Introduction
Caspar Creek Experimental Watershed serves as an important research site for
evaluating the effects of timber management on streamflow, sedimentation, and
erosion in the rainfall-dominated forested watersheds of the northern coast
of California. Caspar Creek includes two watersheds with nested sub-basins:
the North Fork (NFC, 484 ha) and South Fork (SFC, 424 ha). Begun in 1962 as
a cooperative effort between the California Department of Forestry and Fire
Protection and the USDA Forest Service's Pacific Southwest Research Station,
the project has evolved from a simple paired watershed study into one of the
most comprehensive and detailed investigations of its kind. Hydrologic data
collected here include streamflow, subsurface pipeflow, piezometric pressure,
soil moisture tension, suspended sediment, turbidity, bedload transport, air
and water temperature, precipitation, and solar radiation. Channel data include
channel cross sections, stream habitat typing, woody debris recruitment and
riparian canopy evaluations, sediment storage, and pool condition. Hillslope
data include landslide inventories, road evaluations, and vegetative condition.
Cooperators have undertaken benthic investigations, aquatic vertebrate and macroinvertebrate
sampling, and water chemistry monitoring.
Climate
Winters are mild and wet, and summers are moderately cool and dry. About 90
percent of the average annual precipitation of 1,200 mm falls during October
through April. Summer coastal fog is common. Snow is rare and rainfall intensities
are low.
Soils
The soils of the basins are well-drained clay-loams, 1 to 2 m in depth, and
are derived from Franciscan graywacke sandstone and weathered, coarse-grained
shale of Cretaceous Age. They have high hydraulic conductivities, and subsurface
stormflow is rapid, producing saturated areas of only limited extent and duration.
Vegetation
Forest types at Caspar Creek include second-growth mixed conifer, mostly coast
redwood, Douglas-fir, western hemlock, and grand fir.
Long-Term Data Bases
There are long-term data bases on stream discharge, precipitation, suspended
sediment concentration, turbidity, and solar radiation.
Research, Past and Present
Research at Caspar Creek is designed to study the effects of forest practices
on watershed and ecological processes. From 1963 to 1967, both the NFC and SFC
watersheds were calibrated prior to treatment. At that time, these watersheds
supported a 90-year-old, second-growth, mixed conifer forest dominated by coast
redwood and Douglas-fir. From 1967 to 1972, roads were constructed and about
two-thirds of the stand volume was selectively harvested and tractor yarded
from SFC. From 1985 to 1986, 67 percent of an 87-ha ungauged tributary was clearcut
and cable yarded immediately upstream of the North Fork gauging station. Logging
began in the main study portion of the NFC in 1989 and ended in 1991. Three
tributaries in the NFC were left in an untreated control condition. Postlogging
measurements continue in the NFC and SFC watersheds.
Major Research Accomplishments and Effects on Management
The South Fork Caspar Creek selection harvest with tractor yarding (phase 1)
showed that:
- Sediment increased by 335 percent from road building in 1968.
- Sediment increased by 212 percent from tractor logging following the 1970-73
harvest.
- Major landslides accounted for most of the sediment production in the SFC
after logging; more sediment was made available for transport.
- SFC road system persisted as the major source of sediment, annual streamflow
increased by 15 percent, but larger relative increases occurred during summer
low flows; during the late 1960's, the salmonid abundance declined but appeared
to return to predisturbance levels after only 2 years.
In the Caspar Creek/North Fork studies of clearcutting and skyline cable logging,
annual suspended sediment loads increased by 73 percent in the partially clearcut
NFC but by more than 100 percent in the clearcut tributary watersheds. An increase
in landslides was not observed post-harvest; rather, increases in sediment loads
were correlated to the flow increase, length of intermittent channels logged or
burned, and new road construction. In clearcut units, storm peaks increased by
as much as 300 percent, but the mean increase was 35 percent. As basin wetness
increased, peak flow increases lessened. Return to pretreatment flow conditions
appears to be occurring 12 years post-harvest. Debris loading (large-wood) increased
along the NFC stream channel in the first few years after logging due to increased
windthrow. Channel morphology has become more complex with more debris jams, sediment
storage "steps," and greater pool volumes. However, no dramatic changes in the
abundance of steelhead, coho, and Pacific giant salamander were attributed to
logging.
Collaborators
Researchers from the following organizations have worked on Caspar Creek: California
Departments of Forestry and Fire Protection and Fish and Game, National Marine
Fisheries Service, California Water Quality Control Board, Stanford University,
University of California at Davis, University of California at Berkeley, Chico
State University, Humboldt State University, California Polytechnic University,
and Oregon State University.
Research Opportunities
Caspar Creek provides long-term, records of basic hydrologic and geomorphic
processes spanning the downslope sequence of processes from the tree canopy
to third-order channels in two watersheds with 26 nested sub-basins. Large-scale
experimentation is planned for timber harvest and watershed restoration. New
collaborators from a multitude of disciplines, including hydrology, geomorphology,
forestry, meteorology, and aquatic and riparian ecology, are welcomed.
Facilities
Expanded lodging and laboratory facilities are under construction for the Jackson
Learning Center nearby. Caspar Creek offices are located at the Jackson Demonstration
State Forest office, 802 N. Main Street, Fort Bragg, CA.
Lat. 39°22´30�� N, long. 123°40´ W
Contact Information
Caspar Creek Experimental Watershed
USDA Forest Service
Pacific Southwest Research Station
Redwood Sciences Laboratory
1700 Bayview Drive
Arcata, CA 95521
Tel: (707) 825-2930
http://www.fs.fed.us/psw/topics/water/caspar/
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