Abstract
Sediment transport rate is greatly important in establishing reliable
strategies to manage environmental changes. However, few data are
available for estimating the sediment transport rate on a steep slope of
grass with different covers. In this study, the artificial simulated
rainfall test is used to investigate how rainfall intensity, slope and
cover affect the sediment transport rate. Simultaneously, the study
establishes a model for the sediment transport rate using shear stress,
stream power, unit stream power and unit energy on steep grassland
slopes. Results show that the sediment transport rate decreases as the
vegetation cover increases, as described by linear or logarithmic
equations under different rainfall intensities or slopes. The sediment
transport rate increases as an exponential function equation with
rainfall intensity, slope and cover with a Nash–Sutcliffe model
efficiency (NSE) value of 0.864. The effects of slope steepness are
stronger than the effects of rainfall intensity and cover. Regression
analyses show that the sediment transport rate can be predicted from the
power function equations of shear stress, stream power and unit energy.
In addition, the sediment transport rate can be fit to unit stream power
with linear equation (NSE = 0.840). However, shear stress, stream power
and unit energy perform poorly (NSE = 0.394, NSE = 0.498 and NSE =
0.330, respectively). Further analysis shows that the sediment transport
rate is best modelled by a power function equation that includes three
factors, i.e. rainfall intensity, vegetation cover and slope. Moreover,
unit stream power results in the best model for the sediment transport
rate among the different hydrodynamic parameters. The soil erodibility
parameter and critical unit stream power of this experiment are 113.59
and 0.216 m·s-1, respectively, which are six times more than those in
the bare slope. The measurements and calculations of the sediment
transport rate, the calculations of the surface roughness and
characteristic considerations of the vegetation for sheet flow should be
explored in future research, which are important in improving
experimental accuracy and sediment transport rate modelling. These
results provide a basis for establishing process-based erosion models on
steep grassland slopes.