Field experiment investigation into the spatial variability of overland flow velocity and soil erosion

The spatial variability of overland flow velocity and soil erosion, and their relationship under different discharges, were investigated using a field runoff plot combined with the erosion pins. There exists a positive correlation between flow velocity and the distance from the top of slope, with the correlation becoming more significant as discharge increased. Variability of velocity at each cross section was stronger than that of the lateral section. The eroded sediment yield at the top or bottom of slope was greater than those at the middle. Sediment deposition clearly occurred for small flow discharge, and for high flows net erosion dominated the section of 0—2 m from the top of the slope. As flow discharge increased, the deposition zone gradually shifted down, and the proportion of rill erosion to the total amount of erosion increased. When overland flow velocity was greater than 0.30 m/s, the amount of rill erosion exceeded that of inter-rill erosion, and the erosion amount of the whole slope increased rapidly. As flow discharge increased, the overland flow velocity and erosion amount also increased. However, under the same slope, greater overland flow velocity corresponding to the down-slope tended to generate smaller erosion sediment yield, which may be attributed to the deposition of coarse sediment and the almost saturated sediment carrying capacity at the down-slope.