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  • Modeling the response of shoreface-connected sand ridges to sand extraction on an inner shelf

     Nnafie, Abdel; de Swart, Huib E.; Calvete Manrique, Daniel; Garnier, Roland Charles
    Ocean dynamics
    Vol. 64, num. 5, p. 723-740
    DOI: 10.1007/s10236-014-0714-9
    Date of publication: 2014-05-01
    Journal article

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    Shoreface-connected sand ridges are rhythmic bedforms that occur on many storm-dominated inner shelves. The ridges span several kilometers, are a few meters high, and they evolve on a timescale of centuries. A process-based model is used to gain a fundamental insight into the response of these ridges to extraction of sand. Different scenarios of sand extraction (depth, location, and geometry of the extraction area; multiple sand extractions) are imposed. For each scenario, the response timescale as well as the characteristics of the new equilibrium state are determined. Results show that ridges partially restore after extraction, i.e., the disturbed bathymetry recovers on decadal timescales. However, in the end, the ridge original sand volume is not recovered. Initially, most sand that accomplishes the infill of the pit originates from the area upstream of the extraction, as well as from the areas surrounding the pit. The contribution of the latter strongly decreases in the subsequent time period. Depending on the location of the pit, additional sand sources contribute: First, if the pit is located close to the downstream trough, the pit gains sand by reduction of sand transport from the ridge to this trough. Second, if the pit is located close to the adjacent outer shelf, the ridge recovery is stronger due to an import of sand from that area. Furthermore, pits that are located close to the nearshore zone have a weak recovery, deeper pits have longer recovery timescales, wide and shallow pits recover most sand, while multiple sand pits slow down the recovery process.

    Shoreface-connected sand ridges are rhythmic bedforms that occur on many storm-dominated inner shelves. The ridges span several kilometers, are a few meters high, and they evolve on a timescale of centuries. A process-based model is used to gain a fundamental insight into the response of these ridges to extraction of sand. Different scenarios of sand extraction (depth, location, and geometry of the extraction area; multiple sand extractions) are imposed. For each scenario, the response timescale as well as the characteristics of the new equilibrium state are determined. Results show that ridges partially restore after extraction, i.e., the disturbed bathymetry recovers on decadal timescales. However, in the end, the ridge original sand volume is not recovered. Initially, most sand that accomplishes the infill of the pit originates from the area upstream of the extraction, as well as from the areas surrounding the pit. The contribution of the latter strongly decreases in the subsequent time period. Depending on the location of the pit, additional sand sources contribute: First, if the pit is located close to the downstream trough, the pit gains sand by reduction of sand transport from the ridge to this trough. Second, if the pit is located close to the adjacent outer shelf, the ridge recovery is stronger due to an import of sand from that area. Furthermore, pits that are located close to the nearshore zone have a weak recovery, deeper pits have longer recovery timescales, wide and shallow pits recover most sand, while multiple sand pits slow down the recovery process.

  • Effects of sea level rise on the formation and drowning of shoreface-connected sand ridges, a model study

     Nnafie, Abdel; de Swart, Huib E.; Calvete Manrique, Daniel; Garnier, Roland Charles
    Continental shelf research
    Vol. 80, p. 32-48
    DOI: 10.1016/j.csr.2014.02.017
    Date of publication: 2014-06-01
    Journal article

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    Shoreface-connected sand ridges occur on many storm-dominated inner shelves. These rhythmic features have an along-shelf spacing of 2-10 km, a height of 1-12 m, they evolve on timescales of centuries and they migrate several meters per year. An idealized model is used to study the impact of sea level rise on the characteristics of the sand ridges during their initial and long-term evolution. Different scenarios (rates of sea level rise, geometry of inner shelf) are examined. Results show that with increasing sea level the height of sand ridges increases and their migration decreases until they eventually drown. This latter occurs when the near-bed wave orbital velocity drops below the critical velocity for erosion of sediment. In contrast, in the absence of sea level rise, the model simulates shoreface-connected sand ridges with constant heights and migration rates. Model results furthermore indicate that sand ridges do not form if the rate of sea level rise is too high, or if the initial depth of the inner shelf is too small. A larger transverse bottom slope enhances growth and height of sand ridges and they drown quicker. When shoreface retreat due to sea level rise is considered, new ridges form in the landward part of the inner shelf, while ridges on the antecedent part of the shelf become less active and ultimately drown. Only if sea level rise is accounted for, merging of ridges is reduced such that multiple ridges occur in the end state, thereby yielding a better agreement with observations. The physical mechanisms responsible for these findings are also explained. (C) 2014 Elsevier Ltd. All rights reserved.

    Shoreface-connected sand ridges occur on many storm-dominated inner shelves. These rhythmic features have an along-shelf spacing of 2-10 km, a height of 1-12 m, they evolve on timescales of centuries and they migrate several meters per year. An idealized model is used to study the impact of sea level rise on the characteristics of the sand ridges during their initial and long-term evolution. Different scenarios (rates of sea level rise, geometry of inner shelf) are examined. Results show that with increasing sea level the height of sand ridges increases and their migration decreases until they eventually drown. This latter occurs when the near-bed wave orbital velocity drops below the critical velocity for erosion of sediment. In contrast, in the absence of sea level rise, the model simulates shoreface-connected sand ridges with constant heights and migration rates. Model results furthermore indicate that sand ridges do not form if the rate of sea level rise is too high, or if the initial depth of the inner shelf is too small. A larger transverse bottom slope enhances growth and height of sand ridges and they drown quicker. When shoreface retreat due to sea level rise is considered, new ridges form in the landward part of the inner shelf, while ridges on the antecedent part of the shelf become less active and ultimately drown. Only if sea level rise is accounted for, merging of ridges is reduced such that multiple ridges occur in the end state, thereby yielding a better agreement with observations. The physical mechanisms responsible for these findings are also explained. (C) 2014 Elsevier Ltd. All rights reserved.

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    Vulnerability of sandy coasts to climate variability  Open access

     Idier, Deborah; Castelle, Bruno; Poumadère, Marc; Balouin, Yann; Bohn Bertoldo, Raquel; Bouchette, Fréderic; Boulahya, Faiza; Brivois, Olivier; Calvete Manrique, Daniel; Capo, Sylvain; Certain, Raphael; Charles, Elodie; Chateauminois, Eric; Delvallée, Etienne; Falques Serra, Alberto; Fattal, Paul; Garcin, Manuel; Garnier, Roland Charles; Héquette, Arnaud; Larroudé, Philippe; Lecacheux, Sophie; Le Cozannet, Gonéri; Maanan, Mohamed; Mallet, Cyril; Maspataud, Aurélie; Oliveros, Carlos; Paillart, Martin; Parisot, Jean-Paul; Pedreros, Rodrigo; Robin, Nicolas; Robin, Marc; Romieu, Emmanuel; Ruz, Marie-Hélène; Thiebot, Jerome; Vinchon, Charlotte
    Climate research
    Vol. 57, num. 1, p. 19-44
    DOI: 10.3354/cr01153
    Date of publication: 2013-06-13
    Journal article

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    The main objective of the VULSACO (VULnerability of SAndy COasts to climate change and anthropic pressure) project was to investigate present day and potential future vulnerability of sandy coasts at the 2030 horizon, i.e. on a time scale related to climate variability. The method, based on a multidisciplinary approach bringing together geologists, geographers, physicists, social psychologists, engineers and stakeholders, was structured around 4 axes: field data analysis; numerical modelling; analysis of governance and stakeholder perceptions; and development of vulnerability indexes. This approach was designed to investigate vulnerability at a local scale and was applied to 4 contrasting beaches located in France: Sète Lido (Mediterranean Sea), Truc Vert and La Tresson beaches (Atlantic Ocean), and Dewulf (English Channel). The results focus on decadal and multi-annual beach trends at the Truc Vert beach site. There is almost no trend in beach volume at Truc Vert beach, although there is a variation in this parameter on a cycle of 2 to 3 yr, with variations related to wave energy and probably to indexes of climate variability. Numerical modelling identified the sensitivity of beach responses to changes in wave height and direction, especially in terms of subtidal morphology and the potential development of shoreline instability. Together with the observed offshore wave angle at the Biscay Buoy, these model results suggest that a potential change in wave angle due to climate variability could significantly modify the bars¿ morphology. The combination of data analysis and numerical modelling contributed to the development of vulnerability indexes designed for sandy coasts, which take into account climate-dependant variables such as waves. This allowed the differentiation of the sites in terms of vulnerability to erosion: Sète Lido and Truc Vert beach were the most and least vulnerable sites, respectively.

    The main objective of the VULSACO (VULnerability of SAndy COasts to climate change and anthropic pressure) project was to investigate present day and potential future vulnerability of sandy coasts at the 2030 horizon, i.e. on a time scale related to climate variability. The method, based on a multidisciplinary approach bringing together geologists, geographers, physicists, social psychologists, engineers and stakeholders, was structured around 4 axes: field data analysis; numerical modelling; analysis of governance and stakeholder perceptions; and development of vulnerability indexes. This approach was designed to investigate vulnerability at a local scale and was applied to 4 contrasting beaches located in France: Sète Lido (Mediterranean Sea), Truc Vert and La Tresson beaches (Atlantic Ocean), and Dewulf (English Channel). The results focus on decadal and multi-annual beach trends at the Truc Vert beach site. There is almost no trend in beach volume at Truc Vert beach, although there is a variation in this parameter on a cycle of 2 to 3 yr, with variations related to wave energy and probably to indexes of climate variability. Numerical modelling identified the sensitivity of beach responses to changes in wave height and direction, especially in terms of subtidal morphology and the potential development of shoreline instability. Together with the observed offshore wave angle at the Biscay Buoy, these model results suggest that a potential change in wave angle due to climate variability could significantly modify the bars’ morphology. The combination of data analysis and numerical modelling contributed to the development of vulnerability indexes designed for sandy coasts, which take into account climate-dependant variables such as waves. This allowed the differentiation of the sites in terms of vulnerability to erosion: Sète Lido and Truc Vert beach were the most and least vulnerable sites, respectively. These indexes help in identifying the dominant components of beach vulnerability, and provide potential for the study of how anthropogenic factors affect vulnerability. The study of stakeholder perceptions and decision-making with regard to climate-related risk also highlighted potential anthropogenic effects on beach vulnerability, and identified possible site-specific outcomes.

  • On the Predictability of Mid-term Cross-shore Profile Evolution

     Fernandez Mora, Maria de Los Angeles; Calvete Manrique, Daniel; Falques Serra, Alberto; Ribas Prats, Francesca; Idier, Deborah
    Journal of coastal research
    p. 476-481
    DOI: 10.2112/SI65-081.1
    Date of publication: 2013-01-01
    Journal article

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    The aim of the present study is to analyse the mid-term beach profile evolution, considering the hypothesis that the alongshore processes can be neglected for the prediction of the mean profile evolution. To this end, a process-based model for the evolution of the cross-shore profile has been used. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, accounting for the effects of wave skewness and asymmetry on sediment transport. Offshore waves and tides conditions and bathymetric profiles measured at the FRF-USACE Duck are used to simulate a mid-term (72 days) onshore sandbar migration event. The model results agree with observed onshore movement and growth of the sandbar due to the inclusion of the intra-wave oscillatory flow with the skewness and asymmetry effects. The best predictions belongs to the averaging of the modelled evolution of individual cross-shore profiles that is better than the evolution of the mean cross-shore profile since.it takes into account the alongshore variability of the cross-shore profiles. These two methods result on better predictions than the individual profiles during the entire event.

  • A mechanism for sandbar straightening by oblique wave incidence

     Garnier, Roland Charles; Falques Serra, Alberto; Calvete Manrique, Daniel; Thiebot, Jerome; Ribas Prats, Francesca
    Geophysical research letters
    Vol. 40, num. 11, p. 2726-2730
    DOI: 10.1002/grl.50464
    Date of publication: 2013-06-06
    Journal article

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    Breaker bars in the surf zone of sandy beaches generally evolve between straight bars parallel to the shore and meandering crescentic bars associated with intense (dangerous) currents flowing seaward through rip channels. Understanding the behavior of such systems is fundamental as they control the entire surf zone dynamics, the shape of the coastline, and the exchange of floating material with the shoreface. Although the mechanisms behind the meandering of an originally straight bar have been studied extensively, a clear physical explanation on the crescentic bar straightening was missing. Recent field observations have highlighted that this morphological reset can be due to wave obliquity. By using a two-dimensional horizontal morphological model, we show that the bar straightening by oblique waves occurs because the rip current is both weakened in intensity and shifted downdrift from the channel deepest section. The technique employed is useful for the study of other types of bed forms.

  • Observations and modeling of transverse finger bars

     ten Doeschate, Anneke; Ribas Prats, Francesca; de Swart, Huib E.; Ruessink, Gerben; Calvete Manrique, Daniel
    International Conference on Coastal Dynamics
    p. 1643-1654
    Presentation's date: 2013-06-25
    Presentation of work at congresses

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  • Equilibrium morphodynamic profiles under skewed waves

     Fernandez Mora, Maria de Los Angeles; Calvete Manrique, Daniel; Falques Serra, Alberto
    International Conference on Coastal Dynamics
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  • Wave skewness effects on beach profile morphodynamics

     Fernandez Mora, Maria de Los Angeles; Calvete Manrique, Daniel; Falques Serra, Alberto
    IAHR Symposium on River, Coastal and Estuarine Morphodynamics
    Presentation's date: 2013-06-10
    Presentation of work at congresses

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  • Characterization of crescentic patterns in double bar systems

     Calvete Manrique, Daniel; Ribas Prats, Francesca; Coco, Giovanni; de Swart, Huib E.
    IAHR Symposium on River, Coastal and Estuarine Morphodynamics
    p. 1
    Presentation's date: 2013-06-13
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  • A cross - shore profile evolution comparison for different sediment transport parameterizations in a natural beach (Truc Vert, France)

     Fernandez Mora, Maria de Los Angeles; Calvete Manrique, Daniel; Falques Serra, Alberto; Idier, Deborah
    International Coastal Symposium
    p. 381
    Presentation's date: 2013-04-10
    Presentation of work at congresses

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  • Effects of sea level change on the formation and long-term evolution of shoreface-connected sand ridges

     Nna¿e, Abdel; de Swart, Huib E.; Calvete Manrique, Daniel; Garnier, Roland Charles
    IAHR Symposium on River, Coastal and Estuarine Morphodynamics
    p. 1
    Presentation's date: 2013-06-10
    Presentation of work at congresses

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  • Nonlinear response of inner shelf sand ridges to human interventions

     Nnafie, Abdel; de Swart, Huib E.; Garnier, Roland Charles; Calvete Manrique, Daniel
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2013-04-08
    Presentation of work at congresses

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  • Modeling and analyzing observed transverse sand bars in the surf zone

     Ribas Prats, Francesca; de Swart, Huib E.; Calvete Manrique, Daniel; Falques Serra, Alberto
    Journal of geophysical research
    Vol. 117, num. F02013, p. 1-16
    DOI: 10.1029/2011JF002158
    Date of publication: 2012-04-25
    Journal article

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  • On the use of linear stability model to characterize the morphological behaviour of a double bar system. Application to Truc Vert beach (France)

     Brivois, Olivier; Idier, Déborah; Thiébot, Jérôme; Castelle, Bruno; Le Cozannet, Gonéri; Calvete Manrique, Daniel
    Comptes rendus géoscience
    Vol. 344, num. 5, p. 277-287
    DOI: 10.1016/j.crte.2012.02.004
    Date of publication: 2012-05-22
    Journal article

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    Effect of surface rollers on the formation of crescentic bars: large angles of incidence  Open access

     Calvete Manrique, Daniel; Ribas Prats, Francesca; de Swart, Huib E.; Falques Serra, Alberto
    International Conference on Coastal Engineering
    p. 1-5
    DOI: 10.9753/icce.v33.sediment.51
    Presentation's date: 2012-07-05
    Presentation of work at congresses

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    The formation of crescentic bars is examined using a morphodynamic model based in linear stability analysis. The effect of surface rollers for off-normal wave conditions is examined. The effect of the rollers is to increase the e-folding times with increasing the angle of incidence. For angles large enough the formation of crescentic bars is even inhibit. The main effect of the rollers it be through hydrodynamics. The longitudinal changes in current produced by the rollers cause the maximum of sediment concentration to be shifted towards the coast with the final effect of prevent the formation of crecscentic bars.

  • Beach profile evolution for different sediment transport models

     Fernandez Mora, Maria de Los Angeles; Calvete Manrique, Daniel; Falques Serra, Alberto; Ribas Prats, Francesca
    European Fluid Mechanics Conference
    Presentation's date: 2012-09-10
    Presentation of work at congresses

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  • Effect of surface rollers on the formation of crescentic bars

     Calvete Manrique, Daniel; Ribas Prats, Francesca; de Swart, Huib E.; Falques Serra, Alberto
    European Fluid Mechanics Conference
    p. 1
    Presentation's date: 2012-09-10
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  • Nonlinear dynamics of shoreface-connected sand ridges: the role of wave-topography feedbacks and 3D processes

     de Swart, Huib E.; Nnafie, Abdel; Garnier, Roland Charles; Calvete Manrique, Daniel
    European Fluid Mechanics Conference
    p. 1
    Presentation's date: 2012-09-10
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  • Formation of crescentic bars in double sandbar systems

     Calvete Manrique, Daniel; Coco, Giovanni; Ribas Prats, Francesca; de Swart, Huib E.
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2012-04-23
    Presentation of work at congresses

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  • On the wavelength of self-organized shoreline sand waves

     Falques Serra, Alberto; Van den Berg, Niels; Ribas Prats, Francesca; Caballeria, M; Calvete Manrique, Daniel
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2012-04-23
    Presentation of work at congresses

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  • Effects of wave-topography feedbacks and radiation stresses on the nonlinear dynamics of shoreface-connected sand ridges

     de Swart, Huib E.; Nnafie, Abdel; Garnier, Roland Charles; Calvete Manrique, Daniel
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2012-04-23
    Presentation of work at congresses

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  • Modeling waves, currents and sandbars on natural beaches: The effect of surface rollers

     Ribas Prats, Francesca; de Swart, Huib E.; Calvete Manrique, Daniel; Falques Serra, Alberto
    Journal of marine systems
    Vol. 88, num. 1, p. 90-101
    DOI: 10.1016/j.jmarsys.2011.02.016
    Date of publication: 2011-10
    Journal article

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  • Shoreline instability due to very oblique wave incidence: some remarks on the physics

     Falques Serra, Alberto; Calvete Manrique, Daniel; Ribas Prats, Francesca
    Journal of coastal research
    Vol. 27, num. 2, p. 291-295
    DOI: 10.2112/JCOASTRES-D-09-00095.1
    Date of publication: 2011-03
    Journal article

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    Modelling the formation of transverse sand bars: application to Duck beach, USA  Open access

     Ribas Prats, Francesca; de Swart, Huib E.; Calvete Manrique, Daniel; Falques Serra, Alberto
    River Coastal and Estuarine Morphodynamics
    p. 2160-2170
    Presentation's date: 2011-09-08
    Presentation of work at congresses

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    A morphodynamic model has been applied to explain the formation of transverse sand bars at Duck beach, USA. The model describes the feedback between waves, rollers, depth-averaged currents and bed evolution, so that self-organized processes can develop. The wave and bathymetric conditions measured at Duck are used to perform the simulations. Subsequently, modelled bar characteristics are compared with those observed there. Realistic positive feedback leading to formation of the observed bars only occurs if the resuspension of sediment due to bore turbulence is included in the model. Also, the offshore root mean square wave height must be larger than 0.5 m and the offshore wave incidence angle larger than 15o (offshore boundary is at 8 m depth), conditions that occur at Duck only 25% of the time. The modelled shape (wavelength, cross-shore extent and crest orientation) and growth rate agree with data, but the model overestimates the migration rates.

  • Formation of shoreface-connected sand ridges: effects of rigid-lid approach, quasi-steady approach and wave-topography feedbacks

     Nnafie, Abdel; de Swart, Huib E.; Garnier, Roland Charles; Calvete Manrique, Daniel
    River Coastal and Estuarine Morphodynamics
    p. 2114-2123
    Presentation's date: 2011-09-08
    Presentation of work at congresses

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    The initial- and long-term evolution of shoreface-connected sand ridges (sfcr) is investigated with a new nonlinear model (MORFO56) that employs finite difference methods, rather than spectral methods. MORFO56 uses depth-averaged shallow water equations, including sediment transport and bed updating. Moreover, it includes full wave-topography feedbacks, wave shoaling and refraction, and wave radiation stresses. First, effects of relaxing the rigid-lid assumption and quasi-steadiness on the initial growth and migration of sfcr are quantified, by conducting a series of short-term runs. It turns out that assuming a free lid and unsteady flow results in larger wavelengths and larger migration speeds of sfcr. Furthermore, the new model is able to simulate the finite amplitude behaviour of sfcr for more realistic bottom slopes than earlier spectral models. Finally, the role of wave-topography feedbacks in the initial formation of sfcr is examined. Model simulations show that sfcr in the presence of these feedbacks are more trapped to the shoreface, with an offshore extent of approximately 1 km. Moreover, growth of sfcr is enhanced considerably by wave-topography feedbacks. The specific inclusion of radiation stresses does not affect this result.

    Postprint (author’s final draft)

  • Effect of surface rollers on the formation crescentic bars

     Calvete Manrique, Daniel; de Swart, Huib E.; Ribas Prats, Francesca; Falques Serra, Alberto
    River Coastal and Estuarine Morphodynamics
    p. 2152-2159
    Presentation's date: 2011-09-08
    Presentation of work at congresses

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    The effect of surface rollers on the formation of crescentic bars/rip channel systems is examined with a morphodynamic model. A linear stability analysis is applied to find the fastest growing bottom patterns that develop as a result of morphodynamics self-organization. Explorations of sensitivity of model results to varying wave conditions have been performed. Special attention has been paid to off-normal wave conditions. There are noticeable differences in growth rates for large/intermediate angles of wave incidence with respect to shore normal conditions. The effect of the rollers is to increase the e-folding times with increasing the angle of incidence. For angles large enough the formation of crescentic bars is even inhibit. The effect of the rollers in wavelengths, migration velocities of the bedforms and bed morphologies of the FGM is minor. Flow velocities on the rips are a factor 2 smaller in the models with rollers than in the model without rollers.

    Postprint (author’s final draft)

  • MODELIZACIÓN Y MONITARIZACIÓN INTEGRADAS EN MORFODINAMICA DE PLAYAS NATURALES Y REGENERADAS

     Calvete Manrique, Daniel; Ribas Prats, Francesca; Caballeria Suriñach, Miquel; Garnier, Roland Charles; Guillén Aranda, Jorge; Van den Berg, Niels; Fernández Mora, Mª Àngels; Falques Serra, Alberto
    Competitive project

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    Comparison of modelled nearshore transverse sandbars with field observations  Open access

     Ribas Prats, Francesca; Calvete Manrique, Daniel; Falques Serra, Alberto
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2010-05-03
    Presentation of work at congresses

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  • DINAMICA SEDIMENTARIA ACTUAL EN LA TRANSICION PLATAFORMA-TALUD DEL MARGEN CONTINENTAL DEL EBRO

     Calvete Manrique, Daniel; Puig Alenyà, Pere
    Competitive project

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  • A field test of a linear stability model for crescentic bars

     Tiessen, M C H; Leeuwen, S M Van; Calvete Manrique, Daniel; Dodd, N
    Coastal engineering
    Vol. 57, num. 1, p. 41-51
    DOI: 10.1016/j.coastaleng.2009.09.002
    Date of publication: 2010-01
    Journal article

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    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.

  • Modeling sandbar morphodynamics by linear stability analysis: application to the Lido de Sete beach

     Thiebot, Jerome; Idier, Deborah; Falques Serra, Alberto; Calvete Manrique, Daniel; Certain, Raphael; Garnier, Roland Charles
    Houille blanche
    num. 1, p. 97-103
    DOI: 10.1051/lhb/2010011
    Date of publication: 2010
    Journal article

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    Mechanisms controlling crescentic bar amplitude  Open access

     Garnier, Roland Charles; Dodd, Nicholas; Falques Serra, Alberto; Calvete Manrique, Daniel
    Journal of geophysical research
    Vol. 115, num. F02007, p. 1-14
    DOI: 10.1029/2009JF001407
    Date of publication: 2010-04-15
    Journal article

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    The formation of crescentic bars from self-organization of an initially straight shore-parallel bar for shore-normal incident waves is simulated with a two-dimensional horizontal morphodynamical model. The aim is to investigate the mechanisms behind the saturation process defined as the transition between the linear regime (maximum and constant growth of the crescentic pattern) and the saturated state (negligible growth). The global properties of the morphodynamical patterns over the whole computational domain are studied (“global analysis”). In particular, consideration of the balance of the potential energy of the emerging bar gives its growth rate from the difference between a production term (related to the positive feedback leading to the instability) and a damping term (from the gravity-driven downslope transport). The production is approximately proportional to the average over the domain of the cross-shore flow velocity times the bed level perturbation. The damping is essential for the onset of the saturation, but it remains constant while the production decreases. Thus, it is notable that the saturation occurs because of a weakening of the instability mechanism rather than an increase of the damping. A reason for the saturation of the crescentic bar growth is the change in bar shape from its initial stage rather than the growth in amplitude itself. This change is mainly characterized by the narrowing of the rip channels, the onshore migration of the crests, and the change in the mean beach profile due to alongshore variability. These properties agree with observations of mature rip channel systems in nature.

  • Dinàmica de fluids; formació d'estructures i aplicacions geofísiques

     Marques Truyol, Francisco; Falques Serra, Alberto; Alonso Maleta, Maria Aranzazu; Batiste Boleda, Oriol; Calvete Manrique, Daniel; Garnier, Roland Charles; Mellibovsky Elstein, Fernando; Mercader Calvo, Maria Isabel; Meseguer Serrano, Alvaro; Pino Gonzalez, David; Ribas Prats, Francesca; van en Berg, Niels; Panades Guinart, Carles
    Competitive project

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  • A mechanism inhibiting rip channel formation for oblique waves

     Garnier, Roland Charles; Dodd, Nicholas; Falques Serra, Alberto; Calvete Manrique, Daniel
    International Conference on Coastal Dynamics
    p. 1-13
    DOI: 10.1142/9789814282475_0039
    Presentation's date: 2009-09-10
    Presentation of work at congresses

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    Previous numerical modelling studies based on 2DH morphodynamical model show that oblique waves tend to inhibit the formation of rip channel systems, but the mechanisms were not investigated. Field observations do not always agree with this model result, thus, understanding the mechanisms seems essential. To this end, the global analysis technique, originally developed to describe the long term behavior of bars (saturation of the bar growth), is also applied here to the initial stage of the bar evolution (formation of the bars). As a result, rip channels grow slower for larger wave angle because of the weakening of the instability mechanism -that only depends on the cross-shore current- rather than the increase of the damping due to the diffusive bedslope transport.

  • Linear stability analysis in coastal morphodynamics: essential or useless?

     Calvete Manrique, Daniel; Falques Serra, Alberto; de Swart, Huib E.; Guillén Aranda, Jorge; Dodd, Nicholas
    Competitive project

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    Modelling the characteristics and dynamics of surfzone transverse sand bars observed on natural beaches  Open access

     Ribas Prats, Francesca; de Swart, Huib E.; Calvete Manrique, Daniel; Falques Serra, Alberto
    International Liège Colloquium on Ocean Dynamics
    p. 1
    Presentation's date: 2009-05
    Presentation of work at congresses

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    The role of surface rollers on the formation of surfzone transverse sand bars  Open access

     Ribas Prats, Francesca; de Swart, Huib E.; Calvete Manrique, Daniel; Falques Serra, Alberto
    International Conference on Coastal Dynamics
    p. 1-12
    DOI: 10.1142/9789814282475_0057
    Presentation's date: 2009-09
    Presentation of work at congresses

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  • Effect of wave-bedform feedbacks on the formation of, and grain sorting over shoreface-connected sand ridges

     Vis-Star, Nc; Calvete Manrique, Daniel; de Swart, Huib E.
    Ocean dynamics
    Vol. 59, num. 5, p. 731-749
    DOI: 10.1007/s10236-009-0210-9
    Date of publication: 2009-11
    Journal article

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    The influence of wave–bedform feedbacks on both the initial formation of shoreface-connected sand ridges (sfcr) and on grain size sorting over these ridges on micro-tidal inner shelves is studied. Also, the effect of sediment sorting on the growth and the migration of sfcr is investigated. This is done by applying a linear stability analysis to an idealized process-based morphodynamic model, which simulates the initial growth of sfcr due to the positive coupling between waves, currents, and an erodible bed. The sediment consists of sand grains with two different sizes. New elements with respect to earlier studies on grain sorting over sfcr are that wave-topography interactions are explicitly accounted for, entrainment of sediment depends on bottom roughness, and transport of suspended sediment involves settling lag effects. The results of the model indicate that sediment sorting causes a reduction of the growth rate and migration speed of sfcr, whereas the wavelength is only slightly affected. In the case where the entrainment of suspended sediment depends on bottom roughness, the coarsest sediment is found in the troughs; otherwise, the finest sediment occurs in the troughs. Compared to previous work, modeled maximum variations in the mean grain size over the topography are in better agreement with field observations. Settling lag effects are important for the damping of high-wavenumber mode instabilities such that a preferred wavelength of the bedforms is obtained.

  • The role of the depth-averaged concentration in coastal morphodynamics

     Calvete Manrique, Daniel; Falques Serra, Alberto; de Swart, Huib E.; Dodd, Nicholas; Ribas Prats, Francesca; Garnier, Roland Charles
    International Conference on Coastal Dynamics
    p. 10
    DOI: 10.1142/9789814282475_0093
    Presentation's date: 2009-09-10
    Presentation of work at congresses

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    In this contribution a discussion is presented on the development of self-organized coastal morphodynamic patterns which are due to the joint action of gradients in the depth-integrated concentration and the flow. This is done in the context of a depth-averaged shallow water model. Two physical mechanisms produce deposition-erosion patterns. Deposition either occurs where the current flows from high to low depth-averaged concentrations (1) or where the flow diverges (2). If flow conditions are quasi steady (i.e., the time scale on which bedforms evolve is much larger than the hydrodynamic time scales) only the former mechanism contributes to the formation of bottom patterns.

  • The use of linear stability analysis to characterize the variability of multiple sandbar systems

     Calvete Manrique, Daniel; Coco, Giovanni
    International Conference on Coastal Dynamics
    p. 1-11
    DOI: 10.1142/9789814282475_0055
    Presentation's date: 2009-09-07
    Presentation of work at congresses

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    The development and evolution of crescentic patterns in double-barred systems is explored using a morphodynamic stability model. The description of the surf zone hydrodynamics is based on depth and wave averaged conditions while sediment transport is calculated using a total load formula. The linear stability analysis predicts that an initially rectilinear coast, subject to infinitesimal perturbations and under normal wave incidence, is unstable and can result in the development of crescentic shapes that can be coupled either in-phase (highs and lows of both sandbars are at the same alongshore position) or out-of-phase (highs and lows of one sandbar correspond to lows and highs of the other sandbar). Results of numerical simulations are sensitive to some of the parameterizations used in the description of hydrodynamics. Changes in the breaker index can have an effect not only on the spacing and growth rate of the pattern but also on the type of pattern that develops. An increase in the breaker index leads to a faster growth of the pattern but also to a smaller alongshore spacing. The role of parameterizations in lateral mixing and roughness length appear to be limited.

  • Nonlinear dynamics and predictability properties of sand ridges on the inner shelf.

     Calvete Manrique, Daniel
    Dynamics Days Europe 2008
    Presentation's date: 2008-08-25
    Presentation of work at congresses

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  • The role of depth-averaged concentration in coastal morphodynamics

     Calvete Manrique, Daniel; Falques Serra, Alberto; de Swart, Huib E.; Dodd, N; Ribas Prats, Francesca; Garnier, Roland Charles
    European Geosciences Union General Assembly
    Presentation of work at congresses

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  • Nonlinear modelling of nearshore sand bars from self organization processes: a 'Global Analysis'

     Garnier, Roland Charles; Dodd, N; Calvete Manrique, Daniel; Falques Serra, Alberto
    European Geosciences Union General Assembly
    Presentation's date: 2008-04-14
    Presentation of work at congresses

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  • The role of cross-shore profile dynamics on shoreline instability due to high-angle waves

     Falques Serra, Alberto; van den Berg, Niels; Calvete Manrique, Daniel
    International Conference on Coastal Engineering
    p. 1826-1838
    Presentation's date: 2008-09-05
    Presentation of work at congresses

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    If the wave climate is dominated by a wave approach in deep water that is very oblique with respect to the shoreline, the littoral drift may render the rectilinear trend of the shoreline unstable. This instability causes large scale shoreline sand waves (L ~ 1-10 km, T~ 1-10 yr) that grow and propagate along the coast, implying erosional hot spots. This was known to be primarily due to gradients in alongshore transport rate. However, it is here shown that the cross-shore transport is also essential to the instability, the faster the relaxation to the equilibrium profile, the stronger the instability. Furthermore, it is found that the cross-shore location of the initial bathymetric perturbation is very important. The maximum efficiency in triggering the instability corresponds to perturbations spread across both the surf and shoaling zones. In contrast, for a perturbation confined only in the surf zone, the development may be so slow that the instability is hardly relevant to coastal engineering. Preliminary implications for beach nourishments are discussed.

    Postprint (author’s final draft)

  • Análisis de la aplicación de nuevas metodologias docentes en ingenieria

     Bruna Escuer, Pere; Calvete Manrique, Daniel; Crespo Artiaga, Daniel; Pilar, Gil; Gutierrez, Jordi; Torres Gil, Santiago; Alonso Maleta, Maria Aranzazu
    VI Taller Iberoamericano de Educación en Ciencia e Ingeniería de Materiales (TIECIM)
    Presentation's date: 2008-12-02
    Presentation of work at congresses

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  • Modelling the interaction between transverse and crescentic bar systems.

     Calvete Manrique, Daniel
    Dynamics Days Europe 2008
    Presentation's date: 2008-08-25
    Presentation of work at congresses

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  • Modelling the characteristics and dynamics of surfzone transverses sand bars observed at Noordwijk beach.

     Calvete Manrique, Daniel
    Dynamics Days Europe 2008
    Presentation's date: 2008-08-25
    Presentation of work at congresses

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  • Modelling the characteristics and dynamics of surfzone transverse sand bars observed at Noordwijk beach

     Ribas Prats, Francesca; de Swart, Huib E.; Calvete Manrique, Daniel; Falques Serra, Alberto
    Dynamics Days Europe 2008
    Presentation of work at congresses

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  • Rhythmic surf zone bars and morphodynamic self-organization

     Falques Serra, Alberto; Dodd, N; Garnier, Roland Charles; Ribas Prats, Francesca; Machardy, L C; Larroude, Philippe; Calvete Manrique, Daniel; Sancho, Francisco
    Coastal engineering
    Vol. 55, num. 7-8, p. 622-641
    DOI: 10.1016/j.coastaleng.2007.11.012
    Date of publication: 2008-07
    Journal article

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    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.

  • Modelling the formation and the nonlinear evolution of crescentic bars of the Aquitanian coast

     Garnier, Roland Charles; Bonneton, P; Falques Serra, Alberto; Calvete Manrique, Daniel
    Houille blanche
    Vol. 1, num. 3, p. 33-38
    DOI: 10.1051/lhb:2008024
    Date of publication: 2008-07
    Journal article

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    Crescentic bars emerge as free instabilities of the coupling between topography and water motion. Their long term behaviour will be studied in the real case of the French Aquitaine beaches by using the 2DH numerical model MORFO55. For the first time, the equilibrium state of a crescentic bar system is obtained, in the case of steady incident wave conditions. Due to non linear interactions, the final wave length of the system does not inevitably increase with the incident wave height. Finally, the study of variable incident wave conditions suggests that the equilibrium state may depend on the initial conditions.