Salient Features

Location, Reservoir & Hydrology

 Location

Project Area : 27o dergree  to 27.5 degree N, 89 degree to 91 degree E
River                : Wangchu
District            : Chhukha Dzongkhag, Western Bhutan
Dam Site      : Near Wangkha village, 3km
  Downstream of Chhukha Project Tail-race
Power House : Near Tala village

Reservoir

Full Reservoir level                  : 1363m
Minimum draw-down level   : 1352m
Reservoir volume                     : 9.8 million cu.m
Peaking volume                          : 3.2 million cu.m
Surface area at FRL                   : 0.36 sq km

Hydrology

Catchment Area                                               : 4028 sq. km
Average flow at Dam site                             : 99 cu.m/sec
Mean Annual Run-off                                    : 3107 million cu.m
Minimum 10-daily flow 9in 90% year)   : 19.5 cu.m/sec
Mean winter flow (in 90% year)                 : 23.4 cu.m/sec
Annual mean                                                      : 77.6 cu.m/sec
Standard Project Flood                                 : 8575 cu.m/sec
Probable Maximum Flood                           : 10,600 cu.m/sec

Diversion Arrangement & Intakes

Overflow Spillway

No.                                          : 1
Size                                     : 4m (W) x 3m(H)
Crest EI                                 : 1360m
Gates                                            1 no., 4m x 3m, vertical lift fixed wheel
: service gate 1 no., 4m x 3.66m,
  vertical lift fixed wheel emergency gate
Energy Dissipater : Trajectory Bucket
Bucket lip : 105m down stream (D/S) of Dam axis
Trajectory impingement  : About 205m D/S of Dam axis

Intakes

Number : 3
Type : Straight intake with bell-mouth
Location : Right Bank
Intake Tunnels : 3 nos., 4.9m dia, modified horse-shoe
Maximum Discharge                    : 171 cu.m/sec
Intake C/L level : 1343.5m
Gates

   3 nos., 4m x 4.9m vertical lift fixed wheel,
: service gates 1 no., 4m x 4.9m vertical
    lift fixed wheel, emergency gate

Desilting Chambers, Diversion Tunnel, Upstream Coffer Dam & Downstream Coffer Dam

Desilting Chambers

No  : 3
Size : 250m (L) x 13.9m (W) x 18.5m (H)
Design Particle Size  : 0.2mm and above (suspended sediment)
Construction Adit common : 36m, 7m, D-shaped
Top branch : 174m, 6m. D-shaped
Bottom branch :189m, 6m. D-shaped
Gates   : 3 nos., 4.2m (W) x 4.9m (H), vertical lift fixed wheel
 Adit to Gate Chamber : 143m, 6m D-Shaped
 Gate shaft : 7.1m x 2.9m (elliptical shaft) x 27m deep

 Diversion Tunnel

Location : Right Bank
Length : 356m
Size : 6.8m, D-Shaped
Design Discharge : 350 cu.m/sec
Gate : 4.2 x 4.9m, Vertical Lift fixed wheel

Upstream Coffer Dam

Type : Concrete
Length : 94m
Height : 14m

Downstream Coffer Dam 

Type : Rock-fill
Length : 45m
Height : 3m

Dam, Silt Flushing Tunnel, Sluice Spillway & Head-race Tunnel,

Dam

Type : Concrete Gravity
Top of Dam : 1366m
Average river bed elevation : 1291m
Maximum height : 92m
Length of non-overflow dam  : 60.8m
Length of overflow dam : 67.9m
Concreting  : 3,52,000 cu.m

Sluice Spillway

No  : 5
Size : 6.5m (W) x 13.15m (H)
Crest EI : 1320m
Gates

    5 nos., 6.5m x 13.15m radial
 : 2 sets, 6.5m x 19.14m stop-logs

Silt Flushing Tunnel

Size : 3.5m dia D-shaped
Silt Flushing Discharge : 20% (28.5 cu.m/sec)
 Gates : 3 nos., 2.85m x 2.1m, Vertical lift slide gate
Gate Shaft : 5.8m x 3.96m (oval shaft) x 43m deep

Head-race Tunnel

Length : 23.00 km
Dia : 6.8m modified horse-shoe
Design Discharge : 142.5 cu.m/sec
Velocity at Design Discharge : 3.75m/sec
Overloading Discharge : 158.52 cu.m/sec
 Invert level at start : 1338.074m
 Invert level at end : 1257.20m
Bed Slope (average) : 1 in 280

Construction Adits, Underground Surge Shaft, Peripheral Drainage Gallery

Construction Adits

Size : 7m, D-shaped
No : 5 intermediate and 1 at inlet (11 faces) 

Lengths

At inlet : 73.5m
Thiyomachu : 101m
Padechu : 260m
Geduchu : 963m
Mirchingchu : 320m
Kalikhola : 512m

Gates at Adit Junctions

At inlet : 1 no.,2.5m x 2.5m, hinged type
At Mirchingchu : 1 no., 1.2m x 1.5m, flap type

Underground Surge Shaft

Type : Restricted Orifice
Diameter : 12m from bottom to EI. 1310m 15m from El. 1310m  to      El.1425,
Height : 161 m (from orifice slab at El 1265 m to invert of upper  expansion chamber)
Orifice diameter : 1.5 m
Computed Surge Levels (Discharge 158.52 cu m/sec) Load case 100-0-0(up)  : 1423.07 m 
Load case 33-100-0 (up) : 1425.754 m
Load case 100-0-33 (down) : 1279.122 m

Peripheral Drainage Gallery

Size : 3 m (W) x 4 m (H)
Level : 1300 m
Location : 25 m from C/L of Surge Shaft

Construction Adit

To Surge Shaft top : 88 m x 6 m, D-shaped
To Surge Shaft bottom  : 317 m x 7 m, D-shaped
To Drainage Gallery  : 376 m long, 3 m (W) x 4 m (H)
Gates  : 2 Nos. 3.66m x 5.2m vertical lift

Underground Butterfly Valve Chamber, Pressure Shafts & Underground Power House Complex

Underground Butterfly Valve Chamber

Size : 38 m (L) x 9 m (W) x 19 m (H)
No. of Valves : 2 nos. 4.0 m dia
EOT Crane : 1 no., 75/20 T
Crane beam support  : RCC column-beam arrangement
Adit Top : 160 m x 6 m, D-Shaped
Adit Bottom (branch) : 12m x 7 m, D-shaped

Pressure Shafts 

Type

: Steel lined (ASTM A-537 Class II,
    thickness 30 mm to 38 mm;
    ASTM A-517 Grade F, thickness 38 mm to 40 mm)
Size : 2 nos., 4.0m dia
Length  
PS I  : 1069.40 m
PS II  : 1021.00 m
C/C distance between Shafts : 20 m
Inclination with horizontal : 52 degree
Design velocity : 5.6 m/sec
Maximum Design Pressure : 9.24 Mpa, including water hammer
Manifold

: 4 m reduced to 3.2 m at bifurcation;
: 3.2 m bifurcated to 2.3 m and 2.3 m
No. of 2.3 m branches : 6
Bifurcation type : Escher Wyss internal sickle
Construction Adits size : 6 x 7 m D-shaped
El. 1010 m : 591 m
El. 765 m : 820 m
El. 499 m (bottom) : 349 m

Underground Power House Complex

Power House Cavern : 206m (L) x 20.4 m (W) x 44.5m (H)
Installed Capacity : 6 x 170 MW
Drainage/cable anchor gallery : 3 m(W) x 4 m (H), 590 m long
Transformer Hall Cavern : 191 m (L) x 16 m (W) x 26.5 m (H)
Rock pillar between PH/TH : 39.3 m
Bus Duct  : 3 nos., 39.3m x 10 m (W) x 8.5 (H)
Elevation of Service Bay : 514.5 m
Size of Service Bay : 42 m x 20.4 ,
EOT Crane in Power House : 2 Nos, 200 T/40 T/20 T
Crane Span : 19.05 m
Crane beam support : Steel column-beam arrangement
EOT Crane Transformer Hall 1  : no. 5 T
Crane Span : 15 m
Crane beam support : Steel bracket anchored to cavern wall
Main Access Tunnel (MAT) : 377m. 7.5m (W) x 8.0m (H), D- shaped
Construction Adits (D-shaped)

  410m, 7m to top of Power House
 : 70m,7m to top of Transmission Hall
Unit Tail Race Gates : 6 Nos. 4.0m x 4.5m vertical lift wheel type

Tail Race Tunnel, Turbines, Generators, Transformers, Transmission, Inter-Connecting Sub-Station & Malbase, Inter-Connection Transformer

Tail Race Tunnel

Size : 3.1.km, 7.75.m, horse-shoe
Type of flow : Open Channel (Slope 1 in 1200)
Outfall Gate : 1 no. 6.5.m (W) x 7.75.m (H)
Intermediate Adit : 519.m, 7.m D-shaped
Outfall Adit : 130m, 7.m D-shaped

 Turbines

Type : Vertical Pelton
No  :6
Capacity : 173.5 MW
No. of Jets : 5
Nozzle level : 501.5 m
Design Net Head : 819 m
Rated Discharge       : 23.52m3/sec
Speed : 375 rpm

 Generators 

Type : Vertical shaft, Synchronous Machine
No : 6
Capacity : 190 MVA
Voltage : 13.8 kV

Transformers

Type : Single Phase
No. : 18 + 1 (spare)
Capacity : 70 MVA
Rated Voltage : 13.8. kV/400kV
Cable Tunnel : 484 m, 5 m (W) x 5.5 m (H)
Pothead Yard : 122 m x 31.5 m

Transmission 

400kv lines : 2 nos. Double Circuit, 140 circuit km. up to border.

 Inter-Connecting Sub-Station, Malbase. 

400 kV bays : Five Nos.
220 kV bays : Six Nos.
220kV lines

: 1 no. loop-in-loop-out connection each
with Chhukha and Birpara at Malbase
Rated Voltage : 400/220kV

 Inter-Connection Transformer 

Type : Single Phase
No  : 3 + 1 (Spare) x 66.67MVA, 400kV/220kV