This study presents measurements of sheet flow processes, grain sorting, and bedload plus suspended load transport rates around a medium-sand breaker bar in a large-scale wave flume. The results offer insights in effects of wave breaking on bedload and grain sorting processes and in the quantitative contributions by bedload and suspended transport to breaker bar morphodynamics. Sheet flow layer dynamics are highly similar to observations under non-breaking waves, revealing clear effects by velocity asymmetry but no evident effects by breaking-generated turbulence, bed slope, or the cross-shore non-uniform flow. The sheet flow layer thickness can be predicted using existing empirical formulations based on local hydrodynamic forcing. At locations covering the shoaling region up to the bar crest the cross-shore variation in bedload transport rates is explained by variations in wave shape (i.e. velocity skewness and asymmetry). At locations between bar crest and bar trough, bedload transport rate magnitudes correlate positively with bed slope and turbulent kinetic energy. Bedload and suspended load transport rates are of similar magnitude but of opposite sign. Bedload transport is onshore-directed and dominates in the shoaling zone, but after wave breaking, the offshore-directed suspended sediment transport increases in magnitude and exceeds bedload transport rates in the breaking and inner surf zones. Bedload and suspended load transport contribute notably differently to bed profile evolution: bedload transfers sand grains from the offshore slope to the bar crest and additionally leads to erosion of the shoreward bar slope and deposition at the bar trough, while suspended load transport induces an opposite pattern of erosion at the bar trough and accretion at the bar crest. Grain size analysis of suspended sediment samples reveals size-selective entrainment and vertical size segregation in the inner surf zone, but suggest size-indifferent entrainment and vertical mixing by energetic vortices in the breaking region. Size-selective transport by bedload and suspended load leads to a cross-shore coarsening of the bed from shoaling to inner surf zone, with local additional sorting mechanisms around the breaker bar due to bed slope effects.
Van der Zanden, J.; Van Der A, D.; Hurther, D.; Caceres, I.; O'Donoghue, T.; Ribberink, J. Coastal engineering Vol. 125, p. 51-69 DOI: 10.1016/j.coastaleng.2017.03.007 Data de publicació: 2017-07-01 Article en revista
This paper presents novel insights into suspended sediment concentrations and fluxes under a large-scale laboratory plunging wave. Measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar, covering the complete breaking region from shoaling to inner surf zone, with particular high resolution near the bed using an Acoustic Concentration and Velocity Profiler. Wave breaking evidently affects sediment pick-up rates, which increase by an order of magnitude from shoaling to breaking zone. Time-averaged reference concentrations correlate poorly with periodic and time-averaged near-bed velocities, but correlate significantly with near-bed time-averaged turbulent kinetic energy. The net depth-integrated suspended transport is offshore-directed and primarily attributed to current-related fluxes (undertow) at outer-flow elevations (i.e. above the wave bottom boundary layer). The wave-related suspended transport is onshore-directed and is generally confined to the wave bottom boundary layer. Cross-shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick-up and deposition and of cross-shore sediment advection. Suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion, leading to local intra-wave concentration changes. At locations between the breaker bar crest and bar trough, intra-wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer: sediment is entrained in the bar trough during the wave trough phase, almost instantly advected offshore, and deposited near the bar crest during the wave crest phase. Finally, these results are used to suggest improvements for suspended sediment transport models.
A morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandniotor mega-nourishment on the Dutch Delfiand coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow Migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m(2)/s, close to the observed value of 0.0022 m(2)/s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m(2)/s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches prodtices 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold.
Wave extreme events can be understood as the combination of Storm-intensity, Directionality and Intra-time distribution. However, the dependence structure among these factors is still unclear. A methodology has been developed to model wave-storms whose components are linked together. The model is composed by three parts: an intensity module, a wave directionality module, and an intra-time distribution module. In the Storm-intensity sub-model, generalized Pareto distributions and hierarchical Archimedean copulas have been used to characterize the storm energy, unitary energy, peak wave-period and duration. In the Directionality and Intra-time sub-models, the wave direction (at the peak of the storm) and the storm growth–decay rates are linked to the variables from the intensity model, respectively. The model is applied to the Catalan coast (NW Mediterranean). The outcomes denote spatial patterns that coincide with the state of knowledge. The proposed methodology is able to provide boundary conditions for wave and near-shore studies, saving computational time and establishing the dependence of the proposed variables. Such synthetic storms reproduce the inter-variable co-dependence of the original data.
In this paper, large-scale experimental data are presented showing the beach profile morphological evolution induced by four different bi-chromatic wave conditions characterized by very similar energy content between them but varying the modulation period. Important differences were observed in the resultant beach profiles as a function of the wave group periods. Larger variability in the profile evolution is generally observed for larger wave group periods and, more importantly, as the wave group period increases the distance between the generated breaker bar and the shoreline increases. The measured primary wave height to depth ratio (¿) increases with the wave group period, which is consistent with the observed larger wave height at the breaking location. The primary wave breaking location is also observed at increasing distances with respect to the initial shoreline as the wave group period increases. The variation in ¿ with wave group period is related to the selective energy dissipation of the higher primary frequency component (f 1) during the wave group shoaling. Broad bandwith conditions (reduced wave group period) lead to larger dissipation of wave heights at the f 1 component relative to f 2 resulting in a reduction in the wave modulation and primary wave height at the breaking location. Suspended sediment fluxes obtained from collocated velocity and sediment concentration measurements in the surf zone showed a consistently larger contribution of the mean return flow to the suspended sediment fluxes compared with the wave group and primary wave components. The distinct beach profile evolution in terms of bar location is interpreted from an increasing distance of the mean breakpoint location and the location of maximum return flow with respect to the shoreline as the wave group period increases.
The use of a pressuremapping system formeasuring wave impact induced pressures is evaluated in this paper. A set-up and a calibrationmethodology are suggested and employed for thiswork. The system is validated against pressure transducer and load cell measurements and for a range of waves breaking on a vertical seawall. For a large number (120 measurements for each case considered) of breaking and broken waves interacting with the wall, the peak pressure (Ppeak) profiles and the pressure distribution maps reported by the system agree wellwith results acquired using pressure transducers. Although the pressuremapping system tends to underestimate Ppeak, differences on themean of the 3, 5 and 10 highest Ppeak rangewithin±10%, while for themajority of the measurements the error on the integral of the acting pressures (the acting force compared with the force measured by the load cell) ranges within ±20%. It is concluded, that through careful calibration and set-up the pressure mapping system has the capacity to provide pressure distribution maps with a good accuracy. It is not, however, considered to constitute the absolute alternative to pressure transducers and thus a combined use is suggested for applications where a very high level of accuracy is required.
This study presents the analysis of the water surface elevation, velocity and suspended sediment concentration measurements obtained at a large wave flume under mobile bed conditions. The wave reproduced erosive and accretive conditions, and included monochromatic, short waves perturbed with a free long wave, bichromatic and random conditions. Each tested condition started from a handmade 1/15 slope and lasted for an approximate time period of 2.4 h (6 runs of the selected wave condition), to compare the different beach profile developments and, in particular, the events that control sediment transport in the swash and surf zones. All erosive tested conditions produced a shoreline retreat and a bar at the breaking area whose development in time is directly correlated to the length of the breaking area. On the other hand, not all accretive conditions present a shoreward transport, and random conditions do not seem to alter the initial profile. The processed data show the suspended sediment event control produced by the existence or absence of wave–backwash interactions in the swash zone. The existence of these interactions, and their number within the wave group, will be a key parameter in controlling the sediment stirring, water velocity magnitudes and, therefore, the suspended sediment fluxes in the inner surf and outer swash.
Van der Zanden, J.; Alsina, J.; Caceres, I.; Buijsrogge, R. H.; Ribberink, J. Coastal engineering Vol. 105, p. 47-65 DOI: 10.1016/j.coastaleng.2015.08.009 Data de publicació: 2015-11-01 Article en revista
Detailed measurements of bed level motions and sheet flow processes in the lower swash are presented. The measurements are obtained during a large-scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves. A new instrument (CCM+) provides detailed phase-averaged measurements of sheet flow concentrations, particle velocities, and bed level evolution during a complete swash cycle. The bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase. Sheet flow occurs during the early uprush and mid and late backwash phases. Sheet flow sediment fluxes during these instances are highest in the pick-up layer. Sediment entrainment from the pick-up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave-backwash interactions. As opposed to oscillatory sheet flow, the pivot point elevation of the sheet flow layer is time-varying during a swash event. Moreover, the upper sheet flow layer concentrations do not mirror the concentrations in the pick-up layer. Both differences suggest that in the lower swash zone the dynamics of the upper sheet flow layer are not only controlled by vertical sediment exchange (such as in oscillatory sheet flows) but are strongly affected by horizontal advection processes induced by the non-uniformity of the flow
Physical model tests at small and large scales have been carried out to assess the influence of the model scale on the wave reflection of low-reflective quay walls consisting in prefabricated caissons with frontal openings and internal rubble mounds. Both monochromatic and random waves have been modeled. The experiments have been carried out in the small and large scale facilities at Laboratori d'Enginyeria Maritima of the Universitat Politecnica de Catalunya, in Barcelona. The approach described in Burcharth et al. (1999) for the treatment of scale effects for porous flows has been applied to scale down the nominal diameter of the grain material at small scale (1:33). The results with and without correction of scale effects have been compared with large scale ones (1:4). However, there is not plenty of literature on wave reflection of such kind of structure: Matteotti (1991) and Farad et al. (2012) carried out physical model tests for configurations similar to the one analyzed in the present work. Altomare et al. (2013a) applied an innovative data-driven modeling technique to analyze the relationship between wave reflection and hydraulic-geometrical parameter for random waves, basing the analysis on the results from small scale tests. A discussion on similarity or differences with the mentioned studies has been conducted confirming that the approach proposed by Burcharth et al. (1999) led to more accurate results. The main aim of the present work is to provide a reliable description of the behavior of such structure exposed to the wave actions, considered remarkable since a similar quay can be implemented as berthing structure inside the harbors. The paper underlines the importance of the treatment of the scale effects in such kind of modeling and the choice of a proper model scale. Finally a new equation to evaluate the reflection coefficient of such kind of structures is proposed. (C) 2014 Elsevier B.V. All rights reserved.
The present study presents a database of hydrodynamic properties and suspended sediment concentration collected within the inner surf and swash zones aiming to improve the current understanding of the sediment
dynamics occurring within the beach area closest to the shoreline.
Experimental measurements were conducted in a large-scale wave flume under high-energy wave conditions at three cross-shore locations, representing inner surf and swash zone conditions. 47 tests, each one comprising 500 wave trains with identical wave conditions were measured.
Obtained hydrodynamic properties and suspended sediment concentrations were observed to be highly repeatable between successive tests despite the sediment suspension event-like pattern, the beach evolution between tests, and the apparent randomness of the sediment suspension phenomenon.
The hydrodynamics close to the shoreline (inner surf and swash zone) is dominated by short incident broken waves and long-wave water level oscillations induced by wave grouping. The analyzed time series of
measured water surface elevation, horizontal velocity, computed Turbulent Kinetic Energy (TKE), and sediment concentration revealed that the suspended sediment concentration in this coastal zone does not correlate strongly with either the incident bore height, or the short-wave horizontal velocity or the TKE; in other words high/low values of these variables do not always promote high/low values of sediment
suspension. In contrast, the highest suspended sediment concentrations were observed to occur by the combined action of incident bores and the trough of long-period water level oscillations. This pattern was
more apparent in the inner surf than in the swash zone. High suspended sediment concentrations were also observed to coincide with negative peaks in long-wave horizontal velocity modulation resulting in enhanced negative sediment transport rates and beach erosion close to the shoreline.
Foti, E.; Caceres, I.; Marini, A.; Musumeci, R.E.; Sanchez-Arcilla, A. Coastal engineering Vol. 58, num. 7, p. 606-622 DOI: 10.1016/j.coastaleng.2011.01.007 Data de publicació: 2011-07 Article en revista
Van Rijn, L.; Tonnon, P.; Sanchez-Arcilla, A.; Caceres, I.; Grüne, J. Coastal engineering Vol. 58, num. 7, p. 623-636 DOI: 10.1016/j.coastaleng.2011.01.008 Data de publicació: 2011-07 Article en revista
A morphodynamical linear stability analysis is used to predict the natural development of crescentic bed patterns and rip channels. The purpose is to investigate whether this technique, which is useful for understanding the physics of emerging bed-forms, can be used to make quantitative predictions in the field, which may then be of use for coastal engineers.
To this end a morphodynamical linear stability model (Morfo60) is used to describe the development of crescentic bed patterns at the coast at the USACE Field Research Facility in Duck, North Carolina, USA. Wave, tide and alongshore-averaged bathymetry data recorded at Duck over a 2 month period in 1998 are used to model the development of these morphodynamical patterns at an open coast. The model predictions are compared with field observations by van Enckevort et al. (2004) made at Duck using the Argus imaging technique, over the same 2 month period.
Field observations and model predictions show similar length scales of the crescentic bed patterns. Immediately after a storm, large length scales of around 500 to 800 m are predicted and observed, which in a couple of days decrease to around 150 to 400 m, until the next storm occurs. The model predictions show more fluctuations in the predicted length scale than those observed in the field. These fluctuations are due to variations in the wave conditions and tidal level and the lack of pre-existing bed patterns in a linear stability analysis. An algorithm is developed to identify the more physically significant model predictions based on large growth rates and consistency in length scales. The presented algorithm, referred to as a Physically Significant Development (PSD) algorithm, is able systematically to identify the more physically representative model results. These compare better with field observations, as shown by the good agreement between predicted and observed crescentic bed pattern length scales. Accordingly, the conclusion is that linear stability analysis in combination with an appropriate physically based significant development algorithm may be of use to coastal engineers.
Grifoll, M.; Fontan, A.; Ferrer, L.; Mader, J.; González, M.; Espino, M. Coastal engineering Vol. 56, num. 9, p. 907-918 DOI: 10.1016/j.coastaleng.2009.04.001 Data de publicació: 2009-09 Article en revista
A background knowledge of marine dynamics helps harbour managers to control pollution and to manage dredging and traffic operations. This contribution studies the hydrodynamic conditions within Bilbao Harbour, which is enclosed by the Nervión Estuary (in the Basque Country, Spain). The results obtained from hydrographical surveys are compared with numerical simulations obtained using the Regional Ocean Modelling System (ROMS). Hydrodynamic modelling was carried out to determine the inner harbour currents for a specific period in which data were available. Then, numerical experiments were designed in order to quantify the importance of different driving mechanisms in the harbour hydrodynamics. The results show that, in addition to the strong tidal influence on water circulation, the wind forcing and freshwater discharge also have a non-negligible influence on the currents. The computational domain is complex due to the presence of harbour infrastructures (i.e. breakwaters and piers). As a result, topographic eddies are therefore observed in the results. The freshwater influence of the Nervión river can also be observed in residual currents. This paper presents an improvement to the application of numerical modelling to a complex geometry domain, contributing to our understanding of the behaviour of the marine systems in meso-tidal harbours. This can be used to deal with harbour engineering and management problems.
Work undertaken in the EU HUMOR project on morphodynamical modelling, particularly with regard to simulating and understanding rhythmic surf zone bars and related morphodynamic self-organization, is presented. These features are reviewed and their engineering context stated. Hydrodynamical and morphodynamical models developed and/or applied within the HUMOR project in order to address these issues are briefly presented. The linear stability modelling concept and stability studies using fully nonlinear models are contrasted. The stability of a shore-parallel bar under normal or oblique wave incidence is chosen as a test case for the different models. The results are compared and discussed. Lastly, modelling efforts and main results from the project are summarized. Recommendations for further work are made.
Work undertaken in the EU HUMOR project on morphodynamical modelling, particularly with regard to simulating and understanding
rhythmic surf zone bars and related morphodynamic self-organization, is presented. These features are reviewed and their engineering context stated. Hydrodynamical and morphodynamical models developed and/or applied within the HUMOR project in order to address these issues are
briefly presented. The linear stability modelling concept and stability studies using fully nonlinear models are contrasted. The stability of a shoreparallel bar under normal or oblique wave incidence is chosen as a test case for the different models. The results are compared and discussed. Lastly, modelling efforts and main results from the project are summarized. Recommendations for further work are made.
The evolution of shoreface-connected sand ridges on micro-tidal inner shelves and the variations in the mean grain size over these ridges are investigated with process-based models. A review of previous studies is presented, as well as new results that concern the influence of grain sorting on the finite-amplitude behaviour of the ridges, the application of the model to La Barrosa beach and the role of wave-topography feedbacks. The ridges initially form due to morphodynamic self-organisation, in which the presence of waves and a storm-driven current are crucial. Predicted growth time scales, migration speeds, topography and spatial pattern of the mean grain size agree with field data collected on micro-tidal shelves in the case that both bedload and suspended load sediment transport are accounted for, together with spatially non-uniform wave orbital motion. The model can not successfully explain the presence of large-scale ridges observed on La Barrosa inner shelf, because strong and complex behaving tidal currents occur in that area.
Nonlinear model simulations show that on the long term the height of the ridges evolves towards a finite, constant value, whilst their migration speed hardly changes during the evolution. In the saturated stage the ridges have asymmetrical profiles, with steep slopes on the downstream sides. The maximum variation in mean grain size also tends to a constant value and during the evolution the spatial lag between the patterns in the mean grain size and topography decreases. The processes that cause these changes are identified and explained. Model results can be obtained for transverse bottom slopes up to 50% of their observed values on micro-tidal shelves. Extrapolation of results to realistic values of the inner shelf slope yields, in case of Long Island shelf, a final height that agrees with observed ridge heights, but the modelled variation in mean grain size is small compared to field data. Finally, the response of ridges to large-scale interventions is considered. Experiments reveal that extraction of sand on the inner shelf causes a decrease of the sand volume stored in the surf zone.
Jimenez, J.A.; Osorio, A.; Marino-Tapia, I.; Davidson, M.; Medina, R.; Kroon, A.; Archetti, R.; Ciavola, P.; Aarnikhof, S. G. J. Coastal engineering Vol. 54, num. 6-7, p. 507-521 Data de publicació: 2007-07 Article en revista
Van Koningsveld, M.; Davidson, M.; Huntley, D.A.; Medina, R.; Jimenez, J.A.; Aarnikhof, S. G. J.; Ridgewell, J.; de Kruif, A. Coastal engineering Vol. 54, num. 6-7, p. 567-576 Data de publicació: 2007-06 Article en revista
The morphological evolution of a shoreface nourishment is investigated by interpreting the nourishment as a linear perturbation of the natural system. The nourishment is projected onto the subset of linear eigenmodes with negative growth rates of the morphodynamical system. The evolution of these linear modes then determines the temporal behaviour of the shoreface nourishment. The method is presented, and results are shown for shoreface nourishments of different length scales on a straight coast and subject to normal incidence. Shoreface nourishments are represented by their expansions according to the projection method on a 1:50 plane beach profile. All nourishments are shown primarily to be
diffusive features, with long scale nourishments diffusing more slowly than shorter length scale nourishments. Long scale nourishments also exhibit a shoreward movement during their decay. This all indicates that long length scale nourishments may be more beneficial in coastal engineering projects. This study is a first step towards nonlinear projection to study shoreface nourishment behaviour.
Johnson, H.; Theophanis, V.; Ioannis, A.; Zanuttigh, B.; González-Marco, D.; Caceres, I. Coastal engineering Vol. 52, num. 10-11, p. 949-969 DOI: 10.1016/j.coastaleng.2005.09.011 Data de publicació: 2005-11 Article en revista
Caceres, I.; Sanchez-Arcilla, A.; Zanuttigh, B.; Lamberti, A.; Franco, L. Coastal engineering Vol. 52, num. 10-11, p. 931-947 DOI: 10.1016/j.coastaleng.2005.09.004 Data de publicació: 2005-11 Article en revista