Spatiotemporal variability of erosion and accretion in Ganges River using GIS and RS: a comparative study overlapping Rennell’s map of 1760s

Bangladesh has predominantly four major river systems. Ganges (Padma) River is one of the prominent rivers which support the life and livelihoods of millions of people in Bangladesh. The riverine area of Bangladesh has always faced some changing stages for radical accretion and erosion of lands. Areas of erosion and deposition were determined from successive changes in the bankline positions. Erosion is more active in course line and deposition in sandbar of river. In this research, the area which is eroded and deposited during 1760–2015 (more than 250 years) was analyzed. Erosion and accretion are measured by using Rennell’s map and Landsat MSS, TM and ETM+ satellite imagery with an average duration of 20 years. Processing of image analysis such as layer stack, image enhancement, mosaic and re-projection is done by different tools of image processing software. The Raster and spatial data have been analyzed by image analysis approaches and geo-processing techniques, while quantitative data have been analyzed by using some other statistical computer software program. It was analyzed through the spatial and temporal variation in the study reaches. These are identified by geo-processing techniques of riverbanks. The highest amount of erosional area occurred during 1760–1975 is 38,633 ha, depositional area is 55,140, and therefore, difference is 16,507, with the lowest amount of erosion occurring during 1995–2015. On the other hand, highest amount of deposition occurred during 1760–2015 is 57,605 ha, erosional land is 33,320 ha and there difference is 24,285 ha, with the lowest amount of deposition occurring during 1975–2015. The erosion and deposition has been comparatively low during 1975–1995 and 1995–2015. Finally it is identified that deposition is more active than erosion in Ganges–Padma River in a long period of time (during 1760–2015).