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Characteristics of the drainage network of the Kosi Megafan, India and its interaction with the August 2008 flood flow

By
D. Majumder
D. Majumder
Geological Studies Unit, Indian Statistical Institute, 203 B.T. Road, Kolkata 700108, India
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P. Ghosh
P. Ghosh
Geological Studies Unit, Indian Statistical Institute, 203 B.T. Road, Kolkata 700108, India
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Published:
January 01, 2018

Abstract

The Kosi River in India is well known in the fluvial fan literature because of its well-documented avulsive dynamics and because of the relationships between changes in the course of the river and megafan aggradational processes. The radial configuration of the Kosi drainage network was instrumental in the recognition of large, low-gradient, fluvial-dominated counterparts of alluvial fans, commonly defined as megafans, and the system forms a well-constrained example contributing to the recent development of the concept of distributive fluvial systems. A major flood inundated the Kosi Megafan in August 2008. The available data on the temporal evolution of the flood inundation patterns illustrate how the exceptional discharge event travelled across the megafan surface using the pre-existing distributary channel network, how the anthropogenic infrastructure affected the flood path and propagation, and the type of geomorphic changes that were induced by this catastrophic hydrological event. In spite of the large discharge involved in the flood, the fan drainage network appears not to have been significantly modified by the event, probably because the flood wave followed a pre-existing channel network for avulsion and down-fan propagation. Most of the evident aggradation took place on the proximal and medial domains along a well-defined, radially oriented sector of the fan. The observed pattern of flood propagation and associated sedimentation provide important clues to understanding the processes operating during exceptional discharge events, which are an integral part of the long-term, avulsion-dominated evolution of such systems.

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Geological Society, London, Special Publications

Geology and Geomorphology of Alluvial and Fluvial Fans: Terrestrial and Planetary Perspectives

D. Ventra
D. Ventra
Utrecht University, the Netherlands
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L. E. Clarke
L. E. Clarke
University of Gloucestershire, UK
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Geological Society of London
Volume
440
ISBN electronic:
9781786203809
Publication date:
January 01, 2018

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