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Reduced complexity modeling of shoreline response behind offshore breakwaters
Prediction of the shoreline response behind offshore breakwaters is essential for coastal protection projects. Due to the complexity of the processes behind the breakwaters (e.g., wave diffraction, currents, longshore transport), detailed modelling needs high computational efforts. Therefore, simplifying the process effect in a simpler coastline model could be efficient. In this study, the coastline evolution model ShorelineS is used. A new routine was implemented in the model to adjust the wave heights and angles behind the offshore breakwaters. Two approaches from the literature and a newly introduced one were tested in this study. The model free grid system was used to simply track the breaker line; such an advantage also helped to form tombolo, which is not common for these types of models. The tests showed promising results for single and multi breakwaters systems; however, the newly introduced approach still needs further testing and refinement for better performance and less computational cost.
Implications of coral reef mining pits on 2D hydrodynamics
Reef flat mining is one of the most common practices to source the required material for the implementation of coastal protection measures on Small Island Developing States (SIDS). There are strong concerns about this practice, because partial removal of the protective reef could increase wave impacts on the islands. Here we present the potential 2D effects of reef flat excavation pits on nearshore hydrodynamics. More specifically, we aim to assess the impact of excavation pits on nearshore circulation patterns, which could be an indicator of coastal morphological changes.
ICCE 2020 : proceedings of the virtual International Conference Coastal Engineering 2020 (6-9 October 2020)
The use of geological, geomorphological and soil mapping products in palaeolandscape reconstructions for the Netherlands
Geological, geomorphological and soil maps provide important information on the substrate as well as on the past and present physical landscape. For the intensely studied Netherlands coastal plain and Rhine–Meuse delta, many such map datasets have been compiled over the last two centuries. These mapping materials comprise older and younger legacy datasets, often fragmented over regions. They have been compiled within various research traditions and by various parties, involving geologists, soil scientists, geomorphologists and landscape archaeologists. The maps and datasets summarise overwhelming amounts of underlying data accumulated over the last few centuries, and are therefore valuable for reconstructing past landscapes. Digital-infrastructure developments have enhanced possibilities for recombining existing and new data over the last few decades, e.g. through GIS solutions such as palaeogeographical base maps, from which multiple derived map products can be generated. Integration of thematic information from various source maps and underlying data is needed to use the accumulated data diversity to its full potential and to answer applied and fundamental scientific questions. Using diverse information to compile or update maps, however, requires awareness of legacy surveying strategies and the state of knowledge at the time the original data and maps were produced. This paper reviews the soil, geological and geomorphological mapping traditions. We evaluate their products, underlying data and the reasoning behind their compilation, focusing on their use in conventional and digital palaeogeographical mapping. This helps get the most out of large quantities of legacy and modern data, a major challenge for surface and substrate digital mapping in the big-data era.
Augmented satellite InSAR for assessing short-term and long-term surface deformation due to shield tunnelling
In this work, we investigate if, when, and how satellite InSAR can be used for evaluating surface settlements that occur during shield tunnelling in soft soil areas. We evaluate the applicability of InSAR prior, during, and after tunnel construction. Special emphasis is placed on the influence of the InSAR phase ambiguities in relation to short-term settlements that may occur during tunnel construction. We demonstrate that a rough analytic settlement prediction can be sufficient to resolve the most probable phase ambiguity level, leading to an augmented implementation of InSAR. We use the shield tunnel of the in North/South Metro Line Amsterdam as a case study, where surface levelling data is available to assess and validate the results. We conclude that InSAR is a valuable complementary source of information as it provides data outside the area of the conventional surveying benchmarks and it reveals relevant information about settlement patterns before and after traditional construction monitoring periods.
Aanpak droogte vraagt transformatie waterbeheer
Dat de verdroging van ons land zeer nadelig is voor de natuur, is al bijna een halve eeuw bij beleidsmakers en bestuurders bekend. Maar er zal nog het nodige moeten gebeuren voordat de verdroging structureel en op grote schaal wordt aangepakt. Als groep onderzoekers en (ex-)bestuurders willen wij met dit artikel bijdragen aan de discussie over de te nemen maatregelen. Wij zijn bezorgd over de schade die de verdroging aanricht aan onze maatschappij en roepen daarom via dit pleidooi op daar nu snel concrete maatregelen tegen te nemen.
Multiple stressors determine river ecological status at the European scale : towards an integrated understanding of river status deterioration
The biota of European rivers are affected by a wide range of stressors impairing water quality and hydro‐morphology. Only about 40% of Europe’s rivers reach ‘good ecological status’, a target set by the European Water Framework Directive (WFD) and indicated by the biota. It is yet unknown how the different stressors in concert impact ecological status and how the relationship between stressors and status differs between river types. We linked the intensity of seven stressors to recently measured ecological status data for more than 50,000 sub‐catchment units (covering almost 80% of Europe’s surface area), which were distributed among twelve broad river types. Stressor data were either derived from remote sensing data (extent of urban and agricultural land use in the riparian zone) or modelled (alteration of mean annual flow and of base flow, total phosphorous load, total nitrogen load and mixture toxic pressure, a composite metric for toxic substances), while data on ecological status were taken from national statutory reporting of the second WFD River Basin Management Plans for the years 2010 to 2015. We used Boosted Regression Trees to link ecological status to stressor intensities. The stressors explained on average 61% of deviance in ecological status for the twelve individual river types, with all seven stressors contributing considerably to this explanation. On average 39.4% of the deviance was explained by altered hydro‐morphology (morphology: 23.2%; hydrology: 16.2%), 34.4% by nutrient enrichment and 26.2% by toxic substances. More than half of the total deviance was explained by stressor interaction, with nutrient enrichment and toxic substances interacting most frequently and strongly. Our results underline that the biota of all European river types are determined by co‐occurring and interacting multiple stressors, lending support to the conclusion that fundamental management strategies at the catchment‐scale are required to reach the ambitious objective of good ecological status of surface waters.
How are decision-science methods helping design and implement coastal sea-level adaptation projects?
Decision making for adaptation to sea level rise, particularly for projects with long service life and/or long-term societal impact, is challenging due to a variety of reasons. Deep uncertainty due to climate change requires us to move away from “predict and act” paradigm to one of “robust decision making” characterized by continuous learning and dynamic adaptation. While there are many methods of Decision Making under Deep Uncertainty (DMDU), one that is becoming more attractive for planning and phased implementation of projects is the Dynamic Adaptive Policy Pathways (DAPP) approach. In this approach, a plan includes an initial action, with emphasis on monitoring data, and a series of actions over time (pathways) depending on future scenarios that may emerge. In this paper, we briefly describe the DAPP approach and present a case study of applying it to develop adaptation strategies for mitigating future flooding in a coastal basin subject to compounding effects of climate change in Miami Dade County, Florida.
Accounting for multisectoral dynamics in supporting equitable adaptation planning : a case study on the rice agriculture in the Vietnam Mekong Delta
The need for explicitly considering equity in adaptation planning is increasingly being recognized. However, quantitative evaluations of adaptation options often adopt an aggregated perspective, while disaggregation of results is important to learn about who benefits when and where. A typical example is adaptation of rice agriculture in the Vietnam Mekong Delta. In the past two decades, efforts focused on flood protection have mainly benefitted large-scale farmers while harming small-scale farmers. To investigate the distributional consequences of adaptation policies in the Vietnam Mekong Delta, we assess both aggregate efficiency and equity indicators, as well as disaggregated impacts in terms of district-level farmers profitability. Doing so requires an adequate representation of the co-evolutionary dynamics between the human and environmental systems which influence farmers profitability. We develop a spatially-explicit integrated assessment model that couples inundation and sedimentation dynamics, soil fertility and nutrient dynamics, and behavioral land-use change and farmers profitability calculation. We find that inter-district inequality responds in a non-linear way to climatic and socio-economic changes and choices of adaptation policies. Distinctive inequality patterns emerge from even slightly different combinations of policies and realizations of uncertain futures. We also find that there is no simple ranking of alternative adaptation policies, so one should make trade-offs based on the agreed preferences. Accounting for equity implies exploring the distribution of outcomes over different actor groups over a range of uncertain futures. Only by accounting for multisectoral dynamics can planners anticipate the equity consequences of adaptation options and prepare additional measures to aid the worse-off actors.
Ammonia and chromate interaction explains unresolved Hyalella azteca mortality in Flanders’ sediment bioassays
Thorough assessment of the in situ behavior of sediment constituents in bioassays is often not practical. Alternatively, we related physicochemical properties of sediments from field testing to results from bioassays. The case study covers Flemish sediment (incl. Scheldt and Meuse) and mortality of Hyalella azteca, a sensitive bio-indicator. Though variable across Flanders’ main water bodies, heavy metals and ammoniacal nitrogen dominate the observed toxicity according to toxic unit (TU) assessments. Depending on the water body we explain between 50-90% of the variance in the observed H. azteca mortality, substantially more than previous ecotoxicity studies. We attribute the remaining variance to potential incoherently documented biophysicochemical sediment properties and concentrations of non-target biocides, testing conditions/set-ups and/or species variabilities. We discuss the relative influence of heavy metals/metaloxides, nitrogen (e.g. fertilizer), polycyclic aromatics and organochlorides. We highlight both direct and indirect mortality mechanisms. We note potential synergetic mixture effects between ammoniacal nitrogen and chromium. Such synergy may be phenomenological of ‘standard’ aerobic bioassays, and prove a complementary method alongside the ‘acid-volatile sulfide test’ to more effectively link concentration to toxicity. Future study ought to include variation in biophysicochemical properties between sampling locations and batch bioassays. Our approach enables water managers to interpret their monitoring data by converting sediment concentrations to H. azteca mortality and prioritize substances that contribute most.