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| Titel |
Relative role of bed roughness change and bed erosion on peak discharge increase in hyperconcentrated floods |
| VerfasserIn |
W. Li, Z. B. Wang, D. S. van Maren, H. J. Vriend, B. S. Wu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7340
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| Digitales Dokument |
URL |
| Erschienen |
In: Proceedings of river, coastal and estuarine morphodynamics ; Nr. 39 (2014-04-01), S.15-19 |
| Datensatznummer |
250121299
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| Publikation (Nr.) |
 copernicus.org/adgeo-39-15-2014.pdf |
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| Zusammenfassung |
| River floods are usually featured by a downstream
flattening discharge peak whereas a downstream increasing discharge peak is
observed at a rate exceeding the tributary discharge during highly
silt-laden floods (hyperconcentrated floods) in China's Yellow River. It
entails a great challenge in the downstream flood defence and the underlying
mechanisms need to be unravelled. Previous study on this issue only focuses
on one possible mechanism, while the present work aims to reveal the
relative importance of bed roughness change and bed erosion in the
hyperconcentrated flood. Using a newly developed fully coupled morphodynamic
model, we have conducted a numerical study for the 2004 hyperconcentrated
flood in the Xiaolangdi-Jiahetan reach of the Lower Yellow River. In order
to focus on the physical mechanism and to reduce uncertainty from
low-resolution topography data, the numerical modeling was carried out in a
schematized 1-D channel of constant width. The basic understanding that bed
roughness decreases with concentration at moderate concentrations (e.g.
several 10 s to 100 s g L−1) was incorporated by a simple power-law relation
between Manning roughness coefficient and sediment concentration. The
feedback between the bed deformation and the turbid flow, however, was fully
accounted for, in the constituting equations as well as in the numerical
solutions. The model successfully reproduced the downstream flood peak
increase for the 2004 flood when considering the hyperconcentration-induced
bed roughness reduction. As the hyperconcentration lags shortly behind the
flood peak, later parts of the flood wave may experience less friction and
overtake the wave front, leading to the discharge increase. In comparison,
bed erosion is much less important to the discharge increase, at least for
hyperconcentrated flood of moderate sediment concentration. |
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