SEDIMENT BUDGET FOR FRESHWATER CREEK WATERSHED, HUMBOLDT COUNTY, CALIFORNIA

Sediment budget techniques have been in use for over 30 years. Many watershed scale sediment budgets have been developed in Washington and California over the past decade to help guide watershed management efforts, particularly in relation to controlling erosion and sedimentation impacts associated with commercial forestry. High erosion rates accelerated by management activities are widely believed to have negative effects on aquatic habitat of endangered anadromous fish such as coho salmon (O. kisutch) and to degrade water quality.

This presentation summarizes a portion of a Watershed Analysis study performed for Pacific Lumber Company, Scotia, California, focusing on erosion and sedimentation processes and rates in the Freshwater Creek watershed in northwest California. Watershed Analysis modeled on the Washington DNR Methods is required by a negotiated Habitat Conservation Plan in effect on PL's timberlands.

Erosion, sedimentation and transport of sediment were quantified using field surveys, aerial photo interpretation, and modeling approaches for different elements of the study. The resulting sediment budget could be partially checked using recent short-term estimates of suspended sediment yield in Freshwater Creek collected by a community watershed group. The accuracy of bedload sediment yield estimates was evaluated against data from an adjacent watershed, Jacoby Creek, collected by the US Forest Service. In addition, estimated sediment yields could be compared to regional data.

The sediment budget techniques and bedload routing models used for this study provide sediment yield estimates that are in reasonable agreement with available data. These results suggest that sediment budget techniques can be used to provide relatively accurate technical assessments for use by policy makers to help resolve land use conflicts and develop appropriate land management regulations.