Assessment of meander‐bend migration of a major distributary of the Ganges River within Bangladesh. Issue 2 (15th November 2022) - Ferdoush, Jannatul
Abstract: The Arial Khan is an important distributary river of the Ganges River within Bangladesh. The river is meandering, and channel shifting and bend migration are common. This study investigates the bend‐scale morphology of 37 characteristic bends of the river using Landsat imageries, river bathymetries, and hydrological data. The morphological changes of the river are correlated with the temporal shifting of its offtake, which in turn is linked to the dynamic behavior of the river in terms of sinuosity, bend geometry, and bend migration. Alterations in the offtake location, bed elevation, and in‐front bar formation are found to control the flow to the river. The sinuosity varies from 1.62 to 1.95 and is linked to the shifting of its offtake. The lifetimes of the bends increase from upstream to downstream with an average lifetime of 24 years. The radii of the bends vary from upper to lower reaches with an average radius of 921 m. The upper reach is more migration prone, and its average migration rate (108 m/year) is more than twice the other two reaches. A higher migration rate of 70–80 m/year is found for the river during 1981–1999 compared to the rates of 45–50 m/year for the rest of the study periods (1972–2021). An envelope curve depicting the relation between the relative curvature of a bend and its migration rate for the river is also developed. The overall morphology from 1972 to 2021 indicates that a significant increase in sinuosity and a reduction in river width and aspect ratio have occurred. The migration rate has declined slightly and the frequency of bend cutoffs has reduced notably in recent years. Nonetheless, due to the high rates of migration, there exists potential future threat to riverbank erosion in some critical bends, and hence damages to land, property, structure, and project on the vulnerable banks. Abstract : The offtake of the Arial Khan River, an important distributary of the Ganges River, shifts periodically. This shifting of the offtake exerts an important control on the morphology of the river itself. The upper reach of the river is found to be morphologically more unstable than the middle and lower reaches and the bend migration rate is also found to be higher in this reach. An envelope curve depicting the relation between the relative curvature of a bend and its migration is developed for the first time for any Bangladesh river.