Bankline Shifting and Sand Bar Dynamics of the Teesta River Using Multi-Temporal Satellite Images

Abstract

The Teesta River, a major transboundary watercourse in northern Bangladesh, has undergone pronounced geomorphological transformations under the influence of both natural hydrological variability and human interventions. This research explores the spatial and temporal evolution of bankline migration and sandbar formation between 1996 and 2023 using multi-temporal Landsat MSS, TM, and OLI imagery integrated with an area-based Geographic Information System (GIS) framework. The approach, which quantifies total areal changes in erosion and deposition rather than linear displacement, provides a more comprehensive representation of morphodynamic adjustments within a braided river environment. Eight cloud-free satellite epochs were analyzed across a 112 km reach between Khoga Khoribari and Haripur Ghat, complemented by discharge and water-level data from the Dalia and Kaunia stations of the Bangladesh Water Development Board. The findings indicate significant channel widening, with mean left-bank erosion of -2.60 km² per year and right-bank deposition of 1.02 km² per year, resulting in an overall widening rate of 1.58 km² annually. Total sandbar area showed a net accretion of 1.67 km² per year, mainly from temporary bars (3.64 km² per year), while permanent bars experienced a slight loss (−0.47 km² per year), signifying a shift toward a more braided and unstable channel form. The downstream section (Section 4) emerged as the most active reach, exhibiting the highest erosion and deposition magnitudes (-16.4 and 8.98 km² per year, respectively). Correlation analysis revealed strong coupling between discharge and river area (r = 0.52) and between river area and sandbar area (r = 0.88), underscoring the dominance of hydrological forcing in shaping morphological responses. Overall, the study highlights the increasing morphological instability of the Teesta River and its implications for floodplain livelihoods and infrastructure planning. The area-based GIS technique demonstrates superior capacity to capture the volumetric complexity of erosion deposition processes, offering valuable insights for sustainable river management, sediment control, and adaptive basin planning across monsoon-driven deltaic systems.

The Dhaka University Journal of Earth and Environmental Sciences, Vol. 14(2), 2025, P 33-49