3805 resultaten

  • SST observations of upwelling induced by tidal straining in the Rhine ROFI

    Auteurs: Boer, G.J. de; Pietrzak, J.D.; Winterwerp, J.C. (2009)
    Gepubliceerd in: Continental shelf research, volume 29 (2009) nummer 1, pagina 263-277

    In this paper SST imagery and a three-dimensional numerical model of a river plume were employed to detect upwelling induced by tidal straining in the Rhine ROFI (region of fresh water influence). Previous studies have shown that the Rhine ROFI in the North Sea exhibits strong cross-shore density gradients that compete with tidal and wind mixing to establish stratification. During neap periods with low mixing energy an area measuring 30 km offshore by 100 km alongshore becomes stratified. When the ROFI is stratified strong cross-shore currents are observed, with surface currents rotating anti-cyclonically and bottom currents rotating cyclonically. The cross-shore currents interact with the cross-shore density gradients to produce a semi-diurnal cycle of stratification. Due to continuity requirements imposed by the proximity of the coast, the offshore-directed surface currents and onshore-directed bottom currents should lead to coastal upwelling. A 6-day unclouded series of SST-imagery was found in May 1990 with about two images per tide. The ROFI is much warmer than the surrounding water, exhibits a distinct diurnal solar heating response and is clearly delineated by large spatial temperature gradients at the edges. This indicates that the whole ROFI area is stratified. On three consecutive middays, a marked 5–10 km wide and 100 km alongshore band of cold upwelling is visible along the coastline, while in the morning and afternoon this upwelling band is not present. The timing of this upwelling indicates that it is caused by tidal straining. This conclusion was supported with a simulation with a three-dimensional numerical model of an idealized river plume showing the same semi-diurnal cold upwelling band. We believe these are the first SST images to show upwelling induced by tidal straining, as well as the large spatial scale of tidal straining in the Rhine ROFI.

  • Two-phase boundary layer model tested against Couette flow measurements

    Auteur: Talmon, A.M. (2009)

    Re-issue of a conference paper about the theoretical modeling of grain stresses occurring in shear flow of highly concentrated solid-liquid suspensions, verified by classical experiments. Boundary layer theory employed in the Deltares Modular Pipe Flow Model: DeMoPiFlow.

  • Intrinsic steady alternate bars in alluvial channels, part 2 : theoretical analysis

    Auteur: Mosselman, E. (2009)

  • Detailed morphodynamic simulations of shoreface nourishment scenarios

    Auteurs: Werf, J.J. van der; Giardino, A.; Ormondt, M. van; Walstra, D.J.R.; Ramaekers, G. (2009)

  • Consequences of stressor-induced changes in species assemblage for biodiversity indicators

    Auteurs: Vries, P. de; Dalfsen, J.A. van (2010)
    Gepubliceerd in: Environmental toxicology and chemistry, volume 29 (2010) nummer 8, pagina 1868-1876

  • Modelling shellfish growth with dynamic energy budget models : an application for cockles and mussels in the Oosterschelde (southwest Netherlands)

    Auteur: Troost, T.A. (2010)

    Dynamic energy budget models for growth of individual cockles (Cerastoderma edule) and mussels (Mytilus edulis) are adjusted and calibrated to the Oosterschelde by formulating and parametrizing their functional responses using an extensive set of field observations. The resulting model predictions fit the observations satisfactorily. Results indicate that food quality and the importance of detritus as a food source are site-specific as well as species-specific.

  • Upward groundwater flow in boils as the dominant mechanism of salinization in deep polders, The Netherlands

    Auteurs: Louw, P.G.B. de; Oude Essink, G.H.P. (2010)
    Gepubliceerd in: Journal of hydrology, volume 394 (2010) nummer 3-4, pagina 494-506

    As upward seepage of saline groundwater from the upper aquifer is leading to surface water salinization of deep polders in the Netherlands, we monitored the processes involved in the Noordplas Polder, a typical deep polder. Our results show three types of seepage: (1) diffuse seepage through the Holocene confining layer, (2) seepage through paleochannel belts in the Holocene layer, and (3) intense seepage via localized boils. They differ with regard to seepage flux, chloride concentration, and their location in the polder thus, their contributions to surface water salinization also differ. Permeable, sandy paleochannel belts cut through the lower part of the Holocene layer, resulting in higher seepage fluxes than the diffuse seepage through the Holocene layer where there are no paleochannels. The average chloride concentration of paleochannel seepage is about 600 mg/l, which is sixfold higher than the average concentration of diffuse seepage. The highest seepage fluxes and chloride concentrations are found at boils, which are small vents in the Holocene layer through which groundwater preferentially discharges at high velocities. This results in upconing of deeper and more saline groundwater, which produces an average chloride concentration of 1100 mg/l. Despite the fact that seepage fluxes are difficult to measure, we were able to calculate that boils contribute more than 50% of the total chloride load entering the Noordplas Polder and they therefore form the dominant salinization pathway.

  • Zebra mussels as a potential tool in the restoration of eutrophic shallow lakes dominated by toxic cyanobacteria

    Auteurs: Dionisio Pires, L.M.; Ibelings, B.W.; Donk, E. van (2010)

  • Artificial neural network as a data assimilation tool for error distribution and correction

    Auteurs: Wang, X.; Gerritsen, H. (2010)

    While numerical flow modelling is an advisable means to study oceanography, it is not perfect due to reasons such as adoption of various simplifying ssumptions, absence of data for proper boundary/initial condition configuration and so on. Local model error prediction has been well recognized to be effective in correcting errors in model predictions. However, such an approach can only be practiced at stations where observations are collected.

  • Fine sediment dynamics in a shallow lake and implication for design of hydraulic works

    Auteurs: Vijverberg, T.; Winterwerp, J.C.; Aarninkhof, S.G.J.; Drost, H.J. (2011)
    Gepubliceerd in: Ocean Dynamics, volume 61 (2011) nummer 2, pagina 187-202

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