Integrating subsurface stratigraphic records with satellite images to investigate channel change and bar evolution: a case study of the Padma River, Bangladesh

Landsat data and stratigraphic records were employed to determine channel changes and bar evolution of a selected reach of the Padma River in Bangladesh. Analysis of multi-temporal images showed that the selected reach of the Padma River has undergone significant morphological changes since 1973. The mean width of the river has almost doubled, having increased from 5458 m in 1973 to 10,638 m in 2014. Bank erosion, totalling 281 km², was more than double the accretion (123 km²), and the left bank experienced higher levels of erosion than the right bank. Analysis of the stratigraphy of the bar head, middle and tail sections revealed that erosion occurred in the head section, but that the middle section seemed to be stable, whereas accretion was estimated to be high in the tail section of the bar. Sedimentary facies analysis indicated that bar evolution is largely influenced by the variation of both water and sediment flows, as bar areas tend to accrete substantially following large floods. However, the erosion–accretion process of both bars and river banks appeared to be stable during the periods when the river experiences no major flooding. The relationship between bank erosion and bar area expansion showed a moderately positive correlation (r² = 0.64, p = 0.016), while a strong correlation was observed (r² = 0.80; p = 0.008) between channel width and area of the bar, suggesting that river width is highly influenced by bank erosion. This implies that the growth of bars within the reach is largely determined by materials flowing from bank failure.