Morphological Analysis of Bishkhali River Using Multi-temporal Satellite Images and Historical Cross-Sectional Data

Bangladesh lies at the downstream of GBM basin which carries a large number of sediments through its river network which changes the morphological characteristics of rivers. Bishkhali River also experiences morphological changes throughout time. Bishkhali River is located at the south-central region of Bangladesh and discharges directly into the Bay of Bengal. Being a tidal river, its morphological characteristics are governed not only by the changes in flow from upstream but also by the impact of sea-level and tidal characteristics of the Bay of Bengal. Bishkhali River is mainly known for its bank erosion, bar formation, and shifting of thalwegs. This study is aimed at planform analysis and channel bar analysis for the period between 1995 to 2020. This study also includes thalweg analysis for the time period from 2002 to 2020 (based on the availability of cross-sectional data). For the estimation of erosion-accretion along both right-bank, left-bank, and channel bar analysis, LANDSAT images have been collected from USGS (United States Geological Survey) and these two analyses have been conducted by using GIS. Also, for thalweg analysis, historical cross-sectional data has been collected from BWDB (Bangladesh Water Development Board) and this analysis has been performed by using Microsoft Excel and GIS. It has been found from the planform analysis that total erosion and accretion for the right bank from 1995 to 2020 are 1073.68 and 664.61 ha, respectively. Also, for the left bank, total erosion and accretion from 1995 to 2020 were 1062.50 and 831.82 ha. From channel bar analysis, maximum areas for both bars situated near Ramna Launch Ghat and Kalikabari have been recorded in 2020, and these are 105.15 and 74.66 ha, respectively. From thalweg analysis, at (Rajapur Upazila, Daskinpara, Kalikabari, Mar bazar, Patharghata Upazila) stations, thalwegs are shifting towards the left bank, at (Aurabunia Bazar, Kathalia Launch Ghat, Karuna Khal, Patharghata Upazila) stations, thalwegs are shifting towards the center of the river width; and at (AL-Madina Jama Mosque, Kakchira, Rupdhan High School) stations, thalwegs are shifting towards the right bank. To achieve sustainable coastal zone development, policymakers and administrators may use the study’s findings to establish integrated coastal zone management (ICZM), limit the effects of coastal hazards, and develop effective mitigation techniques.