Flow hydraulic characteristic effect on sediment and solute transport on slope erosion

• Data in experiments for two series of soil surface conditions were compared.
• Flow hydraulics, sediment, and solute transport in soil erosion were concerned.
• Rate of Manning roughness coefficient to mean flow depth (n/h) is a good hydraulic indicator for sediment and solute.
• Parameter of n/h represents the energy for water and sediment in erosion.

Different hydraulic parameters, including the hydraulic shear stress, unit length shear force, steam power, unit steam power, and effective stream power were used to quantify flow detachment. Most former studies were conducted for flow detachment under uniform slope surface conditions, while a few studies compared different slope surface conditions. The uniform bare loess was prepared in laboratory experiments. Natural fallowed soil loess with stone covers was prepared in field experiments. The objective of this study was to assess the differences in hydraulic parameters and sediment detachment under these different soil surface conditions. Our results show that the unit sediment load (Rs) has a good linear relationship with the unit runoff rate (Rr) for the flume and field experiments, and the relationship can be expressed as the function: Rs = 0.262Rr − 0.802 (R2 = 0.947). The rate of Manning roughness coefficient to mean flow depth (n/h) is a good hydraulic indicator like as the stream power and Reynolds number for predicting the sediment load. Hydraulic parameters n/h, Re, and ω are good indicators for the unit area sediment load for both the flume and field experiments, while Fr, f, and τ are good indicators for the unit area sediment load only when the flume experiments and field experiments are individually analyzed. Among the three good indicators (ω, Re, and n/h), n/h is better than the other two for predicting sediment load in rill erosion for both flume and field experiments, as well as for the unit solute transport rate (MBr). The parameter of n/h probably is not only a good hydraulic parameter as an indicator for both sediment and solute transport, but also a good hydraulic parameter which link with runoff energies. The parameter n/h represents the flow wave of runoff and is an important factor to represent the energy for water and sediment transport, and the flow wave celerity (vw) is related to n/h by: vw = 1.585(n/h)− 0.527 (R2 = 0.978).