3.Research on Storm Surge and Wave Disasters
Background and Objectives
In recent years, human lives and properties in coastal areas have been severely damaged by extraordinarily huge hurricanes and typhoons worldwide, and hence effective countermeasures against coastal flooding are required. The objective of this research theme is to qualitatively and quantitatively investigate the mechanism of coastal flooding and resulting damage through field measurements, laboratory experiments and numerical simulations to propose effective countermeasures.
The following five topics are focused in this research theme.
- Offshore wave properties
For reducing damage induced by coastal flooding, a new system to effectively utilize offshore wave data obtained through the Nationwide Ocean Wave information network for Ports and Harbours, NOWPHAS, is investigated.
Furthermore, a numerical simulation model for predicting offshore waves is developed.
- Prediction of damage caused by flooding
Models for estimating wave transformation and wave pressure developed by PARI are improved and applied to the overtopping problem, to which the models were not previously applicable. The validities are examined based on laboratory experimental data.
- Prediction of structure deformation
For predicting the deformations of breakwaters and seawalls caused by coastal flooding, a numerical simulation model considering interactions among seawater, soil and structure is developed. A new soil improvement method is proposed to reduce the risk of structure failure.
- Influence of global warming on flooding
The influences of sea level rise and strengthened typhoons caused by global warming on the frequency and intensity of coastal flooding are numerically investigated.
Databases of water depths and numerical models are built and maintained.
Activities in FY 2010
The third generation of a wave assessment model of WAM is applied to the estimated wave height calculation for the 40 years from 1960 to 2000. Based on the results, we have studied the emergence characteristics of the waves in the sea area around Japan. In Nakagusuku port, the annual average heights of the waves from the 1st to the 3rd had no big differences in the 1960s. However in the 1970s in some years, the 1st average height was outstanding compared to the 2nd and 3rd. Since the 1980s, a trend can be seen in which the 1st annual average height became tremendously larger and years with the outstanding 1st height emerged frequently.
Changes in time of the annual 1st, 2nd, 3rd average wave height (bar graph)
In the development of oil spill simulation, a particle drifting model was proposed. Fay's equation, a conventional oil spreading model, was modified to fit the particle model by converting the time-dependent scale length into a repulsive velocity between oil particles.This modification enabled the
model to address a continuous oil spill as well as a flush spill.
The particle model, combined with STOC-ML, was applied to an actual oil spill incident at Taean, South Korea. An excellent reproduction of the oil drift at the site was confirmed.
An observed range in the oil spill incident at Taean South Korea and a calculation result of its drift