Stabilising large grains in self-forming steep channels

Booker, William H.; Eaton, Brett C.

doi:https://doi.org/10.5194/esurf-8-51-2020

Articles | Volume 8, issue 1

https://doi.org/10.5194/esurf-8-51-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/esurf-8-51-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 8, issue 1

Research article

|

28 Jan 2020

Research article |

| 28 Jan 2020

Stabilising large grains in self-forming steep channels

William H. Booker and Brett C. Eaton

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Final revised paper (published on 28 Jan 2020)
Preprint (discussion started on 27 May 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Revision - Booker and Eaton - Stabilising large grains in aggrading steep channels', Anonymous Referee #1, 25 Jun 2019
- AC1: 'Author's reply to Reviewer 1', William Booker, 16 Jul 2019
RC2: 'Reviewer comments on Booker and Eaton', Anonymous Referee #2, 27 Jun 2019
- AC2: 'Author's reply to Reviewer 2', William Booker, 16 Jul 2019
RC3: 'Review- Booker and Eaton', Anonymous Referee #3, 01 Jul 2019
- AC3: 'Author's reply to Reviewer 3', William Booker, 17 Jul 2019
EC1: 'Editorial comment', Jens Turowski, 16 Jul 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by William Booker on behalf of the Authors (03 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Sep 2019) by Jens Turowski

RR by Anonymous Referee #1 (17 Sep 2019)

Suggestions for revision or reasons for rejection

Dear William and Brett,

I reviewed the first version of this article. This new version contains the core of all my suggestions and observations, I really appreciate the effort. It is also a much better article than the previous one. After careful consideration, I believe that it is worth publishing. I suggested technical corrections based on a series of typos, and some missed references that may improve the final article. It is a quite interesting topic and I enjoyed reading it.

Page 2, line 16: There are several studies about organisation into cells. Please consider adding the following:

Dietrich, W. E., Kirchner, J. W., Ikeda, H., & Iseya, F. (1989). Sediment supply and the development of the coarse surface layer in gravel-bedded rivers. Nature, 340, 215–217. https://doi.org/10.1038/340215a0
Dietrich, W. E., Nelson, P. A., Yager, E., Venditti, J. G., Lamb, M. P., & Collins, L. (2005). Sediment patches, sediment supply, and channel morphology. In G. Parker & M. H. Garcia (Eds.), 4th IAHR Symposium on River Coastal and Estuarine Morphodynamics RCEM 2005 (pp. 79–90). Urbana, Illinois, USA: Taylor & Francis Group. https://doi.org/10.1201/9781439833896.ch11
Monsalve, A., & Yager, E. M. (2017). Bed Surface Adjustments to Spatially Variable Flow in Low Relative Submergence Regimes. Water Resources Research, 53(11), 9350–9367. https://doi.org/10.1002/2017WR020845
Nelson, P. A., Venditti, J. G., Dietrich, W. E., Kirchner, J. W., Ikeda, H., Iseya, F., & Sklar, L. S. (2009). Response of bed surface patchiness to reductions in sediment supply. Journal of Geophysical Research: Earth Surface, 114(2), F02005. https://doi.org/10.1029/2008JF001144
Nelson, P. A., Dietrich, W. E., & Venditti, J. G. (2010). Bed topography and the development of forced bed surface patches. Journal of Geophysical Research: Earth Surface, 115, F04024. https://doi.org/10.1029/2010JF001747

Page 2, line 20: Please consider the following references
Dietrich, W. E., Kirchner, J. W., Ikeda, H., & Iseya, F. (1989). Sediment supply and the development of the coarse surface layer in gravel-bedded rivers. Nature, 340, 215–217. https://doi.org/10.1038/340215a0
Nelson, P. A., Venditti, J. G., Dietrich, W. E., Kirchner, J. W., Ikeda, H., Iseya, F., & Sklar, L. S. (2009). Response of bed surface patchiness to reductions in sediment supply. Journal of Geophysical Research: Earth Surface, 114(2), F02005. https://doi.org/10.1029/2008JF001144
Nelson, P. A., Dietrich, W. E., & Venditti, J. G. (2010). Bed topography and the development of forced bed surface patches. Journal of Geophysical Research: Earth Surface, 115, F04024. https://doi.org/10.1029/2010JF001747

Page 3, line 11. Parenthesis was misplaced. It shoud say ... within a mixture (MacKenzie et al ...)

Page 3, line 13. It should say "is to test"

Page 8, first line. References to Table 1 and 2 are misplaced. It should say Mean slopes are given in Table 1 .... size distribution are shown in Table 2.

Page 8, line 6. Typo It should say 59.3%

Page 8, line 10. Table 5 is used before Table 4.

Page 9, line 2. You need to say something like "For GSDbroad the D50..." Notice that you are later comparing it to GSDNarrow.

Page 11, line 24. "bed material, and load, exerts..." Do you need the first comma ?

Page 15, line 19. There is a strange sentence, currently it says "We see the output Our calculations..." It makes no sense.

Page 26, Table 6. "n" is not defined in the text.

That is all,

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RR by Anonymous Referee #4 (06 Nov 2019)

Suggestions for revision or reasons for rejection

Overall, the authors have done a good job addressing the concerns of the three previous reviewers (of which I am not one) and therefore I recommend minor revisions and a slight restructuring of few paragraphs throughout the text. My opinion of the paper though is a bit more critical and I leave these more critical comments as something for the authors to consider as they move beyond the current manuscript.

A major shortcoming of the manuscript is the reliance on discharge as the governing forcing variable with no measurement of the mobility thresholds of the two different grain size distributions through time. Measuring the system average shear stress and back calculating the threshold from flux measurements would seem to be a critical piece to understanding how variation in discharge relates to grain size mobility. At the very least assessing the particle mobility following the work of Wilcock and Colleagues via a mixed grain size transport equation would provide quantitative assessment of the output. It is not clear that slope really should be the primary variable of concern as the experiments show an adjustment of slope, flow depth, and surface GSD which would suggest that a Shields stress is a more apt term for comparison (transport capacity - Shields stress over the threshold - may be even more relevant). These shortcomings limit the transferability of the results here to other systems or experiments. I am not sure there is much that the authors can do about this so it is left as something to consider for future experiments.

A second potential shortcoming of the experiments is that they were not run to an equilibrium or steady state slope and sediment flux output. The cited models of Lane and Church (from my understanding) are for the final steady state profiles. If allowed to run to steady state the grain size distribution of the sediment bed for GSDbroad would need to coarsen and the slope would steepen in order for the flume system to conserve mass (the lack of bed surface GSD precludes measuring this). This is a standard feature of feed flumes (Parker and Wilcock, 1993; 1995). This equilibrium profile may reflect a more realistic grain size distribution for the standard surface based transport equations, which hinge on the transport capacity (shear stress or shields stress relative to the threshold). One way around some of these issues is the adherence to the experiments only exploring 'adjusting' or 'forming' reaches and not the final state, which I believe is their goal. However, this limits the experiments applicability when discussing concepts developed for or at steady state conditions.

Overall, the experiments are interesting and the exploration of the role of the GSD is a worthwhile endeavor. The experimental results are not quantified in a way to close the loop as to what the variables are that one would need to measure in order to accurately predict average transport rates in these systems. Maybe it is the D84 as suggested, but that could be shown in experiments where these quantities can be measured. While the majority of my major comments are fairly critical, I recommend minor revisions as some of these things cannot be addressed with the current data and the authors have addressed the initial review and made substantial revisions. Within these minor revisions, I hope the authors consider the nuance of the models and frameworks that they are challenging and place their results into a context that adds to those models or paints the boundary conditions of those systems more systematically rather than dismissing them.

Line comments.
Ln. 5 - missing 'the'. '...that the largest'

P. 2, Ln. 25 - It is not clear how the work of Parker (1990) and Wilcock and Crowe relate to channel stability. These works produce surface-based bed load transport relations, to my knowledge these equations have not been connected to a channel with deformable banks (i.e. not a flume). Maybe bed stability is the more apt concept here?

For channel stability these works would only likely be valid through the work of Parker (1978, 1979) and that would require the bed to be run to equilibrium under sediment feed conditions at which point (like a fixed wall flume) the coarse grains (if sufficiently less mobile to begin with) could accumulate to build a channel in which they can be transported and changing the grain size distribution. Otherwise it is hard to understand how mass would balance.

P. 3, Ln. 7-20. Could you provide an analogue for what you mean by an aggrading system? Fans are mentioned, but it is not clear how this experimental set up recreates those conditions. In the experiments by Delorme et al. (2017) for a bimodal system two fans were created, a coarse one and a fine one which is similar to many fan profiles. Why wouldn't your system simple recreate this phenomena given sufficient time and space? Is this just an aggrading reach then, because there are no downstream effects which are important for fans. The experiments of Guerit et al stop when they reach the outlet, because deposition is a key feature of fans and at the outlet their experiment becomes a steady state profile.

Due to the name change of the GSDs the video titles no longer match the manuscript. You might just add a line in the manuscript that says (GSDnarrow = GSD2), and same for the broad one as well where the videos are first mentioned this way the videos online don't need to be changed. They are neat to watch.

P. 9, Ln. 1. feed load instead of fed load? Also in line 6, missing an 'L' in overall.

Equations 4 & 5. Could you report the actual values that were calculated rather than just the percent differences? Or put them in one of the tables? One set of these is in a table, but it would be worthwhile to report them in the text as well.

P. 13, Ln. 5-10. This is a straw man argument, that doesn't benefit the paper's key results. Equal mobility is only valid in some cases, the many papers of Wilcock and colleagues (cited within the manuscript) demonstrate partial mobility and fractional transport are likely the norm at low shear stresses. Additionally, the work of Paola and Seal (1995) on particle sorting demonstrate that the tails of the reach GSD can't follow equal mobility in order for sorting profiles to occur (even under an aggrading system sorting can still occur following the experiments of Delorme et al. 2017 as an example)

P. 14, Ln. 6-8. This statement requires evidence or citations, I only say this because the data exist to prove this so the speculation here isn't particularly useful. As far as I have seen, fans tend to have strong sorting profiles such that the upper reaches are coarse and become finer downstream.

P. 14, Ln. 10. In my opinion this is not a particularly nuanced discussion of the models proposed by Lane or Church, which from my reading are implicitly for the equilibrium profile following the adjustment phase. The current experimental systems are stopped when the system runs out of sediment as determined by availability constraints (?) (is this just a logistical issue?). At equilibrium the model may actually match much closer to that of church, b/c at equilibrium or steady state the slope will reflect that needed to transport the coarse grains and the bed will have to reflect a coarser size distribution. This is a basic feature of feed flume systems (see Parker and Wilcock, 1993; 1995)

P. 16, Ln. 8. I am having a hard time following the the channel geometry arguments as there is no analysis of channel geometry within the manuscript, nor are their banks within the flume which seem like a prerequisite feature for understanding channel geometry.

P. 16, Ln. 16. Coarse-grained natural systems seem to be limited to a range of 1 to ~7 in terms of the shear stress relative to the reference threshold shear stress (Phillips & Jerolmack, 2016). This would support the lower discharge claim, but it is also not clear what the actual shear stress range relative to be mobility is within this system.

P. 16, Ln. 24. The entire flume width is not submerged, this is the expected behavior in a flume or a very confined stream table type of experiment which this may be more analogous to.

New references cited within the review provided for convenience (the authors need not feel obligated to cite these)
Delorme, P., Voller, V., Paola, C., Devauchelle, O., Lajeunesse, É., Barrier, L., & Métivier, F. (2017). Self-similar growth of a bimodal laboratory fan. Earth Surface Dynamics, 5(2), 239–252. https://doi.org/10.5194/esurf-5-239-2017

Paola, C., & Seal, R. (1995). Grain-Size Patchiness as a Cause of Selective Deposition and Downstream Fining. Water Resources Research, 31(5), 1395–1407. https://doi.org/10.1029/94WR02975

Parker, G., & Wilcock, P. R. (1993). Sediment Feed and Recirculating Flumes: Fundamental Difference. Journal of Hydraulic Engineering, 119(11), 1192–1204. https://doi.org/10.1061/(ASCE)0733-9429(1993)119:11(1192)

Parker, G., & Wilcock, P. R. (1995). Closure to “Sediment Feed and Recirculating Flumes: Fundamental Difference” by Gary Parker and Peter R. Wilcock. Journal of Hydraulic Engineering, 121(3), 293–294. https://doi.org/10.1061/(ASCE)0733-9429(1995)121:3(293)

Phillips, C. B., & Jerolmack, D. J. (2016). Self-organization of river channels as a critical filter on climate signals. Science, 352(6286), 694–697. https://doi.org/10.1126/science.aad3348

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ED: Publish subject to minor revisions (review by editor) (14 Nov 2019) by Jens Turowski

AR by William Booker on behalf of the Authors (23 Nov 2019) Author's response Manuscript

ED: Publish subject to technical corrections (25 Nov 2019) by Jens Turowski

ED: Publish subject to technical corrections (28 Nov 2019) by Tom Coulthard (Editor)

AR by William Booker on behalf of the Authors (03 Jan 2020) Author's response Manuscript

Short summary

Using experiments, we found that the form and behaviour of a river depends on its ability to move the larger of its constituents. The manner in which all particles move depends upon the rate and calibre of the supplied material, as well as the rate of supplied water. This goes against the prevailing theory of a single important and representative grain size under depositing conditions, and these results may alter how we interpret river deposits to explain their formation.