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71.
Adjustments in channel morphology due to land‐use changes and check dam installation in mountain torrents of Calabria (southern Italy) 下载免费PDF全文
Diego Fortugno Carolina Boix‐Fayos Giuseppe Bombino Pietro Denisi Juan Manuel Quiñonero Rubio Vincenzo Tamburino Demetrio Antonio Zema 《地球表面变化过程与地形》2017,42(14):2469-2483
In Mediterranean semi‐arid conditions, the availability of studies monitoring channel adjustments as a response to reforestation and check dams over representative observation periods, could help develop new management strategies. This investigation is an integrated approach assessing the adjustments of channel morphology in a typical torrent of southern Italy after land‐use changes and check dam construction across a period of about 60 years. A statistical analysis of historical rainfall records, an analysis of land‐use changes in the catchment area and a geomorphological mapping of channel adjustments were carried out and combined with field surveys of bed surface grain‐size over a 5‐km reach including 14 check dams. The analysis of the historical rainfall records showed a slight decrease in the amount and erosivity of precipitation. Mapping of land‐use changes highlighted a general increase of vegetal coverage on the slopes adjacent to the monitored reaches. Together with the check dam network installation, this increase could have induced a reduction in water and sediment supply. The different erosional and depositional forms and adjustments showed a general narrowing between consecutive check dams together with local modifications detected upstream (bed aggradation and cross‐section expansion together with low‐flow realignments) and downstream (local incision) of the installed check dams. Changes in the torrent bends were also detected as a response to erosional and depositional processes with different intensities. The study highlighted: the efficiency of check dams against the disrupting power of intense floods by stabilizing the active channel and the influence of reforestation in increasing hillslope protection from erosion and disconnectivity of water and sediment flows towards the active channel. Only slight management interventions (for instance, the conversion of the existing check dams into open structures) are suggested, in order to mobilize the residual sediment avoiding further generalized incision of the active channel and coast line erosion. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
72.
Simone Mantellini Vincenzo Picotti Abbas Al-Hussainy Nicolò Marchetti Federico Zaina 《Geoarchaeology》2024,39(3):268-299
The last two decades witnessed increasing scholarly interest in the history of water management in southern Mesopotamia. Thanks to many geoarchaeological research projects conducted throughout the central and southern Iraqi floodplains, a general understanding of the macrophases of anthropogenic manipulation of this vast hydraulic landscape has been achieved. However, current narratives mostly rely on studies at a regional scale and are based on excessively long chronological phases (often spanning a whole millennium). A finer-tuned analysis at a submillennial scale is needed to better appreciate the dynamics that led to the development of artificial canals and irrigation systems and the creation of harbours in cities and other navigation-related facilities. The Iraqi-Italian QADIS project is addressing this issue through a systematic geoarchaeological investigation in the south-eastern area of the Qadisiyah province. We aim to update the current narrative by analysing case studies involving specific periods of occupation. We performed 17 boreholes to propose a date on the functioning period of the hydraulic works in five selected archaeological sites of this region. This approach allowed us to understand changes in water management strategies in both the short and the medium term (i.e., on a scale of centuries). In this paper, we present the results for the fourth and third millennia B.C.E. This period witnessed a crucial passage from the basic exploitation of natural watercourses for irrigation and occasional navigation to the emergence of the first system of artificial canals and intraurban harbours. 相似文献
73.
Roberto Bruno Raffaella DAmicis Bruno Bavassano Vincenzo Carbone Luca Sorriso-Valvo 《Planetary and Space Science》2007,55(15):2233-2238
The interplanetary medium is characterized by a very high Reynolds number and is pervaded by fluctuations providing information on a wide range of scales, from fractions of second up to the solar rotation period. In the past decade or so, turbulence in the solar wind has been used as a large wind tunnel to investigate scaling laws of turbulent fluctuations and multifractal models. Moreover, new interesting insights in the theory of turbulence have been derived from the point of view which considers a turbulent flow as a complex system, a sort of benchmark for the theory of dynamical systems. Important finding like the lack of a strict self-similarity of the fluctuations with the consequent nonapplicability of strict scale invariance, the strong anisotropy of velocity and magnetic field fluctuations, the clear lack of equipartition between magnetic and kinetic fluctuations all contributed to suggest the idea that interplanetary fluctuations could possibly be due to a mixture of propagating waves and static structures convected by the wind. In this paper we further discuss this point and bring new evidence about the fact that the presence of a background magnetic field introduces not only a symmetry breaking in interplanetary space but also organizes fluctuations about its large scale orientation. 相似文献
74.
We investigate the properties of intermittency of magnetic turbulence by using magnetic field data collected by the Helios spacecraft in the inner heliosphere. Clear scaling laws for magnetic structure functions are visible in periods where the velocity of the bulk plasma is low. Within these periods we found that intermittency of magnetic turbulence is high with respect to velocity field. A comparison with fluid flows where passive scalars are more intermittent than velocity, yields to consider the magnetic field like a “passive vector”. 相似文献
75.
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
76.
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
77.
Leonardo Casini Stefano Andreucci Daniele Sechi Chun‐Yuan Huang Chuan‐Chou Shen Vincenzo Pascucci 《地学学报》2020,32(4):261-271
Precise dating of the activity of Late Pleistocene to Holocene neo‐tectonic structures is crucial to quantify the rate of deformation in low‐seismicity regions. Sardinia is a relatively stable continental fragment set in the middle of the tectonically active Western Mediterranean belt. This paper provides evidences of significant uplift of northwest Sardinia that support an ongoing tectonic activity since the Marine Isotopic Stage 7 (MIS 7; ca. 220 ka). In particular, it documents for the first time Late Pleistocene to Holocene tectonics based on luminescence dating of travertine sealing a major NNE‐SSW fault. 相似文献
78.
Milagrosa Aldana Vincenzo Costanzo-Álvarez Luis Gómez Carlos González Marisel Díaz Pedro Silva Myriam Rada 《Studia Geophysica et Geodaetica》2011,55(2):343-358
In this work we try to better characterise the shallow magnetic signature of hydrocarbon microseepage in oil fields from eastern
and western Venezuela. To get a better insight of the processes involved, we attempt to find out the main magnetic phases
responsible for the observed oil-related shallow magnetic anomalies. In this way, a new and alternative numerical approach
to decompose Isothermal Remagnetization (IRM) curves is introduced. The method is based on a Direct Signal Analysis (DSA)
of the IRM curve in order to identify the number and type of magnetic components. Representative wells from western (La Victoria)
and eastern (San Joaquín) Venezuelan fields are studied. The DSA approach, together with rock magnetic experimental results,
indicates that in the well from western Venezuela the main magnetic mineralogy associated to hydrocarbon microseepage is magnetite.
Conversely, in the well from eastern Venezuela, these MS anomalies are mainly caused by the presence of Fe-sulphides (i.e.
greigite). These results support the hypothesis of two different authigenic processes. For the well at the western field,
we propose that a net electron transfer from the organic matter, degraded by hydrocarbon gas leakage, should occur precipitating
Fe(II) magnetic minerals (e.g. magnetite). On the other hand, in the well of the eastern field, high concentrations of H2S
at shallow levels, might allow the formation of secondary Fe-sulphides. 相似文献
79.
The Antarctic Ross Orogen was built up during the early Paleozoic in the framework of the convergence between the Paleo-Pacific oceanic plate and the Gondwana continental margin. Models for the Ross Orogen in northern Victoria Land are based on terranes having a variable provenance with respect to the margin. However, recent studies provide evidence for the occurrence of different pieces of the lithospheric puzzle: (i) the Wilson continental magmatic arc, representing the main part of the active Gondwana margin, (ii) the Bowers arc–backarc system, (iii) the Admiralty crustal ribbon including continental material of the Wilson forearc, and (iv) the newly discovered, Cambrian oceanic magmatic Tiger arc, along the Ross Sea coast. An updated model is presented in which, after the Early Cambrian magmatic activity of the Wilson arc, a retreat of the subduction zone in the Early–Middle Cambrian gave way to boudinage of the Wilson forearc, trenchward arc migration, opening of the Bowers backarc basin and inception of the outboard Tiger subduction zone. Renewed convergence resulted in the development of the Middle Cambrian Bowers arc, closure of the backarc and deep underthrusting of portions of it at the Middle–Late Cambrian. Finally, in the latest Cambrian to earliest Ordovician, fast exhumation was coupled in the north with erosion and sediment shed to the northeast, and with extension and potassic magmatism in central and southern Victoria Land. 相似文献
80.
Felice Arena Alfredo Ascanelli Vincenzo Nava Diego Pavone Alessandra Romolo 《Coastal Engineering》2008,55(12):1052-1061
High waves at ocean occur during a complex space–time evolution of wave groups. In this paper the nonlinear structure of three-dimensional sea wave groups at intermediate water depth is investigated. To this purpose, the Boccotti's Quasi-Determinism theory is firstly applied to describe the linear wave groups when a given exceptionally high crest occurs. Then, the second-order correction to the linear solution is derived for the general condition of three-dimensional wave groups, at a finite water depth. Several numerical applications, finally, have been carried out in order to show how both the spectral bandwidth and the directional spreading modify the nonlinear high waves at different water depth. 相似文献