Reconfirmation on Identification of True Source and Headwater of Lancang Jiang (Mekong River)
Zhou Changjin and Guan Zhihua
Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
Geographical Research, May 2001, Vol. 20, No. 2
Translation: Chinese to Japanese by Shiro Kawase, Japanese to English by Tamotsu Nakamura
Lancang Jiang has its source in Qinghai Province of our country, and changes its name to the Mekong River where it flows down into the territory of foreign countries at the border with Yunnan Province. Lancang Jiang is an international river of great importance not only in our country but also in the world. We have carried out field surveys of the characteristics of water drainage, topography, glaciers and river stream, and then identified the true source and headwaters of Lancang Jiang (Mekong River) taking advantages of such technology as GPS (Global Positioning System), GIS (Geographic Information System) and SRS (Satellite Remote Sensing). Placing the first priority on river length and also taking into consideration water discharge and drainage area for the evaluation, we have finally confirmed that the true source of Lancang Jiang is in the Zayaqu. The headwaters of Zayaqu starts from Guosongmucha Mountain of an altitude of 5514 meters above sea level in Zaqing, Zadoi County, Yushu Tibetan Autonomous Prefecture, Qinghai Province. The glacier area of Guosongmucha Mountain is 0.67 sq km, the glacier ends at an altitude of 5224 meters and its geographic location is a longitude of 94 41 44 E and a latitude 33 42 31 N.
Key word: River origin, Headwater, River source, Lancang Jiang, Mekong River, International river. See original publication in Chinese for Figures and References
In June to July of 1999, scientists of the Institute of Geographic Sciences and Natural Resources Research participated in the Scientific Research Expedition to the Source of Lancang Jiang. They conducted extensive comprehensive and scientific surveys and analyses of water drainage, water content, fauna and flora, glaciers, topography and geology of the headwaters area of Lancang Jiang, and consequently could gather directly a great deal of data and information. The party identified the source and headwater of Lancang Jiang (Mekong River) making use of modern technology of GPS, SRG and GIS, etc. The headwater of Lancang Jiang is in Zayaqu and originates in Guosongmucha Mountain of 5514 meters, Zaqing, Zadoi County, Yushu Tibetan Autonomous Prefecture, Qinghai Province.
Notes: The article was originally submitted on October 17, 2000 and revised on February 22, 2001. The principal author is Zhou Chang-jin (1950 -), a man from Shangdong Province, who specializes in scientific research of water resources.
1. Outline of Lancang Jiang
Lancang Jiang is the only international river to connect as many as six countries in Asia. The headwaters originate in Yushu Tibetan Autonomous Prefecture, Qinghai Province. After passing through Qamdo Prefecture of Tibetan Autonomous Region, it flows down to the mountainous area forming deep gorges in Yunnan Province near Yanjing and crosses the border in the northwest of Monpeng where the name of the river changes to the Mekong. The river then flows through Burma, Laos, Cambodia and Vietnam, and finally discharges into the South China Sea. The total river length is 4880 km, total area of drainage basin is 810,000 sq km (1) and annual total discharge excluding underground water into the sea is 463.3 billion cubic meters (2). It is a great river of world fame.
In Chinese territory the area of drainage basin is 167,487 sq km, river length is 2,164 km and mean annual discharge to the other countries is 76 billion cubic meters (3). In terms of river length Chang Jiang/Yangtze River is 6,300 km, Huang Ho/Yellow River is 5,464 km, Heilong Jiang/Amur River is 3,420 km, Songhua Jiang is 2,308 km and Pearl River is 2,214 km (4). Lancang Jiang ranks sixth in China. Potential power generation capacity in dry season is 32,030,000 kw which ranks fourth in China, after Chang Jiang, Yarlung Tsangpo (upper Bramaputra) and Nu Jiang (upper Salween River).
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. Therefore no water transport is well developed. Lancang Jiang is divided into the following three sections: upstream from Qamdo is the upper basin, the section between Qamdo and Jiuzhou is the middle basin and from Jiuzhou down to the border is the lower basin.
In the upper basin there are two major tributaries. The eastern tributary is Zaqu and the western is Ngomqu. The two rivers join together near Qamdo. Zaqu is 518 km long whilst Ngomqu is only 364 km long (5). Zaqu is longer, has a larger drainage area and a bigger discharge than Ngomqu, so it has been determined to be the tributary containing the true source of Lancang Jiang. Zaqu separates again to two tributaries at Ganasongdou (E 94 36 40 and N 33 12 33), 110 km northwest from the town of Zadoi in Zadoi County, Yushu Tibetan Autonomous Prefecture, Qinghai Province. These tributaries are Zayaqu and Zanaqu, which together drain the true headwaters area of the Lancang Jiang.
The middle basin has a length of 790 km (6) where the stream is raging down in a torrent through deep gorge. The mountain ridges in both banks soar as high as 1,000 Ð 2,000 meters forming a V shaped valley. The landscape in the vicinity shows remarkable vertical changes in nature and geography. The valley is warm, dry and less rainy. Shrubs and bushes having hard leaves that are suitable for an arid climate are typical scenery. Mountain slopes are warm and humid normally, but sometimes it gets cold. Forests of evergreen and hard wood trees are seen.
In recent years many foreign universities and scientific research institutions have sent their representatives to the headwaters area. Individually or in collaboration with various organizations of our country, they made scientific surveys in the river source of Lancang Jiang. Foreign and Chinese explorers went deeply to the area of headwaters several times and announced their opinions on the true source. To our surprise someone registered their record to The Royal Geographical Society of Great Britain loudly claiming that they had first discovered the new source of Mekong River (7). However the fact was different. They committed a mistake because both their map investigation and field survey were quite insufficient. Identification of the source of Lancang Jiang must be made on the basis of scientific integration of geographical factors and features of river stream in the headwater area. They confused the true geographical headwater with spiritual (legendary) sources of Lancang Jiang that local Tibetans believe.
2. Various Views on the Headwaters of Lancang Jiang
It is said that the source of Lancang Jiang "locates in the heart of inside Asia, that is, in the highest plateau of Central Asia most scarcely inhabited and inaccessible". The region has the steepest and most treacherous topography on earth. Even in mid summer hail storms are common. Wolves, eagles and other wild animals make frequent appearances. Field survey work in this area, therefore, requires much hardship and difficulty.
Until recently there have been various views regarding the issue on the source of Lancang Jiang, based on inadequate topographical maps or local people who traditionally believe the spiritual source is the true source. Chinese Drainage Pattern Dictionary explains that Lancang Jiang originates in the southwestern foot of Tanglha Mountains, west of the watershed of north Zhidoi County, Qinghai Province (8)]. Chinese Encyclopedia - Geography of China mentions that Lancang Jiang originates in Qinghai-Tibetan Plateau and that there are two tributaries in the source, Zaqu in the east and Ngomqu in the west, the both come from Tanglha Mountains (9). Scientific books and articles sometimes quote the above views for the source of Lancang Jiang (3,10,11) but the reference is used only for general explanation on the source.
The local people have two views on the true source of Lancang Jiang. One is Zanarigen Mountain in Zanaqu which is referred to in some of the scientific reports (6,12). The other is Zaxiqiwa of the upper Zayaqu. There are foreign literatures to describe the said two sources in equal basis. Zanarigen locates 17 km north of Moyun in the middle stream of Zanaqu at E 94 13 40 and N 33 19 20. The mountain top is 5550 meters above sea level. Two streams that flow from the mountain, Maigouqu and Chariqu are nothing but small tributaries. Zaxiqiwa locates in a swamp of the upper Zagaqu at E 94 18 14 and N 33 34 15. The altitude is 4650 meters. Zaxiqiwa is formed with small lakes connecting each other in the swamp and the discharge from Zaxiqiwa shares only very minor portion of the total flow of Zagaqu.
In August to September of 1994, the Chinese Academy of Sciences (CAS) and Tokyo University of Agriculture (TUA) planned and carried out jointly a scientific survey and research of Lancang Jiang. In accordance with the original plan to collect as much as possible information to identify the headwaters and true source of Lancang Jiang, we followed Zanaqu downstream to Ganasongdou, a confluence of Zayaqu and Zanaqu (downstream from Ganasongdou the river is called Zaqu). Here where we surveyed geological features of Zanaqu and Zayaqu, topography and water stream, and also measured area of drainage basin and river length of the two rivers using a 1:100,000 scale topographical map. The field and map study proved that Zayaqu has longer river length, larger drainage area and larger discharge than Zanaqu. This led to the discovery that Zayaqu is recognized to be the headwater of Lancang Jiang. In that fieldwork, however, due to a time constraint, the Chinese experts could not reach and make a proper survey of the source of Lancang Jiang. As a result the first published location (E 94 41 35, N 33 44 13) near Lasagongma Mountain on a small stream called Lasagongma was not accurate.
In September of 1994, Michel Peissel and his French and British colleagues explored and surveyed the source of Lancang Jiang. Having been guided by a local Tibetan, they reached Zanahuohuozhudi (Rupsa Pass), the source of Zajaqu that is the upper Zanaqu. This source is 93 km from Ganasongdou. Michel Peissel wrote in his book "The Last Barbarians - The Discovery of the Source of the Mekong" that the location of the source of the Mekong River is E 93 52.929 (E 93 52 56) and N 33 16.534 (N 33 16 32) at 16,322 feet (4975 meters) above sea level." This place was the true source of Zajaqu of the upper Zanaqu.
In June of 1999, Dr. Liu Shaochuang of the Remote Sensing Office conducted 13 days field survey of the Source of Lancang Jiang. His conclusion was that the headwater of Zayaqu is the source of Lancang Jiang which locates on the border of Zhidoi County and Zadoi County of Qingha Province at E 94 41 12 and N 33 45 35 in Jifu Mountain, 5552 meters above sea level (16).
In June to July of 1999, the China Science Exploration Association organized a large scale expedition for comprehensive scientific survey and research of the source of Lancang Jiang. They carried out extensively their mission and finally identified the headwater and true source of Lancang Jiang (Mekong River). The headwater is in Zayaqu and originates in Guosongmucha Mountain 5514 meters above sea level. (Note: maps and figures in the in the original Chinese publication are not included in this translation. See http://Mekong source maps) for an English language version.
3. Criteria for Identification of the True Source
To judge the river source it is imperative to first identify main tributary and its headwater. In general, however, the following factors have to be taken into an account for identification of the true river source and headwater. Those are river length, discharge, area of drainage basin, tradition and custom, and coincidence of flowing direction. Some place an extreme importance on the river length, but it would not be appropriate. River stream must have discharge and length. Therefore the both factors should always be paid utmost attention. River length and area of drainage basin are closely relevant to each other. In general a river that has the longer length would have the larger area of drainage basin, and the larger drainage basin would result in the larger discharge. Under the common circumstances that many of the river headwaters are in the mountainous regions, both the topography and geographical feature are very complicated. The topography, geographical features and geology exert a considerable influence on the development of river stream. In fact, there exist such rivers as narrow but long river or a wide but short river where river length has no relevance to drainage area. Therefore, in order to identify the river source, drainage area is given an importance as independent factor for the determination.
Where there is no notable difference in river length, drainage area and discharge, the coincidence of flowing direction would have to be taken into consideration (17). As to whether custom and tradition should be one of criteria for identification of river source, no definite view is so far established. Some of the spiritual (traditional and legendary) sources believed by local people have long been a matter of their religious concern. There are many sources having been claimed as a result of the field survey and research that had been previously carried out. We have to pay attention to these efforts, but it is unnecessary to consider spiritual beliefs. When the above criteria are not sufficient to distinguish the river source, such secondary factors as difference in elevation of river stream, history of river development and river width and depth will have meaning.
4. Identification of the True Source of Lancang Jiang
Zaqu, the upper Lancang Jiang, separates into two tributaries of Zayaqu and Zanaqu at the confluence called Ganasongdou (see Fig. 1). The region is sparsely inhabited; also travel and weather conditions are challenging, so that continuous records of river discharge and velocity of flow of Zayaqu and Zanaqu have not been available as there was no point of observation of the river stream. On September 4, 1994 and July 12, 1999, we measured water velocity at the confluence (Ganasongdou) by using LS25-3A Model propeller type flow velocity meter. Figures of the measurement are shown in the following Table 1.
The formula Q=FV has applied to calculation of discharge of river stream. F is section area of the stream (square meters) and V is mean velocity of the stream at the section (m/s). Table 1 indicates that the discharge of Zayaqu measured in 1994 was 54.9 m3/s and that of Zanaqu is 10.6 m3/s whilst in 1999 the discharge of Zayaqu was 117.4 m3/s and that of Zanaqu is 32.3 m3/s. The discharge of Zayaqu was 5.2 times greater than Zanaqu in 1994 and 3.6 times greater in 1999. Analysis of TM Satellite photographs and calculation by computer proved that the river length of Zayaqu from Ganasongdou to Guosongmucha was 101.1 km and that of Zanaqu from Ganasongdou to Zanahuohuozhudi (Rup-sa Pass) of the source of Zajaqu was 93.0 km. The drainage area of Zayaqu was 2,634.0 km2 and that of Zanaqu was 1999.3 km2.
These figures tell us that in every respect: river length, drainage area and discharge, Zayaqu is larger than Zanaqu. At the junction of Zayaqu and Zanaqu it is observed that Zayaqu flows from north to south and Zanaqu flows from west to east and Zaqu after merging of the two tributaries flows to southeast. The fact that Zayaqu coincides with Zaqu in terms of flowing direction of the streams would endorse Zayaqu to be the true source of Lancang Jiang (Fig. 2).
5. Identification of the Headwater of Lancang Jiang
We have determined the true source of Lancang Jiang is Zayaqu. Then, where is the source of the Zayaqu? Observation and study conclude that Guoyonggu river is the principal tributary with the longest river length and largest discharge among many tributaries of the upper Zayaqu. In the upper Guoyonggu, there are two main tributaries. One is Gaoshanguxi river that originates in the glacier of Guosongmucha Mountain. The other is Gaodipu river that originates in Jifu Mountain (E 94 41 12 and N 33 45 35). The confluence of the both rivers is at Yeyongsongdou (E 94 31 26 and N 33 44 18, 4779 meters above sea level). After merging it is called as Guoyonggu (Fig. 3).
To determine which is more likely to be the headwaters of the Lancang Jiang, either Guosongmucha Mountain or Jiju Mountain, we made thorough and detailed analysis of remote sensing photographs of TM Satellite taken on September 1998 and calculated the following figures using computers. Gaoshanguxi had river length of 22.59 km, water drainage area of 97.25 square km and current glacier area of 2.78 square km inside the drainage whilst Gaodipu had river length of 21.62 km, water drainage area of 78.89 square km and current glacier area of 0.60 square km. At 4:00 pm on September 14, 1999 we made measurements using LS25 3A Model propeller type flow velocity meter at Yeyongsongdou, confluence of the both rivers. The discharge of Gaoshanguxi was 9.55 m3/s and that of Gaodipu was 7.94 m3/s. The discharge of Gaoshanguxi obviously exceeded Gaodipu by more than 20 percent (Table 2).
(Width and depth are means. Glacier area within drainage basin: Gaoshanguxi: 0.67 sq km Gaodipu: 0.11 sq km)
From the above figures we know that Gaoshanguxi exceeds Gaodipu in river length, drainage area and discharge. Furthermore it should be noted that the upper portion of Gaodipu from Guyong to Jifu Mountain changes according to seasons. The current glacier of Jifu Mountain locates mostly in the drainage basin of Chang Jiang (Yangtze River) and most of the streams from the glacier flow down to Chang Jiang. Therefore we recognize Guosongmucha Mountain to be the headwater of the true source of Lancang Jiang. The source of Lancang Jiang is fed with melting water coming from the current glacier, of which area is 0.67 sq km, its geographical location is E 94 41 44 and N 33 42 31 and an altitude of the glacier tongue is 5224 meters above sea level. The first drops gushing out from the glacier gather to Lasagongma Creek, enter into Gaoshanguxi, and then merge with Gaodipu at Yeyongsongdou where the name changes to Guoyonggu.
6. Conclusion and Contention
An overall evaluation and assessment of the above-mentioned factors lead to the conclusion that Zayaqu is the true source of Lancang Jiang (Mekong River) as Zayaqu is larger than Zanaqu in all respects of not only river length but drainage area and discharge. The flowing direction of Zayaqu at the confluence has certain similarity with Zaqu. The characteristics of river stream and geographical features justify Zayaqu to be the true source of Lancang Jiang. It originates in Guosongmucha Mountain of 5514 meters above sea level of Zaqing, Zadoi County, Yushu Tibetan Autonomous Prefecture, Qinghai Province.
Concerning river length and drainage area, some differences are found in descriptions and figures of the articles having been published since they are based on a less precise calculation methods. "Issues on the Source of Lancang Jiang" an article of Geographical Research, No. 2, 1995 described that the river length and drainage area of Zanaqu were 90.7 km and 1,983.0 sq km whilst those of Zayaqu were 93.3 km and 2.560.0 sq km respectively which had been calculated on the basis of the 1:100,000 scale topographical map of 1973 (14). The current river length and drainage area that are employed in this article were calculated by computers on the basis of detailed analysis of TM Satellite Photographs of September 1998.
Concerning the discharge of the both rivers, the writer conducted field measurements only twice (September 4, 1994 and July 12, 1999) because it was not possible to conduct continuous measurements due to difficult conditions at the site. However, although there would remain a little uncertainty, we understand that the said data could explain most possible conditions of water discharge of the two rivers in rainy season. We visited local Tibetan people living in the vicinity of Ganasongdu to hear the conditions of water discharge in dry season. According to what they said, the discharge of Zayaqu in dry season is far larger than that of Zanaqu.
Solid-state source (melting water from glacier) for stable and constant water supply in the headwater of both Zayaqu and Zanaqu is affected by many factors such as rain fall and radiant heat of sun, etc. This article has dealt with identifying the source and headwater of both Zayaqu and Zanaqu on the basis of comparison and study of river length, drainage area, discharge and geographical features of the both rivers. A comparison of the relative contributions of rainfall versus glacial melt water (solid-state source) to discharge will have to wait for future survey and investigation.
The scientific Research Expedition to the Source of Lancang Jiang carried out very comprehensive and integrated surveys not only for identification of the river source but also for natural resources and environmental aspects in the headwater and collected a great deal of records and information. We do believe that these outcomes shall be the scientific base data that are important and useful to the development and exploitation of natural resources and the preservation of ecological environments in the near future.
(See original article in Chinese for figures and references.)