Tidal impact on the division of river discharge over distributary channels in the Mahakam Delta |
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Authors: | Maximiliano G Sassi A J F Hoitink Benjamin de Brye Bart Vermeulen Eric Deleersnijder |
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Institution: | 1.Hydrology and Quantitative Water Management Group, Department of Environmental Sciences,Wageningen University,Wageningen, Gld,The Netherlands;2.Institute of Mechanics, Materials and Civil Engineering (IMMC),Université Catholique de Louvain,Louvain-la-Neuve,Belgium;3.Earth and Life Institute (ELI), G. Lema?tre Centre for Earth and Climate Research (TECLIM),Université Catholique de Louvain,Louvain-la-Neuve,Belgium;4.Institute for Marine and Atmospheric Research Utrecht (IMAU), Department of Physical Geography,Utrecht University,Utrecht,The Netherlands |
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Abstract: | Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control
over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in
tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact
on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta
is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels.
A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model
has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was
forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration
was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed
by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate
that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations.
The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper
the discharge division that would occur in the case without tides. |
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