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E.D. Hetherington
levels; soil moisture ; subsurface flow processes; precipitation chemistry;
and precipitation interception.
Summary of Research Results
More than 160 publications have documented the results and progress of
research in the Carnation Creek watershed over the past 20 years (Poulin
& Scrivener, 1988). The findings have been summarized and integrated to
show the interrelationships among the various hydrological, fluvialgeomorphological, thermal, chemical, and biological components, and
the related changes that have taken place as a result of logging (Ha rtman
& Scrivener, 1990). Some of the main findings are reviewed here to
illustrate the nature of the logging impacts.
Hydrology
Forest harvesting has had variable effects on the hydrological processes
within the watershed. Slope water behaviour was studied in the tributary
watersheds Hand J before and after logging, as were summer groundwater levels in the lower floodplain. Postlogging changes in streamflow
have been assessed in preliminary analyses for the main stream at B
weir (40% clearcut) and for tributaries H (90% clearcut) and J (100%
clearcut).
Water Yield, Summer Low Flows, and Floodplain Groundwater Levels
Precipitation data collected beneath the forest canopy and in an adjacent
clearcut indicate a net loss to evaporation of the intercepted rainfall
during both winter and summer. Canopy collection of "fog-drip" precipitation occasionally exceeds interception losses, although fog-drip
amounts at Carnation Creek are less than those reported by Harr (1982)
in one small watershed in Oregon.
Reduced evapotranspiration losses appear to be the main cause of
increases in annual water yield after logging in both clearcut watersheds Hand J of at least 14% initially (Hetherington, 1982; Hartman &
Scrivener, 1990). The increases had only diminished by about 30 to 50%
after 10 years. Increases in yield after harvesting have been documented
both for other coastal watersheds in the United States (Harr, Fredricksen,
& Rothacher 1979; Keppeler & Ziemer, 1990) and world wide (Bosch &
Hewlett , 1982). Summer low flows also increased initially in H watershed
(Hetherington, 1982). Such initial low flow increases have also been
found in Oregon (Harr et al., 1979) and California (Keppeler & Ziemer,
E.D. Hetherington
levels; soil moisture ; subsurface flow processes; precipitation chemistry;
and precipitation interception.
Summary of Research Results
More than 160 publications have documented the results and progress of
research in the Carnation Creek watershed over the past 20 years (Poulin
& Scrivener, 1988). The findings have been summarized and integrated to
show the interrelationships among the various hydrological, fluvialgeomorphological, thermal, chemical, and biological components, and
the related changes that have taken place as a result of logging (Ha rtman
& Scrivener, 1990). Some of the main findings are reviewed here to
illustrate the nature of the logging impacts.
Hydrology
Forest harvesting has had variable effects on the hydrological processes
within the watershed. Slope water behaviour was studied in the tributary
watersheds Hand J before and after logging, as were summer groundwater levels in the lower floodplain. Postlogging changes in streamflow
have been assessed in preliminary analyses for the main stream at B
weir (40% clearcut) and for tributaries H (90% clearcut) and J (100%
clearcut).
Water Yield, Summer Low Flows, and Floodplain Groundwater Levels
Precipitation data collected beneath the forest canopy and in an adjacent
clearcut indicate a net loss to evaporation of the intercepted rainfall
during both winter and summer. Canopy collection of "fog-drip" precipitation occasionally exceeds interception losses, although fog-drip
amounts at Carnation Creek are less than those reported by Harr (1982)
in one small watershed in Oregon.
Reduced evapotranspiration losses appear to be the main cause of
increases in annual water yield after logging in both clearcut watersheds Hand J of at least 14% initially (Hetherington, 1982; Hartman &
Scrivener, 1990). The increases had only diminished by about 30 to 50%
after 10 years. Increases in yield after harvesting have been documented
both for other coastal watersheds in the United States (Harr, Fredricksen,
& Rothacher 1979; Keppeler & Ziemer, 1990) and world wide (Bosch &
Hewlett , 1982). Summer low flows also increased initially in H watershed
(Hetherington, 1982). Such initial low flow increases have also been
found in Oregon (Harr et al., 1979) and California (Keppeler & Ziemer,