Effect of Rock Fragments Cover on Distance of Rill Erosion Initiation and Overland Flow Hydraulics
Rock fragments on the soil surface protect the soil against erosive agents. However, the effect of rock fragments cover on rill initiation is not well documented. The objective of this study was to evaluate the effect of rock fragment cover and the rate of flow discharge on distance and time rill initiation. The investigation was conducted using a flume with 6 m length, 0.5 m width and 3% gradient. The treatments included rock fragment cover (0, 10, 20, 30%) and three levels of flow discharge (3, 6, 9 L min-1). The results showed that the surface cover of rock fragment had significant effect on different erosion processes, as well as rill initiation. Moreover, results indicated that velocity of water flow and the Froude number decreased but the Manning roughness coefficient increased (0.012-0.115 m-1/3 sec) with an increase in rock fragment cover, whereas the Reinholds number remained nearly the same with a small variation among different rock fragment cover percent. This variable was increased with increasing flow discharge. In addition, distance and time of rill initiation increased with a rise in rock fragment cover and diminished with increasing flow discharge.
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