Field experiments were conducted from July 14, 2009 to Nov. 2, 2009 to investigate correlation between sound pressure levels and wave heights at the Hasaki coast, Ibaraki, Japan. From the results, we proposed an equation for estimating significant wave height using sound pressure level and difference in percentile noise level of coastal environment sound. The results of the proposed equation show a good correspondence to the observed results (R = 0.87). Also, the magnitude of the difference in percentile exceeded noise level of coastal environment sound has negative correlation with the significant wave period.
The amount of sand supply from river basin to coast is strongly influenced by hydrological processes in the basin. In this paper, hydrological statistical analyses using annual maximum daily precipitations and river discharges were executed in the Tenryu River basin. Long-term precipitation data at representative three stations were evaluated, in which mean precipitation data of the Tenryu and the Keta River basin during middle-term were checked. Then middle-term river discharge data at three sites along the main stream and one site along the Keta river were validated. It was found that most of hydrological data in the Tenryu River basin are decreasing over time. It was then demonstrated that sand supply from the basin might be decreasing secularly in addition to anthropogenic impacts due to dam constructions or sand and gravel extractions.
Lessons of the catastrophic disaster due to the 2011 Tohoku Earthquake Tsunami call for importance of integrated disaster mitigation strategies over the entire coastal regions. Under this strategy, coastal protection works such as seawalls are expected to avoid fatal collapse and to reduce the energy of overflowing tsunami as much as possible. Quantitative evaluation of such disaster mitigation function of the seawall is therefore essentially important for optimum designs of the integrated disaster mitigation strategies. This study applied numerical models for predictions of tsunami inundation around seawall with various heights and investigated how various disaster factors can be reduced by seawalls. The model was applied to Nakoso and Sen-nan regions attacked by the 2011 tsunami. It was found through the analysis that the relative height of the seawall against the height of attacking tsunami is one of the most dominant factors to determine the level of disaster reduction and this reduction level becomes insignificant when the tsunami height doubles that of seawalls. It was also found that non-uniformity of the heights of seawalls decreases the overall function for energy reduction of the overflowing tsunami and the damage level behind the seawall is dominantly governed by the lowest heights of such non-uniform seawalls.
The present study develops the real-time tsunami inundation prediction method which predicts tsunami arrival time, height, and inundation based on the tsunami waveforms observed at offshore locations such as GPS Buoys. This method consists of three components: estimation of tsunami source by the inversion method, prediction of tsunami waveforms in coastal areas by the linear superposition of database, and prediction of inundation by tsunami numerical calculation accelerated by GPU computing. Moreover, the developed method is applied to the numerical experiment replicating the historical event and to the actually observed data during the 2011 off the Pacific coast of Tohoku Earthquake. The results indicate that the tsunami arrival time, height, and inundation caused by the first wave can be predicted with around 50 % errors in five minutes after the maximum value of the first wave is observed at offshore locations.
The Hokkaido tsunami joint survey group performed a questionnaire survey on tsunami evacuation behaviors of coastal residents in Hokkaido after the event of the 2011 Tohoku earthquake tsunami. This paper presents this survey result summarized in terms of evacuation procedures, conscious for the tsunami disaster and safety as well as disaster prevention education. It is found that a regional evacuation action plan requires being suitable to local landform and social composition, and that further enhancement of disaster prevention education is also necessary for minimizing the human damages owing to tsunamis expected in near future.
A global stochastic tropical cyclone model (GSTM) has been developed as a means for generating a large number of artificial tropical cyclone (TC) samples considering temporal correlation of each value of track, central pressure, and translation speed. This paper presents structure of the GSTM and the results of its verification in detail. A stochastic model is sensitive to approximations of the joint probability distribution functions (PDFs) of TC parameters and temporal correlations. A new method, which employs a principal component analysis and a cluster analysis, has been introduced for approximation of joint PDFs and improves reproducibility of TC parameters. The simulation results were compared with historical observational data in the northwestern Pacific. The grid-averaged mean values and distribution patterns of PDFs of TC parameters fairly agree with observation data.