Salient Features

State/Country Bhutan
 District Trashiyangtse
 River Khorlochhu
 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″

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

 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

 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

 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 1574.00 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

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

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

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

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

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

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

 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)

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.

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

 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

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

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
 Maximum Tail Water Level EL 768.00 m
 Design Head 761.53 m (net)

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

 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

 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

 Design Energy in 90% Dependable year with 95% Plant availability 2568.88 MU
 Annual Load Factor 49.45%
 Construction Period 59 Months from Jan2025
 Total Project Estimated Cost Nu. 6899 Crores