Thailand’s Principle River Systems
Thailand is drained largely by two river systems: the Chao Phraya River in the west and the Mekong River in the east. There is a number of lesser river systems across the country that mostly flow into the Gulf of Thailand.
The Chao Phraya River System
The Chao Phraya River System is the main river system of Thailand, as its basin defines much of the region of central Thailand. The Chao Phraya River begins at the confluence of the Ping and Nan Rivers at Nakhon Sawan. It then flows from north to south for 372 kilometres from the central plains through Bangkok to the Gulf of Thailand.
In Chai Nat Province, the river splits into the main river course and the Tha Chin River, which then flows parallel to the main river and exits to the Gulf of Thailand about 35 kilometres west of Bangkok in Samut Sakhon. In the low alluvial plain which begins below the Chai Nat Dam, many small man-made canals split off from the main river. The canals are used for transportation as well as for the irrigation of the region’s rice paddies.
The Principal Tributaries of the Chao Phraya River are as follow:
- The Ping River (with the Wang River as its principal confluent)
- The Nan River (along with the Yom River as its principal confluent)
- The Pa Sak River
- The Sakae Krang River
- The Tha Chin River
All of the Chao Phraya’s tributaries form an extensive tree-like pattern, with branches flowing through nearly every province in Central and Northern Thailand.
The expanse of the Chao Phraya River and its tributaries (i.e. the Chao Phraya River system, together with the land upon which falling rain drains into these bodies of water) form the Chao Phraya watershed. The Chao Phraya watershed is the largest in Thailand, covering approximately 35 percent of the nation’s area, and irrigating an area of 157,924 square kilometres.
The Mekong River System
The Mekong River is the 11th-longest river in the world, and the 12th-largest by volume (discharging 475 cubic kilometres of water annually). Its estimated length is 4,880 kilometres, and it irrigates an area of 810,000 square kilometres. Mekong therefore ranks as one of the world’s major rivers.
From the Tibetan Plateau it runs through China’s Yunnan Province, Myanmar, Thailand, Laos, Cambodia, and Vietnam where it drains into the South China Sea — all these countries (except China and Myanmar) are members of the “Mekong River Commission”. The extreme seasonal variations in flow and the presence of rapids and waterfalls have made navigation extremely difficult. Approximately half the river’s length is in China, where it is known as the Lancang Jiang (澜沧江 / Láncāng Jiāng) or Meigong in Chinese (湄公河 / Méigōng Hé).
The river meanders through Southwest China for more than half its length before reaching China’s border with Myanmar. From there, it serves as border between China and Myanmar for about ten kilomemtres, and then serves as the border between Myanmar and Laos for about 200 kilometres, at the point which it meets its tributary Ruak River at the Golden Triangle (20° 21′ 20″ N, 100° 4′ 53″ E), where Thailand, Laos and Myanmar share common border. This point also marks the division between the Upper and the Lower Mekong.
The Mekong River serves as Laos and Thailand starting from the Golden Triangle up to Kaeng Pha Dai in Chiang Rai Province, before running a stretch through Laos alone. The river again marks the Lao-Thai border starting from Pho Kok Ngiew in Loei Province. From that location, the Mekong again serves as a natural border between Thailand and Laos, meandering south-eastwards through to Khong Chiam District in Ubon Ratchathani Province in North-eastern Thailand and then continues her course through Laos and Cambodia before draining into the South China Sea in southern Vietnam.
In Cambodia, the river is called the Mékôngk or Tonle Thom (“great river”). Just above Phnom Penh is the confluence with the Tonle Sap, the main Cambodian tributary. Below Phnom Penh, it divides into the Bassac and the Mekong proper, both of which flow into the Mekong Delta in Vietnam.
In Vietnamese, the river as a whole is known as Mê Kông. In Vietnam, the river divides into two major branches, the Tiền Giang (Front River) and Hậu Giang (Back River). These in turn enter the South China Sea through nine estuaries.
The Chi River and the Mun River (that irrigates Northeastern Thailand) flow from West to East and drain into the Mekong near the city of Ubol Ratchathani. The Mekong is the only river system in Thailand which drains into the South China Sea.
Source: https://www.mrcmekong.org/geography/ & https://en.wikipedia.org/wiki/Mekong
Lesser Gulf of Thailand River Systems
There are a number of lesser rivers that flow into the Gulf of Thailand that are worth noting as follows:
- The Bang Pakong River is a river in eastern Thailand. The river originates at the confluence of the Nakhon Nayok River and the Prachinburi River in Prachinburi Province. The watershed of the Bang Pakong is about 17,900 square kilometres.
- The Mae Klong River is a river in western Thailand. The river begins at the confluence of the Khwae Noi and the Khwae Yai rivers in Kanchanaburi Province, passes through Ratchaburi Province and empties into the Gulf of Thailand in Samut Songkhram.
- The Phetchaburi River is a river in western Thailand. It originates in Kaeng Krachan National Park, Kaeng Krachan District and flows for 210 kilometres mostly through Phetchburi Province and drains into the Gulf of Thailand.
- The Pran Buri River is in Prachuap Khiri Khan Province, on the Kra Isthmus of the Malay Peninsula. The Pran Buri River originates in southern part of the Kaeng Krachan National Park, and after 160 kilometres empties into the Gulf of Thailand. The watershed of the Pran Buri River has an area of about 2,000 square kilometres.
- The Tapi River is the longest river in Southern Thailand. The river originates at Khao Luang mountain in Nakhon Si Thammarat Province, and drains into the Gulf of Thailand at Ban Don Bay near the town of Ban Don. It has a length of 230 kilometres. The river irrigates an area of 5,460 square kilometres.
- The Pattani River has a total length of 214 kilometres. It drains into the southern part of the Gulf of Thailand. It originates in Betong district, YalaProvince, and empties into the Gulf of Thailand at the town of Pattani.