Roles of raindrop impact in detachment and transport processes of interrill soil erosion

Authors: Zhang, Xunchang

Submitted to: International Soil and Water Conservation Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2022
Publication Date: 11/12/2022
Citation: Zhang, X.J. 2022. Roles of raindrop impact in detachment and transport processes of interrill soil erosion. International Soil and Water Conservation Research. 11(2023):592-601. https://doi.org/10.1016/j.iswcr.2022.11.001.
DOI: https://doi.org/10.1016/j.iswcr.2022.11.001

Interpretive Summary: To date the roles of raindrop impact in sediment entrainment and transport processes of interrill soil erosion are not yet fully understood. The objectives are to 1) evaluate the effects of raindrop impact on sediment entrainment, 2) quantify the relative importance of raindrop-driven and flow-driven transport, and 3) characterize sediment size distributions in different sediment transport regimes. A loam soil with 48.4% sand and 23% clay was packed into flumes (L×W×H: 1.8×0.5×0.1 m) and subjected to intensities of 60, 90, 120 mm/h at gradients of 5, 10, and 16°. Air filter and tarp covers were used to vary impact energy and slope length. Results show that sediment is largely entrained by raindrop impact and transported by raindrop-impacted flow. Interrill erosion consists of two composite processes: raindrop-induced detachment/entrainment and raindrop-impacted flow transport. The former includes direct detachment by raindrop impact and ‘flow detachment’. The latter includes raindrop-driven and flow-driven transports. The proportions between the two transports vary with slope steepness, slope length, flow depth (or flow discharge, rainfall intensity, and sediment characteristics. Raindrop-driven transport is competent but inefficient, while the opposite is true for flow-driven transport. Because raindrop impact plays dual roles in detaching soil (and/or entraining sediment) and enhancing sediment transport, a factor of raindrop impact energy must be included in interrill erosion models to adequately simulate the dual roles. The results are useful to soil erosion modelers for developing an interrill erosion model that takes into consideration the rainfall energy dissipation by plsny canopies using a raindrop energy function.

Technical Abstract: To date the roles of raindrop impact in sediment entrainment and transport processes of interrill soil erosion are not yet fully quantified. The objectives are to 1) evaluate the effects of raindrop impact on sediment entrainment, 2) quantify the relative importance of raindrop-driven and flow-driven transport, and 3) characterize sediment size distributions in different sediment transport regimes. A loam soil with 48.4% sand and 23% clay was packed into flumes (L×W×H: 1.8×0.5×0.1 m) and subjected to intensities of 60, 90, 120 mm/h at gradients of 5, 10, and 16°. Air filter and tarp covers were used to vary impact energy and slope length. Results show that sediment is largely entrained by raindrop impact and transported by raindrop-impacted flow. Interrill erosion consists of two composite processes: raindrop-induced detachment/entrainment and raindrop-impacted flow transport. The former includes direct detachment by raindrop impact and ‘flow detachment’. The latter includes raindrop-driven and flow-driven transports. The proportions between the two transports vary with slope steepness, slope length, flow depth (or flow discharge, rainfall intensity, and sediment characteristics. Raindrop-driven transport is competent but inefficient, while the opposite is true for flow-driven transport. Because raindrop impact plays dual roles in detaching soil (and/or entraining sediment) and enhancing sediment transport, a drop energy factor must be included in interrill erosion models to adequately simulate the dual roles. More studies are required to derive a drop energy function that takes into consideration the rainfall energy dissipation by canopies of various plants under natural conditions.