GMSWORKS-3 Peace River Side Channel Restoration - BC Hydro

species dominate the system. The temperature regime also influences fish life history activities
(e.g., spawning) by shifting the timing of temperature cues used by fish. As a result, some
populations (e.g., mountain whitefish) initiate spawning much later than similar populations in
unregulated systems.
An important effect of the altered temperature regime is the change in degree days needed for
egg development and fry growth, the consequence of which is an increase in mortality. Water
temperatures in shallow water areas of the Peace River are also influenced by the daily flow
regime. Low flows, particularly in side channels, create shallow water areas that exhibit
elevated water temperatures during warm summer days. These warmer temperatures can be
outside the preferred thermal range of fish or can be lethal to fish.
4.1.4 Fine Sediments, Debris and Ice
Operation of the hydroelectric facilities and their storage reservoirs has had little effect on fine
sediment regimes, due to the lithography of upstream basins (Church, 1995). In general, water
clarity is high upstream of the Halfway River confluence, but can decline dramatically
downstream of this point during periods of high tributary inflows. The absence of suspended
sediments upstream of the Halfway River has likely enhanced primary production.
Downstream of the Halfway River confluence, the effect of elevated fine sediment loads from
tributary inputs combined with an altered annual hydrograph (i.e., reduced mainstem flood
discharge) has resulted in an infilling of side channels and channel margins. This influences the
availability and complexity of fish habitats. Tributary systems also supply wood debris loading
to the Peace River and provide materials for the formation of jams and debris structures.
Thermally altered discharge from PCN results in the delayed formation of ice in and along the
Peace River. Areas above the Halfway River are less affected by ice flows and its effects on the
channel during break‐up. Shore ice may thicken in areas where flow fluctuations occur more
frequently, which may be expected to affect potential debris placement and restoration
opportunities.
4.1.5 Morphology and Physical Characteristics
In regulated rivers, the isolation of side channels occurs due to hydrological modifications and
morphological changes. The impacts can include:
� Downcutting of the primary channel resulting in isolation of secondary channels,
� Infilling of secondary or side channels with fine sediments from lack of regular high flood
flows,
� Channel simplification resulting from reduced sediment or supply of large woody debris,
� Floodplain impacts from flood protection works, and
� Vegetation encroachment and growth associated with sediment infilling.
Peace River Side Channel Restoration 10