Coastal flood risks and seasonal tourism: analysing the effects of tourism dynamics on casualty calculations

Since coastal tourism is one of the fastest growing sectors of tourism industry, coastal areas have become increasingly vulnerable in the case of flooding. While in recent years a number of different methods have been put forward to map coastal flood risks, the implications of tourism dynamics for the assessment of human casualties has remained largely overlooked in these models. This chapter examines to what extent the ignorance of (residential) coastal tourism may bias the calculations of human casualties. To this end, a case study has been conducted on the Belgian coast. Both the dynamic nature of coastal tourism and the behaviour of residential tourists in storm surge scenarios are considered. The results of this study show that including tourism dynamics in flood risk management is justified and appropriate, depending on the tourist attractiveness of the flood-prone area and its temporal fluctuations.     

Analyse quantitative du rifting et de la relaxation thermique de la partie occidentale de la marge transformante nord-africaine: le Rif externe (Maroc)

Résumén

Un résumé de la cinématique du Rif externe central et occidental, de la période de rifting aux événements tectoniques récents, est proposé. L’évolution du Rif externe est abordée sur le plan quantitatif par le biais des principaux mécanismes physiques qui ont pu affecter cette partie de la marge nord-africaine durant le Jurassique, le Crétacé et le Paléocène (processus de dilatation thermique lors du rifting et de contraction thermique lors du refroidissement de la lithosphère, effondrement par flexure de la marge nord-africaine lors de la collision). Les géométries et densités obtenues sont comparées avec les données gravimétriques et de sismique réfraction.

Un des aspects du modèle de Wernicke (1985), la dissymétrie du rifting de la marge africaine, semble se vérifier par l’analyse et à la modélisation de la subsidence. Mais celle-ci montre l’existence d’une fusion adiabatique tardive du manteau supérieur dont le modèle de cisaillement simple ne tient pas compte. Le soulèvement de la marge à la fin du rifting ne serait pas dû uniquement à une dilatation thermique car les données de terrain montrent des discordances angulaires importantes sur la marge africaine. Ce soulèvement est attribué localement à la poussée des rides médio-océaniques naissantes de l’Atlantique et du sillon transformant nord-africain.

La modélisation de la subsidence tectonique permet d’expliquer l’absence d’intumescence sous le Rif. Elle est attribuée aux taux d’amincissement crustaux élevés durant les phases d’extension triasico-jurassiques. Cette approche quantitative confirme l’existence d’un bassin intra-continental avorté au sud-ouest et d’une marge continentale sensu stricto au nord-est. Si l’océanisation paraît plus tardive dans la partie rifaine du sillon transformant nord-africain (Callovien) que dans l’Atlantique Central (Bajocien), la subsidence post-rift ne se distingue pas de celle d’une marge passive classique.     

New method for in situ characterization of loose material for landslide mapping purpose

The assessment of grain size distribution and plasticity of loose geological material, during in situ geological investigations, is not obvious. Visual appreciation allows an approximative quantification of the coarse granulometric fractions, but not of the fine ones. Field soils determination methods suggested until now, are visual and tactile tests leading to a very rough estimate, which is only qualitative and not very reproducible. The new proposed field test (GEOLEP method) allows a quick quantification of the fine fraction of loose material. It allows the determination of the sand fraction (fine and medium grained sands) as well as the methylene blue value of the samples. The necessary equipment to perform this test is light and compact and the time needed to analyze one sample is approximately 15 min. Thus it is also possible to carry out numerous measurements in one day. The calibrations were carried out on a selection of 13 natural samples, chosen for their representativeness of the typical alpine quaternary deposits. The results obtained with GEOLEP method are relevant compared with standardized laboratory tests; the obtained correlation indexes are of 73% for the comparison with laboratory stain test results and of 89% with a laboratory method using a similar procedure than the field test. The correlation we performed with Atterberg's limits tests shows that a rough approximation of plasticity index can also be obtained (R² = 75%). This method thus brings a new tool which should allow taking into account the lithological factor (by some quantitative and representative variables) in a reliable way for the evaluation of landslide hazards.     

Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model

High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis. Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted. Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant, or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction revealed vivianite Fe(II)₃(PO₄)₂.8H₂O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results. The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully applied to recent experimental results on the release of arsenic from Bengal delta sediments.     

An adaptive finite element model for wellbore breakout simulation

A finite element formulation is proposed and implemented for analysing the stability of excavated wells using the DiMaggio-Sandler constitutive elastoplastic model with a typical carbonate reservoir configuration. The quality of the finite element approximation is ensured by applying smooth curved elements adapted to the wellbore geometry, and h − p adaptive finite element meshes in the plastic zone. General purpose procedures are defined to transfer the elastoplastic deformation history to newly created integration points. A breakout damage criterion is proposed based on the second invariant of the deviatoric plastic deformation tensor. This damage criterion is used to apply a mesh movement algorithm to represent material collapse. The automatic successive application of the breakout damage criterion results in elliptical realistically looking geometries obtained in experiments reported in the literature.     

Fluid migration at the basement/sediment interface along the margin of the Southeast basin (France): implications for Pb–Zn ore formation

This study investigates the isotopic composition (C, O, S and Sr) of carbonates, sulphates and sulphide cements in the rock matrix and fracture fillings in geological formations of the Southeast basin of France, using core samples collected during the Deep Geology of France programme (GPF Ardèche theme). The Southeast basin belongs to the Alpine Tethyan margin. It is one of the thickest sedimentary basins in Europe, reaching upwards of 9 km in certain locations. The main fluid transfer from the basin is related to the large Pb–Zn Mississippi Valley-type district along the southern margin of the Massif Central block. A synthesis of the tectonic, mineralogical and petrographic investigations on the GPF boreholes shows that a major fluid circulation event occurred across the Alpine margin of Tethys during the Early Jurassic (Hettangian–Bathonian). It produced a general cementation of the rock porosity through precipitation of dolomite, sulphate and barite. Fracture fillings yield isotopic signatures distinct from the matrix cements. Matrix cements have particular characteristics, i.e. δ³⁴S and δ¹³C that agree with a marine origin. The δ³⁴S values of Permo-Carboniferous to Triassic sulphides from fracture cements are interpreted as resulting from the thermo-chemical reduction of sulphates. Fracture sulphates in the same geological formations yield δ³⁴S values that define a relatively homogeneous end-member, whose composition is similar to sulphates in the Largentière Pb–Zn ore deposit. The source of S is attributed to the Permo-Carboniferous succession. The borehole fracture fillings are attributed to a major fluid circulation stage compatible with the Early Jurassic stage identified from the geological investigation of the boreholes. The formation of the Largentière deposit is considered as resulting from the mixing of this Early Jurassic fluid with continental hydrothermal fluids circulating in a basement horst, along its margin with the sedimentary basin. Other Pb–Zn deposits may also be related to fluid migration along the basement/sedimentary cover interface in the eastern and western parts of the Massif Central. This regional fluid circulation event may represent a geodynamic marker of the Jurassic extensional phase.     

Zinc mineral weathering as affected by plant roots

The re-vegetation of soils contaminated by potentially harmful metals is generally considered a suitable option to reduce the metal dispersion in surrounding environments. A continuous flow experiment was conducted to quantitatively assess the effect of Italian ryegrass (Lolium multiflorum Lam.) root activity on the weathering of smithsonite (ZnCO₃), a common Zn mineral. At the end of the experiment (10 days), the total amount of Zn released by smithsonite was increased by a factor of 2.25 in the presence of plants. This increase was due not only to plant uptake but also to the enhancement of the Zn release into leachates. The rate of Zn release from smithsonite to leachates was 2.9 × 10⁻⁴ μg g⁻¹ s⁻¹ and 1.5 × 10⁻⁴ μg g⁻¹ s⁻¹ in the presence and the absence of plants, respectively. The strong correlation (r = 0.95; p < 0.001) between concentrations of Zn and dissolved organic C (DOC) produced by the rhizosphere activity in leachates indicated that organic root exudates and secretions were closely involved in smithsonite weathering. Although the results are derived from laboratory study, and further in situ investigations over the long term are needed, they clearly highlighted that plants can enhance metal release into the environment by accelerating mineral weathering. Therefore, it is suggested that the ability of plants to alter metal phases in soils should be further taken into account when re-vegetation strategies are proposed for the rehabilitation of metal-polluted soils.