thanks for the revisions on the paper. I have a large number of minor comments. I found a few equations that are not dimensionally balanced (e.g., q = A^m), so please check that everything is correct.
All the best, Jens
1.13 Earth capitalized.
2.2 I would rather say that river incision has commonly been modelled with two end members.
2.25 and following. The review is quite good, but I am not sure I agree with the outlook. As I already stated in the last round of reviews, for a minimum physical description of the landscape, we need two components: an equation describing mass conservation and an equation describing sediment production (i.e., an erosion law). When I read the early literature, I get the impression that the authors who constructed detachment-limited and transport-limited models in the first place were quite aware that these are end-member approximations of this minimum description (with transport-limited models neglecting sediment production and detachment-limited models neglecting mass conservation). In this context, it seems not to be sensible to expect that the one or the other model can describe any landscape. Rather, in field studies, the pertinent question is in what kind of landscapes the one or the other approximation can be applied. In this outlook, the outcomes of Valla et al. and Hobley et al. are not contradictory. Different landscapes obviously lead to different outcomes.
The need for the inclusion of both fundamental equations (mass conservation and sediment production) arises from the process observations that availability of alluvial sediment strongly influences erosion rates, for example through the tools and cover effects. This insight forbids neglecting mass conservation when describing bedrock rivers.
3.12 / section 3: This paragraph is helpful, but terminology and concepts are not currently clearly exposed. I do not agree with the hard boundaries the authors propose here for the four classes. For example, the model described in my recent paper with Rebecca Hodge in ESurf is a description of mass conservation within a channel with a partially alluviated bed. Although we have not included erosion in that paper, it would be straight-forward to do. A similar statement could be made for the Exner-based framework by Inoue et al. The classification put forward here seems to be more aligned with the aims of the particular papers in which they were proposed, and seems therefore artificial, rather than giving a classification that springs from the description of the physics. My suggestion would be to discriminate descriptions of mass conservations (e.g., Inoue et al., Turowski and Hodge, Zhang et al., but also Nelson and Seminara) and descriptions of bedrock erosion (e.g., saltasion-abrasion model and derivatives, stream power etc), and finally combinations of these (Nelson and Seminara, Davy and Lague, the present paper).
3.14 In my view, these are not detachment-limited models. Sediment-flux-dependent models come out of process observations and they aim to quantify the sediment-production equation. They can be used within a detachment-limited framework, but they don’t have to be used as such. An example is the saltation-abrasion model: the mechanistic model was described in the Sklar & Dietrich 2004 paper, the model implications for channel long profiles in a detachment-limited framework were explored in the Sklar & Dietrich 2006 paper and the recent Zhang et al. 2014 paper uses the model in a framework that includes mass conservation.
3.29 I suggest to delete ‘Depending on the specific model formulation used’ – tools and cover effect may be active independent of specific model formulations. There are just some models that include a description of these effects and others do not (whether a model of the one or of the other category is a good description of reality is a different matter…)
3.31 review by Hobley et al.
6.16 similar to what?
7.22 I suggest to remove this sentence and let the community judge the significance of the contribution.
7.34 …used by Sklar and Dietrich…
8.21 I suggest to use the term entrainment for alluvium, to prevent confusion with bedrock erosion
9.19 …discussed by…
10.5 the equation q=A^m needs a multiplicative coefficient; otherwise it is not dimensionally balanced.
10.6 to my knowledge, the scaling exponent is typically 0.7 when bankfull discharge is used and 1 when the long-term average discharge is used. The latter can be argued from mass conservation. See Snyder et al. 2003 for a brief discussion and literature overview.
11.10 by Lague
15.5 should there be a factor accounting for the bedload fraction?
15.12 Again, q=A^m is not dimensionally balanced.
27.27 Earth capitalized.
27.29 Can you give the appropriate references here?
29.25 I guess the citation here should be Turowski et al., 2009.
29.34 Even in plucking-dominated environments, tools may play a large role by driving crack extension. This process is known as macro-abrasion.
30.1 …is underpredicted…
30.21 …as does the model by Nelson and Seminara
32.1 ‘necessary’ used twice in this sentence
32.9 Earth capitalized.