Flow dynamics at channel confluences: few observations from a sub-tropical plateau fringe river of Eastern India

摘要

River confluences are that critical interfaces where significant changes in channel hydrological processes occurs. How and why these changes occur are the elementary questions for scaling-up our understanding of the dynamic hydrological processes occurring at the catchment scale. Confluences of major watersheds of the Chotonagpur plateau fringe fans (eastern counterpart) unlike other of the Gangetic flood plain are attributed by immensely fluctuating gauge level under the circumstances of high-intensity seasonally skewed rainfall. To understand this regional character and in view of the importance of channel confluences, the manuscript is hereby inclined to document the hydrological dynamism at 11 tributary junction sites along 86.4-km stretched river Bakreshwar of Eastern India. From the field survey of the said 11 confluence junctions constituting 7 channel reaches and 33 cross sections in total, it has been affirmed that the tributary junctions represent locations of sudden change in the longitudinal flow rhythm of the main river. The abrupt changes in channel flow due to tributary influxes of water at the confluences have a fair relation with size and length of the tributary rivers. However, tributary basin runoff volume relative to the main river basin is found to be the most influential factor to regulate post-confluence increase in velocity and discharge. The study reported here is a fundamental work and hopefully stimulate ideas for fruitful and coherent scientific inquiry on river confluences and its management particularly in Indian circumstances.