BUDHI GANDAKI – A CRITICAL SOLUTION FOR NEPAL
In a country blessed with Himalayan mountains and rivers, HP is a natural energy source. But when the dry season sees river-flow diminish, reliability of power supply is an issue since most existing or under construction HP projects are of run-of-river type. Budhi Gandaki (+/- 600 MW storage dam and HPP) has long been foreseen as the answer. Read more
DEEP INVESTIGATION REQUIRED
Upgrading an early prefeasibility study; Tractebel Engineering’s mission has involved managing all field investigations (especially geological rock assessments using the Scarabee® method), in order to define the best concept in terms of dam type, scheme design, cost and power to be generated. Read more
3 DESIGN OPTIONS FOR CONSIDERATION
Digging deep to meet deadlines, by March 2014, the team was able to present the Budhi Gandaki Hydroelectric Project Development Committee with 3 viable proposals for taking the project forward… Read more
BUNDI GANDAKI – A CRITICAL SOLUTION FOR NEPAL
In a country blessed with Himalayan mountains and rivers, HP is a natural energy source. But when the dry season sees river-flow diminish, reliability of power supply is an issue since most existing or under construction HP projects are of run-of-river type. Budhi Gandaki (+/- 600 MW storage dam and HPP) has long been foreseen as the answer.
A CONCEPT WITH HISTORY
The Budhi Gandaki HP scheme was first considered in 1984 when an early prefeasibility study was carried out. The project was shelved however as Nepal entered a long era of political changes. But the need for a large storage dam has remained as, while several run-of-river HP exist in Nepal, only one 92 MW HP dam (Kulekhani) has a storage reservoir. In the dry season when many run-of-river HPs dry up, the country is left short of capacity – leading to critical power cuts on many days. An impossible situation for a country wanting to stabilize and grow its economy.
Re-starting the project, the Nepal Electricity Authority (NEA) opened a tender for the feasibility and detailed design studies in 2012. Tractebel Engineering was the preferred bidder of 5 international entrants. Work began immediately; with experts mobilised to Kathmandu early 2013 to take the project forward from prefeasibility stage through to providing the Budhi Gandaki Hydroelectric Project Development Committee (a Government entity appointed for this project ), with feasible, optimised design choices ahead of the Detailed Design and Tender Documentation preparation.
BUDHI GANDAKI HPP – A PROMISING SOLUTION
As all studies confirm, the dam location, 80 km from Kathmandu in a narrow and steep valley on the Budhi Gandaki River, is ideal for a large reservoir-type dam. Initially promising 600 MW with a reservoir of +/- 2,755 million m3, Budhi Gandaki HPP would almost double Nepal’s total installed capacity of 746 MW – and provide seasonal water regulation.
“Evidence of its national importance; Nepal is currently funding this project itself. But we never forget that we are here to deliver our client a bankable project, fully in line with internationally recognised standards and strict environmental and social recommendations.”
Philippe Cazalis, Projects Director, Budhi Gandaki Project Team Leader – Tractebel Engineering (France)
DEEP INVESTIGATION REQUIRED
Upgrading the early prefeasibility study; Tractebel Engineering’s mission has involved managing all field investigations (especially geological rock assessments using the Scarabee® method), in order to define the best concept in terms of dam type, scheme design, cost and power to be generated.
NEW IDEAS FOR BUDHI GANDAKI
Studies carried out alongside vital geological assessment included new design studies, topography, Environmental & Social Impact Assessments (ESIA), economic and financial analysis and more. First ideas for optimising the scheme were quickly formulated; replacing the foreseen +/- 200 m rockfill embankment dam with a higher 263 m concrete arch gravity dam due to the ideal topography, suitable rock foundation conditions and economic benefits (an arch gravity dam actually uses less concrete); and the potential use of tunnelling to increase head while reducing the environmental & social impact of the reservoir. But the value of these suggestions still had to be validated…
EXPERTISE (AND THE SCARABEE® METHOD) CLARIFY OPTIONS
With future proposals based largely on the outcome of geological surveys, specially excavated galleries at the dam site were explored to investigate rock quality using, among others, the Scarabee® acoustic method developed by Tractebel Engineering (France)/Coyne et Bellier in 1960. It is used specifically for the assessment of rock foundations of large dams and underground works. Providing a global assessment of the rock mass, it is the only method which makes it possible to determine the static modulus of a rock foundation on a large scale (about 103m3 per 25-30 m long profile). At Budhi Gandaki 18 profiles (6-8 being the norm) were investigated across 4 galleries.
With full knowledge of what it was dealing with, the Tractebel Engineering team was better able to define a number of different creative, cost-effective and goal-focussed solutions for the client.
3 DESIGN OPTIONS FOR CONSIDERATION
Digging deep to meet deadlines, by March 2014, the team was able to present the Budhi Gandaki Hydroelectric Project Development Committee with 3 viable proposals for taking the project forward…
The report submitted to the client on March 1, 2014 suggested the following:
- OPTION 1: A dam-site powerhouse as first foreseen, with the powerhouse constructed alongside the dam above the point where the Budhi Gandaki River joins the Trishuli River. However with this a second compensation dam was suggested to regulate downstream water flow during peak generation. By adding another small powerhouse and a short tunnel downstream, a second sub-project HP could further increase the scheme capacity. The Tractebel Engineering team also proposed to increase the capacity of the main plant to 945 MW in order to better meet peak energy demand in the dry season. With the second sub-project, the global capacity of the option 1 proposal could be over 1000 MW.
- OPTION 2: A (short tunnel) option moving the powerhouse underground, a short way downstream, with a 1.5 km headrace tunnel to achieve an extra 10 m head.
- OPTION 3: Moving the powerhouse much further downstream, using a twin 8 km headrace tunnel to achieve an extra 50 m head compared to option 2. This would allow a lower reservoir FSL/saving on environmental & social impact costs OR increased power generation.
“The first option seems to be the best one. The consultant company is also of the same view. If we need more electricity during peak hours, it would be better to go for a capacity of 945 MW. We will select one of the three options after which the DPR process will start.”
Dr. Laxmi Prasad Devkota, Executive Chairman of the Budhi Gandaki Hydroelectric Project Development Committee
THE WAY FORWARD
The Budhi Gandaki Hydroelectric Project Development Committee officially confirmed, on 21 March 2014, that it has selected for further Feasibility Study, the first option layout: a 263 m high dam creating a 4.5 billion m3 reservoir with FSL at El.540. The HP plant at the toe of the dam will have an installed capacity of 945 MW. The downstream compensation reservoir and associated sub-HP project is expected to further increase the global capacity and generation output of the Budhi Gandaki project.