Characterizing floods and reviewing flood management strategies for better community resilience in a tropical river basin, India

The present work intends to assess the nature of floods, trigger factors, impacts, and management in the Bhagirathi River Basin (BRB) using mainly secondary data (Survey of India toposheets, Landsat 5 TM, Landsat 7 ETM+, and Sentinel 2 images, Google Earth Imageries, district gazetteers, and annual floods reports) and techniques of normalized difference water index (NDWI), river network change index (RNCI), sinuosity index (SI), and analysis of the previous documents and reports. The results portray that flood frequency in the BRB was found to be increasing during the last century (1901–2020). However, the nature of the floods spatially varies from the rarh (western part of the Bhagirathi River) to the bagri (eastern part). The floods in the rarh region are mainly controlled by dams and barrages constructed on the western tributaries of the Bhagirathi River, while the Farakka barrage and ill-drained decaying distributaries are responsible for the floods in the bagri region. Moreover, two types of the flood were observed in the study area: (1) monsoon flood induced by heavy monsoon rainfall during June–September and (2) lean period inundation caused by the controlled discharge from the Farakka Barrage Project during January–May as per the Indo-Bangladesh water-sharing treaty (1977). Though the monsoon floods wreak havoc on the agricultural and household resources almost every year, the lean period inundation only affects the agricultural lands along the banks of the Bhagirathi River, especially in the community development (CD) blocks Raghunathganj II, Lalgola, and its adjacent areas. During the last century (1900–2020), the year 2000 recorded a colossal flood when 11 CD blocks in Murshidabad and 16 CD blocks in Nadia districts became inundated. To manage the floods, a few structural measures like embankments along the banks of the Bhagirathi River and storage of water in dam reservoirs have been implemented. However, due to the loss of the live capacity of reservoirs caused by the entrapping of suspended sediments, flood management faced challenges. Thus, ‘controlling flood’ becomes difficult in this region, and ‘living with flood’ may be an alternative approach.