Relation between River Hydraulic and Channel Migration: A Case Study on Nagar River, India and Bangladesh

Abstract

Flood plain morphology is intimately related to hydraulic characteristics of channel and rate of channel migration which involves in the evolution of the flood plain as well as the channel pattern. Channel migration is a complex geomorphological process driven by the interaction between fluid flow, alluvial channel beds and banks. Channel migration in alluvial flood plains involves in continuous shifting of channel position horizontaly i.e., oscillation of channel in meander belt, which can be distinguished from abrupt changes occurred by avulsion or by tectonic and climatic events. Increasing channel sinuosity results into channel migration which inturn affect the hydraulic geometry of the channel by changing the gradient, depth and width and flow velocity. Channel interchanges its plaimetry from straight to meandering with higher to a lower discharge in alluvial flood plain. Full bank discharge may have the capacity for maximum down cuts. In the upstream direction Nagar River has an average bed to bank depth 4m and in lower reaches it increases upto 5.5 m having a water depth 30cm to 1.6m respectively during pre-monsoon. Therefore, during the monsoon discharge may increase more than 3 times, which may cause valley deeping and migration too. To understand the channel shifting behaviour hydraulic properties of the river is to be explored. This paper attempts to present a detailed account of river hydraulics and channel migration to evaluate the present scenario of the Nagar River.