Upper Siang Hydroelectric Project

The Upper Siang Hydroelectric Project or Upper Siang Multipurpose Project or Siang Upper Multipurpose Project (SUMP) consists of the construction of several hydroelectric power dams in the Upper Siang district of Arunachal Pradesh, India. Construction work on the project was commenced by the National Hydroelectric Power Corporation (NHPC) in April 2009 and various hydro dams will be constructed in phases over a span of 15–20 years.^[3]

Upper Siang Multipurpose Project
Country	India
Location	Upper Siang district, Arunachal Pradesh
Coordinates	28.6921°N 95.0443°E / 28.6921; 95.0443[1]
Purpose	Hydroelectric & Flood control
Status	Pre-construction works
Construction began	2028
Opening date	2032 (Expected)
Construction cost	US$ 13 billion[2]
Owner(s)	Government of Arunachal Pradesh
Operator(s)	NHPC
Dam and spillways
Impounds	Siang River
Reservoir
Total capacity	320 tmcft
Maximum water depth	300 meters
Power Station
Operator(s)	NHPC
Commission date	2032
Installed capacity	11,000 MW (under construction)[2]
Annual generation	47 billion kWh

The main dam is being constructed across Siang river and upon completion, the dam reservoir will hold 9 billion cubic meters of water. The hydro power project at Siang will alone generate between 11,000 MW, making it the largest hydroelectric dam in the Indian Subcontinent.^[4]

Concerns

Concern on Upstream Flooding

In 2006, Indian media reported that the NHPC was planning to relocate and scale down the project due to concerns on flooding upstream by Chinese government.^[5] In 2025, NHPC is conducting pre-feasibility studies for site selection.^[6]

The height of the dam is nearly 300 meters above the river bed level at dam location to store water up to 750 m MSL.^[7][8] The back waters of the reservoir would touch the foot of the Medog Hydropower Station (60,000 MW) being constructed on the upstream river in Tibet/China so that adequate flood buffer is maintained to safely discharge the peak floods arising out of upstream dam failures due to earthquakes, Glacial Lake Outburst Floods and massive land slides.^[9][2] This dam acts as a regulating basin to release the continuous flows downstream according to the river flow regime when the water released from the upstream mega dam in China is regulated or intermittent as per the needs of power generation on daily and weekly basis.^[10]

The state government of Arunachal Pradesh signed deals with various Indian power companies to develop hydro projects. A total of 42 schemes are planned to generate electricity in excess of 27,000 MW with the Upper Siang project being one of them.^[11]

Environmental impact

In 2010, a student body appealed to India's Environment Ministry to scrap various hydroelectric projects (including Siang project) in Assam and Arunachal Pradesh due to potential adverse environmental impact.^[12] However, the Ministry remarked that though the projects will not be cancelled, necessary precautions will be undertaken to ensure minimal environmental impact.^[13]