1C.Research on Privention and Mitigation of Disasters Caused by High Wave and Storm Surge
Background and Objectives
- Waves of extraordinary heights and periods have caused much damage in recent years, and there are concerns that such damage may worsen due to rising sea levels, stronger typhoons and extratropical cyclones, and other effects of global warming. Therefore, more accurate prediction
and more efficient countermeasures against coastal flooding are required, in addition to a thorough study on the causes of storm surges and high waves, so that such damage can be mitigated.
- The objectives of this research theme are to investigate wave characteristics over a wide range from offshore to coastal areas, as well as the actual conditions and underlying mechanisms of flooding and structure damage through field observations and hydraulic model experiments; and to improve the numerical simulation models.
The effects of global warming on storm surges and high waves are estimated via numerical computation.
Research on storm surge and high wave disaster prevention includes the following three subthemes:
- Measurements and Hindcasts of Offshore Waves
Information acquired via GPS-mounted wave buoys and other devices is analyzed, and an offshore wave database containing estimation data is established in order to investigate wave characteristics.
- Design of Maritime Structures to Prevent Disasters Caused by High Wave and Storm Surge
Numerical models are developed for estimating wave, soil, and structure deformations, with emphasis on the performance design of port and coastal structures. These models take the interactions between wave, soil, and structures into account and enable calculations based on offshore boundary conditions.
- Prediction of Risks due to Global Warming and Countermeasures
In preparation for facility planning in the context of global warming, changes in the mean sea level and the frequency of occurrence of storm surges and high waves due to typhoons and extratropical cyclones are explored using IPCC climate forecasts and other data combined with numerical simulation models.
Activities in FY 2014
- Concerning the creation of databases that link the integrated processing and analysis of oceanographic observation data with estimated values, a basic study was conducted on the directional spectrum method (EMEP method) for the introduction of the NOWPHAS routine process. Also, trial observation using a new type of GPS wave meter was conducted.
Figure 18.104.22.168 Main features of a prototype of a new GPS-mounted wave buoy
- Regarding assessing the risk of coastal disasters using the multi-scale wave transformation model system, we examined methods of approximating horizontal and vertical flow rates, achieved one-way connection between the Boussinesq modeling and the three-dimensional fluid analysis method.
- Regarding the study on forces beyond design caused by unexpected high waves and measures for reducing them, we carried out NOWPHAS wave observation data analysis and calculated the wave deformation in shallow sea areas, and in particular, clarified the regional differences in the probability of occurrence of swell, the increase and concentration of wave height, and the appearance of H1/250 and H1/3 values.
Figure 22.214.171.124 Regional differences in the probability of occurrence of wind waves and swell
- In order to establish a performance verification method by means of a numerical wave tank using random waves, we examined the incidence methods of random waves while speeding up the numerical wave tank using a GPU.
- For evaluating the variation in marine forces under medium-and long-term climate change, we summarized the results of the on-site surveys of damage and estimation of high waves caused by Typhoon Haiyan in 2013, which resulted in serious damage to the Philippines. Focusing on the Seto Inland Sea of Japan, we also carried out theoretical calculations of high waves caused by typhoons as well as sensitivity analysis of the extent of medium- and long-term change and the frequency and scale of excessive external force.
- Regarding the investigation of the wind, high wave, and wave characteristics of catastrophic typhoons in inner bays in Japan, we collected and arranged information on the attributes of typhoons and improved the existing estimation model for high waves.