Pa Sak River

The Pa Sak River (Thai: แม่น้ำป่าสัก, RTGS: Maenam Pa Sak, Pronunciation) is a river in central Thailand. The river originates in the Phetchabun Mountains, Dan Sai District, Loei Province, and passes through Phetchabun Province as the backbone of the Province. It then passes through the eastern part of Lopburi Province and Saraburi Province, until it joins together with the Lopburi River at the northeast of the Ayutthaya Island, before it runs into the Chao Phraya River in the southeast of Ayutthaya island around Phet Fortress area. It has a length of 513 km (319 mi) and drains a watershed of 16,291 km2 (6,290 sq mi). The annual discharge is 2.4 km3 (0.58 cu mi).

The valley of the Pa Sak through the Phetchabun mountains is the main part of Phetchabun Province. As the watershed of the river is rather narrow, the amount of water in the river changes a lot seasonally. To level the drought problems in the lower Pa Sak valley, in 1994 the construction of the Pa Sak Cholasit Dam (เขื่อนป่าสักชลสิทธิ์) in the Lopburi Province was started. The 4,860-meter (15,940 ft) wide and 36.5-meter (120 ft) high high dam keeps a total of 0.785 km3 (0.188 cu mi) of water. Additionally to the water management the dam also supplies about 6.7 MW of hydro-electric power.