Determining and Modeling Dominant Processes of Interrill Soil Erosion

Abstract

Understanding the dominant process of interrill soil erosion is imperative to better modeling interrill sediment delivery rates. The objectives are to (1) determine the limiting erosion process (detachment vs. transport) that controls interrill erosion under the study conditions, (2) quantify the effects of water and/or sediment influxes from upslope on downslope sediment transport and interrill erosion, and (3) evaluate the ability of commonly used hydraulic parameters for simulating interrill sediment delivery. Runoff, sediment delivery, and raindrop splash were simultaneously collected from two flumes (1.8 m × 0.5 m) and a 2.5-cm slot between the flumes for three intensities of 60, 90, and 120 mm/hr at three slopes of 9%, 18%, and 27% under two cover treatments. Results showed that slot splash rates were consistently greater than flume wash rates, indicating that sediment transport capacity limited interrill sediment delivery under the study conditions. Soil detachment by raindrop impact was more influenced by surface water depth, while sediment transport capacity by flow velocity. The former played a bigger role in determining interill sediment delivery under detachment-limited cases while the latter under transport-limited conditions. Linear correlation coefficients between sediment delivery rates and hydraulic predictors were 0.545 for shear stress, 0.946 for stream power, 0.867 for unit stream power, and 0.948 for an empirical lumped model that includes a rainfall intensity term. Stream power and the empirical model were better predictors for interrill sediment delivery. However, their predictive abilities need to be assessed more rigorously at various impact levels of rainfall kinetic energy.