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Title: Concentrated flow erodibility for physically-based erosion models: temporal variability in disturbed and undisturbed rangelands

Author
item AL-HAMDAN, OSAMA - University Of Idaho
item Pierson Jr, Frederick
item Nearing, Mark
item Williams, Christopher - Jason
item Stone, Jeffry
item KORMOS, PATRICK - Boise State University
item BOLL, JAN - University Of Idaho
item Weltz, Mark

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2012
Publication Date: 7/7/2012
Citation: Al-Hamdan, O.Z., Pierson Jr, F.B., Nearing, M.A., Williams, C.J., Stone, J.J., Kormos, P.R., Boll, J., Weltz, M.A. 2012. Concentrated flow erodibility for physically-based erosion models: temporal variability in disturbed and undisturbed rangelands. Water Resources Research. DOI: 10.1029/2011WR011464.

Interpretive Summary: In this study, we developed parameterization equations for concentrated flow erodibility on rangeland. Unlike previous studies, these equations take into the account the changes of the erodibility within a runoff event. Thus, these equations would be a good candidate for the use of the dynamic physically based erosion models. Also, in this research, we developed empirical equations for predicting the changes of erodibility within season's recovery after the disturbance of a rangeland's site. These equations require data that are commonly measured and reported by rangeland managers and researchers. In addition, in this research we characterized the relationship between concentrated flow detachment capacity and commonly derived hydraulic parameters for different rangeland environmental conditions, as well as, investigated the effects of varying degrees of disturbance on magnitude and temporal variability in soil erodibility.

Technical Abstract: Current physically based overland flow erosion models for rangeland application do not separate disturbed and undisturbed conditions in modeling concentrated flow erosion. In this study, concentrated flow simulations on disturbed and undisturbed rangelands were used to estimate the erodibility and to evaluate the performance of linear and power law equations that describe the relationship between erosion rate and several hydraulic parameters. None of the hydraulic parameters consistently predicted the detachment capacity well for all sites, however, stream power performed better than most of other hydraulic parameters. Using power law functions did not improve the detachment relation with respect to that of the linear function. Concentrated flow erodibility increased significantly when a site was exposed to a disturbance such as fire or tree encroachment into sagebrush steppe. This study showed that burning increases erosion by amplifying the erosive power of overland flow through removing obstacles and by changing the soil properties affecting erodibility itself. However, the magnitude of fire impact varied among sites due to inherent differences in site characteristics and variability in burn severity. In most cases we observed concentrated flow erodibility had a high value at overland flow initiation and then started to decline with time due to reduction of sediment availability. Thus we developed an empirical function to predict erodibility variation within a runoff event as a function of cumulative unit discharge. Empirical equations were also developed to predict erodibility variation with time postdisturbance as a function of readily available vegetation cover and surface soil texture data.