1C. Research on Storm Surge and High Wave Disaster Prevention and Mitigation
Background and Objectives
Many instances of damage caused by waves with extraordinary heights and periods have occurred in recent years. There are concerns that such damage will escalate due to the rise of the mean sea level, the intensification of 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 in a wide range from offshore to coastal and inland areas, as well as the actual conditions and underlying mechanisms of flooding and structure damage through field observations and hydraulic model experiments; and to upgrade 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 four sub-themes:
- Oceanographic monitoring using an offshore wave observation network, high-accuracy meteorology and wave models
New information acquired via GPS buoys and other devices is analyzed, and an offshore wave database (including hindcasted data) is updated in order to investigate wave characteristics as a basis for the efficient, appropriate survey and design of coastal areas.
- Upgrading design technology of protective facilities for prevention of coastal damage by storm surges and high waves
Numerical models are developed for the estimation of wave, ground and structure deformations, with emphasis on the performance design of port and coastal structures. In these models the interactions between seawater, soil and structures are taken into account.
- Forecasting and response to risks imposed on coastal areas by global warming
In preparation for facility planning in the context of global warming, the changes in sea-level rise and the occurrence frequency of storm surges and high waves due to stronger typhoons and other phenomena are explored using IPCC climate forecasts and other data combined with numerical simulation models.
- Maintenance and improvement of programs and databases
Programs and databases are maintained as required for the design of coastal structures and other purposes.
Activities in FY 2011
The tsunami waveforms of the 2011 Great East Japan Earthquake were captured using GPS buoys placed in the Tohoku offshore area. The water level exceeded six meters in the Iwate South and Iwate Central offshore areas, and it reached nearly six meters in the Miyagi offshore area. In the Iwate South offshore, a one-meter tsunami was observed even six hours after the earthquake's occurrence, and seven waves were registered during that six-hour period.
A numerical simulation model for wave transformation, from offshore to the coast, based on Boussinesq equations was modified for inundation treatment, thus expanding the applicable field. Although only the directional spectra, which are uniform alongshore, could be set at the offshore boundary in the previous model, the modified model makes it possible to set directional spectra that vary alongshore, thus improving the accuracy of wave-transformation calculation.
Tsunami waveforms of the 2011 Great East Japan Earthquake captured by GPS buoys
Conceptual diagram of directional spectra at the offshore boundary