Budhigandaki Hydroelectric Project Development Committee  
 

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)

 

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