Study of Channel Instability in the Braided Brahmaputra River Using Satellite Imagery

In the present study, instability of the river reach of Brahmaputra was analysed for braided belt width changes, braiding index and bar area. The river reach of the Brahmaputra from its confluence of Lohit, Dibang and Dihang to its confluence with the Tista river was studied from 1973 to 2009. The study was carried out using remotely sensed data from Landsat satellites at different dates. Discharge data synchronized with satellite data was collected by maintaining near-similar water level or discharge. Wavelet of the braided belt change was analysed to get the wavelet power and spatial extent of the changes. Finally, stream power was analysed from the average discharge data during the monsoon period to determine its effect on the instability of parameters considered. Results indicate that stream power does not directly relate to local changes in the braided belt or braiding index. However, with decrease in stream power, an increasing trend of bar area was found. Maximum wavelet power within a period showed a threshold behaviour at stream power of 5 W/km, beyond which the wavelet power raised sharply to a high value with increase in stream power. River response to the stream power was found at a global level rather than local level. Finally, a gradual decrease in stream power over time indicates the stable river reach. However, changes due to local bank erosion cannot be predicted using this analysis.