Information on the rehabilitation works planned at Enguri HPP

8 Dec 2020 The most important component of the project is the repair of the diversion tunnel. It is through this tunnel that water is delivered from the reservoir to the units.

In order to study the condition of the Enguri hydropower plant and to determine the scale and priorities of the necessary rehabilitation works, a study and analysis of the Enguri HPP structures began in 1997. Between 1998 and 2001 a large-scale rehabilitation project for the Enguri hydropower plant was drawn up. Rehabilitation works on the electrical and hydromechanical equipment of Enguri HPP were carried out between 2003 and 2014, and in 2006 some sections of the diversion tunnel were repaired.

To ensure the safe and smooth operation of the hydropower plant, investment and capital works must continue. In 2018–2021 the works foreseen by Phase IV of the Enguri HPP rehabilitation will be carried out with a loan of EUR 38 million from the European Bank for Reconstruction and Development (EBRD). The rehabilitation programme also foresees an additional grant of EUR 7 million from the European Commission.

To ensure the reliable and smooth operation of Enguri HPP, the works foreseen by Phase IV of the rehabilitation must be carried out in 2018–2021. The project comprises the following works:

1. Works on the electrical and hydromechanical equipment at Enguri HPP and Vardnili HPP 1;

2. Repair of the diversion tunnel, meaning the urgent rehabilitation of the most damaged sections;

3. Removal of silt from the Enguri HPP reservoir (the area adjoining the dam);

4. Repair of the access roads to the hydropower plant.

The planned rehabilitation works are to be completed by the end of 2021. The most important component of the project is the repair of the diversion tunnel. It is through this tunnel that water is delivered from the reservoir to the units. Accordingly, draining the tunnel and carrying out the repair works requires the hydropower plant to be shut down completely. The rehabilitation works on the diversion tunnel will run from the second half of January 2021 to the beginning of May.

The rehabilitation works on the diversion tunnel aim to:

- preserve the structural stability of the tunnel;

- reduce water leakage (and accordingly reduce the volume of water lost for electricity generation);

- protect the Enguri hydropower plant from the groundwater produced by leaking water, which presses on the Enguri underground plant and threatens its operation. Over the past three years, damage has been found to the metal pipes of the turbine water conduits (the pipe wall is 40 mm thick) on units #1, #2 and #5. This is caused by increased seepage water and, consequently, by increased back pressure.

An open international tender for the rehabilitation works on the diversion tunnel was held in 2019 (EBRD) and the executing contractor has already begun the corresponding mobilisation procedures. Postponing the rehabilitation works would technically be associated with risks that are difficult to assess. In the event of a failure, the tunnel might have to be drained and restoring the damaged section could take some time. The total loss could exceed the cost of the planned rehabilitation works by three or four times, or even more.

At this stage, water equivalent to about 250 million kWh of electricity is lost from the diversion tunnel. The rehabilitation will not eliminate these leaks entirely, but it should reduce them by about 25%, which means generating roughly 60 million kWh of additional electricity a year.