An approximate solution to the flow field on vegetated intertidal platforms: Applicability and limitations

Tidal wetland evolution is governed by interactions between topography, vegetation, and the flow field. Aiming to provide an appropriate hydrodynamic tool within a long-term geomorphic model of vegetated wetlands, we describe an approximate procedure to model the depth-averaged flow field on vegetated intertidal platforms. The procedure is tested by a qualitative comparison with laboratory experiments and quantitatively comparing with a numerical model, focusing on the influence of spatial variations in friction on the flow field. Overall, satisfactory comparisons are obtained. Nevertheless, some limitations of the approach are apparent. These are discussed in the light of the model assumptions. We analyze the impact of the observed limitations on the ability of the approximate solution to describe the morphodynamic evolution of the bed elevation. This is performed by evaluating the changes in the bed elevation after one tidal cycle on the intertidal platform based on flow velocities obtained with a numerical model and those of the simplified procedure. It is found that the bed evolution on the platform is reasonably described with the approximate solution, even though the accumulation of sediment is underestimated near the watershed divide by the approximate model. Taking into account the computationally economic character of the approximate procedure, the analysis indicates that the model provides a suitable tool to investigate the long-term morphodynamic evolution of tidal wetlands

Comparing field observations of sorting patterns along tidal sand waves with theoretical predictions

We present a site-by-site comparison between field observations and model predictions of grains size variations over tidal sand waves at six sites in the North Sea. To drive the model, at each location, local sediment characteristics are derived from the described field data, while hydrodynamic conditions are determined from a numerical model for tidal wave propagation in the North Sea. It is found that the theoretical model providesreasonable estimates of the occurring tidally generated bed forms. Moreover, at five of the six locations, the modeldescribes a sorting pattern which concurs with the observed sediment grain size variation, indicating that the model provides a fair description of the processes governing the phenomenon

Short-term health effects in the general population following a major train accident with acrylonitrile in Belgium

Background: Following a train derailment, several tons of acrylonitrile (ACN) exploded, inflamed and part of the ACN ended up in the sewage system of the village of Wetteren. More than 2000 residents living in the close vicinity of the accident and along the sewage system were evacuated. A human biomonitoring study of the adduct N-2-cyanoethylvaline (CEV) was carried out days 14-21 after the accident. Objectives: (1) To describe the short-term health effects that were reported by the evacuated residents following the train accident, and (2) to explore the association between the CEV concentrations, extrapolated at the time of the accident, and the self-reported short-term health effects. Methods: Short-term health effects were reported in a questionnaire (n=191). An omnibus test of independence was used to investigate the association between the CEV concentrations and the symptoms. Dose-response relationships were quantified by Generalized Additive Models (GAMs). Results: The most frequently reported symptoms were local symptoms of irritation. In non-smokers, dose-dependency was observed between the CEV levels and the self-reporting of irritation (p=0.007) and nausea (p=0.007). Almost all non-smokers with CEV concentrations above 100 pmol/g globin reported irritation symptoms. Both absence and presence of symptoms was reported by non-smokers with CEV concentrations below the reference value and up to 10 times the reference value. Residents who visited the emergency services reported more symptoms. This trend was seen for the whole range of CEV concentrations, and thus independently of the dose. Discussion and conclusion: The present study is one of the first to relate exposure levels to a chemical released during a chemical incident to short-term (self-reported) health effects. A dose-response relation was observed between the CEV concentrations and the reporting of short-term health effects in the non-smokers. Overall, the value of self-reported symptoms to assess exposure showed to be limited. The results of this study confirm that a critical view should be taken when considering self-reported health complaints and that ideally biomarkers are monitored to allow an objective assessment of exposure

Experimental investigation on consolidation behavior of mud: Subreport 1. Methodology study

Due to the complex nature of mud consolidation within harbours, a robust and accurate guideline to evaluate the nautical depth is still under debate. Besides, alternative dredging techniques (e.g. mud conditioning/fluidising) have proven to be an applicable method to reduce dredging costs in a number of harbours. Yet, before one can define new criteria for nautical depth or implement new dredging techniques, a deeper understanding of the temporal evolution of rheological, mechanical and biological characteristics of mud is needed. In this study, we aim to improve the understanding of the rheological properties of consolidating mud by comparing the consolidation process of mud from 5 different locations namely the harbours of Zeebrugge (ZB) and Deurganckdok (DG) in Belgium, the harbours of Rotterdam (RO) and Ijmuiden (IJ) in the Netherlands and the Emden (EM) harbour in Germany. The main objectives of this project are to examine the effect of the consolidation process on the mechanical, rheological and biological characteristics of mud as well as to explain the differences in consolidation processes between muds from different origins.This sub-report describes the properties of different mud types used for the experiments as well as the experimental setup. The experimental setup includes a detailed description of the governing parameters, experimental design and measurement techniques conducted on two different consolidation columns, small and large

Nautical bottom sediment research: Sub report 11. Cohesive sediments dimensional analysis

The dimensional analysis technique was applied in order to determine possible relationships between the measured parameters in the STT and to identify possible inconsistencies in the measurements.The present dimensional analysis focuses only in the sedimentation and consolidation processes.Relationships between parameters could be used to identify inconsistencies for measured pore pressure, effective stresses and density values. Recommendations are suggested for sampling points and measuring methods