Salient Features
Parameter/Specification Details/Value
State/Country
Bhutan
District
Trashiyangtse
River
Khorlochhu
Nearest Village(Dam Site)
Buyang
Nearest Village(Power House Site)
Doksum
Airport
Paro/Yonphula(Bhutan), Guwahati(Assam, India)
Rail Head
Rangia(Assam, India)
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
Type
Straight Type with Incline Trash Rack
Number/s
2 Nos.
Design Discharge
56.4 cumec each
Invert Level
EL 1546.65 m
Level at Centre of Tunnel
EL 1549.00 m
Top Level
EL 1549.00 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
Parameter/Specification Details/Value
Number/s
2 Nos.
Size
13 (W) x 17.5 (H)
Length
350m
Average Design Discharge (with 10% Overload)
53.85 cumec each
Maximum Particle Size to be Removed
0.2 mm and above
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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.
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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)
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
Maximum Temperature
26°C
Minimum Temperature
4°C
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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)
Parameter/Specification Details/Value
Number/s
2 Nos.
Type
Butterfly Valve
Size of Valve
3.3 m Diameter
Parameter/Specification Details/Value
Type
Undergoround Power House
Location
Right Bank of Drangmechu (Gongrichu)
No. of Cavern/s
2 Nos.
Parameter/Specification Details/Value
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
Parameter/Specification Details/Value
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
Length
1521.73 m Long