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This study addresses the question whether the geomorphology of a tidal inlet (i.e. the coastal inlet and associated tidal basin) can maintain equilibrium under a rising relative sea level. When a tidal inlet system is exposed to a constant rate of sea-level rise (SLR), the system will be permanently in a state that deviates from the Equilibrium State corresponding to zero SLR. This is a physical requirement to create a permanent incentive to import sediment into the system. In case the rate of sediment import matches the rate of sea-level rise, a new state of dynamic morphological equilibrium is reached. If the actual import rate is less than this, the system’s morphological state will deviate increasingly from its equilibrium and finally degenerate. In this case SLR has exceeded an upper boundary (named ‘state limit’, denoted as SLRlimit), and the system will not be able to reach a state of dynamic morphological equilibrium any longer and drown. Because the SLRlimit predictions are sensitive to a variation of internal sediment exchange rate and availability of sediment at the seaward boundary of the system, we assess the SLRlimit predictions quasi-probabilistically to gain quantitative insight into the inherent uncertainties. This technique leads to an estimate of the probability distribution for the SLRlimit of two selected tidal inlet systems in the Dutch Wadden Sea. The calculated probabilities comply with the available fragmentary geological data, which suggest that the former tidal inlets in the western region of the Netherlands were drowned under the influence of a sea-level rise of 80 cm to a few metres per century.

The process-based morphodynamic model Delft3D-MOR and the idealized model of schuttelaars and De Swart (2000) are compared with each other. The differences between the two models in their mathematical-physical formulation as well as the boundary conditions are identified. Their effect on producing cross-sectionally averaged morphological equilibria of tidal inlets with arbitrary length and forced at the seaward boundary by a prescribed M 2 and M 4 sea- surface elevation is studied and an inventory is made of all relevant differences. The physical formulations in the source code of Delft3D-MOR are modified in various steps to resemble the formulations in the idealized model. The effect of each of the differences between the idealized and process-based model are studied by comparing the results of the idealized model to those of the adapted process-based model. The results of the idealized model can be qualitatively reproduced by the process-based model as long as the same morphological boundary condition is applied at the open sea end. This means that the simplifications concerning the mathematical formulation of the physical processes in the idealized model can be justified. Furthermore, it can be inferred that the morphological boundary condition at the open sea end is an essential element in controlling the behaviour of morphodynamic models for tidal inlets and estuaries.

Water injection dredging (WID) is a dredging technique by which the sediment to be removed is fluidised through low-pressure injection of water into the bed. Upon fluidisation, the mud flows as a density current away from the dredging site. In this paper the far-field effects of WID are evaluated—that is, the large-scale dispersion and deposition patterns of the mobilised sediments are determined. This is done with numerical simulations using a two-layered fluid mud model, which takes account of the effects of supercritical fluid mud flow, and for all mud exchange processes in the vertical direction. This model is applied to simulate a dredging work carried out in the River Crouch, UK. The agreement of the numerical results with observed patterns of dispersion and deposition is satisfactory. Next it is shown how this model can be used to evaluate alternative dredging strategies. With respect to the WID operations in the River Crouch, it is concluded that the far-field effects of the work are small.

Water diversions along alluvial rivers cause water and sediment loss, and thereby affect morphological development. Assuming spatially continuous diversions along a constant-width channel, previous studies suggest a longitudinally convex bed at the equilibrium state. However, the validity of a convex bed profile for practically discrete diversions in natural channels of longitudinally varying width remains to be justified. Moreover, such equilibrium analysis does not reveal the morphological time scale (MTS) associated with water diversions. To solve these issues, a general theoretical framework is proposed for predicting the equilibrium state of the fluvial system, which is applicable to both continuous and discrete water diversions in a longitudinally width-varying channel. Numerical experiments complement the MTS studies for water diversions. The effects of diversion intensity, diversion placement (discrete and continuous), and diversion scheme (pure water and water-sediment mixture) are also s...

River floods are usually featured by a downstream flattening discharge peak whereas a downstream increasing discharge peak is observed at a rate exceeding the tributary discharge during highly silt-laden floods (hyperconcentrated floods) in China's Yellow River. It entails a great challenge in the downstream flood defence and the underlying mechanisms need to be unravelled. Previous study on this issue only focuses on one possible mechanism, while the present work aims to reveal the relative importance of bed roughness change and bed erosion in the hyperconcentrated flood. Using a newly developed fully coupled morphodynamic model, we have conducted a numerical study for the 2004 hyperconcentrated flood in the Xiaolangdi-Jiahetan reach of the Lower Yellow River. In order to focus on the physical mechanism and to reduce uncertainty from low-resolution topography data, the numerical modeling was carried out in a schematized 1-D channel of constant width. The basic understanding that bed roughness decreases with concentration at moderate concentrations (e.g. several 10 s to 100 s g L−1) was incorporated by a simple power-law relation between Manning roughness coefficient and sediment concentration. The feedback between the bed deformation and the turbid flow, however, was fully accounted for, in the constituting equations as well as in the numerical solutions. The model successfully reproduced the downstream flood peak increase for the 2004 flood when considering the hyperconcentration-induced bed roughness reduction. As the hyperconcentration lags shortly behind the flood peak, later parts of the flood wave may experience less friction and overtake the wave front, leading to the discharge increase. In comparison, bed erosion is much less important to the discharge increase, at least for hyperconcentrated flood of moderate sediment concentration.

Based on model-technical as well as physical considerations a nodal-point relation at bifurcations is proposed for one-dimensional (ID) network morphodynamic models: the ratio between the sediment transports into the downstream branches is proportional to a power of the discharge ratio. The influence of the nodal-point relation on the behaviour of the morphodynamic model is analyzed theoretically. The exponent in the nodal-point relation appears to be crucial for the stability of the bifurcation in the model. For large values of the exponent, the bifurcation is stable, i.e. the downstream branches remain open. For small values of the exponent, the bifurcation is unstable: only one of the branches tends to remain open. The exponent also has a strong influence on the morphological time scales of the network. The conclusions from the analysis have been verified by numerical simulations using a package for one-dimensional network modelling.

A dynamic model for morphological development in a tidal inlet, “Het Friesche Zeegat”, in the Wadden Sea along the northern coast of the Netherlands, is set up to obtain a better understanding of the behaviour of the morphological system around tidal inlets. The model is based on delmor , a program package for morphological changes, developed at Delft Hydraulics. Computations of the flow, the sediment transport, the initial bed level change rate as well as long-term morphological development have been carried out. The model has proven to be a useful research tool, even though it does not yet reproduce reality in detail.

Large hydrodynamic and morphodynamic changes have taken place in the western Dutch Wadden Sea due to the closure of the Zuider Sea in the early 1930s. Hydrodynamic simulations for three situations, viz. just before the closure, just after the closure and at present, have been carried out in order to investigate the hydrodynamic changes since the closure and to improve our understanding of the observed morphodynamic changes. The model results show a large increase in tidal range after the closure of the Zuider Sea. This increase continued to grow after the closure due to bathymetric change and sea level rise. The morphodynamic analysis focuses on the changed behavior of the ebb-tidal deltas of the Texel Inlet and the Vlie Inlet. Both ebb-tidal deltas have undergone a re-orientation in up-drift direction. Two possible explanations based on the literature for this change are discussed with the help of the hydrodynamic simulations.

The depth-integrated model for suspended sediment transport based on the asymptotic solution of the convection-diffusion equation developed by Galappatti (Galappatti and Vreugdenhil, 1985) is gener...

The morphodynamic system in alluvial, coastal plain estuaries is complex and characterized by various timescales and spatial scales. The current research aims to investigate the interaction between these different scales as well as the estuarine morphodynamic evolution. Use is made of a process-based, numerical model describing 2-D shallow water equations and a straightforward formulation of the sediment transport and the bed level update. This was done for an embayment with a length of 80 km on a timescale of 3200 years, with and without bank erosion effects. Special emphasis is put on analyzing the results in terms of energy dissipation. Model results show that the basins under consideration evolve toward a state of less morphodynamic activity, which is reflected by (among others) relatively stable morphologic patterns and decreasing deepening and widening of the basins. Closer analysis of the tidal wave shows standing wave behavior with resonant characteristics. Under these conditions, results suggest that the basins aim for a balance between the effect of storage and the effect of fluctuating water level on wave celerity with a negligible effect of friction. Evaluating the model results in terms of energy dissipation reflects the major processes and their timescales (pattern formation, widening, and deepening). On the longer term the basin-wide energy dissipation decreases at a decreasingly lower rate and becomes more uniformly distributed along the basin. Analysis by an entropy-based approach suggests that the forced geometry of the configurations prevents the basins from evolving toward a most probable state.

To investigate the near-field and far-field hydrodynamic conditions along the Jiangsu Coast in large scale, a two-dimensional tidal wave model which covers the Bohai Sea, the Yellow Sea and the East China Sea is developed and validated. After a brief review of previous models, some influencing factors, such as tide generating force, river discharges as well as shoreline changes due to land reclamation, are examined in this study. We suggest that whether these factors should be considered in the model depends on the different purposes and geographical regions of interest. Then, a series of experiments are designed to further investigate the previously proposed important factors of influence [i.e. local bathymetry and the role of Shandong Peninsula (SDP)] on the tidal motions in the Yellow Sea. The numerical experimental results show that the interaction between the tidal wave system in the northern Yellow Sea and the incoming tidal wave plays a main role on the formation of the rotating tidal wave system in the southern Yellow Sea, whereas the role of geometric position of the SDP is secondary. With respect to the tidal current, it is found that the radial shape of it is independent of the local bathymetry, but may be generated by the convergent tidal wave formed by the meeting of the rotating tidal wave in the southern Yellow Sea and the incoming tidal wave from the East China Sea. Furthermore, a certain water depth is crucial for the intensity of current velocity to generate the special topography of radial sand ridges.

[1] A three-dimensional hydrodynamic and sediment transport model was used to study the relative impact of (1) vegetation, (2) micro-topography, and (3) water level fluctuations on the spatial flow and sedimentation patterns in a tidal marsh landscape during single inundation events. The model incorporates three-dimensional (3-D) effects of vegetation on the flow (drag and turbulence). After extensive calibration and validation against field data, the model showed that the 3-D vegetation structure is determinant for the flow and sedimentation patterns. As long as the water level is below the top of the vegetation, differences in flow resistance between vegetated and unvegetated areas result in faster flow routing over unvegetated areas, so that vegetated areas are flooded from unvegetated areas, with flow directions more or less perpendicular to the vegetation edge. At the vegetation edge, flow velocities are reduced and sediments are rapidly trapped. In contrast, in between vegetated areas, flow velocities are enhanced, resulting in reduced sedimentation or erosion. As the water level overtops the vegetation, the flow paths described above change to more large-scale sheet flow crossing both vegetated and unvegetated areas. As a result, sedimentation patterns are then spatially more homogeneous. Our results suggest that the presence of a vegetation cover is the key factor controlling the long-term geomorphic development of tidal marsh landforms, leading to the formation of (1) unvegetated tidal channels and (2) vegetated platforms with a levee-basin topography in between these channels.

Biological activity is known to influence sediment strength at bed-water interfaces. However, its precise effect on geomorphology and on bed composition is not known. This paper proposes a parameterization of sediment destabilizing and stabilizing organisms on three parameters that describe the erosion and mixing processes of the sediment bed, namely the critical bed shear stress, the erosion coefficient and the bioturbation coefficient. This parameterization is included in a 3D sand-mud morphodynamic model to form the sand-mud-bio model. The performance of the sand-mud-bio model is demonstrated by testing it on the Paulinapolder intertidal flat in the Western Scheldt estuary of The Netherlands. Model results show that biological influences on sediment strength result in significant morphological change and bed composition variations. Destabilizing organisms always cause a significant decrease in mud content in the bed and an increase of erosion. On the other hand, stabilizing organisms can, but do not necessarily, cause an increase of mud content and additional sedimentation.

We model branching channel patterns in short tidal basins with two methods. A theoretical stability analysis leads to a relationship between the number of channels and physical parameters of the tidal system. The analysis reveals that width and spacing of the channels should decrease as the slope of the bottom profile and the Shields parameter increase and as the mean water depth decreases. In general, the channel depth should halve at every bifurcation. These theoretical results agree well with the field data from the Dutch Wadden Sea. A numerical model based on Delft3D, a software system of WL/Delft Hydraulics, is used to simulate the time evolution of a channel network in a geometrically simplified basin of similar dimensions as the Wadden Sea basins. The resulting channel network displays a three-times branching behavior, similar to the three- to four-times branching patterns observed in the Wadden Sea. The simulated channel pattern satisfies the relation derived from the theoretical analysis. The results of this pattern analysis provide for additional validation of two-dimensional/three-dimensional process-based morphodynamic models of tidal basins.

The morphology of the Eastern Scheldt inlet in the southwestern Netherlands has been changing for the past 25 years in response to the construction of the Eastern Scheldt storm-surge barrier in 198...

The scientific objective of the work is to develop a quantitative understanding of the processes that control the formation of marine stratigraphy over time scales ranging from decades to millennia. This work is based on the creation and application of a series of advanced numerical models representing the dynamics of marine sediment transport, sediment accumulation, morphological change and feedback between the evolving sea floor and the hydrodynamic forcing. Field data are used to both force the models and to verify their results. The models are used to diagnose complex systems and as predictive tools.

The influence of sand and mud transport on the morphological behaviour of a short tidal basin is investigated in this paper. For this purpose, a morphological model is applied in which sand and mud transport are included and the temporal and spatial bed composition variations are taken into account. Initially, the morphological development shows a sand wave near the entrance of the basin and a mud deposition wave more landward. A quasi equilibrium bed level profile is found after a long period (order century) with a sandy bed surface over almost the entire basin and only a small muddy area near the landward end. The dimensionless ratio between the deposition and erosion flux turns out to be a crucial parameter for the understanding of the observed behaviour. Comparison with previous studies on short tidal basins for sand indicates only that the presence of mud in a combined sand mud model does not change the equilibrium bed level profile considerably for the applied parameter settings herein, but drastically decreases the morphological time scale. Comparison between model results and field data of the Wadden Sea suggests that the obtained bed level and bed composition profile are realistic, indicating that the process-based sand mud model is a first step towards a better understanding of sand mud distributions in tidal basins.

Publisher Summary This chapter discusses the morphodynamic evolution of tidal basins and coastal inlets, which is a complex issue. Due to the complexity, scientific attention is spent on uninterrupted coasts and rivers. Ecologically and socio-economically tidal basins and coastal inlets are of high importance. The derivation in the chapter explains that tidal basins with relatively shallow channels require relatively wide flats, and that tidal basins with relatively deep channels require relatively narrow flats to create zero asymmetry-induced sand transport, thus promoting dynamic equilibrium. By accepting these semi-empirical observations of dynamic equilibrium, an aggregated-scale model assesses the macroscale response of tidal basins and ebb-tidal deltas to natural and human forcing. Morphodynamic response of tidal basins consists of a complex mix of several time scales, which may differ in the order-of-magnitude.

The supply of cohesive sediment of marine origin to the entrance area of the harbour of Rotterdam is simulated with a three-dimensional model for the transport of suspended fine sediment. The model reproduces observed transport phenomena. The possible reclamation of land in this area could have a large influence on the transport of suspended fine sediment. Model results of the import of suspended fine sediment into the harbour of Rotterdam in the present situation have been compared to results of calculations in the situation in case of land reclamation.

The channels in the Yangtze Estuary have an ordered-branching structure: The estuary is first divided by the Chongming Island into the North Branch and the South Branch. Then the South Branch is divided into the North Channel and South Channel by the Islands Changxing and Hengsha. The South Channel is again divided into the North and South Passage by the Jiuduansha Shoal. This three-level bifurcation and four-outlet configuration appears to be a natural character of the estuary, also in the past (Chen et al., 1982), although the whole system has been extending into the East China Sea in the southeast direction due to the abundant sediment supply from the Yangtze River. Recently, the natural development of the system seems to be substantially disturbed by human interferences, especially the Deep Navigation Channel Project. For the understanding of the behaviour of the bifurcating channel system in the estuary we present analysis on two aspects: (1) the equilibrium configuration of river delta distributary networks, and (2) influence of tidal flow on the morphological equilibrium of rivers. Based on the analyses we conclude that the branching channel structure of the Yangtze Estuary can be classified as tide-influenced river delta distributary networks. Its basic structure is the same as in case of river dominated delta. The empirical relations describing the basic features of the river-dominated distributary delta networks can be explained by theoretical analysis, although they are not fully satisfied by the Yangtze Estuary because of the influence of the tide. Two major influences of the tide are identified, viz. increasing the resistance to the river flow into the sea and increasing the sediment transport capacity. As consequence of these two influences the cross-sectional area of the river/estuary increases in the seawards direction and the bed slope decreases. The insights from the analyses are helpful for the understanding of the impact of the Deep Navigation Channel Project on the large scale morphological development of the estuary.

A process-based model for the Yangtze Estuary is constructed to study the sediment transport in the estuary. The proposed model covers the entire tidal region of the estuary, the Hangzhou Bay and a large part of the adjacent sea. The dominant processes, fluvial and tidal, are included in the model. The calibration of the model against extensive flow, water level, salinity and suspended sediment data shows a good representation of observed phenomena. With the present calibrated and validated model, the residual flow field and the residual sediment transport field are obtained. The residual sediment transport pattern gives insight into the morphological behaviour of the mouth bars.

Based on an asymptotic solution of the two-dimensional convection-diffusion equation. Galappatti [2] developed a depth-integrated model for suspended sediment transport. In the present study, a the...

The availability of nearly 100 years of bathymetric measurements allows the analysis of the morphodynamic evolution of the Dutch Wadden Sea under rising sea level and increasing human constraint. The historically observed roll-over mechanisms of landward barrier and coastline retreat cannot be sustained naturally due to numerous erosion control measures that have fixed the tidal basin and barrier dimensions. Nevertheless, the large continuous sedimentation in the tidal basins (nearly 600 million m3), the retained inlets and the similar channel-shoal characteristics of the basins during the observation period indicate that the Wadden Sea is resilient to anthropogenic influence, and can import sediment volumes even larger than those needed to compensate the present rate of sea-level rise. The largest sedimentation occurs in the Western Wadden Sea, where the influence of human intervention is dominant. The large infilling rates in closed-off channels, and along the basin shoreline, rather than a gradual increase in channel flat heights, render it likely that this sedimentation is primarily a response to the closure of the Zuiderzee and not an adaptation to sea-level rise. Most of the sediments were supplied by the ebb-tidal deltas. It is, however, unlikely that the sediment volume needed to reach a new equilibrium morphology in the Western Wadden Sea can be delivered by the remaining ebb-tidal deltas alone.

The evolution of the ebb-tidal delta of the Eastern Scheldt tidal basin has changed dramatically in response to the construction of the storm-surge barrier in the inlet, which was finished in 1986. A process-based numerical model has been constructed using the Delft3D modeling system in order to investigate the effects of the barrier on the hydrodynamics and sediment transports on the ebb-tidal delta. Comparison between measurements and model output shows that the model is able to adequately reproduce the dominant features of the tide. Results show that the barrier has caused a general decrease of morphological activity due to the decreased tidal flows and absence of sediment supply from the basin.

In the South Yellow Sea off the Jiangsu coast, there exists a special type of sand bodies, which are known as radial sand ridge field (RSRF). One of the characteristics of this area is the distinctive radial tidal current field. Although many studies have focused on the hydrodynamic environment around radial sand ridges, the knowledge on the genesis of the radial tidal current is still in a very basic stage. This paper attempts to explore the influence of the tidal dynamics in large Shelf Sea on the formation mechanism of the local tidal current pattern using a schematized process-based model. Different incoming tidal signals are applied in this model respectively to investigate the related current pattern in RSRF. The results reveal that the radial current field only exists under some specified tidal signals from open sea. Furthermore, the geometry of the basin also plays a significant role in the formation of the current pattern.

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A two-dimensional tidal wave model for the Chinese marginal seas with high resolution is set up and the verification results demonstrate that it can well simulate the large domain. Based on this model, a series of numerical experiments are constructed to analyze the influence of local bathymetry and reclamation of the Jiangsu coast on the tidal wave system. According to the simulation results, the existence of the radial tidal current pattern have not been obviously influenced by the local bathymetry except the magnitude of the current velocity. However, it effects the tidal wave near the Jiangsu coast considerably. The reclamation affects the radial current field slightly, whereas the tidal wave near the southern Jiangsu coast is impacted significantly. Besides, further experiments by adding thin dam in the Southern Yellow Sea are studied and discussed. The results illustrate the existence of the tidal wave from the Northern Yellow Sea, which is important for the formation of the rotating tidal wave system in the Southern Yellow Sea.

The Rif and the Engelsmanplaat form together a supra- to intertidal flat-complex at the fringe of the ebb-tidal delta and the back barrier area in the Frisian Inlet, located between the Dutch Wadden Sea Islands Ameland and Schiermonnikoog. The complex divides the Frisian Inlet into the Pinkegat Inlet in the west and the Zoutkamperlaag Inlet in the east. During the last decades the Engelsmanplaat has been suffering from serious erosion. This paper presents a study meant to find the causes for the recent erosion, especially to answer the question if the erosion is related to the human interferences in the area. The study is based on literature survey, data analysis and modelling of hydrodynamic processes. It is concluded that the recent erosion fits into the pseudo-cyclic development of the intertidal flat complex. However, the period of erosion may have been longer than normal and the rate of erosion may have been higher than normal. It is also concluded that such abnormal development is probably effects of the closure of the Lauwerszee in 1969 and not due to land subsidence caused by gas mining.