GMSWORKS-3 Peace River Side Channel Restoration - BC Hydro

the significant storage relative to annual inflows, uncontrolled spills from Williston Reservoir
into the lower Peace River are infrequent, thus the magnitude and frequency of peak flows
have been reduced relative to historical unregulated flows. Seasonally, flows are regulated for
ice control on the lower Peace River as well as minimum flows for fish and fish habitat in the
Peace River below PCN.
Peace River has been regulated by Bennett Dam since 1967, with hydroelectric power
generated at GMS and PCN. These two stations produce approximately 29% of British
Columbia’s energy, and also provide critical load following capability to meet hourly power
demand within the interconnected provincial power transmission system. PCN is located
approximately 20 km downstream of W.A.C. Bennett Dam and forms Dinosaur Reservoir, which
extends upstream to the tailwater of W.A.C. Bennett Dam. While the reservoir’s tributary
drainage area is approximately 12,430 km 2 , it provides for limited storage due to a lack of major
tributaries, and flow balance is typically achieved within a day.
Water Survey of Canada [WSC] operates three stream gauging stations between PCN and the
BC Border. These include Peace River at Hudson Hope (basin area 69,900 km²), Peace River
above Pine River (basin area 83,900 km²) and Peace River near Taylor (basin area 97,100 km²).
BC Hydro has also collected data at PCN (basin area 68,900 km²). The period of record at the
Peace River at Hudson Hope and Peace River near Taylor stations includes data that was
collected prior to the construction of Bennett Dam. The seasonal variation in stream flow
observed at the four gauging stations is illustrated in Figure 1 and Figure 2. The data have been
sub‐divided into the pre‐regulation (≤ 1967) and post‐reservoir filling (≥1973) time periods. This
comparison illustrates how storage in Williston Reservoir has reduced the snowmelt freshet in
the spring and resulted in a more regulated hydrograph.
The historical variation in annual maximum daily discharges observed at the Taylor and Hudson
Hope WSC gauge sites is illustrated in Figure 3. Pre‐project data (i.e. ≤1967) indicate that the
annual maximum daily discharges ranged between 4,760 and 8,810 m³/s (average 6,165 m³/s)
at Hudson Hope and between 5,380 and 11,500 m³/s (average 7,525 m³/s) near Taylor.
Regulation has substantially decreased the natural range of peak flood magnitudes. Anomalies
occur in 1972 (spillway test), 1996 (emergency drawdown) and, to a smaller extent, in 1990
when a spring ‘cold low’ storm resulted in substantial inflow from streams draining the east
side of the Rockies. Excluding these three events, post‐regulation annual maximum daily
discharges are presented in Table 1.
Peace River Side Channel Restoration 4