Estimating sediment transport capacity for overland flow

Reliable estimation of sediment transport capacity is essential for soil erosion modeling. The objective of this study was to evaluate the performance of twelve widely used transport capacity functions with a wide range of hydraulic conditions and soil properties. The comparisons with observed data indicated that none of the selected twelve functions gave satisfactory results for transport capacity prediction over all overland flow datasets in this study, and all of them gave very poor predictions for loess soil. Therefore, a new equation was developed for sediment transport capacity estimation. Among these twelve functions, the Ali equation gave the best fit for the whole dataset, but calibration was necessary when using it for large sediment grains (> 2 mm) or loess soil. The Yalin equation and the simplified Yalin equation worked better for soils than sands, and predictions for smaller sands (similar to 0.2 mm) were acceptable. The Govers equation had relatively uniform performance for all datasets. The performance of empirical equations changed dramatically for different datasets. A new function developed in this study was generated based on dimensional analysis and gave good predictions within the range of hydraulic conditions and particle sizes in the datasets considered in this study. The results provide a summary of the transport capacity functions evaluated and suggest an improved function for modeling overland flow sediment transport capacity.