Morphodynamics of a storm-dominated, shallow tidal inlet: the Slufter, the Netherlands (original) (raw)
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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.
Quantification of dune dynamics during a tidal cycle in an inlet channel of the Danish Wadden Sea
Geo-Marine Letters, 2006
High-resolution swath bathymetry measurements at centimetre-scale precision conducted during a tidal cycle in the Grådyb tidal inlet channel in the Danish Wadden Sea reveal the short-term dynamics of a large, ebbdirected compound dune with superimposed small to medium dunes, all composed of medium sand. Dune dynamics were related to simultaneous measurements of flow using an acoustic Doppler current profiler. Spatially, dune crests displayed greater mobility than did dune troughs, due to higher flow velocities at the crests than in the troughs. Temporally, superimposed lower lee-side dunes migrated more during the flood than the ebb tide, due to higher near-bed trough flow velocities during the flood phase, resulting in varying exposure to flow. Net dune migration was flood-directed over the tidal cycle, despite annual net migration being ebb-directed. Hence, extrapolation of short-term migration rates is not possible in this case. The superimposed dunes reversed direction during each half tidal cycle whereas the compound dune only developed a flood cap during flood tide, i.e. the time required for complete reversal of the compound dune was much longer than that available in a half tidal cycle. Over the tidal cycle, the bed level was stable but significant erosion and accretion occurred during the tidal phases. During the ebb tide, bed material was brought into suspension with accelerating flow and settled with decelerating flow, resulting in an average erosion and accretion of the bed of ∼7 cm in each case. During the flood tide, the bed of the compound dune was overall stable, although bed material was eroded from the exposed lower lee side, being partly transported to the crest in bedload and partly brought into suspension. In general, dune height fluctuated during the tidal cycle whereas dune length remained stable. The height of the compound dune responded to changes in water depth, which acts as a limiting factor to dune growth. By contrast, the height of the stoss-side dunes responded to flow velocity, i.e. the stoss-side dunes were water depth-independent.
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.
Ebb and Flood Channel Systems in the Netherlands Tidal Waters
The present paper, ‘‘Eb- en vloedschaarsystemen in de Nederlandse getijwateren’’ (Ebb- and Flood-Channel Systemsin the Dutch Tidal Waters), which was published in 1950, should be considered as Van Veen’s most important publication since his thesis. It summarizes the results of 20 years of intensive study of estuarine and tidal-basin mor-phodynamics in The Netherlands. Unfortunately, Van Veen’s paper was published in Dutch, with only a brief summary in English. Luckily, the figure captions were given in both Dutch and English, allowing international researchers coming across the paper to read it as a kind of ‘‘cartoon.’’ Understandably though, the paper has received very limited recognition in the international literature. We have seized this occasion to publish an English version of Van Veen’s paper. The paper is testimony to Van Veen’s keen observational and artistic skills. His approach is nearly ‘‘Da Vincian,’’ in the sense that he is not only a fascinated observer of nature, but a sharp one as well, and he tries to capture the essentials of the dynamic behavior of complex coastal systems in apparently simple sketches. Many of the natural systems that Van Veen studied have been regulated since; thus, this paper contains a set of irreplaceable, high-quality observations on the natural dynamics of tidal systems. It forms an excellent introduction to the study of channel dynamics in estuaries, tidal inlets, and tidal basins.
Netherlands Journal of Geosciences, 2017
Tidal inlets and the associated ebb-tidal deltas can significantly impact the coastal sediment budget due to their ability to store or release large quantities of sand. Nearly 300 million m3 (mcm) of sediments were eroded from Texel Inlet's ebb-tidal delta and the adjacent coasts following the closure of the Zuiderzee in 1932. This erosion continues even today as a net loss of 77 mcm was observed between 1986 and 2015. To compensate, over 30 mcm of sand has been placed on the adjacent coastlines since 1990, making maintenance of these beaches the most intensive of the entire Dutch coastal system.Highly frequent and detailed observations of both the hydrodynamics and morphodynamics of Texel Inlet have resulted in a unique dataset of this largest inlet of the Wadden Sea, providing an opportunity to investigate inlet sediment dynamics under the influence of anthropogenic pressure. By linking detailed measurements of bathymetric change to direct observations of processes we were abl...
Hydrodynamics and morphodynamics of tidal channels
This chapter analyzes the macro-scale morphological properties of a real estuary. In particular, we intend to determine the most relevant parameters to characterize the Western Scheldt estuary, by focussing the attention on the description of its morphological elements. In the subsequent chapters we will often refer to it as a reference case.
Morphodynamic modelling for a tidal inlet in the Wadden Sea
Marine Geology, 1995
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.
Island-terminus evolution related to changing ebb-tidal-delta configuration: Texel, The Netherlands
Marine Geology, 2006
Historical maps of southwest Texel and the adjacent ebb-tidal delta, supplemented with quartz OSL (Optically Stimulated Luminescence) ages of dune sand, span four centuries and show several links between coastal development and ebb-tidal-delta behavior. Updrift inlet migration governed recurved-spit formation, and changes in ebb-tidal-delta size and shape resulted in the formation of a bulge at the island terminus. Sustained updrift migration of the ebb-tidal delta resulted in a commensurate position shift of the bulge and eventually in flattening of the coastline. Regional coastal-management measures have had a strong influence on tidal-inlet and ebb-tidal-delta behavior, and therefore also on the changing shape of southwest Texel. Identification of relationships between ebb-tidal-delta behavior and changing barrier-terminus erosion-and-accretion patterns on a decadal to century time scale contributes to our understanding of coastal-system dynamics. Any barrier terminus with preserved sets of dune ridges holds a potential record on past ebb-tidal-delta orientations, which provide clues on past changes in tidal prisms and wave versus tide dominance. Under the current ebb-tidal-delta configuration, the entire westward-oriented coast of southwest Texel is too exposed for lasting accretion. Bulges resulting from future merger of shoals with the coast in this area will be eroded rapidly.
Long-term evolution and morphodynamic equilibrium of tidal channels
Journal of Geophysical Research, 2002
1 ] This contr ibution inves tigates the morp hodynam ic equil ibrium of funnel -shape d well-mixe d estua ries and/or tida l channel s. The one-di mensional d e Saint Venant and Exner equations are solve d numerical ly for the ideal case of a fric tionally domi nated estua ry consisti ng of noncoh esive sedim ent and with insignif icant interti dal storage of wat er in tida l flats and salt mars hes. This class of estuaries turns out to be invariabl y flood dominated . The resul ting asym metries in surfa ce elevat ions and tidal curren ts lead to a ne t sediment flux within a tida l cycle which is directed landw ard. As a consequ ence, sedim ents are trapp ed within the estua ry and the bott om profi le evolve s asym ptotical ly toward an equil ibrium confi guration, allo wing a vanishing net sedim ent flux everyw here and, in accordan ce with fiel d observ atio ns, a nearly const ant value of the maxi mum flood /ebb speed. Such an equil ibrium bed profi le is characteri zed by a concavi ty increasing as the estua ry co nvergence incre ases and by a unique ly deter mined value of the depth at the inlet section. The final length of the estua ry is fixed by the longi tudinal extens ion of the very shallow area which tends to form in the landw ard portion of the estuary. Note that sediment advect ion is neglec ted in the analys is, an a ssumption appropriat e to the case of not too fine sediment .