Wasson, Robert, Archarjee, Shukla, and Rakshit, Raghupratim (2022) Towards identification of sediment sources, and processes of sediment production, in the Yarlung-Tsangpo Brahmaputra River catchment for reduction of fluvial sediment loads. Earth-Science Reviews, 226. 103932.

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Abstract

Sedimentation in the Brahmaputra Riverhas led to the widening and shallowing of its channel, resulting in land loss and deposition on agricultural land, exacerbating floods, threatening the viability of flood mitigation embankments, and could even lead to the river bed becoming higher than the floodplain over much of its length with potentially disastrous consequences when embankments breach. Identification of the major sources of the river sediment, the processes that produce it, and the sources that are amenable to management could potentially be used to reduce riverine sedimentation and thereby reduce flood risk and damage. This paper provides a wide-ranging review of the literature from many disciplines with some limited new analysis. The result of this review is that a lot is known, but there is insufficient information upon which targeted soil conservation and land management efforts could be designed and implemented to reduce sediment fluxes. What is known with reasonable confidence is that about 45% of the modern sediment in the Brahmaputra (where it reaches Bangladesh) comes from the Siang river upstream of which is a Gorge downstream of the Yarlung-Tsangpo River in Tibet, and there is limited opportunity to reduce this flux. About 10-20% of the sediment transported by the tributaries downstream of the Siang River and the Gorge (the syntaxis) comes from the Mishmi Hills, 25-40% from the Himalayan part of the catchment, and a few percent from the Indo-Burman Ranges and the Shillong Plateau.Therefore, the focus of management should be on the tributary catchments downstream of the syntaxis with emphasis on the Himalayan section. But more information is needed in these tributary catchments about the proportions of sediment coming from different parts of the mountains, hills, and the plain, linked to land use and erosion process understanding. A strategy for more completely determining the major sources of sediment in the tributary catchments is presented and an assessment made of the extent to which they could be managed. The paper also provides an overview of many aspects of the geomorphology of the Brahmaputra catchment.

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