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

Abstract

ABSTRACTThe 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.