Universal Value of Tateyama Sabo from the Viewpoint of National Resilience

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1 Universal Value of Tateyama Sabo from the Viewpoint of National Resilience Masayuki HAYASHI 1, Shusaku SHIIBA 2, Taku OSADA 3,*, Masayuki TODA 4 1 Public Works Department, Toyama Prefectural Government, Japan (1-7 Shin-Sogawa, Toyama-shi, Toyama , Japan) 2, 3, 4 Sediment Control Division, Public Works Department, Toyama Prefectural Government, Japan (1-7 Shin-Sogawa, Toyama-shi, Toyama , Japan) *Corresponding author. taku.osada@pref.toyama.lg.jp A group of precious sabo facilities with long histories exist along the Joganji River that flows through the Tateyama Caldera located in the southeastern part of Toyama Prefecture, north of the Northern Japan Alps. Those facilities convey the wisdom and efforts of people devoted to protecting Toyama Plain from massive sediment discharge, an undertaking which has continued for over 100 years for the purpose of enhancing national resilience. After a number of challenges and failures, sabo works in the Tateyama area greatly improved the safety of the river basin. We consider it is meaningful to focus on Tateyama Sabo s history and values and convey them to future generations as a shared heritage. It gives us an important lesson, particularly when improving national resilience against natural disasters under the growing influence of global warming. In this report, we attempt to verify the outstanding universal value of those facilities from the viewpoint of national resilience by looking back on their history and introducing their characteristics. Key words: Tateyama Sabo, watershed management, modern sabo, outstanding universal value, world cultural heritage 1. JOGANJI RIVER AND ITS DISASTER HISTORY The Joganji River, with its headwaters located at the Tateyama Caldera, is a steep river, measuring 56 km in length, with a catchment area of 368 km 2 and an average gradient 1/30. (Fig.1) The Tateyama Caldera, formed by the seismic activities of the Atotsugawa fault and the erosion caused by heavy rain, is categorized as an erosion Location 位置 map 図 Toyama Prefecture Route 8 Toyama bay JR Hokuriku Line Hokuriku Shinkansen line Legend Basin boundary River Municipal boundary Toyama City Joganji river basin Toyama Plain Kamiichi Town Location map Joganji River Tateyama Town Hongu Sabo Dam Route 41 Shiraiwa Sabo Dam A series of Dorodani Sabo Dams Mt. Tonbi Sea of Japan Mt. Tonbi Niigata Pref. Atotsugawa Fault Toyama Pref. Joganji river basin Northern Japan Alps Tateyama Sabo Tateyama Caldera Ishikawa Pref. Fukui Pref. Gifu Pref. Nagano Pref. Gifu Pref. Nagano Pref. Fig.1 Location map of Tateyama Sabo

2 caldera. It has a large oval-shaped depression, 6.5 km from east to west and 4.5 km from north to south. The Tateyama Caldera s geology is made up of subaqueous volcanic rock ejected from submarine volcanoes and volcanic ejecta (tuff) produced by volcanic activities after uplifting, and they spread over the granodiorite bedrock. The rocks in the caldera are very argillaceous due to hydrothermal alterations and weathering actions, thus producing a weak and easily collapsible geology. The climate of Toyama Prefecture is similar to that of the Sea of Japan, with large amounts of precipitation in the winter. As high mountain ranges exist at 20 to 30 km from the coast, ascending air currents are generated along the mountain slopes. Combined with this orographic rainfall, the annual rainfall of the mountain area such as the Tateyama Caldera, is more than 5,000 mm. In 1858, the Hietsu Earthquake, with an estimated magnitude of 7.1, occurred around the Atotsugawa fault as the hypocenter. Due to this earthquake, Mt. Tonbi located in the Tateyama Caldera collapsed and formed a landslide dam. This dam burst twice and the resulting debris flow hit the Toyama Plain in the downstream. According to the record, 1,600 houses were swept away, 140 persons were killed, and about 7,000 affected. Due to the 1858 earthquake, it is said that at Mt. Tonbi, about 400 million m 3 of sediment was generated, and half of it flowed out, causing damage downstream. Though estimations vary, approx. 100 to 200 million m 3 of unstable sediment still remains in the Tateyama Caldera. According to the literature, 22 floods occurred in 150 years prior the Hietsu Earthquake, but 79 floods occurred in 150 years after the earthquake(fig.2), a roughly four time increase over the same period. Eventually, the Joganji River came to be called the most violent river in Japan. Fig.2 Frequency of flooding at the Joganji River 2. BACKGROUND OF COUNTERMEASURES FOR SEDIMENT DISCHARGE IN THE JOGANJI RIVER The heavy rain that hit the entire Toyama prefecture in July 1891 caused flooding and levees in the Joganji River to rupture. It became a serious flood disaster, inundating Toyama City for 21 days and forcing 150 households to move to other villages in the prefecture or as far as the remote Hokkaido prefecture. In order to prevent another disaster, the Toyama prefectural government invited Johannis de Rijke, a Dutch engineer who was working for Japan s central government, to get advice about the countermeasures. After seeing the collapsed site at the Tateyama Caldera upstream of the Joganji River, de Rijke said There is nothing we can do about this site and The whole mountain should be covered with copper plates, and left the site untouched. Instead, he advised to take measures in the downstream area, such as merging ditches, diversion of rivers, and construction of open levees. Because of this approach, a huge volume of sediment remained in the upstream of the Joganji River and damage did not stop even after the completion of a river improvement project led by de Rijke in Seeing repeated disasters, the Toyama prefectural government decided to confront sediment at the devastated headwater area. In 1906, they embarked on sabo projects at the Tateyama Caldera to prevent sediment discharge into the Joganji River. The common works at the time were hillside works, revetment works, and stepped sabo dams built by means of stone masonry. Even during the construction, disasters were repeated every year and many facilities were damaged. Faced with technical and financial difficulties of the sabo projects for the Tateyama Caldera, the Toyama prefectural government and the prefecture's private sector jointly asked the central government to undertake those projects as national projects (In those days, the national project was limited to the project whose interest spread over two or more prefectures). In 1924, the Sabo Law was amended and sabo projects at the Tateyama Caldera began to be carried out under the direct control of the central government. Masao Akagi, who is referred to as the Father of modern sabo, was appointed as the first director of the Tateyama Sabo Office. Despite dangers, he himself walked through the proposed site of the Shiraiwa Sabo Dam for about a month and prepared the Joganji River Sabo Construction Plan.

3 3. TATEYAMA SABO S REPRESENTATIVE FACILITIES AND THEIR FEATURES 3.1 Shiraiwa Sabo Dam The Shiraiwa Sabo Dam, located about 42 km upstream of the mouth of Joganji river where the outlet of the caldera is located, was designed by Masao Akagi in order to raise the deeply eroded riverbed and stabilize the Tateyama Caldera and prevent sediment discharge that became active after the Hietsu Earthquake in It is a key sabo dam of the Joganji River Sabo Construction Plan prepared by Akagi and constructed for stabilizing the hillside of the collapsed headwater area and the riverbed. Construction was started in 1929 by the Tateyama Sabo Office of the former Home Ministry and completed in It is regarded as a structure with high academic value which shows one of the technological goals of modern sabo facilities. It became the first sabo facility designated as an important cultural property of Japan in 2009 and has been placed under protection since then. At the site of the Shiraiwa Sabo Dam, the Toyama prefectural government had been constructing a sabo dam before Akagi s construction plan. But, the dam was destroyed twice by floods in 1919 and 1922(Fig.3). It is said that, due to those floods, the left bank which is made up of deposited volcanic ejecta lowered about 39 m compared with the right bank, which has exposed bedrock. Fig.3 Damage to the former Shiraiwa Sabo Dam, 1922 The riverbed (slope) of the section covered by the Construction Plan was very steep (gradient of 1/5 to 1/7) and almost no bedrock was exposed on the riverbed so the riverbed was easily prone to erosion. The flow also tended to meander (bent flow) and scour the spurs. Under these conditions, flooding was considered likely to cause mountain slope failure. As a result, Akagi laid out (groundsill) sabo dams and bank revetment to raise the riverbed to its level prior to the 1922 flood to increase the width of the river to slow down flow and attenuate the eroding force of water. At the same time, he also immobilized the sediments in front of the spurs to stabilize the mountain slopes. Then he decided to construct the Shiraiwa Sabo Dam as the core dam facility at the only place in the Plan section where the bedrock was exposed, and considered which option he should take to raise a deeply eroded riverbed: one dam with high rise dam or multiple stepped low rise dam. (1) A low height dam can be easily buried as the left bank at the site is at risk to collapse. (2) The deeply eroded river has small river width. Therefore, the low rise dam is unable to have an enough flow area. (3) To ensure the safety of the foundation, the flow area must be placed on the bedrock on the right bank, but this is impossible with a dam that is low in height. For these reasons, Akagi decided to construct one high rise dam. The dam height was determined to be 63 m. It was higher than a French sabo dam (8 m), and an Austrian sabo dam (max. 41m) as a sabo dam constructed before WWII. Concerning this, Akagi stated that In terms of cost and dam height, I would say that the construction of the Shiraiwa Sabo Dam is the largest sabo work in the world. In the 1930s, when the Shiraiwa Sabo Dam was constructed, the recommended gradient of the downstream slope of the dam body, namely, the ratio of vertical length to horizontal length, was 1:0.2. However, Akagi considered that applying 1:0.2 to a high rise dam such as the Shiraiwa Sabo Dam was uneconomical, and decided to adopt a different design for the overflow and non-overflow sections.for the left bank part of the dam, he did not adopt a gravity type concrete dam because the deposition of weak volcanic ejecta existed at the foundation. Instead, he adopted a fill type dam consisting of an embankment and checkerboard frames that protect the surface of the embankment.the upstream side of the fill type dam section was covered with revetments so that overflowing debris flow would not damage the downstream side. Several sabo dams were also built on the upstream to guide flowing water to the right bank where bedrock existed. (Fig.5) Those small dams were built at the sedimentation area formed by the Shiraiwa Sabo Dam. In that sense, they were mutually

4 complementary. Furthermore, noting the major earthquake in the Ansei Period, seismic design was adopted for the first time in Japan based on the theory Characteristics of gravity type sabo dams for water storage and their rational design method (Nagaho Mononobe, 1925). According to our survey, there is no other prewar (before the 1940s) sabo dam equivalent to the Shiraiwa Sabo Dam in terms of scale, structural complexity, and seismic design. (Fig.4- Fig.8) In order to carry out the construction safely and effectively, tracks were laid to carry construction materials up to the site. Construction equipments, such as derrick cranes and concrete mixers, were also introduced. As seen, a very modern construction technique was adopted compared with other sabo dams of the same period. Shiraiwa Sabo Dam Design details Catchment area 22.1 km 2 Design flood discharge 380 m 3 /s Gradient of original riverbed 1/7 Design sediment storage 1 million m 3 Dam length 76.0m Dam height (main dam) Overflow section 20.0 m Non-overflow section 63.0 m Altitude of overflow section 1,082 m Dam type Hybrid of gravity type rubble concrete and earth fill Right bank part Gravity type rubble concrete dam (front slope 1:0.2) Center part Gravity type concrete dam (front slope 1:0.64) Left bank part Earth fill dam (covered with checkerboard frames) Construction period (Source: 70-year History of Tateyama Sabo ) Fig.4 Shiraiwa Sabo Dam (completed in 1939) Overflow section Non-overflow section Gravity type rubble concrete dam Right bank 右岸 Gravity type rubble concrete dam Center Earth fill dam Left bank Revetments Right bank Checkerboard frames Left bank Fig.5 Shiraiwa Sabo Dam Plan view

5 Overflow section Gravity type rubble concrete dam Right bank Non-overflow section Gravity type rubble concrete dam Center Earth fill dam Left bank Fig.6 Shiraiwa Sabo Dam Sectional view Fig.7 The checkerboard frames 3.2 Hongu Sabo Dam The Hongu Sabo Dam is a large-scale sabo dam constructed in the midstream of the Joganji River (about 27 km from the mouth of the river) for sediment storage. Its construction was started in 1935 and completed in It was constructed by the Joganji River Dam Office of the former Home Ministry as part of the Joganji River Improvement Project. Construction of this dam was regarded as pre-work for the river improvement in the downstream and its primary purpose was to store sediment flowing from the upstream. The design sediment storage was 5 million m3, the largest in Japan. This dam was registered as a tangible cultural property of Japan in Despite its scale, the Hongu Sabo Dam was completed in just two years by mobilizing Fig.8 Structure of the checkerboard frames construction equipment such as towers, chutes, and concrete mixers. The large sedimentation area of this dam became an important research site to study sediment control by sabo dams, a budding research topic at the time. (Fig9,Fig.10) Hongu Sabo Dam Design details Catchment area km2 Design flood discharge 2,060 m3/s Gradient of original riverbed 1/43 Design sediment storage 5 million m3 Dam length m Dam height 22.0 m Altitude of overflow section 326m Dam type Gravity type rubble concrete dam (front slope 1:0.2) Construction period (Source: 70-year History of Tateyama Sabo )

6 Hongu Sabo Dam Main dam Fig.9 Hongu Sabo Dam Second auxiliary dam Fig.10 Hongu Sabo Dam First auxiliary dam Front apron Sectional view and front view (completed in 1937) 3.3 A series of Dorodani Sabo Dams A series of Dorodani Sabo Dams is made up of stepped sabo dams and hillside works which were constructed downstream of the seriously devastated Doro valley to prevent expansion of erosion. It consists of 3 bed sills, 20 sabo dams and hillside works. Located at the upstream of the Shiraiwa Sabo Dam, the Dorodani Sabo Dam was the first sabo dam undertaken by the Toyama prefectural government. It was first completed in 1916, but sustained devastating damage due to repeated heavy rains. Then, the construction was transferred from the Toyama prefectural government to the Tateyama Sabo Office of the former Home Ministry. The construction of the dams was started in 1930 and completed in 1938.

7 The combination of European-style stepped sabo dams and Japan s unique hillside works such as sodding work produced a distinctive effect. (Fig.11) Surrounded by trees and valley landscape, this sabo dam group is now a good example of achieving both disaster prevention and ecology. It was registered as a tangible cultural property of Japan in 2002(Fig.12). A series of Dorodani Sabo Dams Design details Catchment area 1.2 km 2 Design flood discharge 49 m 3 /s Gradient of original riverbed 1/4 Number of dams 20 Dam type Gravity type concrete dam (front slope 1:0.2) Construction period (Source: 70-year History of Tateyama Sabo ) Fig.11 The hillside of a series of Dorodani Sabo Dams 4. UNIVERSAL VALUE OF TATEYAMA SABO Flooding damage at the Joganji River increased after the Hietsu Earthquake in 1858, but the damage gradually decreased with the advancement of sabo works at the Tateyama Caldera. The city area in the Toyama Plain at the downstream of the Joganji River expanded. Also, greenery came back to the devastated caldera area. (Fig13-Fig15) In the severe sediment environment riddled with steep mountains, brittle geology, frequent earthquakes, and large amounts of precipitation, which is uncommon around the world, Tateyama Sabo completed the construction of the Shiraiwa Sabo Dam, Hongu Sabo Dam, and A series of Dorodani Sabo Dams successively by mobilizing the most advanced technologies and wisdom at all times. The combination of the installed facilities along the large river basin, including those for the control of sediment production at the upstream and others for the storage of flowing sediment at the midstream, is producing an excellent effect as a disaster prevention system for the Toyama Plain. In terms of the scale of the target conservation area, and the mobilized technologies, wisdom, and devices, we can say that Tateyama Sabo is the culmination of modern watershed management technologies involving sediment. It is an excellent example of erosion and sediment control measures and disaster prevention technologies that emerged from severe natural conditions at the Joganji River in Japan, which is located at the boundary of four crustal plates and is susceptible to sediment-related disasters triggered by earthquakes, volcanic eruptions, and typhoons. Tateyama Sabo is a kind of showpiece that presents outstanding solutions to universal common themes, namely, disaster mitigation and national resilience. Zinzu River Zinzu River Under construction (1933) Present status (2014) Fig.12 A series of Dorodani Sabo Dams Joganji River Joganji River Fig.13 Changes of the Toyama city area

8 Shiraiwa Sabo Legend Bare land Sabo facility Shiraiwa Sabo Fig.14 Changes of vegetation at the Tateyama Caldera Period Edo Meiji Taisho Showa Flood damage Damage to water utilization Damage to sabo facilities No record Largest flooding damage Hietsu Earthquake (1858) Ansei Period (5) Start of sabo works by Gov. Start of prefectural sabo works [Sabo plans in Meiji] River improvement by de Rijke Completion of the merged Josai Ditch Completion of Yokoe Sabo Dam Use of tower excavators Start of excavation Completion of Shiraiwa Sabo Dam Completion of Dorodani Sabo Dam Completion of Hongu Sabo Dam Start of river works by Gov. Fig.15 The damage outbreak situation of Joganji River and the enforcement situation of the disaster prevention business Legend Year of disaster 5. CONCLUDING REMARKS W.C.Lowdermilk, U.S. Truman Presidential Technical Committee Chairman of the Supreme, mentioned as follows. Japanese engineers have developed River "Sabo" works on a larger scale than is found in Europe. The author knows of no country that has carried out such elaborate and costly works of reducing stream erosion in mountain valleys as has japan. For this reason the author would like to propose that this type of torrent and mountain stream control be called Sabo Works. Source: minutes recording, Association International Hydrological Sciences, Brussels, Belgium, 1951 Tateyama sabo is the representative example of elaborate Sabo works in a large scale river basin and can give an important lesson to the engineers who will cope with disasters. We will continue the effort to pass down these facilities with their histories to future generations as a shared valuable heritage. ACKNOWLEDGEMENTS The authors are grateful to Prof. Yukio Nishimura of Tokyo University s Research Center for Advanced Science and Technology, Dr. Masao Okamoto who is Chairman of the Japan Society of

9 Erosion Control Engineering, Prof. Hideaki Marui of Niigata University s Research Institute for Natural Hazards and Disaster Recovery, Prof. Haruo Nishimoto of the Graduate School of Tsukuba University, Mr. Andreas Götz who is the president of the Swiss National Platform for Natural Hazards Reduction PLANAT, Dr. Alessandro Pasuto who is the managing director of the Italian National Research Council's Research Institute for Geo-Hydrological Protection in Padova, Prof. Djoko Legono of Indonesia's Gadjah Mada Univeristy, Ms. Maria Patek who is the director general of the Department for Torrent and Avalanche Control of the Austrian Federal Ministry, Tateyama Mountain Area Sabo Office of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), Sabo Frontier Foundation and other persons for providing guidance and cooperation to our survey. MAIN REFERENCES Japan Sabo Association(1974):Masao Akagi Methodologies of Japan s Sabo Works in Meiji and Taisho Periods. Kimio Inoue (2010): Journal of Disaster Research, Vol.5, No.3 Masao Akagi(1936): Journal Suiri to Doboku, November issue, P Masao Akagi(1936): Journal Suiri to Doboku, September issue, P Shun Okubo(2004): Journal Sabo to Chisui, No. 159, P105. Takao Yamakoshi(2006): Journal of Erosion Control Engineering, Vol. 59, No. 2, P60. Tateyama Sabo Office, MLIT(2004): 50-year History of Mizutani Branch Office, P2. Tateyama Sabo Office, MOC(1997): 70-year History of Tateyama Sabo Office, P57-P58. Toyama Work Office, MOC (1962): Joganji River historical record, P102-P136. (The above references are written in Japanese.)