Dynamics of dike effects on tidal circulation around Saemangeum, Korea

•Tidal amplitude change due to the construction of dykes in the Saemangeum was simulated and assessed.•The dykes lessened the tidal phases, weakened the current and lowered the amplitude.•In particular the southern leg has experienced significant effects.•Through numerical simulation, such phenomena were elucidated in this work.

A series of dikes was built in Saemangeum located in southwestern Korea and reduced the tidal phase, the current, and the amplitude. Through two dimensional numerical modeling utilizing a finite volume model, we elucidate the mechanism how these dikes modify the tide. Before the dikes were built, the tide was refracted by the coast and the co-phase line was parallel to the coastline. The dikes removed the shallow coastal zone, resulting in faster wave propagation to reduce the phase. The southern leg is parallel to the co-phase line and more effective in blocking the tide than the northern leg that is oblique to the co-phase line. Greater reductions of the tidal phase and flow were found in front of the southern leg. Before the dike, over the site of the southern leg in the direction to the leg, the temporal changes of momentum, friction, and the pressure gradient balance. Upon the completion of the leg, the tidal current and the temporal changes of momentum and friction weakened. The pressure gradient, then, weakened, reducing the tidal amplitude. The northern dike built oblique to the tidal flow reduced only the component normal to the leg, and the Coriolis force did not affect significantly. To balance the Coriolis force, the pressure gradient and, subsequently, the tidal amplitude weaken by lesser amounts.