Remote Sensing to Characterize River Floodplain Structure and Function

Round 1

Reviewer 1 Report

I want to thanks the authors for their work. It is, in my opinion, very interesting and very well conducted.

From my point of view it is already ok to be published.

I have only some minor comments:

1. please, always use m³/s instead of cms
2. use only SI units
3. line 506: "... between 0 and 1 for lower flow regime."

Author Response

Thank you for your review.

1. All river discharge has been changed to m3/s as suggested
2. We now use only SI units
3. We have clarified the sentence associated with line 503

Reviewer 2 Report

My review comments are as following:

Your article is interesting and has some contribution to the remote sensing applications broadly but the present version gives the reader a sense of working report or partially overview report and it is less scientific presentation. So, I suggest the authors reorganize the article contents and highlight the scientific elements.

The generic comments are as following:

1. The abstract should be rewrite. At present version, there is lack of the sentences related to the reasons and significance of conducting this study as well as the conclusion you found.
2. In the Introduction section, it had better reduce the related summary of river floodplain ecologic system and add more remote sensing related progresses in your study fields or relevant technology you explored in the study.
3. In the results and dissection section, the validation of some key results should be added, such as retrieved flow velocity and water depth, aquatic habitat classification, and the classification of vegetation and riparian patches.

The concrete comments are as following:

1. the fig. 3A should have a legend to explain the water surfaces
2. In the fig. 5, the short name or acronym in the legend should be further explained in the relative paragraph of the article.
3. Fig 6 is confusing with two similar legends. One may be color orientated and another is size orientated.
4. Line 453, duplicated word “were”.
5. Fig. 9, an accuracy evaluation should be given.

Author Response

Thank you for your review.

General comment responses

1. We have added a sentence at the beginning of the Abstract and strengthened the final paragraph of the Introduction to clarify the purpose and direction of this paper. We stress to the reviewer that this paper is not about the detail of Remote Sensing or methodologies; rather, this paper is about using an array of RS tools to answer critical river ecology questions that have previously been illusive at large spatial scales.
2. We respectfully disagree. As stated above, this paper is primarily a river ecology paper and how RS tools were used to solve very specific fluvial ecological questions.
3. Details of remote sensing validation for our work has been published elsewhere. We have appropriately cited that work. 

Specific comment responses

1. Figure 3A is the output of an unsupervised classification of the water component of the image.  A legend of the color output would be inappropriate. We have addressed this in the Figure legend.
2. Agree. We did as requested.
3. We agree that this is confusing as presented - we have clarified this problem by fixing the legend and including explanation in the Figure legend. However, the reviewer missed the point of this figure - the two legends are needed an appropriate. The one legend is for bq/L (Radon concentration). This corresponds to time of the water subsurface in the alluvial aquifer which is given in the Residence Time of the legend.
4. Fixed
5. Agreed. Done in text.

Reviewer 3 Report

The work of Hauer et al. describes hydrogeological and vegetation changes in the Nyack floodplain of Flathead River (Montana) by using remote sensing methods. Although the remote sensing approach in hydrogeology is pretty old, the work is interesting because of two aspects (1) showing the potential of the methodology beyond its basic purpose and (2) new insights into the hydrogeology of the alluvial flow of the Nyack floodplain. Before publication, should be addressed the following issues:

It would be nice to have some terrain work to confirm the vegetation indicated and to assess the difference between remote sensing and direct observations.

Concerning Fig. 7, the authors say that “…ponds with little or no groundwater connectivity will become very warm in summer and freeze completely top to bottom in winter, while ponds with a high flow-through of groundwater stay cool in summer and remain open and 'steamy' in winter [11, 60]."

In this regard, is there any relationship between the nearby geology and estimated groundwater sources? Can the locations of groundwater releases change, and can this change be reconstructed?

Please improve the resolution of the inset of Fig. 8.

The aspect ratio of Fig. 3A should be the same as Fig.3b and c.

Author Response

Thank you for your review

Regarding general comments: We have made it a central focus of the Abstract and Introduction as a stated purpose of the paper is how we used an array of remote sensing tools to answer river ecology question at large spatial scales that are not possible with RS tools. Thus the paper is not so much about the Remote Sensing advances - rather the paper is about how to use RS tools to advance fluvial ecology.

 Responses to Specific Comments:

1. It would be nice to have some terrain work to confirm the vegetation indicated and to assess the difference between remote sensing and direct observations.

   We added a sentence about vegetation validation.

    

   2. Concerning Fig. 7, the authors say that “…ponds with little or no groundwater connectivity will become very warm in summer and freeze completely top to bottom in winter, while ponds with a high flow-through of groundwater stay cool in summer and remain open and 'steamy' in winter [11, 60]."

   In this regard, is there any relationship between the nearby geology and estimated groundwater sources? Can the locations of groundwater releases change, and can this change be reconstructed?

    

   The alluvial aquifer is almost entirely composed of river origin water - not deep groundwater or phreatic groundwaters from side slopes. Thus, the water from the hyporheic zone off the floodplain discharging into ponds or springs and springbrooks result is "winter warm" and "summer cold" discharge.

3. The resolution of Figure 8 inset is at the highest resolution available.

4. Figure 3A #B and 3C have the same aspect ratio

Reviewer 4 Report

This paper analyses the remote sensing technique to characterize river floodplain structure and function. Authors used satellite and airborne imagery of an alluvial gravel-bed river floodplain in western Montana to quantify both riparian and aquatic habitats. Result shows the high complexity of aquatic temperatures linked to groundwater discharge from the alluvial aquifer into specific surface habitats. The paper reads well and can be accepted after minor revision. See the below:

• Abstract: "We"->used almost everywhere (see line 13,16,18, 21, 24) in the abstract and it's a suggestion to re-write. 
• I can see the different fonts, use one font throughout the manuscript.
• Introduction is too long. Somehow, I feel this is a technical report. Please concise. 
• Please mention the pros and cons of the remote sensing technique.
• A flowchart will be suitable to explain the methodology.
• Key findings are still missing in the conclusions. A suggestion will be to show the key results as bullet points. 

Author Response

Thank you for your review

Responses to Specific Comments:

1. The Abstract has been cleaned up with specific reference to this purpose of this paper.
2. The Introduction has been tightened, however, this paper is first about river ecology and the use of RS tools to answer fluvial ecosystem questions.
3. The RS tools we employed are common RS tools. The unique contribution of this paper is how to use these tools in unique ways to address river ecology at scales that have not been possible without Remote Sensing.
4. We put the conclusions main points into bullets as requested.