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根据浙江舟山野鸭山至螺头山岸段海域4个测点的海流观测和含沙量调查(其中1个测点)资料,含沙量用1/10000感量的电光分析天平称量测定,悬沙粒度用AT 型库尔特计数器测定,底质表层泥样用激光粒度仪测定,使用DS3水准仪(其精度标准为四等)测量岸段潮滩高程,对该岸段所在海域的泥沙与潮流特征进行了对比分析并讨论了岸滩的冲淤变化。结果表明,该海域悬沙浓度由表层往底层逐渐增高,且与流速有一定的线性关系;中潮悬沙浓度低于大潮,冬季悬沙浓度高于春、夏季;大、中潮的落潮输沙量大于涨潮,大潮涨、落潮的输沙量大于中潮涨、落潮,大潮全潮单宽净输沙量大于中潮;冬季平均悬沙粒径比夏季大,春季适中;春、夏、冬季悬沙的分选系数属分选极好;悬沙的运移路径以落潮流流向为净输沙的方向;该海域的潮流为往复流,涨潮流历时短于落潮流历时,春、夏、冬季平均落潮流速大于平均涨潮流速,最大流速为1.82m/s(夏季),平均流速为0.70m/s;历史上野鸭山至螺头山的古海湾一直缓慢淤涨,1987年以来,潮滩仍缓慢淤涨,中潮滩平均淤高值约为3cm/a,岸滩平均淤进速度约为0.38m/a。 相似文献
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Two adjacent upland floodplains are compared to establish the local response of floodplains to environmental change. Radiocarbon dating, the analysis of sedimentary exposures, terrace mapping, aerial photography and archaeological evidence are used to examine Late Quaternary valley fill sediments on the Afon Tanat and the Afon Vymwy in the Upper Severn Basin, Wales, UK.The alluvial stratigraphy of the two floodplain systems consists of Late Devensian (last glacial) fluvio-glacial sediments at the valley margins deposited under a braided outwash river regime. Holocene age terraces, with floodplain and palaeochannel deposits composed of gravels overlain by silty-sands, are inset into this older unit and were formed by meandering fluvial channel systems. A combination of field and laboratory data demonstrates that from the mid-late Holocene the two floodplain systems had divergent development. The Afon Vyrnwy has remained vertically stable for the last ca. 4000 yrs. whereas the adjacent Afon Tanat continued to be vertically and laterally active.Both floodplain systems have been affected by Late Quaternary climatic fluctuations and anthropogenic activity from the Bronze Age to the Roman period, but local geomorphic gradient controls, combined with a possibly greater focus of anthropogenic activity in the Tanat catchment, may explain the differential evolution of the two systems. The data demonstrate that multiple reach-scale studies are essential for revealing significant stages in the chronology and historical development of fluvial systems. 相似文献
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Antony G. Brown Stephen Tooth Richard C. Chiverrell James Rose David S. G. Thomas John Wainwright Joanna E. Bullard Varyl R. Thorndycraft Rolf Aalto Peter Downs 《地球表面变化过程与地形》2013,38(4):431-434
The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’ effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and near‐shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Joseph R. McAuliffe Louis A. Scuderi Leslie D. McFadden 《Global and Planetary Change》2006,50(3-4):184-201
Dendrogeomorphologic approaches were used to study hillslope erosion and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, U.S.A. Root exposure in pinyon pines indicated hillslope erosion averaged 1.9 mm/yr over the last 400 yr, but erosion has been highly episodic. Negative increment growth anomalies in hillslope trees are interpreted as the consequence of rapid aerial exposure of roots by erosion. During the last 300 yr, two of three major episodes of these growth anomalies occurred after abrupt transitions from prolonged, multi-year droughts to sustained, lengthy periods of above-average precipitation. The most recent episode of these growth anomalies began within a few years after 1905 and was associated with the largest precipitation shift (drought to wet interval) in the last 400 yr. In contrast to trees on eroding hillslopes, increment growth of trees in more geomorphically stable landscape positions closely tracked the regional precipitation signal. Two major alluvial fills on the adjacent valley floor are also linked to the abrupt changes in precipitation regimes and the associated increases in delivery of runoff and sediments from slopes. The clay-cemented sandstones weather rapidly; rapid weathering and sediment production make slopes highly responsive to decadal precipitation changes. Significant vegetation declines on slopes during extreme drought make hillslope soils more prone to erosion if heavy precipitation follows soon thereafter. 相似文献
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Valley sequences of Late Quaternary alluvial units reflect alluvial preservation as well as alluvial production factors. Effects of lateral channel migration, incision, aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets: cartographically dated and model data based on lateral channel migration; well‐mapped and dated Late Quaternary valley unit surveys; and composite age–frequency plots for dated alluvial units and flood sediments. Despite much expectable variation between sites, and the complex effects of river‐activity combinations, a common characteristic of the data sets examined is the significance of preservation factors. Lateral migration tends to eliminate older units as it creates new alluvial deposits, whereas incision may lead to the preferential preservation of older units beyond the incision slot. Aggradational environments are likely to preserve more complete records, although simultaneous lateral migration may eliminate, possibly repeatedly, the upper parts of alluvial units. The common pattern of inset and incised streams within Pleistocene and early Holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley‐floor units is necessarily at the expense of reprocessing earlier ones. Floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials, thus limiting the preserved record of earlier events. In light of these censoring effects of river activities, the sequence of preserved Late Quaternary units within UK sequences is reconsidered. It is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record, and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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M. G. Macklin D. G. Passmore A. C. Stevenson D. C. Cowley D. N. Edwards C. F. O'Brien 《第四纪科学杂志》1991,6(3):225-232
Archaeological survey and palaeoenvironmental investigations in Coe Burn, Callaly Moor, Northumberland, have examined the chronology and nature of prehistoric and historic land-use change in a small upland river catchment. These studies have revealed an intensively used landscape with evidence of late Neolithic to Bronze Age, medieval and post-medieval land use and settlement. Two episodes of valley floor alluviation are identified and dated to the middle-late Bronze Age and post-medieval periods. Magnetic mineral and geochemical analyses of fine sediments from the older alluvial fill show it to contain a high proportion of topsoil, which is believed to have been produced by soil erosion resulting from Bronze Age tree clearance and cultivation. Deposition of the younger alluvial fill (post AD 1500) was associated with the inwash of relatively unweathered bedrock generated by coal mining in the catchment. It is demonstrated that by integrating archaeological field survey with off-site palaeoenvironmental investigations a much fuller picture of human activity and land-use change has emerged than otherwise would have been the case. Studies of this type may be particularly useful in other upland river catchments where archaeological survival is limited or poor. 相似文献
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