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Title: Soil-erosion models: where do we really stand? Short Communication (Discussion) on the papers by Wainwright et al. (2008a, b, c)

item SMITH, R.E. - Retired ARS Employee
item QUINTON, J. - Lancaster University
item Goodrich, David - Dave
item Nearing, Mark

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2009
Publication Date: 6/1/2010
Citation: Smith, R., Quinton, J., Goodrich, D.C., Nearing, M.A. 2010. Soil-erosion models: where do we really stand? Short Communication (Discussion) on the papers by Wainwright et al. (2008a, b, c). Earth Surface Processes and Landforms.

Interpretive Summary: Erosion of soil poses a threat to our ability to produce food and fiber for the long-term. A number of computer simulation models of erosion have been developed in an attempt to guide and aid farmers and land managers to control erosion. A new erosion model is proposed and developed in a series of three separate papers. The new model is called MAHLERAN. In justification for this new model, several existing ARS erosion models are criticized in regard to their theoretical underpinnings and presumptions. This discussion is a response to criticisms as well general discussion of the true weaknesses of all erosion model. We conclude that the new MAHLERAN model offers no solution to these weaknesses and suffers from several unique weaknesses its own. Further basic research and experimental work will be required to address the shortcomings of general erosion modeling approaches.

Technical Abstract: Wainwright et al. (2008a, b, c) propose a new model for simulating catchment-scale erosion resulting from rainfall-runoff events. In justifi cation for such a new model, several existing process-based models are criticized with regard to their theoretical underpinnings and presumptions. Since the authors do not correctly characterize the models mentioned, it is felt useful to correct the record in that regard, and to put the proposed model of Wainwright et al. in better perspective. The current models named in the criticism by Wainwright et al. include KINEROS (Woolhiser et al., 1990), KINEROS2 (Smith et al., 1995), EUROSEM (Morgan et al., 1998; Smith et al., 1995), and WEPP (Ascough et al., 1997). We refer to these below as the ‘critiqued models.’ The writers’ familiarity with those models and their assumptions provide justification for the clarifi cations presented below. We note here that some of the models critiqued have had developments added, and published, since their initial release. Wainwright et al.’s complaints and misunderstandings regarding existing models appear in our reading to be summarised by the following statements: 1. Existing models assume all sediment travels in suspension, whereas it likely does not. 2. The description of sediment movement relies on an assumption based on steady-state fl ow. 3. The models assume that sediment velocity is the same as water velocity. 4. The Yalin (1972) transport equation is criticized as inapplicable or misapplied [with the clear implication that existing models rely on it]. 5. The models should not use settling velocity or are using it incorrectly (p. 817). Below we address each of these points in detail. In each case the criticisms are ill-founded or result from a misunderstanding of the conceptual robustness of current catchment erosion dynamic models. Being familiar with the ‘critiqued’ models, we point out what we feel to be the true weaknesses of erosion models, for which the MAHLERAN model, developed by Wainwright et al., offers no cure. Their model suffers from many of the same weaknesses as those critiqued, plus some unique ones of its own. Copyright © 2010 John Wiley & Sons, Ltd.