3433 resultaten

  • Long‐term evolution of the Old Rhine estuary : unravelling effects of changing boundary conditions and inherited landscape

    Auteurs: Haas, T. de; Valk, L. van der; Cohen, K.M.; Pierik, H.J.; Weisscher, S.A.H.; Hijma, M.P.; Spek, A.J.F. van der; Kleinhans, M.G. (2018)

    The long‐term morphodynamic evolution of estuaries depends on a combination of antecedent topography and boundary conditions, including fluvial input, sea‐level change and regional‐landscape interactions. Identifying effects of such boundary conditions on estuary evolution is important to anticipate future changes in specific boundary conditions and for hindcasting with numerical and physical models. A comprehensive synthesis of the evolution of the former Old Rhine estuary is presented here, together with its boundary conditions over its full lifespan from 6,500 to 1,000 cal. yr bp. This system formed during a period of sea‐level high stand, during which the estuary served as the main River Rhine outlet. The estuary went through three stages of evolution: a maturation phase in a wide infilling back‐barrier basin, a stable mature phase and an abandoning phase, both in a laterally confined setting. The Old Rhine River formed by a river avulsion around 6,500 cal. yr bp that connected to a tidal channel within a large back‐barrier basin. Decelerating sea‐level rise caused the back‐barrier basin to silt up around 5,700 cal. yr bp, resulting in shoreline progradation by beach‐barrier formation until ∼2,000 cal. yr bp. Beach‐barrier formation along the coast and natural levee formation along the river triggered peat formation in the coastal plain, laterally constraining the estuary and limiting overbank deposition, which caused most sediment to accumulate offshore. The abandoning phase started around 2,200 cal. yr bp when a series of upstream avulsions led to a substantial reduction in fluvial input. This induced a period of enhanced estuarine overbank clay deposition that continued into near‐complete silting up and estuary closure around 1200 ad. These findings exemplify how tidal systems, formed in wide coastal plains during sea‐level high stand, depend on antecedent conditions, and how they respond to connection and disconnection of a large river over long, millennial timescales.

  • Experimental study on the 3D-flow field of a free-surface vortex using stereo PIV

    Auteurs: Duinmeijer, S.P.A.; Oldenziel, D.M.; Clemens, F. (2019)
    Gepubliceerd in: Journal of hydraulic research (2019), pagina 1-15

    In order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is transported through the vortex core. The velocity profiles show that the axial flow is concentrated in a domain bounded by two times the core radius. Despite Burgers’ assumption of radially independent axial velocity profiles, the model quantifies the tangential velocity profile within a relative uncertainty of circa 10%. The measurements show that it seems valid to use Burgers’ model to obtain an estimate for the core radius by taking the average axial velocity over a radial domain of approximately 2.2 times the core radius. The Burgers model quantifies the air core depth with an uncertainty of 20% relative to the measurements. When compared with the magnitude of vorticity diffusion by molecular viscosity, the experiments show that there is no significant diffusion by radial turbulence.

  • Integrating large-scale hydrology and hydrodynamics for nested flood hazard modelling from the mountains to the coast

    Auteurs: Hoch, J.M.; Eilander, D.M.; Ikeuchi, H.; Baart, F.; Winsemius, H.C. (2019)
    Gepubliceerd in: Natural Hazards and Earth System Sciences (2019), pagina 1-18

    Fluvial flood events were, are, and will remain a major threat to people and infrastructure. Typically, flood hazard is driven by hydrologic or river routing and floodplain flow processes. Since they are often simulated by different models, 15 coupling these models may be a viable way to increase the physicality of simulated inundation estimates. To facilitate coupling different models and integrating across flood hazard processes, we here present GLOFRIM 2.0, a globally applicable framework for integrated hydrologic-hydrodynamic modelling. We then tested the hypothesis that smart model coupling can advance inundation modelling in the Amazon and Ganges basins. By means of GLOFRIM, we coupled the global hydrologic model PCR-GLOBWB with the hydrodynamic models CaMa-Flood and LISFLOOD-FP. Results show that replacing the 20 kinematic wave approximation of the hydrologic model with the local inertia equation of CaMa-Flood greatly enhances accuracy of peak discharge simulations as expressed by an increase of NSE from 0.48 to 0.71. Flood maps obtained with LISFLOOD-FP improved representation of observed flood extent (critical success index C=0.46), compared to downscaled products of PCR-GLOBWB and CaMa-Flood (C=0.30 and C=0.25, respectively). Results confirm that model coupling can indeed be a viable way forward towards more integrated flood simulations. However, results also suggest that the accuracy of 25 coupled models still largely depends on the model forcing. Hence, further efforts must be undertaken to improve the magnitude and timing of simulated runoff. Besides, flood risk is, particularly in delta areas, driven by coastal processes. A more holistic representation of flood processes in delta areas, for example by incorporating a tide and surge model, must therefore be a next development step of GLOFRIM, making even more physically-robust estimates possible for adequate flood risk management practices.

  • Development and performance of a parsimonious model to estimate temperature in sewer networks

    Auteurs: Elias-Maxil, J.A.; Hofman, J.; Wols, B.A.; Clemens, F.H.L.R.; Hoek, J.P. van der; Rietveld, L.C. (2017)
    Gepubliceerd in: Urban water journal, volume 14 (2017) nummer 8, pagina 829-838

    This paper presents a model (inspired by another model) to calculate water temperature in free-surface flow with two main innovations: the convective heat transfer occurs only at the wetted perimeter of pipes, and the model was integrated to commercial software used for hydraulic calculations in drainage systems. Given these innovations, we could reduce the number of modeling input data to calculate the temperature of water and soil in the radial and tangential directions along the pipes, with the advantages of using industry-standard software. To test the performance of the model, it was firstly calibrated in two sets of experiments (to calibrate the hydraulic and the thermal parameters separately), and benchmarked with a third controlled discharge against the case model. The results indicate that in unsteady-state situations the parsimonious model can be twice as accurate as the underlying model because the parsimonious model considers the hydraulic influence of sewer infrastructure.

  • 42. Internationales Wasserbau-Symposium (IWASA) : Hochwasser - eine Daueraufgabe (Aachen, 12.-13. Januar 2012)

    Originally published in 2012

  • Outlier detection in UV/Vis spectrophotometric data

    Auteurs: Lepot, M.; Aubin, J.; Clemens, F.H.L.R.; Masic, A. (2017)

    UV/Vis spectrophotometers have been used to monitor water quality since the early 2000s. Calibration of these devices requires sampling campaigns to elaborate relations between recorded spectra and measured concentrations. In order to build robust calibration data sets, several spectra must be recorded per sample. This study compares two approaches – principal component analysis and data depth theory – to identify outliers and select the most representative spectrum (MRS) among the repetitively recorded spectra. Detection of samples that contain outliers is consistent between the methods in more than 70% of the samples. Identification of spectra as outliers is consistent in more than 95% of the cases. The identification of MRS differs depending on the approach used. In their current form, both of the proposed approaches can be used for outlier detection and identification. Further studies are suggested to combine the methods and develop an automated ranking and sorting system.

  • MEDCOAST 2017 : proceedings of the Thirteenth International MEDCOAST Congress on Coastal and Marine Sciences, Engineering, Management and Conservation (31 October - 04 November 2017, Mellieha, Malta)

    Auteur: Ozhan, E. (2017)

  • New Zealand Hydrological Society Annual Conference (Napier, New-Zealand, 28 November - 1 December 2017)

    Originally published in 2017

  • 45. Internationales Wasserbau-Symposium Aachen (IWASA) : Offene Gewässer - Strahlwirkung, Fischaufstieg, Fischabstieg, Sedimente, Schadstoffe (Aachen, 8. und 9. Januar 2015)

    Originally published in 2015

  • Proceedings of the 2nd International symposium on computational geomechanics - COMGEO II (Dubrovnik, 27–29 April 2011)

    Auteurs: Pietruszczak, S.; Pande, G.N. (2011)

Page 1 of Array12345