The effect of transverse bed slope and sediment mobility on bend sorting
S.A.H. Weisscher (Universiteit Utrecht)
Anne Baar (Universiteit Utrecht)
Wim Uijttewaal (TU Delft - Environmental Fluid Mechanics)
MG Kleinhans (Universiteit Utrecht)
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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.