The Chao Phraya watershed constitutes several sub-basin watersheds, which contain the rivers Ping, Wang, Yom, and Nan to the north of the country. In addition to these, it also contains many smaller riverine watersheds such as the Tha Chin, Pasak and Lopburi Rivers.
Illustration showing the drainage area of the Chao Phraya watershed (Source: http://www.maproom.psu.edu/dcw/)