Monsoon-driven seasonal variability in sediment texture of embayed beaches along the central west coast of India

Abstract

This study investigates the seasonal variability in sediment texture and the morphodynamic responses of embayed beaches along the Central West Coast (CWC) of India under monsoonal forcing. Sixteen embayed beaches were analysed using grain-size statistics, beach profiling, and wave-climate data across four seasonal intervals from February 2023 to September 2024 to assess variations in grain-size distribution, sorting, skewness, and kurtosis. The results reveal a distinct monsoon-driven erosion-accretion cycle, with coarser sediments (mean grain size: 0.6–4.84 Φ) and better sorting observed in September, coinciding with peak significant wave height (Hs) and increased erosion (-32.16 m³/m average volume loss). In contrast, finer sediments (mean grain size: 0.8–4.1 Φ) and poorer sorting characterise February, aligning with calmer hydrodynamic conditions and net sediment accretion (average volume gain: 28.61 m³/m). Skewness and kurtosis trends further indicate high-energy wave action driving selective grain transport, while post-monsoonal conditions favour more heterogeneous sediment deposition. The findings suggest that although embayed beaches are morphodynamically semi-isolated, they exhibit sedimentary responses coherent with those of wave-dominated open coasts when subjected to strong seasonal forcing, such as the monsoon. This work emphasises the sensitivity of embayed beach systems to regional hydrodynamics and rising sea levels, offering critical insights for coastal management in monsoon-affected coasts.