Narrow Results

This paper reports the post-disaster survey results of storm surge and waves due to Super Typhoon Meranti (local name: Ferdie), along the coastline of the province of Batanes, Philippines. The survey was conducted by a joint survey team of the University of Tokyo and University of the Philippines from 9 to 12 October 2016, about one month after the disaster. Water levels in the inundated area or runup heights were measured at 37 locations along the coast of the islands of Batan and Sabtang by interviewing local residents and by examining wave runup evidences remaining along the coast. Obtained runup and inundation levels showed significant variations along the coast of islands and higher levels were found on the coast facing north. Especially at Ivana, a small coastal community located at the southwestern tip of the island of Batan, the coast was covered by a convex-shaped fringing reef and observed inundation heights were locally concentrated behind the peak of the convex-shaped reef.

The evolution of crossing sea states and the emergence of rogue waves in such systems are studied via numerical simulations performed using a higher order spectral (HOS) method to solve the free surface Euler equations with a flat bottom. Two classes of crossing sea states are analyzed: one using directional spectra from the Draupner wave crossing at different angles, another considering a Draupner-like spectra crossed with a narrowband JONSWAP state to model spectral growth between wind sea and swell. These two classes of crossing sea states are constructed using the spectral output of a WAVEWATCH III hindcast on the Draupner rogue wave event. We measure ensemble statistical moments as functions of time, finding that although the crossing angle influences the statistical evolution to some degree, there are no significant third-order effects present. Additionally, we pay particular attention to the mean sea level measured beneath extreme crest heights, the elevation of which (set up or set down) is shown to be related to the spectral content in the low wavenumber region of the corresponding spectrum.

Some twenty ultrasonic wave gages were employed to measure the water surface level as well as the bottom sand level near the shoreline in the field. Obtained data during a storm reveals that the long period waves were really dominant in and just outside the swash zone. It is also shown that the long waves provided the swash oscillation in the form of the loop by standing waves. In addition, data recorded for different conditions of beach slopes and incident waves are also presented for comparison with some analysis.