Downstream channel changes and the likely impacts of flow augmentation by a hydropower project in River Dikrong, India

ABSTRACT

The Dikrong River, a tributary of the Brahmaputra River Basin in India, has been receiving additional water from an adjacent river since 2002 under the operation of the 405 MW Ranganadi hydel project. Flow duration curves and indicators of hydrological alteration analyses reveal that the downstream river flow has been significantly altered post-2002. Examination of the channel pattern in a Geographic Information System environment using satellite images from 1973 to 2014 displays that the channel planform has also changed over time, wherein it has become wider, less meandering and more braided. Sinuosity decreased from 1.9 in 1987 to 1.66 in 2002 and has stabilized since then. Simultaneously, braiding increased from 1.55 (1987) to 1.81 (2014). The average bankfull channel width from 1973 to 2014 varied between 378 and 573 m. The river also displays erratic and unevenly distributed bank migration and erosion patterns. However, channel changes could be observed even prior to the hydel project’s influence through flow addition. Thus, this study analyses the temporal and spatial changes in downstream channel morphology of the Dikrong River and examines whether they have been influenced by the hydrological alterations caused by the hydel project.

KEYWORDS:

• Dikrong River
• flow augmentation
• channel widening
• sinuosity
• braid–channel ratio
• bankline migration

Acknowledgements

PLB thanks the Department of Science and Technology for the financial assistance in the form of research fellowship under the DST-INSPIRE Fellowship scheme. The authors also gratefully acknowledge the Water Resources Department, Assam, for providing the hydrological data pertaining to the Dikrong River. The authors thank the two anonymous reviewers, the handling editor and the Editor-in-Chief, James E. Ball, whose constructive comments greatly helped to improve the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 The Brahmaputra River within the Indian sub-basin flows from east to west after entering through Arunachal Pradesh on the country’s northeast. Through its course, the river divides the floodplains of Assam into the north and south banks which are respectively the river’s right and left banks. All the tributaries coming from the river’s north and joining its right bank constitute the north bank tributaries while those coming from the south and joining the river on its left bank constitute the south bank tributaries. Therefore, the Dikrong River in this study which originates in the Dafla hills of Arunachal Pradesh, to the north of River Brahmaputra, is a north-bank tributary of the latter. The Dikrong River, at its lowermost segment, had undergone course change in the past. Although the river presently confluences with River Subansiri, the old channel, currently known as ‘Mora Dikrong’, used to join the Brahmaputra River near Silikhaguri, about 16 km downstream of its present outfall into Subansiri (Dutt and Datta 1976).