... the construction of this powerhouse by six months,” explains Béchard. “The unit cost of interest made it uneconomical to build the downstream facilities before the diversion.”
Interest for Eastmain-1-A was 4.3¢ per installed kilowatt, but for Sarcelle it would have been 8.1¢/kW, Béchard says. Delaying the powerhouse construction saved about $43 million in interest and escalation. The schedule also allowed him to flatten the project’s workforce because he moved workers to Sarcelle after they finished at Rupert. It also saved 200 beds at the Sarcelle work camp, which has 800 beds.
Paving a Path
Hydro-Québec is piloting a dam technology that is new in North America, though common in Europe. The rockfill Nemiscau-1 Dam, more than 300 m long and 14.2 m high near the north end of the Rupert Tailbay, will use asphalt concrete instead of till for its core. Till is widely available in the area, and Hydro-Québec uses it for many other structures on this project. But the utility plans to use asphalt-concrete cores for the 1,550-MW, $5.9-billion La Romaine Hydroelectric Complex, north of Havre-Saint-Pierre, Québec, where till is not so available. That project was launched in May 2009, and engineers wanted to prove the concept first at Nemiscau-1.
Ashley Iserhoff
Dpty. Grand Chief,
He sees tangible benefits from the project for Crees
“We had to choose a dam that was not on our critical path, since if we had to do major correction work, we would have enough time to do it without placing the partial diversion in danger,” says Béchard.
Hydro-Québec retained Norway-based Kolo Veidekke, a contractor with extensive experience in asphalt concrete cores for dams, as its consultant. “You have to be kind of careful with this mix,” Béchard says. The proportion of liquid asphalt and aggregate is critical. There must be 7.8% asphalt, he says. “If you get that wrong, you cannot put in the next layer.” Layers are 225 mm and require three to five days to cure, depending on the temperature. The project required 54 layers, placing about two per day. Kolo Veiddeke supplied the asphalt-placing equipment.
Pavex, a Québec subcontractor, provided the workforce and the rest of the equipment. The asphalt used for the core is much softer than highway-paving material. Its consistency makes it flexible to deform with earth movement while retaining its watertight quality. The core, 800 mm wide at the base and 400 mm above the second layer, is much narrower than cores made with conventional materials. The asphalt core was completed last August and has performed well, Béchard says.
Rupert Diversion
In November, 71% of the Rupert River’s flow will be diverted northward to begin flooding a 50-km-long forebay. After passing nearly 50 m below the surface via a 2.9-km-long transfer tunnel to the 44-km-long tailbay, it will continue north via existing reservoirs through the current project’s two new powerhouses and on to the La Grande River.
Preparations for the Rupert Diversion began in March 2007, when contractor EBC-Neilson started excavating the spillway, 640 m long, 40 m wide and 46 m deep, to temporarily divert the river to allow dam construction in the dry. By the end of July 2008, the spillway was completed and the river diverted, and EBC-Neilson was beginning construction of the 470-m-long, 28.6-m-high rockfill dam’s foundation.
The diversion will launch construction of eight weirs and spur-dikes on the Rupert downstream, designed to maintain as much as possible the natural levels of the river and reduce negative impacts on the fish. Inflow from tributaries will restore some of the Rupert’s flow. When it enters Rupert Bay, the flow will be back up to 48% of its natural volume.
The diversion bays have been shaped into a pair of bowls—228.7 sq km in the forebay and 117.5 sq km in the tailbay—with the construction of 74 dikes and four dams. The 2.9-km transfer tunnel that links them was driven to pass below a lake that could not be incorporated into the project. Simard-Beaudry Construction Inc., Laval, Québec, began excavating overburden in May 2007 and started drilling the 8.6-m-high, 12.7-m-wide tunnel through Canadian Shield bedrock on Aug 31. The jumbo drills holed through in June 2008. Excavation of a 10-m bench was completed by October 2008, making the tunnel ready for operation.
In September 2007, a coalition of more than 20 environmental organizations launched a protest campaign in hopes of halting further construction on the ESR project. But the Paix des braves, ratified by referendum, solidified the support of the Crees for the project. When ENR called on some of the organizations for comment, none responded. Deprived of the fuel of popular outrage, the protest movement had burned out.
