Controlling factors on water and sediment partitioning at deltaic
bifurcations
- Gabriele Barile,
- Paola Passalacqua,
- Siyoon Kwon,
- Marco Tubino
Abstract
Bifurcations in river-dominated deltas are the main actors in the
routing of water and sediments throughout the fluvial network. In spite
of previous acknowledgments of their importance, we still lack a
comprehensive framework on how bifurcation geometry affects the water
and sediment partitioning. To investigate this issue, we firstly combine
previously calibrated 2D hydrodynamic simulations on the Wax Lake Delta
with a Lagrangian particle-tracking model, quantifying the partitioning
of water and sediments with different buoyancy at five bifurcations and
their correlations with differences in channel width, branching angle
and inlet bed elevation between the downstream branches. We compare the
sediment partitioning at bifurcations with available field data to
validate our methodology. We then employ the same modeling tools on a
simplified geometry, whose geometrical and hydraulic features resemble
those of the bifurcations in the Wax Lake Delta. Model results show that
the branching angle does not affect the partitioning of water and
sediments. The combined effect of asymmetries in the channel width and
inlet bed elevation is captured by a simple linear formula that
accurately estimates the partitioning of water at bifurcations returned
by the 2D calibrated hydrodynamic simulations. Our results also
highlight the key role played by transverse gradients in the bathymetry
of the upstream channel in determining the partitioning of sediments,
suggesting that deeper portions of the cross-section of the upstream
channel can cause a proportionately larger fraction of sediments with
larger Rouse number to be routed towards the corresponding bifurcate.13 Nov 2024Submitted to ESS Open Archive 14 Nov 2024Published in ESS Open Archive