Duilong River in Lhasa
The Duilong River (堆龙河), also known as Duilong Qu in Tibetan (Toelung), is a significant right tributary of the Lhasa River (拉萨河), which flows through the capital of Tibet, Lhasa. Spanning approximately 137 kilometers (85 miles) in length, the river plays a vital role in the hydrology and ecosystem of the region.
The Duilong River begins in the Nianqing Tanggula Mountains (年青唐古拉山脉) and flows south towards the Lhasa River, contributing to the water flow and ecosystem of the Tibetan Plateau. The river’s basin area covers 4,988 square kilometers (1,926 square miles), and it has a hydroelectric power generation capacity of 4,000 kW.
The river is notable not only for its size but also for its ecological and economic importance in the region.
Course and Geography
Origin and Flow
The Duilong River originates in the Nianqing Tanggula Mountains (年青唐古拉山脉), a mountain range that forms a natural boundary for the river’s basin. As it flows southward, the Duilong River is confined by two ridges of these mountains, shaping the valley through which it passes. The river eventually joins the Lhasa River (拉萨河) just below the city of Lhasa (拉萨), making it a significant contributor to the region’s water system.
The river’s course is crucial for local water resources and has contributed to the development of the Qinghai-Tibet Railway (青藏铁路). The railway follows the river from Yangpachen (羊八井) through Toelung Dechen County (堆龙德庆县), reaching western Lhasa.
Hydrological Characteristics and Seasonal Flow
Monsoon and Non-Monsoon Seasons
The Duilong River is subject to a seasonal flow pattern typical of the Tibetan Plateau. The non-monsoon season lasts from October to May, while the monsoon season runs from June to October, during which the river receives 80% of its annual precipitation. The monsoon season is influenced by warm and moist air from the south Indian Ocean, which brings significant rainfall to the region.
This seasonal variation in water flow can impact both the river’s ecological balance and its potential for hydropower generation.
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Monsoon Season: June to October
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Non-Monsoon Season: October to May
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Annual Precipitation: 80% during the monsoon season
Water Quality and Environmental Impact
Arsenic Contamination and Geothermal Influence
While rivers in Tibet are generally considered clean, the water quality of the Duilong River has been impacted by geothermal springs (温泉) in the region. These springs, especially near the Yangbajain Geothermal Field (羊八井地热田), contribute to elevated levels of arsenic in the water.
A study conducted in 2015 revealed that during the non-monsoon season, the arsenic concentration in the Duilong River was found to be 205.6 μg/L, which exceeds the WHO drinking water guideline of 10 μg/L. The source of the arsenic pollution is believed to be untreated wastewater from the Yangbajain Geothermal Field power station, and the contamination is detectable up to 90 kilometers downstream from this site.
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Arsenic Levels: 205.6 μg/L (above WHO guidelines)
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Source of Contamination: Yangbajain Geothermal Field power station
Yangjinshi Reservoir and Hydropower Projects
Potential for Hydropower and Irrigation
The Yangjinshi Reservoir (羊津石水库) has been proposed as a solution to balance the competing demands for irrigation and hydroelectric power generation in the region. A study conducted in 1995 concluded that the reservoir would offer a viable balance between these two needs.
The proposed location of the Yangjinshi Reservoir is upstream from the river, covering a catchment area of 1,580 square kilometers (610 square miles), and with an annual runoff of 394 million cubic meters. If constructed at an elevation of 4,360 meters above sea level, the reservoir would have a capacity of 81 million cubic meters and would include a 4,500 kW power station.
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Catchment Area: 1,580 square kilometers
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Reservoir Capacity: 81 million cubic meters
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Hydropower Capacity: 4,500 kW
