13 results on '"Coco, Giovanni"'
Search Results
2. A numerical study of equilibrium states in tidal network morphodynamics
- Author
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Xu, Fan, Coco, Giovanni, Zhou, Zeng, Tao, Jianfeng, and Zhang, Changkuan
- Published
- 2017
- Full Text
- View/download PDF
3. Modeling the morphodynamic response of tidal embayments to sea-level rise
- Author
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van Maanen, Barend, Coco, Giovanni, Bryan, Karin R., and Friedrichs, Carl T.
- Published
- 2013
- Full Text
- View/download PDF
4. A Numerical Model of Bank Collapse and River Meandering.
- Author
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Zhao, Kun, Lanzoni, Stefano, Gong, Zheng, and Coco, Giovanni
- Subjects
MEANDERING rivers ,RIPARIAN areas ,SHEARING force - Abstract
Meander migration results from the interaction between inner bank accretion and outer bank erosion/collapse. This interaction has been usually treated as a long‐term average of a sequence of erosion events determined by flow hydrographs. Little attention has been paid to the role that individual bank collapse events play on meander evolution. To fill this gap, we developed a numerical model of river meandering that describes explicitly bank collapse. Results show that as bend curvature increases due to meander migration and elongation, the initially scattered locations of bank collapse events converge toward the channel section where bed shear stress attains a maximum. Simulations illustrate the observed catch‐up behavior between inner and outer banks, driven by intermittent bank collapse events. Moreover, bank collapse is found to speed up short‐term meander migration and, consistent with field observations, meanders turn out to evolve toward a state characterized by constant channel width. Plain Language Summary: Meanders are one of the most ubiquitous morphological features observed in natural rivers. They consist of a series of alternating bends that, seen from above, display one of the most striking morphological patterns in nature. The migration of meandering rivers is attributed to outer bank retreat, due to erosion, and inner bank accretion, due to deposition. In this work, we propose a morphodynamic model to investigate the effects that repeated bank collapse events have on meander evolution. Our results show that the migration of meander bends can be described through a catch‐up behavior, driven by outer bank collapse and subsequent inner bank accretion, that on average ensures a nearly constant channel width. Key Points: Meander bend migration is described through a catch‐up behavior, driven by intermittent bank collapse eventsAs the river bend evolves increasing its apex curvature, bank collapse tends to occur at the location of maximum shear stressIndividual bank collapse events speed up the short‐term migration rate of meandering rivers [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
5. Modeling sorting dynamics of cohesive and non-cohesive sediments on intertidal flats under the effect of tides and wind waves.
- Author
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Zhou, Zeng, Coco, Giovanni, van der Wegen, Mick, Gong, Zheng, Zhang, Changkuan, and Townend, Ian
- Subjects
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WIND waves , *TIDES , *TIDAL currents , *OCEAN bottom , *SEDIMENTS , *FLOCCULATION , *COMPUTER simulation - Abstract
We extend a numerical model to explore the morphodynamics of intertidal flats, with a specific focus on the sorting dynamics of sand and mud. We investigate the effect of tidal currents, wind waves, sediment properties, external sediment supply, flocculation and initial bed composition on the cross-shore profile shape and sediment sorting of intertidal flats. Consistent with existing analytical theories and benchmark simplified numerical solutions, the equilibrium cross-shore profile of intertidal flats simulated by the extended model is convex-up when tidal currents dominate and it progressively becomes concave-up when the strength of wind waves increases. The equilibrium profile is influenced by the external sediment supply which can lead to the seaward advance of intertidal flats. In line with field observations, mud tends to deposit on the upper intertidal flats when wind waves are relatively weak, while sand is mainly distributed on the middle and lower tidal flats. When wind waves are strong, both sand and mud are more easily resuspended and eroded, resulting in a noticeably concave-up profile near the high water mark. The initial bed composition (e.g., percentage of mud and sand fractions) is also found to play an important role: the intertidal flat is more convex-up in a muddier environment. Numerical modeling demonstrates that sediment properties (e.g., critical shear stress for erosion, settling velocity) and flocculation can pronouncedly influence the sediment sorting dynamics by modifying the initiation threshold and the advection distance of entrained sediments. Application of the extended model to a natural study site indicates a qualitative agreement with field observations. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
6. HOW DO BEDFORMS RESPOND TO CHANGING CONDITIONS? A STUDY USING ABSTRACTED MODELS.
- Author
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Huntley, David and Coco, Giovanni
- Subjects
RIVER channels ,RIVER sediments ,RIPPLES (Fluid dynamics) ,WATER waves ,COASTS - Published
- 2009
7. Beach response to a sequence of extreme storms.
- Author
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Coco, Giovanni, Senechal, N., Rejas, A., Bryan, K.R., Capo, S., Parisot, J.P., Brown, J.A., and MacMahan, J.H.M.
- Subjects
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BEACHES , *STORMS , *SOIL erosion , *VOLUMETRIC analysis , *REGRESSION analysis - Abstract
Abstract: A sequence of daily beach surveys acquired over one month covering an area larger than 100,000m2, was analyzed to study morphological changes resulting from a cluster of storms. The beach response was highly variable in both the cross- and alongshore. A cumulative storm effect was not observed, despite one storm being characterized by a 10-year return period that had significant wave height (Hs) of 8.1m and a peak wave period (Tp) of 17s. Instead, storms that can potentially cause significant erosion in terms of Hs had a limited effect on the morphology because the large wave height was coupled to either neap tides, normally-incident short-waves (f >0.04Hz), or low levels of infragravity (0.004< f <0.04Hz) energy. Multiple linear regression analysis shows that volumetric changes in the upper part of the beachface are explained by offshore wave characteristics (period, height and direction), tidal range or by infragravity energy in the inner surf zone (assessed using pressure and velocity measurements). The results indicate that it is not possible to scale-up single-storm erosion studies into predictions of cluster-storm erosion. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
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8. Modelling the effects of tidal range and initial bathymetry on the morphological evolution of tidal embayments.
- Author
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van Maanen, B., Coco, Giovanni, and Bryan, K.R.
- Subjects
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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
9. Patterns in the sand: From forcing templates to self-organization
- Author
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Coco, Giovanni and Murray, A. Brad
- Subjects
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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
10. Modelling the role of self-weight consolidation on the morphodynamics of accretional mudflats.
- Author
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Zhou, Zeng, van der Wegen, Mick, Jagers, Bert, and Coco, Giovanni
- Subjects
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TIDAL flats , *HYDRODYNAMICS , *SHEARING force , *SEDIMENTS , *MODULAR coordination (Architecture) , *SIMULATION methods & models - Abstract
We develop a consolidation module and merge it into a morphodynamic model to assess the role of consolidation on estuarine morphodynamics. We test the model using two settings: point models without hydrodynamic forcing to validate against two benchmark experimental datasets; and a profile model to simulate a mudflat restoration. The modelled self-weight consolidation influences the simulations by gradually reducing the bed level and decreasing the bed erodibility (i.e., increasing the critical bed shear stress). Both effects modify sediment transport processes on mudflats, leading to long-term morphodynamic effects. Depending on the initial bathymetry, the hydrodynamic forcing and the soil properties, the simulated morphological change of the restored mudflat may differ considerably with and without considering consolidation. The consolidation model developed can be utilised to assess the medium to long term effects related to estuarine development (e.g., wetland restoration) and aims to be a publicly available tool. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
11. Mechanisms underlying the regional morphological differences between the northern and southern radial sand ridges along the Jiangsu Coast, China.
- Author
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Xu, Fan, Tao, Jianfeng, Zhou, Zeng, Coco, Giovanni, and Zhang, Changkuan
- Subjects
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SAND waves , *HYDRODYNAMICS , *MARINE sediment quality , *SEDIMENTATION & deposition , *GEOMORPHOLOGY - Abstract
Radial sand ridges (RSRs) spread in a fan-shaped pattern over the seabed of the southern Yellow Sea along the Jiangsu Coast (China) with pronounced differences between the northern and southern channel-shoals (indicated as “NCS” and “SCS”, respectively). A depth-averaged nested numerical model is employed to analyze the tidal hydrodynamics and sediment dynamics of the RSRs. Model results show considerable regional differences in terms of tidal current vector ellipses: “eight-shaped” ellipses are typical in the NCS where rotational tidal waves dominate, while the SCS are characterized by “egg-shaped” ellipses because of the dominance of progressive tidal waves. Sand ridges tend to be elongated and straight in the NCS while short and dincontinuous in the SCS. Numerical Lagrange particles released near the ridges in the NCS tend to travel across the crest of the ridges rather than move around them as observed in the SCS. Consistently, the patterns of sediment convergence and divergence indicate that suspended sediments converge over the whole Xiaoyinsha Ridge located in the NCS, while converge to the two sides of the Hetunsha Ridge located in the SCS. Model results also highlight the importance of initial sediment compositions in determining patterns of the net sediment fluxes. The suspended sediment concentration (SSC) time series during one tidal cycle may show single or double peaks depending on the grain size and the related lag effect. Bed load transport is much smaller than suspended load. So sediment compositions should be carefully considered when simulating the SSC field, and the hydrodynamic of the morphological evolution of the RSRs at the regional scale. Overall, this study suggests that the NCS and SCS may be treated as two relatively independent geomorphological systems characterized by different tidal flows and sediment compositions. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
12. Geomorphology, complexity, and the emerging science of the Earth's surface
- Author
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Murray, A. Brad, Lazarus, Eli, Ashton, Andrew, Baas, Andreas, Coco, Giovanni, Coulthard, Tom, Fonstad, Mark, Haff, Peter, McNamara, Dylan, Paola, Chris, Pelletier, Jon, and Reinhardt, Liam
- Subjects
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GEOMORPHOLOGY , *COMPLEXITY (Philosophy) , *SELF-organizing systems , *CONFERENCES & conventions , *SURFACE of the earth , *EARTH (Planet) - Abstract
Abstract: The following is a white paper (adapted here for print) for the U.S. National Research Council''s committee on Challenges and Opportunities in Earth Surface Processes, drafted at a National Science Foundation sponsored workshop associated with the 38th Binghamton Geomorphology Symposium, “Complexity in Geomorphology,” held at Duke University in October 2007. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
13. Morphodynamics of tidal networks : processes, feedbacks and long-term evolution
- Author
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Zhou, Zeng, Coco, Giovanni Silvio, Olabarrieta Lizaso, Maitane, Townend, Ian H., and Universidad de Cantabria
- Subjects
Tidal networks ,Morfodinámica ,Canales mareales ,Fluvial influence ,Numerical modeling ,Influencia fluvial ,Bajos intermareales ,Modelado numérico ,Intertidal flats ,Morphodynamics - Abstract
Tidal networks are characterized by an intricate hierarchy of channels and shoals, acting as one of the most striking morphological features in coastal and estuarine environments. Located at the land-sea boundaries, they are shaped by feedbacks between a variety of processes operating over a wide range of temporal and spatial scales. The aim of this thesis is to investigate the effects of the major processes and their associated feedbacks on the long-term morphodynamics of tidal networks. Through a comparative study of physical and numerical modeling of tidal networks, this research indicates that fast- and small-scale models can reproduce the long-term morphological evolution of tidal networks. Quantitative comparisons in terms of a variety of different geometric measures are conducted and suggest that numerical modeling is a useful tool to unravel the mechanisms underlying the morphodynamic behaviors of tidal networks. This research also constructs a comprehensive framework to study the river-influenced tidal network system and explores the physics governing the distribution of different types of sediment on intertidal flats. RESUMEN: Los canales mareales son elementos característicos de los ambientes estuarinos. Estos canales se forman por el predominio de las corrientes de marea sobre el oleaje y los aportes fluviales. Los canales mareales consisten en un intrincado sistema que se caracterizada por la presencia de canales que se van ramificando y por la presencia de bajos mareales que albergan una flora y fauna de gran valor ecológico. El objetivo general de esta investigación es obtener los conocimientos fundamentales de la morfodinámica a largo plazo de los canales mareales, enfocándose principalmente en los procesos y reacciones que dan forma a estos paisajes. Este estudio verifica que los modelos de pequeña escala acelerados pueden reproducir la evolución morfológica a largo plazo de las redes mareales de una manera correcta. Los resultados obtenidos indican concordancia entre las características geométricas de los canales mareales obtenidos numéricamente y los obtenidos de manera experimental. Además, este estudio aborda el efecto del caudal fluvial en la evolución morfológica de los canales mareales, y explora la dinámica de la clasificación de los sedimentos cohesivos y no cohesivos en los bajos mareales.
- Published
- 2015
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