Relative role of bed roughness change and bed erosion on peak discharge increase in hyperconcentrated floods

Relative role of bed roughness change and bed erosion on peak discharge increase in hyperconcentrated floods

Li, W.
Wang, Z.B.
Van Maren, D.S.
De Vriend, H.J.
Wu, B.S.

Civil Engineering and Geosciences

Water Management

2014-04-01

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.

http://resolver.tudelft.nl/uuid:7a605793-b09e-439a-ac11-a03690d241ab

https://doi.org/10.5194/adgeo-39-15-2014

European Geosciences Union

1680-7340

http://www.adv-geosci.net/39/15/2014/

Advances in Geosciences, 39 (1), 2014

Institutional Repository

journal article

(c) 2014 The Authors . CC Attribution 3.0 License.