HR: 0830h
AN: H41E-1047    [PDF]
TI: Sediment Yield From First Order Streams in Managed Redwood Forests: Effects of Recent Harvests and Legacy Management Practices
AU: * Perry, H
EM: chp1@humboldt.edu
AF: Humboldt State University, 1 Harpst Street, Arcata, CA 95521 United States
AU: O'Connor, M
EM: matto@oe-i.com
AF: O'Connor Environmental, Inc., PO Box 794, Healdsburg, CA 95448 United States
AU: McDavitt, W
EM: billm@oe-i.com
AF: O'Connor Environmental, Inc., PO Box 794, Healdsburg, CA 95448 United States
AB: First order streams in the Van Duzen River and lower Eel River watersheds owned by Pacific Lumber Company (Palco) in Humboldt County, California, were surveyed and small sedimentation basins were installed to develop quantitative estimates of sediment yield. A random study design was developed to investigate the potential effects of different geologic substrates and forest management on sediment yield. The drainage area for these streams was about 5 to 10 ha where fluvial characteristics were expressed. The erosion processes within the scope of this investigation included surface erosion from hillslopes and harvest units, rill and gully erosion that may occur in relation to skid trails (recently used or abandoned), and stream channel erosion, including bank erosion and small-scale mass wasting. Temporary sedimentation basins were installed in 30 randomly chosen channels to quantify relative amounts of sediment yield from watersheds with different management conditions (treatment sites) and second-growth stands not recently entered (control sites). Most treatment sites were clearcut harvests. Two classes of treated sites were sampled: sites harvested under stricter regulations of a Habitat Conservation Plan (HCP) and sites harvested prior to implementation of the HCP. Channel surveys were also conducted to characterize conditions and identify existing evidence of channel erosion and surface erosion in areas adjacent to the channel. Results from winter 2001/02 suggested that there may be differences in sediment yield among geologic substrates, with the Wildcat having relatively low sediment yield values. Treatment effects were significantly different (ANOVA, p $<$ 0.05) when two large landslides were removed from the control sites; the HCP sites had significantly lower sediment yield. There was also a significant interaction between treatment and geologic substrates (ANOVA, p $<$ 0.05). Control sites had sediment yield comparable to the pre-HCP treatment sites. The apparent treatment effect on sediment yield may be influenced by the fact that the HCP treatment sites have experienced only one or two post-harvest winters, while the pre-HCP treatment sites experienced relatively severe winters over a longer post-harvest period. In addition, the fact that the control sites tended to have higher sediment yield than the HCP treatment sites suggests that legacy effects of management may also be an important factor.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting