Narrow Results

Wave setup and longshore currents on planar beaches induced by directional spectral waves have been computed for beach slopes ranging from 1/100 to 1/10, waves with deepwater wave steepness from 0.005 to 0.08 and offshore incident angles from 1° to 70°. The author's random wave breaking model PEGBIS (Parabolic Equation with Gradational Breaker Index for Spectral waves) is employed for the evaluation of wave attenuation by breaking. Prediction formulas are empirically derived for estimation of the wave setup at the shoreline and the cross-shore distribution of longshore currents on the basis of numerical computation results. Effects of spectral peakedness and directional spreading, surface roller, and turbulent eddy viscosity on wave setup and longshore currents are examined. The formulas have shown the capability to predict the wave setup and longshore currents observed in several field measurements fairly well.

Wave breaking over a submerged step with a steep front slope and a wide horizontal platform is studied by smoothed particle hydrodynamic (SPH) method. By adding a momentum source term and a velocity attenuation term into the governing equation, a nonreflective wave maker system is introduced in the numerical model. A suitable circuit channel is specifically designed for the present SPH model to avoid the nonphysical rise of the mean water level on the horizontal platform of the submerged step. The predicted free surface elevations and the spatial distributions of wave height and wave setup over the submerged step are validated using the corresponding experimental data. In addition, the vertical distributions of wave-induced current over the submerged step are also investigated at both low and high tides.

Super Typhoon Meranti was one of the strongest typhoon that made landfall in the Philippines in 2016. Following the typhoon event, a post-disaster survey was conducted by Tajima et al. (2017), wherein inundation levels and wave runup heights were measured at 37 locations along the islands of Batan and Sabtang, Batanes. This paper discusses the results of the numerical modeling efforts performed to simulate the storm tide levels in Batanes Islands, and the comparisons of the simulations with the observed water levels. The numerical storm tide model for the study area was developed using the two-way coupled Delft3D-SWAN hydrodynamic and wave models. The observed water levels from the tide monitoring station in Basco Port in Batan Island indicated that the peak water level during the passage of Typhoon Meranti is only 0.87 m above MSL, while the simulated peak water level is 0.72 m above MSL. Comparing the results of the simulations to the findings of the post-disaster survey conducted by Tajima et al. (2017) showed that the simulated peak water levels at the survey locations were consistently and drastically lower than the measured water levels. The observed error in the simulated peak storm tide in Basco Port is less than 20 cm, and therefore does not account for the large differences between the measured inundation levels and simulated and measured inundation levels. The large differences are attributed to other nearshore processes (e.g. surge height amplification due to the fringing reefs) that are not considered in the current storm tide numerical model setup, and shall be investigated in a future study.