The Mattole River Watershed (Figure 1), Humboldt County, California, is listed on the Clean Water Act Section 303(d) list of impaired water bodies, for sediment and temperature. As required by this section and subsequent litigation, the North Coast Regional Water Quality Control Board (NCRWQCB) is under consent decree with the Environmental Protection Agency (EPA) to develop Total Maximum Daily Loads (TMDLs) for these constituents. Sediment and temperature are non-point source pollutants that impair the listed beneficial uses for the river, particularly cold water fisheries for endangered salmonid populations. The Information Center for the Environment (ICE), at the University of California, Davis, has developed analysis procedures for assisting the NCRWQCB in addressing the TMDLs in the Mattole Watershed.
To address the sediment TMDL, roads and mass-wasting features were inventoried. The mass-wasting inventory identified all discreet and chronic sediment sources through the use of five sets of stereoscopic aerial photographs spanning five decades. The road inventory focused on contemporary features and was implemented in a similar manner. Current 1:24,000-scale GIS data served as the base for aerial photobased augmentation.
To support the temperature TMDL, ICE developed GIS-based inputs for the Stream Segment Temperature Model (SSTEMP), such as location, distance upstream from the mouth, elevation, and average shade for each reach in the stream network. Riparian stream shade was calculated using RipTopo, a GIS-based stream shading model, which incorporated streamside vegetation and topography to calculate the amount of effective shade for a given stream reach.