Salient Features

Installed Capacity

600 MW (4x150 MW)

Location

 State/Country  Bhutan
 District  Trashiyangtse
 River  Kholongchhu
 Nearest Village(Dam Site)  Buyang
 Nearest Village(Power House Site)  Duksum
 Access  
 Airport  Paro(Bhutan), Guwahati(Assam, India)
 Rail Head  Rangia(Assam, India)
 Geographical Co-ordinates Dam Site  
 Latitude(N)  27o 32' 50"
 Longitude(E)  91o 30' 49"
 Geographical Co-ordinates Power House  
 Latitude(N)  27o 24' 23"
 Longitude(E)  91o 32' 57"

Meteorology

 Atmospheric Temperature
 Maximum Temperature  26o C
 Minimum Temperature  4o C

Hydrology

 Catchment Area at Diversion Site  1044 Km2
 Snow Catchment(Out of Total)  15 Km2
 Maximum Observed Discharge at Dam Site  929 cumec
 Minimum Observed Discharge at Dam Site  10.3 cumec
 Probable Maximum Flood(PMF)  8750 cumec
 Average Annual Yield  1621 MCM

Reservoir

 Full Reservoir Level(FRL)  EL 1572.00 M
 Minimum Draw Down Level (MDDL)  EL 1558.00 M
 Water Spread at FRL  12.68 Ha
 Gross Storage at FRL  2.9 MCM
 Dead Storage at FRL  1.52 MCM
 Live Storage  1.38 MCM
 Length of Reservoir  1.4 Km

Dam

 Full Reservoir Level(FRL)  EL 1572.00 m
 Minimum Draw Down Level (MDDL)  EL 1558.00 m
Type of Dam  Concrete Gravity Dam
 Top Elevation of Dam  EL 1547.00 m
 River Bed level at Dam Site  EL 1512.00 m
 Dam Height above River bed  62 M
 Deepest Foundation Level  EL 1479.65 m
 Maximum Height above Foundation Level  95 m
 Length of Dam at Top  165 m
 Top Width of Dam  6 m
 Length of Overflow Blocks  69 m
 Length of Non-Overflow Blocks  96 m

Spillway

 Design Flood  8750 cumec(PMF)
 Energy Dissipation System  Trajectory Bucket with naturally formed Plunge Pool
 Lower Tier
 Type  Ogee with Sluice type
 No. of Bays  5 Bays
 Size of Gate  7.8 (W) x 12.5 (H)
 Crest Level  EL 1525.00 m
 Upper Tier
 Type  Ogee with Open Crest
 No. of Bays  1 Bay
 Size of Gate  7.8 (W) x 4.3 (H)
 Crest Level  EL 1568.00 m

Diversion Tunnel

 Location of Diversion Tunnel  Left Bank
 No. of Tunnel/s  1 No.
 Size of Tunnel  10 m Diameter
 Shape of Tunnel  Horse Shoe Shape
 Length of Tunnel  372 m
 Diversion Discharge (25 years)  1112 cumec
 Inlet Invert Level  EL 1521.00 m
 Outlet Invert Level  EL 1508.00 m
 Diversion Tunnel Gate  10 m (W) x 10 m (H)

Power Intake

 Type  Straight Type with Incline Trash Rack
 Number/s  2 Nos.
 Design Discharge(All units running at full load including 20% of Flushing Discharge)  56.4 cumec each
 Invert Level  EL 1546.65 m
 Level at Centre of Tunnel  EL 1549.00 m
 Top Level  EL 1574.00 m
 Intake Feeder Tunnel
 No. of Tunnel/s  2 Nos.
 Size of Tunnel  4.7 m Diameter
 Shape of Tunnel  Horse Shoe Shape
 Length  198 m & 233 m

Desilting Chamber

 Number/s  2 Nos.
 Size  13 (W) x 17.5 (H)
 Lenght  350 m
 Average Design Discharge (with 10% Overload)  53.85 cumec each
 Maximum Particle Size to be Removed  0.2 mm and above

Silt Flushing Tunnel

Main Tunnel
 Size of Tunnel  2.5 (W) x 3.5 (H)
 Shape of Tunnel  D Shape
 Length of Tunnel  97 m
 Branch Tunnel
 Size of Tunnel  1.5 (W) x 2.2 (H)
 Shape of Tunnel  D Shape
 Length of Tunnel  125, 200 m

Head Race Tunnel

 Design Discharge  89 cumec
 Size of Tunnel  5.7 Diameter
 Shape of Tunnel  Horse Shoe Shape
 Length of Tunnel  15.77 km
 Adits  6 Nos. 6.8 Diameter, D Shape

Chapnangchu Diversion

 Location of Diversion Tunnel  Left Bank
 No. of Tunnel/s  1 No.
 Size of Tunnel  10 m Diameter
 Shape of Tunnel  Horse Shoe Shape
 FSL  EL 1576.00 m
 Design Discharge  5 cumec
 Trench Weir  10 (L) x 2.5 (W) x 3 (H)
 Intake Invert Level  EL 1575.30 m
 Feeder Tunnel  2 (W) x 2.5 (H), 110 m Long
 Desilting Chamber  5 (W) x 7 (H), 110 m Long
 Inlet Tunnel to Drop Shaft  2.1 (W) x 2.1 (H), 220 m Long
 Drop Shaft  2.5 m Diameter, 75 m deep, Open to Sky
 Connecting Tunnel-Drop Shaft to HRT  1.8 (W) x 2.1 (H), 485 m Long

Surge Shaft

 Number/s  1 No.
 Type  Restricted Orifice Type
 Size and Shape  9.5 m Diameter, circular
 Height  152.8 m
 Top Level  EL 1640.00 m
 Gates  2.75 (W) x 5.22 (H), 2 Nos.

Valve House

 Number/s  2 Nos.
 Type  Butterfly Valve
 Size of Valve  3.3 m Diameter

Pressure Shaft

 Main Pressure Shaft 
 Number/s  2 Nos.
 Type  Circular
 Size  3.3 m Diameter
 Length  1200.57 m Long each
 Branch Pressure Shaft
 Number/s  4 Nos.
 Type  Circular
 Size  2.35 m Diameter
 Length  187 m Long

Power House Complex

 Type  Undergoround Power House
 Location  Right Bank of Drangmechu (Gongrichu)
 No. of Cavern/s  2 Nos.

Power House - Machine Hall

 Size  123 (L) x 21 (W) x 42.5 (H) m
 Type of Turbine  Pelton Wheel
 Number/s  4 Nos.
 Capacity  150 MW each
 Distributor Centre Line Level  EL 772.50 m
 Turbine Floor Level  EL 775.00 m
 Generator Floor Level  EL 779.50 m
 Service Bay Floor Level  EL 784.00 m
 Mazimum Tail Water Level  EL 768.00 m
 Design Head  761.53 m (net)

Transformer Hall, GIS cum TRT Gate Operation Cavern

 Facilities  Transformer Hall, GIS, TRT Gate Operation
 Size  130 (L) x 16 (W) x 24 (H) m
 Transformer Hall Floor Level  EL 784.00 m

Access Tunnels (PH Complex)

 Main Access Tunnel (MAT)
 Size, Shape & Length  8 m Diameter, D Shape, 255.20 m Long
   
Cable Access Tunnel (CAT)
 Size, Shape & Length  6.5 m Diameter, D Shape, 251 m Long
   
 Ventilation Tunnel
 Size, Shape & Length  6.5 m Diameter, D Shape, 87.99 m Long
   
 Drainage Gallery
 Size, Shape & Length  2.5 m Diameter, D Shape, 219.54 m Long
   
Access Tunnel
 Size, Shape & Length  7 m Diameter, D Shape, 50 m Long
   
Escape Tunnel 
Size, Shape & Length  3 m Diameter, D Shape, 50 m Long

Tail Race Tunnel

 Unit TRT
 Number/s  4 Nos.
 Type  D Shape
 Size  3 (W) x 6 (H) m
 Length  605.19 m Long
Main TRT
 Number/s  1 No.
 Type  D Shape
 Size  6 (W) x 6 (H) m
 Lenght  1521.73 m Long

Power Generation

 Design Energy in 90% Dependable year with 95% Plant availability  2568.88 MU
 Annual Load Factor  49.45%
 Construction Period  59 Months after 18 Months of Pre-Construction Period
 Total Project Estimated Cost  Nu. 3868.67 Crores
 Tariff-1st year sale price at bus bar  4.06 Nu/kWh
 Levellised tariff at bus bar  3.38 Nu/kWh