This study explores causal mechanisms of river metamorphosis and its impacts on regional landscapes. The study also investigates the implications of metamorphosis on associated ecological resources. Advanced GIS and remote sensing technologies were used to delineate morphological parameters describing metamorphosis of the Old Brahmaputra River from historical maps (i.e., Rannell's Map in 1776, Tassin's Map in 1840, Topographic Survey Map in 1943) and remotely sensed optical satellite imagery Sentinel-2 in 2022. Flood frequencies were investigated for different periods by applying Gumbel’s Analytical Method (GAM), Log-Pearson Type III, and Log-Normal Method to estimate probability of flood vulnerability and impacts of flooding on morphodynamics in the central Bengal Basin. During the periods between 1776 and 2022, the area of sedimentation (77,999.43 ha) was greater than the eroded area (2983.29 ha).This difference was attributed to siltation of the channel bed morphology and corresponding accelerated flood vulnerability that accompanied river metamorphosis. Hydrological variables particularly annual average discharge significantly declined from 22 to ~ 18 m³/s per year during the period from 1965 to 2020. The study results demonstrated that the log-normal methods significantly overestimated peak flood discharge compared to Log-Pearson methods and Gumbel’s probability model. The extrapolation of the discharge for the 100-year flood by applying the three methods produced values of 712.66 m³/s, 1750.26 m³/s, and 2462.92 m³/s. Differences of these magnitudes may be critical for planning purposes because these differences in results will generate large-scale projected impacts on morphodynamics of the central Bengal Basin.

本研究探讨了河流变态的因果机制及其对区域景观的影响。该研究还调查了变态对相关生态资源的影响。利用先进的地理信息系统和遥感技术，根据历史地图（即1776 年的兰内尔地图、1840 年的塔辛地图、1943 年的地形测量图）和遥感光学卫星图像Sentinel-2来描绘描述旧雅鲁藏布江变态的形态参数。2022年。应用甘贝尔分析法 (GAM)、Log-Pearson III 型和对数正态法对不同时期的洪水频率进行了调查，以估计洪水脆弱性概率以及洪水对孟加拉盆地中部地貌动力学的影响。1776年至2022年期间，沉积面积（77,999.43 ha）大于侵蚀面积（2983.29 ha）。这种差异归因于河床形态淤积以及伴随河流变质而相应的加速洪水脆弱性。水文变量特别是年平均流量从 22 显着下降至约 18 m ³1965年至2020年期间每年。研究结果表明，与Log-Pearson方法和Gumbel概率模型相比，对数正态方法显着高估了洪峰流量。应用三种方法外推100年一遇洪水的流量，得出的值为712.66 m ³ /s、1750.26 m ³ /s和2462.92 m ³ /s。这些幅度的差异对于规划目的可能至关重要，因为这些结果的差异将对孟加拉盆地中部的地貌动力学产生大规模的预计影响。