Budhi Gandaki Hydropower Project

Introduction

Budhi Gandaki Hydropower Project is a storage type project located in Central/ Western Development redy in late 70's. In 1984, a prefeasibility study of the project was prepared. The ongoing Feasibility studgion on the Budhi Gandaki River of Nepal. This project was identified during the Gandaki Basin Stuy of the Project has recommended 1200 MW capacity plant with FSL 540 masl.

Location And Access

The project is located in the Gorkha and Dading districts of the Western/Central Development Region of Nepal. The project site is accessible via Benighat on the Prithvi Highway (Kathmandu-Pokhara) (approximately 80 km from Kathmandu). From Benigat, you can cross the Trishuli River using a passable compound bridge to reach the dam and power station. Both are located about 1.5 km from the road start. 

Catchment Area:

Gorkha: 2,700 km2

Dhading: 900 km2

Nuwakot: 35 km2

China: 1,365 km2

Total: 5,000 km2

Dam Site:

About 2 km u/s of the confluence between Budhigandaki and Trhshuli at Benighat.

VDC lies in Catchment Area:

Gorkha: 37

Dhading: 27

Nuwakot: 2

Manang: 1

Total: 67

Dam Site:

Ghyalchok VDC (Gorkha)

Salang VDC (Dhading)

Silence features

1. Reservoir
Full Supply Level (FSL)	El. 540 masl
Maximum Flood Water Level	El. 542 masl
Reservoir upper boundary incl. 3m freeboard	El. 545 masl
Minimum Operating Level (MOL)	El. 496 masl
Minimum Operating Level Ultimate (MOL.ult.)	El. 467 masl
Minimum Reservoir Level (MRL)	El. 440 masl
Reservoir Bottom Level	El. 326 masl
Gross Capacity (at FSL)	4 467 Mm3
Active storage between FSL and MOL	2 226 Mm3
Reserve Live Storage between MOL and MOL.ult.	952 Mm3
Conservation volume between MOL.ult. and MRL	582 Mm3
Dead Storage between MRL and reservoir bottom	708 Mm3
Surface Area (at FSL)	63 km²
Surface Area (at MOL)	39 km2
2. Hydrology
Catchment Area	5 005 km2
Long Term Average Flow	222 m3/s (see note at the end of this table)
Construction Flood (20 years)	3 070 m3/s
Design Flood Discharge (10 000 years)	6 260 m3/s
GLOF	3 000 m3/s
LDOF	5 200 m3/s
Probable Maximum Flood	9 800 m3/s
3. Sedimentology
Sediment inflow	9.8 million m3/year
Active storage loss after 50 years	7%
Active storage loss after 100 years	13%
4. Diversion System
Design Flood	3 070 m3/s
Tunnel section, lining	Horseshoe exc., inner circular concrete lining
Number of tunnel	2
Diameter	12 m
Lengths DT N°1 DT N°2	408m 438m
Crest Elevation of U/S Cofferdam	El. 357 masl
Crest Elevation of D/S Cofferdam	El. 332.50 masl
5. Dam
Type	Concrete double curvature arch
Crest Level	El. 542masl + 1.1m u/s parapet
Maximum Height (above dam foundation)	263 m
Crest Length / Width at base/ at crest	760 m / 80m / 8m
Upstream and Downstream Slopes	Variable
Construction materials:
Conventional Vibrated Concrete (CVC)	1.92 million m3
Roller Compacted Concrete (RCC)	3.84 million m3
Total Concrete Volume	5.75 million m3
6. Spillway
Type	Orifice gated spillway with flip bucket
Number of bays	6
Bay dimensions	Width 5.6 m – Height 8.4 m
Crest Level	1 at El.515 masl / 2 at El.495 masl 2 at El.470 masl / 1 at El.460 masl
Design Flood (Routed)	6 280 m3/s for PMF, 4 690 m3/s for Q10000
Gate Type	Radial gate with hydraulic hoists
Gate size	5.6 m x 8.4m, Six gates
7. Waterway and Powerhouse
Intake structures	Bell mouth intake structures close to the dam on the left abutment
Total Rated discharge	6x112=672 m3/s
Number of intake	6
Invert Level of Intake	El. 450masl HRT invert level at El.455.60masl
Gate Size- Stoplog and wheelgate	Span = 4 m / Height = 6m
Headrace Tunnel HRT:
Number of HRT	6
Intake Tunnels	Ø 6m Concrete lined circular 107m Horseshoe Exc. Section
Headrace Tunnels	Ø 5.3m circular Steel lined 22mm From 87m for Unit 6 to 165m for Unit 1 Horseshoe Exc. Section
Pressure Shaft	Ø 5.3m circular Steel lined 28 to 45mm 140m high Circular Section
Penstock	Ø 5.3m circular Steel lined 45mm From 352m (unit 6) to 365m (unit 1) Horseshoe Exc. Section
Powerhouse and transformer building	Type: Outdoor in the left bank
Width, Length and Height	W 40 m x L 185 m x H 40 m
GIS building and potyard	Adjacent PH on platform at El.342
Width, Length and Height	W 60 m x L 112 m x H 15 m
8. Generating Equipment
Turbine:
Type	Francis Type, vertical axis,
Number of units in final stage	6
Net Head at Rated Water Level	200 m
Rated Discharge in finale stage	6 x 112 = 672 m3/s
Installed Capacity	6 x 200 MW = 1 200 MW
Mean Annual Energy (Generation Scenario N°1)	3 383 GWh (see note at the end of this table)
Winter dry season Energy (Generation Scenario N°1)	1 408 GWh (see note at the end of this table)
Summer wet season Energy (Generation Scenario N°1)	1 975 GWh (see note at the end of this table)
Firm Power during dry season	from 1 200 MW 8h/day in Dec. to 934 MW 9h/day May
Firm Power during wet season	from 918 MW 7h/day in June. to 928 MW 4h/day Nov.
Turbine Rated Speed	230.8 rpm
Normal Tailwater level with 6 units in operation	El. 323.30 masl
Generator:
Type	Vertical shaft revolving
Capacity in final stage	6 x 235 MVA = 1 410 MVA
9. Transmission Lines
Number	2
Voltage	400 kV
Circuit	Double circuit
Conductor	Quad Bundle MOOSE
Length BG HPP to Naubise	40.3 km
Length BG HPP to Hetauda	58.7 km
10. Substations
Number	2
Location	1 in Naubise and 1 in Hetauda
11. Costs
Total Capital cost    Environmental and Social Cost    Civil Works    HEM and E&M    HV lines    Infrastructures and roads    Engineering and Administration	2 593 MUSD 612 MUSD 1 265 MUSD 571 MUSD 33 MUSD 55 MUSD 57 MUSD
12. Economic & Financial parameters
Economical Internal Rate of Return EIRR Unchanged for Low, Medium and High load demand forecast (In nominal term)	Generation Sc N°1 Sc N°2 15.5% 16.9% (See note at the end of this table)
Financial Internal Rate of Return FIRR For medium demand forecast	Generation Sc N°1 Sc N°2 7.0% 8.6%
Average energy cost	US¢ 6.4/kWh
Capital recovery period	11 years
Energy Tariff For financing with 80% soft loan at 2% and 20% equity 100% Public Dev. and Return on Equity 10%: Mixed Public/Pvt Dev. and Return on Equity 20%:	Generation Sc N°1 Sc N°2 US¢/kWh 9 7 US¢/kWh 14.5 11.5
13. Benefits
Energy sales from Budhi Gandaki HPP Downstream flood reduction Downstream increase of mean dry season flow of Naranyani river at Devghat and Gandaki Barrage	see 12. Discharge +50% from Jan. To May
14. Manpower requirement
Foreign Skilled Semi-skilled Unskilled Total (persons)	300 570 1 140 3 990 6 000

 

Budi Gandaki runoff at the dam site during the last 5 years (2010-2015) and the recent By measuring the discharge at the Arughat gauge and the discharge at the dam site (see also section 2.1).

Consultants estimate that streamflow at the dam site is likely to be 26% higher than predicted by the hydrological studies in the feasibility report. Parallel measurements have been available for years, according to feasibility reports.

An increase in river flow at this dam site will directly impact the annual production of BG HPP, referred to as Production Scenario #2. This is 26% higher. H. 4,250 GWh per year (1,620 GWh in dry season or 10.8 GWh/day with guaranteed capacity between 970 and 1200 MW).

The consultants believe that five years of parallel flow measurements at the Arughat dam site are sufficient to give the new practice a reasonable level of confidence, but additional projects are needed to expand the database and additional projects. It is recommended to continue measurements at the dam site. Fully supporting generational possibilities.