Chao Phraya River

The Chao Phraya River is the major river in Thailand, with its low alluvial plain forming the centre of the country. It flows through Bangkok and then into the Gulf of Thailand.

Written evidence of the river being referred to by the name Chao Phraya dates only to the reign of King Mongkut (Rama IV, 1850–1868). It is unknown what name, if any at all, was used for the river in older times. The river was likely known simply by the Thai word for 'river', แม่น้ำ (RTGS: mae-nam), and foreign documents and maps, especially by Europeans visiting during the Ayutthaya period, usually named the river the Menam.

The name Chao Phraya likely comes from Bang Chao Phraya (บางเจ้าพระยา), an alternative name, documented from around 1660 in the reign of King Narai, of the settlement that is now Samut Prakan. Historian Praphat Chuvichean suggests that the name, which is a title of nobility, originated from the story of two Khmer idols being unearthed in 1498 at the settlement that was by the mouth of the river at the time. When the delta extended further into the sea, a new settlement was founded to guard the new river mouth, and the new settlement probably gained the name Bang Chao Phraya (bang being a common term for village names) as a reference to the memory of the idols. There are references in records from the time of King Borommakot (r. 1733–1758) to Pak Nam Bang Chao Phraya (ปากน้ำบางเจ้าพระยา, pak nam meaning 'river mouth'), suggesting that the name had become attached to the mouth of the river by that time, and later became used for the entire river.

In the English-language media in Thailand, the name Chao Phraya River is often translated as river of kings.

On the basins of Chao Phraya River rose the earliest civilizations in the southeast Asia, most notably the ancient Mon kingdom and the civilization of Dvaravati from the 7th century to the 11th century. The river played a crucial role in the Lavo kingdom that existed on its left bank in the Upper Chao Phraya valley and then maintained its role in the kingdoms that succeeded the Lavo kingdom. It formed the basis of the Ayodhya Kingdom, which was later incorporated into the Ayutthaya Kingdom in the 14th century, which itself was the precursor of modern Thailand (known formerly as Siam). The river became very significant after the establishment of Rattanakosin (Bangkok) in 1782 on its east bank, the location of Bangkok on the east bank of Chao Phraya River ensuring protection for Siam from the Burmese invasions coming from the west.

The Chao Phraya begins at the confluence of the Ping and Nan rivers at Nakhon Sawan (also called Pak Nam Pho) in Nakhon Sawan province. After this, it flows south for 372 kilometres (231 mi) from the central plains to Bangkok and the Gulf of Thailand. In Chai Nat, the river then splits into the main course and the Tha Chin River, which then flows parallel to the main river and exits in the Gulf of Thailand about 35 kilometres (22 mi) west of Bangkok in Samut Sakhon.

In the low alluvial plain which begins below the Chao Phraya Dam, there are many small canals (khlong) that split off from the main river. The khlongs are used for the irrigation of the region's rice paddies.

The rough coordinates of the river are 13 N, 100 E. This area has a wet monsoon climate, with over 1,400 millimetres (55 in) of rainfall per year. Temperatures range from 24 to 33 °C (75 to 91 °F) in Bangkok.