Technical Note:Remote sensing in the mapping of the Brahmaputra/Jamuna River channel patterns and its relation to various landforms and tectonic environment

摘要

The Brahmaputra River is one of the largest sand-bar braided rivers in the world having a seasonal high discharge, high sediment load and characterized by frequent channel pattern changes and shift. Following natural phenomena, the river has been responding to landform/ground level changes effected by tectonic activity of the region. A satellite image mosaic and temporal Landsat data enabled detailed mapping of the Brahmaputra River revealing some prominent features with regard to change in its course, new channels and influence of landforms and tectonics. Northward shift of the river course are inferred at three different places, which are (1) in the uppermost part of Brahmaputra; (2) in the region north of the Kopili Gap (KG); (3) and north of the Mikir HiDs (MH). However, the river appears to have developed a tendency to shift back in the area north of the MH. These shifts are influenced by tectonic activity in the Himalayan foothills. The Brahmaputra River shows remarkable changes downstream of Guwahati, by forming multiple channels south of the island as well as the formation of channels closer to the Shillong Plateau. The sudden and sharp south-westward to southward turn of the river just after longitude 90° E is in fact caused by a landform north of Dhubri. Development of new channels from the main river along the western and northern edges of the Shillong Massif (SM) and the shift of Kopili River towards the SM are indicators of tectonic activities that the massif suffered.