2023-12-06

Funding Agency: Asian Development Bank (ADB)
Client:Tanahu Hydropower Project
Date: May 2019 –  December 2023

Lower Seti (Tanahu) Hydropower Project lies in Tanahu district of the Western Development Region of Nepal between longitudes of 84017’30” E and 84028’42” E and between 27047’30” N to 27055’00” N. The project lies in the Seti River of the Middle Hilly Region which constitutes a broad complex of hills and valleys. The dam site is located about 19 km upstream of the confluence of Seti and Trishuli Rivers while the powerhouse site is located towards the downstream end of Amdadabesi village on the right bank of the Seti River approximately 2 km downstream from the confluence of Seti and Trishuli Rivers. The elevation of the intake site is about 255 m above the mean sea level (amsl) and that of the powerhouse site is about 200m amsl.

In accordance with the preliminary study, the proposed project with the installed capacity of 126 MW will produce a net average annual energy of 441.61 GWh with a minimum 6 hours peaking even in the dry season. Seti River has a large tributary stream namely Madi River joining the Trishuli River downstream of the intake dam. The river flows almost north to south downstream of the dam site. The catchment area upstream of the proposed intake point is approximately 2849 km2.

The major civil components of the project are as follows:

Headworks consisting of a gated dam and a side intake at the right bank of River. The crest length of the dam is 200m with four radial gates in order to pass the design maximum flood (1 in 10,000) of 7779 m3/s. The height of dam including foundation is 45 m. There will be two numbers of intakes of size 8m *12m each.

The electromechanical equipment consists of two turbines units of Francis Turbines (Rated Power of 53,300 kW each) each coupled with a synchronous generator (Rated Power of 61.2 MVA). The governor is Electronics PID type with speed droop adjustment between 0 and 5%. The generation voltage of 11 kV will be stepped up to 200kV by two nos. of transformers of rated capacity 62 MVA each. The revised rated efficiencies for selected turbines, generators and transformer are 93%, 97.5% and 99.5% respectively.

• A two chambered underground desilting basin of size 180.5*16.5m*20.5m to trap silt/ sand particles larger than 0.2 mm.
• Water conveyance system consisting of inverted D-shaped headrace tunnel of 8 m diameter with total length of 5.5 km.
• A surge shaft of 18 m diameter and 55.26 m height at the end of headrace tunnel
• A vertical drop shaft of 80 m height and 7.2 m in diameter.
• A steel penstock of diameter 6.5 m and length 100 m including bifurcation. The thickness of penstock pipe is estimated to be 20 mm.
• A surface type of powerhouse of size 60 m* 24 m*43 m.
• A tailrace canal of length 250 m to discharge the water from the turbines back to Trishuli River.

The energy generated from the project will be injected to the Damauli- Bharatpur Transmission line to be constructed by Tanahu Hydropower Limited with the switching arrangements.

Overall Services provided:

The overall objectives of consulting services are to carry out the Detail Engineering Design and preparation of Bidding Documents of the project, the scopes shall comprise but not limited to following tasks:

              Task 1 Inception of Assignment

    Task 2 Review and Validation of available Topographical Mappings/ Geological Investigation and recommend further investigations, if required

              Task 3 Hydrological, Sedimentology and Hydraulic Studies

              Task 4 Project Optimization Study

              Task 5 Detail Design, Specification and Drawing

              Task 6 Power Evacuation Study

              Task 7 Construction Planning and Scheduling inclusive of construction power supply

              Task 8 Project Cost Estimate

              Task 9 Economic and Financial Analysis of the Project

              Task 10 Preparation of Complete Tender Documents and Tender Drawings

              Task 11 Analysis of Institutional Arrangement for Project Implementation