Biomorphodynamics of river banks in vegetated channels with self-formed width

Laboratory and field studies investigating the mutual interaction between
riparian vegetation dynamics and river morphodynamics have revealed that
riparian vegetation may play an important role in the evolution of channel
beds and river banks. In order to disentangle this still debated question,
field and modeling techniques have helped to explore and better understand
the time and spatial scales of such processes. Simple morphodynamic models
for river evolution have typically used a constant discharge to describe
in-channel processes and basic relationships for river bank dynamics. In order
to overcome these limits we propose a longitudinally integrated dynamical
model that describes the bank pull - bar push mechanisms in channels
with symmetric cross section. Different hydrographs (constant, periodic and
stochastic discharge) are applied to investigate channel width and vegetation
biomass evolution trajectories and equilibrium values. Results show the
interplay of riparian vegetation and water flow in controlling channel width
evolution and the trajectories of channel adjustment to flow perturbations.
These results also highlight the limit of adopting a constant discharge when
describing mutual flow and vegetation processes affecting channel evolution.

In addition, under stochastic forcing, the model shows the existence of a
range of flood frequencies for which the cooperation between the hydrologic
time scales and that characterizing vegetation colonization induces a regular
pattern in channel width time variations (coherence resonance). Finally,
model application to real case studies confirm the possibility to use the model
to interpret long-term river evolutionary trajectories in realistic applications.
Keywords: bio-morphodynamic model, dynamical system, bank deposition,
vegetation colonization, channel width temporal adjustments, stochastic
water discharge