Influence of soil aggregate characteristics on the sediment transport capacity of overland flow

The sediment transport capacity of overland flow is the core input variable of a process-based soil erosion model. Many studies have focused on the sediment transport capacity for overland flow; however, few studies have explored the relationship between sediment transport capacity and soil aggregate characteristics. The objective of this study was to investigate the effects of soil aggregate characteristics on the sediment transport capacity of overland flow. The unit flow discharge ranged from 0.68 x 10(-3) m(2) s(-1) to 5.41 x 10(-3) m(2) s(-1), and the slope gradient varied from 5.24% to 26.80%. Five types of typical Chinese soil were investigated. The results showed that the best correlation was the relationship between the sediment transport capacity and the mass percentage of aggregates greater than 0.25 mm (WSA(0.25)) under the Le Bissonnais method of wetting stirring conditions. Sediment transport capacity was not correlated to the other soil aggregate characteristics, including the mean weight diameter (MWD) under the Le Bissonnais method of fast wetting and slow wetting conditions and the Yoder method, the degree of aggregation (A), and the fractal dimension (D) under the Yoder method. New equations including WSA(0.25) were developed to predict the sediment transport capacity. The equation including flow discharge, slope gradient and WSA(0.25) provided the best accuracy for predicting sediment transport capacity. The sediment transport capacity increased linearly with the mean flow velocity. Between the hydraulic variables of shear stress and stream power, our results showed that stream power was an optimal predictor for calculating sediment transport capacity. These findings offer a new approach for predicting the sediment transport capacity of overland flow.