Levee effects upon flood levels: an empirical assessment   总被引：1，自引：0，他引：1  

Reuben A. Heine  Nicholas Pinter 《水文研究》2012,26(21):3225-3240

This study used stream gauge records to assess the impact of levees on flood levels, providing an empirical test of theoretical and model predictions of the effects on local flood response. Focusing upon a study area in Illinois and Iowa for which levee records were available, we identified 203 gauges with ≥ 50 years hydrological record, including 15 gauges where a levee was constructed during the period of record. At these sites, step‐change analysis utilizing regression residuals tested levee‐related stage changes and levels of significance and quantified the magnitudes of stage changes. Despite large differences in stream sizes, levee alignments, and degree of floodplain constriction, the post‐levee rating‐curve adjustments showed consistent signatures. For all the study sites, stages for below bankfull (non‐flood) conditions were unaffected by levee construction. For above bankfull (flood) conditions, stages at sites downstream of their associated levees also were statistically indistinguishable before versus after levee construction. However, at all sites upstream of levees or within leveed reaches, stages increased for above bankfull conditions. These increases were abrupt, statistically significant, and generally large in magnitude – ranging up to 2.3 m (Wabash River at Mt. Carmel, IL). Stage increases began when discharge increased above bankfull flow and generally increased in magnitude with discharge until the associated levee(s) were overtopped. Detailed site assessments and supplementary data available from some sites helped document the dominant mechanisms by which levees can increase flood levels. Levee construction reduces the area of the floodplain open to storage of flood waters and reduces the width of the floodplain open to conveyance of flood flow. Floodplain conveyance often is underestimated or ignored, but Acoustic Doppler Current Profiler (ADCP) measurements analysed here confirm previous studies that up to 70% or more of the total discharge during large floods (~3% chance flood) can move over the floodplain. Upstream of levees and levee‐related floodplain constriction, backwater effects reduce flow velocities relative to pre‐levee conditions and, thus, increase stages for a given discharge. The empirical results here confirm a variety of theoretical predictions of levee effects but suggest that many one‐dimensional model‐based predictions of levee‐related stage changes may underestimate actual levee impacts. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Spatial Sciences on Ice: 50 years of Australian activities on the Amery Ice Shelf,East Antarctica     

Volker Janssen  Rachael Hurd 《The Australian geographer》2008,39(4):389-408

The Antarctic climate system involves many complex interactions between the atmosphere, oceans and ice and is sensitive to variations in these components. Ice shelves represent the ice–ocean–atmosphere interface of the Antarctic continent and are therefore very important indicators of climate change in the region. The Amery Ice Shelf is the largest ice shelf in East Antarctica and has been the focus of many scientific research projects over the past 50 years. This paper presents a history of the use of spatial science techniques from basic survey equipment to satellite systems in Australian research projects based on the Amery Ice Shelf (and surrounding glaciers) since 1955. The application of these spatial data to projects based primarily in the fields of geodesy, glaciology, climatology, and oceanography has allowed the measurement and monitoring of the physical, dynamic and environmental characteristics of this large and remote region. This new information provides scientists with a better understanding of the ice shelf/ocean/atmosphere system allowing future monitoring to observe the effects of global climate change.  相似文献   

Species-related risk assessment of antibiotics using the probability distribution of long-term toxicity data as weighting function: a case study     

Conrad Marx  Viktoria Mühlbauer  Peter Krebs  Volker Kuehn 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(8):2073-2085

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Climate impact of high northern vegetation: Late Miocene and present   总被引：1，自引：0，他引：1  

Rainer Schneck  Arne Micheels  Volker Mosbrugger 《International Journal of Earth Sciences》2012,101(1):323-338

The Late Miocene belongs to the late phase of the Cenozoic. Climate at that time was still warmer and more humid as compared to today, especially in the high latitudes. Corresponding to the climate situation, palaeobotanical evidences support that vegetation in the high northern latitudes changed significantly from the Late Miocene until today. To quantify the climate impact of this vegetation change, we analyse how vegetation in the high northern latitudes contribute to climate evolution. For that, we perform climate modelling sensitivity experiments for the present and for the Late Miocene (Tortonian, 11–7 Ma). For our present-day sensitivity experiment, we introduce the Tortonian vegetation in the high northern latitudes. For our Tortonian sensitivity experiment, we introduce the modern vegetation on the same grid cells. In the Tortonian and in the present, the modern vegetation leads to a strong cooling of the northern extratropics (up to −4°C). Nevertheless, the meridional heat transports remain nearly unchanged in both cases. In general, the vegetation impact on climate is similar in the Tortonian and in the present. However, some exceptions occur. Due to the Tethys Ocean in the Tortonian, temperatures decline only weakly in eastern Europe and western Asia. In the Tortonian climate, temperatures on the Sahara realm rise (up to +1.5°C), while the temperatures do not change remarkably in the present-day climate. This different behaviour is caused by a stronger and more sensitive hydrological cycle on the Sahara region during the Tortonian.  相似文献   

Automatic interpretation of digital maps     

Volker Walter  Fen Luo 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(4):519-528

In the past, the availability and/or the acquisition of spatial data were often the main problems of the realization of spatial applications. Meanwhile this situation has changed: on one hand, comprehensive spatial datasets already exist and on the other hand, new sensor technologies have the ability to capture fast and with high quality large amounts of spatial data. More and more responsible for the increasing accessibility of spatial data are also collaborative mapping techniques which enable users to create maps by themselves and to make them available in the internet. However, the potential of this diversity of spatial data can only hardly be utilized. Especially maps in the internet are represented very often only with graphical elements and no explicit information about the map’s scale, extension and content is available. Nevertheless, humans are able to extract this information and to interpret maps. For example, it is possible for a human to distinguish between rural and industrial areas only by looking at the objects’ geometries. Furthermore, a human can easily identify and group map objects that belong together. Also the type, scale and extension of a map can be identified under certain conditions only by looking at the objects’ geometries. All these examples can be subsumed under the term “map interpretation”. In this paper it is discussed how map interpretation can be automated and how automatic map interpretation can be used in order to support other processes. The different kinds of automatic map interpretation are discussed and two approaches are shown in detail.  相似文献   

Editorial for the special issue: vulnerability to natural hazards—the challenge of integration   总被引：8，自引：6，他引：2  

Sven Fuchs  Christian Kuhlicke  Volker Meyer 《Natural Hazards》2011,58(2):609-619

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Assessing the relevance of subsurface processes for the simulation of evapotranspiration and soil moisture dynamics with CLM3.5: comparison with field data and crop model simulations     

Sebastian Gayler  Joachim Ingwersen  Eckart Priesack  Thomas Wöhling  Volker Wulfmeyer  Thilo Streck 《Environmental Earth Sciences》2013,69(2):415-427

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Reconstructing palaeotemperatures for the Early and Middle Pleistocene using the mutual climatic range method based on plant fossils     

Jrg Pross  Stefan Klotz  Volker Mosbrugger 《Quaternary Science Reviews》2000,19(17-18)

A new approach is proposed to obtain quantitative temperature reconstructions from Early and Middle Pleistocene pollen and megafloral records. Utilizing the indicator species concept pioneered by Iversen (1944, Geologiska Föreningen Förhandlingar Stockholm 66, 463–483), the new methodology overcomes the problem of non-analogue plant communities by only taking into account the presence/absence of taxa rather than their relative abundances. Based on the present day thermal tolerances of the taxa from a fossil assemblage, the temperature interval in which all taxa from this assemblage can coexist is determined. A databank containing the climate tolerances of 85 taxa from European pollen records was established. To increase the temperature resolution of the method, procedures were developed to assess the most likely intervals for the actual temperatures within the calculated common thermospheres and the routine evaluation of the mean temperatures of the warmest and coldest months (MTW and MTC). After calibrating the approach on modern assemblages, it was applied to Tiglian and Holsteinian pollen sequences from Lieth (northern Germany) and Lac du Bourget (northern French Alps). For both records the method yields detailed temperature reconstructions of temperate and cold episodes. During the coldest episode of the Lieth section, the MTC may have been as low as −16°C. Corresponding MTW values range from 14.5 to 21°C, thus testifying to a strong continentality at that time. During the warmest period reconstructed for the Lieth section, the MTC was similar to the value as measured in the area today (1.5°C), whereas the MTW was probably higher than at present (20.1°C). For the coldest interval from the Lac du Bourget pollen sequence, the reconstructed MTC values reach a minimum of −15°C. Corresponding MTW values range from 15 to 22°C, again implying a strong continentality. For the warmest period our approach yields MTC values between −2 and 2°C and MTW values between 16.5 and 22°C. For both records, the resolution for the MTW and MTC reaches 1.5 and 2.5°C, respectively.  相似文献   

Coastal erosion vs riverine sediment discharge in the Arctic Shelf seas   总被引：8，自引：0，他引：8  

Volker Rachold  Mikhail N. Grigoriev  Felix E. Are  Steve Solomon  Erk Reimnitz  Heidemarie Kassens  Martin Antonow 《International Journal of Earth Sciences》2000,89(3):450-460

This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45᎒⁶ t a^-1) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10᎒⁶ t a^-1, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4᎒⁶ t a^-1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6᎒⁶ t a^-1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.  相似文献   

Vegetation and climate during the penultimate interglacial of the northeastern Russian Arctic: the Lake El'gygytgyn pollen record     

Wenwei Zhao  Andrei A. Andreev  Pavel E. Tarasov  Volker Wennrich  Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):507-515

We present a high‐resolution reconstruction of the vegetation and climate dynamics during the penultimate interglacial, corresponding with Marine Isotope Stage (MIS) 7, based on detailed palynological analyses of lacustrine sediments from Lake El'gygytgyn, northeastern Siberia. The analysed sediments were deposited between 246 and 181 ka ago (late MIS 8 to early MIS 6.6). The interglacial vegetation was characterized by herb and shrub (mainly alder and birch) dominated plant communities. Pollen‐based biome reconstruction shows a dominance of the tundra (TUND) biome, thus indicating rather open vegetation. Warmer intervals (MIS 7.5, 7.3 and 7.1) were marked by an increase in the cold deciduous forest (CLDE) biome scores and a synchronous decrease in the cold steppe (STEP) biome scores. The thermal maximum occurred during MIS 7.1, as indicated by the highest CLDE biome scores occurring in this period, and lasted ~10 ka, possibly favoured by the high precession‐related summer insolation and the legacy of the preceding mild and dry stadial (MIS 7.2). In contrast, MIS 7.3 and 7.5 were characterized by shorter durations (~4 ka) and lower summer temperatures. The preceding cold glacial and stadial (MIS 8 and 7.4, respectively) might have led to an extensive distribution of permafrost that hindered vegetation development during the subsequent warm intervals. MIS 7.4 and 6.6 were cold and wet, probably triggered by low obliquity values and coevally low precession‐related summer insolation. As a result, these periods were marked by significantly reduced summer temperatures and an enhanced snow‐ice albedo feedback. The obtained reconstructions provide potential scenarios for future climate changes and allow a better understanding of the relationship between vegetation, climate and external/internal forcings in the high latitudes.  相似文献