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Afvoeren in uiterwaarden bepalen met remote sensing technieken
Het doel van deze studie is het verkennen van methodes voor het bepalen van de topografie van het wateroppervlak uit remote sensing, om indirect de onderliggende stroming en of energie te bepalen. In het kader van deze studie zijn de orde groottes van de waterstandsverschillen ten gevolge van volkomen en onvolkomen overlaten in de uiterwaarden gekwantificeerd. Deze effecten liggen in de orde van enkele centimeters tot enkele meters. Op basis van de verwachtte gradiënten in het wateroppervlak uit modelsimulaties is aan te wijzen waar welk type overlaat zal ontstaan.
Late Holocene coastal-plain evolution of the Netherlands : the role of natural preconditions in human-induced sea ingressions
This paper demonstrates the decisive role of natural preconditions on the formation of large late Holocene sea ingressions in peaty coastal plains along the North Sea’s southern shores. Geological and archaeological evidence shows that these sea ingressions (expansion of new tidal systems) were mainly caused by land subsidence, which occurred due to intensified agricultural use of artificially drained peatlands since the Late Iron Age (250–12 BC). This made the coastal plain sensitive to storm-surge ingression through weak spots, e.g., at the location of existing creeks, in the coastline. Using The Netherlands as a case study, we show that natural preconditions (i.e., the geological setting at the time of ingression) played a key role in the pacing and extent of tidal area expansion. Ingressive tidal systems eventually reached most far inland in coastal segments with wide peaty back-barrier plains. In contrast, sea ingression formation was hampered in coastal segments with well-developed natural ingression-protecting geomorphic features (e.g., beach-barriers, supratidal levees). Feedback mechanisms, such as additional peat subsidence by loading of sediment imported into the new tidal area, caused further tidal volume increase and created accommodation space for tidal deposits. These combined effects caused irreversible sea ingression over large areas that consequently became unsuitable for habitation for many centuries. Improved understanding of such sea-ingression mechanisms and their facilitating conditions are essential for the assessment of the sensitivity of many densely populated coastal plains, which experience major human-induced subsidence, eventually leading to coastal plain drowning.
Multiple equilibria for suspended sediment concentrations in rivers and tidal flows
Some estuaries have relatively low suspended sediment concentrations of the order of 100 mg/l, while others are hyper-turbid, with sediment concentrations up to several tens of grams per litre. Over the last decades we also have seen estuaries, such as the Ems and Loire, where a transition occurred from a low to a high concentration, possibly due to human interventions in the estuarine system. Such a regime shift can potentially have devastating effects on the quality of the ecosystem. Winterwerp and Wang (2013) hypothesise that the low and high concentration conditions may both be equilibrium states of an estuary under the same forcing conditions. In this presentation we will test this hypothesis and investigate the behaviour of the most essential physical processes. This is done using a numerical water column model.
Fluvial evolution of the Rhine during the last interglacial-glacial cycle in the southern North Sea basin : a review and look forward
This paper presents the current state of knowledge on the evolution and depositional history of the River Rhine in the southern part of the North Sea basin during the upper Middle and Late Pleistocene, and its response to climate change, sea-level oscillation and glacio-isostasy. The study focuses on the development of the Eemian interglacial lower-delta in the central Netherlands and its relation to records of climate and sea-level rise, and uses the Saalian and Weichselian pre- and postdating periods to place its development in context.
Moving from deterministic towards probabilistic coastal hazard and risk assessment : development of a modelling framework and application to Narrabeen Beach, New South Wales, Australia
Traditionalmethods for assessing coastal hazards have not typically incorporated a rigorous treatment of uncertainty. Such treatment is necessary to enable risk assessments which are now required by emerging risk based coastal zone management/planning frameworks. While unresolved issues remain, relating to the availability of sufficient data for comprehensive uncertainty assessments, this will hopefully improve in coming decades. Here, we present a modelling framework which integrates geological, engineering and economic approaches for assessing the climate change driven economic risk to coastal developments. The framework incorporates means for combining results frommodels that focus on the decadal to century time scales atwhich coasts evolve, and those that focus on the short term and seasonal time scales (storm bite and recovery). This paper demonstrates the functionality of the framework in deriving probabilistic coastal hazard lines and their subsequent use to establish an economically optimal setback line for development at a case study site: the Narrabeen-Collaroy embayment in Sydney, New South Wales.
Lower Rhine historical flood magnitudes of the last 450 years reproduced from grain-size measurements of flood deposits using End Member Modelling
The objective of this research was to unlock the potential of fluvial archives to create flood chronologies, based on grain-size characteristics of flood deposits located in two recently formed fluvio-lacustrine sequences. Grain-size data was compared with contemporaneous discharge measurements (for the Lower Rhine, The Netherlands). Regression relations between coarse-tail grain-size parameters and measured discharge were established for the last 240 years, and applied to the older parts of both cores, resulting in peak discharge estimates back to AD 1550. Grain-size descriptive parameters such as the 95th percentile and end-member modelling outcomes correlate well with discharge and turn out to be sensitive proxies for inferring flood magnitudes. Locally, geomorphological changes influence the relation between peak dischargemagnitudes and flood bed coarseness, but these can be assessed, using continuous flood layer and background sedimentation measurements to standardize grainsize descriptive parameters. Flood records distilled from sedimentary archives hold great potential for extending existing records of observed discharge and aid establishment of design discharge for flood protection measures and assessment of non-stationarity of the flooding regime due to climatic and anthropogenic forcing.
Toxic pressure of herbicides on microalgae in Dutch estuarine and coastal waters
For several decades now, there has been an increase in the sources and types of chemicals in estuarine and coastal waters as a consequence of anthropogenic activities. This has led to considerable concern about the effects of these chemicals on the marine food chain. The fact is that estuarine and coastal waters are the most productive ecosystemswith high primary production bymicroalgae. The toxic pressure of specific phytotoxic chemicals now poses a major threat to these ecosystems. In a previous study, six herbicides (atrazine, diuron, irgarol, isoproturon, terbutryn and terbutylazine) were identified as the main contaminants affecting photosynthesis in marine microalgae. The purpose of this study is to investigate the toxic pressure of these herbicides in the Dutch estuarine and coastal waters in relation to the effective photosystem II efficiency (EPSII) in microalgae. Temporal and spatial variations in the concentrations of these herbicides were analyzed based on monitoring data. Additionally, a field study was carried out in which chemical analysis of water was performed and also a toxicity assessment using the Pulse Amplitude Modulation (PAM) fluorometry assay that measures EPSII. The toxic pressure on EPSII in microalgae has decreased with 55–82% from2003 to 2012,with the Western Scheldt estuary showing the highest toxic pressure. By combining toxicity data from the PAM assay with chemical analysis of herbicide concentrations, we have identified diuron and terbutylazine as themain contributors to the toxic pressure onmicroalgae. Although direct effects are not expected, the toxic pressure is close to the 10% effect level in the PAM assay. A compliance check with the current environmental legislation of the European Union revealed that the quality standards are not sufficient to protect marine microalgae.
Modelling multi-hazard hurricane damages on an urbanized coast with a Bayesian Network approach
Hurricane flood impacts to residential buildings in coastal zones are caused by a number of hazards, such as inundation, overflow currents, erosion, and wave attack. However, traditional hurricane damage models typically make use of stage-damage functions, where the stage is related to flooding depth only. Moreover, these models are deterministic and do not consider the large amount of uncertainty associated with both the processes themselves and with the predictions. This uncertainty becomes increasingly important when multiple hazards (flooding,wave attack, erosion, etc.) are considered simultaneously. This paper focusses on establishing relationships between observed damage andmultiple hazard indicators in order to make better probabilistic predictions. The concept consists of (1) determining Local Hazard Indicators (LHIs) from a hindcasted storm with use of a nearshore morphodynamic model, XBeach, and (2) coupling these LHIs and building characteristics to the observed damages. We chose a Bayesian Network approach in order to make this coupling and used the LHIs ‘Inundation depth’, ‘Flow velocity’, ‘Wave attack’, and ‘Scour depth’ to represent flooding, current, wave impacts, and erosion related hazards. The Bayesian Network approach has several advantages over the market-standard stage-damage functions: the predictive capacity of multiple indicators can be combined; probabilistic predictions can be obtained, which include uncertainty; and quantitative as well as descriptive information can be used simultaneously.
Past hydrological extreme events in a changing climate (preface)
Preface to a special issue that brings together a range of papers that reconstruct regional fluvial chronologies of extreme events based on multiple proxies and documentary information, which evaluate the relationship between river hydrology, climate and atmospheric circulation variability. The research presented in this volume was drawn together within the framework of the INQUA Project 1220 on Hydrological EXtreme Events in Changing Climate (HEX Events), and the 1st Workshop on HEX Events held at Utrecht University on November 29th–30th, 2012.
An automated method for semantic classification of regions in coastal images
Large, long-term coastal imagery datasets are nowadays a low-cost source of information for various coastal research disciplines. However, the applicability of many existing algorithms for coastal image analysis is limited for these large datasets due to a lack of automation and robustness. Therefore manual quality control and site- and time-dependent calibration are often required. In this paper we present a fully automated algorithm that classifies each pixel in an image given a pre-defined set of classes. The necessary robustness is obtained by distinguishing one class of pixels from another based on more than a thousand pixel features and relations between neighboring pixels rather than a handful of color intensities. Using a manually annotated dataset of 192 coastal images, a SSVM is trained and tested to distinguish between the classes water, sand, vegetation, sky and object. The resulting model correctly classifies 93.0% of all pixels in a previously unseen image. Two case studies are used to show how the algorithm extracts beach widths and water lines from a coastal camera station. Both the annotated dataset and the software developed to performthe model training and prediction are provided as free and open-source data sources.