Beyond historical records: Palaeoflood insights for improved flood hazard assessment in the lower Mahi River Basin, western India

Understanding long-term flood variability is crucial for effective flood disaster management, yet systematic gauge data are often limited. Palaeoflood hydrology offers valuable insights using geological and geomorphological archives contributing to better flood risk analysis and infrastructure design. While bedrock reaches have been the focus of many palaeoflood studies, this paper synthesizes the late Holocene palaeoflood record from five sites within the alluvial lower Mahi River Basin in western India, highlighting the role of distinct geomorphic settings in slackwater deposit (SWD) accumulation and preservation. Our synthesis of optically stimulated luminescence and radiocarbon dated SWDs from ravine incisions, tributary confluences, and pediment benches reveals evidence of significant palaeoflood events occurring at approximately 4.6, 1.7, 1.25, 0.73, 0.51, and 0.28 ka. Notably, deeply incised ravines at meander bends in the lower reaches provided ideal backflooding conditions, leading to the accumulation and better preservation of thicker and chronologically longer SWD sequences compared to the more proximal flood benches in the upper reaches. Palaeoflood discharge estimations at select sites indicate past flood magnitudes significantly exceeding historical records. This study underscores the potential of specific alluvial geomorphic settings in monsoon-fed rivers for reconstructing late Holocene palaeoflood histories in regions with limited long-term hydrological data, offering crucial insights for improved flood risk assessment and understanding flood-climate relationships in western India.