Abstract
Abstract. Point bars influence hydraulics, morphodynamics, and channel geometry in
alluvial rivers. Woody riparian vegetation often establishes on point bars
and may cause changes in channel-bend hydraulics as a function of vegetation
density, morphology, and flow conditions. We used a two-dimensional hydraulic
model that accounts for vegetation drag to predict how channel-bend
hydraulics are affected by vegetation recruitment on a point bar in a
gravel-bed river (Bitterroot River, Montana, United States). The calibrated
model shows steep changes in flow hydraulics with vegetation compared to
bare-bar conditions for flows greater than bankfull up to a 10-year flow
(Q10), with limited additional changes thereafter. Vegetation morphology
effects on hydraulics were more pronounced for sparse vegetation compared to
dense vegetation. The main effects were (1) reduced flow velocities upstream
of the bar, (2) flow steered away from the vegetation patch with up to a
30 % increase in thalweg velocity, and (3) a shift of the high-velocity
core of flow toward the cut bank, creating a large cross-stream gradient in
streamwise velocity. These modeled results are consistent with a feedback in
channels whereby vegetation on point bars steers flow towards the opposite
bank, potentially increasing bank erosion at the mid- and downstream ends of
the bend while simultaneously increasing rates of bar accretion.
Funder
Division of Earth Sciences
Subject
Earth-Surface Processes,Geophysics
Cited by
37 articles.
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