Findings
Preliminary data analyses show that first-pass logging over 4% and 8% of the
241 and Dennis Cr. watersheds, respectively, did not result in detectable
changes in the hydrograph. However, since the area logged in the 241 Creek
watershed has been increased to 17%, the highest maximum daily peak flows appear
to have increased and the lowest low flows decreased, while average flows have
remained the same. Changes in annual water yield are within measurement error.
These changes were in addition to the increase in annual water yield from both
the treatment and control watersheds over the years 1996 through 2001 relative
to the pre-logging period, 1985 to 1995. Post-1995 May and June water yields
from the unlogged 240 Cr. watershed averaged 16% and 60% more, respectively,
than during the pre-logging period and total annual yield was 38% higher.
The volume of water accumulating as snow, and the rate at which the snowpack
melts, has increased by up to 30% in the clearcuts relative to the forest. The
size of these changes varies from year to year, with the weather, and with the
type of forest logged. The largest differences in snow accumulation and melt
between a clearcut and a forest have been measured where the forest is dominated
by Engelmann spruce and subalpine fir, compared to lodgepole pine. Measurements
in regenerating forests show that they must be well over 3 metres tall before
they have any measurable effect on snow accumulation and melt.
Measurements at Upper Penticton Creek have shown that 20% to 30% of summer
rainfall is intercepted by the forest canopy and evaporates before reaching the
ground but that the percentage intercepted decreases with increasing rain-storm
size. Evaporation losses from clearcuts re-vegetated with grasses and herbs and
losses from the forest have been found to be similar.
Little change in water quality has been observed so far, with the exception
of turbidity and stream temperature. In late September and October 1998,
elevated turbidity levels were measured at the 241 Creek weir. This increase in
turbidity was attributed to the commencement of harvesting and vehicular
activity in the watershed. A comparison of water temperatures in Dennis Creek in
the open and in the forest showed that water temperatures were 2 C to 3 C higher
on average in the open, and a maximum of 6 C higher, than those under forest
cover.
Monitoring of post-logging changes in streamflow, water quality, site
specific hydrologic processes, channel morphology, and aquatic habitat resulting
from past and future logging is continuing.
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