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In October 2020, we diverted the Peace River. This step, which changes the route of a short section of the river during construction, was one of the most important in the construction of Site C. Diverting the river allows us to build the earthfill dam across the main river channel, while keeping the river flowing.
The river is now flowing through two large diversion tunnels, approximately 750 metres long and 11 metres in diameter, which are located on the north bank of the river.
We’re now focusing on building up two cofferdams – which will eventually measure about six stories high -– across the main channel. Then, we’ll pump the remaining water out of the area between the cofferdams, creating a dry area to build the centre of the dam.
During river diversion, water will accumulate behind the upstream cofferdam in what is called a headpond. The headpond will begin at the dam site and could extend as far back as 15 kilometres – or approximately up to Cache Creek.
The depth of this headpond will change throughout the year, depending on the flow in the river. On average, water levels in the headpond will be several metres higher than the current average river depth.
We expect the headpond to form during winter storms and spring freshet, when water levels are higher. BC Hydro is able to influence head pond depth, thanks to our two upstream dam facilities.