Exploring Sediment–Morphodynamic Coupling in the Evolving Indian Sundarban Delta

The Indian Sundarban Delta (ISD), occupying the southern sector of the Ganga–Brahmaputra–Meghna (GBM) delta along India’s eastern coast, represents one of the world’s most dynamic yet environmentally fragile deltaic systems. Over the past three decades, the ISD has undergone a pronounced morphodynamic transformation driven by the interplay of reduced sediment supply, sea-level rise, and intensified coastal processes. This study investigates the long-term linkage between suspended sediment dynamics and shoreline evolution from 1990 to 2024, integrating multi-temporal satellite observations, Digital Shoreline Analysis System (DSAS)-based metrics, and satellite-derived suspended sediment concentration (SSC).

Multi-decadal Landsat imagery was used to extract shorelines under comparable tidal conditions and estimate SSC using established semi-empirical models. Shoreline change parameters, including Net Shoreline Movement (NSM) and End Point Rate (EPR), were computed at 50-m intervals along approximately 2,980 km of coast, covering eight geomorphic zones. Results reveal extensive shoreline retreat and land loss, with the highest erosion recorded along the ocean-facing margins of the Hooghly River, where EPR exceeded –60 m/yr. Areal analysis shows widespread island fragmentation and loss of tidal flats, indicating ongoing morphological degradation.

The SSC assessment indicates strong seasonal variation, characterized by higher concentrations during the wet season (May–October) and significantly reduced levels in the dry months. Spatially, SSC within the Ganges–Brahmaputra estuarine complex shows a distinct decline seaward, with the highest turbidity typically found near the river mouth or bay head, depending on discharge magnitude and monsoonal intensity. In these high-turbidity zones, concentrations often exceed 150 mg L⁻¹, reflecting the influence of strong fluvial inputs during peak discharge periods.

A marked long-term decline in SSC, particularly across the outer estuarine zones of the Hooghly and Meghna rivers, reflects significant sediment starvation since the 1990s. This decline is attributed to upstream sediment trapping, altered hydrological regimes, and enhanced marine reworking. The reduced sediment supply has intensified shoreline retreat and disrupted the sediment–morphology balance, shifting the delta towards a net erosional state.

Overall, the study underscores a strong sediment–morphodynamic coupling in the Sundarban region, where the combined effects of sediment starvation, sea-level rise, and intensified hydrodynamic forces are reshaping the deltaic landscape. These findings highlight the urgent need for integrated sediment and coastal management approaches to preserve the ecological stability and livelihood security of this globally significant delta.