Measurement of rill and ephemeral gully flow velocities and their model expression affected by flow rate and slope gradient

Water flow velocities in rill and ephemeral gully are useful for estimating hydrodynamics in the study on soil erosion. Laboratory experiments were conducted to measure erosive rill and ephemeral gully flow velocities, including nine unit width flow rates of 0.17, 0.33, 0.67, 1.33, 2.67, 5.33, 10.67, 21.33, and 42.67x10(-3) m(2) s(-1), and five slope gradients of 8.7%, 17.6%, 26.8%, 36.4%, and 46.6%, on sandpaper slope glued with silt loam soil materials to imitate fixed rill and ephemeral gully beds, using an electrolyte tracer method. The flow velocities measured in this research ranged from 0.31 to 3.34 m s(-1) for sediment-free water flow. The flow velocity fitted well with unit width flow rate and slope gradient by a power function, yielding an improved model with higher coefficient of determination than that related flow velocity to flow rate alone. The improved model is applicable for flow velocity and soil erosion predictions.