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ABSTRACT

River systems of part of the Himalayan foreland, northern Bihar plains, India, are described in terms of their channel morphology, hydrology and suspended sediment characteristics. A simple classification of the river systems based mainly on the source area characteristics is proposed: (i) mountain-fed, (ii) foothills-fed, (iii) plains-fed and (iv) mixed-fed rivers. Distinct differences are noted between these classes of river systems. Most rivers show evidence of channel movement, mainly by avulsion, but cut-offs also occur locally. The mountain-fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains-fed rivers have relatively low discharge and high suspended sediment concentration. The foothill-fed rivers have moderate values of discharge and suspended sediment concentration. The mountain-fed rivers have built megafans of large extent, whereas the foothills-fed and plains-fed rivers have formed muddy interfan areas. Semi-quantitative estimates of water and sediment flux suggest that about 99·9% of the mass transfer into the plains is water, with the remaining 0·1% being sediment, and that 10% of the latter (0·01% of the total) is retained in the basin, the remainder being transferred to the Bengal Fan.