3935 results

  • The potential of coastal ecosystems to mitigate the impact of sea level rise in shallow tropical bays

    Authors: Keyzer, L.M.; Herman, P.M.J.; Smits, B.P. (2020)
    Published in: Estuarine, coastal and shelf science (2020), page 1-21

    Shallow tropical bays in the Caribbean, like Orient Bay and Galion Bay in Saint Martin, are often sheltered by coral reefs. In the relatively calm environment behind the reefs, seagrass meadows grow. Together, these ecosystems provide valuable ecosystem services like coastal protection, biodiversity hotspots, nursery grounds for animals and enhancing tourism and fisheries. However, sea-level rise imperils these ecosystems and the services they provide because of changing hydrodynamic conditions, with potential effects on the interdependencies between these ecosystems. By means of a hydrodynamic model that accounts for the interaction with vegetation (Delft3D Flexible Mesh), the impact of sea-level rise (0.87 m in 2100) is investigated for three scenarios of future reef development (i.e. keep-up, give-up and catch-up). If coral reefs cannot keep up with sea-level rise, the wave height and flow velocity increase significantly within associated bays, with the wave height doubling locally in case of eroding reefs in our model simulations. Since the presence of seagrass strongly depends on the hydrodynamic conditions, the response of seagrass to the future hydrodynamic conditions is projected using a habitat suitability model that is based on a logistic regression. The spatial character of the bays determines the response of seagrass. In Orient Bay, which is deeper and partly exposed to higher waves, the seagrass will likely migrate from the deeper parts to shallow areas that become suitable for seagrass because of the surf zone moving landward. In contrast, the conditions for seagrass worsen in Galion Bay for the catch-up and give-up scenario; due to the shallowness of this bay, the seagrass cannot escape to more suitable areas, resulting in significant seagrass loss. It is shown that healthy coastal ecosystems are able to limit the change in hydrodynamic conditions due to sea-level rise. Therefore, preserving these ecosystems is key for ensuring the resilience of shallow tropical bays to sea-level rise and maintaining their ecosystem services.

  • Effect of gate selection on the non-cohesive sedimentation in irrigation schemes

    Authors: Theol, S.A.; Jagers, H.R.A.; Yangkhurung, J.R.; Suryadi, F.X.; Fraiture, C. de (2020)
    Published in: Water, volume 12 (2020) issue 10, page 1-21

    In order to cover the crop water requirements, flow control structures such as gates and weirs are used to transfer the desired amount of water from the canals to the field canals. This paper examines the impact of gate operation and the selection of gates on the deposition of non-cohesive sediment. The Delft3D model is used to simulate the effects of different scenarios regarding gate operation and the location of the gate that is opened. The model results showed that the gate selection affects not only hydraulic parameters but also morphological parameters. It was found that opening the gates closer to the offtake resulted in less sediment deposition at the entrance of the branch canal when compared to opening the gates further away. Gate selection can be used as a tool in sediment management. By alternating the opening of different gates sediments that are already deposited after opening one gate can be eroded when another gate is operated, thus minimizing the additional cost of sediment removal. The use of Delft3D proved beneficial as the selection of different gates leads to asymmetric sediment deposition patterns which would be missed when using a 1D model.

  • Bodemmonster analyse Egmond

    Authors: Blok, B.W.G.; Arentz, L. (2012)

    Dit rapport beschrijft een lab analyse van nieuwe bodemmonsters bij Egmond die is uitgevoerd ten behoeve van beter inzicht in de hoeveelheid slib in de bodem die beschikbaar is voor resuspensie. Deze informatie zal gebruikt worden voor een verdere kalibratie van het slib-buffermodel voor de Nederlandse kustzone.

  • Activiteitenplan 2021 Strategisch Onderzoek Deltares

    Originally published in 2020

    Dit Activiteitenplan 2021 schetst de hoofdlijnen van het Strategisch Onderzoek dat Deltares in 2021 gaat uitvoeren. Eerst presenteren we Deltares en beschrijven de grote maatschappelijke uitdagingen waar Deltares zich op richt. Vervolgens gaan we in op de inhoud van onze vier missiegebieden en geven kerninformatie over onze missiegerichte onderzoeksprogramma’s. De programmering van onze kennisbasis komt aan de orde, en tenslotte een overzicht van de meest actuele financiële kentallen van het Activiteitenplan 2021. In deel 2 zijn de uitgewerkte onderzoeksprogramma’s opgenomen, met meer gedetailleerde informatie over onze programma’s.

  • Winning suppletiezand voor herstel zwakke schakels Noord-Holland : scenariostudies m.b.t. slibtransport, nutriënttransport en primaire productie voor de periode 2013-2014

    Authors: Harezlak, V.; Rooijen, A. van; Friocourt, Y.F.; Kessel, T. van; Los, H.F.J. (2012)

    In dit rapport is het effect van zandwinning ten behoeve van de versterking van de zwakke schakels Noord-Holland op slibconcentraties, doorzicht, nutrienttransport en primaire productie berekend middels numerieke modellen.

  • The natural environment in port development: a ‘green handbrake’ or an equal partner?

    Authors: Taljaard, S.; Slinger, J.H.; Arabi, S.; Weerts, S.P.; Vreugdenhil, H. (2021)
    Published in: Ocean and coastal management, volume 199 (2021), page 1-11

    Rapid urbanization of the coast, growing global trade, stakeholder emancipation and ongoing depletion of natural resources implies that ports can no longer operate and develop without acknowledging and incorporating societal and environmental considerations. Drawing primarily on first-hand experiences in South African ports, supplemented with learning taken from international literature, this paper proposes a conceptual change in the position of the natural environment in port development from that of a ‘green handbrake’ to ‘equal partner’. The argument for this conceptual change is developed in three stages. First, we merge two concepts emerging from the literature, namely natural capital (or natural infrastructure) and infrastructure systems, to embed the natural environment as an integral component or ‘equal partner’ in port development. We then identify practical avenues through which the profile (or value) of the natural environment can be enhanced in port development, drawing on concepts such as Building with Nature (BwN) and multi-use of natural capital. Finally, we build a framework for Integrated Port Management (IPM) by conceptually positioning and aligning environmental processes within the traditional port development cycle, as well as identifying the need for coordination across and continuity between individual environmental assessment processes. In essence, bridging the disconnect between natural environmental issues and port development requires early consideration of the natural environment in port development, and an acknowledgement of multi-use benefits from natural capital. Further, in the operations and maintenance phases, environmental management systems in ports should not only focus on environmental performance, but also embrace multi-use valuation of the natural environment (ecosystem services) to give purpose to the need for environmental protection. However, crucial to effective implementation of an Integrated Port Management (IPM) framework will be its integration in organisational processes, supported by collaborative institutional structures. Only then will the environment take its place as equal partner in port development.

  • Winning suppletiezand Noordzee : scenariostudies m.b.t. slibtransport, nutriënttransport en primaire productie voor de periode 2013-2017

    Authors: Harezlak, V.; Rooijen, A. van; Friocourt, Y.F.; Kessel, T. van; Los, H.F.J. (2012)

    In dit rapport is het effect van zandwinning ten behoeve van reguliere kustsuppletie op slibconcentraties, doorzicht, nutrienttransport en primaire productie berekend middels numerieke modellen. In het rapport zijn met name de effecten in de Natura 2000-gebieden uitgebreid belicht.

  • Combustion in miscible displacement for high-pressure air injection

    Authors: Kokubun, M.A.E.; Khoshnevis Gargar, N.; Marchesin, D.; Bruining, J. (2020)
    Published in: arXiv : Physics - Fluid dynamics (2020), page 1-22

    We develop a theory for the problem of high pressure air injection into deep reservoirs containing light oil. Under these conditions, the injected fluid (oxygen plus inert components) is completely miscible with the oil in the reservoir. Moreover, exothermic reactions between dissolved oxygen and oil are possible. We use Koval's model to account for the miscibility of the components, such that the fractional-flow functions resemble the ones from Buckley-Leverett flow. This allows to decompose the solution of this problem into a series of waves. We then proceed to obtain full analytical solutions in each wave. Of particular interest is the case where the combustion wave presents a singularity in its internal wave profile. Evaluation of the variables of the problem at the singular point determines the macroscopic parameters of the wave, i.e., combustion temperature, wave speed and downstream oil fraction. The waves structure was observed previously for reactive immiscible displacement and we describe it here for the first time for reactive miscible displacement of oil. We validate the developed theory using numerical simulations.

  • An efficient modelling approach for probabilistic assessments of present-day and future fluvial flooding

    Authors: Ngo, H; Ranasinghe, R.; Zevenbergen, C.; Kirezci, E.; Maheng, D.; Radhakrishnan, M.; Pathirana, A. (2020)
    Published in: Natural Hazards and Earth System Sciences (2020), page 1-42

    Flood risk management and planning decisions in many parts of the world have historically utilised flood hazard or risk maps for a very limited number of hazard scenarios (e.g. river water levels), mainly due to computational challenges. With the potentially massive increase in flood risk in future due to the combination of climate change effects (increasing the hazard) and increasing population and developments in floodplains (increasing the consequence), risk-informed flood risk management, which enables balancing the risk with the reward, is now becoming more and more sought after. This requires a comprehensive and quantitative risk assessment, which in turn demands multiple (thousands of) river and flood model simulations. Performing such a large number of model simulations is a challenge, especially for large, complex river systems (e.g. Mekong) due to the associated computational and resource demands. This article presents an efficient modelling approach that combines a simplified 1D hydrodynamic model for the entire Mekong Delta with a detailed 1D/2D coupled model and demonstrates its application at Can Tho city in the Mekong Delta. Probabilistic flood hazard maps, ranging from 0.5 yr to 100 yr return period events, are obtained for the urban centre of Can Tho city under different future scenarios taking into account the impact of climate change forcing (river flow, sea-level rise, storm surge) and land subsidence. Results obtained under present conditions show that more than 12 % of the study area is inundated by the present-day 100 yr return period water level. Future projections show that, if the present rate of land subsistence continues, by 2050 (under both RCP4.5 and RCP8.5 climate scenarios), the 0.5 yr and 100 yr return period flood extents will increase by around 15-fold and 8-fold, respectively, relative to the present-day flood extent. However, without land subsidence, the projected increases in the 0.5 yr and 100 yr return period flood extents by 2050 (under RCP4.5 and RCP8.5) are limited to between a doubling to tripling of the present-day flood extent. Therefore, adaptation measures that can reduce the rate of land subsidence (e.g. limiting groundwater extraction), would substantially mitigate future flood hazards in the study area. A combination of restricted groundwater extraction and the construction of a new and more efficient urban drainage network would facilitate even further reductions in the flood hazard. The projected 15-fold increase in flood extent projected by 2050 for the twice per year (0.5 yr return period) flood event implies that the do nothing management approach is not a feasible option for Can Tho.

  • Multi-scale experiments for a coarse sand barrier against backward erosion piping

    Authors: Rosenbrand, E.; Beek, V.M. van; Bezuijen, A.; Akrami, S.; Terwindt, J.; Koelewijn, A.R.; Förster, U. (2020)
    Published in: Géotechnique (2020), page 1-32

    Backward erosion piping poses a severe threat for embankments founded on sandy deposits. The physical mechanism by which a pipe progresses upstream beneath the embankment is conceptually understood, and assessments indicate high failure probabilities in the Netherlands. Rising sea levels and economic growth increase the risk of flooding, and the need for remediation measures. Conventional measures have undesired side effects, in terms of costs, maintenance, space requirements and sustainability. The coarse sand barrier (CSB) is a novel nature-based solution lacking these side effects. The CSB is a trench filled with coarse sand that is placed below the downstream toe of the embankment, which prevents the pipe from progressing upstream. The effectiveness of the CSB is based on its higher resistance against erosion and its effect on groundwater flow. This paper presents experimental work that was conducted to test the feasibility of a CSB for application at a pilot site in the Netherlands. This involved experiments with seepage lengths of 0.34, 1.34 and 15 m, using different barrier materials and background sands. A conceptual model is presented for the physical mechanism of pipe formation in the presence of a barrier. As the resistance of the barrier can be characterized by a local scale-independent strength criterion, laboratory results are applicable for design practice.

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