Three-dimensional numerical simulations for mitigation of tsunami wave impact using intermittent sea dikes

Sea dikes are nowadays adopted for the protection of onshore infrastructures against devastating tsunami wave. For intermittent/discontinuous sea dikes, the flow fields are 3D in nature, making it necessary for three-dimensional model studies to analyze their effects on the peak tsunami impact force on a downstream structure. In this study, a numerical code based on a suitable turbulence closure model has been used to make simulations for trapezoidal sea dikes. The simulations have been performed for laboratory scale model. The simulation results for different dike length to gap ratios have shown that sea dikes with 25% gaps will be adequate as the peak impact force on an onshore building is reduced by 36%, while a continuous sea dike can reduce the peak impact force approximately by 40%. A composite dike wherein a 50% length of the larger trapezoidal cross-section is alternated with a smaller rectangular section is capable of reducing peak tsunami impact force by approximately 32%. Two staggered rows of intermittent dikes give better protection than a single row of intermittent dike. However, the protection is marginally lesser than that given by a single continuous dike.