Engineering

The Water Transfer Component consists of the following works:
a) a concrete faced rockfill dam (CFRD) at Polihali, downstream of the confluence of the Khubelu and Senqu Rivers,
b) a transfer tunnel that will connect the Polihali reservoir to the Katse reservoir and
c) advanced infrastructure comprising access roads, power supply, telecommunication systems and accommodation
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The Polihali dam contract, based on the LHWP Phase II Feasibility Study Report, consists of the following works:

  • A 163.5 m high CFRD dam on the Senqu River (Polihali Dam);
  • A 49.5 m high CFRD saddle dam;
  • A concrete side-channel spillway with an uncontrolled crest length of 100m, transitioning into a reinforced concrete chute and flip bucket. The flip bucket discharges into a partially excavated plunge pool in rock;
  • A compensation outlet comprising a free-standing reinforced concrete inlet tower;
  • An access bridge connecting the left bank abutment with the inlet tower;
  • A compensation outlet house with a potential hydropower station of between 3 and 8 MW installed capacity;
  • A low level outlet to be constructed in one of the two river diversion tunnels; and
  • Associated construction infrastructure.
The main characteristics of the Polihali Dam and associated works are given in the table below.

Polihali Dam

Item Description
Dam Type Concrete faced rockfill dam
Non-Overspill crest level 2 083.0 at abutments and 2 084.5 masl at deepest section
top of rockfill 2 081.5masl
Full supply level 2075 masl
Upstream slope 1V : 1.4H
Downstream slope 1 V : 1.25 H, with a 5.5 m access road berm at various levels
Lowest foundation level 1 918.0 masl
Embankment height 163.5 m (to top of rockfill)
Crest width 10m
Crest length 915m
Embankment volume 12 311 210 m3
Excavation volume 40 000 m3
Length of plinth 1 150 m
Area of facing slab 123 430 m2
Saddle Dam
Non-Overspill crest level 2 083.0 masl at abutments and 2 083.5 masl at deepest section
Top of rockfill 2 081.5 masl
Embankment volume 664 380 m3
Excavation volume 18 000 m3
Area of facing slab 20 230m2
Upstream slope 1 V : 1.3 H
Downstream slope 1 V : 1.3 H
Lowest foundation level 2 032.0 masl
Embankment height 49.5 m
Crest width 6.5 m
Crest length 520 m
Length of plinth 535 m
Parapet Parapet height at abutment is 4.0 m, increasing to 5.5 m at the center of the main embankment to compensate for long-term creep settlement and subsidence if subjected to the MCE.
Crest road Finished road level - RL 2081.5m (1.5m below top of parapet)
Spillway Reinforced concrete side channel spillway with concrete chute and flip bucket discharging into a partially excavated stilling basin in rock. Length of side channel spillway crest is 100m
Outlet works Free standing intake tower and shaft with dry well
Number of intake 5 No (RL 2 060, 2 045, 2 030, 2 015, 2 000)
Type of intake 1.8 m diameter butterfly valve at each intake
Service gate for intakes Stoplog 3.0 m x 3.0 m
Fine screen Stainless steel with 50 mm openings cleaned by trash rake
Coarse Trashrack Reinforced concrete with 150 mm opening
Diameter of outlet pipe 1.8 m
Access bridge to Intake Tower 4 m wide x 260 m long deck, simply supported by three "T-beams" on piers at 27 m intervals
Low Level Outlet
Gates One slab maintenance gate and one radial service gate
Elevation of low level outlet 1 915.0 masl
River outlet 1 No 1.6 m dia and 1 No 0.8 m dia sleeve valves

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