Zoek binnen publicaties
Effects of self-attraction and loading at a regional scale: a test case for the Northwest European Shelf
Parallel morphodynamic modelling for the Yangtze Estuary
Model input reduction and morphological acceleration techniques to bridge the large time scale of morphological evolution and the small time scale of hydrodynamically driven sediment transport is investigated for the Yangtze Estuary morphodynamic model. The discharge series of the river is schematized into a set of multi-discharge levels. Each discharge level coupled with the spring-neap tide forms one morphodynamic model for the estuary with bed stratigraphy approach applied. These models are used to simulate the bathymetry change of the estuary in parallel with the results merged together base on the Mor-Merge (MM) method. The morphological factor is used to accelerate the bathymetry change during hydrodynamic simulation. The modelled bathymetry change based on MM method is compared with the Quasi Real Time (QRT) simulation result. It shows that the results of the MM model with more discharge levels correlate more significantly with that of the QRT model. Therefore, the MM approach with multi discharges, which achieves an acceptable acceleration for morphological change, results in the feasibility of the medium term morphodynamic model of the Yangtze Estuary.
Assessing future coastline change in the vicinity of tidal inlets via reduced complexity modelling
Coastline change in the vicinity of tidal inlets is mainly influenced by four processes; the Bruun effect, sea level rise driven basin infilling, variations in river discharge and fluvial sedimentation, which are driven by both climate change and anthropogenic activities. However, a coastline change model that accounts for all of the aforementioned processes under both climate change and anthropogenic influences has been lacking. The methodology presented here accounts for climate change and anthropogenic forcing in assessing potential future coastline change in the vicinity of two different types of tidal inlets. Application of this method indicates a coastline progradation of ~20 m at Kalutara inlet (Sri Lanka) and a coastline recession of ~30 m at Alsea estuary (USA) by 2100. Scrutinizing the relative contributions to these predicted coastline changes illustrates that anthropogenic influences could dictate fluvial sediment supply to coasts, underlining the significance of integrating both climate change and anthropogenic influences when assessing future coastline change along inlet-interrupted coastlines.
Hindcast of long-term shoreline change due to coastal interventions at Namhangjin, Korea
Namhangjin beach is protected by multiple submerged breakwaters (SBWs) which were built to protect the ~4 km long sandy beach. A coastline model (UNIBEST) was used to investigate the long term effect of the SBW structures on the beach. The model computes long-term shoreline changes due to coastal structures as a result of the strong longshore sediment transport gradients at the structures. Bathymetry data of the shoreface and nearshore profiles were obtained from a field survey, while wave conditions from offshore WAM hindcast (Wave Modeling Group) were transformed towards the nearshore with the Delft3D+SWAN modelling system. Local wave sheltering by the SBWs was included in the wave model. A situation with and without the SBWs was modelled. A rapid adjustment of the shoreline was observed in the model as a result of the wave conditions in the first two years. After that, the shoreline shape stabilized without significant changes both for the situation with and without SBWs. A smooth curved coastline shape was obtained in the model without SBWs, while the model with SBWs shows a similar overall shoreline shape with undulations of the shoreline shape behind the breakwaters. A similar undulating shoreline was observed in the Sept-2013 imagery at Namhangjin beach. The local accretion behind the SBWs may induce some erosion in the lee area of the SBWs, causing distortions of the shoreline shape. Most sediment accreted at the first SBW (i.e. the northern most SBW where alongshore transport from the North was trapped), while the coastline change rate gradually decreased towards the South. The effectiveness of the SBWs at the considered shoreline section for maintaining the shoreline is somewhat ambiguous as local areas with accretion or erosion are present with respect to the situation without the breakwaters. The results show that multiple SBWs need to be carefully designed to protect beaches as local distortions of the shoreline shape may be present directly downdrift from the structures.
Protocol voor conversie van Baseline schematisatie naar SWAN
In dit document wordt een handreiking gegeven om elementen in het rivierengebied te converteren van een Baseline schematisatie naar een SWAN schematisatie. Hiervoor is als eerste onderzocht welke elementen in Baseline van invloed zijn op de golven in het rivierengebied. Tevens is nagegaan of er elementen, die van invloed zijn op de golven, ontbreken in de Baseline elementenlijst. Dit laatste bleek niet het geval. Voor elk element in de Baseline lijst die van invloed is op de golven is nagegaan hoe het in SWAN meegenomen kan worden. Uit deze analyse volgt dat het Baseline element "Kade" als obstakel meegenomen dient te worden en dat de Baseline hoogtelijnen: "hoogteverschillijnen" , "breuklijnen" en "bandijken" via de bodemschematisatie meegenomen dienen te worden. Verder wordt aangeraden om de elementen in de categorie ruwheid vooralsnog niet mee te nemen in de SWAN schematisatie, omdat a) dit een conservatieve aan pak is en b) het meenemen van ruwheid voor golven fundamenteel verschilt van het meenemen van ruwheid voor stroming. Vervolgens is voor elk van de geselecteerde elementen nagegaan hoe de Baseline informatie vertaald kan worden naar SWAN invoer. De meeste aandacht is hierbij gericht op het meenemen van obstakels in SWAN, aangezien hierbij verschillende praktische eisen en beperkingen aan gesteld zijn binnen SWAN. Tot slot is een case studie uitgevoerd. In deze case studie zijn obstakels toegevoegd aan een deelgebied van de bestaande Rijn-Maasmonding schematisatie. Uit de case studie kan worden geconcludeerd dat het goed mogelijk is om de Baseline 'Kade' elementen om te zetten naar een werkende SWAN schematisatie met obstakels. Er wordt dan ook geadviseerd om de in dit rapport beschreven aanpak over te nemen voor het bepalen van de WTI2017 golfrandvoorwaarden in het benedenrivierengebied. Het overnemen van deze aanpak leidt, naast een consistente aanpak, tot een verlaging, afhankelijk van de locatie tot enkele decimeters, van de golfhoogtes als gevolg van het meenemen van de obstakels.
Quantification of model uncertainty for WAQUA for the Upper River Area
In the context of the Wettelijk Toets Instrumentarium 2017 (WTI) project, the subproject Hydrodynamic modelling aims at identifying and quantifying the model uncertainty of WAQUA regarding the calculated water levels for the primary water systems in the Netherlands. For the Dutch upper rivers, this study aims at delivering the model uncertainty that needs to be added to the calculated water levels. The model uncertainty is specified as a distribution of the uncertainty on the water level, in terms of a bias and standard deviation. The model uncertainty for the other primary water systems in the Netherlands will be quantified in 2014. In the first phase of this project, a literature study was performed and an expert judgment session was organized. The outcome of the first phase revealed that the sources of uncertainty cannot be regarded independently during the uncertainty analysis. Therefore, the model uncertainty should be estimated as a whole. According to the experts the most important source of uncertainty is the use of WAQUA outside the calibration and validation data range. The performance of the WAQUA models under extreme conditions has never been quantified. Since the uncertainty due to the use of the model under extreme conditions is expected to be much larger than the model uncertainty within the calibration range, this study focusses on quantifying the model uncertainty under extreme condition's. However, a quantification of the model uncertainty within the calibration range is also given. The model uncertainty within the calibration range is derived from the calibration results. The uncertainty due to the calibration approach, morphological changes and differences between calculated and actual discharge distribution play an important role in the overall model uncertainty under extreme conditions. The uncertainty due to the calibration approach has been addressed by carrying out an investigation to identify the sensitivity of model results to using a different calibration approach, while the uncertainty due to morphological changes and due to differences between calculated and actual discharge distribution have been addressed in earlier studies 2009 and 2012. The overall model uncertainty under extreme conditions is quantified based on expert judgment, based on the results of the sensitivity analysis and the former studies and is the best estimate that the experts can give at this moment. This leads to an overall estimate of the model uncertainty for the upper river area of the Netherlands of a bias of 0 meter and a standard deviation of 0.8 meter under extreme conditions.
Do salt marshes survive sea level rise? : modelling wave action, morphodynamics and vegetation dynamics
This paper aims to fundamentally assess the resilience of salt marsh-mudflat systems under sea level rise. We applied an open-source schematized 2D area model (Delft3D) that couples intertidal flow, wave-action, sediment transport, geomorphological development with a population dynamics approach including temporal and spatial growth of vegetation and bio-accumulation. Wave-action maintains a high sediment concentration on the mudflat while the tidal motion transports the sediments within the vegetated marsh areas during flood. The marsh-mudflat system attained dynamic equilibrium within 120 years. Sediment deposition and bio-accumulation within the marsh make the system initially resilient to sea level rise scenarios. However, after 50-60 years the marsh system starts to drown with vegetated-levees being the last surviving features. Biomass accumulation and sediment supply are critical determinants for the marsh drowning rate and survival. Our model methodology can be applied to assess the resilience of vegetated coast lines and combined engineering solutions for long-term sustainability.
Monitoring en evaluatie natuur(vriende)lijke oevers Maas - ecologie en morfologie : datarapportage 2017
Voor het realiseren van KRW- en andere natuurontwikkelingsdoelen langs de Maas zijn de natuurlijke oevers een veelbelovende en relatief eenvoudig uit te voeren maatregel. Om de ecologische en morfologische ontwikkeling van natuurlijke oevers te kunnen onderzoeken is een 10-jarig monitoringsprogramma opgezet. Deze datarapportage geeft een overzicht van de monitoring van de linkeroevers in 2017.
North Sea wave analysis using data assimilation and mesoscale model forcing winds
This article explores the use of the ensemble Kalman filter technique to improve the accuracy of North Sea wave field analyses. A nonhydrostatic convective-permitting mesoscale model was used to provide high-resolution forcing winds. These were adjusted by assimilating measurements of offshore wave heights directly into the wave model state. The ensemble Kalman filter data assimilation was shown to be very efficient, leading (compared to the results without data assimilation) to large reductions (up to 60%) in the root-mean-square error of the offshore wave heights and other model state variables, also (up to 40%) at locations other than those of the observations used.
Rip current circulation and surf zone retention on a double barred beach
Rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants, between the surf zone and inner shelf. Concurrent in situ Eulerian and Lagrangian (GPS drifter) data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy, double-barred beach. The data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current, and the exchange process. On both days, there was a prominent clockwise eddy in the surf zone, for which the seaward-heading portion formed a rip current in a well-defined channel rip, incised into the inner bar. Exit rate (measured with drifters) from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar, from 71% exits to 6% over the two days. Exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone. Under higher wave conditions, there were stronger pulsations in surf zone currents and more surf zone exits. However, higher wave conditions caused wave breaking over the outer bar. This breaking increases vorticity around the outside of the surf zone eddy, which increases surf zone retention. This is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies. Under such conditions, drifter exits were rare, and occurred due to vortex shedding. During lower incident wave conditions, eddy vorticity was lower, and drifters could relatively freely exit the surf zone. This is one of the few studies that investigate surf zone circulation on a high energy, double-barred beach.