Indo Gangetic flood plains are subjected to recurring floods due to large low-lying land areas adjacent to major Himalayan Rivers. Recent floods in the Ganga River during the late withdrawal phase of Indian summer monsoon rains in 2019 had reportedly caused death of ∼200–500 people and damaged major infrastructures in different parts of Bihar state, India. This paper presents a detailed analysis of the spatial extent and temporal pattern of flood inundation areas in Patna district of Bihar using Sentinel-1 Synthetic Aperture Radar (SAR) data. The results obtained using K-means classification show that about 1268 km² (20% of the studied portion) of the land area were inundated during the peak flooding conditions on 9th October 2019. The peak flooding lasts for more than 20 days, with a maximum water depth of 18 m in the main river. Owing to the continually changing nature of river morphology by recurring floods, we also analyzed the channel morphology and bar characteristics before, during, and after the floods. Geomorphic change assessment indicates that the total bar occupied area was decreased from 661 km² for pre-flood time to 446 km² in peak flood time, whereas it retains its original shape in post-flood images.

由于喜马拉雅河主要河流附近的大片低洼土地区域，印度恒河洪泛区经常遭受洪水。据报道，在 2019 年印度夏季风雨撤退后期，恒河最近发生的洪水已造成约 200-500 人死亡，并损坏了印度比哈尔邦不同地区的主要基础设施。本文使用 Sentinel-1 合成孔径雷达 (SAR) 数据详细分析了比哈尔邦巴特那地区洪水淹没区的空间范围和时间模式。使用 K-means 分类得到的结果表明，大约 1268 km ²在 2019 年 10 月 9 日的洪水高峰期，陆地面积（研究部分的 20%）被淹没。高峰洪水持续 20 多天，主要河流的最大水深为 18 m。由于反复发生的洪水使河流形态不断变化，我们还分析了洪水之前、期间和之后的河道形态和水坝特征。地貌变化评估表明，坝区总面积从洪水前的661 km ²减少到洪水高峰期的446 km ²，而在洪水后的图像中仍保持其原始形状。