The Bhumibol Dam (formerly known as the Yanhee Dam) is a concrete arch dam on the Ping River, a tributary of the Chao Phraya River, in Amphoe Sam Ngao district of Tak Province, Thailand. It is located about 480 km (298 mi) north of Bangkok and was built for the purposes of water storage, hydroelectric power production, flood control, fisheries and the management of saltwater intrusion downstream with its dry-season releases. The dam was named after King Bhumibol Adulyadej and was Thailand's first multi-purpose project.
The Bhumibol Dam among others in the Chao Phraya basin were constructed beginning in the 1950s to exploit the agricultural and hydroelectric potential of the basin. Construction on the dam began in 1958 and was finished in 1964 while the reservoir was completely filled in 1970. The first two generators were commissioned in 1964. In 1972, the Sirikit Dam was completed on the Nan River, one of two major tributaries of the Chao Phraya including the Ping. The Bhumibol and Sirkit Dams control 22% of the Chao Phraya's annual runoff combined. Both dams also help provide for the irrigation of 1,200,000 ha (4,633 sq mi) in the wet season and 480,000 ha (1,853 sq mi) in the dry season. The dam's power house underwent extensive upgrades and renovations in the 1990s. In 1991, the Lower Mae Ping Dam () was constructed 5 km (3 mi) downstream to create a lower reservoir for the one pumped-storage turbine that was installed. When constructed, the Bhumibol Dam contributed 22% of Thailand's power generation and in 2003 that number was 2%.
The dam is an arch-gravity type and is 154 m (505 ft) tall, 486 m (1,594 ft) long and 8 m (26 ft) wide at its crest. It withholds a reservoir of 13,462,000,000 m3 (10,913,821 acre·ft) of which 9,762,000,000 m3 (7,914,182 acre·ft) is active or "useful" storage. The dam's catchment area is 26,400 km2 (10,193 sq mi) while its surface area is 300 km2 (116 sq mi). Its power plant contains eight different turbines for an installed capacity of 749 MW. Of the eight, six are 76.5 MW Francis-type, one is a 115 MW Pelton turbine and one is a 175 MW Francis pump-turbine. The Lower Mae Ping Dam is 8 m (26 ft) high, 300 m (984 ft) long and has a storage capacity of 5,000,000 m3 (4,054 acre·ft). In off-peak hours, the one pump-turbine returns water back into the Bhumibol (upper) reservoir and when demand is high, the pump serves as a generator for power production.
