July 20, 2017
The United Nations Headquarters
New York, United States of America
I am pleased to give a key-note lecture through video at the Third United Nations Special Thematic Session on Water and Disasters in New York.
This year, we have seen devastating water-related disasters in many countries of the world including Saudi Arabia in February, Peru in March, Thailand in May and Sri Lanka and China in June. Extremely heavy rain also caused severe water-related disasters in Kyushu and many parts of Japan this month. I would like to pray for the repose of the victims of these and other disasters, and to express my deepest condolences and sympathy to their families and other affected people.
In my two lectures at the previous thematic sessions, I have reviewed the relation between human beings and water through historical experiences and lessons on water. Learning from past experiences and lessons is a shortcut to solving our current water issues including water-related disasters. Today, I will attempt to probe deeper into history to further uncover the relations between human beings and water. The focus here is how people have worked with water to enhance the benefits gained while reducing the threats from it.
Let me first touch upon the meaning of learning about water and disasters from history. Please look at this picture（Fig.1）. This is a stone monument built over 600 years ago in Minami Town, Tokushima Prefecture on the Japanese Island of Shikoku. Although the stone surface has been weathered and it is hard to read clearly, Shakamuni triads in Sanskrit characters, names of some 60 people, and the date of November 26th, the 2nd year of Koryaku Era are inscribed on the stone. This stone monument, called Koryaku-hi, is said to have been erected in the 2nd year of Koryaku Era or 1380. It records that sutras were buried underground and memorial services were conducted to pray for the repose of victims who had lost their lives in a huge earthquake and tsunami in 1361. The inscribed names are likely to be priests who transcribed sutras and those who contributed to the memorial services. This Koryaku-hi Monument is said to be the oldest existent monument that records a tsunami disaster in Japan.
The Koryaku-hi Monument is just a memorial stone that indicates the local occurrence of a single earthquake in the past. There are, however, numbers of monuments like this along the coast of Japan. This map is an example of disaster monuments and records in Shikoku Island (Fig.2). These collectively indicate an overall picture of the times and dates of disasters, heights of tsunamis, extent of disaster impacts, and so forth.
Disasters were recorded not only on monuments but also in documents. This picture (Fig.3) shows the record of the Hakuho Earthquake in 684 described in the Nihon-Shoki, the oldest official Japanese history book. Damage caused by the earthquake is shown on the right picture. The state of the tsunami along the coast of present Kochi Prefecture in Shikoku Island is described on the left picture. It says that the tidal wave swirled high, sea water filled the land, and boats were washed away. This is said to be the oldest record of a tsunami in Japan.
Please look at this picture (Fig.4). This is a matching scheme of disaster records from historical documents and geological records. Tsunami deposits are found as layers in geologic strata and treated as evidence of tsunami occurrence in certain periods. With these geological records alone, however, one cannot specify exactly what date and area the tsunami occurred. Similarly, the records of historical documents and monuments by themselves cannot prove the occurrence of a tsunami nor specify its height. If you combine those two records, however, you can identify fairly accurately the date, area and height of a tsunami that occurred hundreds of years ago.
The interval between large scale natural disasters such as earthquakes, tsunamis, and floods is often longer than the life span of a human being. We have to make ourselves prepared for mega-disasters by learning through historical records and documents. “Learning from history” is not an abstract rhetorical phrase but a concrete way to estimate, for example, the size and area of disasters that may come about in the future.
Now let us turn our eyes to the historical relations between water and people. Today, I would like to focus on how people have worked with water in order to reap benefits while reducing its threat. I shall examine cases from Japan and China.
I visited the Shingen Levee in Central Japan last autumn (Fig.5). The Shingen Levee was constructed along the Kamanashi River by Shingen Takeda, a prominent Japanese Warlord during the Period of Warring States in the 16th century (Fig.6). From its name, the Shingen Levee, you may imagine a long linear embankment. It is, however, not a line of levee structure but a holistic river control system in which various structures of different functions are cleverly installed (Fig.7). The system aimed to reduce floods and exploit the abundant flow of the difficult-to-control Kamanashi River which had been recurrently flooding at that time.
How did the Shingen Levee manage the floods of the Kamanashi River? Please look at this map (Fig.8). The map shows the layout of the Shingen Levee and related structures. Let us take a close look at the structures and their functions from upstream to downstream (Fig.9). The Kamanashi River discharges torrential water from the surrounding mountains into the Kofu Valley. The flood flow is first met by “Ishitsumidashi”, mount of layered stones, and is turned to the north to prevent flooding in the south (Fig.10). It is then divided into two by “Shogi-gashira”(Fig.11), a diversion structure that looks like a Japanese chess piece (Fig.12). The divided flow is guided through “Horikiri”, a deep channel dug in the middle of the river (Fig.13). The guided flow collides with “Takaiwa”, a natural hard cliff, dissipating its energy (Fig.14). The flow is met by a tributary called Mae-midai River and further loses its energy. Calmer water is slowly let flow into the hinterland through the opening of the levees. The intake structure for irrigation water is installed at this point (Fig.15) to avoid damage by flood flow and withdraw clearer water with less sand and silt.
I was deeply impressed by the way of working with water through the Shingen Levee system through which torrential floods were strategically guided along the geographical features, and eventually regulated by colliding with a high hill. People did not challenge the force of water but made use of it so that water behaves more friendlily to them.
Let me show you another example. This is the Ishiibi Weir which was constructed around 1620 (Fig.16). It is in Kyushu, the Southern Island of Japan. The Ishiibi Weir system also made use of the natural features of the area to manage the river. These include formations called Elephant’s Trunk and Goblin’s Nose (Fig.17). At a glance, the design of the Ishiibi Weir system may look different from that of the Shingen Levee system. However, you may notice that the two systems are almost identical if you follow the flow from upstream through downstream. The flow is turned to hilly areas at Elephant’s Trunk and divided by Goblin’s Nose (Fig.18). It loses energy by colliding with energy dissipating works called Arako. Less turbid water is withdrawn from the Ishiibi Weir while the rest of the flow merges with the main stream to further reduce its force. The process and the mechanism of flood energy reduction is very similar to that of the Shingen Levee.
You can see similar ways of working with water in other countries and regions. Dujiangyan（ドゥジアンイェン） in Sichuan（シーチュアン） Province, China is an ancient water management system built around 250 B.C (Fig.19). It has been in use for flood management, water utilization, and inland navigation for over 2,200 years and it is still working today. Let us see how the system works with water from upstream through downstream (Fig20). The flood flow of the Min River is met by diversion works of Yuzui（ユーズイ）, or Fish Mouth (Fig.20). It corresponds to Shogigashira or “Japanese chess piece” of the Shingen Levee System. The divided flow is led through a deep channel to collide with a high hill. Part of the decelerated, turbid flow is discharged over Feishayan（フェイシャヤン） or “Flying Sand Weir” to merge with the main stream. The remaining clearer water is let into the irrigation canals through Baopingkou（ボピンコウ） or “Bottle-Neck Channel” (Fig.20).
There is a striking similarity in the schemes of the Shingen Levee, the Ishiibi Weir, and Dujiangyan（ドゥジアンイェン） as shown here in a comparative map (Fig.21). Hydraulic maneuver starts from a water course fixing structure, followed by diversion works, a guiding channel, collision hills or works, discharge works of turbid water, and water inlet. The process is almost identical.
As we have seen here, people have carefully observed water and nature, found underlying natural principles, explored ways to guide water with available knowledge and tools, and realized their dream of making difficult-to-control water controllable. Their way of working with water is still valid today, and might suggest how in the future we should work with water.
Let me take another example of people working with water. Span of time and space is extended. Let me explore how underground water tunnels expanded their horizon.
Human beings have a long history of constructing underground water tunnels. The picture shown here is an underground tunnel which is part of the water supply network called Aflaj (or Falaj in singular form) in Oman (Fig.22). The oldest Falaj is said to have been built more than 2,500 years ago. Aflaj have been used to reduce evaporation and carry water effectively (Fig23). There are still more than 3,000 Aflaj transporting water for irrigation and domestic use, and the support of people’s lives and livelihoods (Fig.24).
As the tunnel boring technology made progress, the use of underground tunnels was expanded to drainage of sewage, rain water, and floods. Let us examine the case of Mexico City. The development of Mexico City was enabled by reclaiming lakes (Fig.25). The remaining part of the lakes can be seen in Xocimilco which I visited in 2006 (Fig.26). The city requires drainage as rain water flow into lowlands where the city is located. Large scale underground tunnel networks were developed in Mexico City to address the problem of frequent flooding. The main tunnels were built in the 19th and the 20th centuries. As the capital city continues to grow, additional tunnels are currently under construction (Fig.27). The growth of the city is supported by invisible water networks under the ground.
Also in the suburban areas of Tokyo, flood disaster risk has been substantially reduced by an underground tunnel river (Fig.28). I felt as if I were in a huge underground pantheon when I stood in the tunnel during my visit. The tunnel itself can temporarily store a substantial amount of river water which is drained out afterwards to reduce the flood peak. Advanced hydraulic knowledge is fully used, for example, to effectively drain water in the form of a spiral (Fig.29).
In Kuala Lumpur, the dual-use tunnel for road transportation and flood drainage is under operation (Fig.30). The tunnel called SMART has been under operation since 2007. The Advanced Information Technology tools including 200 CCTV cameras are used to ensure safety of the facility. SMART is unique in aiming to tackle two typical problems of traffic congestion and flooding that many cities of the world are faced with. I visited SMART last April (Fig.31), and passed through the tunnel by car. I was amazed by the grand design and practicality of the project.
This picture shows the cross sections of underground water tunnels from the ancient to modern period (Fig.32). The picture shown here is Falaj of Oman, the first drainage tunnel in Mexico City, the second one, the Underground River in Tokyo, and SMART in Kuala Lumpur. The concept of carrying water underground has not changed much in the last 2000 years. However, the development of science and technology enabled expansion of the facility in size and capacity, sophistication of flow controlling techniques, and diversification of objectives. The latest facility is certainly not the final form. I am expecting that they will continue to transform with further advancement of knowledge, tools, lessons, and experiences.
The 2030 Agenda for Sustainable Development was adopted at the United Nations in 2015. The Paris agreement on climate change, the Sendai Framework for Disaster Risk Reduction, and the International Decade for Action “Water for Sustainable Development” were also agreed upon. In the 2030 Agenda, SDG6 is dedicated to water. Water and disaster is highlighted in Target 11.5. The international community has successfully agreed on ambitious goals and targets related to water as well as disasters. It is time for action.
The road towards achieving these ambitious goals and targets appears long and difficult. However, human beings have worked with water effectively throughout history. People in every period of our history have tried best to use their knowledge, experiences, and available tools to make their dreams on water come true. Rather than challenging and competing with nature, people have come to terms with it. They skillfully diminished the fury of water and made best use of its endowment. Science and technology progressively enabled us to work with water in more effective manners to satisfy more diverse needs.
As our ancestors did, we can and should observe water and nature around us, consider the current relations between water and people, and harmonize between water and nature, and human beings, and make full use of our experiences, lessons, science and technology. This will open a new path towards the achievement of newly committed goals and targets related to water. I believe that this path is also the short cut towards our common dream of sustainable development, eradication of poverty, and regional stability and peace. Our common future stands on water. I together with you will keep working in every manner for the betterment of water.