Salient Features

Location: Phurumbu VDC, (Currently: Phungling Municipality), Sawadin VDC, (Currently Phaktanglung Rural Municipality) and Khokling VDC, (Currently Mikwa Khola Rural Municipality), Taplejung District, Eastern Development Region (currently Province No. 1) of Nepal
Purpose of Project: To supply for domestic use by connecting to national grid
Catchment Area 2,002.32 km2
Average Flow 126.69 m3/s (minimum monthly flow 19.55 m3/s)
Design Flow 73.71 m3/s (42.71% exceedance flow)
90% Exceedance flow 17.98 m3/s
Design Flood (Q100) 2,791 m3/s
Diversion Dam:
Type Concrete gravity dam
Slope Ogee-profile
Crest Elevation 887 m above msl
Max. Flood Level (100 years return) 895.4 m above msl
Crest Length 60 m
Maximum height 10.5 m (from the Original ground level)
Type Submerged with overflow spillway (2@ 5 m x 5 m)
Invert Elevation 874.50 m above msl
Size (B x H) 5.0 m x 5.0 m
Type Submerged
Number of Orifices 6
Sill Elevation of Orifice 881 m above msl
Top Elevation of Orifice 885 m above msl
Size (B x H ) 4.75 m x 4.0 m (each)
Gravel Trap:
Type Rectangular, RCC (Continuous)
Particle size to be settled 5 mm-100 mm
Number of Chambers 3
Width (each) 12.00 m
Height 11.85 m
Length 15.00 m
Approach Pipe
Type Concrete encased steel pipe
Number 1
Diameter 4.5 m
Total Length (Up to Inlet Portal) 281.52 m and 20 m inside tunnel including Bell-mouth
Longitudinal slope 1:1000 (V:H)
Underground Settling Basin:
Type Conventional flushing
Number of bay 3
Approach Tunnel length 360.244 m (average)
Transition length 35 m
Dimension ( L x B ) 100 m x 13 m (each)
Particle Trap efficiency 90% (for sediment particles equal to or larger than 0.2 mm)
Longitudinal slope 1:50
Length from transition up to outlet gate 22.75 m
Length from gate to vertical drop 30.26 m
Converging tunnel length from drop to main tunnel (Average of three) 109.622 m
Inspection Tunnel:
  Inspection Tunnel (common stretch):
Length 131.758 m
Excavation Diameter 4.9 m
  Inspection Tunnel 1 (to SB inlet):
Length 145.963 m (excluding common stretch)
Excavation Diameter 4.9 m
  Inspection Tunnel 2 (to SB outlet):
Length 289.524 m (excluding common stretch)
Excavation Diameter 4.9 m
Adit-1 (near Nakla Kholsi):
Length 301.562 m
Excavation Diameter 4.9 m
Sediment flushing tunnel:
Number 6
Length from inlet to common tunnel 28.72 m (each)
Size(B X H) 2.4 m x 2.4 m
Length of common tunnel up to portal 327.89 m
Slope of the tunnel 1:50
Size (B x H) 2.4 m x 2.9 m
Length of culvert from portal to outlet 52.778 m
Slope of the culvert 1:50
Size of culvert (B X H) 2 m x 2.5 m
Total Sediment flushing length 409.388 m
Headrace Tunnel:
Length (Excluding settling basin) 3,367 m (up to outlet portal)
Dimensions Inverted U shape 6.5 m (Excavation Diameter)
Support System Concrete lining and shotcrete
Surge Shaft:
Type Vertical, Underground circular section/ dome type
Height 79.93 m
Diameter 16.00 m (Excavation)
Ventilation tunnel for Surge shaft:
Length 199.75 m
Size(B X H) 3.5 m X 3.75 m
Slope 1 in 8.69
Length 264.66 m inclined length of 4.50 m diameter including Bell-mouth up to branching
  After branching,
  11.54 m of 4.5 m diameter including transition
  11.25 m of 3.9 m diameter including transition
  11.47 m of 3.18 m diameter including transition
  153.12m of 2.25 m diameter including transition
  452.04 (Total Length)
Thickness 18 mm to 36 mm thickness
Grade E-350 (IS 2062 or Equivalent)
Power Facilities:
Powerhouse Type Semi-surface
Dimensions ( L x B ) 56.5 m x 26 m
Gross Head 132 m (887.0 m – 755.0 m above msl)
Net Head 115.59 m
Installed capacity 73 MW (4 x 18.25 MW)
Dry energy 64.90 GWh
Wet energy 364.27 GWh
Annual Net Energy Output 429.409 GWh
Tailrace Culvert:
Type RCC, rectangular culvert (double chambered)
Length 75.00 m
Height 5.00 m
Width 4.75 m each
Longitudinal slope 1:500 (V:H)
Maximum Tail water level 755.00 m amsl
Transmission Facilities:
Transmission line length 9 km
Voltage level 220 kV, Double circuit