Decadal to Millennial Evolution of coastline along the Central West Coast of India: Integrating Field Observations, Remote Sensing, and Paleo shoreline Proxies

The central west coast of India presents a dynamic coastal environment where geomorphic evolution is governed by a complex interplay of monsoonal forcing, sea-level fluctuations, and human interventions. This study unravels the morphodynamic behavior of embayed beaches across seasonal, decadal, and millennial timescales using an integrated approach that combines field observations, satellite-based shoreline analysis, and paleo-geomorphic reconstructions. Twenty-seven embayed beaches were systematically classified using an embayment morphometric parameter (γe) derived from the embayment area (Ae) and indentation (a), enabling their categorization into open, semi-exposed, and sheltered systems. Field measurements from sixteen representative beaches revealed a pronounced seasonal rhythm driven by the southwest monsoon. Between February 2023 and September 2024, beach profiles and sediment texture analyses indicated distinct monsoon-induced erosion–accretion cycles. Coarser and better-sorted sediments (mean 0.6–4.84 Φ) accompanied high-energy wave conditions and volumetric losses averaging –32.16 m³/m, while post-monsoon periods favoured the deposition of finer, poorly sorted sediments (0.8–4.1 Φ) and volumetric gains averaging +28.61 m³/m. These observations suggest that even morphodynamically semi-isolated embayments respond synchronously to regional wave energy fluctuations, reflecting a delicate balance between hydrodynamic forcing and sediment supply.Extending the temporal perspective, multi-decadal shoreline analyses (1990–2023) derived from remote sensing data revealed spatially variable responses to climatic and anthropogenic drivers. Correlation with rising sea levels, increasing cyclone frequency, and intensifying wave power suggests that regional climate change has accelerated erosion processes. Additionally, the construction of breakwaters and jetties has disrupted longshore sediment transport, intensifying localized shoreline instability.

To place these short-term observations within a broader evolutionary context, paleo-shoreline reconstruction was carried out using geomorphic proxies such as paleo beach ridges, wave-cut terraces, and topographic and hydrographic sinuosity indices derived from high-resolution SRTM DEMs. The reconstruction reveals that around ~12-10ka BP, when sea level stood 80 m below mean sea level, the shoreline coincided with the present-day ~80 m bathymetric flat, advancing ~+4m landward during mid-Holocene (~6-5 ka BP) transgressive phases. Exploring paleoshorelines is critical as it unveils the imprint of post-glacial sea-level rise and tectonic adjustments, providing the millennial-scale context necessary to interpret modern coastal behavior and anticipate future shoreline trajectories under accelerating climate change also these ancient shoreline and beach-ridge formations are important to society and the economy as they can host valuable heavy mineral deposits and serve as reservoirs for groundwater.

Together, these insights portray a continuous narrative of coastal evolution from monsoon-driven sediment oscillations to decadal shoreline shifts and millennial transgressions highlighting the dynamic and interconnected nature of embayed beach systems along the central west coast of India. This multi-temporal framework enhances our understanding of coastal resilience and supports informed management of monsoon-dominated, morphologically sensitive coasts.