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The study of the transport processes in the riparian environment is currently a subject of great interest. In this context, the evaluation of longitudinal dispersion is a fundamental issue. Although it plays an important role in the transport of chemicals, nutrients, and wood debris, few works have studied the effects of riparian vegetation on the dispersion coefficient in transversally non-uniform streams. Here, a quasi two-dimensional model is proposed to evaluate the transverse profile of the depth-averaged velocity in the presence of any vegetation distribution along the riparian transect. Once velocity profile is obtained, the dispersion coefficient is evaluated and the remarkable role of vegetation is shown. Both the velocity profile and the dispersion coefficient have been validated using our new experimental results and literature data. The work highlights the importance of taking into account the presence of vegetation along river banks. The estimation of the longitudinal dispersion in vegetated rivers can be affected by as much as 70–100% compared to the case without vegetation. 相似文献
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Application of a GIS-aided method for the assessment of volcaniclastic soil sliding susceptibility to sample areas of Campania (Southern Italy) 总被引:2,自引:1,他引:1
Sebastiano Perriello Zampelli Eliana Bellucci Sessa Marco Cavallaro 《Natural Hazards》2012,61(1):155-168
A significant part of Campania is extensively covered by volcaniclastic soils, deriving from the alteration of airfall-sedimented
formations of layered ashes and pumices that were ejected by Campi Flegrei and Mt. Somma–Vesuvius during explosive eruptions.
Where such soils cover steep slopes cut in carbonate bedrock, landforms depend essentially on the morpho-evolution of such
slopes prior to the deposition of the volcaniclastic soils, because these are generally present only as thin veneers, up to
a few meters of total thickness. Historical records and local literature testify that, in this part of Campania, landslides
that originate on carbonate slopes covered by such soils and terminate at their foot or at gully outlets are frequent, following
critical rainfall events. Such landslides can be classified as complex, occurring initially as debris slides, but rapidly evolving into debris avalanches and/or debris flows. The localization
of the initial sliding areas (i.e. “sources”) on the slopes depends on both the spatial distribution of characters of the
soil cover and the spatial distribution of the triggering rainfall events. It therefore appears reasonable to separate the
two aspects of the problem and focus on the former one, in order to attempt an assessment of soil sliding susceptibility in
the event of landslide-triggering rainfall. In this paper, some results of the application of a method aimed at such an assessment
are presented. The method, called SLIDE (from SLiding Initiation areas DEtection), is based on the concept that, for a spatially
homogeneous soil cover and a spatially homogeneous landslide-triggering rainfall sequence, different values of threshold slope
gradient for limit equilibrium conditions exist, depending on morphological characters of the soil cover, such as its continuity
and planform curvature. The method is based on the assessment of (1) soil cover presence, (2) discontinuities within soil
cover, (3) slope gradients and curvature, by means of good resolution DEMs. It has been applied to sample carbonate slopes
of Campania, where landslides originated either repeatedly or recently. Results are encouraging, and a soil sliding susceptibility
map of a large area, based on a simplified version of method, is also presented. 相似文献
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A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years 总被引:1,自引:0,他引:1
Isabella Raffi Jan Backman Eliana Fornaciari Heiko Plike Domenico Rio Lucas Lourens Frits Hilgen 《Quaternary Science Reviews》2006,25(23-24):3113
This paper presents a review of (astrobiochronological) calibration of Recent to late Oligocene calcareous nannofossil datum events. Biohorizons included in the paper are those of the widely used “standard” nannofossil zonations of Martini, E. [1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In: Farinacci, A. (Ed.), Proceedings of the Second International Conference on Planktonic Microfossils Roma. Rome, Ed. Tecnosci. vol. 2, pp. 739–785], and Okada, H., and Bukry, D. [1980. Supplementary Modification and Introduction of Code Numbers to the Low-Latitude Coccolith Biostratigraphy Zonation (Bukry, 1973, 1975). Marine Micropaleontology 51, 321–325], as well as supplementary biohorizons proposed in the literature. The biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness. We emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability, and calibrates their potential correlatability. Astrochronological age estimates rely on the Geologic timescale developed by the ICS in 2004, with some new calibrations included. We provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies. Surprisingly, there are still few high-resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution. 相似文献