PRORIL—An Erosion Model Using Probability Distributions for Rill Flow and Density II. Model Validation
A rill erosion model, PRORIL, simulates the stochastic variability of rill networks, including both variable rill spacing and rill flow rates, on erosion. PRORIL was compared to measured erosion using the Kentucky rainfall simulator at the University of Kentucky Coldstream Farm in 1987 and 1988 for three topsoil and three subsoil plots that were bare and prepared with rough and smooth surfaces. In 1989, additional studies were conducted on 1-m ¥ 1-m plots within the original erosion plots to measure interrill erosion using a single nozzle rainfall simulator. Measured soil erosion and hydrologic parameters were compiled from these field studies for the PRORIL model and used for model validation for the 12 erosion plots. Values of critical shear stress were estimated from other erosion studies with soils having similar rill erodibility and optimized using a selected subset of the validation data. PRORIL predicted the measured erosion values with relative differences of –22 to 91% for the observed sampled data and –24 to 51% for the observed rill profile data. The coefficients of variation of the PRORIL model estimates were 0.35 for the observed sampled data and 0.27 for the observed rill profile data and were comparable to other erosion model validation studies, which had coefficients of variations from 0.20 to 1.48. PRORIL realistically simulates the spatially distributed nature of rill spacings and rill flow rates and provides a new framework to analyze and simulate erosion as a stochastic process.