The effect of transverse bed slope and sediment mobility on bend sorting

Lateral sorting (= bend sorting) is observed in natural meanders, where the inner and outer bend are fairly fine and coarse, respectively (e.g. Julien and Anthony, 2002; Clayton and Pitlick, 2007). This is caused by the mass differences between grains on a transverse slope, leading to coarser grains being dragged down net more than finer grains (Ikeda et al., 1987). The slope of the transverse bed influences the degree of bend sorting greatly. Also vertical sorting occurs. Grainflows at the lee side of dunes result in a net fining upward trend (Kleinhans, 2005). The degree of vertical sorting depends on flow velocity and sediment mixture characteristics. Most previous studies focused on the development of the transverse slope using small ranges of uniform sediment, so spatial sorting was absent. Yet, it was argued that there is a feedback mechanism between bend sorting and the transverse slope (Ikeda et al., 1987). So, it is of key importance to attain better understanding of how sorting in river bends comes about, which can improve current numerical models. It is the objective of this study to examine experimentally the effect of transverse bed slope and sediment mobility on spatial sorting of bed load in a meander. A.J.F. Hoitink, T.V. de Ruijsscher, T.J. Geertsema, B. Makaske, J. Wallinga, J.H.J. Candel, J. Poelman (Eds.) NCR days 2017, Febr. 1-3, 2017. Book of abstracts, NCR publication 41-2017.Environmental Fluid Mechanic