Salient 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 Gandak 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 |
Note:
It is worth mentioning that the recent measurements made during the last five years (2010-2015) on the discharge of the Budhi Gandaki river at dam site and at the long term operated DHM gauging station in Arughat (since 1964) allowed to obtain a better relationship between the discharges at Arughat gauging station and those at the dam site (see also section 2.1).
The Consultant estimates that the river runoff at dam site is likely to be 26% higher than anticipated in the hydrological study of the Feasibility Report which has adopted a conservative approach in the transposition law between discharges measured at Arughat and those at the dam site since only few years of parallel measurements were available when editing the Feasibility Report.
This increase in the river runoff at dam site has a direct consequence on the BG HPP annual generation output called Generation Scenario N°2 which would be 26% higher i.e. reaching 4 250GWh per annum (1 620GWh in dry season or 10.8 GWh/day with guaranteed capacity of 970 to 1200 MW).
The Consultant considers that the 5 years parallel river discharge measurements Arughat-Dam Site are sufficient to have a reasonable degree of confidence in the new transposition law but recommends to continue the measurements at dam site to increase the data base and fully firm up the additional project generation potential.
(see also section 4.2 and 4.4 of this Volume 1 Main Report Ref BG-DDR-Vol 1 Rev0)