Wood retention at inclined racks: Effects on flow and local bedload processes     

Isabella Schalko 《地球表面变化过程与地形》2020,45(9):2036-2047

Large wood (LW) transport can increase greatly during floods, leading to accumulations at river infrastructures. To mitigate the potential flood hazard, racks are a common method to retain LW upstream of endangered settlements or infrastructures. The majority of LW retention racks consist of vertical bars and, therefore, disrupt bedload transport. It can be hypothesized that inclined racks reduce backwater rise and local scour, as wood will block the upper part of the rack, thereby increasing the open flow cross-section below the accumulation. Flume experiments were conducted under clear water conditions to analyse backwater rise and local scour as a function of (1) rack inclination, (2) hydraulic inflow condition, (3) uniform bed material, and (4) LW volume. In addition, the first experiments were performed under live bed scour conditions to study the effect of bedload transport on local scour and backwater rise. Based on the experiments, backwater rise and local scour decrease with decreasing rack angle to the horizontal. LW predominantly accumulated at the upper part of the rack, leading to an open flow cross-section below the accumulation. The effect of rack angle was included in existing design equations for backwater rise and local scour depth. In addition, the first experiments with bedload transport resulted in smaller backwater rise and local scour depth. This study contributes to an enhanced process understanding of wood retention and bedload transport at rack structures and an improved design of LW retention racks. © 2020 John Wiley & Sons, Ltd.  相似文献   

Interannual variability patterns of the world’s total column water content: Amazon River basin     

Isabella Bordi  Roberto De Bonis  Klaus Fraedrich  Alfonso Sutera 《Theoretical and Applied Climatology》2015,122(3-4):441-455

  相似文献   

On the coupling between vegetation and the atmosphere     

Isabella M. Angelini  Michael Garstang  Robert E. Davis  Bruce Hayden  David R. Fitzjarrald  David R. Legates  Steven Greco  Stephen Macko  Vickie Connors 《Theoretical and Applied Climatology》2011,105(1-2):243-261

Recent studies suggest that vegetation can drive large-scale atmospheric circulations and substantially influence the hydrologic cycle. We present observational evidence to quantify the extent of coupling between vegetation and the overlying atmosphere. Within the context of vegetation–atmospheric interactions, we reanalyze existing climatological data from springtime leaf emergence, emissivity, dew point temperatures, and historical records of precipitation and forest coverage. We construct new rainfall transects based on a robust global climatology. Using isotopic analysis of precipitation, we find that rain in Amazonia comes primarily from large-scale weather systems coupling interior regions to the ocean and is not directly driven by local evaporation. We find that changes in vegetative cover and state influence the temperature and moisture content of the surface and atmospheric boundary layer but are not reflected in observable precipitation changes. This analysis reaffirms the view that changes in precipitation over continental reaches are a product of complex processes only partly influenced but not controlled by local water sources or vegetation.  相似文献   

The Calabrian Stage redefined     

Maria Bianca Cita Luca Capraro Neri Ciaranfi Enrico Di Stefano Fabrizio Lirer Patrizia Maiorano Maria Marino Isabella Raffi Domenico Rio Rodolfo Sprovieri Simona Stefanelli Gian Battista Vai 《《幕》》2008,31(4):408-419

The name Calabrian was introduced in the geological literature by the French stratigrapher Maurice Gignoux in 1910, and later described in his important monograph （633 pages） ＂Les formations marines pliocknes et quaternaires de l＇ltalie du sud et de la Sicile ＂published in 1913. Detailed data were provided on several sections （Santa Maria di Catanzaro, Caraffa, Monasterace, Palermo） and on their fossil content. The Calabrian Stage has commonly been used for over fifty years as the oldest subdivision of the Qua- ternary, notably in the time scales of Berggren ＆ van Cou- vering （1974） and Haq ＆ Eysinga （1987）. However, after the GSSP for the Pliocene/Pleistocene boundary （P/P） was approved by INQUA in 1982 and ratified by lUGS in 1984 at the Vrica section of Calabria, there was a decline in the usage of the stage name, and an increasing tendency by many Quaternary workers to question the boundary stratotype. This was because there was increasing evidence that it did not correspond to the beginning of the ＂ice age＂. In doing so, they were not complying with the recommendations presented at the 18th International Geological Congress （IGC） in London, 1948 （Oakley, 1950）.  相似文献   

Structure and distribution of the benthic macrofauna on a Northwest African sandy beach close to a freshwater river discharge     

Abdellatif Chaouti  Isabella Colombini  Mario Fallaci  Elena Gagnarli  Lorenzo Chelazzi  & Abdellatif Bayed 《Marine Ecology》2008,29(S1):99-107

The effects of the freshwater discharge of the Oued Sebou River on the macroinfauna, was studied on the sandy beach of Mehdia through the analysis of the abiotic parameters and of the macrozoobenthos. In autumn 2002 and spring 2003, three beach sites, each with two transects, localized at 50, 3500 and 5720 m from the river mouth respectively, were studied. Positive correlations were recorded for beach slope and pH whereas negative ones were obtained for organic matter content and salinity at increasing distances from the river mouth. Significant differences between beach sites and seasons occurred for median grain size, organic matter content and pH. For each beach site, mean macroinfauna abundance varied between 30 and 100 ind.·m⁻² and in spring there was a significant correlation between this parameter and the increasing distance from the river mouth. No significant correlation was instead found between species richness and the increasing distance, although the farthest beach site from the mouth had the highest number of species during both seasons. The results indicated the importance of organic matter content and salinity for the macrofaunal abundance whereas the diversity indices were more affected by beach slope and grain size. The results showed that there was no clear spatial trend in compound indices of the macrofauna across the sampled sites and the influence of the river discharge of Sebou River did not seem to be significant and consistent on the macrobenthos of this mesotidal shore. Comparison with microtidal shores revealed the influence of the tidal excursion and swell characteristics on the response of the benthic structures of sandy beaches to discharges of freshwater.  相似文献   

A NEW“TETRASPORANGIAL”SPECIES OF LIAGORA(RHODOPHYTA,NEMALIALES)FROM HAWAIT     

Isabella A. Abbott 《中国海洋湖沼学报》1995,(4)

A new species of Liagora,L.perennis sp.nov.from Hawai’i,is described.Unlike dpecies of this genus in China,it is carpotetrasporangial,and at the place of expected carposporangia bears cruciately di-vided tetrasporangia,a detail which differentiates it from the usual species of Liagora without tetraspores that have been reported in China.Notes are provided on other Liagora species that have an impact on the taxonomy of species found in China.  相似文献   

Volcanism and vertical tectonics in the Pacific Basin related to global Cretaceous transgressions     

Seymour O. Schlanger  Hugh C. Jenkyns  Isabella Premoli-Silva 《Earth and Planetary Science Letters》1981,52(2):435-449

The dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the Pacific Basin has been recognised since the time of Charles Darwin. Data gathered on several legs of the Deep Sea Drilling Project (DSDP) and numerous marine expeditions in the past decade have confirmed Menard's postulate that the Pacific Basin was the scene of volcanism on an enormous scale in Mesozoic time. Widespread mid-plate volcanism between ～110 and 70 m.y. B.P. characterised the area bounded by the Line Islands, the Mid-Pacific Mountains and the Nauru Basin-Marshall Islands. Heating of the Pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a “normal” Parsons-Sclater subsidence curve. The Farallon plate, now almost entirely subducted, was also the scene of mid-plate volcanism that produced such features as the Nicoya Plateau now found as an allochthonous ophiolitic terrain landward of the middle America trench. Large, benthonic, reef-associated foraminifera comprising a pseudorbitoid fauna, hitherto considered to be largely restricted to Central America, have now been additionally recorded from DSDP Sites 165, 315 and 316 in the Line Islands, Site 462 in the Nauru Basin, and in New Guinea. The distribution of this fauna, of Campanian/Maastrichtian age, is interpreted as indicating “stepping stone” connections (aseismic ridges, plateaus and seamounts) between the Caribbean, Farallon, and Pacific plates 70–80 m.y. B.P. Similarities between the geology of the Nauru Basin and the Caribbean Ocean crust reinforce the interpretation of the latter as a former part of the Farallon plate. Estimates of the sea-level and continental freeboard change caused by the thermally induced uplift of the Pacific and Farallon plates, as well as substantial areas in the Atlantic and Indian Ocean Basins, indicate that such shallowing of the sea floor could have been the major factor in causing global Cretaceous transgressions.  相似文献   

Re-equilibration of detrital muscovite and the formation of interleaved phyllosilicate grains in low temperature metamorphism,northern Apennines,Italy     

Marcello Franceschelli  Isabella Memmi  Giovanni Gianelli 《Contributions to Mineralogy and Petrology》1991,109(2):151-158

Low temperature metamorphosed clastic rocks of northern Apennines (Verrucano) contain detrital and metamorphic muscovite along with aggregates of interleaved phyllosilicate grains. The extent of celadonite substitution in the metamorphic muscovite progressively increases from Al-rich pyrophyllite-bearing samples to Al-poor K-feldspar-bearing samples and appears to be compatible with the phase relation in the AKF and AKNa diagrams. Some detrital muscovite grains, not equilibrated with the present metamorphic mineral assemblages, seem to be unreacted grains retaining their premetamorphic composition. The chemistry of the re-equilibrated detrital muscovite is mainly controlled by the activity of Al₂O₃ that is implied by mineral assemblages in the host rocks and is independent of the original composition of detrital mica. Four types of phyllosilicate associations in the interleaved phyllosilicate grains were recognized: 1) muscovite- pyrophyllite-sudoite; 2) muscovite-pyrophyllite-chlorite; 3) muscovite-paragonite-chlorite; 4) muscovite-chlorite. A microstructural and petrological model is proposed for the origin of interleaved phyllosilicate grains in the Verrucano rocks. The model supports the idea that the interleaved phyllosilicate grains are the result of the trend towards equilibrium between detrital muscovite, metamorphic mineral assemblages and the fluid phase.  相似文献   

On the feedback between water turbidity and microphytobenthos growth in shallow tidal environments     

Mattia Pivato  Luca Carniello  Isabella Moro  Paolo D'Odorico 《地球表面变化过程与地形》2019,44(5):1192-1206

Shallow tidal environments (e.g. bays, estuaries, lagoons) represent one of the most productive ecosystems in the world, and they are threatened by current climate change and increasing human pressure. Monitoring the bio-morphodynamic evolution of these environments is therefore a crucial task that requires a detailed and holistic scrutiny. The present study aims to investigate the temperature of the water–sediment continuum, its effect on the related microphytobenthos (MPB) growth and the related bio-stabilization of the bed sediment surface under different water depth and water turbidity conditions. We investigated the vertical energy transfer and the temperature dynamics by applying a 1-D model to a shallow coastal lagoon. Our results show that the water temperature does not substantially change under different turbidity conditions, whereas the sediment temperature exhibits important changes. Two major factors driving the MPB photosynthetic growth are the sediment surface temperature and the light availability at the sediment bed, which can both be computed using the vertical energy transfer model. We observed that, in general, clear water conditions better promote MPB growth over the entire year. The limiting factor for the photosynthetic process is usually the light availability at the bottom, which increases under clear water conditions. As MPB provides a bio-stabilizing effect on the bed sediments by producing a biofilm on the sediment surface that reduces sediment resuspension, our results suggest a positive feedback between MPB growth and water column turbidity. Furthermore, MPB growth and the related sediment bio-stabilization are clearly affected by the seasonal variation of surface sediment temperature and light availability. This seasonal variation of MPB growth rate and surface sediment bio-stabilization must be considered when studying the long-term morphodynamic evolution of tidal environments. © 2018 John Wiley & Sons Ltd.  相似文献   

Spatial patterns and temporal trends of precipitation in Iran   总被引：3，自引：0，他引：3  

Tayeb Raziei  Jamal Daryabari  Isabella Bordi  Luis S. Pereira 《Theoretical and Applied Climatology》2014,115(3-4):531-540

Spatial patterns of monthly, seasonal and annual precipitation over Iran and the corresponding long-term trends for the period 1951–2009 are investigated using the Global Precipitation Climatology Centre gridded dataset. Results suggest that the spatial patterns of annual, winter and spring precipitation and the associated coefficients of variation reflect the role of orography and latitudinal extent between central-southern arid and semi-arid regions and northern and western mountainous areas. It is also shown that precipitation occurrence is almost regularly distributed within the year in northern areas while it is more concentrated in a few months in southern Iran. The spatial distribution of Mann–Kendal trend test (Z statistics) for annual precipitation showed downward trend in north-western and south-eastern Iran, whereas western, central and north-eastern exhibited upward trend, though not statistically significant in most regions. Results for winter and autumn revealed upward trend in most parts of the country, with the exception of north-western and south-eastern where a downward trend is observed; in spring and summer, a downward trend seems to prevail in most of Iran. However, for all seasons the areas where the detected trend is statistically significant are limited to a few spot regions. The overall results suggest that the precipitation is decreasing in spring and summer and increasing in autumn and winter in most of Iran, i.e. less precipitation during the warm season with a consequent intensification of seasonality and dryness of the country. However, since the detected trends are often not statistically significant, any stringent conclusion cannot be done on the future tendencies.  相似文献