Nalgad Storage Hydropower Project (Capacity-417MW)

The Nalgad Hydropower Project is located on Nalgad in Jajarkot District in the Karnali Province of Nepal. Nalgad is one of the main tributaries of Bheri River. The project is a storage project with a 248 m high RCC dam. The storage creates a reservoir with total storage volume of 474 MCM and a live storage of 350 MCM. The main dam contains a spillway to pass a flood upto PMF, providing a crest width of 88 m. The dam site of the project is located just downstream of the confluence of Andheri Khola, which is approximately 9.25 km upstream from the confluence of the Nalgad and the BheriRiver and the powerhouse is located on the left bank of Nalgad River approximately 700 m upstream from the suspension bridge at Dalli.

The waterway consists of 8.168 km long concrete lined horseshoe shaped Head Race Tunnel of diameter 5.85m, a surge shaft of diameter 16 m and 165.50 m high, horizontal steel lined penstock tunnel of diameter 4.0 m and length 84.34m (excluding curve part), a 245.91 m and 338.26m long vertical drop shaft 1 and 2 respectively (including upper & lower curves) of diameter 4.0 m and a 907.32 m (horizontal between drop shaft 1 and 2) and 35 m long steel lined pressure tunnel of 4.0 m diameter horizontal bottom pressure tunnel. Two underground caverns for power station and transformer and GIS, housing 4 x 104.25MW Vertical Axis Pelton turbine and generator sets, with an installed capacity of 417 MW, utilizing a rated net head of 610 m and discharge 78.4 m³/s

Salient Features of the Nalgad Hydropower Project

Description

Description/Value

Name of the Project

Nalgad Hydropower Project

District

Jajarkot

Name of the River

Nalgad River

Types of Scheme

Storage

Project Road

25 km

Geology

Dam Site

Dolomite with frequent intercalation of black Shale

Headrace Tunnel

Limestone, Dolomite and Shale

Power station

Sandstone

Hydrology

Catchment Area (up to Dam site)

569 km²

Average Precipitation

2124 mm

Average Monthly Flow

28.67 m³/s

Flood Discharge (1 in 20 years wet season)

653 m³/s

Flood Discharge (1 in 10,000 years wet season)

1975 m³/s

Probable Maximum Flood (PMF)

5051 m³/s

Sediment Yield

1490 t/km²/year

Diversion Tunnel

 

Type, Shape

Partially Lined, D Shaped

Diversion Flow

560 m³/s

Length

374.30m

Dimension

 6 m wide by 7 m high

Reservoir

 

Full Supply Level (FSL)

1580 masl

Minimum Operating Level (MOL)

1498 masl

Total Storage Volume

474 million m³

Live Storage Volume

350 million m³

Dam

Type of Dam

Curved Gravity Roller Compacted Concrete

Height above Foundation

248 m

Crest Elevation

1588 masl

Crest Wall Height

1000 mm

Length of Crest

495 m

Width of Crest

10 m

Environmental In-stream flow release

0.584 m³/s

Spillway

Type

Ogee shaped, non - gated overflow weir

Design flood

1,000 yr        peak inflow 1408 m³/s

10,000 yr      peak inflow 1975 m³/s

PMF              peak inflow 5051 m³/s

Overflow Crest Elevation

EL. 1580 masl

Overflow Crest Width

88 m

Main Intake

Type

Bellmouth

Invert Level

1478.5 masl

Intake Pipe

1 no, 118.0m long, steel lined, circular shape

Intake gates

2 nos. 4.5 m x 3 m

Stoplogs

2 nos. 4.5 m x 3 m

Headrace Tunnel

Length

8168.5 m

Design Discharge

78.4 m³/s

Type

Concrete lined Horse Shoe shape.

Finished Diameter

5.85 m

Surge shaft

Type

Restricted Orifice (Diameter = 3.0 m)

Height

165.5 m

Diameter

16.0 m

Max Water Level

1601.9 masl

Min Water Level

1466.8 masl

Top Level

1603.0 masl

Invert Level (of tunnel below surge shaft)

1437.50 masl

Penstock (Top Horizontal)

Shape

Circular

Type

Steel lined

Inclination

Horizontal (excluding curve part)

Length

84.34 m

Diameter

4 m

Vertical Drop Shaft-1

Shape

Circular

Type

Steel lined

Inclination

Vertical (including upper and lower curve)

Height

 245.91 m

Diameter

4 m

Penstock Tunnel (Horizontal Between Drop shaft-1 & 2)

Shape

Circular

Type

Steel lined

Inclination

Horizontal

Length

907.32 m

Diameter

4 m

Vertical Drop Shaft-2

Shape

Circular

Type

Steel lined

Inclination

Vertical (including upper and lower curve)

Height

338.26 m

Diameter

4 m

High pressure Tunnel

Type

Steel lined

Length

 35m

Finished Diameter

4m

Power Station

 

Type

Underground

Size (L x W x H)

110.9 m x 16 m x 37.5m

Tailwater Level (turbine Pit)

867.12 masl

Transformer Cavern

Type

Underground

Size

111.2 m x 15.2 m x 20.4 m

Turbine

Turbine axis centre line elevation

872.00m

Type and No of Units

Vertical Axis Pelton, 4

Installed capacity

417 MW (4 x 104.25 MW)

Tailrace Tunnel

Type, Shape

Concrete Lined, Inverted D shaped

Tail Water level at turbine pit

867.12m

Length

520 m

Excavation Size (W x H)

7 m x 6 m

Tailrace Canal (Cut and Cover)

Shape

Rectangular

Type

Concrete Box Culvert

Length

170 m

Size (W x H)

5.3 m x 4.3 m

Tailwater Level at outlet

862.00 masl

Transmission Line

Length

112 km

Voltage

400 kV

Circuit

Double

Interconnection Point

Kohalpur S/S

Power

Maximum Gross Head

708.0 m

Design Net Head

610.0 m

Maximum Net Head

692.0 m

Minimum Net head

610.0 m

Design Discharge

78.4 m3/sec

Overall Efficiency

87.80%

Maximum Daily Generation

9 equivalent hours

Minimum Daily Generation

1 equivalent hour

Power Potential Studies

Installed Capacity

417 MW

Annual Potential energy

3655 GWh

Firm Energy

672 GWh

Secondary Energy

608 GWh

Total Energy

1280 GWh

Average Annual Load Factor

35.4%

Dry Season Energy

604.9 GWh

Dry Season Load Factor

33.4 %

Probable Project Cost (with TL)

Civil works Cost including Preliminary Works and internal site Access Roads

923,958,924

Hydro-Mechanical Works

65,226,370

Electro-Mechanical Works Cost

145,245,187

Cost of Transmission Line, Substations and Switchyard

119,271,620

Allowance for Unlisted Items and Scope Contingencies

125,370,210

Markups (Contractor’s Insurance Program, Taxes, Custom, Escalation)

156,439,386

Project Administration and Management

219,985,786

GRAND TOTAL

1,755,497,483 US$