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Tanahu Hydropower Project (Upper Seti HEP)
Dec 13th, 2021

Tanahu Hydropower Project is located on the right bank of Seti River, about 150 km West of Kathmandu near Damauli, the district headquarters of Tanahu District. This is the storage type project, which is planned to have an installed capacity of 140 MW with an estimated annual energy generation of 502.5 GWh. The Project is designed for at least six hours of peaking operation during the driest month of the year.

The project area covers 2 municipalities (Vyas and Bhimad) and 2 rural municipalities (Rhising and Maygde). The Vyas Municipality, with Damauli Town as district headquarter of Tanahun district, is a major urban settlement. The reservoir will extend about 25 km upstream inundating the low-lying lands (415 m) along the Seti River. The Project also include Rural Electrification (RE) and Transmission Lines (TL) component. A new 220 kV double circuits TL will evacuate the generated power to the new Bharatpur Substation. The length of the transmission line corridor is 37 km.

THL signed the contract agreement with M/S Lahmeyer International in association with Manitoba Hydro. International, Canada (“the Consultant”) as Project Supervision Consultant (PSC)on June 29, 2015. The contract period of PSC is twelve years. The consultant will assist one year for pre-construction activities, six years for project construction and last five years for project operation and maintenance.

Major Construction Packages

The Contract Agreement for the construction of Work Package 1 (Dam and River Diversion) was signed on 22 March 2021 with the M/S Song Da-Kalika JV. Likewise, the Contract Agreement for Work Package 2 (Waterway, Powerhouse and Related Equipment) was signed between the THL and M/S Sinohydro Corporation Limited, China on 1st October 2018. For the execution of Work Package 3 (Transmission Line), THL signed Contract Agreement with M/S KEC International Limited, India on 25th December 2018.

Panel of Experts

THL signed the contract agreements for the Panel of Experts (POE) for dam safety, environment, and social safeguards (DSE) on 17th December 2018. The primary responsibility of the DSE member of the POE is to provide independent review of project documentation (technical, environmental and social assessments, EMPs, environmental monitoring on the treatment of safety issues associated with the dam.

Financial Arrangement

The Project is jointly financed by Asian Development bank (ADB), Japan International Cooperation Agency (JICA), European Investment Bank (EIB), Government of Nepal (GoN) and Nepal Electricity Authority (NEA). Loan agreement for an amount of US$ 150 million was signed with ADB on February 21, 2013. Similarly, loan agreement for an amount of US$ 184 million was signed with JICA on March 13, 2013 and loan agreement with European Investment Bank (EIB) was signed on May 7, 2013 for an amount of US$ 70 million, which further increased to 85 million. Fund from GoN and NEA will be used for the preparation of preconstruction infrastructures activities.

Salient Features of Tanahu Hydropower Project

Project ParticularsDetails
ReservoirFull Supply Level (415.0 m)
Minimum Operation Level378.0 m
Available Depth37.0 m
Sedimentation Level320.0 m
Gross Storage Capacity295.1 × 106 m3
Effective Storage Capacityduring first 10 years; 192.8× 106 m3
after 11th years; 181.7 × 106 m3
Diversion TunnelDesign Flood 2,305 m3/s (20 years return period)
 Number and Type of Tunnel(2, concrete lined pressure flow)
 Length(606 m and 666 m)
 Inner Diameter(10 m)
DamType(Concrete gravity)
Elevation of Dam Crest420.0 m
Height of Dam140.0 m
Length of Dam Crest215 m
Volume of Dam929 × 103 m3
Auxillary DamType(Weir resting on bore piles wall)
 Length of Crest(133 m)
 Height(30.6 m)
 Volume(121,980 m3)
Sediment Flushing FacilitiesInlet Sill Elevation(320 m)
Gradient of Conduit1: 15
Upstream Maintenance Gate Span x HeightSlide Type Steel Gate 5 m x 5m
Intermediate Main Gate Span x HeightHigh Pressure Slide Gate 5 m x 5 m
Downstream Auxiliary Gate Span x HeightHigh Pressure Slide Gate 5 m x 5.2 m
SpillwayDesign Flood (7,377 m3/s)
TypeChute
Elevation of Overflow CrestEL. 398.1 m
Width of Overflow Crest51.32 m
Energy DissipaterRoller bucket
Type of GateRadial (4 Nos.)
Size of Gate (span x height)12.83 m x 18.1 m
IntakeNumber : One(1)
Intake TypeTower Type Intake
Gate TypeVertical Lift Fixed Wheel Type Steel Gate
Size of Gate (span x height)6 m x 9 m
Headrace TunnelNumber: One (1)
Inner Diameter7.4 m
Total Length1469.6 m
Surge ShaftType (Restricted Orifice)
 Shaft Height/Diameter:28 m/ 61.5 m
 Diameter/Height of Riser: 7.4 m/22.8 m
 Diameter of Orifice:5 m
PenstockType: Tunnel
NumberOne (1)
Inner Diameter5.7 m to 4 m
Total Length160 m (including one (1) branch pipe length)
Draft TunnelLength: 99.4 m
Type of Draft GateVertical Lift Slide Type Steel Gate
Size of Draft Gate (span x height)5 m x 3.1 m
Tailrace TunnelDiameter: 7.4 m
Length213 m
OutletOutlet Type: Outlet with Draft Pond
Type of Tailrace GateVertical Lift Slide Type Steel Gate
Size of Tailrace Gate (span x height)7.4 m x 7.4 m
PowerhouseType: Underground
 Size: 22 m wide × 45 m high × 89 m long
Development PlanRated Intake Water level: 405.0 m
Tail Water Level289.2 m
Gross Rated Head115.8 m
Maximum/Rated Effective Head121.55 m/111.7 m
Maximum/Rated Discharge131.2 m3/s /127.4 m3/s
Number of UnitTwo (2)
Install CapacityRated capacity; 127 MW Maximum capacity: 140 MW
Peak Time6 hours
Primary Energy178.9 GWh
Secondary Energy323.6 GWh
Total Energy502.5 GWh
TurbineType :Vertical Shaft, Francis Turbine
NumberTwo (2)
Maximum/Rated Output71,800 kW/64,700 kW
Revolving Speed300 min-1
GeneratorType: Three-phases, Synchronous Generator
NumberTwo (2)
Maximum/Rated Output82,300 kVA/74,700 kVA per unit
Revolving Speed300 r/min
Frequency50 Hz
Rated Voltage13.2 kV
Power Factor0.85 lag
Main TransformerType: Indoor, special three-phase, Forced-oil-circulated and forced-water-cooled
NumberTwo (2)
Maximum/Rated Output82,300 kVA/74,600 kVA
Rated VoltagePrimary              13.2 kV
 Secondary 220 kV
SwitchyardType: GIS (Gas Insulated Switchyard)
Bus SystemDouble Buses
Number of BaysFive (5) bays
Voltage220 kV
Generation Facility for EnvironmentalRated/Maximum Effective Head :93 m/103.3 m
Discharge2.4 m3/s
FlowTurbine Type: Horizontal Type, Francis Turbine
Number of Turbine/GeneratorOne (1)
Turbine Rated Output/ Maximum Output1,900 kW /2,100 kW
Generator TypeHorizontal Type, Three-phase Synchronous Generator
Rated Generator Capacity2,300 kVA
Distribution Transformer3-Phase Dry Type, Rated Capacity 2,305 kVA
Average Energyduring first 10 years; 14.0 GWh after 11th years; 13.0 GWh
220 kV Transmission LineConductor Type: 380 mm2 × ACSR (Bison)
Number of CircuitTwo (2)
Voltage220 kV
Length36.9 km
Type of Transmission TowerSteel lattice tower
Number of Steel Tower94
220 kV Bharatpur SubstationNumber of Bays:Five (5) bays, of which Two (2) bays for transmission lines, Two (2) bays for interconnection to 132 kV substation, and One (1) bay for bus coupler
Interbus TransformerCapacity 83,300 kVA x 2 units Primary 220kV, Secondary 132 kV and Tertiary 11 kV