Chi River

The Chi River (Thai: แม่น้ำชี, RTGS: Maenam Chi, ) is the longest river in Thailand; it extends 765 km, but carries less water than the second longest river, the Mun. In the Isan language of this region, as well as in the adjacent Lao language, the name of the river is pronounced and in the romanization of Lao transliterated as "Mae Si" while the transliteration Chi reflects Bangkok-Thai. In wet seasons there are concerns about flash floods in the floodplain of the Chi River basin.

The river rises in the Phetchabun mountains, then runs east through the central Isan provinces of Chaiyaphum, Khon Kaen and Maha Sarakham, then turns south in Roi Et, runs through Yasothon and joins the Mun in Kanthararom district of Sisaket Province. The river carries approximately 9,300 cubic kilometres of water per annum.

The river was an 18th century migration route for the re-peopling of the Khorat Plateau, by ethnic Lao people from the left (east) bank of the Mekong resettling on the right bank. This began in 1718 when the first king of the left-bank Kingdom of Champasak, King Nokasad, sent a group of some 3,000 "subjects" led by an official in his service to found the first settlement in the Chi river valley — and indeed anywhere in the interior of the Khorat Plateau — Muang Suwannaphum in present-day Roi Et Province (a history recorded and remembered, largely in terms of the struggle to expand wet-rice cultivation in the river valley.) Their descendents are now regarded as a separate ethnos from the Lao to the North and the central Thai to the South-West.