Peak runoff contributing area as hydrological signature of the probability distribution of floods

For the analysis of hydrological extremes and particularly in flood prediction, deeper investigation is needed on the relative effects of different hydrological processes acting at the basin scale in different hydroclimatic areas of the world. In this framework, the theoretical derivation of flood distribution shows a great potential for development and knowledge advancement. In addition, another promising path of investigation is represented by the use of distributed hydrological models via simulation modelling (including Monte Carlo, discrete event and continuous simulation). In this paper results of a theoretically derived flood frequency distribution are analyzed and compared with the results of a simulation scheme that uses a distributed hydrological model (DREAM) in cascade with a rainfall generator (IRP). The numerical simulation allows the reproduction of a large number of extreme events and provides insight into the main control for flood generation mechanisms with particular emphasis to the peak runoff contributing areas, highlighting the relevance of soil texture and morphology in different climatic environments. The proposed methodology is applied here to the Agri and the Bradano basin, in Southern Italy.     

Magmatic History of Somma-Vesuvius on the Basis of New Geochemical and Isotopic Data from a Deep Borehole (Camaldoli della Torre)

A continuous-coring borehole recently drilled at Camaldoli dellaTorre on the southern slopes of Somma–Vesuvius providesconstraints on the volcanic and magmatic history of the Vesuvianvolcanic area since c. 126 ka BP. The cored sequence includesvolcanic units, defined on stratigraphical, sedimentological,petrological and geochemical grounds, emitted from both localand distal vents. Some of these units are of known age, suchas one Phlegraean pre-Campanian Ignimbrite, Campanian Ignimbrite(39 ka), Neapolitan Yellow Tuff (14· 9 ka) and VesuvianPlinian deposits, which helps to constrain the relative ageof the other units. The main rock types encountered are shoshonite,phonotephrite, latite, trachyte and phonolite. The sequenceincludes, from the base upwards: a thick succession of pyroclasticunits emplaced between 126 and 39 ka, most of them attributedto eruptions that occurred in the Phlegraean area; the CampanianIgnimbrite; the products of a local tuff cone formed between39 ka and the deposition of the products of the earliest activityof the Mt. Somma volcano; the products of the Somma–Vesuviusvolcano, which include from the base upwards a thick sequenceof lavas, pyroclastic rocks and the products of a local spattercone dated between 3· 7 ka and AD 79. The data obtainedfrom the study of the borehole show that, before the CampanianIgnimbrite eruption, low-energy explosive volcanism took placein the Vesuvian area, whereas mostly high-energy explosive eruptionscharacterized the Campi Flegrei activity. In the Vesuvian area,Campanian Ignimbrite deposition was followed by the eruptionof a local tuff cone and a long repose time, which predatedthe formation of the Mt. Somma edifice. Since 18· 3 ka(Pomici di Base eruption) the activity of Somma–Vesuviusbecame mostly explosive with rare lava effusions. The shallowestcored deposits belong to the Camaldoli della Torre cone, formedbetween the Pomici di Avellino and Pomici di Pompei eruptions(3· 7 ka–AD 79). New geochemical and Sr–Nd–Pb–B-isotopicdata on samples from the drilled core, together with those availablefrom the literature, allow us to further distinguish the volcanicrocks as a function of both their provenance (i.e. Phlegraeanor Vesuvian areas) and age, and to identify different magmaticprocesses acting through time in the Vesuvian mantle source(s)and during magma ascent towards the surface. Isotopically distinctmagmas, rising from a mantle source variably contaminated byslab-derived components, stagnated at mid-crustal depths (8–10km below sea level) where magmas differentiated and were probablycontaminated. Contamination occurred either with Hercynian continentalcrust, mostly during the oldest stages of Vesuvian activity(from 39 to 16 ka), or with Mesozoic limestone, mostly duringrecent Vesuvian activity. Energy constrained assimilation andfractional crystallization (EC-AFC) modelling results show thatcontamination with Hercynian crust probably occurred duringdifferentiation from shoshonite to latite. Contamination withlimestone, which is not well constrained with the availabledata, might have occurred only during the transition from shoshoniteto tephrite. From the ‘deep’ reservoir, magmas rosetowards a series of shallow reservoirs, in which they differentiatedfurther, mixed, and fed volcanic activity. KEY WORDS: Somma–Vesuvius; crustal contamination; source heterogeneity; radiogenic and stable isotopes; magmatic system     

ESR dating of tooth enamel in Mousterian layer 20, El Castillo,Spain

Nine faunal teeth from layer 20 of El Castillo cave in Cantabrian Spain were dated using electron spin resonance (ESR). Two teeth were rejected due to inconsistent subsample ages, while the remaining teeth yielded a mean age that is consistent with the stratigraphic expectations: 42.7±3.5. Uncertainty in the external γ dose rate results in a potential systematic uncertainty of±6.4ka that should affect all samples equally. The results provide independent confirmation of previously reported ¹⁴C ages for layer 20. © 2010 Wiley Periodicals, Inc.     

Geotechnical characterisation of pyroclastic soils involved in huge flowslides

Landslides of the flow type involving granular geo-materials frequently result in casualties and damage to property because of the long travel distance and the high velocities that these may attain. This was true for the events that took place in Campania Region (Southern Italy) in May 1998, involving pyroclastic soils originating from explosive activities of the Somma-Vesuvius volcano. Although these phenomena have frequently affected various areas of the Campania region over the last few centuries, there were no useful geological and geotechnical references available in the aftermath of the May 1998 events. For this reason Salerno University, which was involved in the scientific management of the emergency, addressed the issue of acquiring data on the geological, geomorphological and hydrogeological features of the slopes where the landslides had taken place. The information acquired made it possible to set up a slope evolution model that is able to interpret, from a geological point of view, past and more recent landslides that had occurred in the same area. As preliminary geotechnical analyses had already validated the above model, more detailed investigations were performed both on the pore pressure regimen of the covers still in place as well as on the physical and mechanical properties of pyroclastic soils, in saturated and unsaturated conditions. The present paper begins by discussing the data acquired during the .rst phase of the studies and then goes on to illustrate the laboratory results so far obtained with the aid of approximate procedures. These help advance our knowledge of pyroclastic soils within a reasonable time frame, thus improving landslide triggering analysis.     

Nonsulfide zinc deposits in the Silesia–Cracow district,Southern Poland

The Silesia–Cracow district in Poland has been one of the world’s principal sources of zinc from nonsulfide zinc ore (Polish: galman). The still remaining nonsulfide ore resources can be estimated at 57 Mt at 5.6% Zn and 1.4% Pb. Nonsulfide mineralization is mainly hosted by Lower Muschelkalk (Triassic) limestone and is associated with different generations of the hydrothermal ore-bearing dolomite (OBD I, II, III). A fundamental ore control is believed to have been exerted by the basement faults, which were repeatedly reactivated during the Alpine tectonic cycle, leading to the formation of horst-and-graben structures: these dislocations may have caused short periods of emersion and the circulation of meteoric waters during the Cenozoic. Nonsulfide ores show a wide range of morphological characteristics and textures. They occur as earthy masses, crystalline aggregates, and concretions in cavities. Breccia and replacement textures are also very common. The most important mineral phases are: smithsonite, Fe–smithsonite, Zn–dolomite, goethite, and Fe–Mn(hydr)oxides. Minor hemimorphite and hydrozincite have also been detected. Two distinct nonsulfide ore types occur: the predominant red galman and the rare white galman. In the white galman, Fe–smithsonite and Zn–dolomite are particularly abundant. This ore type is commonly considered as a peripheral hydrothermal alteration product related to the same fluids that precipitated both the OBD II–III and the sulfides. In contrast, a supergene origin is commonly assumed for the red galman. Evidence of the petrographic and mineralogical difference between white and red galman is also found in stable isotope data. Smithsonite from red galman shows a limited range of δ ¹³C_VPDB values (−10.1 to −11.4‰), and δ ¹⁸O_VSMOW values (25.3‰ to 28.5‰, mean 26.8 ± 0.3‰). The uniform and low carbon isotope values of red galman smithsonite are unusual for supergene carbonate-hosted deposits and indicate the predominance of a single organic carbon source. Smithsonite from white galman has a more variable, slightly more positive carbon isotope (−2.9‰ to −7.4‰), but broadly similar oxygen isotope composition (26.8‰ to 28.9‰). The relationship of the white galman ore with the hydrothermal system responsible for OBD II and sulfide generation is still uncertain. The most important paleoweathering events took place in both Lower and Upper Silesia during Late Cretaceous up to Paleogene and early Neogene time. During this period, several short-lasting emersions and intense weathering episodes facilitated the formation of sinkholes in the Triassic carbonate rocks and the oxidation of sulfide orebodies through percolating meteoric waters. These phenomena may have lasted until the Middle Miocene.     

Roughness effect on the correction factor of surface velocity for rill flows

Flow velocity is one of the most important hydrodynamic variables for both channelized (rill and gullies) and interrill erosive phenomena. The dye tracer technique to measure surface flow velocity V_s is based on the measurement of the travel time of a tracer needed to cover a known distance. The measured V_s must be corrected to obtain the mean flow velocity V using a factor α_v = V/V_s which is generally empirically deduced. The V_s measurement can be influenced by the method applied to time the travel of the dye-tracer and α_v can vary in different flow conditions. Experiments were performed by a fixed bed small flume simulating a rill channel for two roughness conditions (sieved soil, gravel). The comparison between a chronometer-based (CB) and video-based (VB) technique to measure V_s was carried out. For each slope-discharge combination, 20 measurements of V_s, characterized by a sample mean V_m, were carried out. For both techniques, the frequency distributions of V_s/V_m resulted independent of slope and discharge. For a given technique, all measurements resulted normally distributed, with a mean equal to one, and featured by a low variability. Therefore, V_m was considered representative of surface flow velocity. Regardless of roughness, the V_m values obtained by the two techniques were very close and characterized by a good measurement precision. The developed analysis on α_v highlighted that it is not correlated with Reynolds number for turbulent flow regime. Moreover, α_v is correlated neither with the Froude number nor with channel slope. However, the analysis of the empirical frequency distributions of the correction factor demonstrated a slope effect. For each technique (CB, VB)-roughness (soil, gravel) combination, a constant correction factor was statistically representative even if resulted in less accurate V estimations compared to those yielded by the slope-specific correction factor.     

Rill flow resistance law under equilibrium bed‐load transport conditions

In this paper, a recently deduced flow resistance equation for open channel flow was tested under equilibrium bed‐load transport conditions in a rill. First, the flow resistance equation was deduced applying dimensional analysis and the incomplete self‐similarity condition for the flow velocity distribution. Then, the following steps were carried out for developing the analysis: (a) a relationship (Equation  13 ) between the Γ function of the velocity profile, the rill slope, and the Froude number was calibrated by the available measurements by Jiang et al.; (b) a relationship (Equation  17 ) between the Γ function, the rill slope, the Shields number, and the Froude number was calibrated by the same measurements; and (c) the Darcy–Weisbach friction factor values measured by Jiang et al. were compared with those calculated by the rill flow resistance equation with Γ estimated by Equations  13 and 17 . This last comparison demonstrated that the rill flow resistance equation, in which slope and Shields number, representative of sediment transport effects, are introduced, is characterized by the lowest values of the estimate errors.     

Measuring hydrological connectivity inside a soil by low field nuclear magnetic resonance relaxometry

Hydrological connectivity inside the soil is related to the spatial patterns inside the soil (i.e., the structural connectivity). This, in turn, is directly associated with the physical and the chemical processes at a molecular level (i.e., the functional connectivity). Nuclear magnetic resonance (NMR) relaxometry can be successfully applied to reveal both structural and functional components of soil hydrological connectivity. In the present study, the low field NMR relaxometry was applied on water suspended soils sampled at the upstream‐ and downstream‐end of three different length plots. Also the sediments collected from the storage tanks at the end of each plot were water suspended and monitored by NMR relaxometry. The results from the NMR investigations were elaborated by using a mathematical approach in order to quantify both the functional and structural connectivity components. In particular, following integration of the T₁ distribution curve, an S‐shaped curve was obtained. It revealed two plateaus corresponding to the shortest (low component) and the longest (high component) intervals of relaxation times, respectively. According to relaxometry theory, the two T₁ intervals, associated to the different plateaus, were attributed to micro and macro soil pores, respectively. The two T₁ intervals were used to define a functional connectivity index, while the central part of the S‐shaped distribution was used to define a structural connectivity index. Here we provide the physical meaning of the our mathematical approach, thereby revealing that functional connectivity index increases with plot length, as a result of a selective eroded particle transport. Moreover, the relationship structural connectivity index versus plot length resulted quasi‐independent of grainsize distribution, whereas the values of the structural connectivity index for the sediment samples resulted lower than those obtained for the corresponding soils.