Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams.
ACS, based in Spain, is one of the most active dam contractors internationally and has constructed 23 arch dams since 1960. Its subsidiary Dragados completed the Portugues Dam, a 67-meter-tall, 275-m-long roller-compacted-concrete thick-arch dam, in Puerto Rico in 2013. And it is nearing completion of the Barro Blanco Dam, in Panama. Barro Blanco is an arch-gravity dam of conventional concrete in the central section and loose materials in the buttresses. It is 55 m tall, with a crest length of 332 m for the concrete section, plus 138 m for the buttresses.
In recent years, ACS’s subsidiary Cobra has been building dams in Panama, Guatemala, Peru and Nicaragua. “There is an added difficulty that has to do with working in depressed regions,” says Javier Hidalgo, Cobra’s director of hydraulic infrastructure.
Regarding arch dams, “the major challenge in terms of construction is the transportation and placement of concrete, which generally requires special tailor-made systems, such as cableways. Additionally, project-specific specialized formwork systems are required, due to the curvature of the dam face,” says Luis Miguel Viartola Laborda, director of technical research, development and investigation for Dragados, a subsidiary of ACS.
MWH, a subsidiary of Stantec, has designed a number of arch dams. The firm provided design review, preparation of construction drawings and on-site construction management of the Tekeze hydropower project, a 190-m-tall double-arch dam with a 300-MW underground powerhouse; sited in Ethiopia, it was completed in 2009. Further, MWH acted as technical adviser on the design of the world’s tallest arch dam, the Jinping I Dam, in China. The firm completed the feasibility-level design of the Susitna-Watana hydroelectric project, in Alaska, a 224-m-tall gravity-arch dam projected to cost $5.2 billion but shelved in June 2016.
MWH served as owner’s engineer for client American Municipal Power as it added powerhouses to four existing locks and dams on the Ohio River. Since only 3% of U.S. dams currently have hydropower, “this is a large, untapped source of clean, renewable power in the U.S.,” says Don Erpenbeck, vice president and global sector leader, water power and dams, Stantec.
"With the deteriorating infrastructure in North America, there will likely be significant growth in the hydropower sector,” comments Mike Lewis, Bechtel’s global heavy civil sector manager.. "As we recently saw at the Oroville Dam in California, there are likely to be a number of hydropower facilities that need significant rehabilitation work in the not too distant future.” The Report Card, issued every four years by the American Society of Civil Engineers, left the dam grade unchanged from 2009 and determined that the U.S. needs to invest an estimated $54 billion over the next five years in order to rehabilitate all the dams that require rehabilitation. Of this amount, $21 billion is needed to repair the nation’s high-hazard potential dams to bring them up to a safe condition.
"South America and Africa both provide significant hydropower opportunities in high-growth developing countries,” says Lewis. "Hydroelectric power generation is one of the most widespread, dependable and renewable power-generation resources on the planet, constituting approximately 15% of the world’s total power supply. Despite this, it has been estimated that only roughly one-fifth of the world’s total hydropower potential has been developed.”
Oil prices have a significant impact on the hydropower market. “There is a decrease in the construction of hydroelectric power stations coinciding with low oil price periods. … We are situated in one of those periods,” says Laborde. “We are currently facing a shortage of supply of new projects. This has increased the competition among companies based on a reduction of margins. New projects are, for the most part, private initiatives following an engineer-procure-construct format, where the contractor assumes the totality of the inherent risks related to the execution.”
The largest arch dam currently under construction in the world is the Baihetan Dam, on China’s Jinsha River at the upper reach of the Yangtze. When completed, it will be 277 m tall. Its underground powerhouse will contain 16 turbines, with a generating capacity of 14,000 MW. The contractor is China International Water & Electric Corp., a subsidiary of China Three Gorges Corp. Construction began in 2013, and the first power is expected to be generated in 2018, with final completion in 2020.
Another huge arch dam under construction is the Yusufeli Dam on the Coruh River in northeast Turkey. When completed, it will be 270 m tall and 490 m long. Dolsar Engineering Inc. Co. is the designer, and the Limak Holding-Cengiz Holding-Kolin consortium is building it. The dam will have a generating capacity of 540 MW. Construction started in 2013 and is expected to be completed in May 2018.