Research PaperNo Access

MITIGATING TSUNAMI DAMAGE BY PROMOTING GROUND EROSION

National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, 1–1–1, Umezono, Tsukuba, Ibaraki 305–8563, Japan

Graduate School of Agricultural Science, Kobe University, 1–1 Rokkodai, Nada, Kobe, Hyogo 657–8501, Japan

E-mail Address: takegawa-naoki@aist.go.jp

Search for more papers by this author

Yutaka Sawada

https://orcid.org/0000-0001-5517-3345

Graduate School of Agricultural Science, Kobe University, 1–1 Rokkodai, Nada, Kobe, Hyogo 657–8501, Japan

E-mail Address: sawa@harbor.kobe-u.ac.jp

Corresponding author.

Search for more papers by this author

, and

Toshinori Kawabata

Graduate School of Agricultural Science, Kobe University, 1–1 Rokkodai, Nada, Kobe, Hyogo 657–8501, Japan

E-mail Address: kawabata@kobe-u.ac.jp

Search for more papers by this author

https://doi.org/10.1142/S179343112150007XCited by:1 (Source: Crossref)

Abstract

To reduce the damage caused when a tsunami overflows coastal dikes, this study performs hydraulic experiments and numerical simulations and proposes a new method for slowing the tsunami by intentionally eroding parts of the ground. The effectiveness of the proposed method is assessed, velocity-reduction mechanism is clarified, and reduced tsunami velocity is predicted. Using crushed expanded polystyrene (EPS) as the ground material, vertical erosion is enhanced and a large depression is formed that changes the flow from supercritical to subcritical, thereby decelerating it. Assuming a constant tsunami overflow rate, the tsunami velocity after deceleration can be predicted with $\sim 20 %$ $\sim 20 %$ uncertainty.

Keywords:

References

Hager, W. and Bretz, N. [1986] “Hydraulic jumps at positive and negative steps,” J. Hydraul. Res. 24(4), 237–253. Crossref, Web of Science, Google Scholar
Hjulstrom, F. [1935] “Studies of the morphological activity of rivers as illustrated by the River Fyris,” Geol. Inst. Upsalsa 25, 221–527. Google Scholar
Iwagaki, Y. [1956] “Hydrodynamical study on critical tractive force,” Trans. Jpn. Soc. Civil Eng. 41, 1–21 (in Japanese). Google Scholar
Iiboshi, T., Maeno, S., Yosida, K., Takata, D. and Yamamura, A. [2015] “Effects of landward slope protection and toe protection work shape at coastal dikes on landward bed scouring caused by tsunami overflow,” Proc. of 36th Int. IAHR World Congress, Hague, Netherlands, pp. 4103–4111. Google Scholar
Kato, F., Suwa, Y., Watanabe, K. and Hatogai, S. [2012] “Mechanisms of coastal dike failure induced by the Great East Japan Earthquake tsunami,” Proc. of 33rd Int. Conf. Coastal Engineering, Santander, Spain. https://doi.org/10.9753/icce.v33.structures.40 Crossref, Google Scholar
Kawasaki, K. [2012] “Fundamental characteristics of tsunami and tsunami disaster due to the 2011 off the Pacific Coast of Tohoku Earthquake,” Jpn. Soc. Multiph. Flow 26(1), 11–18 (in Japanese). Crossref, Google Scholar
Kiri, H., Nakaya, T., Azechi, I. and Matsushima, K. [2015] “Effect of the tsunami dissipation facility that modeled a pool at the toe of back slope of the coastal levees,” J. Jpn. Soc. Civ. Eng., Ser. B1 71(4), I_1369–I_1374 (in Japanese). Google Scholar
Mikami, T., Shibayama, T. and Esteban, M. [2012] “Field survey of the 2011 tohoku earthquake and tsunami in Miyagi and Fukushima Prefectures,” Coast. Eng. J. 54(1), 1–26. Link, Web of Science, Google Scholar
Mitobe, Y., Adityawan, M. B., Tanaka, H., Kawahara, T., Kurosawa, T. and Otsushi, K. [2014] “Experiments on local scour behind coastal dikes induced by tsunami overflow,” Proc. 34th Int. Conf. Coastal Engineering, Seoul, Korea. https://doi.org/10.9753/icce.v34.sediment.62 Crossref, Google Scholar
Moore, W. and Morgan, C. [1957] “The hydraulic jump at an abrupt drop,” J. Hydraul. Div. 83(6), 1–21. Google Scholar
Ohtsu, I. and Yasuda, Y. [1991] “Transition from supercritical to subcritical flow at an abrupt drop,” J. Hydraul. Res. 29(3), 309–328. Crossref, Web of Science, Google Scholar
Rajaratnam, N. and Ortiz, N. V. [1977] “Hydraulic jumps and waves at abrupt drops,” J. Hydraul. Div. 103(HY4), 381–394. Crossref, Google Scholar
Takegawa, N., Sawada, Y. and Kawabata, T. [2020a] “Geogrid-based countermeasures against scour behind coastal dikes under tsunami overflow,” Mar. Georesour. Geotechnol. 38(1), 64–72. Crossref, Web of Science, Google Scholar
Takegawa, N., Sawada, Y. and Kawabata, T. [2020b] “Scour reduction in sand beds against vertical jets by applying sheet-like countermeasures,” Mar. Georesour. Geotechnol. https://doi.org/10.1080/1064119X.2020.1737893 Crossref, Web of Science, Google Scholar
Tanimoto, R., Tokida, K., Kitagawa, H. and Araki, S. [2012] “Investigation on resistance of earth bank and reduction by dug pool against tsunami,” J. Jpn. Soc. Civ. Eng. Ser. B2 68(2), I_316–I_320 (in Japanese). Google Scholar
Tanimoto, R. and Tokida, K. [2012] “Study on structure of dug pool eroded by tsunami flood and its tsunami reduction function,” Int. Symp. Earthq. Eng. 1, 143–150. Google Scholar
The OpenFOAM Foundation [2019] “OpenFOAM User Guide version 7,”. Google Scholar
Tokida, K. and Tanimoto, R. [2014] “Lessons for countermeasures using earth structures against tsunami obtained in the 2011 Off the Pacific Coast of Tohoku Earthquake,” Soils Found. 54(4), 523–543. Crossref, Web of Science, Google Scholar