In the Uva Province of Sri Lanka a hydroelectric power station is being built which will redirect water into a different river system and also aid irrigation.

In addition to generating electricity for the whole of Sri Lanka (>230 GWh/year), the aim is to develop the lower reaches of the Uma Oya river towards Hambantota

Every year an average of 145 million cubic metres of the Uma Oya river will be redirected to the Kirindi river system and used for irrigation. The site, on the edge of the central plateau, will use the water to generate electricity: located underground and with an installed power capacity of 120 MW, the power station will be supplied with water by a 15.3 km long penstock tunnel. The project requires a penstock tunnel, a connecting tunnel and further infrastructure works.

The Uva Province lies in the Sri Lankan highlands. The geological basis is metamorphous rock (mostly gneiss) and is lightly folded. The ground-water table is close to the ground surface, and this led to high levels of water ingress during tunnelling.

We advised the main contractor and successfully optimised the layout of the facility. Amberg also took over on-site construction management between 2013 and 2017.

Special high pressure injections were used to minimise water ingress. Preliminary explorations with TSP (Tunnel Seismic Prediction) were also carried out in order to locate the water-bearing zones before the TBM began work. To prevent water inflow in future, the rock around the tunnel is injected with cement and sealed. These measures also allow the ground-water table to recover.

 

Reference Sheet

Project details

Objective

  • Convey 145 million cubic metres of water a year for irrigation purposes
  • Generate electricity (>230 GWh/year)
  • Power capacity of 120 MW
  • Direct water to the underground power station with a 15.3 km long penstock tunnel and a 628 m deep vertical shaft

Challenges

  • Rural infrastructure
  • Difficult geological conditions

Geology

  • The project is being carried out in Precambrian crystalline with metamorphous rock in the Sri Lankan highlands.
  • The rock formation contains lightly folded charnockite gneiss, quartzite and marble

Amberg services

  • Optimisation of facility layout
  • Study and re-evaluation of the geological and geotechnical conditions
  • Advising main contractor