3836 resultaten

  • The importance of explicitly modelling sea-swell waves for runup on reef-lined coasts

    Auteurs: Quataert, E.; Storlazzi, C.D.; Dongeren, A.R. van; McCall, R.T. (2020)
    Gepubliceerd in: Coastal engineering : an international journal for coastal, harbour and offshore engineers (2020)

    The importance of explicitly modelling sea-swell waves for runup was examined using a 2D XBeach short wave-averaged (surfbeat, “XB-SB”) and a wave-resolving (non-hydrostatic, “XB-NH”) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Field observations on water levels, wave heights, and wave runup were used to drive and evaluate both models, which were subsequently used to determine the effect of sea-level rise and extreme wave conditions on wave runup and its components. Results show that specifically modelling the sea-swell component (using XB-NH) provides a better approximation of the observed runup than XB-SB (which only models the time-variation of the sea-swell wave height), despite good model performance of both models on reef flat water levels and wave heights. XB-SB has a bias of −0.108 – 0.057 m and scatter index of 0.083–0.639, whereas XB-NH has bias of −0.132 – 0.055 m and 0.122–0.490, respectively. However, both models under-predict runup peaks. The difference between XB-SB and XB-NH increases for more extreme wave events and higher sea levels, as XB-NH resolves individual waves and therefore captures SS-wave motions in runup. However, for even larger forcing conditions with offshore wave heights of 6 m, the island is flooded in both XB-SB and XB-NH computations, regardless the sea-swell wave energy contribution. In such cases XB-SB would be adequate to model flooding depths and extents on the island while requiring 4–5 times less computational effort.

  • Signal test for acoustic fibre optics for the purpose of monitoring varying salinity

    Auteurs: Kruiver, P.; Obando Hernandez, E.; Pefkos, M. (2020)

    Salt intrusion of surface waters in the Netherlands poses a problem for fresh water resources, for example at intake points of drinking water. Currently, the tools and instruments to monitor and understand salt water intrusions are insufficient. The point sensors of the monitoring network provide valuable information, but only at fixed point locations. RWS is looking for new technology to gather 2D or 3D information about salinity variations in fresh, brackish and salt waterbodies. Two promising techniques are Distributed Acoustic Sensing (DAS) with fibre optic cables and Electrical Resistivity Tomography (ERT). This report describes the results of a laboratory test using DAS.

  • Signal test for acoustic fibre optics for leakage detection of water bottoms

    Auteurs: Kruiver, P.; Obando Hernandez, E.; Pefkos, M.; Bremmer, C.N. (2019)

    The goal of this project is to analyse the results of the two large laboratory tests in order to assess whether distributed fibre optic sensing can detect the presence or absence of a clay layer in a water bottom. It is about a ‘signal test’ which must show that variations in lithology of the water bottom have an effect in the measured signal. The experiments for which the distributed fibre optic measurements have been performed consisted of experiments at a scale of 18 m x 5.5 m surface area and 2.5 m depth and for which fibre optics cable for acoustic and temperature measurements has been placed in a send bed of 80 cm thickness and covered with a clay layer of 10 cm. Three situations have been analysed.

  • Scaling point-scale (pedo)transfer functions to seamless large-domain parameter estimates for high resolution distributed hydrologic modeling : an example for the Rhine river

    Auteurs: Imhoff, R.O.; Verseveld, W.J. van; Osnabrugge, B. van; Weerts, A.H. (2020)
    Gepubliceerd in: Water resources research, volume 56 (2020) nummer 4

    Moving toward high-resolution gridded hydrologic models asks for novel parametrization approaches. A high-resolution conceptual hydrologic model (wflow_sbm) was parameterized for the Rhine basin in Europe based on point-scale (pedo)transfer functions, without further calibration of effective model parameters on discharge. Parameters were estimated on the data resolution, followed by upscaling of parameter fields to the model resolution. The method was tested using a 6-hourly time step at four model resolutions (1.2, 2.4, 3.6, and 4.8 km), followed by a validation with discharge observations and a comparison with actual evapotranspiration (ETact) estimates from an independent model (DMET Land Surface Analysis Satellite Application Facility). Additionally, the scalability of parameter fields and simulated fluxes was tested. Validation of simulated discharges yielded Kling-Gupta Efficiency (KGE) values ranging from 0.6 to 0.9, except for the Alps where a volume bias caused lower performance. Catchment-averaged temporal ETact dynamics were comparable with independent ET estimates (KGE ≈ 0.7), although wflow_sbm model simulations were on average 115 mm yr−1 higher. Spatially, the two models were less in agreement (SPAEF = 0.10), especially around the Rhine valley. Consistent parameter fields were obtained, and by running the model at the different resolutions, preserved ETact fluxes were found across the scales. For recharge, fluxes were less consistent with relative errors around 30% for regions with high drainage densities. However, catchment-averaged fluxes were better preserved. Routed discharge in headwaters was not consistent across scales, although simulations for the main Rhine River were. Better processing (scale independent) of the river and drainage network may overcome this issue.

  • Geosynthetic-reinforced pile-supported embankments: state of the art

    Auteurs: Eekelen, S.J.M. van; Han, J. (2020)

    Geosynthetic-reinforced pile-supported embankments have been increasingly used worldwide to support earth structures. A significant amount of research has been conducted by many researchers and engineers in recent years. This paper provides a state-of-the-art review of this technology, and of important developments and results obtained throughout the years that help to better understand the mechanisms that play an important role in the design, construction, and performance of these systems. This paper begins with terminologies and historical developments. It then focuses on load transfer mechanisms and practical design and proposes topics for future research. The supplemental material gives tips for construction details and instrumentation for performance evaluation.

  • Deformations in trapdoor tests and piled embankments

    Auteurs: Rui, R.; Zhai, Y.X.; Han, J.; Eekelen, S.J.M. van; Chen, C. (2020)

    Fill deformation and surface settlement can be induced by differential settlement at the bottom of the fill in piled embankments. The deformation patterns and the relationship between the surface settlement and the differential settlement at the bottom of the fill have not been well investigated. Two-dimensional single-trapdoor, twin-trapdoor, and multi-trapdoor tests, including four tests with geosynthetic reinforcement, were conducted using elliptical steel rods as an analog to soil. The deformation pattern and influence regions in the single-trapdoor tests were evaluated using the measured deformations. The fill deformations in the trapdoor tests followed the Gaussian distribution.The superposition results of these Gaussian distribution curves of the single-trapdoor tests were compared with the measured deformations in the twin-trapdoor and multi-trapdoor tests. The differences between the measured and calculated results indicate that additional interaction occurred between adjacent trapdoors. The deformation shapes of the fill at the bottom of the geosyntheticreinforced and unreinforced test sections were different. However, the settlement pattern at the elevation level above 1.5 times the clear spacing of pile caps followed the same Gaussian distribution curve, if the volumetric settlement was the same. A method for predicting the surface settlement of 2D piled embankments is then presented.

  • Long term measurements in the Woerden geosynthetic-reinforced pile-supported embankment

    Auteurs: Eekelen, S.J.M. van; Venmans, A.A.M.; Bezuijen, A.; Tol, A.F. van (2020)

    The purpose of this paper is to present long-term measurements in a full-scale study on a basal reinforced piled embankment that make it possible to validate calculations used for the design of the geosynthetic reinforcement (GR). These calculations are normally carried out in two steps. To validate steps 1 and 2 together, it is necessary to measure GR strains. To validate calculation steps 1 and 2 separately, arching A needs to be measured, which is the pressure on the pile cap above the GR. An extensive monitoring project was conducted over a period of four years, in a basal reinforced piled embankment on 17 m of soft clay and peat. This study presents the measured GR strains and load distribution including arching, accompanied by measured groundwater levels and deformations. The subsoil support of the geosynthetic reinforcement disappeared quickly, arching developed over the first three months, and an annual cycle in the load distribution became apparent. Arching effects increase during the summer when conditions are relatively dry, resulting in a larger load on the piles and a reduction in the load on the GR. Additionally, the measured changes after an extremely rainy week are presented.

  • Computational material flow analysis for thousands of chemicals of emerging concern in European waters

    Auteurs: Gils, J.A.G. van; Posthuma, L.; Cousins, I.T.; Brack, W.; Altenburger, R.; Baveco, H.; Focks, A.; Greskowiak, J.; Kuhne, R.; Kutsarova, S.; Lindim, C.; Markus, A.A.; Meent, D. van de; Munthe, J.; Schueder, R.; Schuurmann, G.; Slobodnik, J.; Zwart, D. de; Wezel, A.P. van (2020)

    Knowledge of exposure to a wide range of chemicals, and the spatio-temporal variability thereof, is urgently needed in the context of protecting and restoring aquatic ecosystems. This paper discusses a computational material flow analysis to predict the occurrence of thousands of man-made organic chemicals on a European scale, based on a novel temporally and spatially resolved modelling framework. The goal was to increase understanding of pressures by emerging chemicals and to complement surface water monitoring data. The ambition was to provide a first step towards a “reallife” mixture exposure situation accounting for as many chemicals as possible. Comparison of simulated concentrations and chemical monitoring data for 226 substance/basin combinations showed that the simulated concentrations were accurate on average. For 65% and 90% of substance/basin combinations the error was within one and two orders of magnitude respectively. An analysis of the relative importance of uncertainties revealed that inaccuracies in use volume or use type information contributed most to the error for individual substances. To resolve this, we suggest better registration of use types of industrial chemicals, investigation of presence/absence of industrial chemicals in wastewater and runoff samples and more scientific information exchange.

  • Investigation of soil-arching development in dense sand by 2D model tests

    Auteurs: Rui, R.; Tol, A.F. van; Xia, Y.Y.; Eekelen, S.J.M. van; Hu, G. (2016)
    Gepubliceerd in: Geotechnical testing journal, volume 39 (2016) nummer 3, pagina 415-430

    A trapdoor system has frequently been used to study soil arching and its development in recent years. The load transfer in the fill of piled embankments is very similar to a trapdoor system with multiple trapdoors. There are multiple arching models described in different standards and guidelines for piled embankments that can be subdivided into three archingmodel families. To study the soil-arching type and its development, a series of model tests with sand fills were carried out in a two-dimensional (2D) multi-trapdoor test setup. The tests considered four factors—the fill height, trapdoor width, pile width, and grain size of the sand—with four values for each factor. Triangular slip surfaces were found at very small deformations using the particle image velocimetry (PIV) technique. These surfaces evolved in ways that could be related to the three types of stress-distribution ratio curves, with development patterns similar to the arching families of piled embankments: (1) the rigidmodel family, (2) the equal-settlement-plane-model family, and (3) the limit-equilibriummodel family. The limit-equilibrium-model family occurred in tests with narrow trapdoor widths.

  • Shifting the discharge mind-set from harmful to habitat : exploring inventive designs and benefits of underwater discharge structures

    Auteurs: Merwe, R. van der; Morelissen, R.; Polman, H.; Jenner, H. (2019)

    With the aim to protect the marine environment, regulations have been set to regulate the brine discharges, and defining environmental criteria in the area close to the outfall. It was however noted, that such criteria are often adopted from generic benchmarks and sometimes from unadoptable locations. Robust and in situ research on the effects of the brine effluent on the marine environment is also lacking. Recent surveys however suggest that the ecological impact of brine outfalls can be very limited or even result in an improvement of biodiversity and marine abundance on the outfall structure. Such observations suggest that some environmental criteria may be archaic, which may result in needlessly expensive outfall designs.

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