CAPABILITIES AND LIMITATIONS OF EROSION MODELS AND DATA

Variability in soil erosion data from replicated plots is large. One might think of the replicated plot as the best "real-world, physical model" of soil erosion, and that the physical model represented by the replicate plot represents a best-case scenario in terms of erosion prediction. In this study, replicated plot pairs for 2061 storms, 797 annual erosion measurements, and 53 multi-year erosion totals were used to estimate the natural variance of erosion data. Coefficients of variation ranged on the order of 14% for a measured soil loss of 20 kg/m 2 to greater than 150% for a measured soil loss of less than 0.01 kg/m 2 . The r 2 for the fit for the replicate plot model was 0.76. This fit sets a benchmark for what one can expect for soil erosion models in general. This paper also discusses the critical nature of continuous simulation modeling in predicting erosion reliably. Results of simulation testing with the WEPP model indicate that 60 to 200 years of continuous simulation are required in order to quantify erosional response to plus or minus 10%. Single storm models do not have the capacity to accurately characterize erosional response of the complex and dynamic erosional system. Additional Keywords: soil erosion, soil conservation planning, uncertainty, data variability