3987 resultaten

  • Does plastic waste kill mangroves? : a field experiment to assess the impact of anthropogenic waste on mangrove growth, stress response and survival

    Auteurs: Bijsterveldt, C.E.J. van; Wesenbeeck, B.K. van; Ramadhani, S.; Raven, O.V.; Gool, F.E. van; Pribadi, R.; Bouma, T.J. (2020)
    Gepubliceerd in: Science of the total environment (2020), pagina 1-38

    The value of mangroves has been widely acknowledged, but mangrove forests continue to decline due to numerous anthropogenic stressors. The impact of plastic waste is however poorly known, even though the amount of plastic litter is the largest in the region where mangroves are declining the fastest: South East Asia. In this study, we examine the extent of the plastic waste problem in mangroves along the north coast of Java, Indonesia. First, we investigate how much of the forest floor is covered by plastic in the field (in number of items per m2 and in percentage of the forest floor covered by plastic), and if plastic is also buried in the upper layers of the sediment. We then experimentally investigate the effects of a range of plastic cover percentages (0%, 50% and 100%) on root growth, stress response of the tree and tree survival over a period of six weeks. Field monitoring showed that plastic was abundant, with 27 plastic items per m2 on average, covering up to 50% of the forest floor at multiple locations. Moreover, core data revealed that plastic was frequently buried in the upper layers of the sediment where it becomes immobile and can create prolonged anoxic conditions. Our experiment subsequently revealed that prolonged suffocation by plastic caused immediate pneumatophore growth and potential leaf loss. However, trees in the 50%-plastic cover treatment proved surprisingly resilient and were able to maintain their canopy over the course of the experiment, whereas trees in the 100%-plastic cover treatment had a significantly decreased leaf area index and survival by the end of the experiment. Our findings demonstrate that mangrove trees are relatively resilient to partial burial by plastic waste. However, mangrove stands are likely to deteriorate eventually if plastic continues to accumulate.

  • Managing erosion of mangrove-mud coasts with permeable dams – lessons learned

    Auteurs: Winterwerp, J.C.; Oost, A.P.; Wesenbeeck, B.K. van (2020)
    Gepubliceerd in: Ecological engineering, volume 158 (2020), pagina 1-27

    Mangrove-mud coasts across the world erode because of uninformed management, conversion of mangrove forests into aquaculture ponds, development of infrastructure and urbanization, and/or extraction of groundwater inducing land subsidence. The accompanied loss of ecosystem values, amongst which safety against flooding, has far reaching consequences for coastal communities, exacerbated by sea-level rise. To halt erosion various nature-based solutions have been implemented as an alternative to hard infrastructure sea defenses, including mangrove planting and erection of low-tech structures such as bamboo fences, permeable brushwood dams, etc. These structures have been designed on the basis of best-engineering practice, lacking sufficient scientific background. This paper investigates the use and success of permeable dams over a period of about 15 years, describing their application in Guyana, Indonesia, Suriname, Thailand and Vietnam, summarizing the lessons-learned, and analyzing their functioning in relation to the physical-biological coastal system. Also an overview of relevant costs is given. The basic philosophy behind the construction of permeable dams is the rehabilitation of mangrove habitat through re-establishment of the (fine) sediment dynamics – we refer to Building with Nature as the overarching principle of this approach. Our main conclusions are that a successful functioning of permeable dams requires (1) a thorough understanding of the physical-biological system and analysis of the relevant processes, (2) patience and persistence, including maintenance, as the natural time scales to rehabilitate mangrove green belts take years to decades, and (3) intensive stakeholder involvement. We give a list of conditions under which permeable dams may be successful, but in qualitative terms, as local site conditions largely govern their success or failure.

  • Estimation of global tropical cyclone wind speed probabilities using the STORM dataset

    Auteurs: Bloemendaal, N.; Moel, H. de; Muis, S.; Haigh, I.D.; Aerts, J.C.J.H. (2020)
    Gepubliceerd in: Scientific data, volume 7 (2020), pagina 1-11

    Tropical cyclones (TC) are one of the deadliest and costliest natural disasters. To mitigate the impact of such disasters, it is essential to know extreme exceedance probabilities, also known as return periods, of TC hazards. In this paper, we demonstrate the use of the STORM dataset, containing synthetic TCs equivalent of 10,000 years under present-day climate conditions, for the calculation of TC wind speed return periods. The temporal length of the STORM dataset allows us to empirically calculate return periods up to 10,000 years without fitting an extreme value distribution. We show that fitting a distribution typically results in higher wind speeds compared to their empirically derived counterparts, especially for return periods exceeding 100-yr. By applying a parametric wind model to the TC tracks, we derive return periods at 10 km resolution in TC-prone regions. The return periods are validated against observations and previous studies, and show a good agreement. The accompanying globalscale wind speed return period dataset is publicly available and can be used for high-resolution TC risk assessments.

  • The impact of wind on flow and sediment transport over intertidal flats

    Auteurs: Colosimo, I.; Vet, P.L.M. de; Maren, D.S. van; Reniers, A.J.H.M.; Winterwerp, J.C.; Prooijen, B.C. van (2020)
    Gepubliceerd in: Journal of marine science and engineering, volume 8 (2020) nummer 11, pagina 1-26

    Sediment transport over intertidal flats is driven by a combination of waves, tides, and wind-driven flow. In this study we aimed at identifying and quantifying the interactions between these processes. A five week long dataset consisting of flow velocities, waves, water depths, suspended sediment concentrations, and bed level changes was collected at two locations across a tidal flat in the Wadden Sea (The Netherlands). A momentum balance was evaluated, based on field data, for windy and non-windy conditions. The results show that wind speed and direction have large impacts on the net flow, and that even moderate wind can reverse the tidal flow. A simple analytical tide–wind interaction model shows that the wind-induced reversal can be predicted as a function of tidal flow amplitude and wind forcing. Asymmetries in sediment transport are not only related to the tide–wind interaction, but also to the intratidal asymmetries in sediment concentration. These asymmetries are influenced by wind-induced circulation interacting with the large scale topography. An analysis of the shear stresses induced by waves and currents revealed the relative contributions of local processes (resuspension) and large-scale processes (advection) at different tidal flat elevations.

  • Minimizing the required surge vessel volume by an improved thermodynamic model

    Auteurs: Zwan, S. van der; Pothof, I.W.M. (2020)
    Gepubliceerd in: Hydrolink (2020) nummer 3, pagina 90-91

    Surge vessels are the main protection mechanisms in most long-distance water transport system. They are designed with the help of water hammer software, which mostly uses the ideal gas law. This leads to a conservative design. This article will show that using a more detailed model of the behavior of the air inside the surge vessel, can lead to a less conservative design and thus reduce the costs of the system. It will summarize the present state of the research into a new model for the thermodynamics of surge vessels.

  • DeltaSand: a state dependent double hardening elasto-plastic model for sand : formulation and validation

    Auteur: Galavi, V. (2021)
    Gepubliceerd in: Computers and geotechnics, volume 129 (2021), pagina 1-12

    Numerical simulations of pile installation in sands require advanced constitutive models which are able to predict the mechanical behaviour of soils in a wide range of soil stresses under different loading conditions such as cyclic and monotonic loadings. In this paper, an elasto-plastic constitutive model within a double hardening framework is described which is capable of reproducing the mechanical behaviour of sands in different soil states (stress and relative density) under deviatoric and volumetric loadings. First, the formulation of the model is described and then the capability of the model is shown by simulating laboratory tests data of Karlsruhe sand for various relative densities, stress states and loading conditions.

  • Deltas for the future : lessons learned from a water innovation programme

    Auteurs: Duin, P. van der; Sule, M.S.; Bruggeman, W.A. (2011)
    Gepubliceerd in: Irrigation and drainage : the journal of the International Commission on Irrigation and Drainage (ICID), volume 60 (2011) nummer S1, pagina 122-128

    Delta regions worldwide have to cope with increasing pressure on land use and the consequences of climate change and rising sea levels. Because existing approaches and solutions are no longer sufficient to face future challenges of flood protection, sustainable energy and freshwater supply, truly innovative approaches and technologies have to be developed and implemented. To that end, Rijkswaterstaat (NL), in collaboration with Deltares, executed a water innovation programme (WINN) in the period 2002–2010. By analysing a selection of the important and interesting results of the WINN programme with the support of the cyclic innovation model (CIM), the aim of this paper is to identify key factors for successful innovation and provide recommendations for effective organization of a government water innovation programme.

  • Field study and supporting analysis of air curtains and other measures to reduce salinity transport through shipping locks

    Auteurs: Keetels, G.H.; Uittenbogaard, R.E.; Cornelisse, J.M.; Villars, M.T.; Pagee, J.A. van (2011)
    Gepubliceerd in: Irrigation and drainage : the journal of the International Commission on Irrigation and Drainage (ICID), volume 60 (2011) nummer S1, pagina 42-50

    This paper presents an overview of a study on salinity intrusion through shiplocks that are located at a saltwater and freshwater interface, and the possible measures that can be taken to reduce this salinity transport. The main focus of the study was to test the effectiveness of several measures against salt intrusion through a shiplock. For this reason a series of field experiments was conducted in the Stevin shiplock in the Afsluitdijk, near Den Oever, the Netherlands, in between theWadden Sea and the IJsselmeer. The measures tested include an air curtain at both ends of the shiplocks, alone and in combination with a water jet, as well as a rigged sill to reduce the effective depth, and flushing of the lock with fresh water. A new type of air curtain with air injectors was designed and built for this study. Prior to the field experiments, a series of laboratory scale experiments and computer simulations of lock exchange flow were conducted to gain insight into the salinity transport process and to support the design of the field study. The study has shown that a significant reduction of salinity intrusion can be attained by using a combination of measures. These findings are relevant for shiplocks located in a saline-freshwater transition zone for which salinity intrusion should be reduced as much as possible.

  • From ripples to large-scale sand transport : the effects of bedform-related roughness on hydrodynamics and sediment transport patterns in Delft3D

    Auteurs: Brakenhoff, L.; Schrijvershof, R.A.; Werf, J.J. van der; Grasmeijer, B.; Ruessink, B.G.; Vegt, M. van der (2020)
    Gepubliceerd in: Journal of marine science and engineering, volume 8 (2020) nummer 11, pagina 1-25

    Bedform-related roughness affects both water movement and sediment transport, so it is important that it is represented correctly in numerical morphodynamic models. The main objective of the present study is to quantify for the first time the importance of ripple- and megaripple-related roughness for modelled hydrodynamics and sediment transport on the wave- and tide-dominated Ameland ebb-tidal delta in the north of the Netherlands. To do so, a sensitivity analysis was performed, in which several types of bedform-related roughness predictors were evaluated using a Delft3D model. Also, modelled ripple roughness was compared to data of ripple heights observed in a six-week field campaign on the Ameland ebb-tidal delta. The present study improves our understanding of how choices in model set-up influence model results. By comparing the results of the model scenarios, it was found that the ripple and megaripple-related roughness affect the depth-averaged current velocity, mainly over the shallow areas of the delta. The small-scale ripples are also important for the suspended load sediment transport, both indirectly through the affected flow and directly. While the current magnitude changes by 10–20% through changes in bedform roughness, the sediment transport magnitude changes by more than 100%.

  • Bodemverbeterende maatregelen: pilot met toevoegen organisch stof : onderzoek naar mogelijk nitraatuitspoeling naar het grondwater

    Auteurs: Weert, J.P.A. de; Rozemeijer, J.C.; Cinjee, A.C.; Vilsteren, E. van; Heinen, M.; Groot, W. de (2020)

    Het onderzoeksprogramma Lumbricus gaat over het klimaatrobuust inrichten en beheren van stroomgebieden op de hogere zandgronden. Binnen het Lumbricus-thema Bewuste Bodem, cluster 2 wordt invullinggegeven aan: i) effectief bodem- en waterbeheer op perceelschaal, ii) maatregelen voor een duurzaam watersysteem, en iii) waterkwantiteit en waterkwaliteit. Het doel van het in dit rapport beschreven deelonderzoek was om vast te stellen in hoeverre het opgebrachte substraat leidt tot uitspoeling van nitraat naar het grondwater. Dit deelonderzoek is uitgevoerd door Deltares en WENR. In de verschillende proefvlakken zijn van november 2019 tot maart 2020 metingen gedaan aan nutriënten in de bodem en het grondwater.

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