Channel and Bed Morphology of a Part of the Brahmaputra River in Assam

The Brahmaputra, one of the largest braided rivers of the world, flows through three countries, viz. China (Tibet), India (Arunachal Pradesh and Assam) and Bangladesh. A study on a 183 km long reach of the river in the eastern part of the Assam Valley reveals that the average bed levels were consistent in some sections and variable in others at different times. The Brahmaputra consists of primary and secondary channels. Primary channels are large, deep and active, while secondary channels are much smaller and shallower than the primary channels. The width and depth of the primary channels as well as the bed profiles vary significantly from place to place with time. Four topographic levels have been recognized on the Brahmaputra river bed. Levels 1 and 2 are subjected to modification by low flows, while level 3 is sculptured by monsoonal flows. Level 4 is affected by peak discharge during the monsoon months. The river bed of the Brahmaputra is infested with bars and islands. There are basically two types of bars, namely, compound bars consisting of mid-channel and side bars which have complex depositional histories attached to them, and unit bars with simpler depositional histories. The Brahmaputra channel has widened significantly with time, and its cross-sections have also changed with time. Migration of the banklines of the river has been inconsistent with distance and time.