Preserving Navigational Channel Depth at the Batang Arau Floodway Mouth, Padang, West Sumatra, Indonesia: A Numerical Study of Jetty Layout Effectiveness

This sedimentation poses a critical threat to the local fishing economy and safe navigation, necessitating effective engineering solutions. At the Batang Arau Floodway Mouth in Padang, West Sumatra, Indonesia, significant sedimentation impedes the operation of fishing vessels exceeding 10 m in length, despite the presence of existing jetty structures. This research investigates the optimization of jetty layout configurations to mitigate sedimentation and enhance the navigational channel depth at this coastal floodway mouth using a numerical simulation approach. Six distinct jetty layout setups, including a baseline, the existing configuration, and four proposed optimized designs, were simulated and analyzed to evaluate their effectiveness. Our hydrodynamic and sediment transport simulations, evaluated by the stability of channel depth (i.e., near-zero sedimentation or erosion) and maintenance of navigational cross-sectional area, reveal that Scenario 5—featuring a short straight right jetty combined with a long-left jetty angled 66° rightward—offers the most effective protection for the floodway mouth against wave action and sedimentation. This configuration consistently yields a stable floodway channel depth with almost no net sedimentation or erosion at the mouth and within the main channel, thereby preserving navigational conditions. This enhanced performance is primarily attributed to the dominant influence of the alongshore current flowing towards the northwest, consistent with the prevailing wave-driven longshore transport in the area. Furthermore, simulations incorporating a floodway dredging scenario under both normal and flood discharge conditions indicate that substantial dredging efforts are necessary to achieve and maintain adequate water depths for the safe passage of larger fishing vessels. Subsequent simulations conducted after the simulated dredging demonstrate a relatively low rate of sedimentation within the dredged navigation channel, suggesting the potential for a long-term improvement in navigability.