A coupled diffusion–deposition analytical model for rapid assessment and optimization of offshore dredged material disposal

Offshore disposal of dredged material generates suspended sediment plumes and seabed deposition that pose risks to marine ecosystems. Numerical models resolving coupled hydro-sediment dynamics are computationally expensive, while analytical approaches seldom predict both water-column concentrations and seabed deposition in a unified, rapid-assessment framework. This study presents an FFT-accelerated analytical model that simultaneously simulates suspended sediment concentration (SSC) and bathymetric change from open-sea disposal. The model couples two-dimensional point-source diffusion with sediment settling, incorporating a BBO-derived kinematic lag correction for particle–fluid traceability, a multi-fraction scheme, and FFT-based convolution. Calibrated and evaluated against SSC and multibeam bathymetric surveys at Skikda Port, Algeria, the model reproduces the observed SSC and deposition. Plume distance and integral >10 cm deposition area/volume are robust for Δ t = 15−120 s and Δ x = 5−10 m; near-field maximum deposition thickness is time-step dependent and reported for reference only. Water depth is the dominant control, reducing the >10 cm seabed area by 31% from 50 m to 100 m depth. At fixed total released mass, discharge duration controls plume extent but not final deposition pattern (a property of the present framework), a marginal-benefit analysis identifies 0.5–1 h as the optimal single-vessel operating range. A three-stage optimization methodology is proposed and demonstrated.