Predicted Changes in Peace River Channel Morphology and Sediment Transport Related to the Site C Clean Energy Project

Author: Craig Nistor, P.Geo., Violeta Martin, Ph.D., P.Eng.
Conference: Canadian Hydrotechnical Conference 2015

The Site C Clean Energy Project is a third dam and 1100 MW hydroelectric generating station on the Peace River in northeastern British Columbia, Canada. BC Hydro plans to start construction in the summer of 2015. This paper presents the predicted changes in channel morphology and suspended sediment dynamics during Project operations that were described in the Environmental Impact Statement (EIS) for the Project.

The reservoir is predicted to trap 70% of the incoming sediment delivered from tributaries and from shoreline erosion induced around the reservoir perimeter. However, sediment deposition on the reservoir bed is predicted to reduce the initial reservoir volume by only 2.5% after 50 years. The mean annual suspended sediment load of the Peace River immediately downstream from the dam is predicted to be reduced by 54% compared to baseline conditions. Farther downstream at the Town of Peace River, Alberta, the predicted reduction in sediment load is only 2%, due to the large sediment inputs delivered to the Peace River by intervening tributaries. The Peace River has a cobble-gravel bed extending for several hundred kilometres downstream from the Site C dam site, and the sediment that will be trapped in the reservoir is much finer than the bed material in this section of the river.

Long-term field observations indicate that the bed material in this part of the river is generally immobile due to flow regulation at the two existing dams, which has led to ongoing bed material aggradation at tributary confluences and vegetation encroachment on gravel bars. The Project will not change the flow regime of the river with respect to bedload transport competence, and so is not expected to cause any incremental change in channel morphology downstream from the Site C Dam under normal operating conditions.