Application of remote sensing and GIS for evaluation of the recent morphological characteristics of the lower Brahmaputra-Jamuna River, Bangladesh

This paper deals with the morphological changes of the lower Brahmaputra-Jamuna River (BJR) in Bangladesh. Within few decades, the planform of the river has been changed abruptly by the combined effect of natural process and human interventions. Morphological features observing in this study were river planform, channel width, bankline migration and channel bed elevation. Eighteen sets of remote sensing data series from 1973 to 2011were analyzed using ERDAS/Imagine and GIS to document the variation of geomorphic elements of the lower BJR. GIS analysis of remote sensing data showed that the changes of channel planform were quite significant over the past 40 years, occurring two major phases of channel development. The changing patterns in the first phase (i.e., between 1973 and 1992) were quite irregular. However, the second phase ranging between 1992 and 2011 was unidirectional (mostly eastward). In general, the studied river reach was widened and the average rate of migration was 225 m y(-1) that was three-folds the values of the first phase. The height and slope of sand bars were gradually increasing, showing the highest value around the Jamuna Multipurpose Bridge (JMB) section. The planform characteristics of BJR at the downstream of JMB showed that the river reach was gradually widening and shifting eastwards. However, the reach at the upstream of the JMB showed westward migration. The recent trends of channel changes suggest that the river planform has lost it's naturally condition and it may, therefore, be predicted that increasing nature of channel width likely to continue in the immediate future.