A consideration of the dune:antidune transition in fine gravel
A consideration of the dune:antidune transition in fine gravel
复制标题
对沙丘的思考：细砾石中的反沙丘过渡
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
A. Shvidchenko
中科院分区：
文献类型：
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作者：
P. Carling;A. Shvidchenko
定义沙丘的水力数据：细砾石中的反沙丘过渡与势流理论进行了比较，信息来自已发表的实验和基于现场的研究。对过渡河床和下游迁移反沙丘的发育都给予了关注。在后一种情况下，大多数数据属于砂层，而不是砾石。经验数据为理论概念提供了一些微弱的支持，即过渡发生在相对深度较大、弗劳德数逐渐降低的地方。虽然临界弗劳德数为0.84可以合理地应用于沙丘向反沙丘转变的开始，但滞后效应（以及可能的深度限制）确保过渡的床型可以在从0.5到1.8的弗劳德数范围内持续存在。后一种观察结果与根据露头资料得出的古水力估计有很大关系。基于势流理论的理论床型存在场在细砾石上的应用以前纯粹是推测性的，而将实验和现场数据添加到这些地块中，为将稳定性理论应用于实际地质问题提供了一定程度的信心。第一次，有关下游迁移砾石反沙丘的实验室数据与理论进行了比较。这些床型已在砂或砾石床上的某些近临界流实验中被报道，但在自然溪流中很少被观察到。然而，没有对天然河流的详细研究，只有一些有争议的鉴定来自露头。然而，有限的水力数据符合理论预期。
Hydraulic data defining the dune:antidune transition in fine gravel are compared with potential flow theory, and information is drawn from published experiments and field‐based studies. Attention is given to both transitional bedforms and the development of downstream‐migrating antidunes. In the latter case, most data pertain to sand beds and not to gravel. Empirical data provide some weak support for the theoretical notion that the transition occurs at progressively lower Froude numbers at greater relative depths. Although a critical Froude number of 0·84 may reasonably be applied for the beginning of the dune to antidune transformation, lag effects (and a possible depth limitation) ensure that transitional bedforms may persist across a broad range of Froude numbers from 0·5 to 1·8. This latter observation has great relevance for palaeohydraulic estimates derived from outcrop data. Whereas the application of theoretical bedform existence fields, based upon potential flow theory, to fine gravel was previously purely speculative, the addition of experimental and field data to these plots provides a degree of confidence in applying stability theory to practical geological problems. For the first time, laboratory data pertaining to downstream‐migrating gravel antidunes are compared with theory. These bedforms have been reported from certain experimental near‐critical flows above sand or gravel beds, but have been observed infrequently in natural streams. However, there are no detailed studies from natural rivers and only a few contentious identifications from outcrops. Nevertheless, the limited hydraulic data conform to theoretical expectations.