Sirikit Dam

The Queen Sirikit Dam is an embankment dam on the Nan River, a tributary of the Chao Phraya River, in Tha Pla District, Uttaradit Province, Thailand. It is at the southeastern edge of the Phi Pan Nam Range. The dam was built for the purpose of irrigation, flood control and hydroelectric power production. It is named after Sirikit, Queen of Thailand.

Background
The Sirikit Dam among others in the Chao Phraya basin were constructed beginning in the 1950s to exploit the agricultural and hydroelectric potential of the basin. Preliminary construction on the dam began in 1968 and it was finished in 1972. The power plant and first three units were commissioned in 1974, the fourth in 1995. Previously in 1964, the Bhumibol Dam was completed on the Ping River, one of two major tributaries of the Chao Phraya including the Nan. The Bhumibol and Sirkit Dams control 22% of the Chao Phraya's annual runoff combined. Both dams also help provide for the irrigation of 1200000 ha in the wet season and 480000 ha in the dry season.

Design
The dam is a 113.6 m high and 800 m long embankment dam that is 630 m wide at its base and 12 m wide at its crest. The dam withholds a reservoir of 9510000000 m3 of which 6666000000 m3 is active or "useful" storage. The reservoir has a surface area of 259 km2. The dam's spillway consists of a tunnel controlled by two radial gates, it has a capacity of 3250 m3/s. The dam's power station contains 4 x 125 MW Francis turbines for an installed capacity of 500 MW.