Morphodynamic modelling for a tidal inlet in the Wadden Sea (original) (raw)
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MORPHOLOGICAL MODELING OF A DANISH TIDAL INLET
Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007
This article presents the results obtained from the application of a recently developed coastal area morphological model to simulate the morphological response of a sandy spit/platform system to meteorological forcing of variable intensity. The morphological model applies an unstructured flexible mesh to resolve the bathymetry and allows fully dynamic coupling of and feedback between the modules used to simulate waves, water levels and fluxes, and sediment transport and bed level changes. Morphological changes predicted by the model are compared to available field measurements.
Morphodynamics of ebb-tidal deltas: a model approach
Estuar Coast Shelf Sci, 2003
The results of 2DH numerical models of the Frisian Inlet (located in the Dutch Wadden Sea) are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb-tidal deltas and of channels and shoals in tide-dominated inlet systems. A hydrodynamic model, extended with sediment transport formulations, was used to verify earlier conceptual models that deal with ebb-tidal delta characteristics. The model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb-tidal deltas and suggests that long-term morphological simulations are needed to understand this aspect. Furthermore, the model indicates that the initial formation of the ebb-tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents, whilst the net sediment transport in the basin is mainly caused by tidal asymmetry. A second model (accounting for feedbacks between tidal motion and the erodible bottom) was used to simulate the long-term bathymetric evolution of the Frisian Inlet under fair weather conditions. This model reproduces the gross characteristics of the observed morphology: the presence of a double-inlet system with two distinct ebb-tidal deltas having different sizes and the presence of channels and shoals. The role of the 'Engelsmanplaat', a consolidated shoal in the middle of the Frisian Inlet, was not found to be crucial for the morphodynamic stability of this inlet system.
Coastal Engineering, 2012
Morphodynamic response to an anthropogenic effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the effect of the initial distribution of sediment fractions is investigated.Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m...
Numerical Modelling of Morphodynamics Around a Tidal Inlet
Coastal Engineering Proceedings, 2014
A two-dimensional morphological model is used to study sediment transport and morphdynamics around a tidal inlet. The model includes the processes of erosion on side slope for the avalanching effects. The model has been tested against a laboratory study of an idealised tidal inlet configuration over 68 tidal cycles. The results show a reasonable agreement between the model and experiment measurements with a typical pattern of accretion at up-drift of the inlet and erosion at the down-drift. This study also reveals the importance of surface waves and cross-shore sediment transport to the evolution and migration of the tidal inlet.
Modelled channel patterns in a schematized tidal inlet
Coastal Engineering, 2009
Tidal inlets in the Dutch Wadden Sea show typical morphological features, i.e. westward oriented main inlet channel and ebb-tidal delta. The objective of this study is to find the governing physical processes of these morphological features. The study uses a 2DH process-based morphodynamic model (Delft3D) on a schematized model domain, with dimensions similar to the Ameland inlet in the Dutch Wadden Sea. Starting from a flat bed the models are forced by tides only. Short-term simulations are made to explore the hydrodynamic characteristics and initial sedimentation and erosion patterns. Long-term morphodynamic simulations are employed to investigate the governing parameters of the main inlet channel and the ebb-tidal delta evolution. Sensitivity of the evolution is described in terms of initial inlet width (1.0 km and 3.5 km), direction and asymmetry of tidal forcing (M 2 , M 4 ), transport formulations and relative position of the tidal basin with respect to the inlet (East (existing), Middle, and West). The results tend to produce morphological features typical to the Ameland inlet. The direction of tidal forcing is the main governing parameter to the present orientation of the main inlet channel and the ebb-tidal delta. The model results generally prove the conceptual hypotheses that describe the orientation of the main inlet channel and the ebbtidal delta.
The Proceedings of the Coastal Sediments 2011, 2011
Over the last decades, efforts have been undertaken to identify the equilibrium and stability state of tidal inlets and to model different morphological time scales and spatial scales of tidal inlet systems using data based models and behaviour based models . These include empirical relationships, such as the tidal prism cross-sectional area relationship ), closure criteria and semi-empirical long-term models such as ASMITA . But better understanding of the underlying processes of tidal inlet evolution toward equilibrium requires detailed information of the hydrodynamics and sedimentary processes at the tidal inlet and in the vicinity of the inlet on short-term and long-term time scales. For this purpose in this study, a processbased model (Delft3D) is used to simulate the morphological evolution of tidal inlets, including basin, ebb and flood delta, forced by various hydraulic conditions.
Long-term morphodynamic evolution of Texel Inlet and its ebb-tidal delta (The Netherlands)
A series of regular bathymetric surveys of Texel Inlet and its ebb-tidal delta spanning a period of over 400 years forms a unique long-term morphodynamic dataset of this largest inlet of the Wadden Sea. The substantial changes in ebb-tidal delta evolution provide a clear example of the response of the inlet system to the cumulative effects of human intervention. Analysis of the evolution of the ebb-tidal delta morphology shows different stages, each characterized by specific orientations of the main channels and shoals. Prior to construction of extensive coastal defense works on the southern shore of the inlet in 1750 A.D., the ebb-tidal delta showed a downdrift asymmetry. Periodic shoal breaching and downdrift channel relocation were the dominant mechanisms for sediment by-passing (major shoal bypassing). After construction of the coastal defence works, a stable ebb-tidal delta with a westward stretching main ebb-channel developed over a period of ca. 60 years. Damming of the Zuiderzee, the major part of the back-barrier basin in 1932 A.D., distorted this stable state and over a period of about 40 years the main channel switched to a southward course, remaining stable ever since. During the pre- and post-damming stable states the sediment bypassing took place as minor shoal by-passing; the main channel remained in position and smaller parts of the swash platform (periodically) migrated landward over the ebb-tidal delta. The well-monitored large-scale changes on the ebb-tidal delta which were initiated by the construction of the coastal defence works and closure of the Zuiderzee show that incorporation of inlet modifications and back-barrier processes is vital for a correct description of the ebb-tidal delta dynamics and processes of Texel Inlet. A conceptual model is introduced to describe the process–response relation between intervention and ebb-tidal delta change.
Modeling the morphodynamics of the mouth of the Scheldt estuary
2015
Recent research on the Scheldt estuary mainly focused on the Western Scheldt. There is now a renewed interest in the mouth of the estuary as the Flemish government explores the feasibility of large-scale morphological interventions in that area. This paper describes the ongoing development of a process-based numerical model (Delft3D) of the Scheldt estuary. The so-called Delft3D-NeVla model computes morphodynamics forced by waves, tide, wind and river discharge, and affected by sediment dredging and dumping to maintain navigation channels at the desired depth. After further calibration and validation, the Delft3D-NeVla model will become an important tool to understand and predict the morphodynamics of the mouth of the estuary due to natural processes and large-scale morphological interventions such as relocation of navigation channels.
Long-term morphological modeling of a tidal inlet: the Arcachon Basin, France
Coastal Engineering, 2001
The Arcachon Lagoon on the French Atlantic coast is a triangular shaped lagoon of 20 km on a side connected to the ocean by a 3-km wide inlet between the mainland and an elongated sand spit. This tidal inlet exhibits a particularly active morphology due to locally strong tidal currents and rough wave conditions. During the past 300 years, minimum and maximum spatial extents of the Cap Ferret sand spit have varied by 8 km while one or two channels have alternately allowed circulation between the lagoon and the ocean. These impressive morphological changes have never prevented regular flushing of the lagoon, eventhough the spit came as close as 300 m from the coast during the 18th century. According to w Ž. x Bruun's concept of tidal inlet stability Theory and Engineering 1978 , 510 pp. , the balance between longshore littoral transport and the tidal prism ensures the perpetuity of the inlet. Process modeling was believed to give better insight into the respective roles of tides and waves in driving the long-term morphological changes of the inlet. A two-dimensional horizontal morphodynamic model was therefore developed, combining modules for hydrodynamics, waves, sediment transport and bathymetry updates. The use of process models at a scale of decades requires a schematization of the input conditions. We defined representative mean annual wave and tide conditions with respect to sediment transport, i.e. conditions that induce the same annual transport as measured in the field. Driven by these representative conditions, simulations run from the 1993 bathymetry show that the tide is responsible for the Ž. opening of a new channel at the extremity of the sand spit where tidal currents are the strongest , while waves induce a littoral transport responsible for the longshore drift of sand bodies across the inlet. One particular simulation consisted in running the model from a hypothetical initial topography where the channels are filled with sand and the entire inlet is set to Ž. a constant depth 3 m. The results show the reproduction of a channel and bar system comparable to historical observations, which supports the idea that the lagoon is unlikely to be disconnected from the ocean, provided tide and wave conditions remain fairly constant in the following decades.
Morphodynamics of a storm-dominated, shallow tidal inlet: the Slufter, the Netherlands
Netherlands Journal of Geosciences, 2012
In this article we study the morphodynamics of the Slufter on the short-term (months) and long-term (years to decades). The Slufter is a small, shallow tidal inlet located on the island of Texel, the Netherlands. A narrow (tens of meters) channel connects the North Sea with a dune valley of 400 ha. This narrow channel is located in between a 400-700 m wide opening in the dunes. Approximately 80% of the basin of the Slufter is located above mean high water level and is flooded only during storms, when a threshold water level is exceeded.Analysis of historical aerial photographs revealed that the inlet channel migrates about 100 m per year. In the 1970's it migrated to the south, while since 1980 it is migrating to the north. When the channel reached the dunes at the north side of the dune breach the channel was relocated to the south by man. The channel inside the backbarrier basin was less dynamic. It shows a gradual growth and southward migration of a meander on a decadal time ...