Intrusion Distance and Flow Discharge in Rivers during the 2011 Tohoku Tsunami

Hitoshi Tanaka,Min Roh,Mikio Sasaki,Makoto Umeda,Nguyen Xuan Tinh,Kosuke Kayane,Nguyen Trong Hiep,Mitsukuni Tsuchiya,Seiki Kawagoe

doi:10.3390/jmse8110882

Abstract

On 11 March 2011, the Great East Japan Earthquake generated huge tsunami waves. Then, tsunami propagation occurred in rivers, resulting in further expansion of the flooded area. Full data sets of tsunami characteristics such as tsunami inland and river propagation distances as well as the river geometries from all rivers within the Tohoku District were compiled and analyzed. It was found that tsunami propagation distance in rivers was about 1.2 to 4.5 times that of the inland area. There was a good correlation between propagation distance in rivers and the river bed slope. Furthermore, new empirical formulae for calculating the damping coefficient of tsunami wave height and tsunami intrusion length were successfully derived based on the current comprehensive data sets covering a wide range of river geometry and bottom slope. Moreover, tsunami-induced flow discharge was evaluated by using measured water level variation.

Highlights

At 14:46 on 11 March 2011, the Great East Japan Earthquake occurred off Sanriku Coast near the oceanic trench located on the boundary between the Pacific Plate and North American Plate
Abe [8] analyzed measured data of water level in five large rivers during the Central Sea of Japan Earthquake in 1983 and concluded that tsunami waves can reach several kilometers upstream of rivers and the tsunami peaks have resulted from resonance within the river
Tanaka et al [9], based on a field investigation along Sri Lankan rivers affected by the 2004 Indian Ocean Tsunami, indicated that the tsunami intrusion into a small river upstream caused flooding and local damage, extending the impact of the tsunami to the upstream cities

Summary

Introduction

At 14:46 on 11 March 2011, the Great East Japan Earthquake occurred off Sanriku Coast near the oceanic trench located on the boundary between the Pacific Plate and North American Plate. In terms of numerical studies, Viana-Baptista et al [14] and Yeh et al [15] made a numerical simulation of tsunami propagation into the Tagus estuary, Lisbon, and a hypothetical case in the Columbia River, respectively. They showed that tsunami propagation in a river causes severe flooding in the upstream area far from the river mouth. The field measurement data of river tsunami intrusion was collected for numerous rivers from three prefectures in Tohoku District, including Iwate, Miyagi, and Fukushima Prefectures, in order to carry out a synthetic investigation of tsunami intrusion into rivers. The outcome of this study is valuable for the coastal and river authorities in order to reduce the tsunami wave impact on local residents, and on infrastructural damages, in the future

Study Area and Data Compilation

Tsunami Intrusion Distance

Evaluation of Tsunami Damping Coefficient

Methodology

Results and Discussion