Determining and modeling dominant processes of interrill soil erosion

Authors: Zhang, Xunchang

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2018
Publication Date: 11/26/2018
Citation: Zhang, X.J. 2018. Determining and modeling dominant processes of interrill soil erosion. Water Resources Research. 55(1):4-20. https://doi.org/10.1029/2018WR023217.
DOI: https://doi.org/10.1029/2018WR023217

Interpretive Summary: Soil erosion on a sloped field is mainly caused by rill and interrill erosion. Rill erosion is caused by small channels that disappear after tillage, while interrill erosion occurs between rills and feeds sediment to rills. Understanding the dominant process of interrill soil erosion is imperative to better controlling interrill erosion. The objectives are to 1) determine the limiting erosion process (soil detachment vs. sediment transport) that controls interrill erosion under various slopes, rainfall intensities, and slope lengths, 2) quantify the effects of water and sediment influxes from upslope on downslope interrill erosion, and 3) evaluate the ability of commonly used hydraulic parameters for simulating interrill sediment transport capacity. Runoff, sediment delivery and raindrop splash were simultaneously collected from two flumes (1.8 m long by 0.5 m wide) and a 2.5-cm gap between the flumes for three intensities of 60, 90, and 120 mm h-1 at three slopes of 9, 18, and 27% under two cover treatments. Results showed that slot splash rates were consistently greater than flume wash rates, indicating that sediment transport capacity limited interrill erosion. Soil detachment by raindrop impact was more influenced by ponding depth, while sediment transport capacity by flow velocity. Linear correlation coefficients between sediment delivery rates and hydraulic predictors were 0.184 for shear stress, 0.854 for stream power, 0.870 for unit stream power, and 0.962 for an empirical lumped model that includes a rainfall intensity term. Since rainfall intensity, or more precisely rainfall kinetic energy, plays a critical role in enhancing interrill sediment transport by stirring up the flow, any hydraulic parameter without an intensity factor is insufficient to accurately predict interrill sediment transport capacity. An empirical model including rainfall intensity, runoff, and slope steepness and length is strongly recommended. This finding would be useful to soil conservationists for reducing interrill erosion by dissipating raindrop impacts by increasing surface and canopy cover such as adoption of no-till or a cover crop.

Technical Abstract: Understanding the dominant process of interrill soil erosion is imperative to better modeling interrill sediment delivery rates. The objectives are to 1) determine the limiting erosion process (detachment vs. transport) that controls interrill erosion under various slopes, rainfall intensities, and slope lengths, 2) quantify the effects of water and sediment influxes from upslope on downslope interrill erosion, and 3) evaluate the ability of commonly used hydraulic parameters for simulating interrill sediment transport capacity. Runoff, sediment delivery and raindrop splash were simultaneously collected from two flumes (1.8 m by 0.5 m) and a 2.5-cm gap between the flumes for three intensities of 60, 90, and 120 mm h-1 at three slopes of 9, 18, and 27% under two cover treatments. Results showed that slot splash rates were consistently greater than flume wash rates, indicating that sediment transport capacity limited interrill sediment delivery. Soil detachment by raindrop impact was more influenced by flow depth, while sediment transport capacity by flow velocity. Linear correlation coefficients between sediment delivery rates and hydraulic predictors were 0.184 for shear stress, 0.854 for stream power, 0.870 for unit stream power, and 0.962 for an empirical lumped model that includes a rainfall intensity term. Since rainfall intensity, or more precisely rainfall kinetic energy, plays a critical role in enhancing interrill sediment transport, any hydraulic parameter without an intensity factor is insufficient to accurately predict interrill sediment transport capacity. An empirical model including rainfall intensity, runoff, and slope steepness and length is strongly recommended.