The Sunni Dam Hydro Electric Project (HEP) is a run-of-the-river type scheme being developed on the Satluj river in Himachal Pradesh, India.

Indian public sector undertaking (PSU) SJVN Limited is the proponent of the 382MW project.

The Sunni Dam is estimated to generate 1,381.77GWh of electricity in a 90% dependable year, and improve power reliability in the northern part of the country.

The Prime Minister of India Narendra Modi launched the ground breaking of the project in December 2021.

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India’s Ministry of Environment, Forest and Climate Change (MoEF&CC) granted Forest Clearance Stage-II for the project in August 2022.

The government’s Cabinet Committee on Economic Affairs (CCEA) approved the investment for the project in January 2023 for an estimated cost of INR26.14bn ($320m). This includes INR138m as budgetary support from the government for cost of enabling infrastructure.

The civil and hydro-mechanical works for Sunni Dam HEP are expected to be completed by November 2027.

Location Details of Sunni Dam HEP

The Sunni DAM HEP is situated near Khaira Village in Shimla and Mandi Districts of Himachal Pradesh.

The site of the project is around 145km from the nearest railhead at Kalka, Haryana. It is accessible by roads and the nearest airport is about 70km from the project site.

Overall, the construction of the project components and other infrastructure will require around 459.45-hectare area.

Sunni Dam Hydro Electric Project Infrastructure

The hydro electric project will involve building a concrete gravity dam across Satluj river and an underground powerhouse on the right bank of it.

The project components will include a 642.21m long with 10m diameter horse shoe shaped river diversion tunnel on the left bank of the river. It will be designed to pass lean season and non-monsoon season diversion flood up to 773 cumecs.

The concrete gravity dam will be ±71m high from river bed level, and 178m long and 8m width at the top. It will have six bays fitted with radial gates of size of 8.5m width x 16m height and Upper level spillway of one bay fitted with Flap gate of size 5m width x 4.5m height to pass 15,473 cumecs (PMF).

Full reservoir level is kept at El.712 metres above mean sea level (masl) and Minimum Draw Level at El.709.5.0masl. The dam would provide 82.5 million cubic metres (MCM) of gross pondage and 7.9MCM of live storage.

Three intake structures will divert water from the reservoir to the dam toe powerhouse on the right bank. It will be provided with intake gates with stoplog gates to enable inspection and maintenance, and prevent sedimentation within pressure shaft entrance area.

Three additional pressure shafts will provide further flexibility in operations and maintenance. The pressure shafts shall be bifurcated further into six to pass discharge of 726.95cumecs.

The 171m x 22.5m x 51.5m underground powerhouse will feature four 73MW Main Units; and one 73MW and one 17MW units in Auxiliary. According to SJVN, the project will use Francis turbines.

The powerhouse cavern will be located around 200m inside the hill with top cover of 300m. A minimum of 50m rock cover will be available between transformer hall and machine hall.

Water from the turbines will be discharged through the draft tubes into two 10.5m and 9m diameters horse-shoe shaped tailrace tunnels.

The tailrace tunnels shall have a length of 288m and 208m.

A Tail Race Tunnel (TRT) outfall gated structure after TRT is expected to be built with crest level of El647.2m for discharging water from TRT to Satluj river.

Electricity Generation

The project seeks to leverage the vast power potential of the Satluj river.

In a hydroelectric power station, the river water flowing is stopped by constructing dams and it is stored in a reservoir. Subsequently, the water is made to flow through pipes on the blades of turbines, which are connected to electric generators.

The rotation of the generator coil produces electricity.

In the case of Sunni Dam HEP, around 59.97m gross head of water stored behind dam will be made to fall through closed water conductor system to strike the blades of six vertical Francis turbines at the surface power house to produce electricity.

Contractors Involved

Rithwik Projects Private Limited (RPPL) secured the Engineering, Procurement, and Construction (EPC) contract of the Sunni Dam Project in January 2023.

The contract covers design and engineering services, civil and hydro-mechanical works of the project.

The draft Environmental Impact Assessment (EIA) report for the Sunni Dam HEP was prepared by Voyants Solutions Private Limited.