Bed deformation in curved alluvial channels

Network response to disturbances in large sand-bed braided rivers

“…As predicted by theory of Struiksma et al (1985), Blondeaux and Seminara (1985), and Crosato and Mosselman (2009), the braiding index increased with widening of the channel by bank erosion. The widening of the channel had a similar rate to that observed along the Brahmaputra.…”

“…Although braiding rivers are known for their dynamics of bars and branches within their braidplain (Lewin and Ashworth, 2014), channel migration and local widening of the braidplain are common (Khan and Islam, 2003;Ashworth and Lewin, 2012). Bank erosion results in local braidplain widening and thus higher braiding intensity as predicted by linearized models (e.g., Struiksma et al, 1985;Blondeaux and Seminara, 1985) and observed in nature (Xu, 1997;Ahktar et al, 2011). It could also result in fixation of bars (Wu and Yeh, 2005).…”

“…Inflow asymmetry enhances the initiation of steady bars and subsequent channel bending that propagates over a distance of at least several meander lengths (Van Dijk et al, 2012), but the direct effect of the disturbance damps rapidly in the downstream direction (Struiksma et al, 1985;Schuurman et al, 2016). Linear theory also explained that a disturbance in a river with, among other things, a sufficient width-depth ratio amplifies in the downstream direction (Struiksma et al, 1985;Crosato and Mosselman, 2009;Kleinhans and Van den Berg, 2011). However, this theory is based on the initial stage of bars on a flat bed, and its application to a developed braiding river is questionable.…”

“…Asymmetrical inflow stimulates bar and bend formation, which has been deployed in flume experiments to generate meander bends (e.g., Peakall et al, 2007;Van Dijk et al, 2012). Inflow asymmetry enhances the initiation of steady bars and subsequent channel bending that propagates over a distance of at least several meander lengths (Van Dijk et al, 2012), but the direct effect of the disturbance damps rapidly in the downstream direction (Struiksma et al, 1985;Schuurman et al, 2016). Linear theory also explained that a disturbance in a river with, among other things, a sufficient width-depth ratio amplifies in the downstream direction (Struiksma et al, 1985;Crosato and Mosselman, 2009;Kleinhans and Van den Berg, 2011).…”

“…The amount of upstream sediment inflow at the upstream boundary was set equal to the local sediment transport capacity, which keeps the bed level along the upstream boundary constant. The transverse bed slope effect, which is the downslope pulling of sediment by gravity and essential in morphodynamic models (e.g., Struiksma et al, 1985;Talmon et al, 1995;Schuurman et al, 2013), is computed according to Koch and Flokstra (1981). After each time step, the bed level was updated using the Exner equation.…”