A Steady-State Model to Simulate Groundwater Flow in Unconfined Aquifer
Round 1
Reviewer 1 Report
The authors present a numerical groundwater flow model that reproduce the hydraulic head distribution in the potential recharge area of the Caposele karst spring (Southern Italy).
Although such a study might be of interest for hydrogeological community, in my opinion, the authors fail to reach their goal. Several main issues are present in the article and in particular:
1) The introduction section is quite confused. The authors describe MOFLOW as the best tool, but forget to mention CFP (Conduit Flow Process) package for MODFLOW. A package specifically designed to simulate turbulent flow inside karst conduits. A MODFLOW model implemented without the use of this package for simulate groundwater flow in a karst aquifer is necessarily realized using the EPM (equivalent porous medium) approach. This should be further highlighted, describing and clarifying the types of approaches available to simulate groundwater flow in this type of aquifers.
2) Also the "materials and methods" section is quite confused and poorly organized. I encourage the authors to rewrite this section focusing on the model implementation phases and describing the used parameters, without unnecessary repetitions.
3) Personally, I think that a DRAIN package (3rd boundary type) associated with a high value of conductance would have been more appropriate to reproduce the spring discharge (e.g. Scanlon et al). Drains remove water from the aquifer as long as the water table is above the elevation of the drain. If the water table falls below the elevation of the drain, the drain has no effect. The first type boudary contidion (CONSTANT HEAD) is used to fix the head value in selected grid cells regardless of the system conditions in the surrounding grid cells, thus acting as an infinite source of water entering the system, or as an infinite sink for water leaving the system. Therefore, constant head bc can have a significant influence on the results of a simulation, and may lead to unrealistic inflow from the spring during the running phase.
4) Another point that doesn't convince me is that the authors outline a conceptual model in which recharge takes place in preferential areas, then they implement a model in which recharge is constant over the whole model domain.
5) The calibration process proposed by the authors is quite weak. They use a single hydraulic head value, located 400 m upstream of a first type boundary condition, to infer the hydraulic conductivity of an area of about 110 km2. In addition to this, they use a type of boundary condition that strongly constrains the solution, without worrying about whether it acts correctly (see point 3 above).
6) The discussion suffers in my opinion from the fact that too many results are repeated and the discussion is not at all critical on the used methods and interpretation.
7) What is the novelty of the approach proposed? The authors describe a procedure standard to numerical model implementation, with several and severe simplification due to the type of aquifer simulated.
The impact of this manuscript is actually too restricted to justify acceptance of this paper.
I would like to encourage the authors to better refine in a future contribution the modeling phase and to enlarge their literature survey on this argument, as well as to emphasize the key learning from their research.
Specific comments on the text are reported in the attached pdf.
Comments for author File: 
Comments.pdf
Author Response
All the revisions are pointed out in the attached file
Author Response File: 
Author Response.docx
Reviewer 2 Report
Suggestions:
This is a very interesting research topic. The groundwater numerical flow model of the Caposele Karst aquifer is also very important for local village people water supply. Your research was focused on flow simulations on this aquifer. You have explained details in all sections, but you need to make it more clear and concrete to improve the manuscript.
Develop:
Abstract: Don’t make two sections in Abstract, merge them and make clearer.
Figure 6: If possible, remove the figure, this is the normal processes for numerical simulations.
Line 375: Please change the name “Particularly trial and error method”.
Methods and results: Please both sections re-structure. Under Methods keep methods and study areas, and all are results should be explained in the result section (Ex. Figure 5, 7, 8 & 9).
Author Response
All revisions are pointed out in the attached file
Author Response File: Author Response.docx
Reviewer 3 Report
In the paper a steady state modeling (by MODFLOW numerical code) of groundwater flow in some approximations is carried out. The principal fact is that the results was calibrated on borehole data available in 2011-2019. The simulation was applied to Caposele aquifer in Southern Italy, taking into account the hydraulic and hydrogeological features for the relationship between the recharge area and discharge zone of the spring catchment with different groundwater path. For the aquifer saturated zone the model was run for different depth.
As a minor suggestion, I believe, it should be reasonable to discuss brieflythe limitations of considered approach. In Physics – there are, first, the principal role of boundary for porous like media conditions, and, second, the Darcy law application. In modeling – the advantages of the analysis by other procedures, e.g. by diffusion process (SIR – Susceptible Infected Removed) under the cellular automata technique. Especially,such comparison is necessary for the complex 3D-topoplogy of the Karst medium for the transient conditions scenarios.
Conclusion. The paper is good for publication with some minor discussion in accordance with above comments,preferable.
Author Response
Please you can find in attachment the revisions
Author Response File: Author Response.docx
Reviewer 4 Report
Authors present a paper presenting a model to simulate the flow of underground water in a karstic aquifer, exemplifying in Caposele aquifer. The methodologies used are widely known and they are well explained, but I think it has proper quality to be published in Applied Sciences and I would suggest a minor revision of the work. Here are my suggestions:
- Authors include some results in section “Materials and Methods”. For instance, they use generic models to exemplify the methodologies applied (Figures 1-3). In my opinion this leads to confusion and I think the section should be explained in other way. Moreover, I understand that modelling of top and bottom layers of the aquifer (Figure 8) and also 9 should were modelled by authors, so they should also be moved to results section.
- Karstic aquifers present a high heterogeneity that affect the flow variables. Especially discharging/recharging or underground velocity. In this work the karst of the Caposele aquifer is not properly described and the model simulations seem too regular. A figure and an explanation including the areas that are more affected by the karst would be optimal.
- Authors say the model is validated but they don't present results according to it. Include the validation of the model.
- Discussion section is felt like an extension of the results. Please, include more comparisons of similar karstic aquifers not only in Italy but also in the world and provide proper references in similar areas to give a proper discussion. The work is interesting, but the way it is currently written it is felt like a report.
- Variables are unexplained in some equations.
- Reference 55 (line 808) is missing.
Author Response
All revisions are listed in the attached file
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
I appreciate the effort of the authors in revising the text, but I still think that the impact of the manuscript is too restricted to justify its acceptance. In particular, I still disagree with the use of a first type boundary condition for the spring outflow simulation.
Author Response
Please you can find in attachment the answers file
Author Response File: Author Response.docx
