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Hydraulic losses through sand boils : measurements and theory
The results of this study illustrate that the head loss across a sand boil (and associated cover layer) is a function of the flow velocity through the boil and the properties (diameter and density) of the sand grains being transported. A simple hydraulic theory was found to favourably predict the trends in the head loss profiles observed in the field. By coupling the hydraulic theory for sand boil head losses to numerical models for predicting BEP, the risk of embankment failure due to BEP can be more accurately assessed.
Large-scale test of a coarse sand barrier as a measure against backward erosion piping
A novel remediation technique against backward erosion piping is being investigated in a multi-scale experimental program. The coarse sand barrier (CSB) is a trench containing densified coarse sand that is placed below an embankment dam or levee in order to prevent the upstream progression of a pipe. The effectiveness of the measure is based on the larger resistance of the densified coarse sand in the barrier against piping erosion, and on the low hydraulic load in the barrier resulting from the conductivity contrast between barrier and background material. This method was investigated in laboratory experiments on a small-scale (aquifer depth 0.10 m) and a medium-scale (aquifer depth 0.40 m) and was found promising. In order to increase the confidence in the potential of the measure for application in the field, two experiments at a larger scale (aquifer depth 3 m) were conducted. This contribution presents the analysis of the piping process of the first large-scale experiment based on measurements during the test and excavation of the sample after the test.
Towards multi-objective optimization of large-scale fluvial landscaping measures
Adapting densely populated deltas to the combined impacts of climate change and socioeconomic developments presents a major challenge for their sustainable development in the 21st century. Decisions for the adaptations require an overview of cost and benefits and the number of stakeholders involved, which can be used in stakeholder discussions. Therefore, we quantified the trade-offs of common measures to compensate for an increase in discharge and sea level rise on the basis of relevant, but inexhaustive, quantitative variables. We modeled the largest delta distributary of the Rhine River with adaptation scenarios driven by (1) the choice of seven measures, (2) the areas owned by the two largest stakeholders (LS) versus all stakeholders (AS) based on a priori stakeholder preferences, and (3) the ecological or hydraulic design principle. We evaluated measures by their efficiency in flood hazard reduction, potential biodiversity, number of stakeholders as a proxy for governance complexity, and measure implementation cost. We found that only floodplain lowering over the whole study area can offset the altered hydrodynamic boundary conditions; for all other measures, additional dike raising is required. LS areas comprise low hanging fruits for water level lowering due to the governance simplicity and hydraulic efficiency. Natural management of meadows (AS), after roughness smoothing and floodplain lowering, represents the optimum combination between potential biodiversity and flood hazard lowering, as it combines a high potential biodiversity with a relatively low hydrodynamic roughness. With this concept, we step up to a multidisciplinary, quantitative multi-parametric, and multiobjective optimization and support the negotiations among stakeholders in the decision-making process.
EWG-IE 27th annual meeting - European Working Group on Internal Erosion in embankment dams, levees and dikes, and their foundations (Vancouver, Canada, 18-21 June 2019) : book of abstracts
Mapping buried Holocene landscapes : past lowland environments, palaeoDEMs and preservation in GIS
In a geological GIS-data recombination project, a digital map was produced that contains information on the Netherlands’ former coastal and delta plain landscapes over the last 14,000 years: the Holocene and the very end of the Pleistocene. The polygon map product is accompanied by a set of palaeoDEMs (Digital Elevation Models) indicating the attention depth for buried land surfaces and aquatic deposits for four time slices. This paper provides conceptual background information on the legend and construction principles behind the polygon maps and the palaeoDEMs, i.e. the decisions taken during the making of. It also provides a basic overview of the map product: landscape structure, burial depth and preservation, visualised for the four time slices in the RCE’s Archaeology Knowledge Kit. The text links coastal plain buried landscape mapping for four time slices to the other Knowledge Kit activities described in this volume, notably that of the Archaeological Landscapes map (for the most recent time slice in the coastal plain area of the Netherlands, and for all time slices in the Pleistocene uplands).
Knowledge for informed choices : tools for more effective and efficient selection of valuable archaeology in the Netherlands
Archaeological heritage management benefits from well-informed and transparent decisionmaking. With the aim of providing ‘knowledge for informed choices’, a series of tools have been developed for archaeological heritage management in the Netherlands. They include digital maps, datasets, methods, guidelines, best practice and web-based applications to facilitate the effective, efficient and transparent selection of valuable archaeological remains. The tools relate to archaeological predictions, disturbances by agriculture and other activities, archaeological heritage maps, prospection methods, research questions, and scientific syntheses to close the archaeological heritage management cycle. They are examined in the various chapters in this publication. The tools were developed as part of the Cultural Heritage Agency’s ‘Archaeology Knowledge Kit’ programme.
Landslide susceptibility mapping of refugee camps in Bangladesh
Over the course of the Rohingya crisis, Cox’s Bazar District (CBD) in Bangladesh has become the main area that accommodates the Rohingya refugees. Many of the refugee camps are located on hilly areas, which have been deforested for accommodation of refugees. Coupling this with the fact that CBD is located in a region with high rainfall intensity and duration makes this area very susceptible to rainfall-induced landslides. Therefore, it is crucial to identify landslide prone zones in CBD and plan accommodation, protection and rescue activities, accordingly. In this study we develop landslide susceptibility maps using only publicly available data. In doing so, we gauge the usability and reliability of such data for an initial hazard assessment. Previous landslide susceptibility maps developed for the refugee camps in CBD considered a single controlling factor, namely slope. In this study, we consider 12 controlling factors: NDVI, slope, aspect, TPI, sand, silt and clay fractions, depth to the bedrock, lithology, and distance to roads, waterways and faults. The Frequency Ratio Method is used to develop the landslide susceptibility maps. Out of the 12 combinations of controlling factors examined in this study, the map that considered NDVI, slope, aspect, TPI, sand fraction, and distance to the roads resulted in the highest accuracy in finding landslide prone areas in the camps. The outcome of the study suggests that publicly available data can be used for initial evaluation of landslide susceptibility in refugee camps. The results and methodology of this study can be helpful for humanitarian organizations who face the challenge of reducing the vulnerability of refugee camps.
Proceedings of the 2nd International Conference on Natural Hazards and Infrastructure - ICONHIC2019 (23-26 June 2019, Chania, Crete Island, Greece)
Mixotrophic protists and a new paradigm for marine ecology : where does plankton research go now?
Many protist plankton are mixotrophs, combining phototrophy and phagotrophy. Their role in freshwater and marine ecology has emerged as a major developing feature of plankton research over recent decades. To better aid discussions, we suggest these organisms are termed “mixoplankton”, as “planktonic protist organisms that express, or have potential to express, phototrophy and phagotrophy”. The term “phytoplankton” then describes phototrophic organisms incapable of phagotrophy. “Protozooplankton” describes phagotrophic protists that do not engage in acquired phototrophy. The complexity of the changes to the conceptual base of the plankton trophic web caused by inclusion of mixoplanktonic activities are such that we suggest that the restructured description is termed the “mixoplankton paradigm”. Implications and opportunities for revision of survey and fieldwork, of laboratory experiments and of simulation modelling are considered. The main challenges are not only with taxonomic and functional identifications, and with measuring rates of potentially competing processes within single cells, but with decades of inertia built around the traditional paradigm that assumes a separation of trophic processes between different organisms. In keeping with the synergistic nature of cooperative photo- and phagotrophy in mixoplankton, a comprehensive multidisciplinary approach will be required to tackle the task ahead.
The costs of living with floods in the Jamuna floodplain in Bangladesh
Bangladeshi people use multiple strategies to live with flooding events and associated riverbank erosion. They relocate, evacuate their homes temporarily, change cropping patterns, and supplement their income from migrating household members. In this way, they can reduce the negative impact of floods on their livelihoods. However, these societal responses also have negative outcomes, such as impoverishment. This research collects quantitative household data and analyzes changes of livelihood conditions over recent decades in a large floodplain area in north-west Bangladesh. It is found that while residents cope with flooding events, they do not achieve successful adaptation. With every flooding, people lose income and assets, which they can only partially recover. As such, they are getting poorer, and therefore less able to make structural adjustments that would allow adaptation in the longer term.