ACCELERATED EROSION IN MANCOS SHALE BADLANDS DISTURBED BY OHV ACTIVITY, CAINEVILLE, UTAH

The impact of OHV activity in areas underlain by the Mancos Shale is one of the more significant and contentious issues facing land managers on the Colorado Plateau today. In an attempt to develop a simple methodology to assess the impact of OHV activity in badlands terrain, a preliminary geomorphic assessment of OHV impacts was made in the Mancos Shale badlands near Caineville, Utah. This assessment is based on a comparative geomorphic analysis of the microtopographic characteristics of undisturbed versus heavily disturbed hillslopes in these badlands. This analysis focuses on a determination of landscape elements that are present in the undisturbed landscape but are missing from disturbed areas. Therefore, it provides a direct measure of the additional erosion that has occurred in disturbed areas.

Three geomorphic elements characteristic of the natural, undisturbed hillslopes within the Caineville badlands were identified and measured: surface soil crust, rills and small gullies, and hillslope regolith (soil and colluvium). Soil crust relief averages approximately 1.5 inches on undisturbed slopes; but soil crust is not present on heavily disturbed hillslopes. Rill depth averages 3.1 inches on undisturbed hillslopes; but rills and small gullies are not present on heavily disturbed hillslopes. Regolith thickness averages 5 inches on undisturbed hillslopes; however, structured regolith is not present on heavily disturbed hillslopes. Instead, these slopes are covered by a thin mantel of pulverized rock and soil with an average thickness of 1.9 inches. The absence of soil crust, rills and small gullies, and structured regolith on hillslopes that have been heavily disturbed by OHV activity demonstrates that at least 3 inches of additional erosion has occurred on these hillslopes as compared to natural, undisturbed slopes. This amount of additional erosion is equivalent to a soil loss of more than 500 metric tons per hillslope acre. This additional erosion is occurring at a rate that is several times higher than late Quaternary rates of hillslope erosion in the Caineville badlands.