River morphological modelling of Brahmaputra River, Assam
Author(s): Kuldeep Pareta
Abstract: The Brahmaputra River is characterized by its highly braided channel pattern with creation of river bars, and it is morphologically very dynamic due to high upstream discharges and large sediment loads during the monsoon. In-order-to comprehend the morphological development of a braided river like the Brahmaputra it is essential to acquire data and information, which can be incorporated into mathematical modelling tools for numerical prediction of the morphological behaviour in the short-term and medium-term. In this study, the Palasbari-Gumi reach of the Brahmaputra River was used to develop a two-dimensional morphological model utilizing the MIKE-21C programme for prediction of erosion for planning of protection works, and morphological development at river reaches. To forecast design variables throughout the river reach, model runs were carried-out with various hydrological scenarios. For the coarse sand fraction, the predicted mean annual sediment load for the 2021 hydrological year and bankfull discharge were 257 and 314 Mt/year, respectively, while the historically recorded sediment load in the Brahmaputra was 400 Mt/year. The model predicted results show excellent similarity with ADCP velocities, design flood levels and yearly sediment load. Difference of peak model velocities with ADCP measurement is lower than 10% with majority of measured data; velocities are compared at five river sections. Predicted flood level for bankfull discharge condition were almost 98% accurate at Gumi site. This study has demonstrated how to improve the planning and execution of river training works in highly braided river like Brahmaputra by predicting morphological changes over a 2-3 year period.