Laboratory Experiments of Rill Initiation and Critical Shear Stress in Loose Soil Material

Dynamic soil erosion processes involve the spatial and time dependent processes of detachment, rill formation, deposition, re-rilling from deposited sediment and scouring of rills. Rill scouring associated with sediment re-detached from a depositional area can be an important phenomenon in rill narrowing and deepening. In this study, an apparatus was designed to measure the parameters for rill cutting in loose material similar to deposited soil. Experimental results were conducted for determining the flow rates at which rill formation starts and ends for each aggregate group and slope. Critical shear stress as related to bed slope was calculated. The results improve our understanding and quantification of rill cutting in loose material as well as the relationship between critical shear stress and slope. The results may be of particular value in developing process models of rill evolution wherein rills re-cut through deposited material.