Evaluation of physical erosivity factor for interrill erosion on steep vegetated hillslopes

Authors: SHIN, SEUNG SOOK - Gangneung-Wonju National University; PARK, SANG DEOG - Gangneung-Wonju National University; Pierson Jr, Frederick; Williams, Christopher - Jason

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2019
Publication Date: 2/8/2019
Citation: Shin, S., Park, S., Pierson, F.B., Williams, C.J. 2019. Evaluation of physical erosivity factor for interrill erosion on steep vegetated hillslopes. Journal of Hydrology. 571:559-572. https://doi.org/10.1016/j.jhydrol.2019.01.064.
DOI: https://doi.org/10.1016/j.jhydrol.2019.01.064

Interpretive Summary: Energy theory has been largely neglected in development of physical erosion models and may present a practical framework for predicting soil loss from well vegetated hillslopes. This study used the main energy components of rainfall on steep, vegetated hillslopes to evaluate soil erosion from experimental plots based on energy conservation theory. The work of soil erosion calculated for experimental plots was strongly correlated with the derived effective input energy for soil erosion across a range of vegetation and rock cover. The magnitude of soil loss was dictated by the effective kinetic energy of rain for densely vegetated plots and by the effective potential energy of runoff under more sparsely vegetated conditions. The results suggest derivation of effective input energy is a good predictor of soil loss from steeply vegetated hillslopes. The findings provide soil erosion modelers and researchers a new approach for advancing predictive capability of physically-based soil erosion models.

Technical Abstract: Soil erosion from vegetated steep hillslopes is mostly dominated by raindrop splash and sheetflow. However energy theory associated with physical processes of hillslope erosion has not been thoroughly investigated due to the complexity of rainfall and surface runoff interaction. In this study the main energy components of rainfall on steep hillslopes were considered to evaluate soil erosion based on energy conservation theory. The effective kinetic energy of raindrop contributing to soil splash was derived as the remaining rainfall energy after deducting dissipation effects of vegetation structure and a litter layer on ground surface. The effective potential energy of runoff contributing to transport of soil particles was derived based on the amount of water available for runoff following interception and infiltration mass allocations. The effective input energy for work of soil erosion was defined as the sum of the effective kinetic energy of raindrop and effective potential energy of surface runoff. Sediment yield and runoff discharge from nine plots on steep hillslopes were used to evaluate effective energy for work of soil erosion. Kinetic energy of rain was greatly reduced by the litter layer on well vegetated hillslopes, and the potential energy of surface runoff was predominantly reduced by infiltration term. Potential energy of infiltration and surface runoff depended significantly on kinetic energy of rain. The work of soil erosion calculated for each plot was strongly correlated with the derived effective input energy for soil erosion across a range of vegetation and rock cover. The magnitude of sediment yield was dictated by effective kinetic energy of rain on densely vegetated slopes and by the prevailing rainfall intensity and effective potential energy of runoff under for sparsely vegetated conditions. Energy efficiency of soil erosion was lowest for moderate rainfall on plots with less than 70% vegetation cover due to the interaction of raindrops with accumulated sheetflow. Results indicate the derived effective input energy is a good predictor or erosivity factor for evaluating soil erosion from steep vegetated hillslopes.