3163 resultaten

  • Morphodynamic feedback loops control stable fringing flats

    Auteurs: Maan, D.C.; Prooijen, B.C. van; Zhu, Q.; Wang, Z.B. (2018)
    Gepubliceerd in: Journal of geophysical research : earth surface (2018), pagina 1-52

    We apply a 2‐D horizontal process based model (Delft3D) to study the feedback mechanisms that control the long‐term evolution of a fringing intertidal flat in the Western Scheldt Estuary. The hydrodynamic model is validated using a comparison with measurements on the intertidal flat and the sediment transport module is calibrated against long‐term morphology data. First, the processes that lead to net sediment exchange between channel and flat are studied. Then, long‐term simulations are performed and the dependency of sediment fluxes on the tidal flat bathymetry, and the corresponding morphodynamic feedback mechanisms are explained. In the long run, relatively stable states can be approached, which are shown to be typical for wave‐dominated fringing mudflats. The system behavior can be explained by the typical feedback mechanisms between the intertidal bathymetry and the hydrodynamic forces on the flat. In the subtidal domain, the impact of small (5‐10cm) wind waves increases with a rising elevation due to decreasing water depths. In the intertidal domain, the wave impact increases with increasing cross‐sectional slope due to wave shoaling. These relationships result in negative (stabilizing) morphodynamic feedback loops. The tidal current velocities and tide‐induced bed shear stresses, on the other hand, are largely determined by the typical horizontal geometry. A stabilizing feedback loop fails, so that there is no trend towards an equilibrium state in the absence of wind waves.

  • Notitie watervraag sectoren drinkwater, industrie en energie

    Auteur: Bel, M. de (2013)

    In deze notitie worden mogelijke toekomstige wateronttrekkingen in beeld gebracht voor de sectoren drinkwater (en proceswater), industrie en energieopwekking vanuit de ontwikkelingen welke geschetst worden binnen de vier deltascenario’s, teneinde te komen tot consistente en onderscheidende ontwikkelingsscenario’s voor de sectoren. Er wordt per sector een kwantitatieve, verhoudingsgewijze inschatting gemaakt van de wateronttrekking in de jaren 2050 en 2100, ten opzichte van de huidige situatie. Voor de vier deltascenario’s STOOM, WARM, DRUK en RUST.

  • Effects of different precipitation inputs on streamflow simulation in the Irrawaddy River Basin, Myanmar

    Auteurs: Sirisena, T.A.J.G.; Maskey, S.; Ranasinghe, R.; Babel, M.S. (2018)
    Gepubliceerd in: Journal of hydrology: regional studies, volume 19 (2018), pagina 265-278

    Precipitation is the most important input variable to numerically simulate the hydrological responses of a river basin. Nowadays, a number of precipitation data products with different spatial and temporal resolutions are available. However, the accuracy of these products may vary greatly and the variations may themselves differ in different river basins. Such differences have direct implications on the use of these datasets in hydrological modelling. Here, using a hydrological model, we investigated the effects of four precipitation datasets (in-situ gauge precipitation with and without interpolation, PERSIANN-CDR, and CHIRPS) on streamflow simulations in the Irrawaddy Basin in Myanmar. We identified considerable differences in streamflow simulation with the use of different precipitation inputs. The four datasets showed varied annual and seasonal precipitation values over the basin. Although the gauge density within the study area is very low, streamflow simulations forced with interpolated gauge data outperformed the models forced with other datasets. However, simulations forced with CHIRPS and PERSIANN-CDR also showed good results in most cases in terms of Nash Efficiency and R2, but mostly with high biases. In calibration, the four precipitation inputs resulted in varied best-fitted parameter values and ranges. All the above observations indicate that the selection of suitable precipitation input(s) is necessary for an accurate investigation of the hydrological responses of any given basin.

  • Contribution of Potential Evaporation Forecasts to 10-day streamflow forecast skill for the Rhine river

    Auteurs: Osnabrugge, B. van; Uijlenhoet, R.; Weerts, A.H. (2018)
    Gepubliceerd in: Hydrology and earth system sciences (2018), pagina 1-23

    Medium term hydrologic forecast uncertainty is strongly dependent on the forecast quality of meteorological variables. Of these variables, the influence of precipitation has been studied most widely, while temperature, radiative forcing and their derived product potential evapotranspiration (PET) have received little attention from the perspective of hydrological forecasting. This study aims to fill this gap by assessing the usability of potential evaporation forecasts for 10-day-ahead streamflow forecasting in the Rhine basin, Europe. In addition, the forecasts of the meteorological variables are compared with observations. Streamflow reforecasts were performed with the daily wflow_hbv model used in previous studies of the Rhine using the ECMWF 20-year meteorological reforecast dataset. Meteorological forecasts were compared with observed rainfall, temperature, global radiation and potential evaporation for 148 subbasins. Secondly, the effect of using PET climatology versus using observation-based estimates of PET was assessed for hydrological state and for streamflow forecast skill. We find that: (1) there is considerable skill in the ECMWF reforecasts to predict PET for all seasons, (2) using dynamical PET forcing based on observed temperature and satellite global radiation estimates results in lower evaporation and wetter initial states, but (3) the effect on forecasted 10-day streamflow is limited. Implications of this finding are that it is reasonable to use meteorological forecasts to forecast potential evaporation and use this is in medium-range streamflow forecasts. However, it can be concluded that an approach using PET climatology is also sufficient, most probably not only for the application shown here, but for most models similar to the HBV concept and for moderate climate zones. As a by-product, this research resulted in gridded datasets for temperature, radiation and potential evaporation based on the Makkink equation for the Rhine basin. The datasets have a spatial resolution of 1.2×1.2km and an hourly timestep for the period from July 1996 through 2015. This dataset complements an earlier precipitation dataset for the same area, period and resolution.

  • Offshore wind farms as potential locations for flat oyster (Ostrea edulis) restoration in the Dutch North Sea

    Auteurs: Kamermans, P.; Walles, B.; Kraan, M.; Duren, L.A. van; Kleissen, F.; Have, T.M. van der; Smaal, A.C.; Poelman, M. (2018)
    Gepubliceerd in: Sustainability, volume 10 (2018) nummer 11, pagina 1-24

    The “Dutch Energy Agreement” motivates governments and industries to invest in renewable energy sources, of which offshore wind energy is one of the solutions to meet the agreed target of 16% of the total energy budget from renewable resources by 2023. An option for the multi-use of wind farms is nature-inclusive building, in which the design and construction of wind farms make use of the potential for co-design with oyster bed restoration. This can support the government’s ambitions, for the Dutch North Sea, to achieve biodiversity goals, restore ecosystem functions, and enhance ecosystem services, including future seafood production. For the recovery of flat oyster (Ostrea edulis) beds, knowledge is required about the conditions under which active restoration of this species in the North Sea can be successfully implemented. This paper gives a framework and presents results to determine suitability of wind farms for flat oyster restoration, and provides recommendations for pilot studies. Our analysis showed that a number of wind farms in the Dutch section of the North Sea are suitable locations for development of flat oyster beds. Combining oyster restoration and oyster culture, as a protein source, is a viable option worth investigating.

  • A statistical simulation method for joint time series of non-stationary hourly wave parameters

    Auteurs: Jager, W.S.; Nagler, T.; Czado, C.; McCall, R.T. (2018)
    Gepubliceerd in: Journal of LATEX templates (2018), pagina 1-27

    Statistically simulated time series of wave parameters are required for many coastal and offshore engineering applications, often at the resolution of approximately one hour. Various studies have relied on autoregressive moving-average (ARMA) processes to simulate synthetic series of wave parameters in a Monte Carlo sense. However, accurately representing inter-series dependencies has remained a challenge. In particular, the relationship between wave height and period statistics is complex, due to the limiting steepness condition. Here, we present a new simulation method for joint time series of signicant wave height, mean zero-crossing periods and a directional regime variable. The latter distinguishes between northern and southwestern waves. The method rests on several model components which include renewal processes, Fourier series with random coecients, ARMA processes, copulas and regime-switching. A particular feature is a data-driven estimate for a wave height-dependent limiting wave steepness condition which is used to facilitate copulabased dependence modeling. The method was developed for and applied to a data set in the Southern North Sea. For this site, the method could simulate time series with realistic annual cycles and inter-annual variability. In the time series data, the bivariate distribution of signicant wave height and mean zero-crossing period was well represented. An inuence of the directional regime on the bivariate distribution could also be modeled. However, the inuence was not as strong in simulated data as in observed data. Finally, simulated series captured duration and inter-arrival time of storm events well. Potential applications for output of the simulation method range from the assessment of coastal risks or design of coastal structures to the planning and budgeting of oshore operations.

  • Designing for stakeholder values in port development in Africa

    Auteurs: Slinger, J.H.; Vreugdenhil, H. (2018)
    Gepubliceerd in: Proceedings of the 34th PIANC World Congress 2018 (Panama City, Panama, May 7 to 11, 2018) (2018), pagina 1-4

    This paper addresses the need for stakeholder-inclusive design in sustainable port development. This involves learning about the values and knowledge resources of local stakeholders at an early stage, but is a step that is often omitted in current port planning processes. However, it is essential in creating added value and in avoiding costly delays when port development is stopped or delayed by social impact findings at a later stage. A stakeholder engagement process for the Port of Tema, Ghana, is used to illustrate the types of activities required and offer insights in the outcomes. In particular, a game structuring method applied in a 50-people workshop in February 2017 demonstrated that the expertise of local stakeholders and insight into their preferences regarding potential futures for the port city and its surroundings can inform planners, port authorities and engineering scientists about what it means to be a sustainable port in a developing country context.

  • Benthic hotspots in the pelagic zone : light and phosphate availability alter aggregates of microalgae and suspended particles in a shallow turbid lake

    Auteurs: Brinkmann, B.W.; Vonk, J.A.; Beusekom, S.A.M. van; Ibanez, M.E.; Lucas Pardo, M.A. de; Noordhuis, R.; Manders, E.M.M.; Verspagen, J.M.H.; Geest, H.G. van der (2018)

    Limnetic aggregates from a turbid delta lake with low dissolved nutrient availability were studied in relation to light and dissolved nutrient availability. Quick light-attenuation restricts the euphotic zone to the top surface layer of the water column, whereas mineralization processes in the sediment specifically provide dissolved nutrients near the lakebed. This suggests neither the pelagic nor the benthic zone provides the combination of resources required for microalgal growth. Nutrient mineralization in aggregates could bridge this apparent spatial gap in light and nutrients by providing dissolved nutrients in the euphotic zone, promoting microalgal growth. To explore this, aggregates obtained from turbid and phosphate-limited lake Markermeer (The Netherlands) were exposed in the laboratory to phosphate-replete and phosphate depleted conditions, at high-light and low-light availability. Confocal microscopy revealed that aggregates exhibited alkaline phosphatase activity and contained microalgae, other microbes, and extracellular polymeric substances. The spatial distribution of the phosphatase activity in aggregates largely matched that of chlorophyll a (Chl a)-lacking microbes, suggesting that these microbes were responsible for the activity. Colorimetric quantification revealed that aggregates exhibited over 1.9-fold higher phosphatase activity than surrounding water. Two-day exposure to different light and phosphate availabilities affected aggregate composition. Phosphate depleted conditions resulted in more Chl a-lacking microbes and more phosphatase activity than phosphate-replete conditions. Low-light intensity resulted in higher abundance of extracellular polymeric substances than high-light intensity. In contrast to aggregates from deep stratified systems, Markermeer aggregates were not enriched with dissolved phosphorus. These results suggest that P-cycling in aggregates differs between shallow turbid and deep stratified ecosystems.

  • Damage characterisation of rock armoured slopes

    Auteurs: Almeida, E. de; Gent, M.R.A. van; Hofland, B. (2018)
    Gepubliceerd in: Coastlab18 : proceedings of the 7th International conference on the application of physical modelling in coastal and port engineering and science (Santander, Spain, May 22-26, 2018) (2018), pagina 1-10

    In order to design reliable coastal structures, for present and future scenarios, universal and precise damage assessment methods are required. This study addresses this need, and presents improved damage characterization methods for coastal structures with rock armoured slopes. The data used in this study was obtained from a test campaign carried out at Deltares within the EU Hydralab+ framework. During these tests, advanced measuring techniques (Digital Stereo Photography) were used, which are able to survey the full extension of the structure and identify local variations of damage. The here proposed damage characterisation method is based on three fundamental aspects: clear damage concepts, precise damage parameters and high resolution measuring techniques. Regarding damage concepts, first the importance of the characterization width is studied. For damage parameters obtained from the maximum erosion depth observed in a given width (E3D,m), the measured damage increases continuously with increased characterization width. But for damage parameters obtained from width-averaged profiles (S and E2D), the measured damage reduces with increased characterization width. Second, a new definition of damage limits (damage initiation, intermediate damage and failure) is presented and calibrated. Regarding the damage parameters, the parameter E3D,5, which describes the maximum erosion depth within the characterization width, is recommended as a robust damage parameter for conventional and non-conventional configurations based on three main characteristics: its low bias, its low random error, the ability to distinguish damage levels and is its validity and suitability for all types of structures (conventional and non-conventional). In addition, the results from this study show that the damage measured with the damage parameter E3D,5 presents an extreme value distribution.

  • Participatory and collaborative modelling; key to sustainable and inclusive development : strengthening stakeholder ownership for informed and participatory water resources management

    Auteur: Basco Carrera, L. (2018)

    Safe access to water is essential for sustainable development. Building resilience towards disaster risks and ensuring water availability by balancing the many competing uses and users of water, while maintaining healthy and diverse ecosystems, are critical elements to ultimately deliver water security. In this Ph.D. thesis, participatory and collaborative modelling is presented as a means towards sustainable development, as it supports informed decision-making and inclusive development. How to develop and use computer-based simulation models is analysed following a participatory or collaborative modelling approach for managing water resources, so their use can be enhanced, and the ownership of the development strengthened. Four methods are presented to engage stakeholders in the development and use of computer-based simulation models. These approaches are tested in nine study cases, from which this thesis focuses on five of them. The covered themes and countries include river basin planning in Indonesia, water quality management in Turkey and Indonesia, adaptive planning in Bangladesh, and flood risk management in Tanzania. Results of the research show that the use of participatory and collaborative modelling makes the modelling process more efficient. Together, modellers and stakeholders share learning, build consensus, have a sense of ownership of the models, tools and solutions developed and trust in the decision-making process.

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