EVALUATION OF THE CREAMS MODEL .4. DERIVATION OF INTERRILL ERODIBILITY PARAMETERS FROM LABORATORY RAINFALL SIMULATOR DATA AND PREDICTION OF SOIL LOSS UNDER A FIELD RAINULATOR USING THE DERIVED PARAMETERS

This study investigated the use of laboratory rainfall simulator data for the derivation of CREAMS (chemicals runoff, and Erosion from Agricultural Management Systems) interrill erodibility parameters K and n(bov). The laboratory rainfall simulator method of collecting erosion data was validated using the surface of an Irving clay (black earth). Reliable CREAMS K and n(bov) values for this Irving clay had previously been determined from field rainulator data. In this study, CREAMS erodibility parameters were derived for the same soil type using laboratory rainfall simulator data. The values of these parameters fell within the 90% confidence region for parameters derived from non-rilled field rainulator plots. Both n(bov) and K, determined from laboratory data, varied with slope, indicating that the slope gradient response predicted by CREAMS may not be applicable for interrill erosion on short, steep slopes. For slopes < 8%, a default value of n(bov) = 0.01 with K = 0.37 (English units) gave good predictions of observed soil losses. However, for slopes > 8%, there was an over-prediction of observed soil loss up to 60% when these parameter values were used. The data indicate that for predictions of interrill soil loss from steeper slopes, n(bov) and K values should be adjusted to achieve greater accuracy. When values of K = 0.37 and n(bov) = 0.01 were used with field data obtained from a site with a slope of 4%, predicted interrill soil losses correlated well with both the estimated interrill component of measured field soil losses and observed soil losses from interrill field plots. It is concluded that the laboratory rainfall simulator used in this study produces hydrology and erosion data that can be used to derive realistic CREAMS parameters for interrill erosion.