IDENTIFICATION OF THE TRUE SOURCE AND HEADWATERS OF LANCANG JIANG (MEKONG RIVER)

Guan Zhihua, Zhou Changjin and Tao Baoxiang

Commission for Integrated Survey of Natural Resources Chinese Academy of Science, Beijing 100101

GEOGRAPHY, October 1999

Translated into English by Tamotsu Nakamura

Abstract

Lancang Jiang has the source in Qinghai Province of our country, and changes its name to the Mekong River when it flows down into a territory of foreign countries. Lancang Jiang is an important international river not only in our country but also in the world. We have identified the true source and headwater of Lancang Jiang (Mekong River) through the field surveys of water drainage, topography, glacier and river stream, etc. taking advantages of such technology as Global Positioning System (GPS), Geographic Information System (GIS) and Satellite Remote Sensing System (SRS), etc.

The river length had the first priority for the evaluation but drainage area, discharge, etc. were also taken into consideration. It has been finally confirmed that the true source of Lancang Jiang is the Zayaqu which starts from Guosongmucha Shan of an altitude of 5,514 meters above sea level in Zaqing, Zadoi County, Yushu Tibetan Autonomous Prefecture, Qinghai Province, and that the headwater of Lancang Jiang is a glacier discharge with an altitude of 5,224 meters above sea level and the geographical location is longitude 94 41 44 E and a latitude 33 42 31 N.

Key words: Lancang Jiang, True source and Headwater

In June to July of 1999, an association of exploration of the Chinese Academy of Science organized 1999 China Dexiang Expedition for the scientific survey and exploration of the headwater of Lancang Jiang. They conducted extensively an integrated scientific survey of water drainage, fauna and flora, glacier, topography and geology, and subsequently could gather a great deal of the updated data by using Global Positioning System (GPS), Satellite Remote Sensing System (SRS) and Geographic Information System (GIS). The survey led to an identification of the true source and headwater of Lancang Jiang (Mekong River). The true source is Zayaqu that originates in Guosongmucha Shan of an attitude of 5,514 meters above sea level in Zaqing, Zadoi County, Yushu Tibetan Autonomous Prefecture, Qinghai Province.

1. Outline of Lancang Jiang

Lancang Jiang is the only international river to connect as many as six countries in Asia. The headwater originates in Yushu Tibetan Autonomous Prefecture, Qinghai Province, once passes through Qamdo Prefecture of Tibet Autonomous Region, flows down to the mountain area Yunnan near Yanjing and crosses the border in the northwest of Monpeng where the name of the river changes to the Mekong. The river further flows through Burma, Laos, Cambodia and Vietnam, and finally pours into South China Sea. The total river length is 4,500 km, the total area of drainage basin is 810,000 sq km and the discharge excluding underground water into the sea is eight times of Yellow River (Note 1). Lancang Jiang is a great river of the world fame.

The drainage basin area in the Chinese territory is 167,486 sq km, the river length is 1,826 km and the mean annual discharge excluding underground water from our country to the foreign countries is 76 billion cubic meters (Note 2) which ranks fifth in China after Chang Jiang (Yangtze), Pearl River, Yarlung Tsangpo (Upper Brahmaputra) and Heilong Jiang (Amur). A potential power generation capacity in the dry season is 32,030,000 kw which ranks forth in China although it is a bit less than those of Chang Jiang, Yarlung Tsangpo and Nu Jiang (Upper Salween). Lancang Jiang is recognized one of the important resources of hydroelectric power generation in our country for a possibility of easier development and exploitation.

The river basin of Lancang Jiang forms a narrow and rectangular topography, and generally speaking tributaries flowing into the both riverbanks are rather small and short. Lancang Jiang is divided into the following three sections of the upper, middle and lower basins. The upper basin is the upstream from Qamdo. The middle basin is from Qamdo down to Jiuzhou. The lower basin is from Jiuzhou to the border. In the upper basin there are two tributaries. The eastern tributary is Zaqu and the western is Ngomqu. The two rivers join near Qamdo of Tibet. Zaqu has an extension of 518 km while that of Ngomqu is 364 km (Note 3). As Zaqu is longer than Ngomqu, Zaqu has been determined to be the true source of Lancang Jiang. Zaqu separates again into two tributaries at Ganasongdou (a longitude 94 36 40 E and a latitude 33 12 33 N), 110 km northwest of Zadoi in Zadoi County, Yushu Prefecture, Qinghai Province. These are Zayaqu and Zanaqu. That the upper stream from Zadoi is the headwaters of Lancang Jiang.

The basin of Lancang Jiang (Mekong River) has an abundance of water resources, minerals, plants and animals, agricultural products and spots for tourism. In recent years, this fact has invited a widespread attention internationally, and foreign explorers visited the area concerned in succession and went deeply into the headwater to carry out a scientific survey. They issued a report on the source of Lancang Jiang. Someone registered their record to The Royal Geographical Society of the United Kingdom and claimed loudly that they had discovered the new source of the Mekong (Note 4).

Apart from this a foreign university and an institution of research and science sent successively a study team independently or jointly with several institutions for scientific researches of our country. However there was not enough time for them to pursue what they attempted to do. Since they could not make a well-prepared field survey nor an analysis based on the current geographical data that were available with them, they were unable to identify the true source and headwater of Lancang Jiang that could have been endorsed by a scientific and realistic background. In other words, we would say, they have been carrying on their baseless claim, thatŐs like putting a fifth wheel on a coach, on the source of Lancang Jiang that has many legendary (spiritual) ones.

A Chinese magazine of the 26th July of 1999 introduced nine sources of Lancang Jiang. There are two well-known sources. One is Zanarigen Shan (Note 5) of the upper Zanaqu and the other is Zaxiqiwa of the upper Zayaqu. Some foreign book mentions these two sources (Note 6). But there are confusions in some of the foreign writings about the said streams. Such a mistake is found that Zanaqu and Zayaqu is the same river (Note 7).

2. Identification of the True Source and Headwater of Lancang Jiang

1) Criteria to identify the True Source

In general the following factors have to be taken into an account for identifying the true source and headwater of river. Those are a river length, discharge, area of drainage basin, tradition and custom, flowing direction and geological history of river valley, among which the river length has the first priority. All the river sources and headwaters of the major rivers in our countries, Chang Jiang, Yellow River and Yarlung Tsangpo, etc. have been determined in accordance with the said criteria. In case a river length is almost same each other, a discharge should play an important roll. A quantity of the discharge exerts a direct influence on the movement of water flow, and consequently it has an effect on the development and change of the relevant river. Where small streams flow adjacently each other, rain falls, evaporation, soil, plants to cover the ground surface and inclination, which have an effect on the water above ground surface, are similar and naturally the area of drainage basin has a direct linkage with the quantity of river discharge.

Where no distinct difference is found in a length, area and discharge, a coincidence of the river flow direction may have a certain meaning to identify the river source. (Note 8) We think that normally it would be unnecessary to take a tradition and custom into consideration as one of the criteria. Their understanding on the rivers is getting deeper. Technologies to measure the river length and discharge the accuracy of these measurements are improving continually. In case that the above criteria could not apply, such factors as a difference in elevation, history of the development and width and depth of the river would be considered for the assessment.

2) Identification of the True Source

Zaqu, the upper Lancang Jiang, separates to two tributaries of Zayaqu and Zanaqu at the confluence called Ganasongdou. In the afternoon on the 4th September of 1994, Zhou Chang-jin and Jin Chang-xing made a field survey at Ganasongdou. They got a result of the measurement in Zanaqu: the river width: 30.0 m, mean depth: 0.33 m, mean flowing velocity: 1.07 m/s, and discharge: 10.6 m3/s, whilst in Zayaqu the figures were the river width: 40.0 m, mean depth: 0.73 m, mean flowing velocity: 1.89 m/s and discharge: 54.9 m3/s. At this time, discharge of Zayaqu was 5.2 times of that of Zanaqu, and the river length and the area of drainage basin calculated being based on the 1:100,000 topographical maps were 90.7 km and 1,983.0 sq km for Zanaqu and 93.3 km and 2,560.0 sq km for Zayaqu, respectively.

On the 12th July of 1999, the 1999 China Dexiang Expedition to survey the source of Lancang Jiang again measured the discharge at the confluence and obtained the following results. Zayaqu: the river width: 62.0 m, maximum depth: 1.30 m, mean depth: 0.73 m, maximum flowing velocity: 4.89 m/s, mean flowing velocity: 2.63 m/s and discharge: 119.0 m3/s. The velocity was measured by a propeller type flow meter of Model LS25-3A. Zanaqu: the river width: 51.0 m, maximum depth: 0.65 m, mean depth: 0.38 m, maximum flowing velocity: 2.52 m/s, mean flowing velocity: 1.81 m/s and discharge: 35.1 m3/s. The velocity was measured by the same flow meter. A this time the discharge of Zayaqu was 3.39 times of that of Zanaqu. Duly corrected TM Satellite Photographs of September 1998 were analyzed and availed for calculation with computers. It was confirmed that the river length and area of drainage basin of Zayaqu were 97.83 km and 2,457.9 sm km and those of Zanaqu were 92.96km and 1,999.3 sq km respectively.

The above figures clearly indicate that Zayaqu is larger than Zanaqu in every point, not only the river length and area of drainage basin but also the discharge, etc. (Table 1). Therefore we recognize Zayaqu to be the true source of Lancang Jiang.

Table 1: Comparison of Features of Zayaqu and Zanaqu
river length drainage width depth velocity flow
km % sq. km. % m % m % m/s % cm/s %
Zayaqu 97.83 105 2457.9 123 62.0 122 0.73 192 2.63 145 119.0 339
Zanaqu 92.96 100 1999.3 100 51.0 100 0.38 100 1.81 100 35.1 100

(The figures of width and depth are those of a mean value.)

3) Identification of the Headwater of Lancang Jiang

The upper Zayaqu toward the headwater from a confluence that Zagaqu having an origin in Zaxiqiwa Lake joins is called Guoyongqu. As Guoyongqu is the longest tributary with the largest discharge of Zayaqu, we determined Guoyongqu to be the true source of Zayaqu. There are two main tributaries in the upper Guoyongqu. One is Gaodepu that originates in Jifu Shan located at a longitude 94 41 12 E and latitude 33 45 35 N. The other is Gaoshanxigu that originates in Guozongmucha Shan, a glacier of which supplies the first drop of water. After these two valleys join, then the stream is called Guoyongqu.

In order to identify which is the headwater of Lancang Jiang, either Guozongmucha Shan or Jifu Shan, we made a careful analysis in details of the corrected Remote Sensing data of TM Satellite of September 1998, and the subsequent data processing of large volumes by computers output the following figures. Gaoshanxigu: the river length: 22.59 km, area of drainage basin: 97.25 sq km, area of a current glacier in the basin - 2.78 sq km. Gaodepu: the river length: 21.62 km, area of drainage basin: 78.83 sq km, area of a current glacier in the basin: 0.60 sq km. At 4:00 PM on the 14th September of 1999, we carried out a field survey with a propeller type flow meter of Model LS25 3A at Yeyongsongdou, a confluence of Gaoshanxigu and Gaodepu. A discharge of Gaoshanxigu was 9.55 m3/s that exceeded 7.94 m3/s, a discharge of Gaodepu by 20 %. (Table 2)

The above figures tell us that being compared with Gaodepu, Gaoshanxigu is longer (1:1.4) in the river length, larger (1:1.23) in the area of drainage basin and larger (1:4.63) in the glacier area too. Accordingly an annual discharge of Gaoshanxigu would likely be larger than that of Gaodepu. The point to further indicate is the fact that the current glacier of Jifu Shan spreads out to the drainage basin of Chang Jiang (Yangtze River) and most melted water from the glacier flows into Chang Jiang. Therefore, we have recognized Guozongmucha Shan to be the headwater of the true source of Lancang Jiang. Melted water from the current glacier is being supplied to the true source of Lancang Jiang. The geographical location of the headwater is longitude 94 41 44 E and latitude 33 42 31 N and the altitude above sea level is 5,224 meters. Narrow streams of melted water from the glacier gather calmly in Lasagongma and then flow into Gaoshanxigu.

Table 2: Comparison of Features of Gaoshanxigu and Gaodepu
river length drainage area glacial area width depth velocity discharge
km sq. km. sq. km. m m m/s cm/s
Gaoshanxigu 22.59 97.25 2.78 9.45 0.30 3.37 9.55
Gaodepu 21.62 78.83 0.60 11.0 0.29 2.49 7.94

(depth & velocity: a mean value)

3. Preservation of Environments in the River Source

From a geographical point of view, the river source of Lancang Jiang is located in a high plateau where plants to cover the soil are scarce and of shorter life. Too many animals are congesting in the field of limited natural pastures. In addition, a disaster caused by grass mouse is very serious. The glass land as a natural resource is deteriorating day by day. An outflow of the water and earth/sand is ceasless, and a transformation of the soil into the desert is being accelerated rapidly. Invaluable wild animals that are protected under the state-controlled scheme of wildlife reservation inhabit the plateau. They are snow leopards, black necked cranes, Tibetan sheep and wild donkeys. The quality and volume of caterpillar fungus that are collected in this region are well known in the world. However an excessive hunting of animals happens incessantly, and materials for valuable traditional medicines are also facing danger from excessive gathering.

A constant increase of the ambient temperature in an earth-wide scale is triggering an expansion of the dried and arid land. It brings about an increase of a social demand of the water consumption too not only in a short term but a medium time frame. In the 21st century, a more critical crisis of the water shortage will take place in a global basis. Water resource per capita of our country is as low as one forth of the world average. To solve an imbalance of the demand and supply of water, we should make the following measures. Firstly the existing water resource must be well maintained. Secondly we must appeal for the reduction of water consumption and thirdly yjr water resource must be developed in such practical ways as to promote an inter-regional swapping of water and to utilize rainwater, dirty water and sea water. Special attention should be drawn to the fact that the source of Lancang Jiang is located adjacent to our mother rivers, Chang Jiang (Yangtze River) and Yellow River and that it is a matter of urgency to protect our mother rivers. For the purpose we herein propose that our government take an action to establish ecological nature reserves in the sources of the three rivers (Chang Jiang, Yellow River and Lancang Jiang) as soon as possible. This will have a great deal of effect on the conservation program not only to strengthen protection of wildlife but also to maintain water supply sources and to keep good soil-water conditions as well.

The sincere thanks are expressed to the Desxiang Business Group of Tianjin to have afforded a substantial support for the research.

Bibliography

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