[[Building Construction]] [[Environmental Design]] [[History and Theory]] [[Research, Analysis & Citations]] [[Structures]] --- --- [[ARCHITECTURE]] [[Buildings and [[Structures]]]] [[Engineering]] [[Furusato]] [[March]] [[Takenaka]] [[dam]] [[tobetsu]] [[wiki-architecture]] # Tobetsu Dam Tobetsu Dam (Tobetsu Dam (当別ダム, Tōbetsu Damu)) is a trapezoidal CSG (Cemented Sand and Gravel) dam located in Tobetsu, Ishikari District, Hokkaido, Japan. The dam represents a significant milestone in dam construction technology as the world's first trapezoidal CSG dam and is recognized as an Outstanding Civil Engineering Achievement by the Japan Society of Civil Engineers. Location and technical specifications The dam is situated on the Tobetsu River, a tributary of the Ishikari River system. The Tobetsu River originates from Mount Satsurai (elevation 590 m (1,940 ft)) in the southern Shokanbetsu mountain range and flows southward through a drainage basin covering 231.1 km2 (89.2 sq mi), eventually joining the Ishikari River approximately 15 km (9.3 mi) from its mouth. Key specifications Dam type: Trapezoidal CSG dam Height: 52.0 m (170.6 ft) Crest length: 432.0 m (1,417.3 ft) Dam volume: 803,000 m3 (651 acre⋅ft) Total reservoir capacity: 74,500,000 m3 (60,400 acre⋅ft) Effective storage capacity: 66,500,000 m3 (53,900 acre⋅ft) Reservoir surface area: 5.8 km2 (1,400 acres) (580 hectares) Catchment area: 231.1 km2 (89.2 sq mi) History and construction Project timeline Construction of Tobetsu Dam began in 1980 as part of the comprehensive Tobetsu River development project. The project experienced a complex 32-year history marked by local opposition, environmental reviews, and technical innovations. Major milestones: 1980: Project initiated by Hokkaido Prefecture 1980–1997: Extended negotiations with local residents over land acquisition and compensation for 350 ha (860 acres) of agricultural land 2004–2005: Project temporarily suspended during national public works review; subsequently approved with reduced scale and adoption of innovative CSG construction method to reduce costs October 8, 2008: Main dam body construction commenced by joint venture of Kajima Corporation, Takenaka Civil Engineering, and Iwakura Construction March 1, 2012: Trial impoundment began June 14, 2012: Trial impoundment completed October 7, 2012: Completion ceremony held October 30, 2012: All construction work finished December 20, 2012: Dam body construction officially completed April 2013: Water supply operations commenced Construction controversy The dam project faced significant opposition from local communities concerned about the loss of agricultural land and environmental impacts. After extended negotiations lasting nearly two decades, the project was temporarily frozen in 2004–2005 during a nationwide review of public works projects. The Hokkaido Public Works Evaluation Committee ultimately approved continuation of the project in 2005, subject to a 3 m (9.8 ft) reduction in dam height and adoption of the more economical trapezoidal CSG construction method. Engineering innovation: trapezoidal CSG technology Tobetsu Dam pioneered the trapezoidal CSG construction method, representing a major advancement in dam engineering developed in Japan. This innovative approach combines the structural advantages of trapezoidal geometry with the economic benefits of CSG (Cemented Sand and Gravel) construction. Technical features Material composition: Uses locally sourced sand, gravel, and stones mixed with cement (60–100 kg/m³) and water Eliminates need for aggregate classification, cleaning, and large-scale processing plants Utilizes excavation materials from the construction site, minimizing environmental impact Structural design: Features identical upstream and downstream slope angles in a trapezoidal configuration Distributes stress over a larger volume compared to conventional concrete gravity dams Provides improved seismic stability through geometric design rather than material strength alone Construction and economic benefits: Estimated 20–25% reduction in construction costs compared to conventional concrete gravity dams Simplified construction facilities and rapid execution Reduced environmental footprint through use of on-site materials The success of Tobetsu Dam's trapezoidal CSG method led to its adoption in subsequent major Japanese dam projects, including Naruse Dam in Akita Prefecture, which became the largest trapezoidal CSG dam in Japan. Purpose and functions Tobetsu Dam serves as a multi-purpose water resource management facility with the following primary functions: Flood control The dam regulates flood flows, with a planned maximum discharge of 1,220 m³/sec at the dam site, of which 760 m³/sec is controlled for flood mitigation. The Tobetsu River basin has historically experienced significant flooding, particularly during typhoon season, with notable events in May 1970 and August 1981. Water resource maintenance Provides consistent water flow to maintain river ecosystem functions and supplement existing water rights. The dam helps stabilize river flow to prevent water quality degradation and protect riverine ecosystems. Agricultural irrigation Supplies irrigation water to 3,194 ha (7,890 acres) of farmland (3,153 ha (7,790 acres) dam-dependent), providing maximum flow of 13.386 m³/sec during irrigation season to support Hokkaido's central agricultural region. Municipal water supply Draws up to 75,900 m³ daily, supplying 69,000 m³ of treated drinking water to municipalities in the Ishikari Western Region, including Sapporo, Otaru, Ishikari, and Tobetsu. Management and operation The dam is owned and operated by Hokkaido Prefecture through the Sorachi General Subprefectural Bureau, Sapporo Construction Management Department. The facility has been in full operation since April 2013. Design and construction team: Owner: Hokkaido Prefecture Designers: Japan Dam Engineering Center, Docon Co., Ltd. Main contractors: Kajima Corporation, Takenaka Civil Engineering & Construction Co., Ltd., Iwakura Construction Co., Ltd. Recognition and awards In fiscal year 2012, the Tobetsu Dam construction project received the Outstanding Civil Engineering Achievement Award (OCEA) from the Japan Society of Civil Engineers (JSCE), recognizing its pioneering use of trapezoidal CSG technology and contributions to advancing dam engineering practices. Reservoir and tourism Fukurōko Lake The reservoir created by Tobetsu Dam is officially named Tobetsu Fukurōko (当別ふくろう湖, "Tobetsu Owl Lake"). The lake has become a regional attraction, particularly renowned for autumn foliage viewing. Naming rights In 2021, Hokkaido Prefecture implemented a naming rights agreement for the dam, officially designating it as Ama no Furusato Tobetsu Dam (亜麻のふるさと当別ダム, "Tobetsu Dam, Hometown of Flax") for the period from April 1, 2024 to March 31, 2027. Dam card As part of Japan's popular "dam card" culture, Tobetsu Dam issues collectible cards to visitors. Cards are distributed at the Tobetsu Dam Management Office during weekdays from 9:00 AM to 12:00 PM (closed on weekends, holidays, and December 29 – January 3). Environmental and regional context Geology The dam site is positioned approximately 11 km (6.8 mi) north of Tobetsu town center. The geological foundation consists of Neogene Bourai Formation (siltstone and sandstone) as bedrock, overlain by terrace deposits and talus deposits. Climate The Tobetsu River basin experiences an inland climate with annual average precipitation of approximately 1,500 mm (59 in) and average temperature of 6 °C (43 °F). Regional development The downstream Tobetsu area has developed into part of Hokkaido's central granary region, with extensive agricultural lands dependent on reliable water supplies from the dam. Academic and research significance Following completion, Tobetsu Dam has served as a full-scale prototype for seismic research and structural analysis. Engineers and researchers have conducted extensive Finite Element Method (FEM) analyses to evaluate the dam's seismic performance, validating the safety and effectiveness of the trapezoidal CSG construction method. These studies have demonstrated that the innovative geometric design provides excellent seismic resistance despite using "weaker" construction materials compared to conventional concrete dams, proving the concept of "geometry over strength" in dam engineering. See also List of dams in Hokkaido List of dams in Japan Naruse Dam – Largest trapezoidal CSG dam in Japan Ishikari River Embankment dam References External links Tobetsu Dam official page – Hokkaido Sorachi General Subprefectural Bureau (in Japanese) Tobetsu Dam at Dams in Japan (Dam Binran) Trapezoidal CSG Dam Construction Method – Naruse Dam official site