Vegetation canopy cover effects on sediment erosion processes in the Upper Colorado River Basin Mancos Shale formation, Price, Utah, USA

•RHEM can be calibrated to an unbiased simulation on saline and sodic soils.•Calibrated Kss and Kω were greater than prior studies from non-saline environments.•Plot-level variability was best captured at the site with more runoff sediment load.•Vegetation pattern correlated with unexplained residual variation in model outputs.

This study investigated erosion processes on the highly erosive, saline soils of the Mancos Shale formation in the Price-San Rafael River Basin in Utah, USA. Rainfall simulations were performed at two sites using a Walnut Gulch rainfall simulator with a variety of slope angles and rainfall intensities. The Rangeland Hydrology Erosion Model (RHEM) was calibrated to provide unbiased estimates of discharge and sediment load in runoff at each site. RHEM simulated the inter-plot variability best at the site with higher slope angles, vegetation cover, and sediment loads. The calibrated surface erosion parameters in RHEM (Kss, Kω) were substantially greater than any published in prior studies from non-saline environments. The spatial distribution of vegetation canopy cover was quantified using photogrammetric modeling and landscape pattern metrics. As the patches of vegetation became more contiguous and the tortuosity of the bare soil area increased, RHEM over-predicted sediment output, suggesting that vegetation-driven spatial heterogeneity influenced erosion in a way that is not captured by the model.