Sediment transport capacity equation for soils from the Loess Plateau and northeast China

Abstract

Sediment transport capacity (Tc) is a relevant component in physical-process-based soil erosion models. At present, the sediment transport capacity prediction model for soils with a low median grain diameter is not fully understood. In this study, the Tc values of three different soils (median grain diameter d50 = 0.015, 0.040, and 0.095 mm) were investigated by conducting indoor experiments at unit flow discharges of 0.19 – 1.89 × 10-3 m2·s−1 and slopes of 0.07–0.21. In addition, data describing the overland flow sediment transport capacity of black soil (d50 = 0.01 mm) were obtained from Yu et al. (2018). First, the performance of seven shear stress, unit stream power, stream power, and mean flow velocity concept-based Tc equations were evaluated based on the measurements. The results confirmed that none of the existing formulas performed well over the entire experimental range. Tc equations derived using soils with a large particle size generally underestimate the Tc of soils containing small particles. The Zhang equation, when calibrated based on the data in this study, can predict overland flow Tc with a PoP of 66 % (PoP refers to the percentage of predictions in which the discrepancy ratio falls between 0.5 and 2.0, whilst the discrepancy ratio is the ratio of the predicted and measured Tc). Based on the general flow parameter concept, a more accurate Tc equation was developed for the four types of soils, which was characterized by a PoP of 83 %. When these equations are beyond the scope of their development conditions, they should be verified further.