Sediment flow behavior in agro-watersheds of the purple soil region in China under different storm types and spatial scales

Bedload sediment is not only a major pollutant, but can also act as a transporter of pollutants. Sediment flow behavior often reflects the characteristics of a watershed, such as land use and management. To clarify the behavior of sediment flow under different spatial scales and storm types in the Chinese purple soil area, the sediment flow behavior in three small agro-watersheds with different catchment areas, physical characteristics and land use types was investigated during natural rainfall events from 1999 to 2000. The results showed that there were three types of sediment hydrographs, waveform or linear with a low sediment concentration (1.13 ± 0.58 g l−1), logarithmic decrease (3.41 ± 4.13 g l−1), and compound linear and logarithmic decrease (9.58 ± 10.90 g l−1). During PP-type rainfall events (high-intensity rainfall occurred during the prophase of the rainfall process) and ML-type rainfall events (high intensity rainfall occurred during the middle of the rainfall event), the waveform or linear type sediment hydrographs or the logarithmic decrease type hydrographs were generated in each of the three agro-watersheds. However, sediment hydrographs produced by IM-type rainfall events (discontinuous rainfall with obvious segments) depended on the spatial scale of the watershed. As the spatial scale decreased, the hydrographs were transformed from the logarithmic decrease type to the compound type. In addition, it was found that the S = aQb model could effectively simulate the sediment hydrologic process of a single rainfall event. The information provided in this study will help evaluate and prevent soil and water loss and non-point source pollution in the purple soil region.