Hydrogeomorphology of asymmetric meandering channels: experiments and
field evidence
Abstract
Meandering channels display complex planform configurations with
upstream- and downstream- skewed bends. Bend orientation is linked to
near-field hydrodynamics, bed morphodynamic regime, bank
characteristics, riparian vegetation, and geological environment, which
are the modulating factors that act specially in high-amplitude and
high-sinuosity conditions. Based on the interaction between
hydrodynamics and morphodynamics, previous studies have suggested that
sub- (β < βR) and super-resonant (β > βR)
morphodynamic regimes (where β is the half width-to-depth ratio of the
channel, and βR is the resonance condition) may trigger a particular
bend orientation (upstream- and downstream-skewed, respectively).
However, natural rivers exhibit both US-skewed and DS-skewed bend
patterns along the same reach, independently of the morphodynamic
regime. Little is known about the hydrogeomorphology (forced and free
morphodynamic patterns) under these bend orientations. Herein, using the
asymmetric Kinoshita laboratory channel, experiments under sub- and
super-resonant conditions (with presence or absence of free bars) for
upstream-and downstream-skewed conditions are performed. Additional,
detailed field measurements at US-skewed and DS-skewed bends of
different skewness along the Tigre River in Peru are presented.
Conditions at field scale at high-sinuosity and high-amplitude bends
filter out the influence of the morphodynamic regime, where nonlinear
processes (e.g. width variation) directly the development of the
three-dimensional flow structure, then to the erosional and depositional
patterns, and then to the lateral migration patterns.