...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Upstream and downstream controls of recent avulsions on the Taquari megafan, Pantanal, south-western Brazil
【24h】

Upstream and downstream controls of recent avulsions on the Taquari megafan, Pantanal, south-western Brazil

机译：巴西西南部潘塔纳尔（Tatanali megafan）最近发生的Taquari巨扇侵袭的上游和下游控制

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Avulsion, the natural relocation of a river, is a key process in the evolution of subaerial fans, river floodplains and deltas. The causes of avulsion are poorly understood, which is partly due to the scarcity of field studies of present avulsions. At present, two avulsions are occurring on the middle and lower Taquari megafan, Pantanal basin, south-western Brazil. Here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes. The middle fan avulsion (started in 1997-1998) is a result of upstream control: overbank aggradation was caused by the (variable) input of sandy sediment into the system, which caused channel-belt superelevation and also created an easily erodible subsurface favouring bank retreat, crevassing, and scour of deep floodplain channels. The sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage. The lower fan avulsion (started c. 1990) results from interplay of upstream and downstream controls, the latter being related to the local base level (the Paraguay River floodplain) at the toe of the fan. Channel and overbank aggradation on the lower fan was influenced by fan sub-lobe progradation and channel backfilling. Fan sub-lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel. Avulsions are commonly supposed to be preferentially triggered by high-magnitude floods, when there is considerable channel-belt superelevation. However, both avulsions studied by us were triggered by small to average floods, with modest channel-belt superelevation. We conclude that flood magnitude and channel-belt superelevation have been overrated as causes of avulsion, and demonstrate additional causes that influence the growth of crevasses into avulsions.
机译：撕裂是河流的自然迁移，是地下风扇，河流漫滩和三角洲演变的关键过程。撕脱的原因了解甚少，部分原因是目前对撕脱的田间研究缺乏。目前，在巴西西南部Pantanal盆地的Taquari巨扇中下部发生了两次撕脱。在此，我们根据现场和遥感数据对这些撕脱的原因进行分析，并显示对巨型风扇的撕脱可通过上游和下游过程进行控制。中间扇形撕脱（始于1997-1998年）是上游控制的结果：堤岸的凝结是由（可变的）沙质沉积物输入系统引起的，这引起了河道带的超高，并且还形成了易于侵蚀的地下有利堤岸撤退，开裂和冲刷深洪泛滥的河道。推断该区域的砂质地下岩层在梯度优势较小的情况下是造成撕裂的主要因素。较低的风扇撕裂（始于1990年）是上游和下游控制装置相互作用的结果，后者与风扇脚趾的当地基准水位（巴拉圭河漫滩）有关。下部风扇的通道和堤岸过度凝结受风扇子瓣的扩展和通道回填的影响。扇形子瓣的扩散导致撕脱通道相对于父通道具有明显的梯度优势。通常，在有相当大的河道带超高时，崩塌通常是由高水位洪水引发的。但是，我们研究的两次撕脱都是由小到平均洪水引发的，河道带超高程度适中。我们得出的结论是，洪水幅度和河道带超高被高估为撕裂的原因，并证明了影响从裂缝到撕裂的增长的其他原因。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号