Quasi-equilibrium channel metamorphosis in planform of a subtropical river in India in post-dam period

Abstract

A basic fluvio-dynamics process in the sediment-energy fluxes is channel meandering and braiding. The construction of dams and barrages has primarily altered the meandering and braiding patterns of the world's large rivers. To this end, the present study aims to analyze post-dam planform characteristics of the Damodar River, a subtropical river in India, based on the analysis of meander geometry, Mueller’s sinuosity index, braiding index, channel count index, and channel length index during the last 50 years (1970–2020) using topographical maps and satellite images. The study also intends to forecast channel meandering and braiding characteristics for 2030 and 2050 using an Artificial Neural Network (ANN) model. The study results show that between 1970 and 2020, the standard sinuosity index (SSI) showed a larger tendency to meander in the middle of the river than the upper and lower courses owing to hydraulic control, while the lower and upper courses were controlled by topographic factors. Similarly, channel braiding indices (BI*, BI, and Pt) exhibit swelling in the upper and middle courses followed by a gradual fall in the lower stretch. The building of dams, the presence of lineaments, faults, and other anthropogenic controls primarily regulate the physical planform characteristics of the river. Regarding allometry, the river's upper segments exhibit both positive and negative allometry in certain combinations, whereas the lower segments primarily exhibit negative allometry. The study demonstrates that over the past 50 years, overall channel meandering has slightly decreased while braiding has slightly increased over time, indicating a quasi-equilibrium channel metamorphosis. However, the prediction with higher accuracy (80–95 %) shows that the river meandering and braiding (BI* and BI) will increase in the short run (2030), and decrease in the long (2050). The study findings may be helpful for the various planners and stakeholders involved in the development of the river basin.