(or Menam), a river on the peninsula of Indochina; the largest river in Thailand. It has a length of approximately 1,200 km. (From the headwaters of the main tributary, the Ping, the length is about 1,500 km.) Basin area, approximately 150,000 sq km.
The Chao Phraya rises on the slopes of the Khun Tan Range and in the Phi Pan Nam Mountains. It flows from north to south, primarily within the Chao Phraya Lowland, and empties into the Gulf of Thailand of the South China Sea, forming a delta that advances 30–60 cm into the sea each year because of the large amount of sediments. The river is fed by rain and has a monsoonal regime. The high water period is from May through November, with a large part of the delta being flooded in October and November; the lowest water level occurs in April. The mean flow rate in the lower course is approximately 2,700 cu m per sec. The water of the Chao Phraya and its tributaries is extensively used for irrigation, mainly of rice paddies. Logs are floated on the river, and there is fishing, with carp being the main fish. The Chao Phraya is navigable for 400 km (to the mouth of the Ping River); in high water it is navigable for 750 km (to the city of Uttaradit). The cities of Bangkok and Ayutthaya are in the delta.