17. Logging Effects on the Aquatic Ecosystem
347
1990). Inaccurate low-flow measurements preclude reliable evaluation of
water yield changes in the main stream at B weir.
In the lower Carnation Creek floodplain, summer groundwater levels
were up to 50em higher after harvesting of both the floodplain and the
adjacent side slopes (Hetherington, 1982). Despite vigorous regrowth of
deciduous vegetation on the floodplain, the increases in summer groundwater levels had barely diminished after 10 years. This result is believed
to be due to the maintenance of higher seepage from the side slopes
where vegetation growth has been slower (Hetherington, 1988).
Slope Groundwater Levels
At one piezometer site on a clearcut slope in H watershed above any road
influence, storm groundwater peaks were up to 20 em higher after logging
than before (Hetherington, 1982). The suspected cause of this change was
surface soil disturbance that possibly caused local modifications in the
pathways of water movement into and through the soil; that is, less water
was moving through the macrochannels andmore through the soil matrix
resulting in a short-lived but significant localized rise in the water table.
At another piezometer site below a road , groundwater peaks were up
to 20 em lower due to interception and lateral diversion of subsurface
seepage by the road (Hetherington, 1982). Changes in slope groundwater
regimes due to road diversion of surface runoff and excessive soil disturbance were presumed to have been major causes of two small landslides near H watershed in 1982 (Hetherington, 1988).
Peak Flows
Preliminary results regarding the question of harvesting effects on peak
streamflows have been variable . The analyses were based on rain-only
conditions because the vast majority of storms fall into this category. In
tributary H, peak flows appear to have increased after road construction
(Hetherington, 1982). This result suggests that the roads may have
accelerated flow to the stream channel by converting some subsurface
seepage into surface runoff. These changes were sustained for at least
three years after harvesting. Road-related peak flow increases in small
watersheds have been observed in Oregon (Harr et aI., 1979) and for
small storms in California (Wright, Sendek, Rice, & Thomas, 1990).
At B weir on Carnation Creek, rain-only peak flows showed no significant changes (Hetherington, 1982). The highly permeable soils retain
high infiltration capacities after disturbance so surface runoff in the
clearcuts apart from the roads remains negligible or nonexistent Thus, in
the larger watershed where roads have a smaller relative effect than in the
very small tributary drainages and where only 40% (versus 90%) of the
347
1990). Inaccurate low-flow measurements preclude reliable evaluation of
water yield changes in the main stream at B weir.
In the lower Carnation Creek floodplain, summer groundwater levels
were up to 50em higher after harvesting of both the floodplain and the
adjacent side slopes (Hetherington, 1982). Despite vigorous regrowth of
deciduous vegetation on the floodplain, the increases in summer groundwater levels had barely diminished after 10 years. This result is believed
to be due to the maintenance of higher seepage from the side slopes
where vegetation growth has been slower (Hetherington, 1988).
Slope Groundwater Levels
At one piezometer site on a clearcut slope in H watershed above any road
influence, storm groundwater peaks were up to 20 em higher after logging
than before (Hetherington, 1982). The suspected cause of this change was
surface soil disturbance that possibly caused local modifications in the
pathways of water movement into and through the soil; that is, less water
was moving through the macrochannels andmore through the soil matrix
resulting in a short-lived but significant localized rise in the water table.
At another piezometer site below a road , groundwater peaks were up
to 20 em lower due to interception and lateral diversion of subsurface
seepage by the road (Hetherington, 1982). Changes in slope groundwater
regimes due to road diversion of surface runoff and excessive soil disturbance were presumed to have been major causes of two small landslides near H watershed in 1982 (Hetherington, 1988).
Peak Flows
Preliminary results regarding the question of harvesting effects on peak
streamflows have been variable . The analyses were based on rain-only
conditions because the vast majority of storms fall into this category. In
tributary H, peak flows appear to have increased after road construction
(Hetherington, 1982). This result suggests that the roads may have
accelerated flow to the stream channel by converting some subsurface
seepage into surface runoff. These changes were sustained for at least
three years after harvesting. Road-related peak flow increases in small
watersheds have been observed in Oregon (Harr et aI., 1979) and for
small storms in California (Wright, Sendek, Rice, & Thomas, 1990).
At B weir on Carnation Creek, rain-only peak flows showed no significant changes (Hetherington, 1982). The highly permeable soils retain
high infiltration capacities after disturbance so surface runoff in the
clearcuts apart from the roads remains negligible or nonexistent Thus, in
the larger watershed where roads have a smaller relative effect than in the
very small tributary drainages and where only 40% (versus 90%) of the