Long‐term evolution and morphodynamic equilibrium of tidal channels

doi:10.1029/2000JC000468

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Long‐term evolution and morphodynamic equilibrium of tidal channels

Journal Article•DOI•

Long‐term evolution and morphodynamic equilibrium of tidal channels

Stefano Lanzoni¹, Giovanni Seminara²•Institutions (2)

University of Padua¹, University of Genoa²

01 Jan 2002-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 107, pp 1-1-1-13

TL;DR: In this article, the morphodynamic equilibrium of funnel-shaped well-mixed estuaries and/or tidal channels is investigated for the ideal case of a frictionally dominated estuary consisting of noncohesive sediment and with insignificant intertidal storage of water in tidal flats and salt marshes.

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Abstract: [1] This contribution investigates the morphodynamic equilibrium of funnel-shaped well-mixed estuaries and/or tidal channels. The one-dimensional de Saint Venant and Exner equations are solved numerically for the ideal case of a frictionally dominated estuary consisting of noncohesive sediment and with insignificant intertidal storage of water in tidal flats and salt marshes. This class of estuaries turns out to be invariably flood dominated. The resulting asymmetries in surface elevations and tidal currents lead to a net sediment flux within a tidal cycle which is directed landward. As a consequence, sediments are trapped within the estuary and the bottom profile evolves asymptotically toward an equilibrium configuration, allowing a vanishing net sediment flux everywhere and, in accordance with field observations, a nearly constant value of the maximum flood/ebb speed. Such an equilibrium bed profile is characterized by a concavity increasing as the estuary convergence increases and by a uniquely determined value of the depth at the inlet section. The final length of the estuary is fixed by the longitudinal extension of the very shallow area which tends to form in the landward portion of the estuary. Note that sediment advection is neglected in the analysis, an assumption appropriate to the case of not too fine sediment.

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Journal Article•DOI•

Landscape evolution in tidal embayments: Modeling the interplay of erosion, sedimentation, and vegetation dynamics

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Andrea D'Alpaos¹, Stefano Lanzoni¹, Marco Marani¹, Andrea Rinaldo¹•Institutions (1)

University of Padua¹

01 Mar 2007-Journal of Geophysical Research

TL;DR: In this article, an ecomorphodynamic model was proposed to investigate the response of tidal morphologies to different scenarios of sediment supply, colonization by halophytes, and changing sea level.

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Abstract: We propose an ecomorphodynamic model which conceptualizes the chief land-forming processes operating on the intertwined, long-term evolution of marsh platforms and embedded tidal networks. The rapid network incision (previously addressed by the authors) is decoupled from the geomorphological dynamics of intertidal areas, governed by sediment erosion and deposition and crucially affected by the presence of vegetation. This allows us to investigate the response of tidal morphologies to different scenarios of sediment supply, colonization by halophytes, and changing sea level. Different morphological evolutionary regimes are shown to depend on marsh ecology. Marsh accretion rates, enhanced by vegetation growth, and the related platform elevations tend to decrease with distance from the creek, measured along suitably defined flow paths. The negative feedback between surface elevation and its inorganic accretion rate is reinforced by the relation between plant productivity and soil elevation in Spartina-dominated marshes and counteracted by positive feedbacks in multispecies-vegetated marshes. When evolving under constant sea level, unvegetated and Spartina-dominated marshes asymptotically tend to mean high water level (MHWL), different from multiple vegetation species marshes, which can make the evolutionary transition to upland. Equilibrium configurations below MHWL can be reached under constant rates of sea level rise, depending on sediment supply and vegetation productivity. Our analyses on marine regressions and transgressions show that when the system is in a supply-limited regime, network retreat and expansion (associated with regressions and transgressions, respectively) tend to be cyclic. Conversely, in a transport-limited regime, network reexpansion following a regression tends to take on a new configuration, showing a hysteretic behavior. Copyright 2007 by the American Geophysical Union.

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307 citations

Cites background from "Long‐term evolution and morphodynam..."

...…mechanism exists according to which sediment transport processes, influenced by the hydrodynamic field, produce changes in the elevation of the marsh platform, which in turn modify both the hydrodynamics and sediment dynamics [e.g., French, 1993; Lanzoni and Seminara, 2002; Mudd et al., 2004]....
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...In fact, a feedback mechanism exists according to which sediment transport processes, influenced by the hydrodynamic field, produce changes in the elevation of the marsh platform, which in turn modify both the hydrodynamics and sediment dynamics [e.g., French, 1993; Lanzoni and Seminara, 2002; Mudd et al., 2004]....
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Journal Article•DOI•

Morphodynamics of Tidal Inlet Systems

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H.E. de Swart¹, J. T. F. Zimmerman•Institutions (1)

Utrecht University¹

01 Jan 2009-Annual Review of Fluid Mechanics

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.

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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.

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285 citations

Landscape evolution in tidal embayments: modeling the interplay of erosion, sedimentation, and vegetation dynamics

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Andrea D'Alpaos¹, Stefano Lanzoni¹, Marco Marani¹, Andrea Rinaldo¹•Institutions (1)

University of Padua¹

01 Dec 2006

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276 citations

Journal Article•DOI•

Long‐term morphodynamic evolution of a tidal embayment using a two‐dimensional, process‐based model

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M. van der Wegen¹, J.A. Roelvink¹•Institutions (1)

UNESCO-IHE Institute for Water Education¹

01 Mar 2008-Journal of Geophysical Research

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.

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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.

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248 citations

Cites background or methods or result from "Long‐term evolution and morphodynam..."

...[98] The water level boundary was used since it makes comparison possible with earlier research by Lanzoni and Seminara [2002] , Hibma et al. [2003a] and Schuttelaars and De Swart [1996, 2000]....
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...They found good agreement with earlier results from a width-averaged one-dimensional (1-D) mathematical model by Lanzoni and Seminara [2002] ....
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...Vriend [1994], Friedrichs and Aubrey [1996], Schuttelaars and De Swart [1996, 2000], Lanzoni and Seminara [2002] and Hibma et al. [2003a] showed that morphodynamic equilibrium can be reached using 1-D models that include width-averaged longitudinal depth profiles....
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...Despite the recognition of these processes, for their model Lanzoni and Seminara [2002] finally choose for formulations of the bed and suspended load transports based on local and instantaneous flow conditions, because their analysis showed that these formulations would be justified at least in terms of leading order effects....
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...[42] Lanzoni and Seminara [2002] included a formulation for wetting and drying of intertidal area and solved the set of shallow water equations in a similar numerical approach as in the current research, although they assumed a different basin geometry with a landward exponentially decaying shape, included both bed load and suspended load transport, applied a different description for drying and flooding and did not extend their duration ......
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Journal Article•DOI•

Tidal network ontogeny: Channel initiation and early development

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Andrea D'Alpaos¹, Stefano Lanzoni¹, Marco Marani¹, Sergio Fagherazzi², Andrea Rinaldo¹ - Show less +1 more•Institutions (2)

University of Padua¹, Florida State University²

01 Jun 2005-Journal of Geophysical Research

TL;DR: In this article, a mathematical model of early development of a tidal channel network is presented, which is assumed to act on timescales considerably shorter than those of other landscape-forming ecomorphodynamical processes of tidal systems.

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Abstract: [1] The long-term morphological evolution of tidal landforms in response to physical and ecological forcings is a subject of great theoretical and practical importance. Toward the goal of a comprehensive theoretical framework suitable for large-scale, long-term applications, we set up a mathematical model of tidal channel network initiation and early development, which is assumed to act on timescales considerably shorter than those of other landscape-forming ecomorphodynamical processes of tidal systems. A hydrodynamic model capable of describing the key landforming features in small tidal embayments is coupled with a morphodynamic model which retains the description of the main physical processes responsible for tidal channel initiation and network ontogeny. The overall model is designed for the further direct inclusion of the chief ecomorphological mechanisms, e.g., related to vegetation dynamics. We assume that water surface elevation gradients provide key elements for the description of the processes that drive incision, in particular the exceedance of a stability (or maintenance) shear stress. The model describes tidal network initiation and its progressive headward extension within tidal flats through the carving of incised cross sections, where the local shear stress exceeds a predefined, possibly site-dependent threshold value. The model proves capable of providing complex network structures and of reproducing several observed characteristics of geomorphic relevance. In particular, the synthetic networks generated through the model meet distinctive network statistics as, among others, unchanneled length and area probability distributions. Copyright 2005 by the American Geophysical Union.

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193 citations

Cites background from "Long‐term evolution and morphodynam..."

...It is interesting to note (Figure 16) that although the seaward growth of B(s) cannot be conclusively linked to an exponential trend as in some field sites [Lanzoni and Seminara, 2002; Marani et al., 2002], it is reasonable to assume such a functional relationship....
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...…tidal channels [e.g., Boon and Byrne, 1981; French and Stoddart, 1992; Friedrichs, 1995; Friedrichs et al., 1998; Schuttelaars and de Swart, 2000; Lanzoni and Seminara, 2002], morphometric analyses of tidal networks [e.g., Myrick and Leopold, 1963; Pestrong, 1965, 1972; Leopold et al., 1993;…...
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...Tidal channels, in fact, quite often exhibit a nearly exponential landward decrease in width [e.g., Myrick and Leopold, 1963; Lanzoni and Seminara, 2002; Marani et al., 2002]....
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..., 2004], the consequences of tidal currents and asymmetries on sediment dynamics and other morphological characteristics of tidal channels [e.g., Boon and Byrne, 1981; French and Stoddart, 1992; Friedrichs, 1995; Friedrichs et al., 1998; Schuttelaars and de Swart, 2000; Lanzoni and Seminara, 2002], morphometric analyses of tidal networks [e....
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...Tidal channels, in fact, quite often exhibit a nearly exponential landward decrease in width [e.g., Myrick and Leopold, 1963; Lanzoni and Seminara, 2002; Marani et al., 2002]....
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References

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Book•

numerical-computation-of-internal-and-external-flows

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Charles Hirsch

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An Approach to the Sediment Transport Problem from General Physics (1966)

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Other•DOI•

An approach to the sediment transport problem from general physics

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R. A. Bagnold

01 Jan 1966

1,796 citations

"Long‐term evolution and morphodynam..." refers background in this paper

...…lower than a second threshold value qcs, depending on the particle Reynolds number Rptð ffiffiffiffiffiffiffiffiffiffiffiffiffi gd s 3 p =n, with n kinematic viscosity of water), which defines the threshold condition for entrainment in suspension [Bagnold, 1966; Engelund, 1965; van Rijn, 1984b]....
[...]

Journal Article•DOI•

Sediment transport; Part I, Bed load transport

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van Rijn, C Leo

01 Oct 1984-Journal of Hydraulic Engineering

TL;DR: In this article, a method is presented which enables the computation of the bed-load transport as the product of the saltation height, the particle velocity and the bed load concentration.

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Abstract: A method is presented which enables the computation of the bed-load transport as the product of the saltation height, the particle velocity and the bed-load concentration. The equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity. Experiments with gravel particles (transported as bed load) are selected to calibrate the mathematical model using the lift coefficient as a free parameter. The model is used to compute the saltation heights and lengths for a range of flow conditions. The computational results are used to determine simple relationships for the saltation characteristics. Measured transport rates of the bed load are used to compute the sediment concentration in the bed-load layer. A simple expression specifying the bed-load concentration as a function of the flow and sediment conditions is proposed. A verification analysis using about 600 (alternative) data shows that about 77% of the predicted bed-load-transport rates are within 0.5 and 2 times the observed values.

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1,653 citations

Journal Article•DOI•

Sediment Transport, Part II: Suspended Load Transport

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Leo C. van Rijn

01 Nov 1984-Journal of Hydraulic Engineering

TL;DR: In this article, a method is presented which enables the computation of the suspended load as the depth-integration of the product of the local concentration and flow velocity, based on the calculation of the reference concentration from the bed-load transport.

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Abstract: A method is presented which enables the computation of the suspended load as the depth-integration of the product of the local concentration and flow velocity. The method is based on the computation of the reference concentration from the bed-load transport. Measured concentration profiles have been used for calibration. New relationships are proposed to represent the size gradation of the bed material and the damping of the turbulence by the sediment particles. A verification analysis using about 800 data shows that about 76% of the predicted values are within 0.5 and 2 times the measured values.

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1,564 citations

"Long‐term evolution and morphodynam..." refers background or methods in this paper

...…approximation, which allows us to calculate the mean total sediment flux by means of classical relationships [e.g., Engelund and Hansen, 1967; van Rijn, 1984b] established for uniform free surface flows, evaluated in terms of the local instantaneous conditions determined at each cross section by…...
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...[24] Various relationships have been proposed in the literature to quantify the bed load transport rate in rivers [e.g., Meyer-Peter and Müller, 1948; van Rijn, 1984a]....
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...…lower than a second threshold value qcs, depending on the particle Reynolds number Rptð ffiffiffiffiffiffiffiffiffiffiffiffiffi gd s 3 p =n, with n kinematic viscosity of water), which defines the threshold condition for entrainment in suspension [Bagnold, 1966; Engelund, 1965; van Rijn, 1984b]....
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