Chi River Basin Located in the northeastern part of Thailand, the Chi River basin has a total drainage area of 49,131.92 square kilometers, or 30,707,453 rai. The majority of its land area is within 14 provinces: Chaiyaphum, Khon Kaen, Nong Bua Lamphu, Udon Thani, Maha Sarakham, Nakhon Ratchasima, Loei, Phetchabun, Kalasin, Roi Et, Yasothon, Ubon Ratchathani, Si Saket, and Mukdahan. The Chi River basin lies between latitudes 15° 30´ North and 17° 30´ North, and between longitudes 101° 30´ East and 104° 30´ East. It is bordered to the north by the Mekong River basin, to the south by the Mun River basin, to the east by the Mekong and Mun River basins, and to the west by the Pa Sak River basin. The topography of the Chi River basin consists of high mountain ranges: the Phu Phan mountain range to the east and north, and the Dong Phaya Yen mountain range to the west, which are the source of the Chi River and several important tributaries. The central area consists of plains to gently undulating hills, with small slopes in the southern part of the basin. The main river is the Chi River, with important tributaries including the Nam Phrom, Nam Phong, Nam Choen, Lam Pao, and Nam Yang rivers.
