# Development of a Practical Evaluation Method for Tsunami Debris and Its Accumulation
## 5 Conclusions  
We used a previously developed method for evaluating the thickness distribution of tsunami debris that uses tsunami computation results and static parameters used for tsunami numerical analysis, including digital elevation models and land use information. Accumulated tsunami debris thicknesses were obtained by LiDAR in inundated regions immediately after the 2011 Tohoku earthquake tsunami. Using this evaluation method, we successfully reproduced tsunami debris accumulation trends. Then, we developed an empirical building fragility function related to the production of debris that tunes damage generation by the tsunami by taking into account the topographic gradient and the proportion of robust buildings. Using these empirical evaluation models for debris accumulation and building damage with conventional tsunami numerical analysis data, we carried out practical tsunami debris predictions for Owase City, Mie Prefecture, which is a potential disaster area for a Nankai Trough mega-earthquake. The results of this prediction indicated that, in the case of a huge tsunami exceeding 10 m in height at the coast, debris was likely to accumulate thickly along the inundation boundary, an area often supposed to be safer than areas nearer to the coast because the inundation depth is shallower there. These results indicate that it is insufficient to characterize the tsunami hazard by inundation area and inundation depth alone when predicting the hazard of a huge tsunami; moreover, more practically, it is necessary to predict the hazard based on the effect of tsunami debris. The future work of this research will be to enhance the applicability of the debris prediction method. The applicability of the proposed debris prediction has limitations because it is an empirical equation based on the actual launch of tsunami debris in the via coast region. The proposed method is applicable to Owase in this study, but it is not applicable to a plain coast. In order to obtain a more universal prediction method, it is necessary to extend the applicability of the debris prediction by effectively using the actual debris data of the Sendai Plain, which was used to construct the building damage function in this research. Moreover, it will be necessary to develop a tsunami fire prediction model by coupling it with a fire spread model [25]. It will be possible to provide more realistic predictions of tsunami disasters. Conceptualization, K.I. ; methodology, K.I. ; software, K.I., T.H. and Y.M. ; validation, K.I. ; resources, K.I. ; data curation, K.I., N.T., and T.M. ; writing--original draft preparation, K.I. ; writing--review and editing, K.I. ; visualization, K.I., T.H., and R.O. ; supervision, T.M. ; project administration, N.T. and T.M. ; funding acquisition, N.T. and T.M. All authors have read and agreed to the published version of the manuscript. **Funding:** This study was supported by Grant-in-Aid for Scientific Research (B) Number 19H02324 from the Japan Society for the Promotion of Science, and also partly by the \"Research project for compound disaster mitigation on the great earthquakes and tsunamis around the Nankai trough region\" of the Ministry of Education, Culture, Sports, Science, and Technology Japan (MEXT). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original LiDAR data for DSM and DEM was provided by Iwate Prefecture. The detailed building information in the Owase city area was provided by Owase City. We used information on building damage caused by the 2011 Tohoku-oki earthquake tsunami from the Reconstruction Assistance Survey Archive by the Ministry of Land, Infrastructure, Transport, and Tourism of Japan. **Acknowledgments:** We are grateful to two anonymous reviewers for their constructive and attentive comments. We express our appreciation to providing LiDAR data for DSM and DEM by Iwate Prefecture, also providing the detailed building information in the Owase city area by Owase City.