20 results on '"Coco, Giovanni"'
Search Results
2. Observations of dune interactions from DEMs using through-water Structure from Motion
- Author
-
Terwisscha van Scheltinga, Renske C., Coco, Giovanni, Kleinhans, Maarten G., Friedrich, Heide, Biogeomorphology of Rivers and Estuaries, Coastal dynamics, Fluvial systems and Global change, Biogeomorphology of Rivers and Estuaries, and Coastal dynamics, Fluvial systems and Global change
- Subjects
Bedform ,010504 meteorology & atmospheric sciences ,Elevation ,Sediment ,Sediment transport ,010502 geochemistry & geophysics ,01 natural sciences ,Dune migration ,Photogrammetry ,Taverne ,Crest deformation ,Structure from motion ,Bedform splitting ,Digital elevation model ,Geomorphology ,Geology ,Level of detail ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The role of three-dimensionality (3D) in modulating both flow and sediment transport remains poorly understood. 3D bed elevation measurements are difficult to obtain due to irregular dune shapes and submergence. Using photogrammetric tools for topographic reconstruction has become popular in surface studies, yet water refraction makes through-water image capturing of submerged dunes still challenging. We show that through-water images and Structure from Motion (SfM) tools can produce accurate Digital Elevation Models (DEMs) of a measured dune field, with a high level of detail. It is a low-cost and non-intrusive alternative for submerged bed elevation measurements. We provide a detailed SfM workflow, introduce and discuss the use of camera coordinates and underwater ground control points, and processing steps needed to obtain high accuracy DEMs. Our method results in DEMs with mm resolution in controlled laboratory conditions. New data for 23 dune field DEMs from 6 experiments were obtained and are presented. The dune field DEM time series provide insights on dune interaction processes. In our experiments, merging and defect creation were most common. Merging decreases the number of bedforms, and defect creation is responsible for more bedforms. Dunes continue to interact and jostle after achieving equilibrium. Simple crests are much more frequently observed than irregular, sinuous or double crests. Two-dimensional (2D) crest shapes were observed, although crest shapes were generally of 3D nature. Observed dune migration rates are not steady and vary in time and space. Bedform splitting speeds up dune migration, whilst neighbouring dunes tend to accelerate or decelerate. We identify a cascade of processes and show that 3D DEMs at high frequency are required to resolve observed rapid deformations and interaction of dunes. The identified dune interaction processes are inherent to sediment flux (variability), whereas the temporal component of the underlying sediment transport processes is still not well understood in relation to average transport.
- Published
- 2020
3. Emerging crescentic patterns in modelled double sandbar systems under normally incident waves
- Author
-
Coco, Giovanni, Calvete, Daniel, Ribas, Francesca, De Swart, Huib E., Falqués, Albert, Dep Natuurkunde, Sub Physical Oceanography, Marine and Atmospheric Research, Dep Natuurkunde, Sub Physical Oceanography, Marine and Atmospheric Research, Universitat Politècnica de Catalunya. Departament de Física, and Universitat Politècnica de Catalunya. DF - Dinàmica de Fluids: formació d'estructures i aplicacions geofísiques
- Subjects
Ones ,010504 meteorology & atmospheric sciences ,lcsh:Dynamic and structural geology ,Surf zone ,Double sandbar systems ,010502 geochemistry & geophysics ,01 natural sciences ,Linear stability analysis ,lcsh:QE500-639.5 ,Beach erosion ,Conservation of mass ,Geomorphology ,Seabed ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Shore ,geography ,geography.geographical_feature_category ,Morphodynamic stability of double-barred beaches ,Física [Àrees temàtiques de la UPC] ,Shoal ,Sand bars ,Amplitude ,Geophysics ,Waves ,Submarine pipeline ,Sediment transport ,Geology ,Platges -- Erosió - Abstract
Double sandbar systems often characterize the surf zone of wave-dominated beaches and display a variety of poorly explained spatial configurations. Here, we explore the morphodynamic stability of double-barred beaches using a model based on linear stability analysis. Surf zone hydrodynamics are described by coupling depth and wave-averaged conservation of mass and momentum with the wave energy and phase equations, including roller dynamics. A simplified sediment transport formulation relates flow to seabed changes. Under normal wave incidence, an alongshore uniform coast with a cross-shore profile characterized by the presence of two sandbars can be unstable, thereby resulting in the development of crescentic and/or rip channel patterns. Our study demonstrates that sandbar coupling can be 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). In line with observations, results of simulations show a large variability in the possible emerging bottom patterns. Our analysis indicates that modes of which the amplitude of the inner sandbar perturbation is larger than that of the outer sandbar are dominant for large height–depth differences between the two sandbar crests and small offshore wave heights. Patterns related to the outer sandbar dominate for small values of the difference in sandbar depth. For intermediate differences between the two sandbar depths, patterns on both longshore bars appear to be fully coupled (similar growth rates and strongly correlated pattern shapes). For relatively large waves and large depth over the outer sandbar, patterns can also develop close to the shoreline and/or inner surf zone together with patterns in the inner or outer sandbar.
- Published
- 2020
4. The role of geological mouth islands on the morphodynamics of back-barrier tidal basins.
- Author
-
Wei, Yizhang, Chen, Yining, Qiu, Jufei, Zhou, Zeng, Yao, Peng, Jiang, Qin, Gong, Zheng, Coco, Giovanni, Townend, Ian, and Zhang, Changkuan
- Subjects
TIDAL basins ,SETTLING basins ,TIDAL currents ,ISLANDS ,SEDIMENTATION & deposition ,SEDIMENT transport - Abstract
Researchers have extensively investigated the back-barrier islands morphodynamics using numerical methods. However, the influence of rocky mouth islands, which may be submerged by sea-level rise, has been rarely explored. Using the Dongshan Bay in southern China as a reference, this study numerically explores the long-term morphodynamic effect of geological constraints (e.g. rocky islands) for back-barrier basins. Model results indicate that the spatial configuration of mouth islands can considerably affect the morphological development of tidal basins. The presence of mouth islands narrows the inlet cross-sectional area, increasing flow velocity and residual current, resulting in more sediment suspension and transport. Meanwhile, mouth islands tend to increase erosion in the tidal basin and sedimentation in the ebb-delta area. Furthermore, the spatial distribution of mouth islands can also affect tidal basin evolution: the basin-side mouth islands tend to cause more basin erosion with higher tidal currents and more sediment transport. In contrast, the delta-side ones may increase relative sediment deposition in the basin. Finally, larger tidal prisms are observed with more mouth islands and with basin-side mouth islands, suggesting that the number and location of islands can affect the relationship between the tidal prism and inlet cross-sectional area. This modelling study furthers the understanding of barrier basin morphodynamics affected by rocky mouth islands and informs management strategies under a changing environment. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
5. Sediment Particle Velocity and Activity During Dune Migration.
- Author
-
Terwisscha van Scheltinga, Renske C., Coco, Giovanni, and Friedrich, Heide
- Subjects
SAND dunes ,THREE-dimensional flow ,PARTICLE motion ,NON-uniform flows (Fluid dynamics) ,SEDIMENT transport - Abstract
The processes underlying sediment transport mechanics are still debated. Here, we present novel ensemble particle bedload measurements, obtained with high‐frequency imaging of particle velocities and activity over various bedform migration stages. We show that the bedload particle flux quickly responds to the unsteady non‐uniform flow over the bed. Mean particle velocity linearly increases over the dune slopes towards the crest. In contrast, particle activity exhibits a power law increase over the dune slopes, with the top layer almost saturating in the saltation regime. Furthermore, the spatial and temporal variability of particle motion over dune slopes is high. For lower flow, spatial and temporal variability from small‐scale topography, such as superposed bedforms, spurs, and irregular crestlines, are shown to be important for quantifying sediment dynamics. With increasing flow, however, the cross‐stream particle velocities increase significantly, influenced by the large‐scale dune topography (transverse slopes). Overall, variability in the particle flux increases with both flow strength and frequency of turbulent events. For the mean particle flux over the dune slopes, however, differences between neighboring dunes are large, which are attributed to dune topography variations and flow acceleration. The presented insights are essential to validate numerical simulations of sediment dynamics in three‐dimensional flow conditions over dune beds. Plain Language Summary: Rivers convey water and sediment, often resulting in bedforms covering riverbeds. Yet, our understanding on how individual sediment particles contribute to the formation of various bedforms remains rudimentary. This major knowledge gap is mainly due to a complete lack of direct particle measurements over bedforms. Here, we present the collection of a novel data set of not only bedforms, but also individual particles that contribute to the formation of the bedforms, for a riverbed in controlled laboratory conditions. Using cameras to visualize and quantify the transport of sediment, we can appreciate and quantify the complexity of sediment transport and the limitation of present theories. Key Points: Particle activity of the bedload layer saturates, whilst particle velocity continues to increase over dune stoss slopesBedload particle flux responds to small‐scale topographic features for lower flows, while it is independent for higher flowsSediment transport peaks over the upper section of the dune stoss slopes [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
6. Infragravity waves: From driving mechanisms to impacts
- Author
-
Bertin, Xavier, de Bakker, A.T.M., van Dongeren, Ap, Coco, Giovanni, Andre, Gael, Ardhuin, F., Bonneton, P., Bouchette, Frederic, Castelle, B., Crawford, Wayne, Davidson, M., Deen, Martha, Dodet, Guillaume, Guerin, Thomas, Inch, Kris, Leckler, Fabien, McCall, Robert, Muller, Heloise, Olabarrieta, Maintane, Roelvink, Dano, Ruessink, B.G., Sous, Damien, Stutzmann, Eleonore, Tissier, M.F.S., Proceskunde, Coastal dynamics, Fluvial systems and Global change, LIttoral ENvironnement et Sociétés - UMRi 7266 (LIENSs), Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS), Department of Physical Geography, Utrecht University [Utrecht]-Faculty of Geosciences, DELTARES (DELTARES), DELTARES, Altran Ouest, Atlantide, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Littoral, Environnement, Télédétection, Géomatique (LETG - Brest), Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), Université de Nantes (UN)-Université de Nantes (UN)-Université de Caen Normandie (UNICAEN), Université de Nantes (UN)-Université de Nantes (UN), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), University of Florida [Gainesville] (UF), Unesco (UNESCO), IHES, Institute for Marine and Atmospheric Research [Utrecht] (IMAU), Utrecht University [Utrecht], Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), LIttoral ENvironnement et Sociétés - UMR 7266 ( LIENSs ), Université de La Rochelle ( ULR ) -Centre National de la Recherche Scientifique ( CNRS ), DELTARES ( DELTARES ), Institut Français de Recherche pour l'Exploitation de la Mer ( IFREMER ), Environnements et Paléoenvironnements OCéaniques ( EPOC ), Observatoire aquitain des sciences de l'univers ( OASU ), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -École pratique des hautes études ( EPHE ) -Centre National de la Recherche Scientifique ( CNRS ), Université des Antilles et de la Guyane ( UAG ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Université de Montpellier ( UM ) -Centre National de la Recherche Scientifique ( CNRS ), Institut de Physique du Globe de Paris ( IPGP ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -IPG PARIS-Université Paris Diderot - Paris 7 ( UPD7 ) -Université de la Réunion ( UR ) -Centre National de la Recherche Scientifique ( CNRS ), Littoral, Environnement, Télédétection, Géomatique ( LETG - Brest ), Littoral, Environnement, Télédétection, Géomatique ( LETG ), Université de Caen Normandie ( UNICAEN ), Normandie Université ( NU ) -Normandie Université ( NU ) -Université d'Angers ( UA ) -Université de Nantes ( UN ) -École pratique des hautes études ( EPHE ) -Université de Brest ( UBO ) -Université de Rennes 2 ( UR2 ), Université de Rennes ( UNIV-RENNES ) -Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Caen Normandie ( UNICAEN ), Université de Rennes ( UNIV-RENNES ) -Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ), Service Hydrographique et Océanographique de la Marine ( SHOM ), Bureau de Recherches Géologiques et Minières (BRGM) ( BRGM ), University of Florida [Gainesville] ( UF ), Unesco ( UNESCO ), Institute for Marine and Atmospheric Research [Utrecht] ( IMAU ), Institut méditerranéen d'océanologie ( MIO ), Centre National de la Recherche Scientifique ( CNRS ) -Université de Toulon ( UTLN ) -Aix Marseille Université ( AMU ) -Institut de Recherche pour le Développement ( IRD ), Proceskunde, Coastal dynamics, Fluvial systems and Global change, LIttoral ENvironnement et Sociétés (LIENSs), La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École Pratique des Hautes Études (EPHE), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN)
- Subjects
[ SDU.OCEAN ] Sciences of the Universe [physics]/Ocean, Atmosphere ,Seiche ,010504 meteorology & atmospheric sciences ,Infragravity wave ,Bound wave ,Reflection ,010502 geochemistry & geophysics ,01 natural sciences ,Earth hum ,14. Life underwater ,Overwash ,Hydraulic jump ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,Infragravity waves ,Front (oceanography) ,Breaking wave ,Geophysics ,Sediment transport ,Waves and shallow water ,13. Climate action ,Dissipation ,Barrier breaching ,Reflection (physics) ,General Earth and Planetary Sciences ,Geology - Abstract
Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated “short waves” (typically below 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1–10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate current velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier breaching. In tidal inlets, IG waves can propagate into the back-barrier lagoon during the flood phase and induce large modulations of currents and sediment transport. Their effect appears to be smaller during the ebb phase, due to blocking by countercurrents, particularly in shallow systems. On coral and rocky reefs, IG waves can dominate over short-waves and control the hydro-sedimentary dynamics over the reef flat and in the lagoon. In harbors and semi-enclosed basins, free IG waves can be amplified by resonance and induce large seiches (resonant oscillations). Lastly, free IG waves that are generated in the nearshore can cross oceans and they can also explain the development of the Earth's “hum” (background free oscillations of the solid earth).
- Published
- 2018
7. Sand particle velocities over a subaqueous dune slope using high‐frequency image capturing.
- Author
-
Terwisscha van Scheltinga, Renske C., Coco, Giovanni, and Friedrich, Heide
- Subjects
SAND dunes ,PARTICLE image velocimetry ,SEDIMENT transport ,SAND ,VELOCITY ,FLOW velocity ,PARTICLES ,PARTICLE motion - Abstract
This work presents measurements and analysis of sand particle velocities over a subaqueous dune with median sand diameter of 0.85 mm. Time‐lapse images of the mobile bed and an automated particle image velocimetry (PIV)‐based cross‐correlation method are used to obtain mean velocity of sand particles. This technique is shown to be consistent with measurements obtained with manual tracing. The measurements indicate an increase in mean particle velocity over a dune slope. Three regions are distinguished over the dune slope: (1) region of fluctuating particle velocity, (2) region of increasing particle velocity, and (3) region of maximum particle velocity. The observations are aligned with experimental and numerical modelling studies, indicating fluctuations in flow velocity over a dune stoss slope. We furthermore show that the standard deviation of the mean particle velocity is affected by the slope location and decreases from the lower slope towards the upper slope. The particle velocity variability is discussed in the context of general onset and cessation of sediment transport, the effect of the reattachment zone, sweep‐transport events, and the existence of superimposed bedforms. With this work we bridge the gap between measurements of bedload transport at the particle‐scale and at the bedform‐scale. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
8. A review of machine learning applications to coastal sediment transport and morphodynamics.
- Author
-
Goldstein, Evan B., Coco, Giovanni, and Plant, Nathaniel G.
- Subjects
- *
MACHINE learning , *NONLINEAR regression , *SAND bars , *COMPUTER science , *COASTAL sediments , *SEDIMENT transport - Abstract
A range of computer science methods termed machine learning (ML) enables the extraction of insight and quantitative relationships from multidimensional datasets. Here, we review the use of ML on supervised regression tasks in studies of coastal morphodynamics and sediment transport. We examine aspects of 'what' and 'why', such as 'what' science problems ML tools have been used to address, 'what' was learned when using ML, and 'why' authors used ML methods. We find a variety of research questions have been addressed, ranging from small-scale predictions of sediment transport to larger-scale sand bar morphodynamics and coastal overwash on a developed island. We find various reasons justify the use of ML, including maximize predictability, emulation of model components, the need for smooth and continuous nonlinear regression, and explicit inclusion of uncertainty. The expanding use of ML has allowed for an expanding set of questions to be addressed. After reviewing the studies we outline a set of best practices for coastal researchers using machine learning methods. Finally we suggest possible areas for future research, including the use of novel machine learning techniques and exploring open data that is becoming increasingly available. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
9. Effects of Density‐Driven Flows on the Long‐Term Morphodynamic Evolution of Funnel‐Shaped Estuaries.
- Author
-
Olabarrieta, Maitane, Geyer, W. Rockwell, Coco, Giovanni, Friedrichs, Carl T., and Cao, Zhendong
- Subjects
FRESHWATER flow into estuaries ,MASS density gradients ,SEDIMENT transport ,FLUVIAL geomorphology ,ESTUARY hydrodynamics - Abstract
Subtidal flows driven by density gradients affect the tide‐averaged sediment transport in estuaries and, therefore, can influence their long‐term morphodynamic evolution. The three‐dimensional Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport modeling system is applied to numerically analyze the effects of baroclinicity and Earth's rotation on the long‐term morphodynamic evolution of idealized funnel‐shaped estuaries. The morphodynamic evolution in all the analyzed cases reproduced structures identified in many tide‐dominated estuaries: a meandering region in the fluvial‐tidal transition zone, a tidal maximum area close to the head, and a turbidity maxima region in the brackish zone. As the morphology of the estuaries evolved, the tidal propagation (including its asymmetry), the salinity gradient, and the strength of subtidal flows changed, which reflects the strong bathymetric control of these systems. The comparison with barotropic simulations showed that the three‐dimensional structure of the flow (induced by density gradients) has leading order effects on the morphodynamic evolution. Density gradient‐driven subtidal flows (1) promote near‐bed flood dominance and, consequently, the import of sediment into the estuary, (2) accelerate the morphodynamic evolution of the upper/middle estuary, (3) promote a more concave shape of the upper estuary and reduce the ebb‐tidal delta volume, and (4) produce an asymmetric bathymetry and inhibit the formation of alternate bars that would form under barotropic conditions. This latter effect is the consequence of the combined effect of Earth's rotation and baroclinicity. Key Points: Density‐driven flows affect the long‐term morphodynamic evolution of estuaries by enhancing near‐bed flood dominanceThe combined effect of baroclinicity and Coriolis acceleration tends to promote cross‐channel bathymetric asymmetryThree‐dimensional process‐based numerical models accounting for salinity variations resemble bathymetric and hydrodynamic features observed in estuaries [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
10. The influence of turbulent bursting on sediment resuspension under unidirectional currents.
- Author
-
Salim, Sarik, Pattiaratchi, Charitha, Tinoco, Rafael, Coco, Giovanni, Hetzel, Yasha, Wijeratne, Sarath, and Jayaratne, Ravindra
- Subjects
SEDIMENT control ,SEDIMENT transport ,TURBULENT flow - Abstract
Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the "bursting" phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1) the contribution of turbulent bursting events remained identical in both experimental conditions, (2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
11. Is “Morphodynamic Equilibrium” an oxymoron?
- Author
-
Zhou, Zeng, Coco, Giovanni, Townend, Ian, Olabarrieta, Maitane, van der Wegen, Mick, Gong, Zheng, D’Alpaos, Andrea, Gao, Shu, Jaffe, Bruce E., Gelfenbaum, Guy, He, Qing, Wang, Yaping, Lanzoni, Stefano, Wang, Zhengbing, Winterwerp, Han, and Zhang, Changkuan
- Subjects
- *
SEDIMENT transport , *GEOMORPHOLOGY , *STATIC equilibrium (Physics) , *SEDIMENTOLOGY , *HYDRODYNAMICS - Abstract
Morphodynamic equilibrium is a widely adopted yet elusive concept in the field of geomorphology of coasts, rivers and estuaries. Based on the Exner equation, an expression of mass conservation of sediment, we distinguish three types of equilibrium defined as static and dynamic, of which two different types exist. Other expressions such as statistical and quasi-equilibrium which do not strictly satisfy the Exner conditions are also acknowledged for their practical use. The choice of a temporal scale is imperative to analyse the type of equilibrium. We discuss the difference between morphodynamic equilibrium in the “real world” (nature) and the “virtual world” (model). Modelling studies rely on simplifications of the real world and lead to understanding of process interactions. A variety of factors affect the use of virtual-world predictions in the real world (e.g., variability in environmental drivers and variability in the setting) so that the concept of morphodynamic equilibrium should be mathematically unequivocal in the virtual world and interpreted over the appropriate spatial and temporal scale in the real world. We draw examples from estuarine settings which are subject to various governing factors which broadly include hydrodynamics, sedimentology and landscape setting. Following the traditional “tide-wave-river” ternary diagram, we summarize studies to date that explore the “virtual world”, discuss the type of equilibrium reached and how it relates to the real world. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
12. On the morphodynamic stability of intertidal environments and the role of vegetation.
- Author
-
Kakeh, Nabil, Coco, Giovanni, and Marani, Marco
- Subjects
- *
ECOGEOMORPHOLOGY , *INTERTIDAL ecology , *BIOFILMS , *SEDIMENT transport , *SALT marshes - Abstract
We describe the coupled biotic and abiotic dynamics in intertidal environments using a point model that includes suspended sediment deposition, wave- and current-driven erosion, biofilm sediment stabilization, and sediment production and stabilization by vegetation. We explore the effects of two widely different types of vegetation: salt-marsh vegetation and mangroves. These two types of vegetation, which colonize distinct geographical areas, are characterized by different biomass productivities and stabilization mechanisms. We show that changing vegetation and biofilm properties result in differing stable states, both in their type and number. The presence of the biofilm exerts a dominant control on the tidal flat (lower intertidal) equilibrium elevation and stability. Vegetation controls the elevation of the marsh platform (i.e., the upper intertidal equilibrium). The two types of vegetation considered lead to similar effects on the stability of the system despite their distinct biophysical interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
13. Modelling the effects of tidal range and initial bathymetry on the morphological evolution of tidal embayments.
- Author
-
van Maanen, B., Coco, Giovanni, and Bryan, K.R.
- Subjects
- *
TIDES , *BATHYMETRY , *GEOMORPHOLOGY , *HYDRODYNAMICS , *SEDIMENT transport , *COMPUTER simulation , *ALTITUDE measurements - Abstract
Abstract: Tidal embayments are characterized by a wide variety of landscape features, often including either complex tidal channel networks or extensive flood-tidal deltas. The origin of these features and the influence of hydrodynamic drivers and initial geological setting on their long-term characteristics are essentially unexplored. A model was applied to simulate the long-term morphological evolution of tidal embayments, with the purpose of providing insight into the environmental conditions that lead to the differences in tidal embayment morphology. Numerical simulations indicated that the interaction between hydrodynamics, sediment transport, and the evolving topography gives rise to the formation of channel networks. The tidal range and the depth of the initially unchannelized tidal basin controlled the way in which the morphology evolved and determined the timescale over which channels and intertidal areas developed. Channel network formation occurred more rapidly when the tidal range increased and/or when the initial basin depth decreased. Tidal basins with a large initial depth showed the development of a flood-tidal delta and for these deep basins channel incision could remain absent over long timescales. Both tidal range and initial bathymetry affected final basin hypsometry and channel network characteristics, including the channel density and the fraction of the basin occupied by the channels. All the simulated morphologies, with different combinations of the tidal range and depth of the basin, evolved towards a state of less morphodynamic activity for which the relative intertidal area was proportional to the ratio of tidal amplitude to basin depth. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
14. Patterns in the sand: From forcing templates to self-organization
- Author
-
Coco, Giovanni and Murray, A. Brad
- Subjects
- *
SEDIMENT transport , *OCEAN bottom , *PHYSICAL geography , *EROSION - Abstract
Abstract: The nearshore region exhibits many striking morphological patterns with a variety of spatial and temporal scales. The formation of these rhythmic features has been initially ascribed, depending on the pattern in question, to spatial structures in the flow or geological constrains. These forcing templates have been hypothesized to provide the spatial structure that becomes imprinted on the shoreline or seabed morphology. More recently, new explanations for rhythmic patterns have involved interactions between fluid flow and sediment transport that create morphological feedbacks and lead to pattern self-organization. While forcing-template models do not explicitly treat transport of the sediment that makes up the pattern, self-organization models focus on the strong couplings within flow/sediment systems, and on interactions between emergent structures. We illustrate the sweeping shift from template explanations to self-organization by discussing four nearshore patterns: beach cusps, surfzone crescentic sandbars, inner-shelf sorted bedforms, and large-scale cuspate shorelines. Models involving self-organization show that local interactions between flow and sediment transport can collectively give rise to patterns with large-scale coherence and that the driving feedbacks can be associated with either topographical or grain-size composition instabilities. An approach based on self-organization also allows researchers to establish limitations in the predictability of the occurrence of rhythmic patterns and characteristics as well as to study mechanisms leading to the observed variability of pattern or lack of regularity. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
15. Investigating the response of wave-generated ripples to changes in wave forcing.
- Author
-
Jin, Chuang, Coco, Giovanni, Tinoco, Rafael O., Perron, J. Taylor, Myrow, Paul M., Huppert, Kimberly L., Friedrich, Heide, Goldstein, Evan B., and Gong, Zheng
- Subjects
- *
WAVE forces , *SEDIMENT transport , *FLUID flow , *WAVELENGTHS - Abstract
Wave-generated ripples are macroscopic roughness elements that influence fluid flow and sediment transport. For a major group of ripples (orbital ripples), morphology (height and wavelength) is set by the wave conditions. In natural conditions, where wave forcing is highly variable, ripple morphology is frequently changing. We investigate the rate of morphological change after changes in wave conditions (i.e., wave height and period), using laboratory experiments with a step-change in wave forcing. The adjustment time of ripple morphology to new conditions –– the hysteresis time scale (hereafter referred to simply as hysteresis) –– is proportional to changes in wave orbital diameter, and the coefficient of proportionality differs for decreasing and increasing orbital diameter. When the Shields parameter is lower than a threshold (0.043), there is no change in ripple morphology (or changes are extremely slow). In addition, we find the presence of defects (irregularities from straight parallel crestlines) reduces the hysteresis time scale. The dependence of hysteresis on defect density implies that a larger density of defects results in faster ripple adjustment, confirming previous theoretical and numerical model results. • Widening and narrowing of orbital diameter corresponds to the different changing rate of hysteresis. • If the Shields parameter is below a certain value, pre-existing ripples do not change or change extremely slowly. • Larger defect densities result in shorter hysteresis for cases with the same Shields parameter. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
16. A one-dimensional biomorphodynamic model of tidal flats: Sediment sorting, marsh distribution, and carbon accumulation under sea level rise.
- Author
-
Zhou, Zeng, Ye, Qinghua, and Coco, Giovanni
- Subjects
- *
VEGETATION dynamics , *SEDIMENT transport , *TIDAL flats , *SALT marshes , *SEA level , *CARBON analysis - Abstract
We develop a biomorphodynamic model to investigate sediment and vegetation dynamics on a schematic intertidal flat characterized by an initially well-mixed sand-mud mixture. Major interactions between tides, wind waves, salt marshes, sediment transport and sea level rise (SLR) are taken into account. For a bare flat under only tidal action, the model predicts a convex cross-shore profile with the surficial distribution of mud and sand on the upper and lower part of the intertidal flat, respectively. When wind waves are strong, the intertidal flat is highly eroded resulting in a concave profile near the high water mark. This behavior is pronouncedly altered when the intertidal flat is vegetated with the presence of salt marshes. Numerical results suggest that a considerable amount of mud can still remain in the vegetated region even when wave action is strong. A steeper transition zone forms at the boundary between salt marshes and bare flats because of the differential sediment deposition in the two neighboring regions. The inclusion of wind waves is found to considerably enhance the size of the marsh-edge transition zone. For the numerical experiments designed in this study, the profile shape and sediment sorting behavior of tidal flats are not significantly modified by a gradual rising sea level. However, the impacts of SLR on vegetated tidal flats are still manifold: (a) driving the landward migration of intertidal zone and salt marshes; (b) enhancing sediment erosion on intertidal flats; and (c) drowning salt marshes under limited sediment supply with the constrain of seawalls. Finally, model results suggest that organic carbon accumulation on marshlands may be enhanced with an increasing SLR rate provided that salt marshes are not drowned. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
17. Onshore sandbar migration at Tairua Beach (New Zealand): Numerical simulations and field measurements
- Author
-
van Maanen, B., de Ruiter, P.J., Coco, Giovanni, Bryan, K.R., and Ruessink, B.G.
- Subjects
- *
MORPHOLOGY , *SEDIMENT transport , *SUSPENDED sediments - Abstract
Abstract: We observed the onshore migration (3.5 m/day) of a nearshore sandbar at Tairua Beach, New Zealand during 4 days of low-energy wave conditions. The morphological observations, together with concurrent measurements of waves and suspended sediment concentrations, were used to test a coupled, wave-averaged, cross-shore model. Because of the coarse bed material and the relatively low-energy conditions, the contribution of the suspended transport to the total transport was predicted and observed to be negligible. The model predicted the bar to move onshore because of the feedback between near-bed wave skewness, bedload, and the sandbar under weakly to non-breaking conditions at high tide. The predicted bathymetric evolution contrasts, however, with the observations that the bar migrated onshore predominantly at low tide. Also, the model flattened the bar, while in the observations the sandbar retained its steep landward-facing flank. A comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water (<0.25 m) may have been responsible for most of the observed bar behaviour. These processes are missing from the applied model and, given that the observed conditions can be considered typical of very shallow sandbars, highlight a priority for further field study and model development. The possibility that the excess water transported by the bores across the bar was channelled alongshore to near-by rip-channels further implies that traditional cross-shore measures to judge the applicability of a cross-shore morphodynamic model may be misleading. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
18. Alongshore variability in berm and sandbar migration patterns on a highly dynamic beach.
- Author
-
Kono-Martínez, Tadashi, Ruiz de Alegría-Arzaburu, Amaia, Mariño-Tapia, Ismael, and Coco, Giovanni
- Subjects
- *
SAND bars , *SHORELINES , *BEACHES , *RIP currents , *EROSION , *SEDIMENT transport , *SPRING , *WAVE energy - Abstract
Sediment exchange between the shoreface and the foreshore is investigated through the analysis of sandbar and berm migration cycles at La Misión beach in Baja California, Mexico. In general, nearshore sandbars migrate onshore during low-energy wave conditions merging with the shoreline to become intertidal sandbars that later contribute to berm rebuilding. However, significant alongshore differences were observed in the sandbar welding and berm rebuilding process, which can be attributed to alongshore wave skewness and near-surfzone flow variations. The analysis of topographic and bathymetric surveys collected monthly over a 5-year period revealed larger shoreline retreat and longer recovery times in the southern beach compared to the north. This was related to the inability of sandbars to weld to the intertidal beach during spring and summer, occurring only during extended periods of low-energy waves. In the southern beach, the berm formation process exhibited less dependence on incoming wave energy, persisting during mild-energy winters, and reforming in the presence of sandbars. Hydrodynamic measurements indicated that the southern part of the beach experienced relatively more intense net offshore flows (up to −0.2 ms−1) due to undertow, and possibly related to the presence of persistent rip currents. In contrast, the berm in the northern beach followed a seasonal erosion and rebuilding process associated with sandbar migrations driven by variations in incoming wave energy and cross-shore sediment transport. This was characterized by larger near-bed wave velocity skewness compared to the south. Net flows in the north were predominantly onshore, reaching up to 0.1 ms−1 during lower-energy periods with oblique wave incidence. This study reveals the presence of considerably distinct sandbar and berm migration cycles along a relatively short beach of 2.2 km long. It also highlights how such variability can be related to the morphodynamic feedback with sandbars affecting hydrodynamics, particularly near-bed wave skewness and near-surfzone flow variations, which in turn influence sediment transport and morphological evolution. • Bar merging affects berm rebuilding, influenced by wave skewness and flow variations. • Net onshore flows and higher skewness allow seasonal berm rebuilding. • Net offshore flows and lower skewness kept the bar offshore but the berm recovered. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
19. Subaerial and upper-shoreface morphodynamics of a highly-dynamic enclosed beach in NW Baja California.
- Author
-
Ruiz de Alegría-Arzaburu, Amaia, Gracia-Barrera, Ashley David, Kono-Martínez, Tadashi, and Coco, Giovanni
- Subjects
- *
SEDIMENT transport , *BEACH erosion , *BEACHES , *CORPORATE profits - Abstract
Estimating sediment budget is a challenge that requires understanding the morphological relationship between the subaerial beach and the upper and lower shoreface. Based on a unique dataset of monthly measured topographic and bathymetric measurements, this study describes the morphodynamics of the subaerial and subtidal sections of a highly-dynamic beach over a 5-year period (2015–2020). Typically, the beach presents a longshore bar trough (LBT) state at the end of the winter, driven by net offshore sediment transport. The nearshore morphology evolves into more reflective states (rhythmic bar beach, RBB; transverse bar rip, TBR; and low tide terrace, LTT) driven by onshore sediment transport when the incident wave-energy decreases over the spring and summer. Seasonal variations of the incident wave-energy resulted in large subaerial-subtidal exchanges of sediment (200–300 m3 m−1), but these exchanges were an order of magnitude smaller in yearly scales. Subaerial and upper-shoreface morphological changes varied alongshore. Larger variations existed in the south, influenced by persistent rip channels. Instead, alongshore processes resulting from changes in wave direction may control the morphodynamics in the center and north. The subtidal section in north and center gained significant amount of sand (300 m3 m−1) during high-energy conditions, which contributed to a net annual gain of 60 m3 m−1. The origin of that sediment is currently unknown, it could have bypassed from an adjacent beach, shifted alongshore or inputted from the lower shoreface deeper than the depth of closure. This research shows the presence of very large monthly-to-seasonal total volume fluctuations relative to net annual or multi-annual changes, and highlights that comparatively small additions to the annual sediment budget could potentially contribute to the long-term stability of the beach. • Largest morphological variations in the south influenced by persistent rip channels. • Very large monthly-to-seasonal volume fluctuations relative to net annual changes. • Small additions to the annual budget could contribute to long-term beach stability. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
20. Sediment sorting and bedding dynamics of tidal flat wetlands: Modeling the signature of storms.
- Author
-
Zhou, Zeng, Wu, Yiming, Fan, Daidu, Wu, Guoxiang, Luo, Feng, Yao, Peng, Gong, Zheng, and Coco, Giovanni
- Subjects
- *
TIDAL flats , *COASTAL wetlands , *WETLANDS , *SEDIMENTS , *SEDIMENT transport , *SHEARING force - Abstract
• Model captures main mechanisms underlying sediment sorting and bedding dynamics. • Storms bring coarser sediment to upper flats, forming sand-dominated layers (SDLs). • Stronger and longer storms cause thicker SDLs with more sand fraction. • Storms occurring during spring tide generate thicker SDLs than that during neap. • Impact of clustered storms is more significant than the sum of individual storms. Field studies suggest that storms can considerably affect the morphology, sedimentology and bedding structure of tidal flat wetlands because of their high-energy, while numerical modeling studies unravelling the underlying mechanisms remain rare. With a tidal flat of the Changjiang Delta, China as a reference site, this study explores the role of storms on sediment sorting and bedding behaviors using a biomorphodynamic model that couples hydrodynamics, sediment transport, marsh dynamics and morphological change. Model results indicate that storms can leave clear signatures on tidal flats in both horizontal and vertical sedimentary features, in agreement with field observations. The high bed shear stress induced by storms can initiate the motion of relatively coarse sediment which can be brought shoreward during the flood and settle on the upper tidal flats (or saltmarshes), altering the typically observed cross-shore "landward fining" phenomenon. The storm-entrained coarse sediment on the higher flat is usually hard to be brought offshore during calm weather, and hence leaving an evident sand-dominated layer (SDL) within neighboring mud-dominated layers (MDL). Storms can also destroy tidal rhythmites formed under calm weather. With the increase in storm intensity and duration, the thickness and the sand fraction of the SDL increase accordingly. The SDL thickness generated by a weaker storm during the spring tide is larger than that of a stronger storm during the neap tide. Storm chronology also plays an important role. In particular, the impact of two overlapping or temporally close storms is larger than the sum of the two individual storms. Overall, this study results in a more in-depth mechanistic understanding of storm impacts on tidal flat biomorphodynamics, providing a scientific facet to make sustainable management strategies for coastal wetlands. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.