Dam. It’s damned controversial creature. It can be humongous. When we go near, they can invoke awe among us. They can be an object of hate. It destroys communities and natural bounties that will be submerged, in order to satisfy the other people who often live far away from the site. Many times, the beneficiaries of dams have not thought the existence of dam and rural villages that have to cope with complete uprooting ... so our city rats have been, I guess. In 2019, at the time Emperor Akihito abdicates his throne to his son Naruhito, dams in Japan have started to gain strange popularity. They even have trading cards, like Major League Baseball players, or those for Premier League. Let me tell you this week and next my adventures with 2 different dams in Kanagawa Prefecture: Miho Dam 三保ダム today, and Miyagase Dam 宮ケ瀬ダム later.
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| Looking down from flood gates of Miho Dam |
The access to Miho Dam is as to Dam Hiroba Park about which I posted on April 5th. It locates in a north-western corner of the Prefecture, creating Lake Tanzawa 丹沢湖. Its construction began in 1971. After 7 years and 82.3 billion yen (which is about 123.8 billion yen = USD 1.24 billion in 2015), the dam started its operation in 1978. At that time, the construction was to satisfy expected increase in water consumption in the prefecture ... Whether this objective is effective or not might be debatable in this age of slow economic growth and shrinking population. But certainly, Kanagawa Prefecture rarely has water shortage, unlike Tokyo. Thank you. The dam keeps up water of Kawachi River 河内川 that is a tributary of Sakawa River 酒匂川 whose catchment area is 576.5 km2. Sakawa River provides roughly 30% of tap water in Kanagawa Prefecture, and water from Miho Dam is about 30% of Sakawa River. It may sounds strange for that amount of money invested in only 10% of water at best? Why did they do such investment? One possible explanation is, the main water sources for Sakawa River are in Shizuoka Prefecture 静岡県 via Ayusawa River 鮎沢川. Damming up neighbor’s water would not be desirable. Another reason could be geographical. To construct a dam to collect water from Sakawa River, that was the max we could expect, and that construction point was the only site for new dam. In any case, the design of the dam shows constraint the engineers faced when they had to build a dam in western Tanzawa. It is a rockfill dam.
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| On dam
property, there are many exhibition panels explaining each location for the dam. This is to show rockfill structure. |
In terms of construction cost, unit price for building concrete dam is definitely cheaper than that for a rockfill. Yet, they had to choose it here as the bedrock for the location was too fragile to sustain a mass of concrete and subsequent water pressure from Lake Tanzawa. This is in Tanzawa Mountains 丹沢 that was created some 6 million years ago by crashes of Eurasian and Philippines Plates. Pushed up sea beds of undersea volcanos are very porous. When we read the blueprint of the dam, beneath the Promenade running from the parking space is the core of the dam with tightly tamped down clay. This part is stabilized from the sides by a bulk of rocks and soils. It creates that 80m tall man-made hill we admired from Dam Hiroba Park. According to the people working for Miho Dam, the place where 5 flood ways now stands was a remnant of a slope of Mt. Furoyama (ASL 928m) 不老山 on the border between Kanagawa and Shizuoka Prefectures. Management of the dam is done by Kanagawa Agency for Public Utility, and Kanagawa Prefectural Office 神奈川県企業庁酒匂水系ダム管理事務所・三保ダム管理事務所. They control the amount of water to be supplied via dam outlets, including flood gates, and mitigate flood damages by storms for downstream.
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| The
former control panel inside the Office. Now it’s just a wall decoration, and actual job is done with newer displays. |
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| Could
you figure out a blue roof at the far end of this photo? They are the flood gates. Their location subtly depicts the former slope from Mt. Furoyama. |
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| The
flood gates of Miho Dam will be opened mechanically by these huge machineries. |
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| Water
ways from flood gates. Hmmmm. The slope of Mt. Furoyama must have been relatively sturdy so that the engineers chose this point of the dam for huge concrete structure and gates. |
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| Seeing the flood gates up close from below. |
As this is a manufactured place, people do daily maintenance works inside the mount. The dam has two work tunnels for personnel to check condition of the interior. Recently I had a chance to enter there with the management people, and found the place looks like a scene of Hollywood’s action or sci-fi movies. A narrow and straight tunnel runs deep, and numerous instruments are located at regular intervals. Not much sound could be heard except our excited conversation. In addition to the horizontal tunnels, the inside has ways of trollies going deep down of the dam, where daily maintenance work is performed as well. Hmmmmmm. It’s unsung, but extremely important job … If some structural problem obstructs smooth supply of water from Miho Dam, we live in a city of Kanagawa will have water scarcity before long. In case a collapse of the structure, that’s an enormous disaster, possibly to the downtown of Odawara City 小田原市. Yeah, many, 223 households of 1026 people, were forced to emigrate because of the construction. About 85 ha of private forests were submerged under the Lake. Their record is displayed in Memorial Hall of Lake Tanzawa 丹沢湖記念館 … Yet, the dam is now there, and we have a huge benefit from it. Can we just say “No Dam! It’s evil!”? I think it’s better to say “Not that fast, please.” And it seems to me I’m not alone to feel like that.
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| An entrance to a tunnel |
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| Hollywood! |
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| A trolley way |
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| A part
of the tunnel was home for bats. They sidled along when we went near to them. Cute. |
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| Is
this baby stalagmite on the wall of tunnel showing something wrong …? |
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| Memorial
Hall of Lake Tanzawa has an old house that was moved before the flood. It’s a museum now to show the old way of life around the Lake Tanzawa. |
According to this article, since around the turn of the century, so-called Otaku people started to see dams in deep mountains like scenery we find in virtual interactive games. First it was a sort of counter-counter culture against actions of baby-boomers who started hugging trees to stop dam constructions. Then, actually visiting massive structures that secretly sustain our very urbane life of the 21st century, the young voice becomes louder to recognize the importance of dams. Yeah, not all dams may be now necessary. Decommissioning dams that ended their function could be a good idea. Look at the removal of Arase Dam 荒瀬ダム, and recovering ecosystem along Kuma River 球磨川 of Kumamoto Prefecture 熊本県. But there is a reason to remove a dam. As of 2018 population of Kumamoto is steadily declining and hence demand for the function of Arase Dam is almost nill. In contrast, we in Kanagawa are still gaining numbers. What is the point to destroy a thing we definitely need? Isn’t it hypocritical to criticize people who are working 24/7 to maintain dams for us, while enjoying a cup of coffee in Starbucks and arguing environmental problems of dams? Number of people visiting dams gradually increased. People exchanged their “I Love Dam” in internet. Then in 2007, a public relations office for Ministry of Land, Infrastructure, and Transport picked up such voices and started to hand out cards of dams, aka Dam Cards.
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| The
office for Miho Dam installed wire mesh fence over the locked entrance to the operation rooms of flood gates. “There are many people these days try to enter that area by climbing the original fence, despite of 80m below of the point is rock solid concrete. We simply don’t understand why they risk their lives, and set up the higher fence, just in case.” Wow. |
To “get” one, you first have to visit the dam of your choice, and ask dam personnel, normally in a management office, for the card. It’s free. The front of a card is a photo of dam you are visiting, and the back describes data and characteristics of the dam. It is now a cultic hit. For example, last year was its 40th birth year for Miho Dam. So, the dam distributed commemorative dam cards for Miho, for free. Now they are auctioned in internet for about 1000 yen (USD10)! Heck, I’ve been there after the stock of the card has gone completely. “sigh” The entire episode about “dam tourism” is now closely watched and studied among policy makers to promote tourism industry in Japan. Oh, yeah.
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| This is the front of Dam Card for Miho. |
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| This
is the back. It depicts the spec of the structure, and the attractions of Lake Tanzawa. |
Next week, I post my adventure of visiting Miyagase Dam. This is the dam that was an initiator of dam tourism in Japan. Yap, going there was thrilling, and April to November is the season to visit there. I tell you why next week. 😉
Dam Management Office for
Sakawa River System / Miho Dam Management Office
神奈川県企業庁酒匂水系ダム管理事務所・三保ダム管理事務所
734 Kamioda, Yamakita Town, Ashigara-kami-gun, 258-0203
〒258-0203 足柄上郡山北町神尾田734
Phone: 0465-78-3711,
FAX: 0465-78-3371
http://www.pref.kanagawa.jp/cnt/f8018/
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