Comment on ‘A transport‐distance based approach to scaling erosion rates’: Parts 1, 2 and 3 by Wainwright et al.

The new model of sediment transport proposed by Wainwright et al. (2008a) and developed in Wainwright et al. (2008b, 2008c) follows a well trodden-path of other sediment movement models, including those derived from Hairsine and Rose (1992a, 1992b). The authors first assert that their new model provides step changes in the conceptualization and understanding of the erosion and transport phenomena, and then build a parameter-rich group of algorithms that are found to perform well in a range of well-measured circumstances. In this comment we provide a critique of this and similar models. We contend that the claims of Wainwright et al. (2008a) are overstated and the MAHLERAN (Model for Assessing Hillslope-landscape Erosion, Runoff and Nutrients), like many others, suffers from the introduction of many parameters that are difficult to evaluate in non-experimental, predictive circumstances. Like most models of the natural world, those developed for sediment transport can be judged by the degree of evaluation against measured data [see the review by Grayson and Bloschl (2000)]. The progression of this evaluation, from basic to demanding, can for example be described by the following hierarchy: