Lancang River

The Lancang River flows through Qinghai, Tibet and Yunnan provinces and leaves Mengla County, Xishuangbanna Dai Autonomous Prefecture, Yunnan Province. It becomes the boundary river between Laos and Myanmar, and later became known as the Mekong River.

Lancang River

Lancang River is the largest international river in Southeast Asia. It originates in the north of Tanggula, Qinghai Province, China, flows through Myanmar, Laos, Thailand and Cambodia, and flows into the South China Sea in Saigon, Vietnam. The total length of the main stream is 4880 km and the catchment area is 81 × 104 km2. The main stream is 2161km long and the catchment area is 167487 km2. In the west, Nushan (biluoxue mountain in the South) and Bangma mountain are separated from Nujiang River. In the East, Yunling mountain and Wuliang Mountain are separated from Jinsha River and Honghe River respectively. Lancang River runs through the Hengduan Mountains and is the most typical north-south river in the world.

The geomorphic types of the basin are complex and diverse, and the different geomorphic types, topography, slope and mountain trend directly affect the redistribution of water and heat conditions. There are significant differences in the natural environment among the upper, middle and lower reaches of the river. From the perspective of topography, the basin shows a downward trend from north to south in a ladder shape, and its main geomorphic features are alternating mountains and valleys. With the extension of the mountains to the south, the distance between the mountains and rivers gradually widens from the upstream to the downstream, which is as tight as a broom.

Flow area

Lancang River is a typical southward river. With the flow of the river from north to south, the river basin almost includes all the natural landscape and climate types except Gobi and desert in the world. In terms of human society, the basin area is a multi-ethnic gathering area. There are 16 ethnic minorities in Yunnan Province, including Dai, Bai, Buyi and Yi, among which Dai, Buyi and Dulong are all cross-border ethnic groups. The customs, lifestyles and religious beliefs of the ethnic minorities have their own characteristics, and most of them are integrated with the local natural environment.

River Source Area

So far, all kinds of records about the source of Lancang River

There are more than a dozen theories, and there are many kinds of river lengths starting from different sources. The estimated length ranges from 4200 km to 4880 km. Originating from the zanarigen mountains on the north side of Tanggula Mountain, the south slope of chajiarima peak (Tibetan, meaning "colorful mountain") and the zaaqu in the depth of moyuntan, it is located on the gongdemuza mountain of lasaigongma, which is 94 ° 41 ′ 44 ″ e, 33 ° 42 ′ 31 ″ n and 5224 m above sea level, in Zaduo County, Yushu prefecture.

The result of remote sensing expert Liu shaochuang's exploration is that the source of Lancang River is in Jifu mountain, Zaduo County, Yushu Tibetan Autonomous Prefecture, Qinghai Province, with an altitude of 5200 meters. The geographical coordinates are 94 degrees 40 minutes 52 seconds east longitude and 33 degrees 45 minutes 48 seconds north latitude. From here on, the length of the Lancang River is 4909 kilometers.

The main stream in the province is 444.1 km long, and the river basin in the province is 2055.2 km long. The basin area is 37482 km2, and the annual runoff is 10.7 billion cubic meters,

There are 20 rivers with a catchment area of more than 500 square kilometers. The main tributaries are ziqu and Hequ. Zaqu (Tibetan, meaning "numerous water flows") flows into Tibet Autonomous Region in the south, with an average annual flow of 148 cubic meters per second and a natural drop of 1544 meters.

In the source area of Lancang River, the river network is vertical and horizontal, the flow is disordered, and the lakes and marshes are densely distributed. The area where the Zaqu river flows through includes dangerous shoals, deep valleys, primitive forest areas, and Pingchuan. The terrain here is complex, with towering ice peaks and swamps all over the place.

The climate in the source region of Lancang River is characterized by cold, dry, strong wind, strong radiation, long cold season and no absolute frost free period. The annual average temperature is generally between 6.0 ℃ and - 4.0 ℃, but it is below 0 ℃ in most areas. The spatial distribution of precipitation decreases from southeast to northwest. The annual average precipitation in the east of the basin is more than 500 mm, and that in the west is about 250 mm. The annual precipitation distribution has the characteristics of less cold season and more warm season.

Geomorphological features

Geomorphological features of the upper reaches

(1) The landform of Heyuan area is special. Heyuan area refers to the basin area above Zaduo County in Qinghai Province. The average altitude of this area is above 4500m, belonging to plateau meadow area. The main geomorphic types are as follows:

Valleys, plains, mountains and glaciers. River valley plain refers to the river valleys on both sides of the trunk and tributaries, with an average altitude of 4500m. It is characterized by flat ground, small relative elevation difference, ground slope less than 10 degrees, and average distribution of swamps in the river valley. High mountains are the main geomorphic types in the headwaters of rivers. The altitude of the mountain ranges from 4500 to 5800 meters. According to the different ground undulation, it can be divided into high altitude hills (undulating less than 200 meters), small undulating mountains (undulating between 200 and 500 meters), medium undulating mountains (undulating between 500 and 1000 meters) and large undulating mountains (undulating more than 1000 meters). These different undulating mountains alternate with valleys. The total area of glaciers in the headwater area is about 60 square kilometers, and they are concentrated on the undulating mountains above 5500 meters in the northern boundary area. These glaciers are basically valley glaciers.

(2) The geomorphological characteristics of Zaduo Changdu reach Zaduo Changdu is a part of the upper reaches of Lancang River, which is called the upper reaches of Lancang River. The geomorphology of this section is a transitional type from the plain landform of high mountain valley in the headwater area to the landform of high mountain valley in the middle reaches, and it is also a transitional type from the Qinghai Tibet Plateau to Hengduan mountainous area. From Zaduo county to the border area between Qinghai and Tibet, there are high mountains and wide valleys with wide valleys. Along the way, there are river islands and floodplains. The average elevation of the valley is 3500-4000 meters, and the elevation of the mountains on both sides is 5000 meters. From the border between Qinghai and Tibet to Changdu, the mountains on both sides are 5000-5500 meters above sea level, and the river bed is 3150-3500 meters above sea level, forming some "V" shaped canyons with a depth of 500-1000 meters, showing the landform of high mountains and canyons.

Geomorphological features of the middle reaches

From Changdu to Gongguo bridge in Yunnan, it is the middle reaches of Lancang River. This area is a typical mountain canyon landform. High mountains and valleys alternate with each other, the terrain fluctuates greatly, and the drainage basin is narrow. This area is located in the area of three parallel rivers in Hengduan Mountain, and the relative height difference between high mountain and gorge is 3000-4000 meters. The main peaks on both sides of the valley are over 5500 meters above sea level. The dry water level of this section of the main river is 3150 ~ 1240m from top to bottom. In the middle reaches of Lancang River, the relative elevation difference is the largest and the narrowest. The most fluctuating section is the liutongjiang estuary in Deqin, Yunnan, with a dry water level of 2054m. The main peak of Meili Snow Mountain on its right bank is 6740m above sea level, with a relative height difference of 4686m. The narrowest section of the basin is near Yunling in Yunnan, with a watershed of only 20-25 km.

Geomorphological features of the lower reaches

The lower reach of Lancang River is from Gongguo bridge to nan'a estuary. From Gongguoqiao to jingyunqiao is a broad valley area in Zhongshan, which is the transition zone from Qinghai Tibet Plateau to Yunnan Guizhou Plateau. The terrain of the area is broken, the valley is strongly cut, the main Valley is still "V" shape, and the relative height difference of high mountains and valleys is 3500 ~ 1000m. From Jingyun bridge to nan'a river mouth, it is a geomorphic landscape of middle low mountain and wide valley (basin). The altitude is 500-1000 meters, the valley bottom width is 150-300 meters, and the maximum is 800-1200 meters. There are some small basins scattered in the mountains. The development of the valley and the distribution of the river system are still controlled by the broom shaped mountain system in the south of Hengduan Mountains, but the erosion and cutting of the running water also play an important role.

Water system and runoff

River and water system

Lancang Mekong River belongs to the Pacific water system. To the north of Changdu, it is divided into East and West sources. Zhaqu in Dongyuan is 518 km long, and angqu in Xiyuan is 364 km long.

The main stream of the upper Lancang River is 565.4 km long. In Qinghai Province, the main stream is 448 km long, the valley is wide, the river island and floodplain branch flow are developed, and the flow is gentle. The average gradient of the main stream in the upper reaches of Tibet is 4.0% ~ 4.5%, and the maximum is 10% ~ 15%, which is the largest gradient of the whole basin, and is 10 ~ 15 times of the whole average value of the main stream. In this section, the water system is relatively developed, and the main and tributaries are mostly oblique confluence, showing a "branch" distribution pattern.

The middle reaches of Lancang River is a high mountain gorge area, and the main deep valley is a typical "V" shaped valley. Most of the water systems are developed along faults. The tributaries on the West Bank are short and intersect with the main stream. The water system structure is arranged in a "non" shape and belongs to a "pinnate" water system.

The lower reaches of Lancang River are located in the middle mountain gorge, middle and low mountain wide valley landform area, and the valley is still dominated by "V" shape, which varies from width to width along the way. The valley is 150-300 meters wide, and the maximum is 800-1200 meters; the water surface is 50-100 meters wide, and the maximum is 100-150 meters. The average river bed gradient is 0.9%, and the maximum is 8% - 11%. The development of river valley and the distribution of water system are still controlled by the broom shaped mountain system in the south of Hengduan Mountains.

There are 100 dangerous shoals and 54 larger ones in 361km from Nana river mouth to bankelong. The main river valley in this section is still in "V" shape, with stable riverbed and single channel, with an average gradient of 0.42%. The main mountains on both sides are mainly in the north-south direction, and there are many tributaries along the foothills

Chinese PinYin : Lan Cang Jiang