Wahleach Project Water Use Plan Wahleach Reservoir ... - BC Hydro

4. Results
4.1 Reservoir elevation
The reservoir is generally recharged in May to July through snow melt and the
reservoir is held relatively constant during the fertilization period (Fig. 5). The
drawdown which occurs from November to April was 15.6 m, 11.8 m and 10.7 m for
2004, 2005 and 2006. The minimum reservoir level in 2004 was below the long term
mean and below the elevation level recommended by Perrin and Stables (2000) to
protect habitat for spawning rainbow trout. Following record drawdowns in 1996 to
624.6 m an entire year class of rainbow trout was absent from the reservoir possibly
due to restricted access to spawning sites. Minimum elevations vary annual but
generally occur in mid-April while the maximum level occurs from July to September.
Refill rates were similar for 2004 and 2006 while in 2005 the elevation of the
reservoir was below the long term average approximately from June-October.
Elevation (m, GSC)
645
640
635
630
625
1984-06
2006
2005
2004
620
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 5. Water surface elevation (m) of Wahleach Reservoir, 2004-2006. Shaded
area in figure represents mean elevation from 1984-2006, arrows indicate the start
and end date of fertilization and dashed line at 627 m elevation is the water surface
recommended by Perrin and Stables (2000) for successful spawning.
4.2 Physical Parameters
At the beginning of each field season surface temperatures were ranged from 12-
14ºC and weak temperature stratification was present (Fig. 7). In the summer the
surface temperatures reached 18.5ºC in 2004, 22.5ºC in 2005, and 18.3ºC in 2006.
There was little variation in hypolimnetic waters, varying in temperature by less than
2ºC over the three year study period. By September and October the thermocline
was deepening, the density differences were weakening and fall turn over was
immanent (Fig. 6).
Wahleach Reservoir Fertilization Project, 2004-2006.
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