Decadal length changes in the fluvial planform of the River Ganga: bringing a mega-river to life with Landsat archives

Abstract

The Landsat programme, which was started in 1972, initiated an era of space-based Earth observation relevant to the study of large river systems through the provision of spatially continuous, synoptic and temporally repetitive multispectral data. Free access to the Landsat archive via the Internet from mid-2008 has enabled the scientific community to reconstruct the Earth's changing surface and, in particular, to reconstruct the planform dynamics of the world's largest rivers. The present research reconstructed the planform changes occurring in the lower reaches of one of the Asian mega-rivers, the River Ganga (Ganges), from 1972 to 2010 using the Landsat archive. Sequential river planform maps generated from the time-series revealed the pattern of evolution of the river system over the study period. Specifically, within the observed sequence, the river started as a single-thread channel that then began meandering at four locations. The meander bends increased in sinuosity until chute cut-offs were triggered, returning the river to a state similar to that at the beginning of the sequence. This periodic pattern is constrained by several hard points in the geology, and by the Farakka Barrage, meaning that the observed cyclic pulsing is likely to continue into the future. This constrained pattern has significant implications for local planners who may currently fear that the river is migrating laterally.