The Brahmaputra River is a highly braided, meandering river with innumerable river islands, alluvial fans, sand bars, ox-bow lakes, and marshes. The valley is built by deposition of alluvium upon a sag formed during the period of the rise of the Himalaya. The Brahmaputra has more than 35 major tributaries.
Floods are an annual menace to agriculture and settlements in the valley.
Vast amounts of silt and debris, already a problem, are increased many folds with continuing deforestation of the mountain slopes.