Monitoring erosion related to timber operations: what works and what doesn't

The amount of forestry-related water quality monitoring in California has increased significantly in the past ten years. Factors leading to more monitoring include federal and state listing of fish species (i.e., coho salmon, Chinook salmon, steelhead trout) as threatened or endangered, listing of watersheds in northwestern California as sediment impaired under Section 303(d) of the federal Clean Water Act, and new requirements by the State’s Regional Water Quality Control Boards for monitoring of Timber Harvesting Plans (THPs). As a result, several large private timberland owners are now monitoring suspended sediment concentration and turbidity at automated stream gauging stations (Harris et al. 2007). This type of monitoring can provide useful information about longterm trends in water quality and the potential impacts of timber harvesting operations, but automated instream monitoring stations are very expensive to install and maintain for the extended time periods needed to measure background, treatment, and post-treatment conditions (commonly a decade or more). Also, data collected at these stations integrate sediment yields from different erosion processes (bank erosion, road and hillslope surface erosion, mass wasting erosion, creep, etc.) and multiple time periods (that can mix the effects of legacy and current project impacts), all of which makes it difficult to link effects of current practices to changes in suspended sediment or turbidity. Detecting management-induced changes in sediment yields can be difficult and require substantial time and resource commitment when natural variability in sediment yields is high – typically the norm, not the exception for most Pacific Northwest watersheds (Bunte and MacDonald 1999). The lack of reference watersheds also makes it difficult to adequately evaluate the natural variability in sediment yields (MacDonald 2000).