Intensified Sediment Disasters in Japan: The 2011 Kii Peninsula Torrential Rain Disasters

Description:

The 2011 Kii Peninsula disaster was postwar Japan’s largest sediment and flood disaster. This book analyzes the disaster and the emergency response and subsequent disaster-prevention efforts. It also provides an international comparison and recommendations for mitigation and recovery efforts.

Although the scale and intensity of the disaster were expected to occur just once every 100 years, global warming has seen the intensification of such disasters around the globe. This book therefore presents an invaluable in-depth reference for readers on how to prepare for such a disaster, identify risk factors, and react accordingly. Contributors draw on the results of field surveys conducted by the Japanese Geotechnical Society at the time of the disaster and subsequent developments. First, they explain the factors that contributed to the disaster, including the meteorological, topographical, and geological conditions at the time of the disaster. They then describe the mechanisms of slope failure and damage caused by the slope failures across Nara, Wakayama, and Mie prefectures. Finally, they describe the post-disaster response, including the recovery and reconstruction and disaster-prevention and mitigation efforts in the affected area. Readers will therefore understand the importance of the contributing factors and be able to improve disaster mitigation strategies and response plans that will save lives and prevent damage to local infrastructure and economies.

This book is an invaluable resource for researchers, geologists, practicing engineers, and government officials who are involved in disaster prevention and response. Upper undergraduate and graduate students will also benefit from the book’s in-depth approach.

Preface

Japan is a nation of natural disasters. Earthquakes, typhoons, torrential rains, heavy snowfalls, and volcanic eruptions are among the many causes. Our ancestors suffered and endured these disasters, and somehow managed to overcome them. It is no exaggeration to say that we Japanese are still struggling against natural disasters on a daily basis. On the other hand, it may be said that we are insensitive to environmental changes caused by global warming. It may be that because there are so many natural disasters, it is difficult to notice the increase in such disasters caused by global warming.

The year 2011 was an unforgettable year for the Japanese people. More than 20,000 people were killed by the 9.0 magnitude earthquake that struck off the Pacific coast of Tohoku on March 11, 2011. The Kii Peninsula Disaster, the subject of this book, occurred in September of the same year and claimed nearly 100 victims, making it a once-in-a-century disaster in terms of the scale of the rainfall and the amount of collapsed sediment. From 2011 until 2021, large-scale sediment and flood disasters occurred every year, each claiming dozens of victims. We believe that Japanese people themselves should pay more attention to the abnormality of this situation. Disasters are so familiar to the Japanese that they are not perceived as unusual. Behind the scenes, anomalies, such as the first time in the history of observation something has taken place, have been occurring frequently. An example is the location of where typhoons hit land. Typhoons that hit Japan usually make landfall in Kyushu, Shikoku, and the southern part of Honshu from the Pacific Ocean or the South China Sea. However, extremely unusual conditions emerged in August 2016, with Tropical Storm Chanthu (1607) and Tropical Storm Kompasu (1611) making landfall in Hokkaido directly from the Pacific Ocean, and Typhoon Lionrock (1610) in August 2016 making landfall in Iwate Prefecture in the northern Tohoku region from the Pacific Ocean. In addition, in the torrential rains that have occurred since 2011, abnormal amounts of rain have been observed at many locations in various regions, the most in recorded history. It is normal to think that some kind of change in weather conditions is taking place.

Here, I would like to discuss the notation of typhoons in this book. According to the Japan Meteorological Agency’s definition, a storm is defined as a “typhoon” if its maximum wind speed, which is the maximum value of the average wind speed over a 10-minute period, is 17 m/sec or higher. They are numbered according to the order of occurrence since the beginning of the year. On the other hand, international standards define typhoons differently. A “tropical storm” is defined as a storm with a maximum wind speed of 17–24 m/sec, a “severe tropical storm” as a storm with a maximum wind speed of 24–32 m/sec, and a “typhoon” as a storm with a maximum wind speed of 32 m/sec or higher. Typhoon No. 12 of 2011 or Typhoon (1112), the main subject of this publication, is referred to as “Severe Tropical Storm Talas” by international standards. In this publication, all typhoon designations follow the international standard.

Let me also explain a few technical terms related to sediment disasters. Sediment disasters are diverse. In this book, technical terms such as large-scale slope failure, debris flow, and landslide are frequently used. However, it is difficult to strictly unify these terms, to the extent that the definitions and terminology of these terms may differ slightly from one academic society to another. Many disaster-related terms used in newspaper reports and other media are not recognized as academic terms. The terms used in this book are those in standard use in academic societies. For simple definitions, please refer to Section 7.2.1 first.

This book was written under the circumstances described above. Although this book is written primarily for people outside of Japan, I hope that Japanese people will read it as well, in the sense that the effects of global warming should be taken a little more seriously.

Although the main theme of this book is sediment disasters, it also devotes many pages to flood disasters. However, the book does not focus on the hydrological aspects of flood disasters, such as flood flows, but mainly on the destruction of riverbanks and levees, and the destruction of bridges over rivers. In this sense, it can be said that this book is mainly concerned with sediment disasters.

The author specializes in geotechnical hazards. When analyzing slope failure phenomena, at a minimum, rainfall conditions, topographic and geologic conditions of the slope of interest, and the time of occurrence of the failure must be known. Merely describing collapse phenomena does not help with the challenge of predicting slope failure phenomena. The occurrence of the last collapse time is the most difficult factor to identify. For large-scale slope failures, methods have been developed to estimate the location and time of occurrence based on information from seismic intensity gauges installed throughout Japan, but for small-scale slope failures, the time of occurrence is often unknown. The topography and geology of the slope are not easy to ascertain. It is common for one slope to collapse while an adjacent one avoids collapse. However, it is often difficult to explain why. As mentioned, looking at sediment disasters analytically is not an easy task. This publication is the product of many members’ struggles with sediment disasters. We sincerely hope that it will be informative and useful to many of you.

Ryoichi Fukagawa

Ritsumeikan University

Table of contents :

Cover
Half Title
Title Page
Copyright Page
Contents
Acknowledgments
Preface
1. Introduction
1.1 Motivation
1.2 Kii Peninsula Disasters
1.3 Research and Analysis of Kii Peninsula Disaster
1.4 Purpose of This Book
1.5 Outline of This Book
References
2. Intensification of Sediment Disasters in the World and in Japan
2.1 What Happens in the World?
2.1.1 Global Warming and Extreme Weather
2.1.2 Sediment Disasters in the World
2.1.3 2009 Debris Flow Disaster in Xiaolin Village, Taiwan [18] 2.1.4 2010 Debris Flow Disaster in Zhouqu County, China [19] 2.1.5 2012 Philippine Typhoon Bopha Disaster [20-22] 2.2 What Happens in Japan
2.2.1 A Disaster-Prone Country
2.2.2 Sediment Disasters in Japan
2.2.3 2012 Sediment Disaster at Northern Kyushu [29,30] 2.2.4 2013 Debris Flow Disaster at Izu-Oshima Island [31,32] 2.2.5 2014 Debris Flow Disaster at Hiroshima [33,34] 2.2.6 2017 Heavy Rain Disaster at Northern Kyushu [37,38] 2.2.7 2018 Heavy Rain Disaster in Western Japan [39] 2.2.8 2019 Eastern Japan Typhoon Disaster [40] 2.2.9 2020 July Heavy Rain Disaster [41] 2.3 Summary
References
3. Rainfall Characteristics of Severe Tropical Storm Talas and Topographical and Geological Features of the Kii Peninsula
3.1 Introduction
3.2 Rainfall Characteristics Related to the Disaster
3.2.1 Rainfall Caused by Typhoon
3.2.2 Comparison of Heavy Rainfall Distribution and Disaster Concentration Areas
3.2.3 Transition of Rainfall Intensity and Return Periods
3.2.4 Precursors of Collapse and Preceding Rainfall
3.2.5 Relationship between Rainfall and Large-Scale Slope Failure
3.3 Topography and Geology
3.3.1 Topographical Outline
3.3.2 Geological Outline
3.3.3 Structure of Accretionary Complex
3.3.4 Summary
References
4. Disasters in Nara Prefecture
4.1 Introduction
4.2 Large-Scale Slope Failure
4.2.1 Tsubonouchi Area in Tenkawa Village
4.2.2 Nigoridani Area in Totsukawa Village
4.2.3 Nojiri Area in Totsukawa Village
4.2.4 Factors of Large-Scale Slope Failures in Accretionary Complexes
4.2.4.1 Vulnerability
4.2.4.2 Structural Orientation
4.2.4.3 Hydrologic Conditions
4.3 Surface Failure
4.3.1 Relationship with Rainfall
4.3.2 Topographic Features
4.3.3 Mechanism of Surface Failure
4.4 Damages along Rivers
4.4.1 Damage of Revetment Works and Hinterland
4.4.2 Damage of Bridges
4.4.3 Sediment Inflow
4.4.4 Inundation due to River Channel Blockage
4.4.5 Peculiar Example
4.5 Summary
References
5. Disasters in Wakayama Prefecture
5.1 Introduction
5.2 Geological Characteristics in the Southern Part of Wakayama Prefecture [1,2] 5.3 Characteristics of Rainfall That Caused Geotechnical Disasters
5.4 Large-Scale Slope Failures Occurred in Accretionary Prism
5.4.1 Topography and Geological Characteristics of the Collapsed Area
5.4.2 Large-Scale Slope Failures with Geological Structure Like Dip Slope
5.4.3 Large-Scale Slope Failure without Geological Structure Like Dip Slope
5.5 Surface Failures and Debris Flow in Igneous and Sedimentary Rocks
5.5.1 Kumano Acid Igneous Rocks [9-11] 5.5.2 Kumano Group
5.6 Damage to Structures around Rivers
5.6.1 Progress in River Improvement and Scale of Flood Damage
5.6.2 Damages Caused by ‘Unexpected’ Heavy Rain
5.6.3 Damage of the River Levee
5.6.4 Collapse of EPS Backfill
5.6.5 Bridge Damage (Pier Displacement, Overturning)
5.6.6 River Maintenance and Damage Caused by ‘Unexpected’ Heavy Rains
5.6.7 ‘Unexpected’ Heavy Rain and Damage to Structures around Rivers
5.7 Damage to Cultural Property
5.7.1 Cultural Properties of Wakayama and the Damage due to Severe Tropical Storm Talas
5.7.2 Damage to Kumano Nachi Taisha Shrine
5.7.3 Future Tasks for Disaster Prevention of Cultural Heritages
5.8 Summary
References
6. Disasters in Mie Prefecture
6.1 Introductions
6.2 Large-Scale Slope Failures
6.2.1 Large-Scale Slope Failure at Higashimata Valley
6.2.2 Conditions of the Kajiyamata Valley
6.2.3 Rainfall Conditions in the Vicinity of the Large-Scale Slope Failures
6.3 Surface Failures
6.3.1 Conditions of Surface Failures in the Higashi-Kishu Region
6.3.2 Relationship between Precipitation and Slope Failures at the Higashi-Kishu Region
6.4 World Heritage
6.4.1 Yokogaki Pass on the Iseji Route, Kumano Kodō
6.4.2 Damage to the Yokogaki Pass
6.5 River Disasters [7] 6.5.1 Omata River
6.5.2 Ido River
6.5.3 Kumano River and Onodani River
6.6 Summary
References
7. Slope Protection Measures in Japan and Restoration and Recovery Measures in the Kii Peninsula Disaster
7.1 Introduction
7.2 Slope Failure Protection Works in Japan
7.2.1 Classification and Definition of Slopes and Sediment Disasters
7.2.2 Outline of Slope Protection Works
7.2.3 Measures for Slope Failure
7.2.4 Measures for Rockfall
7.2.5 Measures against Bedrock Collapse
7.2.6 Measures for Landslide
7.2.7 Measures for Debris Flow
7.3 Slope Rehabilitation and Reconstruction Project in the Kii Peninsula Disaster
7.3.1 Slope Rehabilitation and Reconstruction Project in Nara Prefecture
7.3.1.1 Measures after a Major Collapse in the Akadani Area of Totsukawa Village [6-8] 7.3.1.2 Measures after a Major Collapse in the Nagatono Area of Totsukawa Village [6,7] 7.3.1.3 Measures after a Large-Scale Slope Failure in the Ui (Shimizu) Area of Gojo City [6,7] 7.3.2 Restoration and Reconstruction Projects in Wakayama Prefecture
7.3.2.1 Debris Flow Measures in the Nachi River Basin [6] 7.3.3 Restoration and Reconstruction Projects in Mie Prefecture
7.3.3.1 Measures after a Large-Scale Slope Failure in the Higashimata Valley Area [9] 7.3.3.2 Measures after a Large-Scale Slope Failure in the Kajiyamata Valley Area [9] 7.3.4 Cultural Heritage Restoration and Reconstruction Projects [10] 7.4 Summary
References
8. Disaster-Prevention and Mitigation Measures Following the Kii Peninsula Disaster
8.1 Introduction
8.2 Disaster-Prevention and Mitigation Measures Based on the Kii Peninsula Disaster
8.2.1 Monitoring Deep-Seated Landslide Risks in Totsukawa Village
8.2.2 Flood and Inundation Measures Taken by Shingu City and Other Local Governments
8.2.2.1 Non-structural Measures Based on Local Characteristics
8.2.2.2 Structural Measures to Speed Up Reconstruction
8.2.3 Development of Kiho Town’s Version of a Timeline
8.2.3.1 Effectiveness and Issues of Self-Help and Cooperation
8.2.3.2 The Kiho Town Timeline in Mie Prefecture
8.3 Initiatives by Road and Railway Operators
8.3.1 Highway Slope Health Diagnosis System during Heavy Rainfall
8.3.2 Examination of New Standards for Responses to Heavy Rainfalls on Train Operations
8.3.2.1 The Summary of Standards for Regulating Responses to Heavy Rainfalls on JR West Train Operations
8.3.2.2 Setting the Standards for Regulating the Response to Heavy Rainfalls on the JR West Train Operations
8.3.2.3 Meteorological Hazard Management System
8.4 Summary
References
9. Response to Sediment and Flood Disasters Caused by “Unexpected” Heavy Rainfall and Lessons Learned
9.1 Introduction
9.2 Consider the “Unexpected”
9.3 Recommendations on Disaster Forms
9.3.1 Sediment Disasters
9.3.1.1 Know the Relationship among Rainfall Patterns, Geologic Conditions, and Sediment Disasters
9.3.1.2 Predict Sediment Disasters
9.3.1.3 Build Partnerships for Sediment Disaster Mitigation
9.3.1.4 Identify the Disaster Resilience of the Target Site and Utilize a Monitoring System
9.3.2 Flood Disasters
9.3.2.1 Learn from Past Flood Traces and History
9.3.2.2 Pass on Local Flood Lore to Future Generations
9.3.2.3 Recognize the Possibility That “Unexpected” Events May Occur
9.3.2.4 Know the Capabilities and Limitations of Current Flood Protection Measures
9.3.2.5 Know the Functions and Limitations of Facilities around Rivers during Floods
9.3.2.6 Recognize the Importance of Facilities around Rivers during Floods
9.4 Recommendations on External Forces That Caused the Disaster
9.4.1 Rainfall
9.4.1.1 Consider Disaster-Prevention Measures in Response to Rainfall Patterns
9.4.2 River Water Level
9.4.2.1 Analyze the Situation, and Build an Evacuation System Based on Rainfall Data over a Wider Area
9.5 Recommendations for Disaster Emergency Response and Recovery Activities
9.5.1 Establish a System That Allows Both the Public and Private Sectors to Respond Immediately to Assess the Actual Damage in the Event of a Large-Scale Disaster
9.5.2 Establish a Disaster-Related Information Database
9.5.3 Utilize the Experiences and Information of Those Who Have Responded to Disasters
9.5.4 Organize a Manual for the Findings Related to Geological Investigations Accumulated at Large-Scale Slope Failure and Debris Flow Sites
9.6 Proposals for Emergency Response Technologies
9.6.1 Record and Preserve the Location and Magnitude of the Disasters
9.6.2 Establish a Restoration Plan for the Facility Based on the Actual Disaster Conditions
9.6.3 Evacuate to an Appropriate Evacuation Site in a Timely Manner
9.6.4 Conduct Disaster Drills That Sustain Residents’ Interest
9.7 Proposals for the Preservation of Cultural Heritage
9.7.1 Develop a Centralized Management System and Legislation for the Conservation of World Heritage Sites
9.7.2 Form a Common Understanding of Cultural Heritage Disaster Prevention
9.7.3 Improve the Efficiency of Cultural Heritage Maintenance Work
9.7.4 Consider Crisis Management for Important Cultural Heritage
9.7.5 Consider Cultural Heritage Disaster Prevention Multilateraly
9.7.6 Improve the Level of Disaster Preparedness by Use of Monitoring Technology
9.7.7 Create a Social Consensus That Cultural Heritage That Cannot Be Fully Restored Is also Valuable
9.8 Recommendations for Local Residents
9.8.1 Recognize That Disasters Can Occur Anywhere
9.8.2 Prepare for Disasters on a Daily Basis
9.8.3 Enhance Local Disaster Preparedness
9.8.4 Communicate the Experience of the Disaster
9.8.5 Consider Disasters as Tourism Resources
9.9 Summary
Reference
Index