Spatial distribution of sheet flow velocity along slope under simulated rainfall conditions

Velocity of sheet flow is an important parameter for understanding the process of inter-rill erosion on a hill slope under rainfall conditions. A solute centroid method was employed to measure velocity distribution of sheet flow basing on solute transport process in the flow in an 8 m long flume. The flow velocity measurements were made at slope lengths of 3, 5, 6 and 7 m under slope gradients of 5°, 10° and 20°, and rainfall intensities of 80, 120 and 160 mm h−1, respectively. The measurements clearly showed that mean flow velocity ranged from 0.050 to 0.352 m s−1 and increased with slope gradient and rainfall intensity. Velocity of sheet flow increased with slope length, while the increase rate slowed down before approaching a steady velocity. The distance for sheet flow velocity to reach its maximum became shorter under greater slope gradient and rainfall intensity. Water depth was <2 mm under all experimental conditions. The water flow was subcritical laminar on upper slope <3 m from slope top, while it experienced supercritical laminar on the remaining slope. Experimental results showed that solute centroid method applied to velocity measurement of sheet flow under rainfall conditions. This study helps understanding of hillslope hydrodynamics under rainfall conditions.