Reply to comments on “Characterizing detachment and transport processes of interrill soil erosion, Geoderma (2020) 114549”

Authors: Zhang, Xunchang; ZHENG, FENLI - Northwest A&f University; CHEN, JIE - Wuhan University; GARBRECHT, JURGEN - Retired ARS Employee

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2021
Publication Date: 5/6/2021
Citation: Zhang, X.J., Zheng, F., Chen, J., Garbrecht, J. 2021. Reply to comments on “Characterizing detachment and transport processes of interrill soil erosion, Geoderma (2020) 114549”. Geoderma. 402:115183. https://doi.org/10.1016/j.geoderma.2021.115183.
DOI: https://doi.org/10.1016/j.geoderma.2021.115183

Interpretive Summary: This is to reply to a letter by Dr. Kinnell who commented on an article published by Zhang et al. in the journal of Geoderma in 2019. In the article a new complex experimental protocol was carried out to 1) determine the dominant process of sheet flow erosion in the inter-rill areas (between rill), 2) improve the understanding of sediment transport mechanisms, and further estimate the proportion between raindrop-driven and flow-driven sediment transport. Two primary treatments were the screen and tarp cover, and two secondary treatments were slope and rainfall intensity. The screen cover was to dissipate raindrop impact energy to mimic crop canopy cover, which controls sediment input by reducing raindrop detachment of air splash without changing surface runoff. The tarp cover was to control both water and sediment inflows from upslope by varying slope lengths. Combined with three levels of rainfall intensities and slope gradients, the complex dataset afforded a unique opportunity to understand sheet flow erosion processes. Based on the new understanding, raindrop-driven and flow-driven sediment transport were separately measured. The findings are useful to erosion scientists and soil conservationists for modeling and estimating sheet flow erosion. This reply is to clarify Dr. Kinnell’s misunderstandings and to shed light on a few disagreements on interpretation and explanation of some results.

Technical Abstract: A new complex experimental protocol was carried out to 1) determine the dominant process of interrill erosion, 2) improve the understanding of sediment transport mechanisms, and 3) estimate the proportion between flow-driven and raindrop-driven sediment transport. Two primary treatments were the screen and tarp cover, and two secondary treatments were slope and rainfall intensity. The screen treatment was to control sediment inflow by reducing raindrop impact detachment without modifying runoff rates, which mimics interrill erosion under canopy cover. The tarp treatment was to control both water and sediment inflows by varying slope lengths. Combined with three levels of rainfall intensities and slope gradients, the complex dataset afforded a unique opportunity to attack the three objectives above. Two sets of equations (one for each cover treatment) were proposed to gain insights into sediment transport processes in time and space, both of which provided valuable information from different view angles for deducing sediment transport processes. Dr. Kinnell’s misunderstanding on equation (1) that provided apparent net sediment contribution from the newly exposed soil segment to the sediment discharge at the outlet in the screen treatment was clarified. The proposed concept on soil detachment by raindrop impacted flow was further defined, explained and discussed. The current understanding on interrill erosion processes was also reviewed, synthesized, and unified under the new concept of flow detachment. The new framework would be useful to erosion scientists for understanding and modeling interrill erosion processes.