A Digital Surface Soil Erosion Hazard Rating for California Forest Management Using Gssurgo and Digital Spatial Data.

The Erosion Hazard Rating was developed by California (CA) soil scientists in the late-1980’s to estimate the hazard from soil erosion for timber harvesting operations in CA.  It is required by the CA Forest Practice Rules for approval of timber harvest plans.  It has also been used by CA Natural Resources Conservation Service (NRCS) for conservation programs and planning.  Until this project, the rating was manually calculated using a representative slope and set of soil properties.  CA Department of Forestry and Fire Protection (CAL FIRE), under the authorities of the CA Board of Forestry, requested assistance from NRCS to develop a digital model for Surface Soil Erosion Hazard Rating that could link to SSURGO data directly.  This rating is required on CA Environmental Quality Assessment (SEQA) review of forest management activities.  Tables from Instructions CA State Board of Forestry Technical Rule Addendum No. 1 Erosion Hazard Rating (EHR) System for Sheet and Rill Erosion (1989, Rev. 2001), were subjected to regression analysis, plotted and new tables were constructed to match values suitable for the SSURGO data structure. Raster-based gSSURGO data was joined the 10m DEMs to analyze for slopes.  A layer linking an area of interest (AOI) or defined project area, along with a user-defined field observation input score for protective vegetation cover to be left after disturbance, was developed to calculate a number rating, as Low, Moderate, High and Extreme Erosion Hazard for each raster cell in the AOI.  Analysis and display of the results across the AOI is then possible.  The model was field tested during Spring of 2014 and has been adopted by NRCS in CA for ranking Environmental Quality Incentives Program (EQIP) forestry projects and deployed to field offices for use. CAL FIRE is evaluating how the tool can be provided to their customers and incorporated into their regulatory process.