Map 6: Surface water drinking water source areas with NRCS Soil Erosion Hazard Ratings - Off-Road/Off-Trail (for management activities such as silviculture, grazing, mining, urban development, fire, firebreaks, etc with <75% soil surface disturbance)
This dataset provides surface erosion hazard ratings for areas where up to 75% of the soil surface is disturbed by non-road and non-trail uses (such as uncontrolled grazing, forestry, heavy equipment use, fire control, and mining). The erosion hazard ratings are calculated by the Natural Resource Conservation Service using inherent soil properties for whole soil erodibility and slope. This method underestimates erosion hazard for Histosol soils and for gully erosion, plowing or other disturbances that “disturb up to nearly 100 percent of the area and change the character of the soil”. Other assessment methods (see Map 7) may be more appropriate for flatter terrains with 75-100% soil disturbance. In the Updated Source Water Assessments, DEQ mapped only those locations where risk is moderate or higher AND that are within 300 feet of surface water in order to estimate those places where delivery to water is possible. Where NRCS soils data is not available (typically National Forest Lands) Soil Resource Inventory information from the US Forest Service can be used to evaluate erosion potential (see Map 2).