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1.
Late Holocene upper bounds of flood magnitudes and twentieth century large floods in the ungauged, hyperarid alluvial Nahal Arava, Israel 总被引：1，自引：0，他引：1
Yael Jacoby Tamir Grodek Yehouda Enzel Naomi Porat Eric V. McDonald Ofer Dahan 《Geomorphology》2008,95(3-4):274-294
The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine long-term upper bounds to flood stages and magnitudes. Along most of its course Nahal Paran, a major tributary that impacts the morphology, floods and sediments of Nahal Arava at the study reach, is a coarse-gravel, braided ephemeral stream. Downstream of the Arava–Paran confluence, aeolian and fluvial sand delivered from eastern Arava valley alters the channel morphology. The sand has accreted up to 2.5 m above the distinct current channels, facilitating the recording of large floods. This sand enhances the establishment of denser riparian vegetation (mainly Tamarix nilotica and Haloxylon persicum) that interacts with floods and affects stream morphology. A temporal association was found between specific floods recorded upstream and tree-ring ages of re-growth of flood-damaged tamarix trees (‘Sigafoos trees’) in the past 30 years. This association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region. The minimum magnitude of the largest flood that covered the entire channel width, estimated from flood deposits, is approximately 1700–1800 m3s− 1. This is a larger magnitude than the largest gauged flood of 1150 m3s− 1 that occurred in 1970 about 30 km upstream in Nahal Paran. Our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods. Based on Holocene alluvial stratigraphy and OSL dating in the study reach we also conclude that flood stages did not reach the late Holocene ( 2.2 ka) surface and therefore we estimate a non-exceedance upper bound of 2000 m3s− 1 flood magnitudes for Nahal Arava during that interval. This study indicates that in unfavorable areas the combination of hydrology, fluvial morphology and botanic evidence can increase our understanding of ungauged basins and give information crucial for hydrology planning. 相似文献
2.
Australia and New Zealand have been at the forefront of many advances in river management through policy and legislative initiatives and the introduction of participatory frameworks. In part this leadership role is a response to the pervasive extent and impact of post-colonial societies on Australasian environments. Core geographical concepts have contributed significantly to the increased recognition of a ‘sense of place’ in management practice. Grounded and authentic applications recognise explicitly the complexity of interactions across an array of biophysical and social scales. The contribution of geography to river management is particularly significant in the implementation of catchment-framed programmes, the development of generic scientific tools that can be used on a catchment-by-catchment basis, and the application of adaptive management principles that are operationalised within participatory frameworks. Failing to acknowledge geographical concepts can lead to a placeless universalism in river management that is unsustainable and unacceptable in biophysical and social terms. 相似文献
3.
Moore M Lefkovitz L Hall M Hillman R Mitchell D Burnett J 《Marine pollution bulletin》2005,50(2):156-166
Effluent upgrades for metropolitan Boston have included toxicant reduction, primary and secondary treatment and outfall extension. Between 1992 and 2003 winter flounder at five stations were surveyed annually for liver and muscle burden and chronic hepatic sub-lethal impacts of polynuclear and halogenated aromatic hydrocarbons, and metals. Trends in flounder availability and fin condition were also examined. In 1988 12% of the adult winter flounder in Boston Harbor exhibited hepatic neoplasms and up to 80% had hepatic hydropic vacuolation (HV). Tumor prevalence fell to 0-2% and HV to <50% by 1996. Since then tumors have been absent, while a steady prevalence of HV has persisted, consistent with lower hydrocarbon loading and tissue levels. Contaminants and HV also fell with distance from the Boston outfall. After the outfall extension was activated in 2000, there has been no significant change in flounder liver health at the new outfall site. 相似文献
4.
The Dead Sea has been continuously dropping 0·4–1·0 m yr?1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non‐tectonic base‐level fall. The aim of this work is to study the short‐term ongoing erosive response to a rapid base‐level drop in a small, steep‐fronted, erodible fan‐delta setting. The work explores the controls of the steep Qedem fan‐delta, guided by its clinoform structure, on its incision. Longitudinal profiles of the fan‐delta and of its entrenched channel were measured in the field. Sedimentary facies changes – fluviatile, shallow lacustrine and beach – were followed along exposures. The existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision. The field study was combined with digital elevation models (DEMs) that were extracted from pairs of overlapping aerial photos. Maps of erosion and deposition were prepared using a change detection algorithm. The longitudinal profile of the entrenched channel was found to be steep and linear. The outlet temporarily ‘hangs’ elevated and ungraded above the retreating lake level, indicating years without incision flow events, which cause lags in response to the rapid lake level drop. In spite of the large boulders, the small drainage basin and precipitation volume over the basin of the Qedem, the recorded vertical incision rates in the unconsolidated sediments are as high as 0·8 m yr?1, i.e. similar to those of the largest wadis draining to the Dead Sea. The steep front of the fan‐delta is suggested to be a main factor controlling the efficient incision. A unique transport mechanism of rolling boulders, following undercutting, contributed to the entrenchment efficiency. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
5.
Sakurajima volcano: a physico-chemical study of the health consequences of long-term exposure to volcanic ash 总被引：1，自引：1，他引：0
S. E. Hillman C. J. Horwell A. L. Densmore D. E. Damby B. Fubini Y. Ishimine M. Tomatis 《Bulletin of Volcanology》2012,74(4):913-930
Regular eruptions from Sakurajima volcano, Japan, repeatedly cover local urban areas with volcanic ash. The frequency of exposure
of local populations to the ash led to substantial concerns about possible respiratory health hazards, resulting in many epidemiological
and toxicological studies being carried out in the 1980s. However, very few mineralogical data were available for determination
of whether the ash was sufficiently fine to present a respiratory hazard. In this study, we review the existing studies and
carry out mineralogical, geochemical and toxicological analyses to address whether the ash from Sakurajima has the potential
to cause respiratory health problems. The results show that the amount of respirable (<4 μm) material produced by the volcano
is highly variable in different eruptions (1.1–18.8 vol.%). The finest samples derive from historical, plinian eruptions but
considerable amounts of respirable material were also produced from the most recent vulcanian eruptive phase (since 1955).
The amount of cristobalite, a crystalline silica polymorph which has the potential to cause chronic respiratory diseases,
is ~3–5 wt.% in the bulk ash. Scanning electron microscope and transmission electron microscope imaging showed no fibrous
particles similar to asbestos particles. Surface reactivity tests showed that the ash did not produce significant amounts
of highly reactive hydroxyl radicals (0.09–1.35 μmol m−2 at 30 min.) in comparison to other volcanic ash types. A basic toxicology assay to assess the ability of ash to rupture the
membrane of red blood cells showed low propensity for haemolysis. The findings suggest that the potential health hazard of
the ash is low, but exposure and respiratory conditions should still be monitored given the high frequency and durations of
exposure. 相似文献
6.
Multitemporal ALSM change detection,sediment delivery,and process mapping at an active earthflow 总被引：1，自引：0，他引：1
Remote mapping and measurement of surface processes at high spatial resolution is among the frontiers in Earth surface process research. Remote measurements that allow meter‐scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales. At Mill Gulch in northern California, USA, an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping (ALSM), enabling meter‐scale quantification of landscape change. We calculate four‐year volumetric flux from the earthflow and compare it to long‐term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds. We also present detailed maps of changing features on the earthflow, from which we can derive velocity estimates and infer dominant process. These measurements rely on proper digital elevation model (DEM) generation and a simple surface‐matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset. The mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 ± 1 mm/yr from 2003 to 2007. By making the conservative assumption that these features were the dominant contributor of sediment flux from the entire Mill Gulch drainage basin during this time interval, we calculate a minimum catchment‐averaged erosion rate of 0·30 ± 0·02 mm/yr. Analysis of beryllium‐10 (10Be) concentrations in fluvial sand from nearby Russian Gulch and the South Fork Gualala River provide catchment averaged erosion rates of 0·21 ± 0·04 and 0·23 ± 0·03 mm/yr respectively. From translated landscape features, we can infer surface velocities ranging from 0·5 m/yr in the wide upper ‘source’ portion of the flow to 5 m/yr in the narrow middle ‘transport’ portion of the flow. This study re‐affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
7.
Braiding has been widely studied in humid‐temperate climates though rarely in arid environments. Morpho‐texture of braided streams refers to the morphological‐textural organization in a braid‐cell (stream section including bars, anabranches and chutes) that may strongly relate to different processes and hydrological regimes. The objective of this study is to compare the morpho‐texture of braided streams governed by diverse flow recessions in different climates. Measurements were conducted in the wadis Ze'elim and Rahaf, southeast hyper‐arid Israel, in the Mediterranean Barranca‐de‐los‐Pinos, central Spain and in humid‐temperate braided systems, the La‐Bléone River, Haute‐Provence, France and in the Saisera and Cimoliana torrents, northeast Italy. Terrestrial laser scanning was used to produce point clouds and high resolution digital elevation models of the braid‐cells. Wet braid‐cells in humid‐temperate environments were surveyed by a Total Station. Roughness and the upper tail of grain size distributions were derived from the scanned point clouds or from Wolman sampling. We found that anabranches are commonly finer‐grained than the bars in dryland systems and in semi‐arid sandy braided systems, contrary to the humid‐temperate braided systems. In both climates, chutes are similar or coarser‐grained than the bars which they dissect, in accordance with their steeper gradients due to the considerable bar‐anabranch relief. The Saisera's morpho‐texture is similar to that of the dryland braided channels, despite the very humid‐temperate environment in which it is located, due to its short‐lived, ephemeral type hydrograph. Hydrograph shape, specifically the duration of flow recession, typical of a climate but not confined to it, determines the morpho‐texture of braided streams and the textural differentiation between a depositional bar and the adjacent anabranches. The morpho‐texture of chutes and bars results also from local erosional processes affected by local topography, i.e. ungraded longitudinal profiles, and is not solely determined by flow recession. This new morpho‐textural model enables identifying primary depositional and erosional braiding processes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
The morpho‐textural signature of large bedforms in ephemeral gravel‐bed channels of various planforms 
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下载免费PDF全文 This study adopts a fresh approach to find the similarities between river planforms in contrast to many previous studies that have presented distinguishing characteristics and thresholds. This new approach links textural and morphological attributes of bedforms, termed morpho‐texture, with process and hydrological regime thereby indicated. The study was carried out in depositional features of ephemeral rivers having a range of planforms and located in the Judean Desert. High‐resolution terrestrial laser scanning was undertaken to extract morphological and textural (roughness) characteristics. Results strongly indicate that bars are statistically coarser grained than the adjacent thalweg or anabranches where depositional processes occur. This suggests universal processes within ephemeral rivers regardless of their planform, where rapid flow recession causes the coarse tail of the bedload to be deposited as bars whereas the finer fractions deposit in the thalweg and thereby prevent the development of bed armour. 相似文献
9.
Jean‐Paul Bravard Ashraf Mostafa Romain Garcier Gaëlle Tallet Pascale Ballet Yael Chevalier Herv Tronchre 《Geoarchaeology》2016,31(6):467-486
The present study examines the geoarchaeological history of an oasis in Kharga Depression in central Egypt. El‐Deir is renowned for its Ptolemaic temple and Roman fortress on the road from former Hibis (Kharga) to the Nile Valley. During the survey, spring mounds and irrigation soils belonging to an ancient agricultural zone were discovered, and further documented by ceramics found on the site. Our methodology combines the geomorphological interpretation of landforms (especially yardangs) with ceramics and 14C‐dated charcoal to distinguish and date former agricultural areas in El‐Deir. The results show that the oasis experienced several phases of soil accretion and destruction through time. Playa sediments were deposited in the humid early Holocene and severely eroded by deflation before the onset of irrigated agriculture between Pharaonic and Persian times. Very fast vertical soil accretion occurred in the Ptolemaic period, but irrigation soils were later destroyed during the Roman period by a combination of wind deflation and flash floods (second to fourth century A.D.), suggesting a period of climate instability. The case of El‐Deir invites reevaluation of constructive agencies for the development of irrigated land and destructive agencies as limiting factors for the sustainability of agricultural practices in late antiquity. 相似文献
10.
Drake Deming John J. Hillman Theodor Kostiuk Michael J. Mumma David M. Zipoy 《Solar physics》1984,94(1):57-74
We have obtained low noise (S/N > 103), high spectral resolution (/ 10
6) observations of two pure rotation transitions of OH from the solar photosphere. The observations were obtained using the technique of optically null-balanced infrared heterodyne spectroscopy, and consist of center-to-limb line profiles of a = 1 and a = 0 transition near 12 m. These lines should be formed in local thermodynamic equilibrium (LTE), and are diagnostics of the thermal structure of the upper photosphere. We find that the = 0R22(24.5)e line strengthens at the solar limb, in contradiction to the predictions of current one-dimensional photospheric models. Our data for this line support a two-dimensional model in which horizontal thermal fluctuations of order ±800 K occur in the region 5000 10–3–10–2. This thermal bifurcation may be maintained by the presence of magnetic flux tubes, and may be related to the solar limb extensions observed in the 30–200 m region.Observations of the = 1R11(29.5)f line, at 885.643 cm–1, show that it is anomalously weak in the photospheric spectrum. We argue that the source function in the core of this line has been substantially increased by interaction with the 9j-7i transition of Mgi at 885.524 cm–1, which is itself too weak to appear in the disk center spectrum.Visiting Astronomer, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation. 相似文献