Determining ephemeral gully erosion process with the volume replacement method.

Background Ephemeral gully erosion is an important form of hillslope erosion all over the world. It is of high significance to understand its erosion mechanism. Objective A new volume replacement method is proposed to determine ephemeral gully erosion process. Styrofoam particles of hard granules were used to refill the eroded ephemeral gully sections lined with gauze sheet to the original elevation, before their volumes were measured for estimating sediment concentration distribution along the ephemeral gully. The measurement and the computational methodologies are illustrated in details. Method A series of flume experiments were conducted with a silt loam (loess) soil to study ephemeral gully erosion process under four slope gradients and three flow rates. The ephemeral gully was pre-formed before each experimental run. The volumes of the eroded ephemeral gully sections were measured and the distribution of sediment concentration along the gully was computed at 1 m intervals. For comparison purpose, the sediment concentration distribution along the eroded gully was also measured by manual sampling of the sediment-laden water flow with cups. Results The results showed that both the sediment processes estimated by the volume replacement and measured by the sampling method were very similar. The estimated and measured sediment concentrations increased with ephemeral gully length under a given flow rate. The increase rate decreased gradually as the sediment concentration gradually approached its limit. Conclusions Under different flow rates and slope gradients, the sediment concentrations at different distances, as estimated by the volume replacement method were about the same as those measured with the sampling method. The new method provides a useful and efficient way in determining the ephemeral gully erosion, and helps to understand ephemeral gully erosion process. [ABSTRACT FROM AUTHOR]