Map of Soil Erosion Risk for the Mancos Shale Formation

This product used the rangeland hydrology and erosion model (RHEM) to map erosion risks affecting water quality of the Colorado River that originate on the Mancos Shale formation in Utah, Colorado, New Mexico, and Arizona. The Mancos Shale is a significant source of salinity, and a portion of that salt load derives from erosion of rangeland soils. Inputs to RHEM included digital elevation data, statistically modeled maps of soil properties, the LANDFIRE vegetation map, Landsat and MODIS satellite imagery, field data from the Rangeland National Resource Inventory program of the U.S. Natural Resources Conservation Service, and rainfall data from Atlas 14 of the U.S. National Atmospheric and Oceanographic Administration. RHEM predicted sediment yield at a 30 m spatial resolution for a storm with a 60-minute duration whose intensity corresponded to a 25-year return frequency. Results corresponded reasonably with prior field experiments that used the Walnut Gulch Rainfall Simulator (WGRS), with a Spearman’s rank-order correlation of 0.76 for cumulative sediment yield after 20 minutes of rainfall. This high-resolution map of erosion risk developed from RHEM can help to prioritize specific areas for more intensive study and action. This dataset represents areas of the Mancos Shale geological formation that do not have high levels of urban or agricultural development and which have slopes less than 35%.