Tidal Estuary Response to Bridge Construction Using DSAS Shoreline Analysis along Vaitarna River, India

Abstract

Estuarine systems are highly sensitive to hydraulic modifications, and bridge construction can significantly alter sediment transport, shoreline dynamics, and geomorphic stability. The present study aims to assess the geomorphic impact of bridge construction on the Vaitarna River estuary and evaluate the influence of bridge-related disturbance on sediment movement; shoreline change and erosion-deposition patterns in the estuary. This study examines the geomorphic impacts of bridge construction on the Vaitarna River estuary. This study employs an integrated design that combines bathymetric survey transects, shoreline analysis (Landsat 1998–2022) using the DSAS model across the Vaitarna estuary. The study area was the Vaitarna River estuary, Palghar District, Maharashtra, India. Shoreline change was analysed for the period 1998 to 2022, while the Vaitarna bridge, constructed in 1886, was considered the key structure influencing geomorphic change. The study used bathymetric cross-profiling, shoreline change analysis, sediment granulometric analysis, hydrodynamic simulation, and DSAS v6.0 shoreline analysis. These methods helped identify scour near bridge piers, bed incision, upstream aggradation, and changes in tidal sediment movement. The Vaitarna estuary showed strong geomorphic instability, including pier-induced scour, downstream bed incision, and upstream aggradation. Bathymetric profiles at Vaitarna revealed pier-induced scour and downstream deepening (>18,000 m³ net erosion, 1998–2022), contrasting with depositional trends. DSAS model resulted in a range of -6.85 to to 7.34 m yr-1 erosion at Vaitarna, confirming tidal control on sediment dynamics. The findings highlighted that bridge construction has significantly altered the geomorphic balance of the Vaitarna River estuary. The study highlights the need for scour protection, regular monitoring, and mangrove restoration to improve estuarine resilience.