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寒冷地域の河口域における津波災害とその影響評価手法に関する研究
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| Title: | 寒冷地域の河口域における津波災害とその影響評価手法に関する研究 |
| Other Titles: | STUDY ON TSUNAMI DISASTERS IN COLD-REGIONESTUARIES AND THEIR IMPACT ESTIMATION METHOD |
| Authors: | 阿部, 孝章 Browse this author |
| Issue Date: | 25-Sep-2014 |
| Publisher: | Hokkaido University |
| Abstract: | Only a few studies are conducted on tsunami run-up with ice-covered conditions in cold-regionestuaries. Quantitative assessment of the ice floe transport and dynamics on rivers, coasts andlakes and specifications of ice sheet during tsunami events are important considerations in designingriver engineering and other public works. Although the need for such targeting is clear enough,the prediction of ice dynamics in river channels, river mouths and coastal areas is hampered by thelack of reliable information on broken ice covers and accompanying tremendous number of ice floeproduction.The earthquake of a Moment Magnitude (Mw =) 9.0 that centered off the coast of Sanriku onMarch 11, 2011 at 14:46 (UTC+09:00) generated a series of tsunami waves, which devastated thecoastal areas throughout the Pacific Coast of Northern Japan. Shortly after that, a number oftsunami waves triggered by the earthquake were observed on the whole coast line of Hokkaido. Thetsunami did not do such serious damage in Hokkaido as they did in the Tohoku area, but intrusionswere confirmed to have occurred in many rivers. In addition, the tsunami was also characterized bythe breaking of river ice and a tremendous number of ice sheet deposits on the river channels andnear sluice ways. In order to investigate the characteristics of ice floes in riverine areas, we madeconcurrent and accurate measurements of ice and a series of field survey in multiple reaches of riverswhose mouths are on the Pacific Coast of Hokkaido island.In chapter 3, the propagation of the tsunami into rivers in Hokkaido, generated by the 2011 TohokuPacific Coast Earthquake, is described using data from water level gauges in rivers. The tsunami firststruck the Ohtsu (Tokachi River) and the Tottori (Shin-Kushiro River) gauge stations at the sametime around 15:47 (UTC+09:00). The tsunami also intruded other six Class-1 rivers in Hokkaido.Detided water levels, recorded at the stations within these rivers, show the tsunami intruded severaltimes, not once. Then a one-dimensional numerical method is applied to the simulation of the tsunamipropagation up Tokachi River and Shin-Kushiro River in order to investigate the spatial waveformsand wave dispersion phenomena. The water levels estimated by the present method agreed well withthose observed in both rivers, and significant differences were found in dispersive wave trains at thewave fronts in each river.The tsunami of 2011 Tohoku Pacific-Coast Earthquake broke river ice and transported thousandsof meter-long ice floes in rivers whose mouths are on the Pacific Coast. The objectives of capter 4are to investigate sizes and areas of ice floes by using photographs obtained during the field surveyconducted after the tsunami and, on that basis, to estimate the masses of floes transported by thetsunami. Sizes and areas of them were measured using an image analysis technique and ice thicknessesare measured on site. In an extreme case, the estimated masses were approximately 1.2 to 20 ton onaverage and 5.0 to 170 ton as maximums of floes retained near the bridge piers. This work highlightsthe potential risks of ice floes, which can be hazardous to river structures such as bridge piers.In chapter 5, the interaction is detailed between the dispersive wave train and ice floe in tsunamiinducedwave propagation upstream in rivers. First we conducted hydraulic experiments to investigatethe effects of ice floe length and thickness using field observation data obtained when river ice breakupand scattering occurred. We measured transportation velocities of ice floes using an image analysistechnique. Second, particle based numerical simulation was conducted, by which we can easily handlewith violent free surface motion and ice floe movements. Direct comparisons of experimental photosand their corresponding simulation snapshots are made in terms of the reproduced waveforms andthe ice floe displacement. This work clarifies the mechanism of ice floe movements when tsunami-I -propagation upstream in a river occurs.In chapter 6, a tsunami absorbing pile for a sluice gate is proposed. In the event of tsunamigenerated by the 2011 Tohoku Earthquake, videotaped imagery showed the tsunami which propagatedinto Shin-Kushiro River struck a sluice gate with wave breaking. The main aim of this chapter isto develop a 3D particle based simulation model for analysis of interaction between river-tsunamiand river facilities such as sluice gates. The model is applied to the estimation of wave impact onthe sluice gate. Two cases of installation of tsunami absorbing piles are considered to confirm theireffectiveness for attenuation of wave impact load on river structures.The results of the above-mentioned studies and findings can be an effective tools for defining designstandards for riverine and coastal structures. In addition, numerical models used in this dissertationare applicable to various kinds of engineering problems related to ice-hazards during tsunami run-up. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 乙第6939号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Examination Committee Members: | (主査) 教授 清水 康行, 教授 泉 典洋, 准教授 渡部 靖憲 |
| Degree Affiliation: | 工学院 |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/57244 |
| Appears in Collections: | 学位論文 (Theses) > 博士 （工学）
論文博士 (Doctorate by way of Dissertation) > 工学院(Graduate School of Engineering)
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