Fresh groundwater resources in a large sand replenishment

Huizer, Sebastian; Oude Essink, Gualbert H. P.; Bierkens, Marc F. P.

doi:https://doi.org/10.5194/hess-20-3149-2016

Articles | Volume 20, issue 8

https://doi.org/10.5194/hess-20-3149-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-20-3149-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 20, issue 8

Research article

|

04 Aug 2016

Research article |

| 04 Aug 2016

Fresh groundwater resources in a large sand replenishment

Sebastian Huizer, Gualbert H. P. Oude Essink, and Marc F. P. Bierkens

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Final revised paper (published on 04 Aug 2016)
Preprint (discussion started on 19 Jan 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review', Anonymous Referee #1, 08 Feb 2016
- AC2: 'Reply to Referee 1', Sebastian Huizer, 04 Apr 2016
RC2: 'HESS2016-5', Anonymous Referee #2, 09 Feb 2016
- AC3: 'Reply to Referee 2', Sebastian Huizer, 04 Apr 2016
RC3: 'Review of 'Fresh groundwater resources in a large sand replenishment'', Anonymous Referee #3, 26 Feb 2016
- AC1: 'Reply to Referee 3', Sebastian Huizer, 31 Mar 2016

Peer-review completion

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

ED: Reconsider after major revisions (20 Apr 2016) by Insa Neuweiler

AR by Sebastian Huizer on behalf of the Authors (31 May 2016)

ED: Referee Nomination & Report Request started (02 Jun 2016) by Insa Neuweiler

RR by Anonymous Referee #2 (03 Jun 2016)

RR by Anonymous Referee #1 (07 Jun 2016)

Suggestions for revision or reasons for rejection

Paper Review for Hydrology and Earth System Sciences

Authors Huizer et al. have submitted the revision 1 of their manuscript (ms) entitled “Fresh groundwater resources in a large sand replenishment” to Hydrology and Earth System Sciences.

The changes made by the authors have improved the ms. Nevertheless, there are still three points that need to be addressed more rigorously as discussed below. The numerical numbers refer to my original comments.

1. Appendix A. The grid convergence test is now somewhat clearer but some questions remain unanswered and some deficiencies persist. In general, the wording in Appendix A is in some ways complicated. For example, why don’t you simply list the spatial and temporal discretization schemes in a simple table, so that the reader has a quick overview of all simulations you ran to attain grid convergence? Also, it must be clearly stated that different time-step sizes were not tested because apparently, the time-step size is always Courant number controlled. So strictly speaking, convergence of the solution with regard to temporal discretization is not shown. L6f: Here, you are using the term implicit and GCG in the same phrase, but the two have nothing to do with each other. “Implicit” denotes a time weighting scheme, and “GCG” is a type of matrix solver. It appears here that the authors are erroneously using numerical terms.

The same applies to L23ff: It appears that “explicit coupling” and “implicit coupling” are ill-used. Physically coupled processes (like flow and transport) can in fact be explicitly coupled, which is called a sequential iterative approach. In this case, coupled equations are solved independently from each other, but they are coupled through equations of state. Physically coupled processes can also be implicitly coupled, which is called a one-step or direct approach. In that case, coupled equations are in fact solved in a single step, requiring a single system matrix where the entries contain contributions of both coupled and disretized equations. I do not believe that this is what the authors mean because different software packages are used and because the underlying equations are probably unknown. I think by “explicit coupling” or “implicit coupling”, the authors simply mean that the underlying time-weighting scheme is explicit or implicit. But this is something totally different, and it has nothing to do with the coupling scheme of the equations! The authors should re-think all this, and correctly formulate the numerical details in the ms accordingly.

Also, results from Fig. A1 do not convincingly show that grid effects are excluded. A grid convergence test requires a criterion, for which error the result has converged, and thus, which grid is then selected. That criterion is not discussed and an error analysis is absent. Grid convergence is therefore not shown. This must be improved.

5. Section 3.3 somewhat clarifies the deformation story, but not entirely. I understand that this ms will be read mostly by modelers who will understand terms like “re-meshing” or “grid deformation”. I think these terms more appropriately describe your numerical approach.

6. Section 4.1 still does not clearly state that the transient model is uncalibrated. For scientific integrity, this must be said.

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ED: Publish subject to minor revisions (Editor review) (16 Jun 2016) by Insa Neuweiler

AR by Sebastian Huizer on behalf of the Authors (26 Jun 2016) Author's response Manuscript

ED: Publish as is (04 Jul 2016) by Insa Neuweiler

AR by Sebastian Huizer on behalf of the Authors (13 Jul 2016)

Short summary

The anticipation of sea-level rise has led to an innovative project called the Sand Engine, where a large volume of sand was placed on the Dutch coast. The intention is that the sand is redistributed by wind, current and tide, reinforcing coastal defence structures. Model simulations show that this large sand replenishment can result in a substantial growth of fresh groundwater resources. Thus, sand replenishments could combine coastal protection with an increase of fresh groundwater resources.