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

Abstract

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.