Storm Driven Seasonal Variation in the Thermal Response of the Streambed Water of a Low-Gradient Stream

Round 1

Reviewer 1 Report

The subject of paper is important and interesting. Storm events strongly influence water temperatures in the saturated substrate underlying stream channels, or the hyporheic zone which may affect a thermal refuge for stream biota and greater overall ecosystem stability. The research was well planned and carried out, although it has the features of a case study related to specific hydrogeological and meteorological conditions. This could be a treated as potential as a regional and specific problem. So I would suggest changing the title. My basic remarks to the paper:
• Literature review is correct and contains basic items. The work contains a very detailed discussion of previous studies. This is the basic advantage of this paper.
• The results of the study were well statistically analyzed.
• The examined problem is a regional issue and it may limit the interest of potential readers. Missing some strong comments pointing to broad research problem.This should be complemented!
• In my opinion, the conclusions can be expanded a bit and refer to the results in more detail.
The submitted paper made a good impression on me. It felicitously combines successes in a full-scale experiment and a calculation, as well as a reasonable discussion of the presented results. Therefore, I have no strong remarks. The manuscript is well structured and deserves publication after some minor revisions.

Author Response

Our response to the comments are in blue and italicized

Reviewer 1

The subject of paper is important and interesting. Storm events strongly influence water temperatures in the saturated substrate underlying stream channels, or the hyporheic zone which may affect a thermal refuge for stream biota and greater overall ecosystem stability. The research was well planned and carried out, although it has the features of a case study related to specific hydrogeological and meteorological conditions. This could be a treated as potential as a regional and specific problem. So I would suggest changing the title. The title was modified to include a distinction that helps distinguish the importance of the work – a focus on a low-gradient stream.

My basic remarks to the paper:
• Literature review is correct and contains basic items. The work contains a very detailed discussion of previous studies. This is the basic advantage of this paper.
• The results of the study were well statistically analyzed.
• The examined problem is a regional issue and it may limit the interest of potential readers. Missing some strong comments pointing to broad research problem. This should be complemented!

• 
  In my opinion, the conclusions can be expanded a bit and refer to the results in more detail. The conclusions are expanded with some results included to address this concern.

The submitted paper made a good impression on me. It felicitously combines successes in a full-scale experiment and a calculation, as well as a reasonable discussion of the presented results. Therefore, I have no strong remarks. The manuscript is well structured and deserves publication after some minor revisions.

Reviewer 2 Report

The study used thermal responses at different depths in the hyporheic zone to evaluate the variations driven by storm events. The temperature data was collected from 6 depths ( 30 cm, 60 cm, 90 cm, and 150 cm) at 6 locations (W1, W2, W3, W4, W5 and W6) along a strait stretch in Illinois, USA. To analyze the HZ temperature profiles, two additional sensors were installed to record upstream and downstream surface water temperatures. The amplitudes of the streambed and stream thermal pulses due to the storm pulse were determined by subtracting the pre-storm temperature from the peak-storm temperature. The maximum or minimum temperature observed during the storm were used to obtain the post-storm thermal change (T). I have read the manuscript and gone through the detail of the content. In summary, the data collection was well designed and the paper is well organized. However, the novelty of the idea of the paper is not clear to me. Moreover, the theoretical and technical parts are not well elaborated. I recommend the manuscript need a moderated revision to be able to publish in Water. The following is my comments for the manuscript.

General comments:

1. In Introduction. The author points out two main research questions of this paper but did not address the importance of these issues. What is the connection between the study and the ecosystem?
2. In Materials and Methods. In order to understand the thermal transfer behavior. Does the author try to collect samples at different depths to measure the thermal and hydraulic properties?
3. In Materials and Methods. The temperature loggers with accuracy ± 0.53 °C and resolution at 25 °C is 0.14 °C. Does it enough for measuring the T at HZ?
4. Same paragraph. How were the depths of the sensors be determined? Is there guidelines for the installation of the sensors?
5. In Materials and Methods. Does the author considered the ambient temperature and decided to ignore it?
6. In order to refine the analysis, I will recommend the author describe more about the storm events, maybe have the classification of the storm events to see the thermal response under different stress.
7. In the temperature results, the data presented in Figure 5 was obtained from which well? Or, is it the average of all the 6 wells? Please clarify them.
8. The discussions and conclusions have detailed description of observation results but lack of new information from the analysis of the data.

Author Response

Response to the reviewer comments are in blue and italicized.

Reviewer 2

The study used thermal responses at different depths in the hyporheic zone to evaluate the variations driven by storm events. The temperature data was collected from 6 depths ( 30 cm, 60 cm, 90 cm, and 150 cm) at 6 locations (W1, W2, W3, W4, W5 and W6) along a strait stretch in Illinois, USA. To analyze the HZ temperature profiles, two additional sensors were installed to record upstream and downstream surface water temperatures. The amplitudes of the streambed and stream thermal pulses due to the storm pulse were determined by subtracting the pre-storm temperature from the peak-storm temperature. The maximum or minimum temperature observed during the storm were used to obtain the post-storm thermal change (T). I have read the manuscript and gone through the detail of the content. In summary, the data collection was well designed and the paper is well organized. However, the novelty of the idea of the paper is not clear to me. In terms of the novelty of the study, while similar studies have been done in other environments, this contribution focuses on storm-induced events on thermal variations in the hyporheic zone of low gradient sand and gravel bedded streams. Please, see lines 57 to 65.

Moreover, the theoretical and technical parts are not well elaborated. I recommend the manuscript need a moderated revision to be able to publish in Water. The following is my comments for the manuscript.

 General comments:

1. In Introduction. The author points out two main research questions of this paper but did not address the importance of these issues. What is the connection between the study and the ecosystem? To establish a direct connection between the study and the ecosystem, we’ve added the following sentence “Given the importance of thermal stability to the survival of aquatic organisms [30], understanding how storm events disturb the thermal stability of the hyporheic zone is critically important to aquatic resource management [lines 55-57].”

2. In Materials and Methods. In order to understand the thermal transfer behavior. Does the author try to collect samples at different depths to measure the thermal and hydraulic properties?

While the general aquifer structure and hydraulic properties (Cahokia formation) are provided [please, see lines 73 to 75], the thermal and hydraulic properties at the various depths were not specifically measured in this study.

3. In Materials and Methods. The temperature loggers with accuracy ± 0.53 °C and resolution at 25 °C is 0.14 °C. Does it enough for measuring the T at HZ? For the substrate, we observed mean temperature changes ranging from 1.58 °C - 2.14 °C during the summer [Table 2], so the ± 0.53 °C accuracy and 0.14 °C resolution at 25 °C are enough to accurately detect those changes in the HZ.
4. Same paragraph. How were the depths of the sensors be determined? Is there guidelines for the installation of the sensors? There are no specific guidelines for the installation of the sensors. The depths were strategically selected to obtain responses from the shallow (30-60 cm) and deeper (90-150 cm) HZs.

5. In Materials and Methods. Does the author considered the ambient temperature and decided to ignore it? Patterns in the ambient surface temperatures are generally captured in the stream temperatures, which were considered. So, we indirectly considered ambient temperatures. 

6. In order to refine the analysis, I will recommend the author describe more about the storm events, maybe have the classification of the storm events to see the thermal response under different stress. We agree that further classification of the storm events will be insightful. However, the scope of this paper was limited to investigation of seasonal variations. Consequently, we followed the storm categorization of Beach and Peterson (2013) and Dogwiler and Wicks (2005) [see lines 120 to 121].

7. In the temperature results, the data presented in Figure 5 was obtained from which well? Or, is it the average of all the 6 wells? Please clarify them. Clarification provided on line 164.

8. The discussions and conclusions have detailed description of observation results but lack of new information from the analysis of the data.