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Article
Peer-Review Record

Using Freshwater Heads to Analyze Flow Directions in Saline Aquifers of the Pingtung Plain, Taiwan

Water 2021, 13(24), 3491; https://doi.org/10.3390/w13243491
Reviewer 1: Chiu-Shia Fen
Reviewer 2: Anonymous
Water 2021, 13(24), 3491; https://doi.org/10.3390/w13243491
Received: 25 October 2021 / Revised: 1 December 2021 / Accepted: 2 December 2021 / Published: 7 December 2021
(This article belongs to the Special Issue Coastal Aquifers: Seawater/Saltwater Intrusion)

Round 1

Reviewer 1 Report

This manuscript presents a practice to assess sea water intrusion problem for the aquifer system of the Pingtung Plain, Taiwan.  The authors used the freshwater head analysis to illustrate the deviation of horizontal groundwater flow direction from those assessed by point hydraulic head measured in the field.  They also present EC measurements in different depths and in different seasons and argue that EC logging with a month interval is necessary for those variable-density aquifers.  I think this manuscript is lack of depth in the analysis and needs to be modified in several aspects.  I point out some problems I found and give suggestions:

  1. Why were the 2012 well observed data analyzed in this study? I expect to see analysis of the data in the most recent year or the situation of the deteriorated groundwater quality of the aquifer system for the past years.
  2. Sections 2 and 3 have the same title. These two sections need to be focused on separate points, e.g., different aquifers, temporal variations of head contours in a specific aquifer.
  3. 6(B) can be removed because it is the same as Fig. 7(D).
  4. 8(A) and 8(B) have pictured the trends of the observed hydraulic heads and freshwater heads. Table 4 which shows the data of these figures can be removed.
  5. In section 5, the vertical EC profiles presented in Figs. 9 and 10 were based on the measurements in wells KT and TK at different depths.  However, these measurements are representative of EC value of groundwater in different aquifers as presented in Fig. 3.  It is wrong to use these vertical EC profiles to justify density variations of a water column observed in a well located in a single aquifer.

 

Author Response

Reviewer 1

  1. Why were the 2012 well observed data analyzed in this study? I expect to see analysis of the data in the most recent year or the situation of the deteriorated groundwater quality of the aquifer system for the past years.

RESPONSE: The latest EC survey by using an EC probe for all 134 observation wells was in 2012.

 

  1. Sections 3 and 4 have the same title. These two sections need to be focused on separate points, e.g., different aquifers, temporal variations of head contours in a specific aquifer.

RESPONSE: The title of the Section 4 has been corrected as “Flow history along the profile TK-CC”.

 

  1. 6(B) can be removed because it is the same as Fig. 7(D).

RESPONSE: Fig. 7(D) is removed.

 

  1. 8(A) and 8(B) have pictured the trends of the observed hydraulic heads and freshwater heads. Table 4 which shows the data of these figures can be removed.

RESPONSE: Table 4 is removed.

 

  1. In section 5, the vertical EC profiles presented in Figs. 9 and 10 were based on the measurements in wells KT and TK at different depths.  However, these measurements are representative of EC value of groundwater in different aquifers as presented in Fig. 3.  It is wrong to use these vertical EC profiles to justify density variations of a water column observed in a well located in a single aquifer.

RESPONSE: The EC values in Fig. 3 are from different wells. For example, there are four wells at the TK site.

Reviewer 2 Report

Review for Water 1455764-V1

The manuscript converted the measured hydraulic heads to freshwater heads to analyze flow directions in saline aquifers of the Pingtung Plain, Taiwan. Although the methodology is not innovative, the analysis is still necessary and can provide better management decision-making. It is well written and ready for publishing with minor revision although some detailed information may be not necessary for a technical paper.

 

Minor comments:

Introduction

Line 36, please define SEAWAT explicitly.

Line 51-58, the fundamental equation is defined here without reference. Is this the methodology developed by the study?

The objective of the study is preferring to be specified clearly in the introduction.

 

Distribution of saline groundwater

Table 4 and Figure 8 have repeated information, which is not recommended for publication. Figure 8 A and B can be combined to demonstrate the comparison better.

EC values within observation wells

Figure 10, three lines are during the dry season and only one line is represented the rainy season. The lines for February and April are almost identical and very close to the line in June. The summary drawn from this Figure is questionable.

Author Response

x

Reviewer 2

Introduction

  1. Line 36, please define SEAWAT explicitly.

RESPONSE: Revised. Lines 37-39.

  1. Line 51-58, the fundamental equation is defined here without reference. Is this the methodology developed by the study?

RESPONSE: References added. Line 54.

  1. The objective of the study is preferring to be specified clearly in the introduction.

 RESPONSE: The objective of our study is in Lines 62-65: present a case study for using the “equivalent freshwater head (Hfi)” instead of an “observed hydraulic head” for analyzing the flow paths of saline groundwater within the coastal Pingtung Plain, Taiwan. We also provide recommendations for water level data collection from a saline groundwater area.

 

Distribution of saline groundwater

  1. Table 4 and Figure 8 have repeated information, which is not recommended for publication. Figure 8 A and B can be combined to demonstrate the comparison better.

RESPONSE: Table 4 is removed. Figure 8 A and B are combined.

 

EC values within observation wells

  1. Figure 10, three lines are during the dry season and only one line is represented the rainy season. The lines for February and April are almost identical and very close to the line in June. The summary drawn from this Figure is questionable.

RESPONSE: Revised. Lines 231-232. Values were higher during the dry season (Feb 2021) and lower during the rainy season (Sep 2020).

Round 2

Reviewer 1 Report

I don't think the authors clearly answered my questions for no. 1 and 5:

1. I expect to see analysis of the data in the most recent year or the situation of the deteriorated groundwater quality of the aquifer system for the past years (2012 and later).

5.Are the EC profiles in Figs. 9 and 10 obtained for aquifer F3-1 and F3-2, respectively?  I think it is not proper to use these vertical EC profiles to justify density variations at different depths (0 to 150 m or 0-200 m) of these aquifers. 

Author Response

  1. I expect to see analysis of the data in the most recent year or the situation of the deteriorated groundwater quality of the aquifer system for the past years (2012 and later).
    RESPONSE: A new figure (Fig. 7) is added. The figure 7 shows groundwater EC (µS/cm at 25℃) in the F3-2 during 2004-2019. The area marked by a red dashed line represents a saline area in which ECs were > 1500 µS/cm.

  2. Are the EC profiles in Figs. 10 and 11 obtained for aquifer F3-1 and F3-2, respectively?  I think it is not proper to use these vertical EC profiles to justify density variations at different depths (0 to 150 m or 0-200 m) of these aquifers. 

RESPONSE: The EC profiles in Figs. 10 and 11 are used for freshwater heads calculation (Fig.1 and Eq.1). Those vertical EC profiles show density variations at different depths (0 to 150 m or 0-200 m) within observation wells. Those data are important for freshwater head calculation.

Round 3

Reviewer 1 Report

I still think it is not proper to plot the vertical EC profiles  in Figs. 10, 11 for data obtained from different aquifers to justify density variations at different depths (0 to 150 m or 0-200 m).  Because these data are obtained for different aquifers.

I give suggestions for this two figures:

  1. don't use  line  to connect these EC values for a well, just indicate EC values with symbol in these figs.
  2. The titles of these figures need to be modified : they are well TK and KT for fig 10 and well TK for Fig 11.
  3. carefully correct the arguments in text for these figures

Author Response

I still think it is not proper to plot the vertical EC profiles in Figs. 10, 11 for data obtained from different aquifers to justify density variations at different depths (0 to 150 m or 0-200 m).  Because these data are obtained for different aquifers.

I give suggestions for this two figures:

  1. don't use line to connect these EC values for a well, just indicate EC values with symbol in these figs.
  2. The titles of these figures need to be modified: they are well TK and KT for fig 10 and well TK for Fig 11.
  3. carefully correct the arguments in text for these figure

 

RESPONSE: Figure 3 is revised. For example, there are four wells, TK1 to TK4 at the TK site. Lines 217-223 are also revised. The EC values in Figs. 10, 11 are from EC logging, not from pumping and sampling. The titles of these figures are modified: Figure 10. Vertical EC logging values within wells KT2 and TK3 on 19 July 2021. Figure 11. Vertical EC logging values within well TK4 during 2020-2021. The EC profiles in Figs. 10 and 11 are used for freshwater heads calculation (Fig.1 and Eq.1). Those vertical EC logging profiles show density variations at different depths (0 to 150 m or 0-200 m) within observation wells (not obtained from different aquifers). Those data are important for freshwater head calculation.

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