Salient Features

About Salient Features of Sanima Middle Tamor Hydropower Ltd

Based on the current Revised Feasibility Study, the installed capacity of the project is 73 MW with the design discharge of 73.71 m3/s, corresponding to 42.71% exceedance flow. The catchment area of the Project is 2,002 km2 and the gross head is 132 m. The 50 m long weir has its crest level at 887 m above mean sea level (amsl). The maximum height of weir crest from its original ground level is 10.5 m which diverts the required flow to the Intake. Two undersluice gates maintain the design water level for intake and flush excessive deposits deposited in front of the intake area. Intake comprises of 6 openings to withdraw the design discharge to the Project. The flow from the Intake is conveyed to the gravel trap and successively towards underground settling basin via a concrete cased approach pipe of about 281.52 m length. A 100 m long underground settling basin (with additional 50 m of inlet and outlet chamber) designed with 90% trap efficiency passes the clean water into the headrace tunnel. About 3,367 m long headrace tunnel (concrete lining and shotcrete) with excavated diameter of 6.5 m passes the design discharge to the penstock. Proposed penstock is of 4.5 m (internal diameter) till the branching length of about 264.66 m after which four penstock pipes of internal diameter ranging 2.25 m, 3.18 m, 3.9 m and 4.5 m supplies the water to the powerhouse.

Powerhouse is 56.5 m long and 26 m wide with the tail water level at 755 m amsl. Four units of vertical axis Francis turbine each of 18.25 MW capacity have been proposed to generate the designed output of 73 MW. After the power generation (non-consumptive use), the tail water is discharged back to the Tamor River via a 75 m long tailrace culvert. The generated electricity is supplied through a 9 km long 220 kV double circuit transmission line (with 24 towers), to Dhunge Sanghu substation of the Koshi Corridor which is being constructed by Nepal Electricity Authority (NEA). The estimated annual energy generation as per the PPA is 429.409 GWh.

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
Hydrology:
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)
Spillway/Undersluice:
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
Intake:
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
Penstock:
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