In the event of a tsunami, saltwater flows into rivers and water purification plants must stop taking water from rivers to prevent entry of saline water into the plant owing to potential damage to machinery and contamination of the system. This leads to interruption of water supply during disaster. In this study, a salinity transport simulation model that can carry out a three-dimensional salinity behavior analysis in a specific area and a horizontal two-dimensional tsunami propagation analysis simultaneously was developed to predict saltwater behavior in rivers during a tsunami. These models are structured so that the influence of the boundary of the 3D domain can be excluded without significantly increasing the calculation load. The model was used to simulate saltwater behavior in the Yodo River in Japan during a tsunami. The spatial distribution and temporal change of saltwater under various river flows were quantitatively predicted, and the effectiveness of possible countermeasures in diminishing the duration of water-intake shutdown and the presence of brackish water in upstream areas was assessed.

1. [1] Y. Yoshikawa, T. Abe, M. Nakatsugawa, and J. Funaki, “A Study of Salinity Intrusion by Tsunami in River,” J. of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), Vol.71, Issue 2, pp. I_403-I_408, 2015.
2. [2] R. Samejima, K. Yamano, N. Tanaka, T. Nakai, T. Mishima, and H. Sato, “Study on Influence for Water Intake in Yodo River Caused by the Tonankai-Nankai Earthquake Tsunami,” Proc. of Annual Meeting of Japan Society of Civil Engineers, Vol.62, pp. 573-574, 2007.
3. [3] H. Matsumiya, N. Yoneyama, N. Tanaka, R. Samejima, and H. Sato, “Numerical Analysis of Saltwater Behavior Caused by River-Runup of Tsunami in the Upstream Part of the Yodo River Weir,” J. of Natural Disaster Science, Vol.28, Issue 2, pp. 125-135, 2009.
4. [4] N. Yoneyama, H. Matsumiya, and R. Samejima, “Three Dimensional Numerical Analysis for Saltwater Behavior Caused by River-Runup of Tsunami in the Yodo River,” Advances in River Engineering, Vol.16, pp. 265-270, 2010.
5. [5] N. Yoneyama and M. Inoue, “Prediction Method for Water Temperature and Turbidity in Pumped Storage Reservoir Using 3D Numerical Simulation Code,” J. of Japan Society of Civil Engineers, No.684, II-56, pp. 127-140, 2001.
6. [6] W. J. Pringle and N. Yoneyama, “The Application of a Hybrid 2D/3D Numerical Tsunami Inundation-Propagation Flow Model to the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami,” J. of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), Vol.69, Issue 2, pp. I_306-I_310, 2013.
7. [7] W. J. Pringle, N. Yoneyama, and N. Mori, “Two-way coupled long wave – RANS model: Solitary wave transformation and breaking on a plane beach,” Coastal Engineering, Vol.114, pp. 99-118, 2016.
8. [8] N. Yoneyama, M. Matsuyama, and H. Tanaka, “Numerical Analysis for Locally High Runup of 1993 Hokkaido Nansei-oki Seismic Tsunami,” J. of Japan Society of Civil Engineers, No.705, II-59, pp. 139-150, 2002.
9. [9] C. W. Hirt and B. D. Nichols, “Volume of Fluid (VOF) Method for the Dynamics of Free Boundaries,” J. of Computational Physics, Vol.39, pp. 201-225, 1981.
10. [10] C. W. Hirt and J. M. Sicilian, “A Porosity Technique for the Definition Obstacles in Rectangular Cell Meshes,” Proc. of 4th Int. Conf. on Numerical Ship Hydrodynamics, 1985.
11. [11] The Editorial Committee of the Record of the Construction of the Yodogawa Estuary Barrage, “The Official Record of the Construction of the Yodogawa Estuary Barrage,” 1983
12. [12] Study Meeting on the Model of the Nankai Trough Great Earthquake, “The Second Report of the Study Meeting on the Nankai Trough Great Earthquake – Part of Fault Model,” Cabinet Office, Government of Japan, 2012.
13. [13] H. Nagashima, S. Sasaki, W. J. Pringle, and N. Yoneyama, “Numerical Assessment of Critical Locations for Tsunami Inundation,” J. of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), Vol.71, Issue 2, pp. I_509–I_514, 2015.
14. [14] Ministerial Ordinance on Water Quality Standards (online), http://law.e-gov.go.jp/htmldata/H15/H15F19001000101.html, 2003. [accessed September 1, 2015]
15. [15] Japan Meteorological Agency, “Ocean Observation Guidelines,” 1999.