Eastmain-1 Hydroelectric Facility – Bypass Tunnel

The Eastmain-1 hydroelectric facility is made up of two hydroelectric power stations, a damn and a reservoir on the Eastmain River in Québec. This project was undertaken by the James Bay Energy Company for Hydro-Québec between 2002 and 2012. Opened in 2007 and located 88 kilometers north of Nemiscau, in the Nord-du-Québec administrative region, the Eastmain-1 power station has an installed capacity of 507 megawatts. JANIN ATLAS undertook the construction of the temporary Bypass Tunnel for the construction of Eastmain-1.


The Eastmain-1 development is component of the La Grande complex as part of the James Bay Hydropower Project. The power stations are located on the west bank along a North-South axis.
During Construction, the 3 turbine-alternator groups of the Eastmain-1 power station had a combined power output of 480 megawatts, with annual production reaching 2.7 terawatts/hour. The normal drop height was of 63m, with an estimated water flowrate of 840 m3/s.
The adjacent Eastmain-1-A power station is fed by additional water flows from a partial diversion of the Rupert River, and was opened in November 2009 as part of the same Project. It is located 700 metres to the East of its sister power station, which whom it shares several characteristics.


The construction activities undertaken by JANIN ATLAS for the excavation and realization of the Bypass Tunnel included grubbing and deforestation, installation of the cofferdam and the upstream plug, rock excavation, rock consolidation, protection of the superficial layer of rock, high-pressure shotcreting of the tunnel walls, safety barriers, concreting and stripping, installation of rebar, construction of primary buried foundations for the valves and breathers, installation of pipes and bypass valves, drilling and injections.



Since the full completion of the Project, both power stations are open and work conjointly. The addition of the Eastmain-1-A power station on the Rupert River added an additional 2.3 terawatts/hour of capacity, bringing the total power output of the Project to 5.0 terawatts/hour. The use-factor of these power stations is 47%.

Project participants

James Bay Energy Company

Hydro-Québec Production

Key figures

Implementation dates
March 2003 to June 2004

Topsoil Excavation: 60,000 m3

Open-Cut Rock Excavation: 500,000 m3

Underground Rock Excavation: 90,000 m3

Concrete: 7,800 m3

Toulnustouc hydroelectric power project