Modeling of Hydrodynamics and Cohesive Sediment Processes in an Estuarine System: Study Case in Danshui River |
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Authors: | Amir Etemad-Shahidi Arash Shahkolahi Wen-Cheng Liu |
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Institution: | (1) School of Civil Engineering, Iran University of Science and Technology, P.O. Box 16765-163, Tehran, Iran;(2) Department of Civil and Disaster Prevention Engineering, National United University, Miaoli, 36003, Taiwan |
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Abstract: | The Danshui River estuarine system is the largest estuarine system in northern Taiwan and is formed by the confluence of Tahan
Stream, Hsintien Stream, and Keelung River. A comprehensive one-dimensional (1-D) model was used to model the hydrodynamics
and cohesive sediment transport in this branched river estuarine system. The applied unsteady model uses advection/dispersion
equation to model the cohesive sediment transport. The erosion and deposition processes are modeled as source/sink terms.
The equations are solved numerically using an implicit finite difference scheme. Water surface elevation and longitudinal
velocity time series were used to calibrate and verify the hydrodynamics of the system. To calibrate and verify the mixing
process, the salinity time series was used and the dispersion coefficient of the advection/dispersion equation was determined.
The cohesive sediment module was calibrated by comparing the simulated and field measured sediment concentration data and
the erosion coefficient of the system was determined. A minimum mean absolute error of 4.22 mg/L was obtained and the snapshots
of model results and field measurements showed a reasonable agreement. Our modeling showed that a 1-D model is capable of
simulating the hydrodynamics and sediment processes in this estuary and the sediment concentration has a local maximum at
the limit of salinity intrusion. Furthermore, it was indicated that for Q
50 (the flow which is equaled or exceeded 50% times), the turbidity maximum location during neap tide is about 1 km closer to
the mouth compared to that during spring tide. It was found that deposition is the dominant sediment transport process in
the river during spring–neap periods. It was shown that, while sediment concentration at the upstream depends on the river
discharge, the concentration in the downstream is not a function of river discharge. |
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