More on the evolution of bed material waves in alluvial rivers

Abstract

Sediment waves or pulses can form in rivers following variations in input from landslides, debris flows, and other sources. The question as to how rivers cope with such sediment inputs is of considerable practical interest. Experimental, numerical and field evidence assembled by the authors suggests that in mountain gravel-bed streams, such pulses show relatively little translation, instead mostly dispersing in place. This research has recently been the subject of discussion. In particular it has been suggested that (a) the equations of flow and sediment mass balance used in the analyses, and in most other morphodynamic analyses, require correction; (b) the dominance of dispersion appears only because the hyperbolic nature of the governing equations has not been adequately considered; and (c) the sediment transport equation used in the analyses does not lead to generalizable results. Here we suggest that (a) the relations for mass balance do not require the indicated correction; (b) the hyperbolic nature of the governing equations does not preclude the result of dispersion dominating translation in mountain streams; and (c) the general behaviour of an appropriate hyperbolic model of sediment waves (pulses) includes the relative roles of dispersion and translation, and is not affected by the precise choice of a sediment transport relation (as long as the choice is reasonable for the case in question).

Morphological Response of the Brahmaputra–Padma–Lower Meghna River System to the Assam Earthquake of 1950

“…The conceptual model presented in Figure 6.11 and described here builds on and extends the approaches of previous authors particularly Lane (1955), Schumm (1969), Bettess and White (1983), Nicholas (1995), Jiongxin (1996), Simon (1989), Lisle et al (2001) and Cui et al (2005). Slope adjustments are often considered to be a key element of dynamic process-response and have been used to describe why complex response occurs in disturbed fluvial systems (Schumm, 1977).…”

Experimental and Numerical Investigation of Bed-Load Transport under Unsteady Flows

“…Bed load sediment transport has been widely studied under steady flow (Soni 1981;Yen et al 1992;Yang 1996;Wilcock 2001) and unsteady-flow conditions (Wu and Wang 2004;Lee et al 2004;Singh et al 2004;Cui et al 2005). Experiments conducted by several researchers provided an understanding of the sediment transport rate under unsteady-flow as compared to the steady flow conditions.…”

Further perspectives on the evolution of bed material waves in alluvial rivers

“…First of all, the contribution of Cui et al (2005) in relation to our short comment (Cao and Carling, 2003) on the work of Lisle et al (2003) is warmly welcomed. In Cao and Carling (2003), we intended to briefly highlight aspects of mathematical river modelling which require closer attention, and we appreciate the opportunity to expand our arguments here.…”

“…Hyperbolic systems admit not only rarefaction waves, but also shock waves (Toro, 2001;LeVeque, 2002). This communication, along with the related work by Lisle et al (2001) and Cui et al (2005) focuses on the evolution of bed material waves only. However, bed material waves should not be construed as the only category of waves present in fluvial systems.…”

“…In Cao and Carling (2003), we intended to briefly highlight aspects of mathematical river modelling which require closer attention, and we appreciate the opportunity to expand our arguments here. The strong interaction between water flow, sediment transport and morphological evolution in alluvial rivers necessitates an integrated methodology, and it is important that a rigorous foundation is developed through cordial communications such as that of Cui et al (2005), and our perspectives below.…”