Effect of sediment load on soil detachment and deposition in rills

According to theory, the rate of detachment of soil particles in rills is reduced as a first-order function of the amount of sediment load in the flow. The first objective of this study was to determine if experimental results confirmed current detachment-transport coupling theory. The second objective was to investigate two hypothesized mechanisms responsible for any coupling effect observed: The first mechanism was that since turbulence is known to be a critical factor in detachment by flow, and since it is also known that sediment in water reduces turbulent intensity, it was suggested that sediment in flow reduces detachment via a correspondent reduction in turbulent intensities. This hypothesis was tested indirectly by adding a sediment load that was carried entirely in the suspended state. The second mechanism was that sediment covering the soil bed during the erosion process shields the soil from the forces of flow, thus reducing detachment. This hypothesis was tested by introducing bed-load sediment. Sediment loads exiting the rill and detachment and deposition along the rill were measured. Detachment was reduced and deposition increased as a linear function of the amount of sediment introduced into the flow. Results indicated that, in general, detachment did decrease according to current theory, but discrepancies in the erosional patterns were observed, which none of the current models explain. Both hypothesized mechanisms of reduction in detachment rates were apparently active in reducing detachment rates, though the shielding mechanism appeared to have a greater impact than did the mechanism associated with a reduction in turbulent intensity.