The Myodo waterway within Gwangyang Port presents navigational challenges due to its narrow 150-m width and numerous surrounding obstacles, increasing the risk of maritime accidents. Expansion and dredging efforts have been deemed essential to enhance the operational competitiveness of the port. Consequently, the responsible authority is undertaking the Myodo waterway expansion and realignment project, scheduled for completion between 2024 and 2030. Revising the navigation rules will be essential following the completion of these modifications. This study evaluates risk levels before and after the expansion of the waterway using the environmental stress (ES) model and proposes appropriate speed limits. Six scenarios were developed, followed by maritime traffic flow simulations. The simulation results indicate that increasing the maximum speed limit from 8 knots to 10 knots is feasible, alongside the transition from one-way to two-way navigation. These findings provide valuable insights for formulating navigation regulations post-expansion. However, the study did not consider the potential impact of wake waves on nearby vessels..