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

uns through a mud flat with cover largely composed of sediments however, small
pools of gravel were observed within 350 m of the streams confluence. Throughout
the creek there is high crown closure providing areas of shade.
Escapements have increased dramatically in Boulder Creek, from approximately 200
spawners in 2004 to over 4,300 in 2006 and the number of spawners in Flat Creek
have seen a 5 fold increase, from approximately 450 spawners in 2004 to over 2,500
in 2006 (Fig. 17). Escapements have remained unchanged in Jones Creek where
approximately 1,200 spawners used the creek in 2004 and 2006 (Fig. 17). The large
dramatic increases observed in Boulder Creek and Flat Creek are likely due to the
proximity of the creeks to the area of stocking. It is well documented that several
species of hatchery-reared salmonids, including sockeye salmon, will return to
spawn in their stream of release (Scholz et al 1992). In Wahleach Reservoir the fish
were stocked into the reservoir from the boat launch which is immediately south of
the confluence of Boulder Creek and approximately 5 km north of Flat Creek (Fig. 1).
Imprinting likely explains the dramatic increases of kokanee in Boulder Creek and
Flat Creek because these streams are most readily accessible.
Imprinting may also explain why kokanee spawners in Wahleach Reservoir chose a
stream with sub-optimal habitat. Spawning habitat in Boulder Creek is largely
composed of large cobbles and boulders and limited gravel offering sub-optimal
spawning habitat which would likely impede spawning success yet large numbers of
spawners were observed in this creek. In addition, in terms of area, Flat Creek has
more available spawning habitat relative to Boulder Creek yet fewer spawners were
observed in Flat Creek (~2500). This is likely due to less imprinting of stocked
kokanee to Flat Creek due to its greater distance from the stocking location. In
2006, a log jam spanning the width of Flat Creek, approximately 850 m upstream
from the bridge, prevented kokanee spawners from migrating upstream. No
kokanee were observed above this log jam. In previous assessments, there is no
mention of this structure, and it remains to be seen whether this migration barrier will
be ephemeral, or a permanent structure in Flat Creek’s stream channel. Despite
Jones Creek having the most suitable spawning habitat for kokanee compared to
Boulder Creek and Flat Creek (Greenbank 2002), low numbers of spawner in Jones
is likely due to the distance from the stocking location.
In 2006, the combination of low water flows and the presence of a weir in Boulder
Creek for diversion of water to augment flows in Lower Jones Creek, the migration of
kokanee to the upper reaches of Boulder Creek was blocked. The weir is located
approximately 400 m upstream of the confluence of the creek and no kokanee were
observed upstream of the weir. As a result, access to the upper reaches of Boulder
was prevented which may have prevented access to over half of the available habitat
in Boulder Creek. Fortunately the substrate of the lower reaches of Boulder Creek
(approximately 0-75 m from its confluence with Wahleach Reservoir) is a mixture of
gravel and fine sediments, which may provide some suitable spawning habitat and
100-200 m upstream from Boulder Creek’s confluence with Wahleach Reservoir,
gravel substrates are present near the edges of the stream and in pool tail-outs
Wahleach Reservoir Fertilization Project, 2004-2006.
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