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首页> 外文期刊>Journal of Hydrology >Dynamic morphology in a bridge-contracted compound channel during extreme floods: Effects of abutments, bed-forms and scour countermeasures
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Dynamic morphology in a bridge-contracted compound channel during extreme floods: Effects of abutments, bed-forms and scour countermeasures

机译：极端洪水中桥接复合渠道中的动态形态：基台，床位和冲刷对策的影响

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摘要

Fluvial morphology in compound river channels usually undergoes drastic variation during extreme floods due to scour and erosion processes. Those processes can be highly dynamic consisting of multiple elements (e.g. bed-form migration, bank erosion, riprap break-down, etc) that are inter-dependent. The existence of bridge abutments and embankments that lead to flow contraction on the floodplain brings more complexity and uncertainty. The present study investigated flood-related processes around bridge sites in a compound channel with different abutment/embankment configurations. Results show that a longer abutment/embankment pushes the high-shearing zone on the floodplain (around abutment toe) further towards the bank slope and causes a higher risk of undercutting at the toe area, while vertical flow pressurization had a more significant effect on enhancing general bed shearing. The main channel bank tends to retain a constant slope (2:1) as scour progresses gradually during floods. The channel bed scour is closely related to the unit discharge contraction ratio determined by both lateral and vertical flow contractions. Regarding the interaction between dynamic processes, migrating bed-forms enhanced sediment erosion by cyclic "embedment-winnowing" processes when they met destabilized loose riprap rocks. Thus, rocks sliding into the main channel may cause a higher risk of bed subsidence and then embankment failure. In total, four bed-form migration types (i.e. interaction types) are observed for different abutment/embankment lengths and flow intensities. In general, the observed processes provide a clear picture of how channel morphology is altered dynamically by multiple factors during extreme floods. Additionally, the findings in this study are integrated under a framework to evaluate the potential scour and erosion hazards in a real river section. It is found that those hazards may go beyond individual sites, affecting each other and then the morphological evolution at a catchment scale. A more comprehensive study in the future will enable this framework to performed more quantitative analysis.
机译：在极端洪水期间，由于冲刷和侵蚀过程，复合河道中的河流形态通常会发生剧烈变化。这些过程可以是高度动态的，由相互依赖的多个元素组成（例如河床形态迁移、河岸侵蚀、抛石崩塌等）。导致漫滩水流收缩的桥台和路堤的存在带来了更多的复杂性和不确定性。本研究调查了具有不同桥台/路堤配置的复合渠道中桥址周围的洪水相关过程。结果表明，较长的桥台/路堤将漫滩上（桥台坡脚周围）的高剪切带进一步推向岸坡，并在坡脚区域造成更高的底切风险，而垂直流加压对增强一般河床剪切有更显著的影响。洪水期间，随着冲刷的逐渐进行，主河道河岸往往保持恒定坡度（2:1）。河床冲刷与由横向和垂直水流收缩确定的单位流量收缩比密切相关。关于动力过程之间的相互作用，迁移床在遇到不稳定的松散抛石岩石时，通过周期性的“嵌入-扬尘”过程形成增强的泥沙侵蚀。因此，滑入主河道的岩石可能会导致更高的河床沉降风险，进而导致路堤破坏。总的来说，对于不同的桥台/路堤长度和流量强度，观察到四种床形迁移类型（即相互作用类型）。总的来说，观察到的过程提供了一幅清晰的画面，说明在极端洪水期间，河道形态是如何被多种因素动态改变的。此外，本研究的结果被整合在一个框架下，以评估真实河段的潜在冲刷和侵蚀危害。研究发现，这些危害可能会超出单个地点，相互影响，然后在集水区范围内影响形态演变。未来更全面的研究将使该框架能够进行更多的定量分析。

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