Hydrodynamics and Sediment Transport Under River-Coastal Forcing in Malili Estuary

Abstract

Malili Estuary experiences progressive channel shoaling driven by interactions among river discharge, tidal currents and wave forcing. As a navigation route serving Balantang Port and Malili Fish Landing Port (PPI Malili), understanding sediment dynamics is essential to maintain hydraulic capacity and navigability. This study analyses hydrodynamic characteristics and sediment transport under coupled river–tidal–wave forcing using a two-dimensional numerical model integrating hydrodynamic (HD), spectral wave (SW) and sediment transport modules (ST). Model validation shows good agreement with field observations, with MAPE values of 3% for water level, 9.4% for current velocity, and 16% for suspended sediment concentration.

Results indicate that sediment transport varies throughout the tidal cycle, with ebb and flood phases influencing redistribution along the estuarine channel. River discharge primarily controls current velocity, while wave-current interaction near the estuary mouth increases near-bed shear stress and sediment mobilization. Simulated bed level changes reveal gradual suspended-load accumulation of approximately ±0.02 m, whereas bed load transport produces larger bed elevation changes from 0.2 - 0.3 m within three-month simulation period, confirming its dominant role in morphological evolution. These findings highlight the importance of integrated river-tidal-wave interactions in controlling channel shoaling and supporting sustainable navigation management.