Viscosity Controls Rapid Infiltration and Drainage, Not the Macropores
Round 1
Reviewer 1 Report
The manuscript was carefully prepared. The authors presented an impressive and interesting work and reached the conclusion that the universal approaches to infiltration and drainage in permeable media need to be replaced by a dual process approach. However, the title of the manuscript is too vague and broad. It implied that porous media is the focus of the research but actually the manuscript mainly focused on soil hydrology. Some rules mentioned in the manuscript can apply to both soil and other porous media, such as gravel, aggregate layer used in infiltration trench and porous pavement. However, in certain conditions, porous media such as porous concrete follows Forchheimer law instead of Darcy law. Therefore, it is suggested that the title should be more precise.Author Response
The manuscript was carefully prepared. The authors presented an impressive and interesting work and reached the conclusion that the universal approaches to infiltration and drainage in permeable media need to be replaced by a dual process approach.
However, the title of the manuscript is too vague and broad. It implied that porous media is the focus of the research but actually the manuscript mainly focused on soil hydrology.
-The title has changed to better reflect the aim and the content of the manuscript
Some rules mentioned in the manuscript can apply to both soil and other porous media, such as gravel, aggregate layer used in infiltration trench and porous pavement. However, in certain conditions, porous media such as porous concrete follows Forchheimer law instead of Darcy law. Therefore, it is suggested that the title should be more precise.
-Again, the title has changed. Moreover, Forchheimer's law is presented and discussed in view of the paper's aim: ll. 357 ff.
Submission Date
12 November 2019
Date of this review
05 Dec 2019 15:12:07
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript presents the approach and the mathematical model of Newton’s shear flow to describe infiltration and drainage processes in permeable media. The author discussed physical principles of water infiltration in soils, and developed the novel theory to simulate investigated processes. The experimental support for the model presumptions is provided. The manuscript is of certain interest for the researchers and hydrologists dealing with variable saturation water flow in soils. The article is very well organized and written. I recommend it for publication in Water. Some clarifications/corrections are needed before the manuscript can be published.
Comments
The author introduces first presumption as existence of sharp wetting shock fronts. Why shock? This can confuse readers. In fluid mechanics, shock is usually associated with a wave having velocity higher than the local speed of sound, while flow processes considered in the manuscript are much slower. Please clarify.
Based on the Keil sand tank experimental data, it would be interesting to compare the simulation results of the Newton’s shear flow model with simulations using the Richards equation, and to elucidate differences between them. However, it’s just a recommendation.
Technical comments
Lines 58, 60: “the capillary potential…” – better use “the capillary pressure” since units are Pa. Line 90: “at -15 bars” – to be consistent with previously used units, better convert it to Pa. Line 164: “according to the rules of Newton's shear flow”. – Please provide these rules. Line 186: “the shear force” – this is shear stress (force/area), and it has units of stress (line 188). Line 204: “(m3 s-1)” – I assume it must be (m s-1). Figure 3: Need to improve the quality of this figure, especially the axes titles and the legend. Line 344: “0.254 and 0.175 (m3)” – I assume the unit must be m3m-2. Line 377: “the capillary head” – Better using “the capillary pressure head”. Line 395: “prmits” – permits. In the conclusion section, I recommend along with the advances also presenting possible limitations/drawbacks of the model. Lines 507-508: Two numbers 4 and 5 are used for one reference.Author Response
Comments
The author introduces first presumption as existence of sharp wetting shock fronts. Why shock? This can confuse readers. In fluid mechanics, shock is usually associated with a wave having velocity higher than the local speed of sound, while flow processes considered in the manuscript are much slower. Please clarify.
The reviewer just defined shock waves with sharp fronts. They do not only apply to sound but to any fluid moving with a wave speed higher than the velocity of the shock front (eg., avalanches). Taken care of the request in l 189.
Based on the Keil sand tank experimental data, it would be interesting to compare the simulation results of the Newton’s shear flow model with simulations using the Richards equation, and to elucidate differences between them. However, it’s just a recommendation.
Germann and Hensel (2004) compared the two approaches. That paper is briefly summarized in ll. 380 ff.
Technical comments
Lines 58, 60: “the capillary potential…” – better use “the capillary pressure” since units are Pa.
Because ψ<0, a negative pressure, seems to me more confusing than the dimension of pressure in a potential. See my explanations at ll. 66 to 73. Moreover PWP is soil water content at -15 bars: It is not easy to imagine such a 'pressure'
Line 90: “at -15 bars” – to be consistent with previously used units, better convert it to Pa.
Done at l. 101
Line 164: “according to the rules of Newton's shear flow”. – Please provide these rules.
Explained from l. 177 to l. 181
Line 186: “the shear force” – this is shear stress (force/area), and it has units of stress (line 188).
Changed to stress in l.217
Line 204: “(m3 s-1)” – I assume it must be (m s-1).
Changed in l. 225
Figure 3: Need to improve the quality of this figure, especially the axes titles and the legend.
Figure deleted
Line 344: “0.254 and 0.175 (m3)” – I assume the unit must be m3m-2.
Paragraph is deleted
Line 377: “the capillary head” – Better using “the capillary pressure head”.
See discussion above: head is in (m) and represents energy per unit weight, potential is in (Pa) and represent energy per unit volume. Pressure is something squeezing, pressure of -15 bars is difficult to imagine.
Line 395: “prmits” – permits. Thank you
In the conclusion section, I recommend along with the advances also presenting possible limitations/drawbacks of the model.
Done, ll.482 ff.
Lines 507-508: Two numbers 4 and 5 are used for one reference.
That's not my problem, goes to the editorial office
Submission Date
12 November 2019
Date of this review
27 Nov 2019 10:24:37
Formularende
Author Response File: Author Response.docx
Reviewer 3 Report
Review of “Newton's shear flow applied to infiltration and drainage in permeable media“ by Peter Germann submitted to MDPI Water
As a preamble to this review I want to assure that all criticism is meant fully constructive. I highly value the work and contributions of the author Peter Germann. He is undoubtedly one of the leading pedohydrologists of our times and his work, including this manuscript, is highly inspiring.
The manuscript presents his film flow approach to model infiltration processes into soils. Following the brief introduction, he presents a very well-written review of the theoretical developments in the scientific field, which lead to the current impasse with diffusion-focussed approaches to advection-diffusion problems in pedohydrology. By referring to some more recent literature, some arguments for the application of the Newton's shear flow for infiltration are laid out.
The third and fourth section mainly reiterate the approach of Newton's shear flow and some application examples, which have been presented before in at least four excellent papers of the first author (Germann, 2018a,b,c, Germann and Karlen, 2016) and his very instructive book (Germann, 2014). At some points, the arguments for the development of the approach appear to have sharpened since the first publication but do not carry substantial novelty here.
Although the manuscript states to be invited to a special issue, the Editor should be aware that large parts of the manuscript are not exactly novel with respect to the journal’s standards. (The guidelines of the journal state: Manuscripts should only report results that have not been submitted or published before, even in part.) Most equations and all figures can be found in Germann (2014). Most content of section 3 and 4 have been published multiple times now, which I find largely disturbing – despite all validity of the presented content. Its reiteration without any novel applications in the current form does not appear justified to me.
The discussion in the fifth section necessarily suffers the same overlap.
The central novelty of this manuscript is the review section, which I find very compelling in general. I could imagine that putting clear focus on this part would make the manuscript original and an inspiring contribution.
Also if the overlap to previous papers might have been agreed to during the invitation to the special issue, I suggest to at least firmly state the reiterative nature of the presentation and cite the papers and the book in a compact form. This should be done as soon as in the introduction to avoid any claims of self-plagiarism. If it was only the book, I would not push this argument so far. Maybe a more compact version could also be a means to sharpen the paper, when not all 41 equations might be required and the shear flow approach is put into broader perspective? This could also be in better balance with the review section.
Finally for the general comments, I find the claim in the conclusion (L492) that “Newton's shear flow seems to have solved the 7th Unsolved Problem in Hydrology” quite strong and largely unsupported in the presented manuscript. First of all, the why question is not answered by the presentation of the film flow approach, nor are co-evolution and scalability touched. I do not intend to underrate the value of the approach nor the achievements of Peter Germann in the field, but for any other author, this claim in such a manuscript would never be accepted. To be a little provocative here, I suspect that the author could have related in the same way to the sixth UPH: “What are the hydrologic laws at the catchment scale and how do they change with scale?”.
More specifically, the claim does not hold, because the assumption of a “sharp wetting shock front” is exactly one core issue about non-uniform infiltration: As soon there are structures in the soil, the propagation of infiltration in the inter-aggregate voids and macropores is mostly controlled by the interaction with and across the soil-fluid interface. Dual-domain models try to comprise this as some exchange term. It has been demonstrated that the interfaces impact is depending on the antecedent soil moisture. For my understanding of the manuscript, the shear flow approach here cannot (directly) account for antecedent moisture in this respect. Given that this would only be the entry point for a more throughout analysis of interaction with the soil, I also do not see how the co-evolution with the critical zone is tackled.
Since I see the review in section two to be the most important and original part of the manuscript, this section might be revised along the following lines.
The text is quite dense. Moreover and while it is informative, I fear that some arguments become a little one-sided, when the more recent developments are subsumed to “hues of HYDRUS” (L82) and a debate about Jarvis et al. (2016). There is much more progress in the field that tried to fix the highlighted impasse and that might corroborate arguments for distinguishing fast advective infiltration and slow capillary soil water redistribution in a more specific manner (including scale and scalability). As stated before, the author is one of the leading pedohydrologists in the field and I am sure that it would be highly interesting, if his review would extend beyond the given examples, which are very closely related to him and his teams.
I.e. the whole field of dual- or multiple-domain/permeability approaches is omitted. Given the situation that these models are the state of the art “answers” to the discussed issue, they should be included. Maybe a comparison of Newton shear flow to dual-domain approaches could be done elucidating some of the issues raised e.g. by Glaser et al. (2019) about when locally observed non-uniform infiltration is relevant for larger scales? Another path could be relating to the Scaleway (Vogel and Roth, 2003). Moreover, the ideas of Davies et al. (2011) and Jackisch and Zehe (2018) using a Lagrangian approach to water movement could be referred to.
Another line of debate which is omitted in the review relates to the work of Lehmann et al. (2012) and Or et al. (2015) with respect to the argumentation about plant available soil water (L87ff.). Again, I follow the argumentation by the author but I regard it as a missed opportunity to combine and consolidate concepts which have a common lines of thought (i.e. critical length scales and dynamic fluid interfaces). This could also open up ways to relax the pressure to already “have solved the 7th Unsolved Problem in Hydrology”.
Section 3 - 6
The introduction of the Newton's shear flow approach in section 3 (L149ff.) is quite steep given the more general review in the section before. The details about the approach somewhat counteract to the discursive style of the 2nd section. Given the statement in L122ff. (which I would fully support), I would expect examples which address this claim. I am not convinced that one sand box experiment is exactly connecting to the issues that lead to “the obsession with pores, channels, flow paths, and their connectivity, tortuosity and necks”…
Some details I spotted on the way:
L163: WCW is abbreviated here for the first time. At least for me, the term is not very familiar and a very brief statement about the conceptual foundation could elucidate the idea a little better. Moreover, the reader would be better prepared to the many abbreviations that will follow.
L170 and L176: zW(t) might be one of the critical aspects of the approach. First of all it should be clarified that z is depth. I find it more easy to read with the correct subscript $z_W(t)$ (which might be simply a matter with the typesetting template). I could imagine that a change in perspective to determine zW(t) and
L319 and L410: eq. 37 appears twice.
L513: The citation doi has a typo. Correct is: 10.1080/02626667.2019.1620507 (with a 1 leading the first block)
L542: The citation doi has a typo. Correct is: 10.2136/msa2016.0121 (with dot in first block)
Davies, J., K. Beven, L. Nyberg, and A. Rodhe (2011), A discrete particle representation of hillslope hydrology: hypothesis testing in reproducing a tracer experiment at Gårdsjön, Sweden,, 25(23), 3602–3612, doi:10.1002/hyp.8085.
Germann, P. (2018a), Preferential Flow at the Darcy Scale: Parameters from Water Content Time Series, Methods of Soil Analysis, sssabookseries(msaonline2018), 0, doi:10.2136/msa2016.0121.
Germann, P. F. (2018b), Hydromechanics and Kinematics in Preferential Flow, Soil Science, 183(1), 1, doi:10.1097/SS.0000000000000226.
Germann, P. F. (2018c), Viscosity—The weak link between Darcy“s law and Richards” capillary flow, Hydrological Processes, 32(9), 1166–1172, doi:10.1002/hyp.11450.
Germann, P. F., and M. Karlen (2016), Viscous-Flow Approach to In Situ Infiltration and In Vitro Saturated Hydraulic Conductivity Determination, Vadose Zone Journal, 15(2), 0, doi:10.2136/vzj2015.05.0065.
Germann, P. F. (2014), Preferential Flow, Geographica Bernensia, Institute of Geography, University of Bern, Bern.
Glaser, B., C. Jackisch, L. Hopp, and J. Klaus (2019), How Meaningful are Plot-Scale Observations and Simulations of Preferential Flow for Catchment Models? Vadose Zone Journal, 18(1), 0, doi:10.2136/vzj2018.08.0146.
Jackisch, C., and E. Zehe (2018), Ecohydrological particle model based on representative domains, Hydrol. Earth Syst. Sci., 22(7), 3639–3662, doi:10.5194/hess-22-3639-2018.
Jarvis, N., J. Koestel, and M. Larsbo (2016), Understanding Preferential Flow in the Vadose Zone: Recent Advances and Future Prospects, Vadose Zone Journal, 15(12), 0, doi:10.2136/vzj2016.09.0075.
Lehmann, P., I. Neuweiler, J. Vanderborght, and H.-J. Vogel (2012), Dynamics of Fluid Interfaces and Flow and Transport across Material Interfaces in Porous Media—Modeling and Observations, Vadose Zone Journal, 11(3), 0, doi:10.2136/vzj2012.0105.
Or, D., P. Lehmann, and S. Assouline (2015), Natural length scales define the range of applicability of the Richards equation for capillary flows, Water Resources Research, 51(9), 7130–7144, doi:10.1002/2015WR017034.
Vogel, H.-J., and K. Roth (2003), Moving through scales of flow and transport in soil, Journal of Hydrology, 272(1-4), 95–106, doi:10.1016/S0022-1694(02)00257-3.
Author Response
Review of “Newton's shear flow applied to infiltration and drainage in permeable media“ by Peter Germann submitted to MDPI Water
1. As a preamble to this review I want to assure that all criticism is meant fully constructive. I highly value the work and contributions of the author Peter Germann. He is undoubtedly one of the leading pedohydrologists of our times and his work, including this manuscript, is highly inspiring.
Thank you for the roses. However, I consider myself not primarily as leading pedohydrologist but as a fairly narrow-minded and stubborn engineer, who attacked over the last forty years from various sides the problem of macropore-, preferential-, non-equilibrium, etc. flow. Gradually, a concept emerged that is based on first principles of hydro-mechanics, including the continuity requirements, and that requires just the two parameters F and L. Numerous student projects produced the supportive data from simple field experiments to sophisticated neutron radiographs and acoustic tomography.
2. The manuscript presents his film flow approach to model infiltration processes into soils. Following the brief introduction, he presents a very well-written review of the theoretical developments in the scientific field, which lead to the current impasse with diffusion-focussed approaches to advection-diffusion problems in pedohydrology. By referring to some more recent literature, some arguments for the application of the Newton's shear flow for infiltration are laid out.
The third and fourth section mainly reiterate the approach of Newton's shear flow and some application examples, which have been presented before in at least four excellent papers of the first author (Germann, 2018a,b,c, Germann and Karlen, 2016) and his very instructive book (Germann, 2014). At some points, the arguments for the development of the approach appear to have sharpened since the first publication but do not carry substantial novelty here.
Although the manuscript states to be invited to a special issue, the Editor should be aware that large parts of the manuscript are not exactly novel with respect to the journal’s standards. (The guidelines of the journal state: Manuscripts should only report results that have not been submitted or published before, even in part.) Most equations and all figures can be found in Germann (2014). Most content of section 3 and 4 have been published multiple times now, which I find largely disturbing – despite all validity of the presented content. Its reiteration without any novel applications in the current form does not appear justified to me.
The invitation of the Guest Editor was based on my paper 'Viscosity - the weak link between Darcy's law and Richards' capillary flow' that was first submitted to VZJ, got rejected, and accepted by Hydrological Processes. Apparently still a controversial subject.
3. The discussion in the fifth section necessarily suffers the same overlap.
I greatly reduced the equation-part, did no more dwell on defending the basic arguments of Newton's approach, but added more examples to the applicability of the approach that, I thought, are adding to its applicability.
It is exactly this topic of my early inquiry addressed to the Guest Editor: Should I present the entire development of the approach or may I presuppose some basics? His response was to let the reviewers decide. The first version of the manuscript adhered to the first, while this version to the second part of the questions.
4. The central novelty of this manuscript is the review section, which I find very compelling in general. I could imagine that putting clear focus on this part would make the manuscript original and an inspiring contribution.
Most prominently, I changed the title. I think, this is the first manuscript of my list that addresses directly the short falls of the Buckingham-Richards construct as not very applicable to infiltration and drainage at large (not just preferential etc. flow). Statements expressing this view are introduced at various places in the revised manuscript.
5. Also if the overlap to previous papers might have been agreed to during the invitation to the special issue, I suggest to at least firmly state the reiterative nature of the presentation and cite the papers and the book in a compact form. This should be done as soon as in the introduction to avoid any claims of self-plagiarism. If it was only the book, I would not push this argument so far. Maybe a more compact version could also be a means to sharpen the paper, when not all 41 equations might be required and the shear flow approach is put into broader perspective? This could also be in better balance with the review section.
6.Finally for the general comments, I find the claim in the conclusion (L492) that “Newton's shear flow seems to have solved the 7th Unsolved Problem in Hydrology” quite strong and largely unsupported in the presented manuscript. First of all, the why question is not answered by the presentation of the film flow approach, nor are co-evolution and scalability touched. I do not intend to underrate the value of the approach nor the achievements of Peter Germann in the field, but for any other author, this claim in such a manuscript would never be accepted. To be a little provocative here, I suspect that the author could have related in the same way to the sixth UPH: “What are the hydrologic laws at the catchment scale and how do they change with scale?”.
I agree with the reviewer, perhaps from another point of view: Many of the 23 UPHs are based on hydrological experience and do not necessarily offer solid starting points for in-depth research. Therefore, I just dropped the entire issue of UPHs.
7.More specifically, the claim does not hold, because the assumption of a “sharp wetting shock front” is exactly one core issue about non-uniform infiltration: As soon there are structures in the soil, the propagation of infiltration in the inter-aggregate voids and macropores is mostly controlled by the interaction with and across the soil-fluid interface. Dual-domain models try to comprise this as some exchange term. It has been demonstrated that the interfaces impact is depending on the antecedent soil moisture. For my understanding of the manuscript, the shear flow approach here cannot (directly) account for antecedent moisture in this respect. Given that this would only be the entry point for a more throughout analysis of interaction with the soil, I also do not see how the co-evolution with the critical zone is tackled.
I think I explained the UPH-part above. The issue of structures is now explained in details in ll. 350-362. Again, the statements are experimentally supported at the hydro-mechanical process scale.
8.Since I see the review in section two to be the most important and original part of the manuscript, this section might be revised along the following lines.
The text is quite dense. Moreover and while it is informative, I fear that some arguments become a little one-sided, when the more recent developments are subsumed to “hues of HYDRUS” (L82) and a debate about Jarvis et al. (2016). There is much more progress in the field that tried to fix the highlighted impasse and that might corroborate arguments for distinguishing fast advective infiltration and slow capillary soil water redistribution in a more specific manner (including scale and scalability). As stated before, the author is one of the leading pedohydrologists in the field and I am sure that it would be highly interesting, if his review would extend beyond the given examples, which are very closely related to him and his teams.
Referring to my solution-oriented engineering approach to infiltration and drainage, I think the lengthy introduction referring to the evolution of concepts should suffice for leading to the main thrusts of the manuscript, that are: Doubts on Buckingham-Richards universal approach, two-parameter approach, consistency of the approach's drainage flow with the water content version, flow under atmospheric pressure, and the various docking points for further experiences (i.e., qS > Ksat)
9. I.e. the whole field of dual- or multiple-domain/permeability approaches is omitted. Given the situation that these models are the state of the art “answers” to the discussed issue, they should be included. Maybe a comparison of Newton shear flow to dual-domain approaches could be done elucidating some of the issues raised e.g. by Glaser et al. (2019) about when locally observed non-uniform infiltration is relevant for larger scales? Another path could be relating to the Scaleway (Vogel and Roth, 2003). Moreover, the ideas of Davies et al. (2011) and Jackisch and Zehe (2018) using a Lagrangian approach to water movement could be referred to
That's fine. Should I add another review to the many already in existence? Were I really the admired pedohydrologist, as the reviewer kindly supposed, I should probably discuss all those and many other investigations from a 'responsibility' point of view. However, have not many of these compilations contributed to the management of the problem, thus to its persistence, rather than to its solution?
10. Another line of debate which is omitted in the review relates to the work of Lehmann et al. (2012) and Or et al. (2015) with respect to the argumentation about plant available soil water (L87ff.). Again, I follow the argumentation by the author but I regard it as a missed opportunity to combine and consolidate concepts which have a common lines of thought (i.e. critical length scales and dynamic fluid interfaces). This could also open up ways to relax the pressure to already “have solved the 7th Unsolved Problem in Hydrology”.
Again, I cancelled the discussion about the UPHs altogether. About time scales: Infiltration and drainage within the rooting depth of about 1 to 2 (m) is a matter of hours to single days, whereas water uptake by plants is at the same time scale as capillary redistribution, thus not subject of this paper, but addressed, for instance, in ll 395 ff. Honestly, I was sort of disenchanted by Or et al. (2015): It is well known that fine roots grow as fast towards a better water supply than water moves towards roots. So, who impacts whose scale in natural systems? See above. Moreover, spatio-temporal diffusion process scale according to D=Δz2/Δt, where D is diffusivity in the Richards-equation and depends on the K-ψ-θ relationships that completely ignore plant properties.
11.Section 3 - 6
The introduction of the Newton's shear flow approach in section 3 (L149ff.) is quite steep given the more general review in the section before. The details about the approach somewhat counteract to the discursive style of the 2nd section.
I do not see a problem now, because all of it has previously been published.
12. Given the statement in L122ff. (which I would fully support), I would expect examples which address this claim. I am not convinced that one sand box experiment is exactly connecting to the issues that lead to “the obsession with pores, channels, flow paths, and their connectivity, tortuosity and necks”…
Here, I do not understand the statement. However, avoiding any discussion on UPHs may have eased the request.
13. Some details I spotted on the way:
L163: WCW is abbreviated here for the first time. At least for me, the term is not very familiar and a very brief statement about the conceptual foundation could elucidate the idea a little better. Moreover, the reader would be better prepared to the many abbreviations that will follow.
Fixed in ll. 178 ff.
L170 and L176: zW(t) might be one of the critical aspects of the approach. First of all it should be clarified that z is depth.
See l. 189.
I find it more easy to read with the correct subscript $z_W(t)$ (which might be simply a matter with the typesetting template). I could imagine that a change in perspective to determine zW(t) and
That's the type setting.
L319 and L410: eq. 37 appears twice.
Can't see the problem.
L513: The citation doi has a typo. Correct is: 10.1080/02626667.2019.1620507 (with a 1 leading the first block)
L542: The citation doi has a typo. Correct is: 10.2136/msa2016.0121 (with dot in first block)
Thank you.
Davies, J., K. Beven, L. Nyberg, and A. Rodhe (2011), A discrete particle representation of hillslope hydrology: hypothesis testing in reproducing a tracer experiment at Gårdsjön, Sweden,, 25(23), 3602–3612, doi:10.1002/hyp.8085.
Germann, P. (2018a), Preferential Flow at the Darcy Scale: Parameters from Water Content Time Series, Methods of Soil Analysis, sssabookseries(msaonline2018), 0, doi:10.2136/msa2016.0121.
Germann, P. F. (2018b), Hydromechanics and Kinematics in Preferential Flow, Soil Science, 183(1), 1, doi:10.1097/SS.0000000000000226.
Germann, P. F. (2018c), Viscosity—The weak link between Darcy“s law and Richards” capillary flow, Hydrological Processes, 32(9), 1166–1172, doi:10.1002/hyp.11450.
Germann, P. F., and M. Karlen (2016), Viscous-Flow Approach to In Situ Infiltration and In Vitro Saturated Hydraulic Conductivity Determination, Vadose Zone Journal, 15(2), 0, doi:10.2136/vzj2015.05.0065.
Germann, P. F. (2014), Preferential Flow, Geographica Bernensia, Institute of Geography, University of Bern, Bern.
Glaser, B., C. Jackisch, L. Hopp, and J. Klaus (2019), How Meaningful are Plot-Scale Observations and Simulations of Preferential Flow for Catchment Models? Vadose Zone Journal, 18(1), 0, doi:10.2136/vzj2018.08.0146.
Jackisch, C., and E. Zehe (2018), Ecohydrological particle model based on representative domains, Hydrol. Earth Syst. Sci., 22(7), 3639–3662, doi:10.5194/hess-22-3639-2018.
Jarvis, N., J. Koestel, and M. Larsbo (2016), Understanding Preferential Flow in the Vadose Zone: Recent Advances and Future Prospects, Vadose Zone Journal, 15(12), 0, doi:10.2136/vzj2016.09.0075.
Lehmann, P., I. Neuweiler, J. Vanderborght, and H.-J. Vogel (2012), Dynamics of Fluid Interfaces and Flow and Transport across Material Interfaces in Porous Media—Modeling and Observations, Vadose Zone Journal, 11(3), 0, doi:10.2136/vzj2012.0105.
Or, D., P. Lehmann, and S. Assouline (2015), Natural length scales define the range of applicability of the Richards equation for capillary flows, Water Resources Research, 51(9), 7130–7144, doi:10.1002/2015WR017034.
Vogel, H.-J., and K. Roth (2003), Moving through scales of flow and transport in soil, Journal of Hydrology, 272(1-4), 95–106, doi:10.1016/S0022-1694(02)00257-3.
Submission Date
12 November 2019
Date of this review
02 Dec 2019 16:14:31
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Review of the revised manuscript submitted to MDPI Water by Peter Germann
“Viscosity Controls Rapid Infiltration and Drainage, not the Macropores”
Peter Germann has greatly improved his manuscript and has eased my two main concerns:
Self-plagiarism is now clearly avoided by referring to the former works and the introductory statement in section 3. The reference to the “Unsolved Problems in Hydrology” is omitted.Moreover, he has clarified the intention and arguments in the manuscript which make it far more original now. I find most of the replies well founded and agree that a solution oriented paper is more worthwhile than any other review.
The throughout revision and largely fully new writing of sections 3 - 5 have led to a completely new manuscript, which has massively improved and sharpened. However, I think the manuscript deserves a round of minor revisions to really streamline the arguments and ease their reception.
General suggestions:
I would find it helpful to have more guidance along the arguments in the respective parts. I.e. in section 2 subsections could name the path leading to the current situation or in the words in the reply:
“Doubts on Buckingham-Richards universal approach, two-parameter approach, consistency of the approach's drainage flow with the water content version, flow under atmospheric pressure, and the various docking points for further experiences (i.e., qS > Ksat)”
I very much endorse the reply to the author’s self-perception: I consider myself not primarily as leading pedohydrologist but as a fairly narrow-minded and stubborn engineer, who attacked over the last forty years from various sides the problem of macropore-, preferential-, non-equilibrium, etc. flow. Gradually, a concept emerged that is based on first principles of hydro-mechanics, including the continuity requirements, and that requires just the two parameters F and L. Numerous student projects produced the supportive data from simple field experiments to sophisticated neutron radiographs and acoustic tomography.
I find this statement very elucidating. Moreover, it is a nice introductory guidance to the manuscript which could be used in a rephrased version in the introduction. (Maybe somewhere around L32.). The summary L438ff. does organise the manuscript very nicely but a posteriori. Maybe the two passages could be revised correspondingly to help the readers to take up the valuable contributions of the manuscript. The very last sentence could be a very nice place to include the above statement in some personal way?
Cited work:
I acknowledge the contribution of Peter Germann and his scholars. And I can understand the situation progressively addressed by the author in and L469ff. However, I have come across multiple possibilities where citations to recent publications of colleagues in other working groups suggest themselves. The author is part in 22 of the 57 cited works. Given the 17 classic citations older than 60 years, this makes more than 50% of the debate with more current work. Referring to the self-perception above, I can fully understand this situation. However, as reviewer I have to at least highlight this situation and demand for more references outside the direct field of gravity of the author – especially with regard to alternative concepts to the Darcy-Richards approach. I would expect that a more balanced and positive attitude towards the work of other groups could eventually prepare for a broader reception of the NFS (Newton’s shear flow) approach in the community.
Specific issues:
L24,25 and more coming: Why are units sometimes in brackets, although they belong to the stated values? Please revise.
L32: “Here” - maybe “In this study” for more clarity?
L35: I think it is more the evolution of the concepts than the flow itself? (word missing)
L35ff: The response to the reviews is more clear about the structure of the manuscript. I think this is a little to brief here. I suggest to clarify or argue along the main statement which led to the new title.
L98ff: I prefer italic typesetting for quotations, as has been used in L56ff.
L148: Why is there a hyphen between 2.4 and m? (This notation is used in other places, too.) Please revise.
L153ff: The summary sentence appears to be a rather important element of the main argumentation of the paper. I still think such poles could stick out more clearly for better reception. Maybe it could be combined with the introductory sentence at the beginning of section 3 wrapping the evolution of concepts and to clarify the difference of the Newton’s shear flow approach to the former concepts?
L162: I suggest to separate the introduction to the section from the actual content by a line break. However, I see the general nature of the forthcoming sentences…
L217: “not shown here” could be pointing to Germann and Karlen (2016) Eq. 16, if I am not mistaken.
L260: Citing a study under way is always difficult. I would leave it out – especially given the general citation style.
L272f: Maybe pointing out that these studies corroborate the prerequisite implied in eq. 3 directly? (Instead of leaving this to the reader to make the connection.)
L276f: Why is it Re, which demands for a closer look? Maybe there is a better wording?
L278f: With the revisions, this prerequisite appears to lack motivation now. Maybe a brief reference to its clarification in L314ff is helpful?
L293/296: Maybe state already in L293: With replacing the kinematic viscosity (η) with the dynamic viscosity (μ = ρ η (Pa s)) from Eq. 1 follows…
L315: is patm = patms?
L326ff: If I follow the argument correctly, the implication of p≥patm and small Re is that the Forchheimer concept does not apply to the conditions of the NSF (Newton’s shear flow). Maybe such a statement is sufficient, since Eq. 17 is not used any further?
L352ff: The cosine makes sense but I do not see the connection with the rest of the argument about momentum dissipation and capillarity in the paragraph. Maybe a simple statement about the relatively quick collapse of the wetting front and thus the gravity dominated stage of water redistribution could be helpful and open numerous links to applications of the NSF approach in existing model concepts? This could also form a more easily understandable link to the last paragraph?
L430ff: I am not sure if this statement is necessary and justified here. Wiekenkamp et al. 2016 (doi 10.1016/j.jhydrol.2016.09.037) did a quite convincing analysis of the water balance at the stands. As far as I recall, they based their conclusions about preferential flow on the mere reaction-timing of the soil moisture sensors (similar to the study of Demand et al. 2019 cited in the manuscript). My main point here is that the study at hand does not relate to interception and interception might not be the issue for applying the NSF approach? I suggest to omit the subsection or to rewrite it with much closer reference to NSF.
L438f: Would it be easier to write that rapid flow was 150 to 700 times faster than the slow transport of contaminants through the English chalk?
L471ff: I suggest to reformulate this statement to come back to the more personally motivated statement from the author’s reply.
Author Response
General
I was not able to download the Reviewer's comments to directly write into it my comments. So I have to refer to his/her statements in the report.
*Please find it in attachment
Author Response File: Author Response.docx
