ABSTRACT Sand bed braided rivers, such as the Brahmaputra, are highly dynamic in nature. The braided rivers change their course frequently, which causes huge bank erosion and sand bar migration. During the monsoon season the braided river has higher sediment-carrying capacity and the erosion power. A large amount of energy dissipation takes place in terms of river fragmentation and sand bar migration and bar erosion. These are common morphological characteristics within the sand bed braided rivers. The dynamic river bed and planform offer varying resistance to flow based on the hydrologic regime and reach characteristics of the river. Estimation of channel roughness coefficient is important for hydraulic modelling of the river. In this study, roughness characteristics of the Brahmaputra river were estimated using altimetry derived river stage records at different reaches of the river. The estimated Manning's roughness coefficients were incorporated in one-dimensional hydraulic model to perform simulations over the middle reach of the Brahmaputra River. Comparison of seasonal water level differences at different reaches of the river was performed using altimetry retrieved and model simulated water level for 2014 and 2015, respectively. The simulated water levels from altimetry derived Manning's roughness coefficient were found to be in close range with altimetry retrieved water levels for 2014 and 2015. It was found that the spatio-temporal variation of Manning's roughness coefficient proved to be an important parameter for modelling braided river systems such as the Brahmaputra.
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