Coastal morphodynamic evolution techniques
TL;DR: In this paper, different strategies of morphological updating, as an important component of integrated modelling, are discussed, starting with the classical "tide-averaging" approach in combination with the "continuity correction" method.
About: This article is published in Coastal Engineering.The article was published on 2006-02-01. It has received 471 citations till now.
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TL;DR: A three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit.
715 citations
Cites background from "Coastal morphodynamic evolution tec..."
...Strategies for morphological updating are described by Roelvink (2006)....
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TL;DR: In this paper, the authors discuss the morphodynamics of different units that characterize a tidal inlet system: the overall system, the ebb-tidal delta, the tidal channels, channel networks, tidal bars and meanders, and finally the intertidal zone of tidal flats and salt marshes.
Abstract: In this review we discuss the morphodynamics of tidal inlet systems that are typical of barrier coasts formed during a period of continuous sea-level rise during the Holocene. The morphodynamics concerns feedbacks between three major components: the hydrodynamics of tidal currents and wind waves; the erosion, deposition, and transport of sediment under the action of the former hydrodynamic agencies; and the morphology proper, which results from the divergence of the sediment transport. We discuss the morphodynamics of the different units that characterize a tidal inlet system: the overall system, the ebb-tidal delta, the tidal channels, channel networks, tidal bars and meanders, and finally the intertidal zone of tidal flats and salt marshes. In most of these units, stability analysis is a major guide to the establishment of equilibrium structures.
285 citations
TL;DR: In this paper, the authors investigated the long-term evolution of estuarine morphodynamics with special emphasis on the impact of pattern formation using a two-dimensional (2-D), numerical, process-based model.
Abstract: [1] The research objective is to investigate long-term evolution of estuarine morphodynamics with special emphasis on the impact of pattern formation. Use is made of a two-dimensional (2-D), numerical, process-based model. The standard model configuration is a rectangular 80 km long and 2.5 km wide basin. Equilibrium conditions of the longitudinal profile are analyzed using the model in 1-D mode after 8000 years. Two-dimensional model results show two distinct timescales. The first timescale is related to pattern formation taking place within the first decades and followed by minor adaptation according to the second timescale of continuous deepening of the longitudinal profile during 1600 years. The resulting longitudinal profiles of the 1-D and 2-D runs are similar apart from small deviations near the mouth. The 2-D results correspond well to empirically derived relationships between the tidal prism and the channel cross section and between the tidal prism and the channel volume. Also, comparison between the current model results and data from the Western Scheldt estuary (in terms of bar length, hypsometry, percentage of intertidal area and values for the ratio of shoal volume and channel volume against the ratio of tidal amplitude and water depth) shows satisfying agreement. On the basis of the model results a relationship for a characteristic morphological wavelength was derived on the basis of the tidal excursion and the basin width and an exponentially varying function was suggested for describing a dimensionless hypsometric curve for the basin. Furthermore, special attention is given to an analysis of the numerical morphodynamic update scheme applied.
248 citations
Cites methods from "Coastal morphodynamic evolution tec..."
...Roelvink [2006] compares a tide averaging method with continuity correction (RAM) to the ‘‘online’’ method and concludes that the ‘‘online’’ approach is most favorable....
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...The sensitivity tests carried out by Roelvink [2006] are based on tidal inlet geometry somewhat differing from the current research geometry....
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TL;DR: In this article, a review aims to promote the adoption of best practice in local scale assessments of potential physical impacts of climate change on open sandy coasts by summarising the potential first order physical impacts, suggesting a standard modelling framework for local scale CC impact assessments, identifying future research needs to facilitate the effective implementation of the prescribed modelling framework, and suggesting ways to address the identified research needs.
221 citations
Cites background or methods from "Coastal morphodynamic evolution tec..."
...Since the 1990s, there have been numerous attempts, using very different approaches, to overcome this problem (De Vriend et al., 1993; Dabees and Kamphuis, 2000; Hanson et al., 2003; Roelvink, 2006)....
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...When using currently popular morphological upscaling methods such as MORFAC (Roelvink, 2006; Ranasinghe et al., 2011) to accelerate morphodynamic evolution, such instabilities could growrapidly in time, eventually leading tononsensicalmodel predictions....
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TL;DR: In this paper, a physics-based morphological model for sand-bed braided rivers has been proposed to reproduce morphology and dynamics characteristic of braided river and determine the model sensitivity to generally used constitutive relations for flow and sediment transport.
Abstract: [1] Braided rivers have complicated and dynamic bar patterns, which are challenging to fully understand and to predict both qualitatively and quantitatively. Linear theory ignores nonlinear processes that dominate fully developed bars, whereas natural river patterns are determined by the combined effects of boundary conditions, initial conditions such as planimetric forcing by fixed banks and the physical processes. Here we determine the capability of a state-of-the-art physics-based morphological model to reproduce morphology and dynamics characteristic of braided rivers and determine the model sensitivity to generally used constitutive relations for flow and sediment transport. We use the 2-D depth-averaged morphodynamic model Delft3D, which includes the necessary spiral flow and bed slope effects on morphology. We present idealized scenarios with the smallest possible number of enforced details in the planform and boundary conditions in order to allow free development of bars driven by the physical processes in the model. We analyze bar and channel shapes and dynamics quantified by a number of complementary metrics and compare these with imagery, field data captured in empirical relations, flume experiments, and predictions by linear analyses. The results show that the chosen set of boundary conditions and physics in the numerical model is sufficient to produce many morphological characteristics and dynamics of a braided river but insufficient for long-term modeling. Initially, braiding intensity with low-amplitude bars is high in agreement with linear analysis. In a second stage when bars merge, split, and increase amplitude up to the water surface, the shape, size, and dynamics of individual bars compare well to those in natural rivers. However, long-term modeling results in a reduction of bar and channel dynamics and formation of exaggerated bar height and length. This suggests that additional processes, such as physics-based bank erosion, or enforced fluctuations in boundary conditions, such as spatial-temporal discharge variation, are necessary for the simulation of a dynamic equilibrium river. The most important outcome is that the modeled pattern of bars and channels is highly sensitive to the constitutive relation for bed slope effects that is used in many morphological models. Regardless of this sensitivity and present model limitations of many models, this study shows that physics-based modeling of sand-bed braided improves our understanding and prediction of morphological patterns and dynamics in sand-bed braided rivers.
156 citations
Cites background from "Coastal morphodynamic evolution tec..."
...Values reported in literature range from 1 (no acceleration) [e.g., Jang and Shimizu, 2005] to 10–25 [Crosato et al., 2011, 2012] to 40 [Roelvink, 2006] to 400 [Van der Wegen and Roelvink, 2008] and 500 [Lesser et al., 2004]....
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...Consequently, the bed level change within a hydrodynamic time step t is negligible even with MorFac >> 1 and the flow field adapts quickly to any change in bed topography [Roelvink, 2006; Crosato et al., 2011]....
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...Delft3D has been applied in a wide range of scientific projects for river, estuarine, and coastal systems [e.g., Roelvink, 2006; Van Maren, 2007; Van der Wegen and Roelvink, 2008; Crosato and Saleh, 2010; Crosato et al., 2011, 2012]....
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References
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TL;DR: The DELFT3D-FLOW module as discussed by the authors is a 3D flow solver for modeling sediment transport patterns in the water column of the DELFT-3D flow model, which is used to model both suspended and bedload transport of noncohesive sediment.
1,641 citations
TL;DR: In this article, the morphodynamic response of the nearshore zone of an embayed beach induced by wave groups is examined with a numerical model, which utilizes the nonlinear shallow water equations to phase resolve the mean and infragravity motions in combination with an advection-diffusion equation for the sediment transport.
Abstract: [1] The morphodynamic response of the nearshore zone of an embayed beach induced by wave groups is examined with a numerical model. The model utilizes the nonlinear shallow water equations to phase resolve the mean and infragravity motions in combination with an advection-diffusion equation for the sediment transport. The sediment transport associated with the short-wave asymmetry is accounted for by means of a time-integrated contribution of the wave nonlinearity using stream function theory. The two-dimensional (2-D) computations consider wave group energy made up of directionally spread, short waves with a zero mean approach angle with respect to the shore normal, incident on an initially alongshore uniform barred beach. Prior to the 2-D computations, the model is calibrated with prototype flume measurements of waves, currents, and bed level changes during erosive and accretive conditions. The most prominent feature of the 2-D model computations is the development of an alongshore quasi-periodic bathymetry of shoals cut by rip channels. Without directional spreading, the smallest alongshore separation of the rip channels is obtained, and the beach response is self-organizing in nature. Introducing a small amount of directional spreading (less than 2°) results in a strong increase in the alongshore length scales as the beach response changes from self-organizing to being quasi-forced. A further increase in directional spreading leads again to smaller length scales. The hypothesized correlation between the observed rip spacing and wave group forced edge waves over the initially alongshore uniform bathymetry is not found. However, there is a correlation between the alongshore length scales of the wave group-induced quasi-steady flow circulations and the eventual alongshore spacing of the rip channels. This suggests that the scouring associated with the quasi-steady flow induced by the initial wave groups triggers the development of rip channels via a positive feedback mechanism in which the small scour holes start attracting more and more discharge.
348 citations
TL;DR: In this article, the state-of-the-art in depth-averaged mathematical modelling of 3D coastal morphology is described for the medium-term morphodynamic model type, in which constituent models of waves, currents and sediment transport based on first physical principles are linked together to describe the time-evolution of the bed topography.
231 citations
TL;DR: In this paper, a two-dimensional horizontal morphodynamic model was developed, combining modules for hydrodynamics, waves, sediment transport and bathymetry updates, which supported the idea that the Arcachon lagoon is unlikely to be disconnected from the ocean, provided tide and wave conditions remain fairly constant in the following decades.
205 citations
TL;DR: Four methods aiming at the increase of the effective morphological time step are described and tested; as a matter of fact, they lead to quite cheaper computations, while the error specifically linked to this time schematization remains quite small.
163 citations