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41.
Sampling the collected suspension in a storage tank is a common procedure to obtain soil loss data. A calibration curve of the tank has to be used to obtain actual concentration values from those measured by sampling. However, literature suggests that using a tank calibration curve was not a common procedure in the past. For the clay soil of the Sparacia (Italy) experimental station, this investigation aimed to establish a link between the relative performances of the USLE‐M and USLE‐MM models, usable to predict plot soil loss at the event temporal scale, and soil loss measurement errors. Using all available soil loss data, lower soil loss prediction errors were obtained with the USLE‐MM (exponent of the erosivity term, b1 > 1) than the USLE‐M (b1 = 1). A systematic error of the soil loss data is unexpected for the Sparacia soil because the calibration curve does not depend on the water level in the tank. In any case, this type of error does not have any effect on the b1 exponent. Instead, this exponent decreases as the level of underestimation increases for increasing soil loss values. This type of error can occur at Sparacia if it is assumed that a soil loss measurement can be obtained by a bottle sampler dipped close to the bottom of the tank after mixing the suspension and assuming that the measured concentration coincides with the actual one. In this case, the risk is to obtain a lower b1 value than the actual one. In conclusion, additional investigations on the factors determining errors in soil loss data collected by a sampling procedure are advisable because these errors can have a noticeable effect on the calibrated empirical models for soil loss prediction. 相似文献
42.
Testing the use of an image‐based technique to measure gully erosion at Sparacia experimental area 下载免费PDF全文
Costanza Di Stefano Vito Ferro Vincenzo Palmeri Vincenzo Pampalone Fabrizio Agnello 《水文研究》2017,31(3):573-585
The first part of this investigation was aimed at testing the use of a three‐dimensional (3D) digital terrain model and a quasi‐tridimensional (2.5D) digital elevation model obtained by a large series of oblique images of eroded channels taken from consumer un‐calibrated and non‐metric cameras. For two closed earth channels having a different sinuosity, the ground measurement of some cross sections by a profilometer (P) was carried out and their real volume was also measured. The comparison among the three methods (3D, 2.5D, and P) pointed out that a limited underestimation of the total volume always occurs and that the 3D method is characterized by the minimum difference between measured and real volume. For this reason, 3D model can be used as benchmark. In the subsequent part of the investigation, the three ground measurement methods were applied for surveying of an ephemeral gully (EG) channel at the Sparacia area. The morphological and hydraulic variable values of the 24 surveyed cross sections determined by both 2.5D model and profilometer were compared. This comparison showed that the estimate error is generally less than ±10%. The EG measurements carried out by the three methods supported the applicability both of the empirical relationship between EG length and its eroded volume and the theoretical dimensionless relationship among the morphological variables describing the channelized erosion process. Finally, it was demonstrated that the effect of the distance interval on the EG volume measurement by 3D and 2.5D models is negligible for the investigated EG. 相似文献
43.
Large scale climate and rainfall seasonality in a Mediterranean Area: Insights from a non‐homogeneous Markov model applied to the Agro‐Pontino plain 下载免费PDF全文
Francesco Cioffi Federico Conticello Upmanu Lall Lucia Marotta Vito Telesca 《水文研究》2017,31(3):668-686
In the context of climate change and variability, there is considerable interest in how large scale climate indicators influence regional precipitation occurrence and its seasonality. Seasonal and longer climate projections from coupled ocean–atmosphere models need to be downscaled to regional levels for hydrologic applications, and the identification of appropriate state variables from such models that can best inform this process is also of direct interest. Here, a Non‐Homogeneous Hidden Markov Model (NHMM) for downscaling daily rainfall is developed for the Agro‐Pontino Plain, a coastal reclamation region very vulnerable to changes of hydrological cycle. The NHMM, through a set of atmospheric predictors, provides the link between large scale meteorological features and local rainfall patterns. Atmospheric data from the NCEP/NCAR archive and 56‐years record (1951–2004) of daily rainfall measurements from 7 stations in Agro‐Pontino Plain are analyzed. A number of validation tests are carried out, in order to: 1) identify the best set of atmospheric predictors to model local rainfall; 2) evaluate the model performance to capture realistically relevant rainfall attributes as the inter‐annual and seasonal variability, as well as average and extreme rainfall patterns. Validation tests show that the best set of atmospheric predictors are the following: mean sea level pressure, temperature at 1000 hPa, meridional and zonal wind at 850 hPa and precipitable water, from 20°N to 80°N of latitude and from 80°W to 60°E of longitude. Furthermore, the validation tests show that the rainfall attributes are simulated realistically and accurately. The capability of the NHMM to be used as a forecasting tool to quantify changes of rainfall patterns forced by alteration of atmospheric circulation under climate change and variability scenarios is discussed. 相似文献
44.
45.
The Averno 2 fissure eruption: a recent small-size explosive event at the Campi Flegrei Caldera (Italy) 总被引:1,自引:0,他引:1
Mauro Antonio Di Vito Ilenia Arienzo Giuseppe Braia Lucia Civetta Massimo D’Antonio Valeria Di Renzo Giovanni Orsi 《Bulletin of Volcanology》2011,73(3):295-320
The Averno 2 eruption (3,700 ± 50 a B.P.) was an explosive low-magnitude event characterized by magmatic and phreatomagmatic
explosions, generating mainly fall and surge beds, respectively. It occurred in the Western sector of the Campi Flegrei caldera
(Campanian Region, South Italy) at the intersection of two active fault systems, oriented NE and NW. The morphologically complex
crater area, largely filled by the Averno lake, resulted from vent activation and migration along the NE-trending fault system.
The eruption generated a complex sequence of pyroclastic deposits, including pumice fall deposits in the lower portion, and
prevailing surge beds in the intermediate-upper portion. The pyroclastic sequence has been studied through stratigraphical,
morphostructural and petrological investigations, and subdivided into three members named A through C. Member A was emplaced
during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of
10 km. During this phase the eruption reached its climax with a mass discharge rate of 3.2 106 kg/s. Intense fracturing and fault activation favored entry of a significant amount of water into the system, which produced
explosions driven by variably efficient water-magma interaction. These explosions generated wet to dry surge deposits that
emplaced Member B and C, respectively. Isopachs and isopleths maps, as well as areal distribution of ballistic fragments and
facies variation of surge deposits allow definition of four vents that opened along a NE oriented, 2 km long fissure. The
total volume of magma extruded during the eruption has been estimated at about 0.07 km3 (DRE). The erupted products range in composition from initial, weakly peralkaline alkali-trachyte, to last-emplaced alkali-trachyte.
Isotopic data and modeling suggest that mixing occurred during the Averno 2 eruption between a more evolved, less radiogenic
stored magma, and a less evolved, more radiogenic magma that entered the shallow reservoir to trigger the eruption. The early
phases of the eruption, during which the vent migrated from SW to the center of the present lake, were fed by the more evolved,
uppermost magma, while the following phases extruded the less evolved, lowermost magma. Integration of the geological and
petrological results suggests that the Averno 2 complex eruption was fed from a dyke-shaped shallow reservoir intruded into
the NE-SW fault system bordering to the west the La Starza resurgent block, within the caldera floor. 相似文献
46.
In this paper, the morphology of step–pool features is analysed using rill measurements and literature data for streams. Close-range photogrammetry was used to carry out ground measurements on rills with step–pool units, shaped on a plot having slope equal to 14, 15, 22, 24 and 26%. Data were used to compare the relationships between H/L, in which H is the step height and L is the step length, and the mean gradient of the step–pool sequence, Sm, for streams or the slope of the step–pool unit, S, for rills. The relationship of H/L against Sm is widely used to test the occurrence of the maximum flow resistance condition in streams, which is associated with the range 1 ≤ (H/L)/Sm ≤ 2. Further analyses were carried out to compare both the formation process and the profile of the pool in rills with those related to streams. Moreover, for a single rill channel, an analysis of flow characteristics expressed in terms of Darcy–Weisbach friction factor and Froude number was developed. The results allowed us to state: (i) the relationships of H/L versus Sm and S are quite similar and the steepness ratio for streams, (H/L)/Sm, and for rills, (H/L)/S, generally ranges from 1 to 2; (ii) the formation process and the profile of the pool in rills are not consistent with those occurring in streams; (iii) in the rills, the longitudinal size of the pool is dominant with respect to the maximum scour depth; (iv) the presence of a sequence of step–pool units within a rill segment noticeably increases flow resistance compared to segments with a flat bed; (v) the Froude number of the flow over the sequence of step–pool units in rills is slightly below the range of 0.8–1 corresponding to the maximum flow resistance in step–pool units. 相似文献
47.
48.
Lourdes Vazquez‐Gomez Achille de Battisti Sergio Ferro Monica Cerro Silvia Reyna Carlos A. Martínez‐Huitle Marco A. Quiroz 《洁净——土壤、空气、水》2012,40(4):408-415
The electrochemical oxidation (EO) of diethyl phthalate (DEP) in aqueous solution was studied at Pb/PbO2 and Ti/SnO2 anode materials under galvanostatic‐experimental conditions. Results obtained clearly demonstrated that the anode plays a significant role for the optimization of the oxidation process, deciding the mechanisms and by‐products formed. DEP and by‐products of oxidation were also analyzed during various stages of the electrolysis reaction by HPLC and GC/MS techniques. Before the analysis by GC/MS technique, the samples were treated by solid phase microextraction (SPME) in order to concentrate the compounds from the reaction solution and identify all electrolysis intermediates. Current efficiencies (instantaneous current efficiency; ICE and total current efficiency; TCE) achieved during EO experiments were dependent on anode used and current density (20–40 mA cm?2) at 40°C. The results obtained demonstrated that the environmental electrochemical methods can be a feasible alternative for the wastewater treatment containing hazardous phthalates. 相似文献
49.
50.
R. Sulpizio R. Bonasia P. Dellino D. Mele M. A. Di Vito L. La Volpe 《Bulletin of Volcanology》2010,72(5):559-577
Pyroclastic density currents (PDCs) generated during the Plinian eruption of the Pomici di Avellino (PdA) of Somma–Vesuvius
were investigated through field and laboratory studies, which allowed the detailed reconstruction of their eruptive and transportation
dynamics and the calculation of key physical parameters of the currents. PDCs were generated during all the three phases that
characterised the eruption, with eruptive dynamics driven by both magmatic and phreatomagmatic fragmentation. Flows generated
during phases 1 and 2 (EU1 and EU3pf, magmatic fragmentation) have small dispersal areas and affected only part of the volcano
slopes. Lithofacies analysis demonstrates that the flow-boundary zones were dominated by granular-flow regimes, which sometimes
show transitions to traction regimes. PDCs generated during eruptive phase 3 (EU5, phreatomagmatic fragmentation) were the
most voluminous and widespread in the whole of Somma–Vesuvius’ eruptive history, and affected a wide area around the volcano
with deposit thicknesses of a few centimetres up to more than 25 km from source. Lithofacies analysis shows that the flow-boundary
zones of EU5 PDCs were dominated by granular flows and traction regimes. Deposits of EU5 PDC show strong lithofacies variation
northwards, from proximally thick, massive to stratified beds towards dominantly alternating beds of coarse and fine ash in
distal reaches. The EU5 lithofacies also show strong lateral variability in proximal areas, passing from the western and northern
to the eastern and southern volcano slopes, where the deposits are stacked beds of massive, accretionary lapilli-bearing fine
ash. The sedimentological model developed for the PDCs of the PdA eruption explains these strong lithofacies variations in
the light of the volcano’s morphology at the time of the eruption. In particular, the EU5 PDCs survived to pass over the break
in slope between the volcano sides and the surrounding volcaniclastic apron–alluvial plain, with development of new flows
from the previously suspended load. Pulses were developed within individual currents, leading to stepwise deposition on both
the volcano slopes and the surrounding volcaniclastic apron and alluvial plain. Physical parameters including velocity, density
and concentration profile with height were calculated for a flow of the phreatomagmatic phase of the eruption by applying
a sedimentological method, and the values of the dynamic pressure were derived. Some hazard considerations are summarised
on the assumption that, although not very probable, similar PDCs could develop during future eruptions of Somma–Vesuvius. 相似文献