A Terrestrial record of ∼3000 years of extreme floods from the Kaveri and adjacent river basins, Tamil Nadu, India

Abstract

Extreme flood events have played a crucial role in shaping the fluvial landscape of the Kaveri River basin, impacting agriculture, water resources, and human settlements. However, due to the limited availability of instrumental and historical records, the long-term recurrence of these extreme events and their relationship with climatic fluctuations remain poorly understood. This study reconstructs the history of extreme flood events in the lower Kaveri Basin and adjoining river systems, over the past 3000 years using detailed sedimentological analysis and Optically Stimulated Luminescence (OSL) dating. Field investigations identified well-preserved slack water deposits (SWDs), levee sediments, and overbank flood layers, which serve as reliable archives of past high-magnitude flood events. These deposits exhibit distinctive sedimentary facies, including fining-upward sequences, abrupt basal contacts, and poorly sorted sand-silt-clay layers, which confirm their deposition under high-energy flood conditions rather than by gradual channel migration processes. The OSL dating results indicate major flood events at approximately 40 years, 150 years, 1.7 ka, and 2.85 ka, demonstrating episodic flood recurrence over millennial timescales. The 40-year event closely aligns with the timeframe of the catastrophic 1977 flood, while the older flood events correspond to major climatic transitions. The recurrence of extreme flood events in the Kaveri Basin suggests a strong link between flood magnitude and Indian Monsoon variability, with monsoon intensification, shifts in the Inter-Tropical Convergence Zone (ITCZ), and cyclone activity in the Bay of Bengal acting as primary drivers of hydrological extremes in the region. Additionally, sediment transport mechanisms and depositional environments influence the bleaching efficiency of quartz grains, affecting the reliability of luminescence ages.