3765 results

  • Vlaamse Baaien Flexible Mesh Model (VlaBa-FM)

    Authors: Lugt, M.A. van der; Werf, J.J. van der; Röbke, B.R. (2020)

    For mid-term morphological models over a 30-km long domain, this report demonstrates that the 2DH morphodynamic functionality of Delft3D-4 such as morphological acceleration, multiple sediment fractions, dredging and dumping work well in Delft3D-FM. Therefore, this study gives confidence in developing the next generation morphodynamic models in the new model suite. In future studies of the Vlaamse Baaien region with Delft3D-FM it is advised to move to a fit-for-purpose unstructured grid tomake optimal use of the local grid refinement capabilities of Delft3D-FM.

  • Understanding the morphological processes at Ameland Inlet : Kustgenese 2.0 synthesis of the tidal inlet research

    Authors: Elias, E.P.L.; Pearson, S.; Spek, A.J.F. van der (2020)

    The objective of this Coastal Genesis 2.0 report is to synthesize the current understanding of the role of the Ameland ebb-tidal delta in the coastal system, and the processes underlying meso-scale ebb-tidal delta dynamics. Such knowledge is not only essential for future sustainable coastal management of Ameland Inlet, but also provides valuable lessons for the other inlets of the Wadden Sea and the (closed off) inlets in the Voordelta. This report serves as technical background document for the technical advice on the possibilities for ebb-tidal delta nourishments and their potential added value in coastal management.

  • A practical quantification of error sources in regional-scale airborne groundwater salinity mapping

    Originally published in 2020
    Published in: Environmental research letters (2020), page 1-19

    To inform suitable coastal groundwater management strategies, regional-scale mapping of fresh and salt groundwater occurrence is extremely beneficial. This mapping is usually based on conventional ground-based methods. However, these are not only slow and expensive, but result in localized and disconnected information which is uneconomical and impractical on the large scales required. Airborne electromagnetic (AEM) surveys have been proven a frugal and rapid way to overcome these shortcomings. Consequently, AEM methods are increasingly being used globally. Little is known about the effects of flightline spacing and additional ground-based data on the quality of mapping results, and in general the accuracy of AEM, other than validation against often sparse ground measurements. Understanding this is therefore invaluable as input to groundwater management strategies, survey planning and decision making. Here, we use a regional scale (900 km2), high-resolution (50m x 50m x 0.5m) 3D synthetic model of electrical conductivity and geological properties, to investigate the effects of data availability on the accuracy of regional-scale groundwater salinity mapping. This was undertaken by simulating commonly used AEM parameters and realistic data acquisition methods. Two key data components are considered: (1) the AEM survey itself, and (2) geological information used to convert the AEM results into groundwater salinity. Spatially, different data-densities of these two components are quantitatively compared to highlight ideal geometrical configurations for given accuracy requirements. Our results indicate that in terms of optimising costs versus benefits, the value of additional lithological information is dependent on how well the initial distribution of electrical conductivity is resolved by the acquisition and inversion process.

  • Non-intrusive hierarchical coupling strategies for multi-scale simulations in gravitational dynamics

    Authors: Portegies Zwart, S.; Pelupessy, I.; Martinez-Barbosa, C.; Elteren, A.G. van; McMillan, S. (2020)

    Hierarchical code coupling strategies make it possible to combine the results of individual numerical solvers into a self-consistent symplectic solution. We explore the possibility of allowing such a coupling strategy to be non-intrusive. In that case, the underlying numerical implementation is not affected by the coupling itself, but its functionality is carried over in the interface. This method is efficient for solving the equations of motion for a self-gravitating system over a wide range of scales. We adopt a dedicated integrator for solving each particular part of the problem and combine the results to a self-consistent solution. In particular, we explore the possibilities of combining the evolution of one or more microscopic systems that are embedded in a macroscopic system. The here presented generalizations of BRIDGE include higher-order coupling strategies (from the classic 2nd order up to 10th-order), but we also demonstrate how multiple bridges can be nested and how additional processes can be introduced at the bridge time-step to enrich the physics, for example by incorporating dissipative processesor. Such augmentation allows for including additional processes in a classic Newtonian N-body integrator without alterations to the underlying code. These additional processes include for example the Yarkovsky effect, dynamical friction or relativistic dynamics. Some of these processes operate on all particles whereas others apply only to a subset. The presented method is non-intrusive in the sense that the underlying methods remain operational without changes to the code (apart from adding the get- and set-functions to enable the bridge operator). As a result, the fundamental integrators continue to operate with their internal time step and preserve their local optimizations and parallelism. Multiple bridges can be nested and coupled hierarchically, allowing for the construction of a complex environment of multiple nested augmented bridges. While the coupling topology may become rather complicated, we introduce the hierarchical coupling language (HCL), a meta language in which complex bridge topologies can be described. The meta language is meant for stimulating the discussion on even more complex hierarchies in which the bridge operators are introduced as patterns We present example applications for several of these cases and discuss the conditions under which these integrators can be applied. Typical applications range over 10 orders of magnitude in temporal and spatial scales when we apply the method to simulating planetary systems (au spatial and year-temporal scale) in a star cluster that orbits in the Galaxy (100 kpc-spatial and 10 Gyr-temporal scale).

  • Crowdsourcing and interactive modelling for urban flood management

    Authors: Gebremedhin, E.T.; Basco Carrera, L.; Jonoski, A.; Iliffe, M.; Winsemius, H.C. (2020)
    Published in: Journal of flood risk management (2020), page 1-15

    Participatory modelling has become a growing concept in environmental modelling, as it allows stakeholders to be involved in various stages of model development. The majority of studies, however, have focused on the participation during model use for scenario analysis and strategy evaluation after the model has been developed. Large-scale community mapping efforts create new opportunities to establish, detail and improve flood models at the development stage by working together with local stakeholders. In this article, we propose a novel participatory modelling and mapping approach. It builds on the community mapping projects across the most vulnerable wards in Dar es Salaam, Tanzania, which uses OpenStreetMap as a data platform. The approach consists of community mapping, an automated flood inundation model development and facilitation of stakeholder involvement. The participation of stakeholders in data collection helped achieving a more accurate flood model. The participatory modelling approach made participants aware of the skills necessary to develop an urban flood model with OpenStreetMap, necessary for creating a resilient society. The level of improvement obtained through the applied participatory modelling and mapping approach demonstrates its value in hydrodynamic model development and its potential for application in data scarce areas prone to urban floods.

  • Global sensitivity analysis of dike stability under maximum static groundwater heads

    Authors: Woerkom, T. van; Beek, L.P.H. van; Middelkoop, H.; Bierkens, M.F.P. (2020)
    Published in: Water resources research (2020), page 1-18

    Precise calculations of dike stability under adverse loading conditions will become increasingly important, though the hydrological impacts on dike stability, particularly the effects of groundwater flow, are often oversimplified in stability calculations. To include these effects, we use a coupled hydro-stability model to indicate relations between the geometry, subsurface materials, groundwater hydrology and stability of a dike regarding soil slip and basal sliding mechanisms. Sensitivity analyses are performed with this model using a large number of parameter combinations, while assessing both the individual sensitivity as combined effects. The analyses show that the material type of the dike and its slope are the more important parameters influencing the stability, followed by the shallow subsurface type and dike crest elevation. The material of the dike and shallow subsurface is additionally important, as a change towards sandier material can result in either an increase or a decrease of the stability. A database created by an extensive Monte Carlo analysis provides further evidence for these relations and is used to estimate failure probabilities for dike stretches that have not been assessed in detail. Despite the use of a simplified model, not including small-scale heterogeneity, remaining soil strength and transient groundwater flow, the application of the method to a case study proves its applicability.

  • Wave-driven mean flow dynamics in submerged canopies

    Authors: Rooijen, A.A. van; Lowe, R.J.; Rijnsdorp, D.P.; Ghisalberti, M.; Jacobsen, N.G.; McCall, R.T. (2020)

    The physical roughness (canopies) formed by organisms within aquatic ecosystems (e.g., seagrass, kelp, and mangroves) modifies the local wave‐driven hydrodynamics within coastal and estuarine regions. In wave‐dominated environments, an understanding of the mean wave‐driven flows generated within and above canopies is important, as it governs material transport (e.g., of nutrients, sediment, and biota). However, until recently the effect of submerged canopies on wave‐current interactions and the resulting mean (wave‐averaged) flow dynamics has received relatively little attention. In this study, a combination of wave flume experiments and numerical modeling is used to investigate the wave‐induced mean flow profiles in the presence of a submerged canopy. The measured velocities and vegetation forces were used to derive bulk drag and inertia coefficients, and to validate a nonhydrostatic 2DV wave‐flow model. The numerical model results were used to conduct an in‐depth analysis of the mean horizontal momentum terms responsible for driving the mean (horizontal) flow within and above the submerged canopies. We show that the mean canopy hydrodynamics are driven by vertical gradients in wave and turbulent Reynolds stresses, balanced by the mean canopy drag forces. The wave Reynolds stress gradient is the dominant force driving the in‐canopy mean flow and is directly related to the vorticity that is generated when the wave orbital motions become rotational near the canopy interface. This study provides new insight in the mechanisms responsible for wave‐driven mean flows within submerged canopies and guidance for how these hydrodynamics can be predicted in coastal wave‐circulation models.

  • An integrated review of river bars for engineering, management and transdisciplinary research

    Authors: Crosato, A.; Mosselman, E. (2020)
    Published in: Water, volume 12 (2020) issue 2, page 1-18

    River training and river restoration often imply modifying the patterns and dimensions of bars, channels, and pools. Research since the 1980s has greatly advanced and matured our knowledge on the formation and behavior of river bars, thanks to field work, laboratory experiments, theoretical analyses, and numerical modelling by several research groups. However, this knowledge is not easily accessible to design engineers, river managers, and ecologists who need to apply it. This is mainly due to confusing differences in terminology as well as to difficult mathematical theories. Moreover, existing scientific publications generally focus on specific aspects, so an overall review of the findings and their applications is still lacking. In many cases, the knowledge achieved so far would allow minimizing hard engineering interventions and thus obtaining more natural rivers. We present an integrated review of the major findings of river bar studies. Our aim is to provide accessible state-of-the-art knowledge for nature-based bar management and successful river training and river restoration. To this end we review the results from analytical, numerical, experimental, and field studies, explain the background of bar theories, and discuss applications in river engineering and river restoration.

  • An assessment of measured and computed depth of closure around Japan

    Authors: Udo, K.; Ranasinghe, R.; Takeda, Y. (2020)
    Published in: Scientific reports : an open-access multidisciplinary journal, volume 10 (2020), page 1-8

    A priori knowledge of the so called depth of closure (DoC) is a pre-requisite to understand and model coastal morphological response to wave forcing, which in turn enables the design of appropriate coastal adaption/protection measures. In the absence of long term measurements of coastal profile data, the DoC is often computed using Hallermeier’s formulations or derivatives thereof, for applications around the world. However, there are two major unresolved issues associated with computing the DoC in this way: the accuracy of the wave data required for reliable DoC computations, and the generic applicability of the coefficients used in DoC equations. This study exploits the availability of DoCs derived from multiple measurements of coastal profiles and wave data along the Japanese coast together with wave reanalysis products to evaluate the validity of DoC calculation approaches. Results show that the accuracy of computed DoC values determined using wave reanalysis data is limited, particularly when the spatial resolution of the wave reanalysis data is lower. Furthermore, coefficients of DoC equations proposed in previous and present studies appear to be location specific and points toward the need for a concerted worldwide meta-analysis that compares observed and derived DoC in order to derive a globally applicable formulation for DoC computations.

  • Using in situ density and strength measurements for sediment maintenance in ports and waterways

    Authors: Kirichek, A.; Shakeel, A.; Chassagne, C. (2020)
    Published in: Journal of soils and sediments (2020), page 1-7

    Fluid mud layers can be substantial in waterways and they can jeopardise navigation when the ship’s keel comes in its vicinity. The nautical bottom has therefore to be properly characterised. Mud density and yield stress are usd as criteria to characterise the nautical bottom. For a decade, measuring these parameters in situ has been a challenging task. The goal of this paper is to compare the parameters obtained from recently developed in situ measuring instruments. Our results show that the correlation between density and yield stress measurements, as a function of different measuring equipment, strongly depends on the type of mud. Therefore, a proper calibration should be performed by establishing a reference database for each equipment. In order to decrease the amount of in situ survey, it is also necessary to develop models that can accurately predict the consolidation over time.

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