Basic information is given over to wikipedia and other sources (times have changed since the internet became widespread, and research tool is equal to everyone), but it seems that the Honenike-dam is usually mentioned by anyone who asks about it in the history of dams in Japan. If you ask people to name ten masterpiece dams in Japan, they will usually all mention it. The reasons why it is a masterpiece are given on the website of the Ministry of Agriculture, Forestry and Fisheries. The construction was completed in 1930 (Showa 5), and it is said to have used a number of methods that were revolutionary at the time in Japan and astonished all concerned. It was built in masonry, and in recent years, it has been experiencing leakage due to ageing, but it has been properly renovated and is still in use. The renovation work was completed in 1994. The new part was still visible in 2023 when I visited (see photo). The atmosphere of these old stone buildings is certainly reminiscent of the UK. I found out that it is designated as a monumental monument.

In this essay, I have objectively summarised three points of note by consulting documents and other sources, and subjectively analogised the hows and whys of the design. The last chapter also contains a subjective discussion.  

1) History and background; imminent water shortage
2) Period and structural technology; multiple arch form
3) Strange design; siphon flood discharge with an open mouth
4) Subjective discussion
5) Miscellaneous Impressions


 基礎情報はwikipedia などに譲る(ネットが普及したので、時代が変わった、調べ物はみな平等)が、豊稔池ダムはたいてい誰に聞いても日本のダム史に残るもの日本で名作ダムを10基挙げろと言われれば、たいてい皆が取り上げる。その理由は、農水省のWEBにも記されている。竣工が1930年(=昭和5年)で、日本で当時としては画期的な方法をいくつも採用して関係者の度肝を抜いたとのこと。メーソンリー造なので、近年は老朽化で漏水が見られたらしいが、そのあたりもちゃんと改修されていて現役。改修工事が平成6年竣工とある。私が訪れた2023年にも新しい部分は見て分かった。こういった古い組積造の建造物の趣はたしかに英国を思わせる。調べてみると重文にも指定されているらしい。




1) Location, Imminent Background

I have learnt since I was a child that Kagawa Prefecture ≒ Sanuki is surrounded by mountains and has frequent water shortages due to its topography and climate, and there were often real-time restrictions on tap water intake during the period I lived there.

The Kunita-River flows northwards around the western Kagawa plain called Onohara, and flows into the sea around Kanonji City. According to literature, the Onohara fan area was said to have suffered from water shortages to the extent that it was said to 'burn in the moonlit night'. Plans to dam the Kunita-River, which flows from the Shikoku Mountains, began before the Taisho era (1912-1926), and even a brief history of the project shows that there were repeated droughts and farmers' revolts. In 1924, two years before construction began, there were droughts and peasant revolts, according to records. These records alone provide an analogy to the urgent situation at the time. The completion of the Hounenike Dam and its irrigation in 1930 led to the development of rice, wheat and leaf tobacco cultivation, and the area is still one of the leading onion and lettuce production areas in Japan.

It also states that the dykes were partially undertaken by local residents, including a total of 150,000 farmers in the Taisho era, and were completed in just three years and eight months. Although the times may be different today, I feel that I have been shown a true public works project. This story, as well as the monument on the right bank of the river, shows that this was a long-held dream of the local community. 



 「柞田川」大野原と呼ばれる香川県西部の平野を北に回り込むように、観音寺市のあたりで海にそそぐ、比較的短い河川である。文献によると下流の大野原扇状地では「月夜に焼ける月の光でさえ水が蒸発する」といわれるほどの水不足地帯であったそう、そのためか開墾がほかの地域に比べて遅れた四国山脈から注ぐ柞田川をせき止める計画は大正時代以前からあり、歴史を軽く漁るだけでも度重なる旱魃が挙げられている。着工の二年前、1924年(大正13年)にも、旱魃に加え農民一揆があったと記録にある 。こういった記録をさらうだけでも、当時の切迫した状況を想像できる、水がないと何もできない、ましてや農業をや。右岸にある碑をみても、この地域の念願であったことがうかがい知れる。それが、1930年の豊稔池ダムとその灌漑の完成により、いまでは日本国内でも有数の玉ねぎ、レタス産地となったようだ。


地形をよく見てね。引用;北本 朝展 @ 国立情報学研究所(NII)よりリンク

2) Time and Technology; Multiple-Arch 

The oldest dam in Japan is Sayama Pond (Osaka, 616?), which is mentioned in the Chronicles of Japan, but the Sanuki region, not to be outdone, is said to have had water problems since ancient times. Mannoike (Kagawa, 704?), also in central Kagawa, is so old that Kukai appears in its history. However, there is no end to the history from this period, so I will briefly describe it by technology in the context of Western engineering technology from the Meiji to Taisho periods, which is a little more modern.

Technical mermarks as follows; One is the water storage technology introduced from the UK. One project was the Honkouchi High Dam (Nagasaki, 1891), which was the first water supply dam built in Japan. Later, an additional Honkouchi Low-Part Dam (Nagasaki, 1903) was built downstream and is still in use today after renovation. In terms of structural form, the oldest arch dam in Japan is the Ominato No. 1 Water Reservoir Weir (Aomori, 1909), which was completed by the Imperial Japanese Navy in 1909. Photographs show that it was built of masonry and designed by an engineer studying at the University of London. Lastly, the materials used. The construction of dams using concrete began in earnest at the end of the Meiji period, and the Nunobiki-Gohonmatsu Dam in Hyogo and the Ueda-ike weir on Awaji Island are said to be representative early structures. Incidentally, instead of being constructed of reinforced concrete as we know it today, the above dam was a composite production of coarse stone and middle filling, and is now also known as the Masonry Dam.

Although the current understanding simply imagines gravity-type reinforced concrete, it is frequently documented in various sources that these materials and construction methods were used in Japan at a time when the use of concrete for large civil engineering structures was late, and  the quality of concrete was poor, and it was expensive. The Honenike-Dam (Tano-no-ike Dike at the time) was built of stone around the perimeter and filled inside with foundation stones and mortar. It is only in the Heisei era that leaks became noticeable, but the aforementioned Gohonmatsu Dam was already leaking water at the time, so this material and construction method was used as an improvement plan, according to the report. A search of the literature shows that the design was basically rationalistic.




It was basically understood that this form, which is called buttress in English, has a Gothic aspect of construction, i.e. structural rationality was given the highest priority. Reference books also state that the multiple-arch dam form is generally employed when the bedrock on either side of the bank is not strong enough to support the load by itself.


The dam was designed and planned by Midori Matsuura and Nobuo Suzuki, engineers from the Ministry of Agriculture and Forestry, under the guidance of civil engineer Dr Tojiro Sano (the monument says 'advisor'). This form is rare in Japan, with only two surviving. Dr Sano was originally employed by Osaka City and Daido Electric Power Company, and as he was on a return trip to the UK and India, it is easy to imagine that he had a deep knowledge of civil engineering techniques using concrete in various parts of the world at the time. Dr Sano also states in his paper that he used the techniques of Rankine, Delocre and Weggman. 

According to several documents from the Japan Society of Civil Engineers (JSCE), several American multiple-arch style dams were featured in the society at the time (Ikeda, et al., 1998), particularly the Erewa Dam at the northern end of the USA (Tsuji, et al., 2011). Examination of photographs shows that it does indeed have a somewhat similar design form with a continuous flood discharge at the top, called a tenter gate. Incidentally, the original Erewa Dam in the US was completed in 1913 and removed in 2012.

It is also mentioned that engineers had been brought in from the USA for the larger Oi Dam (1924, Gifu), which had been planned some time earlier, so even if it was not a multiple-arch dam, they must have seen and heard about the buttress-style split-anchorage form.



 このダムの建造に際して土木技術者、佐野藤次郎博士の指導の下(碑には顧問とある)、農林省の技師である松浦翠、鈴木信夫が設計・施工計画を行ったとある。この形式は 日本ではレアで、現存するものは2基のみということだ。佐野博士はもともと大阪市や大同電力等で務めていたということらしく、英国およびインドの洋行帰りということもあり、当時のコンクリートを用いた世界各地の土木技術に関して造詣が深かったことは容易に想像できる。また、佐野博士は、自身の論文の中で、Rankine,Delocre,Weggmanの技術を援用したと、明記している。 




Dams likely to have been referred to by Dr Sano/佐野博士が参考にした可能性の高いダムたち

❷Reasonsfor this form of dam design (including analogy) 

Leaving this background aside, when Dr Sano, the design and construction advisor, first visited the site in 1925, he initially planned to design a gravity-type dam, which had already been used elsewhere. As it turned out, the planned site of the Hounenike Dam was unexpectedly hit by bedrock during the excavation of the riverbed, and the design was hastily changed (Ikeda et al., 1998). Now, there are several descriptions of the reasons for the change from the gravity type to the composite retaining wall type

From the above, it can be concluded that this form was derived from the form that was beginning to be adopted in other countries at the time, the presence of intellectuals who had seen and heard about it, and practical reasons on the ground.




Now, I will briefly summarise what I have learnt from the multiple-arch form. 

First, it is sort of self-explanatory if you follow the history of Gothic architecture, etc., but let me reiterate the language. The mechanism of the buttress is an attempt to artificially create even the bearing capacity, thus building a part of the earth or, strictly speaking, an intermediate object between the earth and the artefact, which is a terribly artificial act. The word artificial can also be translated as constructive or architectural. In other words, whatever the conditions of the ground, it is a human-controlled arrangement of a mechanism that can receive and return the stresses of the material and the reaction forces for its function, and keep it stationary. From the designer's point of view, this suggests unlimited buildability and can be a tool to aid his megalomania.

As for the arch, it is not an invention here, but has to do with combining small material units - bricks and blocks - that could be made by humans, to make the span fly. In order to escape the yoke of mechanics, this force-line-aware structural form manifests itself time and again, even in form. As the design supervisor says, "We designed them so that the hydraulic forces applied were the same", and here too they functioned to channel the tremendous loads equally over the buttresses, which were divided into smaller sections. 

These forms are evident in the Roman aqueducts and modern civil engineering structures in the UK, where humans have built massive structures from a series of smaller units.





 Given that there are two dams in Japan of the same type, one wonders what the other, Okura Dam (Miyagi Prefecture), is like, but looking at the photographs, they are quite different. The Hounenike example is classic, while the other is a huge two-arch, with a wide span and reminiscent of topographical constraints. The Okura Dam is said to have had a strong bedrock, but the site was quite large, so an artificial weight was placed in the centre. In both cases, artificial weights seem to be vulnerable to earthquakes and are not widely used in Japan. However, from my knowledge, there are some civil engineering techniques, such as the anchorage between the North Bisan Seto and South Bisan Seto Bridges, so it must be difficult to build them. As for other dams with buttress structures, such as the Marunuma Dam (Tochigi Prefecture), there are examples in Japan of space frames due to the same concrete price problem, but they have not been adopted in recent years, not only because of the difficulty of design and construction, but also because of the problem of deterioration from freezing and thawing.


3) Strange design; flood vents open their mouths in anguish

The design is often described as "reminiscent of an old European castle", but this is not by chance, and is understandable in view of the background of the advisor, Dr Sano. He has been to the West many times and has seen the English and Scottish landscapes in particular. If we follow Dr Sano's other work, we can read more into his intentions. There is no doubt that he had knowledge and interest in style and decoration at the Gohonmatsu-Dam, even though there was no uniformity of order, such as the neoclassical ornamentation that was popular in Britain, the Renaissance essence at the top of the arches and the introduction of Indian-style costumes in the tower house. 

Thus as a result, it is not surprising that the building is reminiscent of an ancient castle. However, they are of course different in terms of function - a dam and a water outlet as opposed to a castle and a window. (I will add to this when I have calmed down a little more).





The Honenike-Dam is a hybrid of a siphon hole and full overflow for the treatment of excess water. There are not many examples in Japan of siphon systems being used for flood discharges. A siphon is a mechanism for transferring liquid from a higher position to a lower position using pipes, and has been widely studied from ancient Egypt until the 17th century. The advantages of using this in dams can be summarised as follows.  

Weaknesses also exist 

It was often decided to use a separate route for the British-style flood discharge from the embankment, and according to British theory, the construction of a conduit route within the embankment should be avoided. By analogy with these principles and Dr Sano's other work at the time, the top of the arch was narrow, making it difficult to install a large flood discharge. Therefore, the basic design relied on this siphon, and a mechanism to release the water from the foundation of the embankment to a distant location with high efficiency was probably considered.

It is also interesting to note that the overflow is allowed from the top of the arch. Basically, excess water overflows the entire top of the embankment and then hydraulically gouges the foundation downstream of the embankment, which is not a good idea. This is not a problem here, as a similar stone platform has been provided at a lower position in the downstream section of the embankment. In some places, the structural strength of the embankment was being attacked by masonry construction at the time, and this system was probably adopted as a supplement to prevent critical collapse in the event of flooding, in addition to the overflow from the top of the embankment. However, as will be discussed later, there may also have been design considerations.

ref; https://theconstructor.org/water-resources/hydraulic-structures/different-types-spillways/32484/






The drawing of Part of siphone tube, and Picture by Auther(reffering from Kagawa Pref.) 筆者ドローイングと筆者撮影写真(参考;香川県)

2) Analogy to why only the design of the Hounenike dam is different

A quick look at Dr Sano's past designs shows that, although there are differences in detail, the main type is a simple gravity-type embankment (trapezoidal shape with a bulging lower section). As can be seen from the plan and elevation, they are asymmetrical, with depth for buttresses. Why was this type and form  adopted only in the Kagawa example? The differences in design and the reasons may be summarised as follows. 

(1) The water load is carried by a thin surface
→ to reduce the capacity of the material
→ to reduce material costs, transport time and dead weight.

2) The footprint shape is clearly different (rectangular and buttress) → The supporting ground or bedrock was not strong enough or there were cracks
→ Unsupportable or water enters through cracks and creates lift pressure
→ Collapse or overturning

3) The type of flood discharge is different
→ The curved surface is designed so that the direct stress is constant, so it is not necessary to make a hole
→Skip so that the immediate rear of the support structure is not dug up by the water flow
→Siphon type  

According to the documents, the unexpected support ground conditions in the geotechnical industry and the overturning accident of the Bouzey dam (France) caused the original gravity dam design to be changed (Ikeda, 1998).




   →支持できない or 亀裂から水が浸入し揚圧力を生む
    →崩壊 or 転倒



Figure cited, and add some by auther Construction and refurbishment of the 80-year-old multiple-arch concrete dam Houenike Dam (adapted from Tsuji and Miyahara 2011, Figure 2) First, planarly, the asymmetry and the different buttress prospects of No. 1 to No. 6. Elevationally, the support heights of the buttresses and the depths of the rootings are different. Cross-sectionally, it is not surprising that the gravity type differs from the gravity type because the surfaces subjected to water pressure are different.


Well-thought-out coalescing forces, oblique lines of force in riverbeds that could only be stopped by friction, and designs that aid frictional forces by vertical drag. The structually rationale of the form that was determined by a deep consideration of the boundary conditions of the built structure and natural condition. / よく考えられた合力、摩擦で止めるしかなかった河床部に、斜めに入る力線、垂直抗力で摩擦力を助ける設計。形の合理性もわかるが、構造物の境界条件に対する深い考察からきた構造形式

5) Miscellaneous Impressions in 2023

When travelling abroad, especially to emerging economies, it is often the case that the ground beneath the feet of magnificent buildings is so uneven that it is not only impossible to walk properly, but is also littered with peeling tiles and other debris, making it look derelict. It is not always clear how this happens, whether it is a civil engineering problem or an organisational problem, but it is a stark reminder that the foundations of infrastructure are literally below the ground. It must be said that it was very astute that a 100-year-old structure is still standing in earthquake and flood-prone Japan.

It is a massive, elegant structure set in a tranquil rural landscape, but a study of the social conditions of the time and the ground beneath the site shows the rationality of its design to be surprisingly convincing. The research gradually revealed that the design team was sensitive to accidents overseas, ever-evolving engineering technology and unexpected rock conditions at the site, and struggled to incorporate them flexibly into practice. Looking at the past work of the same design supervisor, this work was unique, and I was wondering why.

The first point of comment is the design methods of civil engineers and their focus. I was reminded once again of the seriousness of the way in which man-made and natural objects are joined. In architectural education, the thinking flow was to unconsciously determine the concept of the structure above ground and decide what is below ground. Yet the civil engineer defines the boundaries of the design by imagining the ground and the transmission of forces at the joints, and as a result, the above structure emerges. At least this asymmetrical buttress seems to be a phenotype adapted to the terrain in this way.

Secondly, unlike buildings, which are built in cul-de-sacs according to the wishes of individual clients, civil engineering design seems to emerge from a synthesis of mechanics, materials, construction methods and the social conditions of the time. The structure, which was built with the help of local people, seems to be trying to invoke what Pope and Schulz call the genius. The sincerity of the engineers oozes out, and there is a sense of serious tension despite the fact that it is just an object. In fact, this is a common attraction of the dam, but it is not an occult ghost, but a realistic demand, which is figurative and eerie.

I feel as if I have been able to verbalise the reasons why the design of buildings, my speciality, is somewhat bland to third parties. This structure was originally man-made, but now I am not sure whether it is natural or man-made, and as a young third party, it looks to me like an Extended Organism (Turner, 2002) somewhere in between. It is still in use nearly 100 years after its construction and stands tall and majestic in the mountains of Udon Prefecture. 

*I'm sorry for being so uncharacteristically serious

*I'll write about it elsewhere, because today's civil engineering structures in the UK are so aggressive.






私の専門とする、建築物のデザインが第三者にとってやや白けてしまう理由が言語化できたような気もする。この構造物はもともと人工物だが、今となっては自然なのか人工物なのか、若輩で第三者の私にはその中間のEextended Organismターナー, 2002)にも見える。建設後100年近くを経て現役であり、屹然としてうどん県の山間に兎に角いまも佇む。


A structural analysis on a typical embankment shape with various boundary conditions. The horizontal load values were gradually increased and the colours are displacements. Three types are used here: (1) three-sided; both banks + fixed riverbed scheme (gravity arch type assumed), (2) two-sided fixed; both banks fixed + riverbed supports weight but rollers (arch type assumed), (3) one-sided; fixed riverbed (gravity type assumed). Assumed that it would be interesting if the antechamber form could be derived from the boundary conditions, to be added.一般的な堤の形状で、境界条件をいろいろと変えて、構造解析をやってみた。水平荷重の値を徐々に増やして、色は変位。ここでは三種類、①三面;両岸+河床固定スキーム(重力アーチ式想定)、②二面固定;両岸固定+河床は重さは支えるがローラー(アーチ式想定)、③一面;河床固定(重力式想定)。控壁形式が境界条件から導出出来たら面白いなと想定した、加筆予定。