ROckfall risk MAnagement assessment: the RO.MA. approach

The analysis of risk for vehicles and drivers as a result of rockfall on a road is relevant to design management in geotechnical engineering. This process is very complex due to the large number of parameters involved. In this paper, we discuss risk analysis and management procedures for roads subject to rockfall phenomena. To this aims, we are proposing a quantitative method (the RO.MA. approach). We developed an abacus to define the threshold values of acceptable rockfall risk for a given road. Rockfall risk is calculated using an Event Tree approach and compared with the abacus thresholds to evaluate road safety and the need for additional protective measures to reduce the risk to an acceptable level. The approach was successfully applied at a test site located in Bard, Aosta Valley, north-western Italy.     

Physical infrastructure interdependency and regional resilience index after the 2011 Tohoku Earthquake in Japan

A resilience index is used to quantify preventive measures, emergency measures, and restoration measures of complex systems, such as physical infrastructures, when they are subjected to natural disasters like earthquakes, hurricanes, floods, etc. Interdependencies among these systems can generate cascading failures or amplification effects, which can also affect the restoration measures right after an extreme event and generate a reduction of the resilience index. In this article, a method is proposed to evaluate the physical infrastructure resilience of a region affected by a disaster considering infrastructure interdependency. It is illustrated using available restoration curves from the March 11 2011 Tohoku Earthquake in Japan. The weights assigned to each infrastructure, which are used to determine resilience, are evaluated using the degree of interdependency indices which are obtain by time series analysis. Results show that the weight coefficients thus obtained do not influence the resilience index significantly; however, the methodology proposed is unbiased from subjective judgment and is able to identify the critical lifelines. Furthermore, the results of the case study presented here suggest that to obtain meaningful estimation of the weight coefficients, it is necessary to consider the period range between two perturbations (e.g., main shock and aftershock). Future infrastructure disruption data (from this and other earthquakes) would be needed to generalize this finding that will allow also to quantify the changes in the restoration curves caused by the magnitude and distance of the shocks from the epicenter, as well as the intrinsic properties of the physical infrastructures. Copyright © 2014 John Wiley & Sons, Ltd.     

Sand transport measurements in Chioggia inlet,Venice lagoon: Theory versus observations

This paper presents results of recent measurements of sand transport made in Chioggia inlet as part of an extensive monitoring programme in the Venetian inlets. Measurements were made in order: (1) to define a relationship between sand transport magnitude and tidal flow; (2) to derive the thresholds for sand transport; (3) to identify the dominant modes of transport; (4) to evaluate the concentration profiles of sand within the benthic boundary layer; (5) to compare bedload transport observations with model predictions using existent bedload formulae; and (6) to produce yearly estimates of bedload transport across the inlet. The vertical distribution of sand in the water column was sampled using modified Helley–Smith bedload samplers at three sites. Transport was found to vary according to the flow and bed grain size, with considerable temporal and spatial variability. A difference of up to three orders of magnitude in transport was observed through the inlet, with higher transport rates measured on the seaward part. The dominant mode of transport in the central inlet was suspension, while bedload was dominant in the mouths. The measured profiles of sand concentration varied with the tidal stage and seabed grain size according to the Rouse parameter (R). R was high at the inlet mouths (1<R<2), indicative of a well-developed bedload layer. The inverse movability number (W_s/U_*) was also higher at these sites and appeared to be grain size dependant. Formulae for bedload transport were tested against field data; stochastic methods such as Einstein–Brown, Engelund–Hansen and Van Rijn produce the best fits. The coupled model SHYFEM-Sedtrans05 appears to simulate well observed transport for most conditions of flow. Long-term bedload predictions indicate a dominant export of sand, with a yearly average of 4500 m³.     

Upper Pleistocene tectonics in western Sardinia (Italy): Insights from the Sinis peninsula structural high

The Corsica‐Sardinia block is a lithospheric fragment whose recent role in the geodynamics of the central‐Western Mediterranean basin is still enigmatic. The most recent regional structure in Sardinia is the Plio‐Pleistocene Campidano Basin, which is considered in a ‘post‐rift’ stage since the Middle Pleistocene. New structural and stratigraphic geological surveys along with luminescence ages provide evidence to support an ongoing tectonic activity since the Marine Isotopic Stage 7 (MIS7; ca. 220 ka) on the Sinis peninsula, the structural high that bounds the north‐western side of the Campidano Basin. In particular, this paper reveals for the first time the presence of N–S striking normal faults system offsetting late Pleistocene aeolianites (130 ± 12 ka; 82 ± 9 ka).     

Effects of pore-scale dispersion,degree of heterogeneity,sampling size,and source volume on the concentration moments of conservative solutes in heterogeneous formations

Pore-scale dispersion (PSD), aquifer heterogeneity, sampling volume, and source size influence solute concentrations of conservative tracers transported in heterogeneous porous formations. In this work, we developed a new set of analytical solutions for the concentration ensemble mean, variance, and coefficient of variation (CV), which consider the effects of all these factors. We developed these models as generalizations of the first-order solutions in the log-conductivity variance of point concentration proposed by [Fiori A, Dagan G. Concentration fluctuations in aquifer transport: a rigorous first-order solution and applications. J Contam Hydrol 2000;45(1–2):139–163]. Our first-order solutions compare well with numerical simulations for small and moderate formation heterogeneity and from small to large sampling and source volumes. However, their performance deteriorates for highly heterogeneous formations. Successively, we used our models to study the interplay among sampler size, source volume, and PSD. Our analysis shows a complex and important interaction among these factors. Additionally, we show that the relative importance of these factors is also a function of plume age, of aquifer heterogeneity, and of the measurement location with respect to the mean plume center of gravity. We found that the concentration moments are chiefly controlled by the sampling volume with pore-scale dispersion playing a minor role at short times and for small source volumes. However, the effect of the source volume cannot be neglected when it is larger than the sampling volume. A different behavior occurs for long periods, which may be relevant for old contaminations, or for small injection volumes. In these cases, PSD causes a significant dilution, which is reflected in the concentration statistics. Additionally, at the center of the mean plume, where high concentrations are most likely to occur, we found that sampling volume and PSD are attenuating mechanisms for both concentration ensemble mean and coefficient of variation, except at very large source and sampler sizes, where the coefficient of variation increases with sampler size and PSD. Formation heterogeneity causes a faster reduction of the ensemble mean concentrations and a larger uncertainty at the center of the mean plume. Therefore, our results highlight the importance of considering the combined effect of formation heterogeneity, exposure volume, PSD, source size, and measurement location in performing risk assessment.     

Temporal partitioning of microhabitat use among four juvenile fish species of the genus Diplodus (Pisces: Perciformes,Sparidae)

Timing, microhabitat selection and behavior from the onset of settlement to recruitment to the adult population of juvenile fishes of the genus Diplodus (Pisces: Sparidae) were investigated along a rocky coastline in the Central Mediterranean Sea. The settlement periods in Diplodus sargus and Diplodus annularis were concentrated in spring, between late May and early June, and the recruits leave the nursery grounds in late September–October. Juvenile fishes of Diplodus puntazzo and Diplodus vulgaris showed a partial time overlapping, sharing the same zones in winter and early spring, from February to May. Multiple correspondence analysis showed that sea breams settle in well‐defined habitats. The smallest juveniles of D. sargus and D. puntazzo settled primarily in the shallowest sheltered pebbly areas, located in sciaphilous crannies covered by red algae. Diplodus vulgaris settlers were observed on a wider range of substrata: rock on sand, gravel and pebbles without algal cover or large boulders, generally in deeper waters. The intermediate‐size juveniles of D. sargus, D. puntazzo and D. vulgaris showed a preference for rocky substrata with substantial algal cover, with arborescent structures (Phaeophyceae). Diplodus annularis juveniles showed high fidelity to seagrass beds (Posidonia oceanica). The home range increased over time in all species, highlighting a loss of substrate specificity: larger juveniles were even observed in deeper and different microhabitats outside nursery grounds. This study suggests that shallow infra‐littoral rocky communities with photophilic algae play a key role in recruitment of sparid fishes, affecting the distribution and abundance of juvenile fishes and therefore determining the renewal of populations and the structure of adult assemblages.     

Net autotrophy in a fluvial lake: the relative role of phytoplankton and floating-leaved macrophytes

This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of dissolved O₂, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously, benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O₂ and CO₂ across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle Lake exhibited CO₂ supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O₂ production (6.35 ± 2.05 mol m⁻² y⁻¹), DIC consumption (−31.18 ± 18.77 mol m⁻² y⁻¹) and net export of Chl a downstream (8.38 ± 0.95 mol C m⁻² y⁻¹). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O₂ m⁻² y⁻¹, corresponding to a sequestration of 4.18 and 0.26 mol m⁻² y⁻¹ of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m⁻² of C, N and P, respectively. Surficial sediments were a sink for O₂ (−14.47 ± 0.65 mol O₂ m⁻² y⁻¹) and a source of DIC and NH₄ ⁺ (18.84 ± 2.80 mol DIC m⁻² y⁻¹ and 0.83 ± 0.16 mol NH₄ ⁺ m⁻² y⁻¹), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO₃ ⁻ m⁻² y⁻¹). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads. This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks, although they simultaneously release CO₂ to the atmosphere.     

S-wave splitting intensity analysis and inversion

Analysing S-wave splitting has become a routine step in processing multicomponent data. Typically, this analysis leads to determining the principal directions of a transversely isotropic medium with a horizontal symmetry axis, which is assumed to be responsible for azimuthal anisotropy, and to the time delays between the fast and slow S-waves. These parameters are commonly estimated layer-by-layer from the top. Errors in layer stripping occurring in shallow layers might propagate to deeper layers. We propose a method for S-wave splitting analysis and compensation that consists of inverting interval values of splitting intensity to obtain a model of anisotropic parameters that vary with time and/or depth. Splitting intensity is a robust attribute with respect to structural variations and is commutative, which means that it can be summed along a ray (or throughout a sensitivity kernel volume) and can be linearly related to anisotropic perturbations at depth. Therefore, it is possible to estimate anisotropic properties within a geological formation (e.g. the reservoir) by analysing the differences of splitting intensity measured at the top and at the bottom of the layer. This allows us to avoid layer stripping, in particular, for shallow layers where anisotropic parameters are difficult to estimate due to poor coverage, and it makes S-wave splitting analysis simpler to apply. We demonstrate this method on synthetic and real data. Because the splitting intensity attribute shows usefulness in S-wave splitting analysis in transversely isotropic media, we extend the splitting intensity theory to lower symmetry classes. It enables the characterization of tilted transversely isotropic and tilted orthorhombic media, opening new opportunities for anisotropic model building.