Project Spotlight: 140-MW Tanahu hydropower facility

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    Tanahu Hydro Ltd. (THL), a wholly-owned subsidiary of the Nepal Electricity Authority (NEA), is developing the 140-MW Tanahu hydro project, which is estimated to cost about US$550 million.

    The project, scheduled for completion in 2021, is located about 150 km west of Kathmandu on Seti River near Damauli of Tanahu district, and is expected to supply peak power daily for a minimum of 6 hours through a 40-km-long 220-kV double circuit transmission line to New Bharatpur substation.

    According to NEA and THL, some of the main Tanahu project features include:

    • Dam: A 140-m-high concrete gravity dam that has a crest length of 175 m impounding Seti River creating a reservoir that will have a total surface area of 7.26 km2.
    • Dam gates: Gate design has been reduced from six gates to three gates to reduce the distance between the retaining walls (i.e., to prevent overtopping) at the base of the spillway.
    • Waterway: The waterway consists of a 7.4-m diameter by 1,203-m-long headrace tunnel on the right bank for the river.
    • Headrace intake: The headrace intake has been set at 362 meters above sea level (masl), which is 16 m below the minimum operating level of 378 masl.
    • Sediment flushing facilities: These facilities consist of two sets of inlets through the base of the dam wall, in the middle of the river cross-section, with a sill elevation of 319.4 masl.
    • Powerhouse: An underground powerhouse measuring 27-m wide by 46-m high by 97-m long will be built about 6 km downstream of the dam site.
    • Tailrace: A 190-m-long tailrace tunnel will discharge tail water back into Seti River.
    • Transmission line alignment: The location of the alignment near the power plant has been moved by up to 300 m and changed very slightly at other locations to account for local topography.

    On March 13, 2013, the Japan International Cooperation Agency (JICA) signed a Japanese ODA loan agreement with the government of Nepal for up to $142.7 million for the Tanahu hydro project.

    In addition to JICA, Nepal Energy Forum reports Asian Development Bank, European Investment Bank and the NEA are funding the project.

    In Nepal, according to JICA, hydropower potential can be harnessed by establishing a greater number of small and medium-sized storage-type plants than large ones, to minimize social safeguard impacts. To make a concrete road map that can deal with this development focus, JICA said it is providing technical assistance for preparing a master plan for more medium-sized hydropower projects.

    THL is also constructing another hydro plant in Tanahu.

    In November 2017, THL received approval from Nepal’s Department of Electricity Development (DoED) to construct the 104-MW Lower Seti hydro plant, which will also utilize flow from the Tanahu project’s reservoir during the dry season, according to NEA.

    Nabin Raj Singh, DoED director general, said, “The Ministry of Energy has decided to issue the license of Lower Seti to Tanahu Hydropower Ltd. and the license will be valid for two years.”

    The Lower Seti Dam will be built at Keshartar, Tanahu, which is 20 km below the Tanahu hydropower project powerhouse and about 19 km upstream from the convergence of Seti and Trishuli rivers, according to NEA.

    Source : HydroWorld