Peace Project Water Use Plan - BC Hydro

Peace Project Water Use Plan
Annual Report: 2010
5.1.10.2 Contractor’s Report
The following physical changes have been observed and/or inferred in the Peace River since
regulation and may be related in an incremental way to the reported water intake problems.
1. Peace River freshet flows have been reduced, while sediment inputs to the river during
freshet have been much less affected, meaning that suspended sediment concentrations
in the Peace River have likely increased during spring and summer. However, it is
unclear at this time which of the Peace or Pine Rivers has higher sediment
concentrations overall or how the seasonal variations in concentration compare between
the two rivers.
2. Peace River peak flows have been reduced, which has resulted in the river losing its
competence to transport formerly mobile bed material. This has caused an increase in
fine sediment content on (and possibly within) the bed material, which in turn may have
reduced the porosity and hydraulic conductivity of the bed material.
3. The loss of transport competence in the Peace River has affected channel morphology in
the vicinity of the Pine River confluence. Bedload sediments delivered by the Pine River
are no longer transported downstream as readily by the Peace River, and have been
accumulating near the confluence. This has resulted in aggradation of the Peace River
bed, bed material accumulation and lateral instability in the lower Pine River, and the
progradation of Pine River bed material deposits out into the Peace River channel. The
Peace River has been constricted at the confluence, and the approach angle of the Pine
River has shifted from 45 to 90 degrees relative to the Peace River above the confluence.
4. The ratio of Pine River freshet flows relative to Peace River freshet flows has increased.
Combined with the channel constriction of the Peace River and the change in approach
angle of the Pine River, it is possible that the Pine River plume now spreads more widely
across the Peace River and mixes more quickly with the Peace River than it used to.
Based on the available air photo evidence, however, it is unlikely that the Pine River
plume reaches the north bank of the Peace River under normal post-regulation freshet
conditions. It should be noted that this has been difficult to assess definitively from the
historical air photo record and that further investigation would be required to confirm this
conclusion.
5. Summer water temperatures in the Peace River are approximately 3°C to 5°C lower than
in the Pine River, presumably due to the cooling effect of deep-level releases from the
reservoirs. Temperatures along the north bank of the Peace River are likely influenced
primarily by upstream Peace River temperatures rather than Pine River temperatures
under most flow conditions. Again, however, it is difficult to state definitively at this time
how the mixing of the two river plumes affects summer water temperature at the Spectra
intake site.
ALTERNATE HYPOTHESES
Based on these observations and inferences, the following alternate hypotheses are
proposed:
1. Sediment deposition at the Spectra intake facility is caused by the general increase in
Peace River bed elevation in that reach of the river, and by the sheltered hydraulic
conditions at the intake that promote suspended sediment deposition.
2. Suspended sediment concentrations in the Peace and Pine Rivers are not substantially
different, so the mixing of the Peace and Pine River sediment plumes does not provide a
significant control on sediment concentration in the water extracted at the Spectra intake.
Furthermore, the mixing of the Peace and Pine River sediment plumes does not take
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