研究課題
We have analyzed what lead to the destructive tsunami-like bore in Hernani, Philippines, during typhoon Haiyan. Abrupt and energetic wave breaking at an the edge of a fringing reef facilitated the release of infra-gravity (IG) wave energy over the reef flat. The width of the wave breaking zone was very narrow so that hardly any long wave energy was dissipated. The resulting long-period oscillations shoaled at the beach and steepened into a destructive bore.These findings were obtained through analyses of numerical model runs.We then transferred this knowledge to assess storm wave impacts in Japan, in particular at the Sendai coast, Tohoku. The conditions along the continental coast are different; the surf zone is much wider and the swell period often short (in the range of 10-12 sec). here, wave breaking causes energy dissipation for short (swell) waves and also IG waves. The result in a less-energetic surf beat, which only shows up as water level fluctuations with a period of 1-2 min and amplitudes of up to 1 m (for swells with Hs > 2m). Though the surf beat does not steepen into a destructive bore but provides an energetic envelope for gravity waves to travel atop. The superposition enables the swell waves to reach higher runup points, which in turn results in beach and dune erosion and demolition of coastal infrastructure. An example is the area of Sendai Port where the described process caused dune erosion of about 20 m in only one year.
2: おおむね順調に進展している
We are progressing on track. However, we decided to add more computations (with larger domains) to the originally planned outline.
An important aspect to look into is the influence of tidal fluctuations on nearshore waves. The research that goes far beyond this study will address the following problems:How are wave processes near Sendai Port influenced by the offshore wave conditions, local bathymetry, and tidal fluctuations? What leads to infragravity wave and coastal erosion hotspots? Is there a long-period variability? What are the magnitudes of the amplitude changes of these phenomena under typical and atypical sea level changes? And to what extend are changes in the local bathymetry altering the flooding scenarios?We will address these question with numerical models as well as with field work. The field work component includes drone surveys of the beach near Sendai Port. Surveys before and after characteristic swell events will show the changes in the beach profile and sediment budget.The computations will then focus on key swell events that have caused significant flooding and coastal erosion. Such events do not require extreme waves generated by tropical and extra-tropical storms, but rather average swell waves that occur once a month. We will also consider tide levels in the computations. Permutations of the input conditions will show the local sensitivities on specific wave parameters such as water level, significant wave height, peak period, and directionality of the wave spectrum. In addition, the precomputed scenarios will be used to derive a statistical database that reveals the changing coastal vulnerability under various scenarios of sea level rise and wave energetics.
Changes in travel had to be accommodated for.
Travel to conference.
すべて 2017 2016
すべて 雑誌論文 (4件) (うち国際共著 4件、 査読あり 4件、 オープンアクセス 3件、 謝辞記載あり 1件) 学会発表 (2件) (うち招待講演 1件)
Ocean Modelling
巻: 5 ページ: 1, 15
Mountain Research and Development
巻: 37 ページ: 5,15
10.1659/MRD-JOURNAL-D-16-00043.1
International Journal of Disaster Risk Reduction
巻: 21 ページ: 323, 330
doi:10.1016/j.ijdrr.2016.12.016
Renewable Energy
巻: 1 ページ: 1, 14
10.1016/j.renene.2016.06.049
