Flood Forecasting and Warning at the River Basin and at the European Scale

Application of recent advances in numerical weather prediction (NWP) has the potential of allowing delivery of flood warning to extend well beyond the typical lead times of operational flood warning at the river basin scale. A prototype system, a European Flood Forecasting System (EFFS) developed to deliver such pre-warnings, aiming at providing a pre-warning at lead times of between 5 and 10 days is described. Considerable uncertainty in the weather forecast at these lead times, however, means that resulting forecasts must be treated probabilistically, and although probabilistic forecasts may be easy to disseminate, these are difficult to understand. This paper explores the structure of operational flood warning, and shows that integration in the flood warning process is required if the pre-warning is to fulfil its potential. A simple method of summarising the information in the pre-warning is presented, and the system in hindcast mode is shown to give clear indication of an upcoming major event in the Rhine basin up to 10 days before the actual event. Finally recommendations on the use of data assimilation to embed the EFFS system within an operational environment are given.     

Mechanisms of galena dissolution in oxygen-saturated solutions: Evaluation of pH effect on apparent activation energies and mineral-water interface

This work describes a laboratory investigation of processes ruling the dissolution of galena (PbS) under conditions that mimic oxidising Earth surface environments. Freshly cleaved (001) galena surface was partially dissolved in solutions at different pH (HCl, pH between 1.2 and 5.8) and temperature (298 K) levels for several weeks in a flow-through reactor. Analysis of the galena surface after exposure to oxygen-saturated solutions was performed by XPS. The estimated thickness of surface layer formed after interaction for four weeks with solution at pH 5.8 was ∼0.5 nm. After the same time of interaction with solution at pH 1, the surface layer was at least 9 nm thick. Stationary dissolution rates were measured at different pH (between 1 and 5.8) and temperatures (298, 323, 348 K). Reaction order with respect to hydrogen ion averages 0.6 and slightly decreases with temperature. Dissolution rates, plotted vs. the reciprocal values of temperature, follow Arrhenius behaviour. Activation energies show a sharply discontinuous variation with pH. They are 13.5 ± 2 kJmol⁻¹ at pH = 1.2 and 2.87, whereas at pH of 4.08, 4.7, and 5.8, they show, respectively, values of 48.8 ± 3.5, 45 ± 4, and 51 ± 4 kJmol⁻¹. The apparent activation energy was also investigated by starting the experiment from pH 5.8 and then decreasing to pH 1.2. In this case, the apparent activation energies were 44 ± 4 kJmol⁻¹ and 21 ± 4 kJmol⁻¹, respectively.Apparent activation energies indicate a diffusion-controlled kinetic regime for pH <3, and a mixture of surface and diffusion control for pH between ∼4 and 5.8. A strong effect of solution pH on the mineral-water interface is revealed also by the observed pH dependence of surface-layer thickness. On the basis of the high-resolution XPS signals, the dependence of activation energies on solution pH should reflect a change of structure, and also chemical composition, of the mineral-water interface.     

Analytical solutions for transport of decaying solutes in rivers with transient storage

Analytical solutions are presented for solute transport in rivers including the effects of transient storage and first order decay. The solute transport model considers an advection–dispersion equation for transport in the main channel linked to a first order mass exchange between the main channel and the transient storage zones. In case of a conservative tracer, it is shown that different analytical solutions presented in the literature are mathematically identical. For non-conservative solutes, first order decay reactions are considered with different reaction rate coefficients in the main river channel and in the dead zones. New analytical solutions are presented for different boundary conditions, i.e. instantaneous injection in an infinite river reach, and variable concentration time series input in a semi-infinite river reach. The correctness and accuracy of the analytical solutions is verified by comparison with the OTIS numerical model. The results of analytical and numerical approaches compare favourably and small differences can be attributed to the influence of boundary conditions. It is concluded that the presented analytical solutions for solute transport in rivers with transient storage and solute decay are accurate and correct, and can be usefully applied for analyses of tracer experiments and transport characteristics in rivers with mass exchange in dead zones.     

Soil erosion prediction at the basin scale using the revised universal soil loss equation (RUSLE) in a catchment of Sicily (southern Italy)

Soil erosion by water is a serious problem in southern Italy, particularly in Sicily which is one of the Italian administrative regions prone to desertification. Soil erosion not only affects soil quality, in terms of agricultural productivity, but also reduces the availability of water in reservoirs. This study was conducted in the Comunelli catchment in south-central Sicily, to predict potential annual soil loss using the revised universal soil loss equation (RUSLE) and to test the reliability of this methodology to predict reservoirs siltation. The RUSLE factors were calculated for the catchment using survey data and rain gauge measurement data. The R-factor was calculated from daily, monthly and annual precipitation data. The K-factor was calculated from soil samples collected in May and November 2004. The LS topographic factor was calculated from a 20 m digital elevation model. The C- and P-factors, in absence of detailed data, were set to 1. The results were compared with those obtained from another soil loss estimation method based on ¹³⁷Cs and with the soil loss estimated from the sediment volume stored in the Comunelli reservoir between 1968 and 2004.     

Short-term vertical velocity field in the Apennines (Italy) revealed by geodetic levelling data

We estimate current vertical movements along the Apennines (Italy) through repeatedly measured high precision levelling routes. In order to highlight regional crustal deformation the analysis of a geodetic database, with a minimum benchmark density of 0.7 bm/km (1943–2003 time period), is carried out. We evaluate systematic and random error and their propagation along the levelling routes. Tests on original raw height data have been carried out to define error propagation. The computed relative vertical rates stand significantly above error propagation. A series of traverses along and across the Apennines and a map of relative vertical velocities reveal a geodetic signal characterised by values up to 2.5–3.0 mm/a and by wavelengths up to 100 km.     

Comparative Study of Nucleation by Different Alcoholic Solutions of Benzoin, and Benzoin Dust

Nucleation properties of different alcoholic solutions of Benzoin and Benzoin dust have been studied by varying the seeding temperature in a laboratory Cold Chamber. In the present study, three different alcoholic solutions are being used and these are due to the standard Ethyl alcohol, one higher alcohol i.e. Isopropyle alcohol and one lower alcohol i.e. Methyl alcohol. In addition, Benzil dust and droplets of Acetone and Chloroform have been used to examine if these agents have any ice nucleation ability. It has been observed that all alcoholic solutions of Benzoin have sufficient ice nucleation ability at the negative side of 0^°C, with the maximum concentration occurring at −14.4^°C. In case of Benzoin dust, the nucleation ability is better on the positive side of 0^°C than the negative side. On the other hand, Benzil dust has insignificant nucleation ability and the droplets of two other agents have no nucleation ability at all.Considering the chemical as well as crystalline structure, one can conclude that the presence of OH group in the seeding molecule plays the central role in ice nucleation/hydrate crystal formation. In fact, a number of supplementary experiments like crystal growth in an incubator, XRD analysis and NMR study are performed to identify the nature of crystals formed by Benzoin dust above 0^°C. One can conclude that these are hydrate crystals of Benzoin with water caging around Benzoin crystals.     

Assessing soil erosion rates in cultivated areas of Navarre (Spain)

Although there is much evidence of intense soil erosion in cultivated areas of Navarre (Spain), information on it is currently scarce. Rill and ephemeral gully volumes can be used as a guide to minimum erosion rates. With the main purpose of determining the annual soil loss rates in cultivated areas of central Navarre, a detailed assessment of rainfall and of rill and gully erosion was made in 19 small catchments from October 1999 to September 2001. Seventeen of them were randomly selected, and were cultivated with winter cereals, vineyards or sunflowers. The other two catchments were selected to represent partially uncultivated lands abandoned for ten years. Channel cross‐sections were measured by using a 1‐m‐wide micro‐topographic profile meter, describing 632 cross‐sections and processing information from 31 600 pins. Erosive events happened every year in the three study areas. For cereal catchments, soil losses occurred in only one or two rainfall events each year, usually at the end of autumn and in some summers, with high erosion rates (0·20–11·50 kg m^?2 a^?1). In vineyards, soil losses occurred several times per year, and in any season. This is attributed to the small percentage of surface covered by the crop throughout the year. Again, high erosion rates were found (0·33–16·19 kg m^?2 a^?1), with ephemeral gully erosion causing more loss than rill erosion. No‐till is proposed as an effective conservation measure. From this large data set, it can be stated that rill erosion and ephemeral gully erosion are widespread in Mediterranean regions, and that much more attention should be paid to the problem. Abandoned fields showed very high erosion rates (16·19 kg m^?2 a^?1 on average), suggesting that the abandonment of marginal lands without implementing any erosion control can lead to severe erosion rates. Copyright © 2005 John Wiley & Sons, Ltd.     

A cellular model of river meandering

River meandering has been successfully modelled using vector based methods, but these can not simulate multiple or braided channels. Conversely, cellular braided river models fail to replicate meandering. This paper describes a new method to simulate river meandering within a cellular model (CAESAR). A novel technique for determining bend radius of curvature on a cell by cell basis is described, that importantly allows regional information on bend curvature to be transferred to local points. This local curvature is then used to drive meandering and lateral erosion through two methods. Key difficulties are identified, including the deposition of material on point bars and cut off development, but the method illustrates how meandering can be integrated within a cellular framework. This demonstrates the potential to produce a single model that can incorporate both meandering and braiding. Copyright © 2006 John Wiley & Sons, Ltd.     

Quantifying Damage, Saturation and Anisotropy in Cracked Rocks by Inverting Elastic Wave Velocities

Crack damage results in a decrease of elastic wave velocities and in the development of anisotropy. Using non-interactive crack effective medium theory as a fundamental tool, we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor, average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties. Using this same tool, we show that both the anisotropy and shear-wave splitting of elastic waves can be derived. Two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation, reaching up to 60% in the dry case. Comparison with experimental data on two granites, a basalt and a marble, shows that the range of validity of the non-interactive effective medium theory model extends to a total crack density of approximately 0.5, considering symmetries up to orthorhombic. In the isotropic case, Kachanov's (1994) non-interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions. Inversions are stable and give coherent results in terms of crack density and aperture evolution. Crack density variations can be interpreted in terms of crack growth and/or changes of the crack surface contact areas as cracks are being closed or opened respectively. More importantly, the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio (and therefore aperture) with pressure, which has broader geophysical implications, in particular on fluid flow. The recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure. In the anisotropic cases—both transverse isotropic and orthorhombic symmetries were considered—anisotropy and saturation patterns were well reproduced by the modelling, and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging. Our results point out that: (1) It is possible to predict damage, anisotropy and saturation in terms of a crack density tensor and mean crack aspect ratio and orientation; (2) using well constrained wave velocity data, it is possible to extrapolate the contemporaneous evolution of crack density, anisotropy and saturation using wave velocity inversion as a tool; 3) using such an inversion tool opens the door in linking elastic properties, variations to permeability.