| Location | Yamanouchi, Nagano Prefecture, Japan. |
|---|---|
| Coordinates | 36°45′47″N 138°37′42″E / 36.76306°N 138.62833°E / 36.76306; 138.62833 |
| Construction began | 1953 |
| Opening date | 1955 |
| Dam and spillways | |
| Impounds | Nakatsu River |
| Height | 20.7 m |
| Length | 33.75 m |
| Reservoir | |
| Total capacity | 19,000 m |
| Catchment area | 504.5 km |
| Surface area | 1.1 hectares |
Shibusawa Dam (Japanese: 渋沢ダム) is a dam constructed on the Nakatsu River within the Shinano River system on the border between Yamanouchi Town and the Shimotakai District of Nagano Prefecture and near Sakae Village in the Shimotakai District. It is a 20.7-meter-high gravity-type concrete dam used for power generation by Tokyo Electric Power Company's renewable energy subsidiary. Water from the river is fed to the Kiriake Power Plant, generating a maximum of 20,000 kilowatts of electricity.
History
The basin of the Nakatsu River, which originates at Lake Nozori in Gunma Prefecture and flows through Nagano Prefecture and then into Niigata Prefecture, lies in the scenic Akiyamago region. A hydroelectric power plant using the Shinano River's water was constructed in the Taishō era (1912-1926), and the area was redeveloped by the Tokyo Electric Power Company, which inherited the water rights shortly after World War II. When the Nakatsu River was then dammed, Lake Nozori was created.
Construction of the Kiriaki Power Station and Shibusawa Dam began in 1953 and was completed in 1955. The Shibusawa Dam is located downstream of Lake Nozori, and in addition to the normal flow of water, water from Lake Nozori can be released to supply the plant in times of water shortage. After generating up to 20,000 kW of electricity at the power plant, the water is pumped through the spillway to the Nakatsugawa No. 1 Power Plant and the Koyasan Dam.
Surroundings
Kiriaki is a remote village in the Akiyamago region and is famous for its onsen (hot springs). This region has long had poor access to transportation, which may have contributed to the development of its unique culture.
Road access was improved to facilitate the construction of the power plant, making it easier for large vehicles to pass through, and today National Route 405 is a tourist road that can be used to reach Kiriaki Hot Springs by car. However, the road from Kiriake to Lake Nozori via Shibusawa Dam remains an unimproved national highway and is closed in winter due to heavy snowfall.
Incidents
In December 20, 2006 and January 10, 2007 press releases, TEPCO admitted to fraud concerning Shibusawa Dam: water level data had been falsified in a 1998 report for the Ministry of International Trade and Industry (now the Ministry of Economy, Trade and Industry.) Since Shibusawa Dam serves as a flood discharge dam, the falsified data was egregious. Shibusawa Dam has only one sluice as a flood outlet. In the event of a flood, this is opened to allow the large volume of water rushing into the dam to pass through, thereby ensuring the dam's safety. However, the area surrounding the dam often receives heavy snowfall, with as much as three meters of snow accumulating each year. In winter, the gates are sometimes rendered inoperable due to heavy snow and low temperatures.
During an April 1997 flood, the sluice gate failed to open and water levels exceeded their recommended levels, causing water to overflow from the dam's top edge. The Shibusawa Dam was originally designed to allow the entire dam to overflow and release water in anticipation of floods that would be too large to be released through the flood sluice gate. The fact that water flowed over the top of the dam itself was not a serious safety concern, but the fact that the water level constantly exceeded the recommended levels, even during non-flood conditions, was considered a problem, so the dam's water level data for April 5–11, 1997 was falsified to report levels lower than they actually were.
References
- "Tōkyōdenryoku Rinyūaburupawā Kabushikigaisha Kiriake Hatsudenjo" 東京電力リニューアブルパワー株式会社 切明発電所 [TEPCO Renewable Power Co., Ltd. Kiriake Power Station] (in Japanese). suiryoku.com. 17 February 2023. Archived from the original on 16 February 2023.
- Japan Dam Foundation (2012). "Shibusawa Dam". Japan Dam Foundation. Archived from the original on 30 March 2023. Retrieved 30 March 2023.
- Niigata Prefecture Tourism Association (n.d.). "The Hidden Border Akiyamago". Enjoy Niigata : Official Travel Guide. Niigata Prefecture Tourism Association. Archived from the original on 24 January 2023. Retrieved 24 January 2023.
- "Nozoriko (yomi) Nozoriko" 野反湖（読み）のぞりこ [Lake Nozori]. Kotobank (in Japanese). Digitalio. n.d. Archived from the original on 29 March 2023. Retrieved 29 March 2023.
- YamaReco (2005). 渋沢ダム [Shibusawa Dam] (in Japanese). YamaReco. Archived from the original on 24 January 2023. Retrieved 24 January 2023.
- "Nakatsugawa Dai-ichi Hatsudenjo Setsubi Gaiyō" 中津川第一発電所 設備概要 [Nakatsugawa No. 1 Power Station Facility Overview] (PDF) (in Japanese). TEPCO. n.d. Archived from the original (PDF) on 16 February 2023. Retrieved 16 February 2023.
- "Akiyamago (Nagano) | Hot springs deep inside Japan". Mountain Trad. n.d. Archived from the original on 16 February 2023. Retrieved 16 February 2023.
- "Kiriake Onsen Kawahara no Yu" 切明温泉 河原の湯 [Kiriake and Kawahara Hot Springs] (in Japanese). Sakaemura Akiyamago Tourism Association. n.d. Archived from the original on 30 March 2023. Retrieved 30 March 2023.
- "Tōsha suiryoku hatsudenjo ni okeru dēta kaizan oyobi tetsudzuki fubi no gaiyō" 当社水力発電所におけるデータ改ざん及び手続き不備の概要 [Overview of Data Falsification and Procedural Deficiencies at Tepco Hydroelectric Power Plants] (PDF) (in Japanese). TEPCO. n.d. Archived from the original (PDF) on 16 February 2023. Retrieved 16 February 2023.