Study of Morphological Changes in Braided River Reach

Abstract

Temporal variability of flows and sediments and bank erosion is fundamental to understand river dynamics. The temporal variability of sediment load and effective discharge class is one of essential information which is require to improve the barrage and canal operations for flow diversion into the canals. Similarly, bank erosion causes substantial land loss along the river banks due to erosion. Moreover, understanding for the impact of flood events on bank erosion are also lacking for sand bed braided river reaches. Similarly, quantitative relationship between branch channel movement and river bank erosion also have not attained significant attention. The river reach just starting from downstream of the Marala barrage to the 7 km downstream was selected to study the bank erosion. The reach is braided with small unstable sand bars and few semi-stable islands and river flows in multiple channels during low flows. The major proportion of the flows in the Chenab River occurs during monsoon season, which brings lot of sediments from the catchment. Thus, sediments in the river flows not only cause changes in the morphology of river but also diversion of highly sediment laden flows into the canals which creates sedimentation issues. Therefore, firstly, sediment rating curve, variation of sediment load and effective discharge for different temporal scales were examined. Secondly, the changes in the river were assessed and the relationships of river bank erosion with branch channels movement and floods magnitudes (during different flow regimes) were developed. Thirdly, two dimensional (2D) hydrodynamic numerical model was simulated for the flows/floods of 2010 and the results were coupled with the excess shear stress approach to predict the bank erosion and identify the river bank locations more vulnerable to erosion.