348
E.D. Hetherington
area was clearcut , it is not surprising that changes in peak flows were not
detected. Mid-winter rain-only peak flows in Oregon (Harr et al. , 1979)
and those during larger storms in California (Wright et al., 1990) were
also not significantly changed after harvesting. However , peak flowsduring
a major rain-on-snow event at Carnation Creek in 1982 (after logging)
were higher than might be expected from rain only. Data from Oregon
also indicate that harvesting probably does increase rain-on-snow peaks in
the transient snow zone where the snowpack is relatively shallow and
intermittent (Harr, 1986).
Erosion and Sediment Production
Despite steep slopes and high rainfall, erosion on the logged slopes and
input of sediment to Carnation Creek has been modest (Hetherington,
1988; Scrivener, 1988). Sediment input to small tributary streams was
monitored during road construction (Ottens & Rudd , 1977), and minor
ditch erosion has occurred on steeper sections of the road network. A few
landslides, some very small, and debris torrents in gullies have occurred
during major storms after logging in both clearcut and uncut areas
(Hartman & Scrivener, 1990; Hetherington, 1988). Only a few of these
events actually put soil and debris into the stream . Much of the extra
sediment observed in the stream after logging has come from within the
stream channel itself, as noted below.
Stream Channel
The morphology and structure of the main steam channel changed
dramatically following streamside logging primarily due to deterioration
of stream banks, destabilization and removal of instream logs, and introduction of small organic debris. In the intensively disturbed section of the
stream , channel width increased up to 8 m after logging (Powell, 1988)
with a concurrent 2.7-fold increase in volume of eroded stream bank
sediments (Scrivener, 1988). Sand content of spawning gravels in lower
Carnation Creek increased by 5.8% and was still accumulating 10 years
after logging (Scrivener, 1988). Bedload movement at B weir increased
from 251 t/yr before logging, to 289 t/yr during logging and 270 t/yr
after logging (Hartman & Scrivener, 1990). This increase came from
mobilization of stored gravel within the channel plus extra input by
landslides and debris torrents. The channel has straightened in several
sections and has fewer pool-riffle stages.
Water Quality
Carnation Creek stream water is very low in dissolved nutrients and
minerals and is weakly acidic (pH 6.0-7.1) (Hedin & Hetherington,
Chapter 4; Scrivener, 1975). Minor changes in stream water quality
E.D. Hetherington
area was clearcut , it is not surprising that changes in peak flows were not
detected. Mid-winter rain-only peak flows in Oregon (Harr et al. , 1979)
and those during larger storms in California (Wright et al., 1990) were
also not significantly changed after harvesting. However , peak flowsduring
a major rain-on-snow event at Carnation Creek in 1982 (after logging)
were higher than might be expected from rain only. Data from Oregon
also indicate that harvesting probably does increase rain-on-snow peaks in
the transient snow zone where the snowpack is relatively shallow and
intermittent (Harr, 1986).
Erosion and Sediment Production
Despite steep slopes and high rainfall, erosion on the logged slopes and
input of sediment to Carnation Creek has been modest (Hetherington,
1988; Scrivener, 1988). Sediment input to small tributary streams was
monitored during road construction (Ottens & Rudd , 1977), and minor
ditch erosion has occurred on steeper sections of the road network. A few
landslides, some very small, and debris torrents in gullies have occurred
during major storms after logging in both clearcut and uncut areas
(Hartman & Scrivener, 1990; Hetherington, 1988). Only a few of these
events actually put soil and debris into the stream . Much of the extra
sediment observed in the stream after logging has come from within the
stream channel itself, as noted below.
Stream Channel
The morphology and structure of the main steam channel changed
dramatically following streamside logging primarily due to deterioration
of stream banks, destabilization and removal of instream logs, and introduction of small organic debris. In the intensively disturbed section of the
stream , channel width increased up to 8 m after logging (Powell, 1988)
with a concurrent 2.7-fold increase in volume of eroded stream bank
sediments (Scrivener, 1988). Sand content of spawning gravels in lower
Carnation Creek increased by 5.8% and was still accumulating 10 years
after logging (Scrivener, 1988). Bedload movement at B weir increased
from 251 t/yr before logging, to 289 t/yr during logging and 270 t/yr
after logging (Hartman & Scrivener, 1990). This increase came from
mobilization of stored gravel within the channel plus extra input by
landslides and debris torrents. The channel has straightened in several
sections and has fewer pool-riffle stages.
Water Quality
Carnation Creek stream water is very low in dissolved nutrients and
minerals and is weakly acidic (pH 6.0-7.1) (Hedin & Hetherington,
Chapter 4; Scrivener, 1975). Minor changes in stream water quality