Integrated process-based modeling of channelized flow and soil erosion in small watersheds

Abstract. One of the main issues of sustainable agriculture is an excessive soil erosion causing degradation of arable land. Many best management practices were implemented on agricultural fields, nevertheless, rills, gullies, and channels remain the significant sources of sediment. Thus, a better understanding of the problem and new innovative approaches for the estimation of soil losses are still necessary. The goal of this study was to develop a novel process-based small watershed-scale model for estimation of soil erosion from ephemeral channels. The model accounted for water fluxes from headcut and sidewall catchments, variable channel geometry along the channel, and variable erosion parameters due to re-distribution of soil subsurface fluxes. WEPP model was used for determination of the hydrograph and sheet and rill erosion rates to account for the effects of best management practices. The water flow was routed within the channel with the kinematic wave scheme. Soil erosion was computed based on the current discharge for each channel section with the modified approach of Foster and Lane. Soil erodibility and critical shear stress were adjusted due to the seepage/drainage forces based on the computed infiltration gradients by a solution of the Richards equation. The model was evaluated on the data obtained from the field experiment of the previous ephemeral gully erosion study giving an NSE value of 0.72. The developed model allowed to compute ephemeral gully erosion while accounting for antecedent soil moisture conditions. Results showed significant differences in performance of best management practices for initially dry and wet soils.