The effect of dike geometry on different resistivity configurations

Geoelectrical profiling with multi-electrode systems has become an important tool for monitoring dike embankments bordering rivers. Profiles running perpendicular to the dike axis are affected by the dike topography, with the amplitude of this effect dependent on the surface geometry and the choice of the electrode configuration. Investigations using seven different electrode configurations have shown that some configurations are less sensitive to the topography than others.The topography correction method (TCM) is an important tool for processing data from measurements at river dikes. This method is generally recommended for flank angles steeper than 10°. The topography effect is calculated by two-dimensional finite element modelling. The resulting synthetic data of a homogeneous dike body are used to apply a topographic correction for each measurement.The topographic effect and correction procedure is demonstrated for synthetic dike data and for a data set from a river dike in Thai Binh province (Vietnam). The topography can be ignored for flank angles less than 25° if an averaged Half-Wenner electrode configuration is used. This configuration has proved to be less affected by undulated topography and the focusing effect of averaging the two data sets provides reliable structural information without the need for time-consuming data inversion.     

Complex systems in aeolian geomorphology

Aeolian geomorphology provides a rich ground for investigating Earth surface processes and landforms as complex systems. Sand transport by wind is a classic dissipative process with non-linear dynamics, while dune field evolution is a prototypical self-organisation phenomenon. Both of these broad areas of aeolian geomorphology are discussed and analysed in the context of complexity and a systems approach. A feedback loop analysis of the aeolian boundary-layer-flow/sediment-transport/bedform interactions, based on contemporary physical models, reveals that the system is fundamentally unstable (or at most meta-stable) and likely to exhibit chaotic behaviour. Recent field-experimental research on aeolian streamers and spatio-temporal transport patterns, however, indicates that sand transport by wind may be wholly controlled by a self-similar turbulence cascade in the boundary layer flow, and that key aspects of transport event time-series can be fully reproduced from a combination of (self-organised) 1/f forcing, motion threshold, and saltation inertia. The evolution of various types of bare-sand dunes and dune field patterns have been simulated successfully with self-organising cellular automata that incorporate only simplified physically-based interactions (rules). Because of their undefined physical scale, however, it not clear whether they in fact simulate ripples (bedforms) or dunes (landforms), raising fundamental cross-cutting questions regarding the difference between aeolian dunes, impact ripples, and subaqueous (current) ripples and dunes. An extended cellular automaton (CA) model, currently under development, incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas, blow-outs, and parabolic coastal dunes. Preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes. Progress is limited, however, by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale. State variables currently used in the bare-sand models are far from capturing the rich 3D topography and patterns and are not sufficiently discriminative to distinguish different attractors. The vegetation component in the extended model, and indeed ecogeomorphic systems in general, pose even graver challenges to establishing appropriate state variables. A re-examination of older concepts, such as landscape entropy, perhaps complemented by recent developments in information theory, may be a potentially fruitful avenue for research, although the outlines of such an implementation are still rather vague.     

An efficient discontinuous Galerkin method for advective transport in porous media

We consider a discontinuous Galerkin scheme for computing transport in heterogeneous media. An efficient solution of the resulting linear system of equations is possible by taking advantage of a priori knowledge of the direction of flow. By arranging the elements in a suitable sequence, one does not need to assemble the full system and may compute the solution in an element-by-element fashion. We demonstrate this procedure on boundary-value problems for tracer transport and time-of-flight.     

Distribution and speciation of arsenic around roots in a contaminated riparian floodplain soil: Micro-XRF element mapping and EXAFS spectroscopy

Riparian soils are periodically flooded, leading to temporarily reducing conditions. Diffusion of O₂ through plants into the rhizosphere maintains oxic conditions around roots, thereby promoting trace element fractionation along a redox gradient from the reduced soil matrix towards the oxic rhizosphere. The aim of this study was to determine the distribution and speciation of arsenic around plant roots in a contaminated (170-280 mg/kg As) riparian floodplain soil (gleyic Fluvisol). The analysis of soil thin sections by synchrotron micro-X-ray fluorescence (μ-XRF) spectrometry showed that As and Fe were enriched around roots and that As was closely correlated with Fe. Arsenic contents of three manually separated rhizosphere soil samples from the subsoil were 5-9 times higher than respective bulk As contents. This corresponds to the accumulation of about half of the total As in the subsoil in Fe-enrichments around roots. The speciation of As in the soil was assessed by oxalate extractions at pH 3.0 as well as by X-ray absorption near edge structure (XANES) and extended X-ray fine structure (EXAFS) spectroscopy. More than 77% of the total As was oxalate extractable in all samples. XANES and EXAFS spectra demonstrated that As was predominantly As(V). For the accurate analysis of the EXAFS data with respect to the bonding of As(V) to the Fe- or Al-octahedra of (hydr)oxides and clays, all 3-leg and 4-leg multiple scattering paths within the As^(V)O₄-tetrahedron were considered in a fully constrained fitting scheme. We found that As(V) was predominantly associated with Fe-(hydr)oxides, and that sorption to Al- and Mn-hydroxides was negligible. The accumulation of As in the rhizosphere may affect As uptake by plants. Regarding the mobility of As, our results suggest that by oxygenation of the rhizosphere, plants attenuate the leaching of As from riparian floodplain soils during periods of high groundwater levels or flooding.     

Hierarchical evaluation of IPCC AR4 coupled climate models with systematic consideration of model uncertainties

The capability of reproducing observed surface air temperature (SAT) changes for the twentieth century is assessed using 22 multi-models which contribute to the Intergovernmental Panel on Climate Change Fourth Assessment Report. A Bayesian method is utilized for model evaluation by which model uncertainties are considered systematically. We provide a hierarchical analysis for global to sub-continental regions with two settings. First, regions of different size are evaluated separately at global, hemispheric, continental, and sub-continental scales. Second, the global SAT trend patterns are evaluated with gradual refinement of horizontal scales (higher dimensional analysis). Results show that models with natural plus anthropogenic forcing (MME_ALL) generally exhibit better skill than models with anthropogenic only forcing (MME_ANTH) at all spatial scales for different trend periods (entire twentieth century and its first and second halves). This confirms previous studies that suggest the important role of natural forcing. For the second half of the century, we found that MME_ANTH performs well compared to MME_ALL except for a few models with overestimated warming. This indicates not only major contributions of anthropogenic forcing over that period but also the applicability of both MMEs to observationally-constrained future predictions of climate changes. In addition, the skill-weighted averages with the Bayes factors [Bayesian model averaging (BMA)] show a general superiority over other error-based weighted averaging methods, suggesting a potential advantage of BMA for climate change predictions.     

On the nature of turbulent kinetic energy in a steep and narrow Alpine valley

This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions. The Riviera Valley in southern Switzerland was chosen for a detailed case study, in which the evaluation of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350-m horizontal grid spacing) large-eddy simulations using the numerical model ARPS. The simulations verify what has already been observed on the basis of measurements: TKE profiles scale surprisingly well if the convective velocity scale w _* is obtained from the sun-exposed eastern slope rather than from the surface directly beneath the profiles considered. ARPS is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production mechanism. Therefore, the surface heat flux (and thus w _*) on the eastern slope does not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction of thermally-driven cross-valley and along-valley flows. Excellent correlation between w _* and the up-valley wind speed solidifies this hypothesis.     

Paleogeography of the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB) from Eocene to Pliocene

Twenty paleogeographic maps are presented for Middle Eocene (Lutetian) to Late Pliocene times according to the stratigraphical data given in the companion paper by Berger et al. this volume. Following a first lacustrine-continental sedimentation during the Middle Eocene, two and locally three Rupelian transgressive events were identified with the first corresponding with the Early Rupelian Middle Pechelbronn beds and the second and third with the Late Rupelian Serie Grise (Fischschiefer and equivalents). During the Early Rupelian (Middle Pechelbronn beds), a connection between North Sea and URG is clearly demonstrated, but a general connection between North Sea, URG and Paratethys, via the Alpine sea, is proposed, but not proved, during the late Rupelian. Whereas in the southern URG, a major hiatus spans Early Aquitanian to Pliocene times, Early and Middle Miocene marine, brackish and freshwater facies occur in the northern URG and in the Molasse Basin (OMM, OSM); however, no marine connections between these basins could be demonstrated during this time. After the deposition of the molasse series, a very complex drainage pattern developed during the Late Miocene and Pliocene, with a clear connection to the Bresse Graben during the Piacenzian (Sundgau gravels). During the Late Miocene, Pliocene and Quaternary sedimentation persisted in the northern URG with hardly any interruptions. The present drainage pattern of the Rhine river (from Alpine area to the lower Rhine Embayment) was not established before the Early Pleistocene.     

Recent vertical movements from precise levelling in the vicinity of the city of Basel, Switzerland

The southern end of the Upper Rhine Graben is one of the zones in Switzerland where recent crustal movements can be expected because of ongoing seismotectonic processes as witnessed by seismicity clusters occurring in this region. Therefore, in 1973 a control network with levelling profiles across the eastern Rhine Graben fault was installed and measured in the vicinity of the city of Basel in order to measure relative vertical movements and investigate their relationship with seismic events. As a contribution to EUCOR-URGENT, the profiles were observed a third time in the years 2002 and 2003 and connected to the Swiss national levelling network. The results of these local measurements are discussed in terms of accuracy and significance. Furthermore, they are combined and interpreted together with the extensive data set of recent vertical movements in Switzerland (Jura Mountains, Central Plateau and the Alps). In order to be able to prove height changes with precise levelling, their values should amount to at least 3–4 mm (1). The present investigations, however, have not shown any significant vertical movements over the past 30 years.     

Studying the City Plume of Berlin on 20 July 1998 with Three Different Modelling Approaches

In this paper we try to identify and describe the specifics of the Berlin city plume characterised by a zone of enhanced photochemical activity downwind of the urban area, where the major emissions of ozone precursors (NO_x and VOC) take place. Two Eulerian CTM systems (EURAD and REM3/CALGRID) and one Euler–Lagrangian model (LaMM5) are applied to thearea of Berlin/Brandenburg to investigate the processes involved in the evolution of the Berlin plume inherent to the models. The study focuses on 20 July 1998,the first special observation period (SOP) during BERLIOZ. The examination includes (1) the role of turbulence and transport and the role of mass flux to the surface during the evolution of the plume, (2) the import situation of the ground based measurement sites, (3)the terms of the ozone budget equation and their contribution to precursor distribution and ozone formation, (4) the substructures of the plume defined by its chemical regimes. Main results show that the complex meteorological conditions during this SOP with considerable turbulent transports demand an Euler–Lagrangian approach to determine the source receptor relationshipsfor the ground based measurement sites. These relations reveal that only a minor part (5%) of the air approaching Pabstthum and the more downwind (north-western) stations origins from Berlin and that the mutual transport between all sites was limited. The latter result afflicts the joint interpretation of data from different stations because the presumption to measure the same air mass is violated in many cases for this SOP. The CTM results reveal that the local net production of ozone within the plume was controlled by transport ad chemical processes both owning the same importance but tending to counteract each other. At this SOP far distance sources of ozone precursors originating from the Bohemian basin did not interfere the Berlin city plume although they generally have the potential to do so.