Impacts of Artificial Regulation on Karst Spring Hydrograph in Northern China: Laboratory Study and Numerical Simulations
Round 1
Reviewer 1 Report
In the submitted manuscript „Impacts of Artificial Regulation on Karst Spring Hydrograph in the Northern China: Laboratory Study and Numerical Simulations“, Wu et al present an analysis that deals with the assessment of anthropogenic changes on karst aquifer dynamics using physical lab-scale model and a numerical model of a real karst system in Northwest China. For their two models, they develop a series of anthropogenic pumping scenarios and they show how the different parts of the recession after recharge events change for the different scenarios.
The study provides some very interesting insights into karst recession that were hardly measurable in a real system as the application of pumping and injection scenarios is almost impossible. For that reason, I believe that the presented study is a valuable contribution for Water Journal. However, some more elaboration especially on the downscaling to the lab experiment and the transferability of the findings to real karst system is necessary.
Physical models have the great advantage of trying out different scenarios and measuring all possible changes inside the system. The problem is whether scale and hydraulic properties are adequately chosen to reflect the real system. It would be helpful if the authors would discuss this problem in section 2.2 and provide some justification why their setup is a good approximation of the real system.
In particular, when it comes to turbulent flow condition, the scale matters a lot. In the real system, turbulent flow in the conduits may be much more pronounced compared to the downscaled system in the lab. Please discuss this in an adequate way.
The discussion interprets well the results but some discussion on the uncertainties and assumptions that go along with downscaling the real system into a lab-scale experiment would be helpful. Also, the other way around, it is important to discuss how these results can be up-scaled again to the real system and how such approach could be also transferred to other systems.
Some more specific and technical remarks are provided in the attached pdf. I am sure that the others can address these concerns and I am looking forward to reading a revised version of the paper.
Comments for author File: 
Comments.pdf
Author Response
Main questions:
In the submitted manuscript, Impacts of Artificial Regulation on Karst Spring Hydrograph in the Northern China: Laboratory Study and Numerical Simulations“, Wu et al. present an analysis that deals with the assessment of anthropogenic changes on karst aquifer dynamics using physical lab-scale model and a numerical model of a real karst system in Northwest China. For their two models, they develop a series of anthropogenic pumping scenarios and they show how the different parts of the recession after recharge events change for the different scenarios.
The study provides some very interesting insights into karst recession that were hardly measurable in a real system as the application of pumping and injection scenarios is almost impossible. For that reason, I believe that the presented study is a valuable contribution for Water Journal. However, some more elaboration especially on the downscaling to the lab experiment and the transferability of the findings to real karst system is necessary.
Physical models have the great advantage of trying out different scenarios and measuring all possible changes inside the system. The problem is whether scale and hydraulic properties are adequately chosen to reflect the real system. It would be helpful if the authors would discuss this problem in section 2.2 and provide some justification why their setup is a good approximation of the real system.
In particular, when it comes to turbulent flow condition, the scale matters a lot. In the real system, turbulent flow in the conduits may be much more pronounced compared to the downscaled system in the lab. Please discuss this in an adequate way.
The discussion interprets well the results but some discussion on the uncertainties and assumptions that go along with downscaling the real system into a lab-scale experiment would be helpful. Also, the other way around, it is important to discuss how these results can be up-scaled again to the real system and how such approach could be also transferred to other systems.
Some more specific and technical remarks are provided in the attached pdf. I am sure that the others can address these concerns and I am looking forward to reading a revised version of the paper.
Response:
Thank you for your kindly comments. Just as we know, karst aquifers are characterized by extreme heterogeneity due to the presence of karst conduits with higher hydraulic conductivity and the surrounded matrix with a much lower hydraulic conductivity [1, 2], which can lead to well-known permeability scale effects [3]. Some karst areas, such as Sete Lagoas aquifer in Brazil[3], Edwards Aquifer located in the United States[4] and Juras Mountain in Switzerland[5], have increases in permeability in scale effects from small- to regional-scale. The nature of the hydrogeological responses of karst catchments is scale dependent due to the scale dependence of hydrogeological parameters [6]. Hydrogeological processes occur at a wide range of scales are a central topic in hydrology, within which the uncertainties of results at a certain scale is fundamental. For example, wang et al. [7] found that both soil nutrient variations and the determinant factors involved varied with scale in a karst area. Wood et al. [8] noticed that runoff production changes with spatial scale while the variance of runoff reduces as the scale increases. Chen et al.’s [6] results showed that runoff depth (or runoff coefficient) decreases with increasing scale. Field studies, at the same time, are hampered by a scarcity of data, e.g. a limited resolution of measurements, the interference of simultaneously occurring processes and the difficulty of quantifying heterogeneity at different scales [9]. For these reasons, in this study, lab-scale tank model and the corresponding numerical simulation model were not established for the purpose of reflecting the medium structures and hydraulic properties of the real system strictly with a downscaled system in the lab. Which is also not achievable. Here, the study was carried out to get insight of the variation of hydrological processes in heterogeneous anisotropic dual medium under the driven of artificial regulations according to the groundwater circulation in Jinan city. Where the groundwater is recharged by precipitation in south mountain zones, flowing through the conduits and fissures medium, and then discharged in the way of ascending springs in the city areas. (Line 422-444 in the tracked version)
Some more specific and technical remarks:
1、Line 61: references
Response: The reference provided by the reviewer has been added to the revised version (Line 61 in the tracked version).
2、Line 80: references
Response: The reference provided by the reviewer has been added to the revised version (Line 80 in the tracked version).
3、Line 88 and 91: language questions.
Response: The “aquifer management program” has been changed with “The aquifer management program” (Line 88 and 91 in the tracked version).
4、Response: Some justifications about the set of lab-experiments have been provided in the revised version (Line 152-155 in the tracked version).
5、Will the degree of turbulent flow agree with the dynamic that take place in the real system?
Response: In the fact, conduit flow is mainly laminar flow in this study, which is also proved by the verification results of NuRe and NlRe.
6、Language question.
Response: The “thickness of distance spacers” has been changed with “thickness of distance spacer” (Line 261 in the tracked version).
7、Spelling mistake
Response: The “regelation” has been changed with “regulation” (Line 411 in the tracked version).
8、Response: Results only shown for this experiment have been pointed out in line 462 in the tracked version.
9、Line 431: the “changing world” is “changing boundary conditions”？
Response: The “changing world” here means the world driven by human activities (Line 466 in the tracked version).
10、“Stagnation points” is not clear here.
Response: “Stagnation points” has been described here in the tracked version (Line 476-477).
11、Provide some outlook on possible future work.
Response: Some possible future works have been pointed out in the revised version. (Line 534-538 in the tracked version)
Reference:
[1] Hartmann A, Baker A. Modelling karst vadose zone hydrology and its relevance for paleoclimate reconstruction[J]. Earth-Science Reviews. 2017, 172: 178-192.
[2] Borghi A, Renard P, Cornaton F, et al. Can one identify karst conduit networks geometry and properties from hydraulic and tracer test data[J]. Advances in Water Resources. 2016, (90): 99-115.
[3] Galvao P, Halihan T, Hirata R. The karst permeability scale effect of Sete Lagoas, MG, Brazil[J]. Journal of Hydrology. 2016, 532: 149-162.
[4] T. Halihan, Sharp Jr., J.M., Mace, R.E., 2000. Flow in the San Antonio Segment of the Edwards Aquifer: Matrix, Fractures, or Conduits? In: Wicks, C.M., Sasowsky, I.D. (Eds.), Groundwater Flow and Contaminant Transport in Carbonate Aquifers. Balkema, Rotterdam, the Netherlands, Pp. 129–146.
[5] L. Király, 1975. Rapport Sur L'état Actuel Des Connaissances Dans Le Domaine Des Caractères Physique Des Roches Karstique. In: Burger, A., Dubertet, L. (Eds.), Hydrogeology of Karstic Terrains. International Association of Hydrogeologists, Paris, Pp. 53–67, Series B, No. 3.
[6] Chen L, Sela S, Svoray T, et al. Scale dependence of Hortonian rainfall-runoff processes in a semiarid environment[J]. Water Resources Research. 2016, 52 (7): 5149-5166.
[7] Miaomiao Wang, Hongsong Chen, Wei Zhang, et al. Influencing factors on soil nutrients at different scales in a karst area[J]. Catena. 2019, 175: 411-420.
[8] Wood E F, M Sivapalan, K Beven, et al. Effects of spatial variability and scale with implications to hydrologic modeling,. 1988, Journal of hydrology (102): 1-4.
[9] Houben G J, Stoeckl L, Mariner K E, et al. The influence of heterogeneity on coastal groundwater flow - physical and numerical modeling of fringing reefs, dykes and structured conductivity fields[J]. Advances in Water Resources. 2018, 113: 155-166.
Author Response File: 
Author Response.docx
Reviewer 2 Report
My comments are in the attached file. I especially focused on the modeling approach, the results are difficult to interpret as the modeling approach is not clear. The authors may indicate which CFP module they used, there are 2 and there is a big difference between them. Calibration table may absolutely Indicate the parameters used. Also, the authors may discuss the values used. Such modeling approach have been already done. Please highlight on your contribution (something new, that was not done that way).
Comments for author File: Comments.pdf
Author Response
Main questions:
My comments are in the attached file. I especially focused on the modeling approach; the results are difficult to interpret as the modeling approach is not clear. The authors may indicate which CFP module they used, there are 2 and there is a big difference between them. Calibration table may absolutely Indicate the parameters used. Also, the authors may discuss the values used. Such modeling approach have been already done. Please highlight on your contribution (something new, that was not done that way).
Response:
Following your kindly comments, the manuscript has been revised carefully, especially the methods section. We are sorry for not describing the methods clearly in the former version. The CFPM1 (Line 214 in the tracked version) was used for our simulations and something wrong in the calibration results have also been revised in this version. Furthermore, our contribution has been highlighted (Line 499-502 in the tracked version).
Some more specific and technical remarks:
1 Wrong numbering in Table 1.
Response: the wrong numbering in scenario B has been changed with “B12”.
2 Only on the unconfined portion of the aquifer. No flow boundary condition on the top of the confined aquifer.
Response: Neumann-Type boundary was set for the unconfined aquifer surface (Line 198 in the tracked version).
3 remove "is the".
Response: the “is the” has been removed in the revised version (Line 206 in the tracked version).
4 mistakes in the equation.
Response: It should be a square diameter and not diameter at the power of 4 (Line 225 in the tracked version).
5 Why two calibration phases? one on scenario B at W4 and after on the hydraulic heads and spring hydrograph for the scenario B.
Response: Actually, the variation of hydraulic heads when injected at W4 in scenario B were used for the calibration (Line 245, 248 and Fig. 5 in the tracked version).
6 which observation wells are represented on this figure.
Response: Observation wells have been pointed out in the revised version (Fig 5).
7 need to give some explanation of the variables.
Response: explanation of the variables has been given in the revised version (Table 2).
Author Response File: Author Response.docx
Reviewer 3 Report
I’ve found this as an interesting paper that is focused on the problem of laboratory tests of karst spring hydrograph being supported by numerical model in karst area of northern China. Karst areas are always of extreme caution in the assessment of water resources security that’s why each new concept can have meaning. A monoclinic structure of the Jinan karst aquifer system has been recreated using a physical model composed of karst medium, precipitation system, hydraulic head and spring flow monitoring system. And several scenarios were performed taking into account as well pumping as injection settings. A corresponding numerical models with a single conduit surrounded by low permeability a 2-D fissure zone were considered. Moreover a linear or turbulent flow has been considered in cylindrical conduits including the Colebrook-White equation. So methodically this is a very right approach. Results of the models after calibration are presented in several figures of calculated spring hydrographs with recession curves analysis. The variation of groundwater flow dynamics for different scenarios is described as well.
The sub-section 2.1 Field investigation should be titled as Description of study area or even include in the introduction, but not in Methodology section.
In the fig. 2 as impermeable rocks is pattern of sands (if alluvia?-so should be permeable)
Some minor shortcomings can be found like:
In the fig. 3 the marks (b) (c) & (d) are shifted to the wrong places
Line 160 Flow with a lowercase letter
Line 487 ....fissure zone are totally different....
The paper is clearly written, with sufficient explanation of the methods. The problem was solved and the conclusions are properly presented. All the references are sufficient and cited in the paper.
Author Response
Main questions:
1 The sub-section 2.1 Field investigation should be titled as Description of study area or even include in the introduction, but not in Methodology section.
Response: Description of study area has been set as a separate part in the revised version (Line 112 in the tracked version).
2 In the fig. 2 as impermeable rocks is pattern of sands (if alluvia?-so should be permeable)
Response: Impermeable rocks in Fig.2 is magmatic rock. (Line 169 in the tracked version)
3 In the fig. 3 the marks (b) (c) & (d) are shifted to the wrong places.
Response: Marks have been revised in the tracked version.
4 Line 160 Flow with a lowercase letter
Response: “Flow” has been changed with “flow” in the tracked version (Line 166 in the tracked version).
5 Line 487 ....fissure zone are totally different....
Response: “are” has been added here (Line 526 in the tracked version).
Round 2
Reviewer 2 Report
It seems that the paper has been revised according to my comments.
Best regards
