Simulation of Groundwater Flow Dynamics under Different Stresses Using MODFLOW in Rechna Doab, Pakistan

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Review Report: “Groundwater Modeling for Spatial and Temporal Analysis of Groundwater flow dynamics in Rechna Doab, Pakistan.” by Awais et al.,

• A brief summary 

With the objective of understanding future groundwater use and trend in water level change, a three-dimensional groundwater simulation is performed for steady and transient condition. The model was calibrated and validate with observed water level data. Furthermore, the model output is used for three scenarios considering changing in climate condition and pumping condition to foresee the and predict the impact of change in water level in the Recha Doab watershed Pakistan. The author recommended the management practice based on three scenarios. It is also a good practice to put the limitation of the research work.

• Broad comments 

The title should be clear and depicting the result output. The authors need to modify the title of the paper to match the outcome of their results. The abstract need to modify in a way ease explain the research question. Try to avoid abbreviations, if necessary please explain the meaning of the abbreviations at first uses. One of my concern is that the authors recommended a water management scenario where the author compared the result with current conditions and historical trend of pumping conditions. What is the critic to select this? because, the business as usual case, showed the lowest water level change range compared to other two scenarios. Two comment I have is (1) please be as much descriptive as you can on your output in figures and (2) avoid unnecessary abbreviations.

 

• Specific comments 

Line 116: Figure 2. This figure in under 2.1 and it just appear from nowhere. Can you describe it in one section for mythology to use this figure more effectively? Figure description need to more detailed than the present. The legend visibility is not good, can you add background only for the legend?

Line 133: What is FD in the flowchart?

Line 178: Figure 3 is not visible at all

Line 146: You can add “Model development section” and list all below that as sub-section.

Author Response

General  Comments 

The title should be clear and depicting the result output. The authors need to modify the title of the paper to match the outcome of their results. The abstract need to modify in a way ease explain the research question. Try to avoid abbreviations, if necessary please explain the meaning of the abbreviations at first uses. One of my concern is that the authors recommended a water management scenario where the author compared the result with current conditions and historical trend of pumping conditions. What is the critic to select this? because, the business as usual case, showed the lowest water level change range compared to other two scenarios. Two comment I have is (1) please be as much descriptive as you can on your output in figures and (2) avoid unnecessary abbreviations.

Authors Response: The title of the paper is changed, and abstract section is also improved. Abbreviations are avoided in the text but where used are properly explained e.g. at line 56 (BCM) is used and explained that it is “billion cubic meter” and at line 111  (LCC) is explained as Lower Chenab Canal etc.

The authors appreciate the comments. There are three scenario developed for future projection of ground water levels in the study area 1. Business as usual scenario, 2. Historical trend of pumping and 3. Water management scenario. The results of business as usual scenario revealed that there will be net gain of water in upper parts of the study area because in upper parts of the study area there is more recharge in the form of precipitation and extensive irrigation network whereas lowering of water levels is anticipated in central and lower regions where recharge is less  in comparison to pumping. Similarly there is a historical trend of excessive pumping in the study area and small to medium sized tube wells are installed by the farmers at a rapid pace as indicated in the result. Therefore, if the present rate of pumping remains the same for the future projected period whereas recharge remains unchanged there would be drastic drawdown in the study area. Therefore, a new water management scenario is proposed which suggest that in areas where pumping is less, and recharge is more surface water supplies could be diverted to the areas where there is excessive pumping and comparatively less recharge so as to create a balance between pumping and recharge. The critic behind was that if present rate of pumping continued for the projected period and recharge remained unchanged a drastic effect could be anticipated to the aquifer therefore by managing the recharge through diverging surface water supplies would decrease the reliance of farmers on pumping thereby reducing the stress on the aquifer .

The figures are used to show the fluctuations in groundwater level with respect to time in the study area and are properly explained in the text. The abbreviations used in the figures are actually the wells representing the respective irrigation sub divisions to which they belong  are  properly explained in the section 2.12.3 in the text.     

Specific Comments:

1. 1. Figure 2. This figure in under 2.1 and it just appear from nowhere. Can you describe it in one section for mythology to use this figure more effectively? Figure description need to more detailed than the present. The legend visibility is not good, can you add background only for the legend?

Authors Response: The figure is described in section 2.1 and more detail  is added to its description. The legend visibility is also improved by changing the back ground of the image. 

2. What is FD in the flowchart?

Authors Response : The term ‘FD’ is used for Finite Difference method used in MODFLOW model setup. There are two methods used for groundwater flow modeling. One is finite difference and the  other is finite element. Finite difference approach is used in this research and the abbreviation is also updated in the flowchart. 

3. Figure 3. is not visible at all

Authors Response: Figure 3. Visibility is tried to improve as much as possible.

4. You can add “Model development section” and list all below that as sub-section.

Authors Response: Corrected as suggested at section 2.3.

Reviewer 2 Report (Previous Reviewer 2)

The previous comments are addressed.

Author Response

Thanks

Reviewer 3 Report (New Reviewer)

Reviewer highly appreciates the authors for this work.

1- The title  must be change to : Simulation the  groundwater flow dynamics under different stresses using MODFLOW in Rechna  Doab, Pakistan.

2- Geological section for the study area should be added in the manuscript (also geological map).

3- The groundwater aquifer, water level data, hydrogeological cross section, and pimping pumping tests (hydraulic parameters),  all these are very important to simulate the groundwater flow in the area. please add.

4-  In Results  are good in terms of using diagrams that express the changes of water levels with time.

 

5-  Conclusions: this section is very poor; authors should improve this section.

6- References, authors must update the references, you can see; http://dx.doi.org/10.1016/j.jafrearsci.2013.03.009

https://doi.org/10.1007/s12517-018-3945-0

 

 

 

Author Response

1- The title must be change to : Simulation the  groundwater flow dynamics under different stresses using MODFLOW in Rechna  Doab, Pakistan.

Authors Response: The Title is changed as suggested.

 

2- Geological section for the study area should be added in the manuscript (also geological map).

Author's Response: The information about the geology of the study has been incorporated in the study area section on the page No 5 & Geological Map is included as Fig -1b.

3- The groundwater aquifer water level data, hydrogeological cross section, and pimping pumping tests (hydraulic parameters), all these are very important to simulate the groundwater flow in the area. please add.

Authors Response: The authors agree with the comment that various hydrogeological parameters are very important for simulating groundwater flow. These parameters are part of the  methodology section e.g. Hydraulic conductivity estimation is described in sections 2.4.1-2, information about  initial water levels is in section 2.5, Specific yield in 2.9.1 and recharge is presented in 2.9.2.  The values of hydraulic parameters are also added as Table-1 in the manuscript.

 

4- In Results are good in terms of using diagrams that express the changes of water levels with time.

Author's Response: The authors agree with the comment that the results are best expressed by diagrams containing water level changes with respect to time. This has already been done in the results sections and figures 8,10 & 12 clearly show the water level fluctuations with respect to time.

 

5- Conclusions: this section is very poor; authors should improve this section.

Authors Response: The conclusion section is revised.

Reviewer 4 Report (New Reviewer)

Groundwater is a very precious fresh water resource, and its sustainable utilization plays an important role in human life and economic development. This paper predicts the changes of groundwater through the model, which has an important warning effect on the rational utilization of groundwater. And innovative revisions to any model should be encouraged.But there are still some problems with the manuscript.

 

1. The abstract section needs to be refined. The author uses too much language to write about the development of the model and needs to focus on his own results.

2. In the lines of 63-75, This part was written too broadly. It is best to focus on the content of the model research for predicting the decline and increase of groundwater, as well as the limitations in the development process of the model, so as to draw out the innovation and significance of your research.

3. In the line 100, it is better to use soil types with international standards. Such as IRB：International Reference Base for Soil Classification, or American Soil Classification System. “Medium to fine-textured soil” is not the soil type, but is the texture of soil.

4. More information need to add to deeply explain why the decline/increase of groundwater in the study regions in the models.

 

Author Response

1. The abstract section needs to be refined. The author uses too much language to write about the development of the model and needs to focus on his results.

Author's Response: The authors appreciate the reviewer's comment. The main focus of the present study was on the simulation of groundwater flows by developing a flow model and predicting the future behavior of the aquifer under different stress conditions therefore all these aspects are tried to cover in the abstract section. Some information is provided on model development followed by the future scenarios which are the stresses employed for future projection of water levels. Then the results of all three scenarios are briefed followed by the conclusion part of the study. So a balance among all these sections is tried to maintain in the abstract section. Moreover keeping in view the limitation of the length of the abstract section all aspects are covered briefly and explained in detail in the manuscript.

2. 2. In the lines of 63-75, This part was written too broadly. It is best to focus on the content of the model research for predicting the decline and increase of groundwater, as well as the limitations in the development process of the model, so as to draw out the innovation and significance of your research.

Authors Response: This section is revised and narrowed down with the addition of more relevant data about the study area.

3. In the line 100, it is better to use soil types with international standards. Such as IRB：International Reference Base for Soil Classification, or American Soil Classification System. “Medium to fine-textured soil” is not the soil type but is the texture of soil.

Authors Response: The soil types in the study area are updated and are explained in detail in geological section from lines 105-109.

4. More information need to add to deeply explain why the decline/increase of groundwater in the study regions in the models.

Authors Response: The reasons for the decline of water levels as well as improvement in the model regions is explained in the results and discussion section and more explanation is added in this context in the discussion part.

Round 2

Reviewer 4 Report (New Reviewer)

The abstract apart still need to improve.

Author Response

Comment: The abstract apart still need to improve.

Authors Response: Thanks for your valuable comment. The abstract  is significantly improved. Please see the revised manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Based on the content of the paper, I recommend modifying the title to “Groundwater Modeling for Spatial and Temporal Analysis of Groundwater flow dynamics in Rechna Doab, Pakistan.

 The paper uses a comprehensive hydrogeological data to develop a hydrogeological conceptual model and based on this, the hydrostratigraphy of the real conditions are represented by three model layers. The model is calibrated and validate for steady and transient conditions. Further scenario analysis is detailed in result and conclusion section of the paper.

Advantage of the work is that its usage spatially and temporally distributed monitoring wells and the methodologies are well presented (Figure 2) and presented well according.

My only two concerns of the work are the reasoning of layer selection to develop the groundwater model simulation, how are the local geological and hydrogeological condition determining? (2) why are the model so perfectly fitting the observed data (Figure 6)? Do you think this much accuracy can lead over fitting of the parameter which can lead inadequate representation of the real condition?

Author Response

Reviewers Comment-1: The reasoning of layer selection to develop the groundwater model simulation, how are the local geological and hydrogeological condition determining?

Authors Response: 

The hydrogeological conditions of the area normally helps to determine the layering of flow models. As mostly three-dimensional flow models like Modflow are used for modeling the flow domain which employs the finite difference approach. To avoid the non-convergence of the model and to simplify the complex site-specific hydrogeology model was vertically discretized. This was done by sub-dividing the model into vertical layers to represent common hydrogeologic properties.

Reviewers Comment-2:  Why are the model so perfectly fitting the observed data (Figure 6)? Do you think this much accuracy can lead over fitting of the parameter which can lead inadequate representation of the real condition?  

Authors Response: 

To address many hydrological problems and predict the future behavior of the aquifer under different stress conditions the calibration of the groundwater flow model is very necessary. The calibration in simplest form is the alteration of input parameters to make the model closely fit with the observed hydraulic head data. To assess the accuracy of the model it is re-checked against different statistical parameters. Therefore the model was calibrated and then validated against the observed data and the 1:1 calibration curve was drawn for both steady and transient state flow conditions.  The scatter plot showed a close match with the observed data. The calibration results were further checked against statistical parameters and all the values were under the allowable limits as evident from table 1. As the coefficient of determination of the model and several errors were within the safe limit it is highly likely that the model will give more reasonable predictions. As the model results are an estimation of the real conditions so more the accuracy in calibration lesser the chances of inadequate representation of the real aquifer system.   

Reviewer 2 Report

see attachment

Comments for author File: Comments.pdf

Author Response

Comment 1: The authors concluded that the net gain and loss of groundwater water levels was random within the study area. For example under scenario I, there was a net gain in one region while net lowering in another region. Was the groundwater level solely based on pumping and recharge? Were there any factors that govern the net change in water levels? Please elaborate on other possible reasons that have caused the overall change in groundwater levels under each scenario.

Authors Response: 

The net gain and loss of groundwater levels are not random within the study area rather it has a set pattern which is evident from the results. For example, under future scenario-1 where business as usual scenario was simulated, there was a net gain of water levels in upper study regions with net loss at the lower and few central parts due to the difference in agro-climatic conditions of the region. In the upper regions which represent the rice-wheat rotation with appreciable average annual precipitation coupled with more surface water supplies recharge is more in comparison to pumping. However, in lower parts, the mixed cropping pattern dominates along with comparatively less precipitation resulting in more pumping and lowering of groundwater levels. Similarly, there is a net loss of groundwater levels under scenario II in the complete study area. While the water management scenario III gave an improvement in water levels in lower regions where recharge was allowed to increase and a decline of water levels was observed in upper parts due to reduced recharge. Therefore the pattern of recharge and pumping primarily dictates the pattern of groundwater levels in the study area.

Comment 2: How was the observed data collected? Was the groundwater level data continuous throughout one season? Please clarify the simulation period and time step for this simulation. Authors just mentioned that the simulation start date was January 2005.

Authors Response: 

The observed groundwater data were obtained from the Land reclamation wing of the Irrigation department, Government of Punjab. The department has installed many observation wells in the study area where data were collected twice a year i.e. pre-monsoon (June) and post-monsoon (October). The beginning of the simulation period was denoted by the start date in the model. It was important to define a relevant start date since the field measurements (observed heads and pumping schedules) would be defined with absolute date measurements, and must lie within the simulation period. For the study, Jan-2005 was selected as the start date of the simulation period keeping in view the field data availability. The observed wells data were used from the year 2006-13 for the calibration and validation of the transient flow model. Two stress periods i.e. Kharif (Summer) and Rabi (Winter), having 182 and 183 days along with monthly time steps, were introduced for this simulation. To simulate the future response of the aquifer (2013-33) time span was chosen (clearly mentioned in the manuscript).

Comment 3: The authors have used a SRTM data for a 30m resolution. Is this resolution not coarse for this study?

Authors Response: 

The authors agree that 30m resolution is coarse particularly for local scale groundwater models as it could make the comparison with observations challenging. However, the global, continental or regional scale models could be developed with coarse spatial resolution due to the non-availability of fine resolution digital elevations model without restraint. That is why due to the regional scale of the study a bit coarse resolution was used where one simulated head value represents an average observed head for a cell representing an appropriately aggregated volume of the groundwater system.

Comment 4: Typo at line 147. “– pre-defined”

Authors Response: The typo mistake is corrected