approach is new in the sense that the analysis concentrates on individual breaking waves, as opposed to the more commonly used time-exposure technique, which averages the information over wave group time scales. A new parameter of interest is derived from the video observations based on the instantaneous intensity maximum, which propagates with the roller. The parameter is shown to provide high-resolution information regarding the onset of wave breaking and the spatial evolution of the wave roller. These observations provide a new and quite rigorous test for phase-resolving shallow water wave models.

The main driving force of 3D nearshore currents is radiation stresses, and three types of vertical profile of the radiation stresses have been proposed. This paper shows a vertical profile of each radiation stress with an improved type proposed in this study, and a capacity of nearshore current prediction under a condition of a regular and an irregular wave, respectively. At the end of this study, radiation stresses of wave dissipation type became the most appropriate driving force for 3D nearshore current model.

Regional, long-term changes in shore morphology were examined using the process-based numerical model SCAPE (Soft Cliff And Platform Erosion model). Key features of the model include an emphasis on providing appropriate representations of the main interactions that occur within ‘whole' eroding coastal systems, and the stability that the model achieves through negative feedback, particularly between the interaction of beach and shore platform. In this study, comparison of model predictions with measured cliff-recession rates provided validation over a period of more than 100 years. Scenario-testing over the period 2000–2100 suggest that cliff erosion rates in northeast Norfolk may be particularly sensitive to increased rates of sea-level rise (SLR), although the effects are not linear alongshore, whereas changes in offshore wave direction and height have moderate and minor impacts respectively. Comparison of climate-change impacts with impacts arising from hypothetical management scenarios indicates that human decisions will continue to exert a fundamental control on coastal evolution over the next 100 years.

A system of hydrodynamic, morphodynamic and reliability models have been coupled to generate insights into the effects of climate change and coastal management practices on coastal erosion and flood risk over 50km of coastline and up to 100 years in the future. Offshore wave conditions were propagated inshore using TOMAWAC and the SCAPE soft cliff and platform erosion model was then used to predict recession of the soft coastal cliffs, the effects of cliff protection and sediment supplies to low-lying down-drift coasts. A reliability model, based upon joint probabilities of wave heights and water levels, has been used to estimate the probability of failure of the sea dikes on the low-lying coast, and a simple 2D inundation model and GIS have been used to estimate flood risk.

The SCAPE (Soft Cliff and Platform Erosion) model of cliff toe retreat, and a cliff-top recession model, have been linked with a new flexible GIS tool (SCAPEGIS) to provide visualisation and analytical capability for the model results. 45 model runs exploring different sea-level rise and wave climate scenarios and protection choices are available. Outputs are available in the form of maps, dynamic visualisation, and descriptive statistics of key parameters such as cliff toe and cliff top position. It also allows analysis with other datasets such as land use and building location for impact evaluation, and hence supports shoreline management and cliff-top land use planning. Some preliminary results and ideas for further development are presented.

It is evident from the existing literature that additional investigations into the evolution of offshore sandbanks are needed. In this paper we presented an analysis of the model output and relationship between the flow statistics and the historical sandbank configurations based on this background. A two-dimensional hydrodynamic model has been set up to investigate the long-term evolution of offshore sandbanks. Tidal simulations were performed with a nested model covering the Southern North Sea and Great Yarmouth zone (east coast of the UK). Simulations were carried out for a period corresponding to several spring-neap cycles and were compared directly with field measurements. The time series of velocities at each grid point were used to determine time mean tidal velocities and vorticity. The time series were also used to determine Reynolds stresses eddy vorticity fluxes. The spatial patterns of these quantities are studied for two separate charts, relating to 1945 and 1954. The correlation between the evolution of the sandbanks and the residual and eddy flow statistics suggests that they could be a useful tool for coastal planners to develop an improved method of estimating long-term sandbanks changes.

Studies were undertaken by HR Wallingford in respect of the prediction of morphological changes at Saemangeum in response to the tideland reclamation involving closure of three remaining gaps in a long sea dike. The numerical modelling studies were challenging, requiring the application of state-of-the-art hydrodynamic and sediment transport models to this complex system and the requirement to resolve the detail of the morphological evolution over relatively long timescales. Filtering techniques were applied to reduce the computational task so that morphological predictions up to 2016 were achieved. Morphological simulations were carried out to predict the seabed evolution following closure of the northern-most gap in the sea dike from 2003 until 2006, and thereafter following closure of all three gaps.

The study is focussed on the morphological modelling (based on DELFT3D model) of an artificial sand rige at the Dutch shoreface near Hoek van Holland close to the harbour of Rotterdam. The ridge is perpendicular to the coast and to the tidal flow. The sediment size is about 0.3 mm. The tidal range is about 2 m. The peak flood velocities (to north) and ebb velocities (to south) are about 0.6 and 0.55 m/s. Using a 1DH (depth-averaged) model approach, the growth and migration of a sand ridge can not be simulated properly as the modification of the velocity profiles can not be represented. This latter effect can only be simulated by using a 2DV (two-dimensional vertical) or a 3D model approach. Growth of the sand ridge can occur when bed-load transport is dominant. Decay (flattening) of the ridge occurs when suspended load transport is dominant, particularly when waves are important.

The increased rate in sea level rise and other predicted effects of climate change associated with global warming, will inevitably lead to geomorphic changes on the Roberts Bank tidal flats on the Fraser River delta of southwest British Columbia. A dyked landward edge limits the amount of accommodation space available for the tidal flats and marsh to adjust to higher sea levels. This lack of space combined with the training of the Fraser River, which has contributed to a shortage of sediment supply, will affect the morphologic changes of the ecologically important tidal flat. Current biosedimentological zonation maps and cross-shore profile data are used to identify and understand potential morphologic changes.

Dunkerque-Est beach, in northern France, is a typical example of a beach with barred intertidal topography in a macrotidal environment. Data synthesized from several field experimental measurements were used to characterize the short-term morphodynamic behaviour of this beach. Topographic surveys show small adjustments of the topography around mean sea level (MSL) and more significant morphological change on the upper beach. Morphologic changes are induced by waves variably modulated by tidal excursion rates, by mean tide-dominated currents, and by wind forcing. However, the morphology shows some resistance due to self-stabilisation and a long morphological relaxation time.

Experiments were conducted in a laboratory facility under with a fixed bathymetric profile containing a single bar. A hybrid data set was collected consisting of remotely sensed wave data combined with model-generated wave amplitude profiles. The data is used to test the improvements in depth retrieval through the use of a nonlinear composite dispersion that is applicable in arbitrary water depths. The dispersion relation relates the wave properties with the local water depth and the results suggest that inclusion of nonlinearity improves depth estimation on shallow water.

In this study, the ability of two data-based approaches in analysing and modelling beach morphology and wave data at Duck, North Carolina, USA, was investigated. Dynamic Harmonic Regression (DHR) was used to analyse bed elevation and wave height time series in order to identify the long-term trends and dominant periodic components characterising the morphological changes and wave climate at Duck. A linear Transfer Function (TF) modelling approach was used to relate bed elevation time series to nearshore wave height time series with the aim of investigating the suitability of such a simple model in predicting the longer-term morphological changes. The DHR analysis showed multi-scale variability of the beach profile and was in good agreement with observations made in previous studies. The linear TF model showed limited capability with only a small proportion of the data being described by the model.

Predictions of process-based numerical models contain inherent uncertainties owing to model structural errors, such as poorly described or missing processes, to inaccuracies in the data, and to limited knowledge of the model's free parameters. The aim of this paper is to show how parameter uncertainty in nearshore process modeling and associated uncertainty ranges in the model output can be estimated in an objective manner by means of Markov Chain Monte Carlo (MCMC). This work should be seen as a first step in quantifying (the relevant importance of) all uncertainty sources in process modeling, which may ultimately lead to improved process knowledge and system understanding by learning from and understanding model-data misfit. MCMC performs a thorough sampling of feasible parameter space to approximate the posterior distribution of the model's parameters, given a specific model structure and data. The approach is illustrated with a one-dimensional, time-averaged alongshore current model based on the alongshore momentum equation and data collected at six instrumented positions across the inner subtidal bar at Egmond aan Zee (Netherlands).

A process-based model is compared with field measurements to test and improve our ability to predict nearshore morphological change at seasonal time scales. The field experiment, along the dissipative beaches adjacent to Grays Harbor, Washington USA, successfully captured the transition between the high-energy erosive conditions of winter and the low-energy beach-building conditions typical of summer. The experiment documented shoreline progradation on the order of 20 m and as much as 175 m of onshore bar migration. Significant alongshore variability was observed in the morphological response of the sandbars over a 4 km reach of coast. A detailed sensitivity analysis suggests that the model results are more sensitive to adjusting the sediment transport associated with asymmetric oscillatory wave motions than to adjusting the transport due to mean currents. Initial results suggest that alongshore variations in the initial bathymetry are partially responsible for the observed alongshore variable morphological response during the experiment.

Coastline evolution is often modelled adopting single line theory, i.e. the active part of the cross-shore profiles moves back and forth with erosion and accretion without a change in the profile shape. The advantage of these single line models is that they are easy to use, run fast and their results are easy to interpret. However, because of the limitations of single-line theory, these models are less suited to simulate the local coastline evolution around engineering constructions like breakwaters accurately. To calculate the effect of constructions on nearshore wave climate and sediment transport (e.g. the bypass function of breakwaters), local 2D models on hydrodynamics and wave propagation are often required. The approach adopted in the present study is to couple 1D and 2D models to determine the bypass rate of breakwaters more accurately.

The depth of sand activation on a beach under the action of waves is a key parameter for many scientific and applied projects in coastal engineering. Although there is a good literature on field studies, the work presented here represents the first laboratory study of its kind. Two nourished beaches from the Venice barrier-island system were reconstructed in a large wave flume and sediment activation was studies using trenches filled with colored sand. The results confirm the control by Significative Wave Height (H_s) and Peak Wave Period (T_s). The spatially averaged Sediment Mixing Depth (Z_m) resulted to be respectively 20% of H_s and 8% of T_p. In the case of the beach protected by a breakwater (Pellestrina) wave steepness resulted to be an additional indicator, possibly because of variable transmission rates over the structure.

The objective of the present study is to study the effects of beachrocks (i.e. of coastal formations consisting of beach material consolidated in situ by mainly carbonate cements) on beach morphodynamics. Towards this objective a detailed study of the beachrock-infected beach of Vatera Bay (Lesvos, Greece) has been carried out using both field sedimentological and morphological data and 1-D morphodynamic modelling. The results of the study show that (a) the beachrock spatial distribution along the Vatera beach is controlled by wave energy levels and beach sediment size; (b) beachrock-infected beaches are characterised by relatively small variability in the morphology of their upper part and their ‘mean' profile is controlled by that of the exposed and/or buried beachrock surface and (c) beachrocks have significant impacts on beach morphodynamics as they facilitate the formation of characteristic morphological features (e.g. ‘scour steps' at the offshore beachrock margins) and increase beach erosion.

In order to design suitable breakwaters for beach protection, morphological modelling is required. This modelling can be utilised to determine the effectiveness of different structures and the position that sand is likely to move to when a stable, equilibrium morphology develops. The majority of morphological models currently used are time-step based. They involve the interaction of wave, current, sediment transport and sediment balance modules. Sediment is transported over a small amount of time, after which the modules are updated and sediment transport calculations begin again. In this paper a new method is put forward, where the need to time step is avoided. Different morphologies are compared directly, based on an objective function, where morphologies closer to the desired equilibrium have a smaller net sediment transport. Morphologies are modified using global optimisation techniques. This new method is able to predict sediment deposition in the lee of detached shore parallel breakwaters.

A 1-D phase resolving numerical wave model, based on the Boussinesq equations is coupled to a multiple sized grain sediment transport module and a morphodynamic module. The sediment transport module includes a hiding function to estimate sediment transport rates for the different sediment fractions in the sediment. The morphodynamic module integrates the sediment flow rate to model an evolving bed, and models the change in sediment fraction composition by a sorting algorithm. The evolution of a sloped coarse-grained (shingle) sea bed in front of a reflecting sea wall under the action of a non-breaking regular wave field is examined. The response of the bed to tidal changes is also modelled.

Laboratory 2D experiments have been carried out in 3 m wide wave flume to investigate wave transmission, wave induced-setup and current over submerged breakwater/reef structures. This paper is aimed at advancing the understanding of overtopping flow across submerged breakwater with different crest widths under different submergences. The experiments have been carried out in a central 1m wide channel so as to minimize/prevent return flow over the structure. Analysis of data shows that flux is most influenced by breakwater crest width rather than other variables. The models provided by Symonds et al. and Gourlay and Colleter are investigated for calculating current passing over the breakwater/reef due to wave breaking. With adjustment to the calibration factors and modification of models predictive capabilities are improved.

The analysis of bathymetric profiles opposite and on either side of a seawall built at the shoreline on a barred sandy coast indicates an increase in sedimentary losses and a deepening of the trough at the foot of the structure. A longitudinal pattern is observed in relation to the dominant littoral drift, suggesting that the impact of a seawall should be analysed both transversely and longitudinally.

Submerged barriers are one of the most promising kind of shoreline protecting structures. The advantages offered vs. the conventional emerged structures are somehow off set because they are much more difficult to project. This decreases their use and limits their application potential. The paper presents some results, obtained by using numerical models on the hydro-morphodynamic behaviour of such structural concept. They illustrate the observed interactions between the freeboard of the structure, its distance to the coast and the resulting wave field, induced circulation and sediment transport patterns.

Waves and wave induced currents are the main forcings acting on beaches. As a consequence of the interaction of these forcings with coastal geometry and available sediment, long-shore transport and morphological changes appear. These changes generate a constant reshaping of the profile and plan form of beaches that define the beach equilibrium and/or the beach evolution. If human activities introduce a modification in the available sediment or in the coastal geometry the existing coastal equilibrium disappears and the beach evolve to a new state. In this paper a case study is shown where a marina is built in the middle of a coastal stretch and some beach nourishment project are carried out. General background and beach nourishment works are detailed. Results from morphodynamic analysis will be shown and beach behavior will be described.

This paper describes an experiment to stop the migration of the tidal channel "Oostgat" in the coastal zone of the Westerschelde, The Netherlands, by nourishing the landward slope of the channel. The goals of the experiment were to determine whether nourishing the steep slope of a channel is technically possible and to investigate morphological developments and sediment transport. In the experiment glauconitic sand was used as a tracer material. Surveys were conducted during one year, using multi beam soundings and the MEDUSA mapping system. Results show that nourishment of a steep slope (1:7) is possible. Sediment transport could be clearly observed and after one year a large percentage of nourished material was still present. Questions remain on the influence of the steepness of the slope and on the scale of the experiment. A full scale nourishments has been planned on the slope of the Oostgat, which will be closely monitored.

Beach profile change due to overwash has a major impact on both developed and undeveloped coasts following storms. The ability to predict such profile change has been further developed within a numerical beach profile change model, taking into account lateral spreading and infiltration on the back slope of the beach, and overwash where the beach crest becomes inundated. These new capabilities were tested for overwash of a low flat barrier and where dunes are present, reproducing well both the volume and shape of the overwash deposits.

Failure of a dike is usually a serious accident and in most cases induces huge disaster. A model which is able to predict the dike breach erosion process as well as the breach flow hydrograph is therefore of outstanding significance for disaster mitigation, damage assessment and risk analysis, etc. A model for breach erosion in clay-dikes (i.e. dikes constructed with cohesive soil) is outlined. The model is based on the breach erosion process as described by Zhu et al. The model has been tested with the data of three laboratory experiments undertaken at HR Wallingford in the UK. Both the breach flow hydrograph and the breach development have been predicted by the model and the agreements between the model predictions and the experimental data are good.

This paper presents the application of a process-based hydrodynamics, waves, sediment transport, and morphological model to assess the performance of a barrier island restoration project in coastal Louisiana, USA. The results show that process-based numerical models can be very helpful during the design and optimization of restoration projects exposed to frequent storm impacts, including barrier island inundation and overwash. However, continued improvement of existing numerical models and modeling protocols is still required.

A process-based morphodynamic coastal area model (TIMOR3) is applied to simulate the virtual breaching of Hiddensee Island at the southwestern coast of the Baltic Sea during a storm flood. Furthermore the medium-term (3 years) development of the initial breach and of an adjacent inlet is simulated using a new approach of model input filtering for a nontidal site. The input filtering of forcing- and boundary conditions is based on typical weather patterns and on wind statistics. The modeled island breach is similar to a historic breach measured in 1866. The adjacent inlet adapts its morphology to the new hydraulic situation due to the island breach mainly within one year. A comparison study with and without a breaching of Hiddensee Island reveals that sedimentation in the adjacent inlet is less in the case of breaching.

This paper critically examines three mathematical expressions for headland-bay shoreline shapes in the context of engineering design. The expressions are first reviewed, and discussion is given on sensitivities to key parameters defining the shapes, including uncertainty, problems with fitting to measurements, and selection of appropriate wave direction, recommended to be the direction of nearshore mean wave energy flux. Needs for fitting software for engineering design are also discussed.

Coastline retreat is more and more abated in The Netherlands with shoreface nourishments. A fast growing bathymetric database enables one to mutually compare the effects of various nourishments. The latter turn out to differ despite similarities in their design and their relative proximity, enabling one to try to (ultimately) pinpoint the cause of the differences. The nourishments are shown to influence the coastal system through interacting with the breaker bar system and are transformed in months into an extra bar, in most cases, that is incorporated in a few years into the natural bar cycle.

A X-band nautical radar system has been employed to observe sea surface patterns of shallow coastal waters during a storm event. Wave gauges and current meters are employed in a conventional field test; however, the deployment of the instruments is limited, especially in the surf zone. In this context, a radar system is introduced here, which can remotely and broadly infer the sea surface state even during a severe sea conditions. The radar system was operated at the research pier HORS and radar echo images were collected during a passage of a storm in the vicinity of the pier. Analyses on radar echo images were done and the results demonstrate the potential of the system in observation of sea states, especially for discussion on morphological features and wave run-up motions. Analyses on radar echo images were done and (i) longshore distribution of mean shoreline positions and intertidal foreshore slopes, and (ii) temporal and spatial variation of wave run-up, are discussed.

The daily maximum landward position of the waterline at the sandy beach of Noordwijk, the Netherlands is measured with an Argus video system over 2001 and 2002, and used to compute exceendence lines for different time periods. The maximum landward position is related to the high-tide level and wave induced water level elevations, like storm surge levels and wave set-up levels. Seasonal variations of positions are clearly observed, with the maximum landward positions and the largest cross-shore spreading of the exceedence lines in the fall and winter season. The spatial variations over a 600 m stretch along the shore are small and mainly influenced by the intertidal barred beach morphology under low-energetic wave conditions.

Information on the actual state of the nearshore zone — in terms of topographic variability, surface waves, and circulation patterns — is crucial in many naval and civilian applications. Spatial scales of interest generally span distances on the order of hundreds of meters to a few kilometers. Obtaining this information form in situ measurements or model predictions alone is not feasible. This paper presents results of the first efforts in assimilating high-resolution video observations of the surf zone with a 2DH morphological model to map 3D bathymetry in the surf zone. Two pilot applications demonstrate the model's potential, returning a realistic rip channelled beach topography at Monterey (CA, USA) and preserving the characteristic bar-trough configuration at Egmond (NL) throughout the entire 9 month simulation period. Being fully embedded in the Delft3D modelling system, the assimilation model can be combined with any regular hydrodynamic or morphological model run. This sophisticated use of high-resolution video observations in combination with a 2DH morphological model opens the door towards the nowcasting of nearshore bathymetric evolution.

Inter-disciplinary medium term monitoring of a small coastal cell of the Northern Adriatic, Lido di Dante Beach, was undertaken starting from 2001. In association with the EU-CoastView Project, coastal state indicators were developed and surveyed. This paper presents the observations done during 3 years of surveys: beach morphodynamics, intertidal bars, dune morphology and vegetation, overwash observation and risk. Results evidence two areas with different dynamics: the Southern part of the beach is dependent on the Bevano River by-pass processes and all indicators are positive (stable vegetation, large beach) while the Northern part is very narrow, eroding (10m/year) and the dune is easily overwashed. This atypical behavior is though to be due to the groin that disturbs the protective function of the nearshore bar system.

An optical system has been designed for measuring the bed level, sand grain motions inside the soil and the presence of suspension at the toe of a coastal structure exposed to breaking waves. These measurements were conducted in the framework of the LIMAS project. We show that the soil is not strictly stable even at great depths (about 1 m). The generation of pressure differences in the soil is the main mechanism for this instability at the wall facing the waves. At the corner of the structure, the shear induced by large longitudinal velocities enhances the sediment transport and scour.

The morphological behaviour of three of Barcelona City beaches (Bogatell, Nova Icaria and La Barceloneta) in response to storms and to an artificial nourishment was studied from November 2001 to December 2003 by means of an Argus video system used to obtain time-series of shoreline position and emerged beach area. Major shoreline fluctuations were due to beach rotation caused by alongshore sediment transport during storms. La Barceloneta and Bogatell beaches presented morphological responses depending on their orientation with respect to the storm direction. However, shoreline evolution in Nova Icaria was strongly affected by defence structures. Although the artificial nourishment caused strong beach accretion and increased the beach surface for some months, the erosive processes prevailed causing, a year and a half later, beach areas equivalent or smaller than those before nourishment was implemented. Significant sediment exchange has been detected between Bogatell and Nova Icaria beaches bypassing the submerged breakwater.

Teignmouth is a busy commercial and leisure port situated at the mouth of the river Teign, in the south west of the UK. This study describes quantitatively the evolution of a sand bar system present at the Teignmouth estuary mouth. This is based on 5 years of observation utilising a video monitoring system supplemented by bathymetric surveys. Observations suggest that previous models of the sand bars behaviour at Teignmouth describing cyclical dynamics of the sand bar system are no longer completely valid. Instead phases of the cyclical dynamics are observed to occur with increased frequency. There is a strong suggestion that this deviation in behaviour is due in part to the anthropogenic influence of a dredging regime which maintains an adequate navigation channel for shipping access to the inner estuary.

Shoreline sand waves are undulations of the shoreline which often propagate along the coast. In this paper features with wavelengths of km's and time scales of years are considered. The generation of sand waves by an instability related to alongshore sediment transport due to waves approaching the coast at a high angle is examined. Also, the propagation of such waves along the coast is studied. A one-line coastline model is used. It is found that the traditional one-line models are unable to describe either shoreline instability or sand wave propagation. A new one-line model is presented which allows for both excitation and propagation of sand waves. The model is tested against the shoreline sand waves observed along the Dutch coast. The propagation of these features is well predicted. Although there is some uncertainty with regard to the cross-shore bathymetric profile related to the sand waves, there is an indication that the origin of these sand waves might be a free instability of the coastline.

The morphodynamic instability of a plane sloping beach for oblique wave incidence has been studied by using a nonlinear numerical model based on a wave and depth averaged shallow water equations solver with wave driver, sediment transport and bed updating. The depth integrated sediment flux formulation is defined as a stirring factor times the depth averaged current plus a downslope term. Two formulae for the stirring factor have been selected: a constant and a function based on the Soulsby and Van Rijn formula. In each case, oblique bars appear with a specific orientation (up-current or down-current), with specific shapes and with specific migration velocities. Not only the initial formation is described but also the finite amplitude dynamics and, in particular, the saturation of the growth.

Nearshore crescentic bars are observed all year long along the French Aquitanian Coast. Their shape can vary from a typical crescentic shape to a strongly dissymmetric shape, and their dynamic is still poorly understood. Nonlinear nearshore model and field survey are used to investigate Aquitanian Coast crescentic bar formation development and particularly their dissymmetric behaviour. Results show that circulation eddies are a key component of nearshore crescentic bar morphodynamic and that long periods of oblique swell can result in a dissymmetric crescent shape. This study leads to a conceptual model which is in agreement with field observations.

A process-based morphodynamic model of the swash zone, which includes the effects of infiltration and bed diffusion, is used to simulate the formation of beach cusps. Preliminary results suggest that infiltration is essential for producing deposition in the swash zone and for maintaining beach cusps.

The morpholgy and hydrodynamics of the macrotidal beach of Dune d'Amont, in northern France, characterised by intertidal bars, were surveyed during storm conditions. The absence of clear cross-shore bar migration in spite of the energetic context was due to weak cross-shore currents, although significant storm wave heights attained up to 1.5 m. However, tide-induced longshore flows considerably strengthened by wind forcing during the storms was responsible for the longshore migration pattern shown by the bar-trough systems. These longshore flows also account for the longshore variations in cross-shore profile volumes.

The variability of nearshore bar responses to hydrodynamic conditions is investigated using a 2DH process-based model. Two hydrodynamic conditions were consecutively applied to an initially longshore uniform double barred profile, mimicking an up-state transition with four different transition moments. The bathymetrical evolution is analysed on the extent of adapting towards a state that relates to the up-state condition. It was found that the earlier the transition moment, the better the bars adjust their length scales to the length scales related to the up-state condition. The computed results show merging behaviour and variations in length scales that compare well with field observations.

Two different approaches were performed on a microtidal beach in Sète (Mediterranean Sea, France). (1) Quantification of sand reservoir on the shoreface based on very high-resolution seismic data to assess the sand volume repartition and check the link with the littoral drift. (2) Displaying morphodynamics models for the bar changes. Results show that the volume increases in the longshore drift direction and become the highest downdrift, where erosion is the weaker. The morphological evolution of the sedimentary bars on the area can be synthesized according to two conceptual models in reaction to hydrodynamic variability. The two approaches finally contribute in a way complementary to a better knowledge of the littoral system behaviour and provide a new way to foreknow the beach vulnerability. For beach in erosion, all the sediment available can be removed during the bar changes. Furthermore, depending on the size of the total sand reservoir on the shoreface, the hydrodynamic forcing don't seem to have the same impact on the beach and on the shoreface evolution.

Two models are discussed that describe the initial formation of nearshore large-scale rhythmic morphology due to feedbacks between the wave-driven large-scale flow and the erodible bottom. The aim is to gain fundamental knowledge about the sensitivity of modeled bar characteristics to the description of waves and sediment transport, in case of obliquely incident waves and planar reference beach profiles. The two models differ mostly in the wave description (with different degrees of complexity) and both of them are supplied with two different sediment transport formulations. Systems of sand bars with longshore rhythmicity emerge as free instabilities of the system. Including randomness in wave heights largely affects the modeled bar growth and dynamics. Results are also different for the two sediment transport formulations. In particular, the differences in the cross-shore distribution of the wave stirring function lead to different characteristics of the fastest growing modes.

The sediment transport and sandbank building mechanisms of the Bristol Channel have been investigated using an idealised numerical model. The model consists of a theoretical semi-Gaussian shaped headland comparable to Nash Point in the Central Bristol Channel U.K. Under low energy conditions we see two principle zones of sediment accretion develop, a larger one extending into the constricted upstream channel and a smaller deposit in the downstream wake of the headland. Large gradients in transient tidal velocities mark these principal depositional areas. The relationship between the residual velocity field and areas of sediment accretion is less clear. However, confined regions of upwelling to the north east and south west of the headland, correspond well with positions of cubic velocity residual gyre centres and mark limited regions of sediment accretion. This suggests the possible influence of secondary flows on post-depositional sandbank building processes. Adjustment of the near-headland geometry, to include a gently sloping coastal ‘apron' surrounding the headland, has the effect of increasing the amount of sediment transport. This is in response to both continuity and bed slope effects, which augment offshore acceleration and induce enhanced sediment scour. Under higher energy conditions, we see the disappearance of the upstream accretionary zone and a large increase in deposition downstream of the headland. These results show good agreement with conditions observed in the real environment, where strong tidal flows upstream of Nash Point restrict accretion east of the headland. The final test, conducted using an initial bed perturbation to represent a bedrock outcrop or sandbank ‘core', demonstrate that under low energy conditions such a feature promotes secondary flow mechanisms and local accretion.

Sand waves are wavelike bed patterns occurring in shelf seas. Their height, length and migration speed vary over time and space. This variability is not yet fully understood. In this paper we try to understand the influence on modelling sand wave characteristics of two sources, i.e. grain size variability and various sediment transport equations. Hereto, we implement these sources in a numerical morphodynamic model. We find that local grain size can influence growth rate as well as equilibrium height. We also found that the effect of grain size variation highly depends on the used sediment equation. For large grain sizes the predicted sand wave height becomes 10% lower. Furthermore, the predicted growth rate can vary a factor 100 depending on the used sediment transport equation and grain size.

A series of experiments have been carried out in the DHI Shallow Water Basin in order to identify possible effects of a double peaked wave spectrum on sediment transport related processes. Wave conditions for different tests were chosen on the basis of a constant total amount of energy but with different distribution of this energy in the two peaks. Results show an increase in time averaged concentrations when a small swell component is added to a wind sea dominated spectrum. Similarly, a reduction takes place when a small wind sea component is added to a spectrum accounting for swell conditions. The analysis of the vertical distribution of turbulence and bed roughness features provides indicators of the origin of these variations in suspended sediment concentrations.

A series of field experiments were conducted to investigate sediment re-suspension and cross-shore cycling in nearshore environments with special emphasis on different frequency components (wind waves, swell, infra-gravity waves etc.). Measurements included simultaneous records of surface elevation, cross-shore current velocities, and suspended sediment concentrations both inside and outside of the breaker zone. Measurement locations were selected to cover a range of hydrodynamic and sedimentological conditions. The results indicated that wave groups appeared to be more capable of re-suspending sediments than incident waves. Results of co-spectral analysis indicated that the direction of cross-shore (suspended) sediment flux on the frequency domain was different for each location under different conditions. This leads to the hypothesis that there are additional factors such as the local wave climate, grain size, beach slope, bed forms, etc., governing the pattern of cross-shore suspended sediment transport flux in the frequency domain.

The aim of this paper is to determine the capability of Evolutionary Computation (EC) method in predicting sediment suspension from the velocity field. EC is a robust search and optimisation technique based on the Darwinian principle of natural evolution, where the fittest will survive. There are different algorithms to simulate natural evolution in computer system. In this paper we use Genetic Programming (GP) methodology to explore a better correlation between the temporal pattern of fluid field and sediment transport. GP code developed by Langdon is modified for sediment transport modelling. Two datasets are used, one from numerical model results and other from field data (Sandy Duck), to evolve symbolic expression for sediment transport. The results from the numerical models are encouraging though the GP found it hard to find relationships from the field data.

A multianual analysis of the littoral drift along the Maresme Coast (Northern Spanish Mediterranean Coast) is carried out. Energetic littoral drift formulas have been applied and validated with historical field data. The study has been conducted in order to design a sand "by pass" system at a marina harbour. The work shows the relevance of the multianual variability of the littoral transport in the definition of the by-pass system and more specifically en the defining of the sand trap.

We have developed a numerical model that couples geologic framework effects and alongshore sediment transport processes to investigate large-scale, long-term shoreline evolution in sediment-limited environments. Shoreline segments underlain by material composed of higher proportions of fine sediment (i.e. mud) than adjacent segments tend to form shoreline indentations. However, wave-driven alongshore transport tends to fill in such indentations where wave climates are dominated by ‘low-angle' waves that smooth shorelines. In the long term, shoreline retreat rates become spatially uniform, and the indentations remain fairly subtle. The modeling suggests that sea-level-rise acceleration will tend to increase the amplitude of the indentations. In the limit of very rapid sea-level rise, and associated high rates of shoreline retreat, continuous and relatively smooth sandy shorelines may not be possible, giving way instead to headland-and-pocket beach coastlines.

The present study focuses at improving our basic understanding of size-graded sand transport mechanisms under oscillatory sheet-flow conditions using different transport models. Moreover, the study aims at improving the performance of different transport model concepts for the description of both the rate and size-composition of the transported sand. Quasi-steady and intermediate models are investigated, in combination with a large dataset of oscillatory sediment transport measurements (sheet-flow conditions) as collected from two oscillatory water tunnels. A comparison is made between the measured net transport rates and transport rates per size fraction and the results from various transport formulas. First, the comparison is based on a 1-fraction approach i.e. the sand is modeled using D₅₀ of the mixture. Second, a size-fraction approach is tested and developed further using the experimental dataset. Exposure corrections are proposed for fine and coarse size fractions in the sand mixture to improve model performance.

We have implemented two schemes that use sediment transport predictions from a detailed discrete particle model (DPM) to compute long-term, equilibrium morphology. This analysis directly couples processes acting at the grain scale (mm) to the scale of a nearshore profile (km). In the first scheme, the DPM was applied iteratively to find an equilibrium profile that resulted primarily from a balance between offshore-directed down-slope transport and onshore-directed transport driven by strong pressure gradients acting on relatively coarse sand grains. In the second scheme, the predictions from the first scheme were parameterized and the parameterized model was applied iteratively. In this case equilibrium resulted from a balance between down slope transport and a parameterization based on near bed slope and flow velocity and acceleration skewnesses. While both approaches yielded qualitatively similar results, the parameterization approach had the advantage of filtering numerical noise as well as much-reduced computational effort.

This paper describes on site field measurements of sand transport with two different types of instruments at 13 m water depth at a location 2 km off the coast of Noordwijk aan Zee, The Netherlands. The measurements are compared with results from four practical model combinations using different predictors for the combined current and wave-related shear stress, the reference concentration and the wave boundary layer thickness. Measurements are also compared with results from the Bailard suspended load sand transport model. Best overall predictions of the measured suspended transport rates are made with the Bailard model.

A series of prototype-scale laboratory experiments was performed in the Aberdeen Oscillatory Flow Tunnel to investigate the intra-wave sediment transport processes in the ripple regime. Detailed measurements of velocities and concentrations were carried out for three different regular oscillatory flow conditions. It is found that the time- and bed-averaged concentrations fit an exponential profile reasonably well, and that the concentration decay length is strongly related to the ripple height. The intra-wave concentration field is dominated by the formation and ejection of vortices on the onshore (in the direction of flow asymmetry) ripple flank. In a lower layer of about two ripple heights, the net current-related flux and net wave-related flux are in the offshore direction and the wave-related flux dominates. Higher up in the flow the net wave-related flux is still offshore-directed, but the net current-related flux is onshore-directed and is dominant, resulting in an onshore total net flux.

The applicability of grain-size trend analysis for determining sediment transport pathways was investigated on a macrotidal shoreface of the southern North Sea, following the Gao and Collins method. The sediment transport pattern inferred from the grain-size trend analysis shows a good correspondence with tidally-driven near-bottom currents measured in the vicinity of the sediment sampling sites, which were setting alongshore. Comparison of threshold shear velocity for sediment motion with estimates of bed shear velocity obtained from near-bottom current data recorded simultaneously with sediment sampling indicates that sediment transport was certainly occurring when sediment samples were collected, suggesting that the grain-size trends observed in the surface sediments probably reflect the last transport event. Our results show that grain-size trend analysis can be very efficient for determining the transport pattern of the last sediment transport event when sampling is limited to the thickness of the active layer of sediment remobilization.

Grain size is an important input parameter for longshore transport calculations. However, measurements and sampling in the longshore transport zone can be difficult and costly. This paper presents initial investigations aimed at predicting the median grain size in the longshore transport zone, based on measuring only the beach grain size. The data analysed to date suggests that the longshore transport zone grain size is close to half that found on the beach. Factors that could influence this relation are mentioned. The work is ongoing.

Suspended sediment concentration, water surface elevation and horizontal velocities were measured near the shoreline during a storm, when long period waves were developed. The oscillatory component of cross-shore sediment transport rate was shoreward and had a nonnegligible contribution to the net seaward transport rate as previous studies showed. In the oscillatory component, the infragravity component with frequencies between 0.004 Hz and 0.04 Hz and the gravity component with frequencies larger than 0.04 Hz were mostly shoreward and dominant, whereas the far infragravity component with frequencies lower than 0.004 Hz was mostly seaward and small. The infragravity and gravity components of the cross-shore sediment transport rate had correlations with the acceleration asymmetry.

The sensitivity of the newly developed two-phase flow model is investigated on the effect of wave period and the free-stream velocity. Preliminary comparisons with the experimental data of Horikawa et al. are performed. Further comparisons with experimental data by Dohmen-Janssen show the two-phase flow model is capable of simulating the sediment movement processes accurately. The calculated net transport rates are compared with 25 experimental measurements under combined wave/current sheetflow regime, which includes various flow and sediment conditions.

The morphodynamic control on coastal drivers at plan and profile scales presents differences of various orders of magnitude both in time and space. This is due mainly to the different associated physical processes (refraction, diffraction, depth induced breaking and friction,...) which act at various scales. The paper analyzes the morphodynamic control in both plan and profile scales using practical examples from the Ebre delta coast (in the Spanish Mediterranean). During these analyses, some conclusions have been derived regarding the effect of hydrodynamic processes over the probabilistic distributions and their parameters.

Annual as well as monthly time-series of the morphological evolution of a small study area in the German Wadden Sea were used to study the reasons for morphodynamic model shortcomings. The long-term morphodynamic trend shows the filling of a tidal channel and retreat of the coastline. Monthly datasets reveal that in contrast to almost no bathymetric changes during fair-weather periods, extreme events can be determined as the main morphodynamic drivers. Hence, highly parameterized boundary conditions as single "representative tides" cannot provide the necessary diversity of forcing to drive realistic morphodynamic model simulations. Instead, morphodynamic models should use open boundary conditions, which consider the variation in tidal and meteorological forcing rather than characteristic single tides.

The morphodynamic response of shingle barrier beaches is examined, in response to a range of hydrodynamic conditions, in context with the pre-storm barrier geometry, and at a temporal scale based on typical storm events. Key variables affecting the crest evolution of shingle barriers to storm activity are identified and quantified. The barrier inertia parameter, an empirical dimensionless predictive overwashing threshold framework, has been tested in the field and the limits of applicability identified. The model has been applied in predictive mode to assess the risk of breaching at several sites in southern England.

In this study sand bars were analyzed using remote sensing techniques. An Argus system was installed at Lido di Dante, a small village near Ravenna, in northern Italy. The study period is between April 2003 and May 2004. Timex video images were used to analyze bar dynamics. Pixel luminosity intensity was sampled along 15 cross-shore profiles, 50m spaced. The system was perturbed by a storm event occurred in December 2003. Before this event the bars were undulated with 2 wide crescents, after the event the crescents became 5. Before and after this event the system was stable and it maintained a constant configuration. A preliminary conceptual model is presented: the system is self-organized, by redistribution of sand within a delimited longshore area, even under low energy conditions. When an energetic event occurs, the system changes, but it recovers its stable configuration within a short time (6 days).

Wave and coastal circulation modeling are combined with multibeam bathymetry, high-resolution beach surveys, cross-shore Personal Water Craft surveys, digital bed sediment camera surveys, and real-time video monitoring to quantify morphological change and nearshore processes at Ocean Beach, San Francisco. Initial SWAN (Simulating Waves Nearshore) wave modeling results show a focusing of wave energy at the location of an erosion hot spot on the southern end of Ocean Beach during prevailing northwest swell conditions. During El Niño winters, swell out of the west and southwest dominates the region, and although the wave energy is focused further to the north on Ocean Beach, the oblique wave approach sets up a strong northerly littoral drift, thereby starving the southern end of sediment, leaving it increasingly vulnerable to wave attack when the persistent northwest swell returns. An accurate assessment of the interaction between wave and tidal processes is crucial for evaluating coastal management options in an area that includes the annual dredging and disposal of ship channel sediment and an erosion hot spot that is posing a threat to local infrastructure.

Post-storm field inspections and surveys were conducted on two nourished beaches (Boca Raton and Town of Palm Beach) to determine morphological impacts of H. Frances and H. Jeanne on these beaches. As a general trend, the expected cross-shore response (beach cut and offshore bar formation) was observed. Alongshore variability of profile response and erosion rates and hot spot development (due to variable causes) were also observed, these may be attributed to a number of factors including irregular offshore bathymetry, presence of surf zone rock outcrops and irregular (curved) nourishment planform. Erosion of the project templates ranged from 24% to 37.5% of the original placed volume in Town of Palm Beach and Boca Raton respectively. Beach nourishment performance is summarized in this paper and hypothesis to explain the observed beach behavior are presented.

Storms along the Catalonian coast previously classified in terms of their energy content are re-analyzed to take into account their erosion potential effects on the coast. This was done in two-step procedure. The first step consists in modeling their effects on two representative beach profiles by using SBEACH. The coastal response was characterized through two bulk erosion parameters, beach retreat and eroded volume. In the second step, the effort was devoted to look for a parametric way to estimate the storm erosion potential in such a way that by simply using synthetic information on storm characteristics, similar bulk erosion values to the obtained by using SBEACH be obtained. To do this, several beach profile change dimensionless predictors were tested. Although the use of some of these predictors gave reasonable predictions, it was found that the inclusion of the storm duration was a key variable to reduce the scatter in the response. Moreover, to properly reproduce reflective and dissipative beach profile erosion, predictors explicitly including beach slope have to be used. Here we propose to use the JA parameter multiplied by the storm duration. Using the JA t parameter a final 5-classes scale based on the erosion potential and beach retreat ranging from I (lowest erosion potential) to V (highest erosion potential) was obtained.

For the calculation of turbulent mixing in the bottom boundary layer, we present simple analytical tools for the mixing velocity w_m and the mixing length l_m. Based on observations of turbulence intensity measurements, the mixing velocity w_m is represented by an exponential function decaying with z. We suggest two theoretical functions for the mixing length, a first l_m1 obtained from the k-equation written as a constant modeled fluctuating kinetic energy flux and a second l_m2 based on von Kármán's similarity hypothesis. These analytical tools were used in the finite-mixing-length model of Nielsen and Teakle. The modeling of time-mean sediment concentration profiles C(z) over wave ripples shows that at the opposite of the second equation l_m2 which increases the upward convexity of C(z), the first equation l_m1 increases the upward concavity of C(z) and is able to reproduce the shape of the measured concentrations for coarse sand.

A common assumption in modelling tidal flow in coastal areas is that in the vicinity of the bottom the vertical flow profile attains a logarithmic shape. Some consequences of this type of assumption are studied in the present paper. In a diagnostic setting, the tide-residual transport of sediment is depicted as a function of the thickness of the assumed log-layer. In this respect, the tide is schematised to a combination of the M₂ and M₄ constituents and the water depth is chosen in a range typical for the shoreface (10–25m). The computational results indicate that assuming a log-layer may lead to an error in the cross-shore transport in the order of 1% of the alongshore transport.

Observations of instantaneous and spatial mean water surface slopes and flow depths in the surf and swash zone are presented. With the assumption of hydrostatic pressure and small shear stress at the free surface, the surface slope is equivalent to the horizontal pressure gradient which is directly proportional to the total fluid acceleration. In the swash, the water surface slope is observed to be positive (dipping seaward/rising landward) and the total fluid acceleration to be negative for the majority of the uprush and the entire backwash, contrary to some recent suggestions. Intantaneous swash depth profiles show that the uprush lens is weakly convex in shape, consistent with previous work and friction effects at the run-up tip. In addition, a simple method is presented for obtaining rapid inter-swash bed level measurements and hence the cross-shore variation in net total sediment flux for individual swash events.

Simultaneous high frequency field measurements of water depth, flow velocity and groundwater elevation, coincident with observations of bed level change were made across the swash zone of a steep gravel beach. Groundwater oscillations were forced directly by swash events on the beachface but the antecedent elevation of the water table was important in determining the net groundwater response. The instantaneous swash flux was used as an indicator of infiltration/exfiltration and was highly asymmetric across the swash zone. A region of strong infiltration in the mid-to-upper-swash termed the Swash Recharge Zone (SRZ) and a transition region in the lower-swash where infiltration/exfiltration balance were identified. Morphological change over the tidal cycle was exclusively onshore and associated with berm construction. Accretion occurred close to the uprush limit within the SRZ whilst morphological change across the transition region was minimal. It is suggested that swash volume asymmetry caused by infiltration in the SRZ biases sediment transport onshore by reducing the sediment transport competency of the backwash.

This paper describes almost 300 hours of velocity data collected in the swash and surf zone of a dissipative and reflective beach. During both field surveys, the upper part of the beach experienced progressive accretion, indicating that onshore sediment transport prevailed in the swash and inner surf zone. The associated cross-shore flow field was, however, dominated by offshore-directed mean flows, especially under energetic wave conditions on the steeper beach. Velocity skewness (defined as 〈u³〉/〈u²〉^1.5, where u is the cross-shore velocity) was negative (i.e., offshore-directed), implying that energetics-based sediment transport models are unable to predict the direction of sediment transport. Significant longshore flows were recorded in the swash zone and it is argued that the extra bed shear stress due to the longshore current assists the offshore flows more than the offshore flows. Longshore swash flows may therefore be an important contributing factor to beach erosion.

Beach groundwater is a complex and dynamic system interacting with tides, waves and swash. Groundwater fluctuations driven by oceanic oscillations enhance water exchange between the ocean and coastal aquifer. This alters total submarine groundwater discharge (SGD) rates and the breakthrough concentration and exit times for contaminants entering coastal waters. Interaction between swash dynamics and groundwater may also be important with regard to onshore sediment transport and beach profile evolution. There is currently limited understanding of how the beach groundwater system responds to oceanic forcing at various frequencies. This paper presents field measurements collected on Belongil Beach (Byron Bay, NSW, Australia) during the period between 12^th and 25^th June 2004. Data includes piezometric head measurements from a cross-shore piezometer transect and vertical head gradients from transducers installed in nested piezometers. The data is discussed in terms of small amplitude groundwater theory and indicates similar magnitudes of horizontal and vertical flows in the intertidal zone. The latter are frequently ignored in beach groundwater models.

A numerical model of sediment transport in the swash zone has been recently developed. The followed approach relies on the solution of the vertical distribution of suspended sediment concentration and incorporates the horizontal advection of suspended sediment from the bore collapse and local pickup using a Lagrangian computing scheme. Computed sediment transport rates are compared to measurements on a reflective beach on the central east coast of Australia. The model has proved to contribute to the explanation of the sedimentary process in the swash zone, predicting accretion on a reflective beach where classical swash sediment transport concepts would give erosion.

The statistical distribution of swash maxima has been analyzed using video-based observations of wave runup excursions during 3 experiments ("DozerDuck") performed on an ocean beach in North Carolina (USA). The distribution of swash runup maxima compared well with the theoretical one when the beach was planar. The comparison is less satisfactory once beach cusps developed. The possibility that such discrepancy is a result of swash interactions (primarily affecting time series of shoreline elevation collected in front of beach cusp bays) has been analyzed using a simplified (frictionless) ballistic model. This model, modified to account for the effect of swash interactions, indicates that swash interactions do affect the distribution of swash maxima and results are also in agreement with the available observations.

This paper introduces a general methodology for applying the Inlet Reservoir Model in regional sand management at inlets. The procedure is based on numerical modeling and data analysis for various spatial and time scales to evaluate the inlet evolution, existing condition, and alternatives for a proposed design. The methodology is discussed through a case study for Hurricane Pass, on Florida gulf coast. The case study addresses potential consequences of proposed dredging of the Hurricane Pass ebb shoal for restoration of the beach on Honeymoon Island State Park. The analysis is based on observed inlet evolution, and modeling of regional hydrodynamics, waves, and sediment transport at various times marking main stages of the inlet system evolution. Modeling results serve as input to the Inlet Reservoir Model to quantify volumetric change and bypassing rates between the different morphologic features that comprise the inlet shoal system. The model is then applied to assess the long-term consequences of proposed dredging on the adjacent beaches and recovery rate of the borrow area.

Inlets are part of the coastal sediment-sharing system, and the presence of a new inlet will greatly modify the nearshore and bay morphology, as well as the up-drift and down-drift shorelines. Morphologic response to an inlet varies over several time and spatial scales. This paper analyzes general morphologic responses to the presence of a new coastal inlet in the context of functional design considerations that typically must balance navigation and shore-protection requirements.

Analysis of thirteen-hour ADCP observations of flow revealed complex residual flow patterns in the inlet gorge and main ebb-delta channel of Texel Inlet (the Netherlands). Main features are the dominance of axial residual flow velocities over the transverse velocities, and a typical density-driven distribution of ebb-dominant flow in the top-layers and flood-dominant flow in the near-bed regions. Numerical simulations were made using the process-based model Delft3d Online Morphology. The model is capable of reproducing the dominant features of the residual flow patterns accurately when fresh-water discharge in the basin is included. Analysis of the model results shows that density differences are essential to create the tilt of the residual flow distribution from horizontal to the observed vertical shear. The resulting more pronounced segregation of ebb and flood flow results in augmented residual ebb-velocities along the Texel coastline and Noorderhaaks, and residual flood velocities along the North-Holland coast.

A new modeling system for estuarine and coastal morphodynamic evolution, MORSYS2D, is under development at LNEC. The objective of the present work is to assess the behavior of MORSYS2D in a test case at a real scale, for short- and long-term simulations. For short-term simulations, MORSYS2D results are compared with the ones from another system. For long-term simulations, MORSYS2D results are compared with empirical ones. Comparison of the two systems forced by tides only was very encouraging, minor differences being mainly due to the different empirical formulae for sediment flux calculations. MORSYS2D simulations for the tide and fair weather wave were hampered by the lack of radiation stress forcing of the hydrodynamic model. Long-term simulations illustrated the good performance of the model, without any signs of oscillations in a 10-year simulation. Model results are consistent with empirical models and pointed out the dynamical equilibrium of the inlet throat.

The East Frisian tidal inlets tend to migrate with the prevailing eastward drift in the southern North Sea. For Harle inlet eastward migration was accelerated by the adaption of tidal basin and inlet to the resedimentation of a medieval storm surge bay. To prevent further migration a large-scale groyne was built in the eastern part of Harle inlet between 1938 and 1940. Nowadays this structure still keeps the main channel in position and restricts the extent of a secondary channel. But in the last two decades redistribution of tidal gullies in the catchment area significantly increases the tidal prism of the secondary channel and accordingly its cross-section starts to expand. Investigation in light of empirical equilibrium conditions indicate that the partial cross-sections in Harle inlet show a retarded adjustment to the modified hydrodynamical conditions. But future adaptation of equilibrium conditions through further erosion of the secondary channel is anticipated.

Óbidos lagoon is a small coastal system connected to the sea through a shallow mobile inlet. The lagoon that is the support of an important ecosystem, beyond a natural accretion tendency, common to these coastal lagoons, suffers from cyclic water quality problems related with the difficulties in renewing the water due to the closing of its inlet. Beyond these problems it is common to have strong coastal erosion in the lagoon margins with consequences for the safety of the local houses. In these occasions it is necessary to take emergency coastal protection measures in order to avoid the occurrence of major disasters. In order to try to understand the lagoon dynamics an integrated lagoon model capable to simulate the water quality and the sediment transport by the combined effects of waves and currents was implemented. In this paper the discussion of some of the results obtained is presented and discussed.

When surface water waves travel over a soft mud bed, an inter-surface wave between the water layer and the mud layer is generated resulting to high wave attenuation and mass transport in mud layer. The present paper offers a numerical model which includes a multi-layered visco-elastic-plastic model to predict the wave attenuation under regular waves due to muddy bed. The model is based on mild slope equations and it includes combined wave refraction, diffraction, reflection, breaking and wave attenuation due to fluid mud layer. An artificial neural network is used as a part of wave attenuation calculation to speed up the computation. Applying the model in the East Bay, Louisiana shows a reasonable agreement with wave height measurement.

For a stationary wave field, spectral models represent the surface wave motion sufficiently accurately. There are however two drawbacks in using nonlinear spectral models: a) The computational time involved when simulating the random wave field; the number of operations needed is O(N²) (N is the number of frequency components) b) Spectral models are usually one-equation reduction of the two-equation time domain model, which does not then have the same characteristics of the original model. Here we explore two approaches to solve these problems. First, we use the hybrid FFT technique both to speed up the calculations and to incorporate higher order nonlinear terms. Second, we look at frequency domain transformation without reducing the model to one equation. Significant improvement in computational speed was obtained with the hybrid FFT approach. The models also show good agreement to the data reported by Mase and Kirby.

In this paper an incompressible Smoothed Particle Hydrodynamics (SPH) method combined with a Large Eddy Simulation (LES) model is used to investigate wave overtopping. SPH is a pure Lagrangian approach which can handle large deformations of the free surface with high accuracy. Two different cases are used to test the model, namely storm wave overtopping of a fixed horizontal deck and random wave overtopping of a sloping seawall. The computations are validated against experimental and numerical data in the literature and good agreement is found.

The paper presents an experimental investigation of obliquely incident wave reflection at low-crested structures within the EU-funded project DELOS. The physical model tests were carried out with incident wave attack angles varying over a wide range from 0° to 60° at a multidirectional wave basin. Data comparisons suggest that long-crested and short-crested waves give similar reflection from low-crested structures. The reflection coefficient is noticeably dependent on the wave angle of incidence. On the basis of the test data, two wave reflection formulae including the influence of incident angles are proposed for low-crested rubble mound structures and smooth structures respectively. Wave spectra analyses show that the reflected peak period is quite close to the incident peak period, and the reflected directional waves more widely spread than the incident waves.

Interactions of regular waves with a double, fixed, pontoon type, floating breakwater (FB) are studied numerically with the use of a 2DV Unsteady Reynolds Averaged Navier-Stokes (URANS) model. The study is focused on the effect of the structure width and spacing, both made dimensionless with the wave length (W/L and S/L), on the reflection, transmission and dissipation characteristics. The results of the numerical model are in good agreement with available large scale experimental data. C_t decreases with increasing W/L for all S/L; for a 100% increase of W/L a 62% (maximum) and a 34 % (minimum) decrease of C_t is found for S/L=0.25 and S/L=1.04 respectively. The effect of relative spacing S/L is not monotonic since C_t exhibits several maxima and minima with S/L. Better results are obtained for S/L<0.75 with C_t values less than 0.1.

Analytical formulas are derived for the migration velocity and infill time of (dredged) trenches in the marine environment, using an harmonic analysis of simplified 1D basic equations for the morphodynamic system. The formulas can be used as simple engineering tools for the design of trenches and pits. They also provide insight into the main process parameters (waves, currents, depth, sediment properties) controlling the morphological behaviour and the role of the trench dimensions and shape (depth, length, side slopes). The formulas are verified with more sophisticated numerical models, laboratory experiments and a number of field cases in the North Sea.