Spatiotemporal analysis of 2020 monsoon floods and its impacts along selected reaches of the Padma River, Bangladesh

Abstract

ABSTRACT The 2020 Monsoon Floods in Bangladesh had the longest duration since 1998 and affected 37% of the country. This study explored the impacts of flooding along selected reaches of the Padma River by analysing flood dynamics and bank erosion using Sentinel SAR-C and MSI image datasets, hydrologic, and field data. It involved mapping and validating the spatiotemporal distribution of flooding, erosion, and water turbulence. There were three phases of onset and recession of flooding between 1st July and 4th October, 2020. Image analysis showed that the highest floodwater extents during these phases were 14%, 20%, and 15% of the study area on 1st July, 6th August, and 23rd September, respectively. It was also found that a total of 92.8 km2 of riverbank area was eroded between 6th April and 7th November. The distribution of water turbulence and bank erosion showed concurrence in most parts while exceptions were also observed. From June to October 2020, Pearson’s correlation coefficients for monthly hydrologic data and erosion estimates were calculated to be (a) 0.791 between average river discharge and total eroded area, (b) 0.956 between maximum river discharge and total eroded area, (c) 0.741 between average water level and total eroded area, (d) 0.991 between average river discharge and average water level, (e) 0.519 between average water level and total rainfall, and (f) 0.484 between average water level and total rainfall. GIS analysis showed a total of 297 educational and healthcare facilities were flooded while 15 facilities were lost to bank erosion. A total of 489.75 km of road and 60.03 km2 of settlements were inundated.