Seasonal variations of inner shelf sediment dynamics and granulometric characteristics along the Nagapattinam coast of the Cauvery basin, Southern India

This study investigates the seasonal sediment dynamics and granulometric characteristics of inner-shelf sediments along the Nagapattinam coast of southern India, based on pre- and post-monsoon sampling. Inverse Distance Weighting (IDW) interpolation showed sand dominance in high-energy offshore zones (up to 99% pre-monsoon; 98% post-monsoon) and silt–clay enrichment in sheltered nearshore and estuarine areas (silt up to 69% pre-monsoon; 67% post-monsoon; clay up to 11% pre-monsoon; 8% post-monsoon). The observed seasonal variations in sediment characteristics, including increased silt–clay enrichment in sheltered nearshore and estuarine zones, were supported by grain size analysis, which showed medium to very fine sands (mean size 1.533–3.767φ pre-monsoon; 1.267–4.233φ post-monsoon) with predominantly poor sorting, reflecting variable energy conditions and continuous sediment reworking. Skewness values (–0.620 to 0.614φ pre-monsoon; –0.425 to 0.496φ post-monsoon) were mostly positive, indicating fine sediment accumulation, while localized negative skewness reflected winnowing in nearshore and offshore areas. Correlation analysis revealed strong inverse relationships between sand and silt (r = –1.00) and between sand and clay (r = –0.88), as well as strong positive correlations between silt and clay (r = 0.85). High inter-seasonal correlations (r = 0.95) indicate that spatial patterns remain consistent despite seasonal redistribution. Data-driven statistical models, such as CCA, EMMA, Principal Component Analysis (PC1: 48.0%, PC2: 26.6%), and Hierarchical Cluster Analysis, identified three depositional settings: sand-rich, high-energy zones; transitional sand–silt environments influenced by estuarine mixing; and fine-rich, low-energy zones that persisted across seasons. The results show that while monsoonal processes cause short-term sediment redistribution, the long-term granulometric framework of the Nagapattinam coast is maintained by stable hydrodynamic and geomorphological processes.