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Wave orbital motion on the Dutch lower shoreface : observations, parameterizations and effects on bed-load sediment transport
As part of the Coastal Genesis 2.0 campaign, orbital wave velocities are measured with Acoustic Doppler Velocimeters at two different locations on the lower shoreface near the Amelander Zeegat, at -16m and -20m NAP. Using the Van Rijn (2007) sediment transport formulations, year-round weighted averaged bed-load sediment transports due to wave orbital motion of 11,5 m3/y/m and 3,2 m3/y/m are found for -16m and -20m NAP respectively in a direction almost in line with the wave direction. Parameterizations by Isobe & Horikawa (1982) and Ruessink et al. (2012) predict a near-bed wave velocity profile as a function of surface wave characteristics. The velocity profile is compared with the orbital wave velocities, measured with the ADV’s. The Isobe&Horikawa parameterization shows more skewed waves than the Ruessink parameterization, but lower significant orbital velocities. Orbital wave velocities have a larger influence on bed-load sediment transport than skewness. Bed-load sediment transports calculated with the Isobe & Horikawa parameterization approximates the bed-load sediment transport rates, calculated from measured orbital velocities best. The found sediment transport rates at -20m could be used to make an estimation about net-sediment transport into the coastal foundation. The -20m NAP contour is the seaward border of the coastal foundation, which must be maintained by sand nourishments. In the 3rd Coastal Memorandum (3e Kustnota) is decided that yearly 12Mm3 sand should be nourished to the coastal foundation, assuming negligible sediment transport takes place over the -20m NAP contour. The found bed-load sediment transport rate at -20m NAP of 3,5 m3/y/m comes down to nearly 1 Mm3 per year. Extrapolated to the entire Dutch shoreline, this is a considerable amount.
Hydrodynamics and sand transport on the lower shoreface of the Ameland tidal inlet
The objective of this master thesis was twofold. First, to obtain better understanding about the hydrodynamics and sediment transport processes on the lower shoreface of the Ameland tidal inlet, in particular about the contribution of wave-driven currents to the total current and about physical mechanisms that determine the net annual sediment transport. Second, to validate the new sediment transport modelling approach for the lower shoreface of the Ameland tidal inlet.
Duurzame energie projectgebied Grebbedijk : achtergrondrapport
De Grebbedijk tussen Wageningen en Rhenen moet worden versterkt om in de toekomst het achterland voldoende te beschermen tegen hoogwater in de Nederrijn. In de gebieds-ontwikkeling rondom het dijkversterkingsproject zijn drie kansrijke alternatieven voor dijkversterking uitgewerkt: (1) een smalle Grebbedijk, (2) een brede Grebbedijk en (3) een integrale Grebbedijk. In dit rapport is voor elk alternatief het (technisch) potentieel voor zonne-energie, windenergie en thermische energie uit oppervlaktewater (TEO) onderzocht en in kaart gebracht. Daarnaast zijn de no-regret-maatregelen geïdentificeerd: wat kan je nu al eenvoudig opnemen in het dijkontwerp waardoor zonne-energie, windenergie of TEO op termijn realiseerbaar worden. Tot slot zijn de mogelijkheden voor een energieneutrale Rijnhaven bestudeerd.
Datareport Kustgenese 2.0
Het programma Kustgenese 2.0 onderzoekt tussen 2015 en 2028 hoeveel zand op lange termijn nodig is, waar en wanneer het zand nodig is en hoe we het zand kunnen toevoegen aan de kust. In dit rapport is de gehele opzet en uitvoering van de meetcampagne, de dataprocessing, dataopslag en indicatieve resultaten van de gemeten data beschreven.
Modelling hydrodynamics in the Ameland inlet as a basis for studying sand transport
Within the framework of the Coastal Genesis II Program a coupled hydrodynamic-wave model has been setup, calibrated and validated in and around Ameland Inlet. The model will be used as a basis for modeling sand transport at the lower shoreface and sediment exchange through the Ameland inlet in the next phase of the project. This paper presents the setup, calibration and validation of the hydrodynamic model. Calibration and validation show that the model is well capable of representing the water levels, currents and waves in and near the Ameland inlet. Hence, the model is considered well suitable as a base for sediment transport modeling in the next phases of the project.
Method for calculating annual sand transports on the Dutch lower shoreface to assess the offshore boundary of the Dutch coastal foundation
This paper presents results of research performed in the Coastal Genesis 2.0 project. We developed an efficient approach to compute the annual sand transport rates along the lower shoreface of the Dutch coast, based on the 3D Dutch Continental Shelf Model developed in D-HYDRO Flexible Mesh (3D DCSM-FM), a wave transformation matrix for the Dutch coast and a 1DV sand transport module. First preliminary calculations were made for the years 2013–2017. Calculated wave heights, peak flood velocities and residual velocities increase when moving northward from Scheveningen to Callantsoog along the NAP-20 m contour of the Dutch coast. This results in an increase of the mean net annual transports rates moving northward along this contour. Calculated transport rates are 1–20% smaller at the NAP-15 contour. The cross-shore and alongshore component of these transport rates depends on the definition of the coast angle.
Coastal Sediments 2019 : proceedings of the 9th international conference (Tampa/St. Petersburg, Florida, USA, 27-31 May 2019)
Understanding the present-day morphodynamics of Ameland inlet, part 2
The Kustgenese 2.0 program has resulted in unique high-resolution bed surveys of Ameland inlet. These measurements allow us to (1) investigate, analyse and better understand the morphodynamic changes on its ebb-tidal delta, and (2) to investigate the half-yearly changes in sediment budget. A time series of near yearly ebb-tidal delta bathymetries over the past decade, displays how initial small-scale perturbations in the central part of the ebb-tidal delta (the ebb-chute and shield systems) develop, grow, migrate and start to dominate the developments of the entire ebb-tidal delta. The realisation that small-scale perturbations result in ebb-tidal delta scale relocation of channels and shoals has important implications for the future morphadynamie modelling of the area. These morphodynamic models will have to contain sufficient resolution and detailed processes to capture such distortions. The high-resolution multi-beam data obtained in Ameland inlet provides valuable information on the prevailing sediment transport directions. Such knowledge is essential for the future validation of our process-based sediment transport models. Based on these surveys, we are able to construct sediment transport patterns for the proximal part of the ebb-tidal delta; Borndiep is primarily ebb-dominant and Westgat flood-dominant. These transport directions correspond to the sediment transport patterns derived from the morphodynamic changes. Correspondences in repeat surveys on the ebb-tidal delta confirm that (1) bedform asymmetry is an indicator for bedform migration, and (2) coherent, consistent, bedform fields occur through the various surveys.
Bench-mark morphodynamic model Ameland Inlet
The bench-mark study specifically aims to identify which trends and patterns in morphodynamic behaviour can or can't be reproduced. The model results presented in the bench-mark simulation show that morphodynamically stable simulations over a timescale of 5 to 10 years can be obtained with Delft3D. The use of a parallel online approach, in combination with a low-resolution model grid, allows us to run with acceptable computational times. A qualitative comparison of bed-levels reveals a major short-coming of the bench-mark model. The modelled morphodynamic response overpredicts the measured changes of the ebb-tidal delta; the ebb-tidal delta develops beyond observed limits. However, the comparison of the observed trends shows, in the bench-mark simulation and all sensitivity tests, that the model is capable of reproducing the dominant trends. Conceptual descriptions show that wave-dominated ebb-tidal deltas tend to be pushed closer to the inlet throat. In the model, it is likely that the balance between the offshore directed tidal component, and the onshore directed wave-driven transports is not resolved accurately enough. By selecting a highly efficient bench-mark model we can easily implement, test and verify new insights, model developments and advances as these are obtained in the Kustgenese 2.0 project.
Understanding the present-day morphodynamics of Ameland inlet
This literature study describes the present-day morphodynamics of Ameland inlet including the main transport patterns and mechanisms. This knowledge is essential for future sustainable coastal management of Ameland inlet and teaches us valuable lessons for the other inlets present in the Netherlands. An extensive summary of the main findings and their contribution to answering the research questions of sub-project 'Systeemkennis Zeegaten' of Kustgenese 2.0 is presented in the report.