According to a statement by project builders, Salini Costruttori, an unforeseen geological event provoked a rockfall involving about 15m of the 26km long headrace tunnel.

Salini said maintenance will be carried out over the next two months to recover full operational capability at the 420MW project.

The project was officially inaugurated on the 13 January in a ceremony attended by foreign and Ethiopian government officials, media and business leaders. The plant is currently the largest hydro scheme in Ethiopia, featuring 4 x 105MW pelton units, the TBM tunnel, penstocks and surface powerhouse.