Salween River
The Salween is a Southeast Asian river, about long, flowing from the Tibetan Plateau south into the Andaman Sea. The Salween flows primarily within southwest China and eastern Myanmar, with a short section forming the border of Myanmar and Thailand. Throughout most of its course, it runs swiftly through rugged mountain canyons. Despite the river's great length, only the last are navigable, where it forms a modest estuary and delta at Mawlamyine. The river is known by various names along its course, including the Thanlwin in Myanmar and the Nu Jiang in China. The commonly used spelling "Salween" is an anglicisation of the Burmese name dating from 19th-century British maps.
Due to its great range of elevation and latitude coupled with geographic isolation, the Salween basin is considered one of the most ecologically diverse regions in the world, containing an estimated 25 percent of the world's terrestrial animal species and thousands of plant species. Along its course the Salween provides water for agriculture and supports abundant fisheries, especially in the delta region. The Salween basin is home to numerous ethnic minority groups, whose ancestors largely originated in the Tibetan Plateau and northwest China. Starting about 5,000 years ago, people began migrating south along the river, establishing small kingdoms and city-states.
During the last 1,000 years, the Salween has defined various frontiers of the Burmese empires to the west, the Kingdom of Siam to the south, and Imperial China to the east, with the Shan States along the middle Salween being a frequently contested area. In the 19th century, the British Empire invaded Burma with Mawlamyine serving as the colonial capital for many decades. Since Burmese independence in 1948, the Salween basin has been a battleground for several fronts of the Myanmar civil war, with large areas in Shan State and Karen State contested between the Myanmar military and local ethnic militias.
The Salween is one of the least fragmented large river systems in Asia, with only a few small dams in the headwaters of the river and on tributaries. The river has extremely high hydropower potential, with a fall of more than from its source. Since the 1970s, the Myanmar and Thai governments have sought to build massive hydroelectric dams along the river. China also planned to dam the upper Salween, but in 2016 these plans were dropped in favor of establishing a national park. The future of dam projects in Myanmar and Thailand remains uncertain.
Geography and naming
The Salween basin includes about, of which 48 percent is in China, 44 percent in Myanmar, and 8 percent in Thailand. The basin is extremely long and narrow, situated between the Irrawaddy and Brahmaputra river systems on the west and the Mekong system on the east, and sharing a shorter boundary with the Yangtze system to the north. With a mean elevation of, the Salween basin includes numerous glaciated mountain ranges, and the river flows for much of its length at high elevation. In China, the Salween basin is situated in Tibet Autonomous Region and Yunnan. In Myanmar the Salween flows through Shan State, Karenni State, Karen State and Mon State. In Thailand the Salween borders only on Mae Hong Son province, with tributaries extending into Chiang Mai, Tak and Kanchanaburi province.The average flow rate at the China–Myanmar border is.
Along the Myanmar–Thailand border the Salween carries an average annual flow of. The estimated flow rate at the mouth is. About 89 percent of the annual flow occurs in the monsoon season, and only 11 percent in the remainder of the year.
The average volume of sediment in the Salween Delta is around 180 million tonnes per year.
The population of the Salween basin is estimated at 24 million, or 76 persons/km2. About 10 million people live adjacent or close to the river proper. People of the Salween basin represent a large diversity of ethnic groups. In China, the Salween basin is home to Blang, Derung, Lisu, Nu, Palaung, Shan, Tibetan and Wa. In Myanmar, the major ethnic groups include Akha, Lahu, Lisu, Hmong, Kachin, Karen, Karenni, Kokang, Pa'O, Shan and Yao. The highest population densities are in Mon State and Yunnan, while the lowest population density is in Tibet.
Upper Salween (China)
The Salween originates in the Tanggula Mountains in the central Tibetan Plateau. The headwaters are located near Dengka Peak, east of Tanggula Pass. The highest source is Jiangmeiergang Galou glacier, above sea level. The various headwater streams flow southwest through high mountain valleys and accumulate in Cona Lake, at. Downstream of the lake, the Tibetan section of the river is called Gyalmo Nagqu, "black river". In Tibet the river flows mostly within Nagqu prefecture.From Cona Lake, the river flows south and turns east near Nagqu Town, where the Chalong hydroelectric station is situated. Further east, the river is dammed at the smaller Jiquan hydroelectric station. As of 2017, these are the only two dams on the Salween River proper. Continuing east, it is joined by the Ka, Suo and Ga rivers, all flowing from the southern slope of the Tanggula Mountains. In Biru County, the river begins a series of turns south and southeast, passing through Nyingchi prefecture. Shortly before entering Yunnan, it is joined from the east by the Yu River, its longest tributary within China.
The Tibetan portion of the Salween basin is lightly populated, especially in the frigid headwater regions where precipitation is scarce and river flow depends almost entirely on glacier melt. The upper Salween basin includes more than of glaciers.
In Yunnan, the Salween is known as the Nujiang or Nu River, after the indigenous Nu people, but also translating literally to "angry river". For more than the Salween runs parallel to, and west of the headwaters of the Mekong and Yangtze, separated by high mountain ridges of the Hengduan Mountains. The Gaoligong Mountains west of the Salween form the border between China and Myanmar. Between the Salween and Mekong rivers around the Tibet–Yunnan boundary are the Meili Xue Shan, which include Kawagarbo, the highest peak in the Salween basin at.
Much of the river within Yunnan is part of the Three Parallel Rivers of Yunnan Protected Areas, a World Heritage Site. Forming canyons up to deep, this section is often called the "Grand Canyon of the East".
Continuing south, the river crosses the Yunnan–Guizhou Plateau via a series of deep canyons broken by wider valleys. In Longling County it is joined by the Kuke River and turns west, entering Myanmar. The total length of the river in China is, not including a short segment along the China–Myanmar border. By the time it leaves China the Salween has descended more than from its source.
Lower Salween (Myanmar and Thailand)
In Myanmar the Salween river is officially known as Thanlwin; in Shan State, which the river enters immediately upon leaving China, it is also known as Nam Khone. Turning south, the river slices a winding course through the vast upland region known as the Shan Hills. This area is characterized by a complex, broken topography of small mountain ranges, plateaus and cliffs, through which the Salween has cut an extensive series of gorges. As the Salween flows south and descends in elevation, it travels from temperate to subtropical and finally tropical climate zones, with yearly precipitation ranging from in the Shan Hills area. The total length of the river in Myanmar and Thailand is.In Shan State and Karenni State the river is joined by several large tributaries, including the Nanding River and Hka River from the east, and the Pang, Teng, and Pawn Rivers from the west. The Pang River is noted for its extensive limestone formations near the confluence with the Salween, where it breaks into a myriad of cataracts, channels and islets known as Kun Heng, "Thousand Islands". Inle Lake, the second largest lake in Myanmar and a World Biosphere Reserve, drains into the Salween by way of the Pawn River.
Further south, the river enters Karen State and forms the border between Myanmar and Thailand for about. In Thailand the river is known as Salawin; much of the Thai side of the border is part of Salawin National Park and the Salawin Wildlife Sanctuary. At the south end of the border section it is joined by the northwest-flowing Moei River, which forms the Myanmar–Thailand border south of this point. In Karen State, the river flows through karst limestone hills where numerous caves and unusual rock formations line the banks, particularly around the city of Hpa-An.
The Salween emerges from the mountains into the coastal plain near Hlaingbwe Township. Near the coast, annual rainfall is as high as, supporting dense tropical rainforest as well as a productive rice industry. The river flows for a further before terminating at a modestly sized delta and estuary in Mawlamyine in Mon State. The Salween is tidally influenced up to inland. Here it is joined by the Gyaing River from the east and the Ataran river from the southeast. The Thanlwin Bridge, the second longest bridge in Myanmar, connects Mawlamyine to Mottama. The combined river then breaks into the Dayebauk and Mawlamyine channels, forming Bilugyun Island before emptying into the Gulf of Martaban.
List of tributaries
Major tributaries by average flow :Discharge
Flow regime at Hpa-an Station of Thanlwin River:Monthly flow pattern Thanlwin river at Hpa-an during 2009 to 2013:
Geology
The present course of the Salween began to form about 5 million years ago as the Indian subcontinent collided with Asia, resulting in the uplift of the Himalaya mountains and the Tibetan Plateau. Prior to the Himalaya orogeny, what are now the upper Irrawaddy, Salween, Mekong and Yangtze rivers may have all flowed into the Red River, emptying into the South China Sea. The landscape was hilly but not particularly rugged, with average elevations of or less. As the continents converged, a complex jumble of mountains arose, breaking the ancestral Red into different drainage systems, with the Yangtze heading east towards the Pacific, and the Mekong and Salween flowing south into what is now Thailand's Chao Phraya River. About 1.5 million years ago, volcanic activity diverted the Salween west towards the Andaman Sea, roughly creating the modern path of the river.Image:怒江峡谷_-_panoramio.jpg|thumb|right|Salween river in Tibet
The parallel modern courses of the upper Salween, Mekong and Yangtze are located where the eastern Tibetan Plateau intersects the uplands of the Yunnan–Guizhou Plateau. The mountain ranges separating these rivers are individual terranes that accreted separately to the Asian continent – forming a basin and range landscape with drainage running from north to south – then compressed together such that the rivers flow only apart in places. As the mountains continued to rise, the rivers incised into the landscape along parallel fault zones, creating the deep canyons of the present day. The Nujiang fault zone stretches over along the river in Yunnan.
The formation of the Himalayas blocked drainage from the Tibetan Plateau south towards the Indian Ocean, forcing drainage north of the mountains east towards the Yangtze river. This east-flowing river, the predecessor of the modern Yarlung Tsangpo river, was repeatedly captured into drainages to the south, finding various routes to the sea via the Red, Mekong, Salween and Irrawaddy rivers. The combined Salween–Yarlung Tsangpo drainage would have been much longer than the modern Salween, stretching an additional west across the Tibetan Plateau. Ultimately the Yarlung Tsangpo was captured by the Brahmaputra River in present-day India. The Salween may once have had additional tributaries above its present source, but due to the uplift of the Himalaya blocking moisture from the Indian Ocean, these tributaries dried up, leaving the numerous terminal lakes scattered across Nagqu today.
The Salween carries an estimated 108 to 237 million tonnes of sediment per year. About 92 percent of sediment is delivered to the ocean during the monsoon season. The Salween delta is physically contiguous with the Irrawaddy and Sittaung deltas. The Irrawaddy–Sittaung–Salween delta is relatively stable, with the coastline advancing an average of per year between 1925 and 2006. Sediment accumulation is largely balanced out by subsidence and transport by ocean currents. However, proposed dams along the Salween would trap much of the sediment with potential detrimental impacts to coastal erosion.