Channel evolution of the Himalayan tributaries in northern Brahmaputra plain in recent centuries

Abstract

Himalayan tributaries of the northern Brahmaputra plain are vulnerable to rapid channel shift and planform adjustment. Yet, the information and knowledge of their morphological changes are sparse. This paper uses multiple geo-informational data such as archival maps, aerial and satellite imaginaries, field mapping and interviews with the locals, and previous literature to document the channel evolution of the tributaries in recent centuries, which can be an essential input to understand the contemporary adjustments of the Himalayan rivers. We infer that several tributaries along the northern plain of Brahmaputra have gone through major avulsions. Fingerprints of those avulsions, identified from archival maps and satellite imageries, suggest that the tributaries had a hop of an average distance of ~ 5.5 km. However, those migrations did not follow any geometric scale and select their path randomly. Paleochannel fingerprints indicate that the rivers once meandering have transformed into straight, braided and anastomosing channels. Intriguingly, the majority of the tributaries have widened by ~ 2.5–5 times compared to their parent courses. Evidence suggests that several river migrations are driven by surface warps, most likely, induced by seismic activities. Large rupture in the hilly catchments of Jiadhal (and its eastern tributaries) and associated sedimentation due to 1950 Assam earthquake have affected their channel morphologies. It suggests the potential role of the high sedimentation in the channel evolution of the tributaries. Consistency in the planform changes of the tributaries affirms that the northern plain of Brahmaputra is going through a spell of intensified sedimentation in recent times. The Brahmaputra is a young basin where ample surface signatures are available to link up the process–response mechanism of its tributaries. An extensive study should be a future priority to examine the nature of the tributaries more closely.