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1.
Trace metals distribution pattern in floodplain sediments of a lowland river in relation to contemporary valley bottom morphodynamics 
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下载免费PDF全文 The distribution of trace metals in alluvial sediments depends on their natural background concentrations, and on the dynamics of contemporary depositional and erosional (mainly flood‐induced) processes. Geological and geochemical investigations were carried out in the valley of Vistula River near Magnuszew (central Poland). Sediment samples were collected from a depth of 35 cm and comprise sediments of all defined geomorphological features. Identification and geological interpretation of the morphodynamic sediment features was supported by aerial photographs and high‐resolution satellite images. These studies revealed that the distribution of trace metals is closely linked to the morphogenesis of the alluvial floodplain. The highest concentrations of Cu, Co, Zn, V, Cr and Ni were observed in crevasse‐splays deposits. By contrast, Sr, Pb and As were concentrated in deposits which fill oxbow lakes (partly infilled with organic deposits). The lowest concentrations of trace metals were detected in flood sediments deposited within erosional troughs. The geomorphological and sedimentological history of the fluvial features explains the pattern of heavy metal distribution on the current floodplain surface. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
William W. Haible 《地球表面变化过程与地形》1980,5(3):249-264
Walker Creek in Marin County, California is a coastal stream draining to Tomales Bay, which lies in the San Andreas Rift Zone. Its valley contains an alluvial fill with a basal gravel dated at 5000 years BP. In upstream parts of the watershed, channels are incised arroyo-like in the fill leaving the valley floor standing as a high terrace averaging 5·5 m (18 ft) high. Below this terrace is an inner terrace of historic age that stands 2·4 m (8 ft) above the streambed. The stratigraphy and morphology of this valley are seen in others nearby, and indicate that in the last half of Holocene time in this region a single episode of valley alluviation was followed by two episodes of valley cutting. The second episode of valley cutting is occurring in the present time. During the last 60 years the flow has become seasonal, the stream has incised 1·5 m (5 ft) below the inner terrace in upstream reaches, aggraded 1·2 m (4 ft) in downstream reaches, and extended its estuary. Incision upstream has begun to re-expose the bedrock valley floor and is associated with aggradation downstream that has caused the flood plain to overtop both terraces. This has decreased the stream's gradient. Using a stream that is currently effecting major changes in its valley and channel morphology, two aspects of hydraulic adjustment in fluvial systems are examined. The changes in the average slope of the longitudinal profile are small but measureable. Profile concavity has not changed measurably. The various profiles that have existed in Holocene time show that stream gradient can be, but is not necessarily, slightly adjusted during valley filling and cutting. Flow measurements at a high discharge show that the channel has begun to assume the hydraulic geometry of an ephemeral channel. Adjustments of depth, velocity, and roughness appear to be hydraulic adjustments in response to changing watershed conditions. 相似文献
3.
针对具有饱和土沉积层的充水河谷对平面瑞雷波的散射问题,把半空间场地用单相弹性介质模拟,河谷中的饱和土沉积层用Biot饱和多孔介质动力理论模拟,河谷中的水假定为无黏性流体（理想流体）,利用波函数展开法在频域内给出了具有饱和土沉积层的圆弧形充水河谷对平面瑞雷波散射问题的解析解答.文中给出了算例,计算了不同输入频率和高宽比时河谷谷底的位移幅值.算例表明由于具有饱和土沉积层的充水河谷存在,使得河谷谷底的位移幅值放大4倍多,并且它的幅值随着河谷谷底位置的不同而产生较大的变化. 相似文献
4.
The age of a large alluvial fan debouching onto the valley floor of the River Tweed, in southern Scotland, and the sequence of events relating to this, are investigated using geomorphological, sedimentological, palynological, archaeological and radiocarbon dating evidence. Prior to fan deposition, the Tweed valley floor seems to have been covered by a wooded peat at a time of low fluvial activity. The fan commenced deposition in the 11th century AD, and appears to have been a local event, the Tweed showing no response to this accelerated sedimentation. Later, perhaps 200 years later, the Tweed commenced overbank deposition of the only Flandrian terrace preserved. Local proxy data are examined in order to define the causes of these events, but difficulties in temporal correlation, despite the good resolution of the radiocarbon chronology, mean that the causes of these events remain unknown. 相似文献
5.
The dynamics and the surface evolution of a post‐LGM debris‐flow‐dominated alluvial fan (Tartano alluvial fan), which lies on the floor of an alpine valley (Valtellina, Northern Italy), have been investigated by means of an integrated study comprising geomorphological field work, a sedimentological study, photointerpretation, quantitative geomorphology, analysis of ancient to modern cartography and consultation of historical documents and records. The fan catchment meteoclimatic, geological and geomorphological characteristics result in fast rates of geomorphic reorganization of the fan surface (2 km2). The dynamics of the fan are determined by the alternation of low‐return period catastrophic alluvial events dominated by non‐cohesive debris flows triggered by extreme rainstorms which caused aggradation and steepening of the fan and avulsion of its main channel, with periods of low to moderate streamflow discharge punctuated by low‐ to intermediate‐magnitude flood events, causing slower but steady topographic reworking. The most ancient parts of the fan surface date back at least to the first half of the 19th century, but most of the fan surface has been restructured after 1911, mainly during the debris‐flow‐dominated events of 1911 and 1987. Phases of rapid fan toe incision and fan degradation have been recognized; since the 1930s or 1940s, the Tartano fan has been subjected to a state of deep entrenchment and narrowing of the main trunk channel and distributary area. Post‐Little Ice Age climate change and present‐day surface uplift rates have been considered as possible explanations for the observed geomorphic evolution, but tectonic or climatic controls cannot account for the order of magnitude of the erosional pace. Anthropogenic controls plausibly override the natural ones: in particular, the building of a dam in the late 1920s, about 2 km upstream of the fan, seems to have triggered fan dissection, having altered the sediment discharge through sediment retention. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
6.
Jürgen Herget 《地球表面变化过程与地形》2000,25(3):293-305
The characteristics of the Holocene valley floor of the River Lippe, Germany, are atypical for a river in central Europe. The valley floor consists of three terrace levels, which are not always clearly separated from each other. Analysis of the sediments making up the terraces indicates that they accumulated during the course of the entire Holocene, although there is insufficient information available to allow detailed determination of phases of fluvial change and stability responsible for terrace formation. Two of the terraces exist only in the lower reaches of the valley, where they converge and diverge with the third. The lowest terrace consists only of a narrow strip, running parallel to the river channel. The configuration of the valley floor may be explained by a series of anthropogenic influences. The earliest human impact probably occurred about 2000 years ago when, during their campaign against German tribes, the Romans built a towpath and may have changed the channel planform from its natural, anabranching pattern to a meandering form by building small dams on local distributary forks. Implementation of artificial meander cut‐offs to improve navigation on the river began in medieval times. The morphological response to these human interventions was primarily degradational. In the 19th century, artificial lateral fill was used to narrow the channel and the towpath was renewed several times. The trace of the most recent towpath is still discernible as a narrow strip parallel to the river channel, and it constitutes the lowest terrace level. Comparison between the bankfull discharge of a 4000‐year‐old abandoned channel and the formative flow for the modern channel supports the premise that, prior to anthropomorphic influence, the natural planform was anabranched. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
7.
J. Rutkowski 《地球表面变化过程与地形》1986,11(3):321-326
Carboniferous pit coal is the most important anthropogenic component of the contemporaneous Vistula river gravels and sands with individual fractions containing from 10 to 98 per cent coal fragments. Coal concentration is connected with differences in the bulk density between coal and other gravel components. The lower sediments date from the first half of the nineteenth century when the coal began to appear in large quantities in the Vistula channel. The presence of coal is also an indicator of the depth of channel sediment reworking during floods in the nineteenth and twentieth centuries. 相似文献
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Eduardo Kausel 《Soil Dynamics and Earthquake Engineering》2010,30(9):822-832
Soil–structure interaction is an interdisciplinary field of endeavor which lies at the intersection of soil and structural mechanics, soil and structural dynamics, earthquake engineering, geophysics and geomechanics, material science, computational and numerical methods, and diverse other technical disciplines. Its origins trace back to the late 19th century, evolved and matured gradually in the ensuing decades and during the first half of the 20th century, and progressed rapidly in the second half stimulated mainly by the needs of the nuclear power and offshore industries, by the debut of powerful computers and simulation tools such as finite elements, and by the needs for improvements in seismic safety. The pages that follow provide a concise review of some of the leading developments that paved the way for the state of the art as it is known today. Inasmuch as static foundation stiffnesses are also widely used in engineering analyses and code formulas for SSI effects, this work includes a brief survey of such static solutions. 相似文献
10.
A recently exposed section across a ?rst‐order valley buried beneath the regional blanket peat on hillside slopes in the upper Liffey valley, Co. Wicklow, is described. The section shows two alluvia within a shallow valley form underlain by an extensive boulder and stone line over regional till and weathered granite. 14C dates from wood in the alluvia indicate the older alluvium to have formed between 4324 ± 53 BP and 4126 ± 45 BP and the younger between 3217 ± 53 BP and 2975 ± 53 BP . The basal layer of the overlying peat yielded a date of 2208 ± 61 BP . The younger alluvium shows the effects of soil paludi?cation prior to the peat expansion. Dated pollen analyses elsewhere in the upper catchment con?rm the spread of blanket peat over most areas above 350 m after 4000–3600 BP . The buried valley was contributing sediments to the mid‐Holocene ?oodplains in the upper Liffey valley prior to the extension of blanket peat over the catchment after which sediment yields from it and the other catchment slopes declined. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
11.
A. Caserta S. Martino F. Bozzano A. Govoni F. Marra 《Bulletin of Earthquake Engineering》2012,10(4):1133-1162
The presence of peats and high compressibility inorganic clays within alluvial fills on the left-side tributaries of the Tiber River, close to Rome’s historic center in Italy, is well documented in literature. Nevertheless, few literature data exist until now on the dynamic properties of these deposits by undisturbed bore-hole samples. The Galba test-site was set up to characterise dynamic properties of the alluvial deposits by using lab-tests as well as to derive velocity profiles by seismic noise measurements. These were performed in the Giustiniano Imperatore area located in the Grottaperfetta valley, about 2?km south of Rome’s historic centre. The alluvial deposits filled a paleovalley excavated in the bedrock during the Würm glacial (18–20 ky). The stratigraphic setting of the alluvial body was reconstructed along three geological cross-sections by means of the available logs; seven lithotecnical horizons can be distinguished within the alluvial body, some tens of meters thick, based on both log-stratigraphic data and in-site geotechnical tests. These horizons include peaty layers (T) and high compressibility inorganic clays (AGI), which characterise the alluvial deposits in the Grottaperfetta valley. They do not have direct correlation with the alluvial horizons which constitute the alluvial body of the main Tiber valley in Rome’s historical centre. These alluvial horizons which are distinguished and characterised at the Galba test-site can be regarded as typical of other lateral valleys of the Tiber River in Southern Rome. They are characterised by the presence of similar high compressibility clayey deposits as well as peaty layers up to some meters thick. Undisturbed samples were also obtained at the Galba test-site for dynamic testing via resonant column and cyclic torsional shear tests. In order to attribute dynamic properties to the alluvial body at the Grottaperfetta valley, an extrapolation process was performed based on a detailed engineering-geology model of the alluvial body which was reconstructed along three transversal geological sections of the valley using bore-hole data. Three subsoil profiles, considered representative of the geological setting along the three reconstructed transversal cross sections, were analysed by seismic noise measurements performed specifically to derive S-waves velocity profiles. The results obtained show a very low velocity (<180 m/s) for the layers T and AGI. 1D modelling of seismic shaking was performed by the code Shake91, in order to evaluate the influence of the low-velocity strata on maximum shear strains induced within the alluvial deposits under the maximum expected seismic action. The results of the numerical modelling indicate that the AGI and the T layers play a key role in: (i) concentrating the maximum shear strain along the subsoil profiles, even though the volumetric threshold is never exceeded; (ii) increasing the maximum shear strain along the subsoil profiles; (iii) causing the resonance frequency of the alluvial fill to assume an almost constant value (about 1Hz) which is quite similar to that measured in the main Tiber River valley, despite a significant change in thickness of the alluvial body along the Grottaperfetta valley. 相似文献
12.
Little is known of Holocene landform development in Upland Britain. This paper describes a site at Middle Langdale in the Howgill Fells of Cumbria where large, but now stabilized and inactive gullies cut through periglacial material. At the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor. On these sediments and buried by the debris cones is a well-developed organic soil from which two 14C dates have been obtained in an attempt to estimate the age range of the soil. These dates range from 2580±55 years BP for the fine particulate fraction from the base of the organic horizon to 940±95 years BP for fossil rootlets from the uppermost organic layer, immediately below the overlying debris cones. The pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a Juncus marsh with birch, alder and hazel nearby. The pollen, from the surrounding upland area suggests woodland on the valley sides, dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present. The magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil. The evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation, although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period. The evidence then points to major geomorphological changes; a wave of soil erosion, gully development and debris cone deposition, perhaps following the Scandinavian introduction of sheep farming in the tenth century A.D. 相似文献
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Tomasz Kolerski 《Acta Geophysica》2014,62(4):893-914
The mouth of the Vistula River, which is a river outlet located in tideless area, is analyzed. The Vistula River mouth is a man-made, artificial channel which was built in the 19th century in order to prevent the formation of ice jams in the natural river delta. Since the artificial river outlet was constructed, no severe ice-related flood risk situations have ever occurred. However, periodic ice-related phenomena still have an impact on the river operation. In the paper, ice processes in the natural river delta are presented first to refer to the historical jams observed in the Vistula delta. Next, the calibrated mathematical model was applied to perform a series of simulations in the Vistula River mouth for winter storm condition to determine the effects of ice on the water level in the Vistula River and ice jam potential of the river outlet. 相似文献
16.
Variations in floodplain channel water levels and valley floor groundwater levels (measured in piezometers and boreholes) are examined at selected points along the course of the River Lambourn, a chalk river in southern England. A local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river's perennial profile. Variations in hydraulic gradient between local borehole levels and/or floodplain channel water levels are described for three sites in the seasonal section of the channel at Bockhampton, East Garston and West Shefford. The results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain. However, as the floodplain widens and the alluvial gravel aquifer increases in size, the gravel aquifer accounts for a substantial down-valley component of groundwater flow with a diffuse vertical water flux. In the lower catchment, the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water-table variability, providing a stable hydrological regime for valley-bottom wetlands. Catchment controls upon the local, valley-bottom, wetland regime are demonstrated with the application of a simple groundwater model developed using MODFLOW. The model is used to simulate groundwater discharge to the river in the upper and lower catchment, in addition to the water level regime at selected points in the valley bottom in the lower catchment. The results demonstrate the importance of taking catchment-scale water flow into account when managing isolated wetlands in a permeable catchment. 相似文献
17.
平面SV波在层状半空间中沉积谷地周围的散射 总被引：2，自引：0，他引：2
采用间接边界元方法求解了入射平面SV波在层状半空间中沉积谷地周围的散射问题.问题的解答包含自由场和散射场两部分.自由场可由直接刚度法求得,散射场由层状半空间中斜线荷载动力格林函数来模拟.文中以入射平面SV波在基岩上单一土层中沉积谷地周围散射为例研究了土层和沉积谷地周围的影响.结果表明,由于考虑了土层的动力特性,平面SV... 相似文献
18.
圆弧状沉积盆地与软土单覆盖层出平面地表运动对比 总被引：2，自引：0，他引：2
采用解析方法，通过圆弧状沉积盆地与同样参数的软土均匀单覆盖层的对比，研究沉积盆地对平面SH波二维散射效应和其出平面地表运动。数值对比结果表明：（1）波垂直入射时盆地中央地表位移幅值反应，其随频率变化形式与软土单覆盖层的地表运动有较强的对应性，且此时单覆盖层地表位移幅值为其下降；（2）盆地的二维散射效应特点显著波的汇聚作用使盆地中的地表运动显著放大，总体上较软土单覆盖层的地表位移幅值要大，其频域内的最大反应则明显大于单覆盖层情况，但最大反应在盆地表面出现的位置依赖于入射波角度、盆地深宽比和盆地的软硬程度；（3）沉积盆地中地表位移运动有强烈扭转效应，且随盆地变软和入射波频率增高而增强。 相似文献
19.
The paper presents the history of measurements of the geomagnetic field parameters over the territory of Russia in the 18th
century derived from archival and literature sources. Topographical mapping of the European territory and neighboring seas
of the Russian Empire from the late 17th to the mid 18th century during which magnetic measurements were made was of great
importance for determining magnetic declination. The magnetic declination in Siberia and its neighboring seas was measured
for the first time during the first expedition of V. Bering in 1728 and then during his second expedition (the Great Northern
Expedition) in 1733–1742. Magnetic measurements were carried out along the northern coast of Siberia and in the Bering Sea.
The academic group of the expedition performed magnetic declination measurements over southern regions of Siberia (Krasnoyarsk,
Irkutsk, Nerchinsk, Yakutsk, etc.) in 1735 and 1736. During the second half of the 18th century, Russian expeditions determined
geographical coordinates of the cities of European Russia and carried out magnetic declination measurements for them. During
these expeditions Inokhodtsev paid attention to the anomalous magnetic declination in the Kursk region. In his opinion, the
anomaly could have been caused by the presence of iron ore. 相似文献
20.
采用有限元模拟方法建立了建筑群-沉积谷地二维模型,并在土体截断边界上施加粘弹性人工边界,在频域与时域中对比分析此体系和单独沉积谷地的地震反应,观察地震时沉积谷地与建筑群之间的动力相互作用规律。分析表明,沉积谷地中建筑群对谷地本身的地震反应具有显著影响。入射波频率较低时,由于共振效应的存在,在部分区域处建筑群-沉积谷地体系的地表位移响应幅值会大于单独沉积谷地,但随着入射波频率的增加,建筑群的存在又会对地震反应产生明显的减弱效果;建筑群对谷地的影响还与建筑高度和建筑间距有关,且不同位置处的响应也存在很大差异。计算结果可为沉积谷地中设防烈度的设置以及工程抗震设计提供部分理论依据。 相似文献