A Numerical Study on Bank Erosion of a Braided Channel: Case Study of the “Tangail and Manikganj Districts Along the Brahmaputra River”
Islam Md Masbahul*,**, Atsuhiro Yorozuya*,, Daisuke Harada*, and Shinji Egashira*
*International Centre for Water Hazard and Risk Management (ICHARM), Public Works Research Institute (PWRI)
1-6 Minamihara, Tsukuba, Ibaraki 305-8516, Japan
**Bangladesh Water Development Board (BWDB), Dhaka, Bangladesh
Brahmaputra River comprises the characteristics of a braided channel and suspended sediment-dominant river. Frequent changes in the river course have led to severe bank erosion. In particular, Tangail and Manikganj districts have recently become bank erosion-prone areas. To predict vulnerable locations based on bank erosion, we aimed to understand the behavior of the braided channel by conducting a numerical simulation and satellite data analysis in this study. We employed a depth-integrated 2-D numerical model for water and sediment transport, which was originally proposed by Takebayashi et al. and modified by Harada et al. by introducing a new treatment of suspended sediment. In addition, bathymetry data were created using a series of satellite data information to successfully conduct the simulation. In this study, we focused on two aspects. The first point is the skewing of flow discharge along multiple channels, which belongs to the area of interest, as a large-scale phenomenon. The second point is changing the local geometry of the sand bar and changing the flow pattern, as a small-scale phenomenon. To consider the two different scales, we employed the computation domain as an entire channel. Our results indicate that the numerical model is successfully verified using satellite data information, and the two-scale phenomena are successfully described. Regarding the large-scale phenomenon, our results indicate that the distribution of higher flow rates activates various geomorphological changes, including riverbed evolution, channel changes, and bank erosion. On the other hand, small-scale phenomena, such as the rapid appearance of sand bars and changes in the water course, are directly related to bank erosion.
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