Chronic landsliding in the Thomes Creek watershed, Tehama County, California

Methodology was created to assess slope stability and to estimate the climatologic, hydrologic, geologic and anthropogenic processes that result in chronic landsliding in the in the upper Thomes Creek watershed located in Tehama County, California. Using a combination of slope stability analysis, field experimentation and aerial photographic study it was determined that most slopes in the upper Thomes Creek watershed are prone to re-occurring failures. Landslides were found to fail due to high-intensity precipitation events, extreme creek discharges or a combination of both. The primary contribution of sediment to the channel in the upper watershed is from chronic, relatively small scale debris slides located at the base of larger rotational landslides. Volumetric quantities of sediment supplied to the channel from the debris slides were quantified from aerial photographs for the years 1988, 1993, 1998, and 2003.