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Suzanne J M H Hulscher - One of the best experts on this subject based on the ideXlab platform.
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biogeomorphology in the marine landscape modelling the feedbacks between patches of the polychaete worm lanice conchilega and tidal Sand Waves
Earth Surface Processes and Landforms, 2020Co-Authors: Johan Hendrik Damveld, Bastiaan Wijnand Borsje, Pieter C Roos, Suzanne J M H HulscherAbstract:Tidal Sand Waves are dynamic bedforms found in coastal shelf seas. Moreover, these areas are inhabited by numerous benthic species, of which the spatial distribution is linked to the morphological structure of Sand Waves. Especially the tube‐building worm Lanice conchilega is of interest as this organism forms small mounds on the seabed which provide shelter to other organisms. We investigate how the interactions between small‐scale mounds (height ~dm) and large‐scale Sand Waves (height~m) shape the bed of the marine environment. To this end, we present a two‐way coupled process‐based model of Sand Waves and tube‐building worm patches in Delft3D. The population density evolves according to a general law of logistic growth, with the bed shear stress controlling the carrying capacity. Worm patches are randomly seeded and the tubes are mimicked by small cylinders which influence flow and turbulence, thereby altering sediment dynamics. Model results relate the patches with the highest worm densities to the Sand Wave troughs, which qualitatively agrees with field observations. Furthermore, the L. conchilega tubes trigger the formation of Sandy mounds on the seabed. Due to the population density distribution, the mounds in the troughs can be several centimetres higher than on the crests. Regarding Sand Wave morphology, the combination of patches and mounds are found to shorten the time‐to‐equilibrium. Also, if the initial bed comprised small sinusoidal Sand Waves, the equilibrium Wave height decreased with a few decimetres compared to the situation without worm patches. As the time scale of mound formation (years) is shorter than that of Sand Wave evolution (decades), the mounds induce (and accelerate) Sand Wave growth on a similar spatial scale as the mounds. Initially this leads to shorter Sand Waves than they would be in an abiotic environment. However, near equilibrium the Wavelengths tend towards their abiotic counterparts again.
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the influence of storms on Sand Wave evolution a nonlinear idealized modeling approach
Journal of Geophysical Research, 2018Co-Authors: Gerhardus Hermanus Petrus Campmans, Pieter C Roos, H J De Vriend, Suzanne J M H HulscherAbstract:We present a new 2DV nonlinear process-based morphodynamic model to investigate the effects of storms, specifically wind-driven flow and wind Waves, on finite amplitude tidal Sand Wave evolution. Simulations are performed on periodic domains of two lengths: (i) on a 350-m domain, comparable to the Wavelength of observed Sand Waves, we study the evolution toward equilibrium shapes, and (ii) on a 4-km domain, we study the evolution from a randomly perturbed seabed. Our model results demonstrate that both wind-driven flow and wind Waves reduce Sand Wave height and tend to increase Wavelength. Wind-driven flow breaks the tidal symmetry, resulting in horizontal Sand Wave asymmetry and migration. Waves alone do not induce migration but can enhance migration induced by, for example, tidal asymmetry and wind-driven flow. On the 350-m domain, we further find that migration rates decrease with increasing Sand Wave height. However, in an irregular Sand Wave field, large Sand Waves tend to overtake the smaller ones, suggesting a complicated interaction among neighboring bed forms. The above results concern steady state storm conditions. However, since storms occur on an intermittent basis, we also simulated a synthetic storm climate consisting of alternating short periods of storm conditions and long periods of fair-weather conditions. Simulations reveal a dynamic equilibrium with Sand Wave heights significantly below those obtained for tide-only conditions, also for relatively short storm duration. Our work identifies mechanisms that explain why Sand Wave heights are generally overpredicted by numerical models that do not include storm processes.
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modelling the effect of suspended load transport and tidal asymmetry on the equilibrium tidal Sand Wave height
Coastal Engineering, 2018Co-Authors: W Van Gerwen, Johan Hendrik Damveld, Bastiaan Wijnand Borsje, Suzanne J M H HulscherAbstract:Abstract Tidal Sand Waves are rhythmic bed forms found in shallow Sandy coastal seas, reaching heights up to ten meters and migration rates of several meters per year. Because of their dynamic behaviour, unravelling the physical processes behind the growth of these bed forms is of particular interest to science and offshore industries. Various modelling efforts have given a good description of the initial stages of Sand Wave formation by adopting a linear stability analysis on the coupled system of water movement and the Sandy seabed. However, the physical processes causing Sand Waves to grow towards equilibrium are far from understood. We adopt a numerical shallow water model (Delft3D) to study the growth of Sand Waves towards a stable equilibrium. It is shown that both suspended load transport and tidal asymmetry reduce the equilibrium Sand Wave height. A residual current results in asymmetrical bed forms that migrate in the direction of the residual current. The combination of suspended load transport and tidal asymmetry results in predicted equilibrium Wave heights comparable to Wave heights found in the field.
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spatially varying environmental properties controlling observed Sand Wave morphology
Journal of Geophysical Research, 2018Co-Authors: Johannes Marinus Damen, T A G P Van Dijk, Suzanne J M H HulscherAbstract:Sand Wave morphology and dynamics on continental shelves vary substantially, and we hypothesize that these spatial variations depend on local bed properties and hydrodynamic characteristics. To date, process-based modeling studies have not been able to simulate realistic equilibrium Sand Wave heights and empirical studies are mostly limited to case studies. In order to explain the spatial variation in the morphology of equilibrium Sand Waves on continental shelves with processes and local bed conditions, a large-scale investigation is required. In this paper, we use high-resolution multibeam echo soundings, hydrodynamic models, and databases and sedimentary data for the analysis of, respectively, Sand Wave shape characteristics and the comparison to hydrodynamic and sedimentary characteristics for the Netherlands Continental Shelf. The results are quantified lengths, heights, and asymmetry of all Sand Waves in the Dutch part of the North Sea. Furthermore, we show that the mode of sediment transport (bed load or suspended) is a dominant factor in explaining Sand Wavelength, height, and asymmetry. Full results of shape characteristics of all Sand Waves on the Netherlands Continental Shelf together with the tidal velocity, water depth, surface Wave height, and median grain size are provided in a repository with this paper (http://doi.org/10.4121/uuid:0d7e016d-2182-46ea-bc19-cdfda5c20308). These results are highly valuable for applied offshore engineering projects and to modelers for validating their morphodynamic model results.
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modeling the influence of storms on Sand Wave formation a linear stability approach
Computer Science Symposium in Russia, 2017Co-Authors: Gerhardus Hermanus Petrus Campmans, Pieter C Roos, H J De Vriend, Suzanne J M H HulscherAbstract:We present an idealized process-based morphodynamic model to study the effect of storms on Sand Wave formation. To this end, we include wind Waves, wind-driven flow and, in addition to bed load transport, suspended load sediment transport. A linear stability analysis is applied to systematically study the influence of Wave and wind conditions on growth and migration rates of small-amplitude wavy bed undulations. The effects of the wind and Waves of various magnitudes and directions are investigated. Waves turn out to decrease the growth rate of Sand Waves, because their effect on the downhill gravitational transport component is stronger than their growth-enhancing effect. The wind Wave effect is strongest for wind Waves perpendicular to the tidal current. In the case of a symmetrical tidal current, wind-driven flow tends to breach the symmetry, thus causing Sand Wave migration. Wind effects on Sand Wave behavior are strongly influenced by the Coriolis effect, in magnitude as well as direction. Stirring due to wind Waves enhances Sand Wave migration. Next to bed load transport, suspended load also has a growing and a decaying mechanism, being the perturbed flow and the perturbed suspended sediment concentration respectively. The decaying mechanism outcompetes the growing mechanism for bed forms with shorter Wavelengths, resulting in an increase in the preferred Wavelength. Wind Waves increase the growth rate due to suspended load, but this is outcompeted by the reduction in growth rate by wind Waves due to bed load transport. We conclude that storms significantly influence Sand Wave dynamics in their formation stage.
Laura L Govers - One of the best experts on this subject based on the ideXlab platform.
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linking the morphology and ecology of subtidal soft bottom marine benthic habitats a novel multiscale approach
Estuarine Coastal and Shelf Science, 2020Co-Authors: Sebastiaan Mestdagh, A R Amirisimkooei, Karin J Van Der Reijden, L Koop, Sarah Oflynn, Mirjam Snellen, Christiaan Van Sluis, Laura L GoversAbstract:High-resolution surveying techniques of subtidal soft-bottom seafloor habitats show higher small-scale variation in topography and sediment type than previously thought, but the ecological relevance of this variation remains unclear. In addition, high-resolution surveys of benthic fauna show a large spatial variability in community composition, but this has yet poorly been linked to seafloor morphology and sediment composition. For instance, on soft-bottom coastal shelves, hydrodynamic forces from winds and tidal currents can cause nested multiscale morphological features ranging from metre-scale (mega)ripples, to Sand Waves and kilometre-scale linear Sandbanks. This multiscale habitat heterogeneity is generally disregarded in the ecological assessments of benthic habitats. We therefore developed and tested a novel multiscale assessment toolbox that combines standard bathymetry, multibeam backscatter classification, video surveying of epibenthos and box core samples of sediment and macrobenthos. In a study on the Brown Bank, a Sandbank in the southern North Sea, we found that these methods are greatly complementary and allow for more detail in the interpretation of benthic surveys. Acoustic and video data characterised the seafloor surface and subsurface, and macrobenthos communities were found to be structured by both Sandbank and Sand Wave topography. We found indications that acoustic techniques can be used to determine the location of epibenthic reefs. The multiscale assessment toolbox furthermore allows formulating recommendations for conservation management related to the impact of sea floor disturbances through dredging and trawling.
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video transects reveal that tidal Sand Waves affect the spatial distribution of benthic organisms and Sand ripples
Geophysical Research Letters, 2018Co-Authors: Johan Hendrik Damveld, Karin J Van Der Reijden, L Koop, Laura L Govers, Bastiaan Wijnand Borsje, C Cheng, L R Haaksma, C A J Walsh, Karline SoetaertAbstract:The Sandy seabed of shallow coastal shelf seas displays morphological patterns of various dimensions. The seabed also harbors a rich ecosystem. Increasing pressure from human-induced disturbances necessitates further study on drivers of benthic community distributions over morphological patterns. Moreover, a greater understanding of the Sand ripple distribution over tidal Sand Waves may improve morphological model predictions. Here we analyzed the biotic abundance and ripple morphology in Sand Wave troughs and crests using video transects. We found that both the epibenthos and endobenthos are significantly more abundant in Sand Wave troughs, where ripples are less abundant and more irregularly shaped. Finally, we show that camera systems are relatively quick and effective tools to study biotic spatial patterns in relation to seabed morphology.
A R Amirisimkooei - One of the best experts on this subject based on the ideXlab platform.
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linking the morphology and ecology of subtidal soft bottom marine benthic habitats a novel multiscale approach
Estuarine Coastal and Shelf Science, 2020Co-Authors: Sebastiaan Mestdagh, A R Amirisimkooei, Karin J Van Der Reijden, L Koop, Sarah Oflynn, Mirjam Snellen, Christiaan Van Sluis, Laura L GoversAbstract:High-resolution surveying techniques of subtidal soft-bottom seafloor habitats show higher small-scale variation in topography and sediment type than previously thought, but the ecological relevance of this variation remains unclear. In addition, high-resolution surveys of benthic fauna show a large spatial variability in community composition, but this has yet poorly been linked to seafloor morphology and sediment composition. For instance, on soft-bottom coastal shelves, hydrodynamic forces from winds and tidal currents can cause nested multiscale morphological features ranging from metre-scale (mega)ripples, to Sand Waves and kilometre-scale linear Sandbanks. This multiscale habitat heterogeneity is generally disregarded in the ecological assessments of benthic habitats. We therefore developed and tested a novel multiscale assessment toolbox that combines standard bathymetry, multibeam backscatter classification, video surveying of epibenthos and box core samples of sediment and macrobenthos. In a study on the Brown Bank, a Sandbank in the southern North Sea, we found that these methods are greatly complementary and allow for more detail in the interpretation of benthic surveys. Acoustic and video data characterised the seafloor surface and subsurface, and macrobenthos communities were found to be structured by both Sandbank and Sand Wave topography. We found indications that acoustic techniques can be used to determine the location of epibenthic reefs. The multiscale assessment toolbox furthermore allows formulating recommendations for conservation management related to the impact of sea floor disturbances through dredging and trawling.
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seafloor classification in a Sand Wave environment on the dutch continental shelf using multibeam echosounder backscatter data
Geosciences (Switzerland), 2019Co-Authors: Leo Koop, A R Amirisimkooei, Sarah Oflynn, Mirjam Snellen, Karin J Van Der Reijden, Dick G SimonsAbstract:High resolution maps of Sandy seafloors are valuable to understand seafloor dynamics, plan engineering projects, and create detailed benthic habitat maps. This paper presents multibeam echosounder backscatter classification results of the Brown Bank area of the North Sea. We apply the Bayesian classification method in a megaripple and Sand Wave area with significant slopes. Prior to the classification, corrections are implemented to account for the slopes. This includes corrections on the backscatter value and its corresponding incident angle. A trade-off in classification resolutions is found. A higher geo-acoustic resolution is obtained at the price of losing spatial resolution, however, the Bayesian classification method remains robust with respect to these trade-off decisions. The classification results are compared to grab sample particle size analysis and classified video footage. In non-distinctive sedimentary environments, the acoustic classes are not attributed to only the mean grain size of the grab samples but to the full spectrum of the grain sizes. Finally, we show the Bayesian classification results can be used to characterize the sedimentary composition of megaripples. Coarser sediments were found in the troughs and on the crests, finer sediments on the stoss slopes and a mixture of sediments on the lee slopes.
Gary H Greene - One of the best experts on this subject based on the ideXlab platform.
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hazards evaluation of a valuable vulnerable Sand Wave field forage fish habitat in the marginal central salish sea using a submersible
Oceanologia, 2021Co-Authors: Gary H Greene, Matthew R Baker, John Aschoff, Robert E PacunskiAbstract:Abstract The Salish Sea is a marginal inland sea of the NE Pacific (NW North America) that includes the Georgia Strait-Gulf Islands Archipelago of British Columbia, Canada and the San Juan Archipelago, Strait of Juan de Fuca, and the Lower Puget Sound of Washington State, USA. This marginal seafloor has been extensively mapped and according to criteria presented and discussed at GeoHab conferences critical marine benthic habitat types are identified. One such habitat that is the focus of this paper is the deep-water sub-tidal habitat of Pacific Sand lance (PSL). The PSL (Ammodytes personatus) is a critical forage fish for a variety of mammals, birds and fish including minke whales and salmon as it preys upon zooplankton and acts as an energy transfer species from the lower to higher trophic levels. Pacific Sand lance seeks refuge and overwinters in Sand-Wave fields consisting of dynamic bedforms. The species prefers loosely packed, well-aerated, well-sorted, medium- to coarse-grain (~1 phi [φ], 500 µm) Sand that it can burrow into easily. Such geomorphic features as active dynamic bedforms provide preferable habitats for PSL and depends on specific and unique oceanographic processes that can maintain the habitat's morphology and grain sizes. Understanding these processes is essential in forecasting alteration or destruction of such features, including changes that may be brought about by sea level rise. Using the five-person submersible Cyclops 1, we recently examined a well-studied Sand-Wave field in the San Juan Archipelago of Washington State, USA, which has been reported to harbor up to 12 million PSL. Observations, video recordings, and photography from this vehicle allowed us to assess modern seafloor processes of the central Salish Sea that can be used along with fish and sediment sample data to determine physical preferences this fish needs to sustain its population. Changes in the seafloor current regime, sediment source, and anthropogenic disturbances can critically alter these dynamic bedforms. This research provides insight into the structure of these bedforms, their composition, their persistence, their resilience to disturbance, and the susceptibility as an impact and becoming impacted.
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characteristics and dynamics of a large sub tidal Sand Wave field habitat for pacific Sand lance ammodytes personatus salish sea washington usa
Geosciences, 2017Co-Authors: Gary H Greene, David A Cacchione, Monty A HamptonAbstract:Deep-water Sand Wave fields in the San Juan Archipelago of the Salish Sea and Pacific Northwest Washington, USA, have been found to harbor Pacific Sand lance (PSL, Ammodytes personatus), a critical forage fish of the region. Little is known of the dynamics of these Sand Waves and the stability of the PSL sub-tidal habitats. Therefore, we have undertaken an initial investigation to determine the dynamic conditions of a well-known PSL habitat in the San Juan Channel within the Archipelago using bottom sediment sampling, an acoustical doppler current profiling (ADCP) system, and multi-beam echo sounder (MBES) bathymetry. Our study indicates that the San Juan Channel Sand Wave field maintained its shape and bedforms geometry throughout the years it has been studied. Based on bed phase diagrams for channelized bedforms, the Sand Waves appear to be in a dynamic equilibrium condition. Sea level rise may change the current regime within the Archipelago and may alter some of the deep-water or sub-tidal PSL habitats mapped there. Our findings have global significance in that these dynamic bedforms that harbor PSL and Sand-eels elsewhere along the west coast of North America and in the North Sea may also be in a marginally dynamic equilibrium condition and may be prone to alteration by sea level rise, indicating an urgency in locating and investigating these habitats in order to sustain the forage fish.
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Characteristics and Dynamics of a Large Sub-Tidal Sand Wave Field—Habitat for Pacific Sand Lance (Ammodytes personatus), Salish Sea, Washington, USA
MDPI AG, 2017Co-Authors: Gary H Greene, David A Cacchione, Monty A HamptonAbstract:Deep-water Sand Wave fields in the San Juan Archipelago of the Salish Sea and Pacific Northwest Washington, USA, have been found to harbor Pacific Sand lance (PSL, Ammodytes personatus), a critical forage fish of the region. Little is known of the dynamics of these Sand Waves and the stability of the PSL sub-tidal habitats. Therefore, we have undertaken an initial investigation to determine the dynamic conditions of a well-known PSL habitat in the San Juan Channel within the Archipelago using bottom sediment sampling, an acoustical doppler current profiling (ADCP) system, and multi-beam echo sounder (MBES) bathymetry. Our study indicates that the San Juan Channel Sand Wave field maintained its shape and bedforms geometry throughout the years it has been studied. Based on bed phase diagrams for channelized bedforms, the Sand Waves appear to be in a dynamic equilibrium condition. Sea level rise may change the current regime within the Archipelago and may alter some of the deep-water or sub-tidal PSL habitats mapped there. Our findings have global significance in that these dynamic bedforms that harbor PSL and Sand-eels elsewhere along the west coast of North America and in the North Sea may also be in a marginally dynamic equilibrium condition and may be prone to alteration by sea level rise, indicating an urgency in locating and investigating these habitats in order to sustain the forage fish
Bastiaan Wijnand Borsje - One of the best experts on this subject based on the ideXlab platform.
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biogeomorphology in the marine landscape modelling the feedbacks between patches of the polychaete worm lanice conchilega and tidal Sand Waves
Earth Surface Processes and Landforms, 2020Co-Authors: Johan Hendrik Damveld, Bastiaan Wijnand Borsje, Pieter C Roos, Suzanne J M H HulscherAbstract:Tidal Sand Waves are dynamic bedforms found in coastal shelf seas. Moreover, these areas are inhabited by numerous benthic species, of which the spatial distribution is linked to the morphological structure of Sand Waves. Especially the tube‐building worm Lanice conchilega is of interest as this organism forms small mounds on the seabed which provide shelter to other organisms. We investigate how the interactions between small‐scale mounds (height ~dm) and large‐scale Sand Waves (height~m) shape the bed of the marine environment. To this end, we present a two‐way coupled process‐based model of Sand Waves and tube‐building worm patches in Delft3D. The population density evolves according to a general law of logistic growth, with the bed shear stress controlling the carrying capacity. Worm patches are randomly seeded and the tubes are mimicked by small cylinders which influence flow and turbulence, thereby altering sediment dynamics. Model results relate the patches with the highest worm densities to the Sand Wave troughs, which qualitatively agrees with field observations. Furthermore, the L. conchilega tubes trigger the formation of Sandy mounds on the seabed. Due to the population density distribution, the mounds in the troughs can be several centimetres higher than on the crests. Regarding Sand Wave morphology, the combination of patches and mounds are found to shorten the time‐to‐equilibrium. Also, if the initial bed comprised small sinusoidal Sand Waves, the equilibrium Wave height decreased with a few decimetres compared to the situation without worm patches. As the time scale of mound formation (years) is shorter than that of Sand Wave evolution (decades), the mounds induce (and accelerate) Sand Wave growth on a similar spatial scale as the mounds. Initially this leads to shorter Sand Waves than they would be in an abiotic environment. However, near equilibrium the Wavelengths tend towards their abiotic counterparts again.
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video transects reveal that tidal Sand Waves affect the spatial distribution of benthic organisms and Sand ripples
Geophysical Research Letters, 2018Co-Authors: Johan Hendrik Damveld, Karin J Van Der Reijden, L Koop, Laura L Govers, Bastiaan Wijnand Borsje, C Cheng, L R Haaksma, C A J Walsh, Karline SoetaertAbstract:The Sandy seabed of shallow coastal shelf seas displays morphological patterns of various dimensions. The seabed also harbors a rich ecosystem. Increasing pressure from human-induced disturbances necessitates further study on drivers of benthic community distributions over morphological patterns. Moreover, a greater understanding of the Sand ripple distribution over tidal Sand Waves may improve morphological model predictions. Here we analyzed the biotic abundance and ripple morphology in Sand Wave troughs and crests using video transects. We found that both the epibenthos and endobenthos are significantly more abundant in Sand Wave troughs, where ripples are less abundant and more irregularly shaped. Finally, we show that camera systems are relatively quick and effective tools to study biotic spatial patterns in relation to seabed morphology.
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modelling the effect of suspended load transport and tidal asymmetry on the equilibrium tidal Sand Wave height
Coastal Engineering, 2018Co-Authors: W Van Gerwen, Johan Hendrik Damveld, Bastiaan Wijnand Borsje, Suzanne J M H HulscherAbstract:Abstract Tidal Sand Waves are rhythmic bed forms found in shallow Sandy coastal seas, reaching heights up to ten meters and migration rates of several meters per year. Because of their dynamic behaviour, unravelling the physical processes behind the growth of these bed forms is of particular interest to science and offshore industries. Various modelling efforts have given a good description of the initial stages of Sand Wave formation by adopting a linear stability analysis on the coupled system of water movement and the Sandy seabed. However, the physical processes causing Sand Waves to grow towards equilibrium are far from understood. We adopt a numerical shallow water model (Delft3D) to study the growth of Sand Waves towards a stable equilibrium. It is shown that both suspended load transport and tidal asymmetry reduce the equilibrium Sand Wave height. A residual current results in asymmetrical bed forms that migrate in the direction of the residual current. The combination of suspended load transport and tidal asymmetry results in predicted equilibrium Wave heights comparable to Wave heights found in the field.
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modeling tidal Sand Wave formation in a numerical shallow water model the role of turbulence formulation
Computer Science Symposium in Russia, 2013Co-Authors: Bastiaan Wijnand Borsje, Pieter C Roos, Wouter Kranenburg, Suzanne J M H HulscherAbstract:Tidal Sand Waves are prominent dynamic bottom features in shallow Sandy seas. Up to now, the processes controlling the formation of these bedforms have only been studied in stability Sand Wave models, in which geometry, boundary conditions and turbulence models are schematized. In this paper we present simulations of Sand Wave formation and migration with a numerical shallow water model (Delft3D), in which we restrict us to bedload transport and analyse the initial formation stage only. First, it is shown that the reproduction of the basic Sand Wave formation mechanisms in a numerical shallow water model requires careful treatment of model geometry, initial profile, vertical resolution and lateral boundary conditions. Second, an intercomparison between the Delft3D model and a nonlinear stability Sand Wave model is performed. Next, we compare the results for two of the built-in turbulence models: constant vertical eddy viscosity model (commonly used in stability Sand Wave models) and a more advanced spatially and temporally variable vertical eddy viscosity model (k–e turbulence model). Finally, the model results are compared with field data on Sand Wave length. The k–e turbulence model shows good agreement with the field data, whereas the constant vertical eddy viscosity model overestimates the Wave length of the Sand Waves considerably
