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 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 subthemes:
- Oceanographic monitoring using an offshore wave observation network, high-accuracy meteorology and wave models
New information acquired via GPS-mounted wave buoys and other devices is analyzed, and an offshore wave database (including hindcasted data) is established 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, soil and structure deformations, with emphasis on the performance design of port and coastal structures. In these models the interactions between wave, 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 the mean sea-level and the occurrence frequency 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.
- Maintenance of Programs and Databases and Improvement of Systems
Programs and databases are maintained as required for the design of coastal structures and other purposes.
Activities in FY 2012
- Offshore wave monitoring data accumulated over more than five years by GPS buoys of the Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS) was used to investigate annual, interannual and spatial fluctuations in offshore waves, and compare them to data gathered by coastal wave gauges. Consideration was also given to ways of ascertaining directional spectra from the GPS buoy motions. Data from GPS wave meters and coastal tide gauges were also used to analyze the frequency spectrum of the 2011 Great East Japan Earthquake tsunami, which was then compared to the wave height and period of other tsunamis such as the one that travelled from Chile in 2010.
Data on monthly-mean significant wave heights gathered through
GPS buoys off the Pacific coast of the Tohoku region
- Calculations were carried out to simulate one-dimensional wave transmission over breakwaters with a variety of relative crest heights using a Boussinesq model incorporating a wave overtopping model. Moreover, calculations were carried out on wave monitoring data gathered inside and outside Kanazawa Port to simulate wave transmission over breakwaters, which occur frequently in winter. Then by examining the accuracy of these calculations we expanded the applicability to which Boussinesq model could be applied in calculating local wave fields.
Results of simulations based on wave spectra observed inside and outside Kanazawa Port