The Disaster Protection System of Mountainous Rivers in Japan: The Example of the Akatani Watershed’s Reconstruction

Round 1

Reviewer 1 Report

I appreciate the authors efforts of exploring and presenting the historical developments in flood/disaster management approach in Japan which would be a very good piece of reference article for international researchers and practitioners. A few things can make the article better and comprehensive :

1. The paper was more focused on structural interventions. But the non-structural interventions are also very important and that is actually more important to follow from the disaster management perspective. How they really changing their approach and gradually giving more focus on non-structural measures would be interesting to read.

2. It could be interesting if the author could compare the new approach of river/watershed management in developed world e.g. room for river, Nature based Solution, adaptive pathway, etc. with the Japanese approaches.  The answer I was looking for while reading the paper was - whether they have adopted such concept. The figure 8 gives an indication that they have provided more area to river after the disaster, however, it is unclear whether that concept/approach is comparable with room for river or similar ideas.

3. The author mentioned that the soft measures/non-structural measures along with environmental concerns were getting attraction and adopted after 2000s. However, what kind of environmental measures and soft measures were considered after 2000s were not discussed.

4. Role of community in river management was completely missing in this paper.

5. Nakamura & Oki (2018) (https://doi.org/10.1029/2017WR022509) claimed that the concept of modern river engineering was imported from Netherland during the Meiji period but this paper indicates different. It would be interesting to read whether the finding of this paper are in line with the other similar research or different.

Author Response

Dear reviewer, we thank you for your time and your recommendations. We took them into consideration to improve our paper. You made four recommendations. 

Recommendation 1 - the importance of non-structural measures
We have improved the consideration given to non-structural measures in our article by presenting some advances made by Japan, and by showing the need to couple structural measures with non-structural ones. Recommendations have also been made along these lines.

Recommendation 2 - Comparison of Japanese approach and other developed world’s management
We added some western references (France and USA) in terms of river management to compare them with Japan’s management. We also mention some examples of Japanese river restoration. The constructions are primarly designed to contain the river during hydro-gravity hazards occur. 

Recommendation 3 - Discussion of soft measures post-2000
We developed the history of non-structural measures in Japan and cited or mentioned some ideas which go into non-structural measures improvement.

Recommendation 4 - Role of community
We understand your concern regarding the role of community. We further described the role of local authorities in the reconstruction processes.

Recommandation 5 - Article of Nakamura & Oki
We thank you for the reference and we added it within our contribution. In fact, Japan imported techniques from Netherlands.  

Reviewer 2 Report

The paper may interet readers outside Japan.

Comments for author File: Comments.pdf

Author Response

Dear reviewer, we thank you for your time. You made the following recommendations for our contribution :

Line 171; jisaki sabo >>> chisaki sabo

Line 327; from Germany >>> from Holland

Line 424; Kyushu Kitabu >>> Kyushu Hokubu

 

We took them into consideration and modified our document.

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

Dear reviewer, we thank you for your time and your recommendations. We took them into consideration to improve our contribution.  

Recommendation 1 - Structure of the paper
We understand the confusion in the previous structure and we apologize for that. We modified it according to your recommendation. 

Recommendation 2 - Flowchart for the methodology
We ameliorated the figure 2 (now figure 3), which presents the methodology.

Recommendation 3 - compare with similar studies
We added information regarding the effect of sabo works through laboratory experiments and in situ investigation. We mentioned the similarity of the sabo system with the french system. We also mentioned other studies related to improvement needed for soft measures.

Reviewer 4 Report

This article introduces the disaster protection system of mountainous rivers in Japan through examples of small watershed reconstruction. The article provides a detailed introduction to the Sabo system, including its specific functions, forms, building materials, and historical evolution. Some questions are as follows:

1. The research topic of this article is unclear and the strategic significance is not prominent.

2. This article devotes a large amount of space to introducing the functions, forms, building materials, and historical evolution of the Sabo system. These are all basic materials. However, the actual research work of this article is limited in length.

3. The actual effect of Sabo system in disaster prevention and control of mountainous rivers is not reflected in the text. Suggest supplementing corresponding research and analysis, such as analyzing the effect of the Sabo system in an actual hydrological disaster through measured data, or analyzing the disaster prevention and reduction effects that the Sabo system can achieve under typical flood conditions through numerical simulation.

4. Other minor flaws:

(1) Line 296，the text suggests that “apreservationist logic” was existing in “The Edo period”, while line 400 “Since 2000’s, ecological issues are gradually considered in Japan”. There are logical contradictions.

(2) Line 160, this should be the third section.

(3) The description in Figure 10 has a text numbering error.

Author Response

Dear reviewer, we thank you for your time and your recommendations. We took them into consideration to improve our paper.  . 

Recommendation 1 - Clarification of the article topic and strategic significance
We modified the research topic and its significance in the introduction and in the conclusion. We hope that is more clear in this new version.

Recommendation 2 - Limitation of research work
We reduced the length of this part as much as we could. However, we consider it as important to understand the actual choices made in our study area. We also detailed discussion and conclusion + recommendation in this new version.

Recommendation 3 - Actual effect of sabo system
We mention some articles studying the effect of sabo works through laboratory experiments and in situ investigation. We also presented the situation in Akatani watershed after heavy rainfall which happened in the beginning of July 2023. After the heavy rainfall of this year, it would be important to evaluate the damages on the new constructions and around to further analyze their actual effect in our study area. 

Recommendation 4 - Minor flaws
We thank you and took the minor flaws you mentioned into consideration.

Round 2

Reviewer 4 Report

This article introduces the disaster protection system of mountainous rivers in Japan through examples of small watershed reconstruction. Further research is needed on the real effect and cost-effectiveness ratio of Sabo system in disaster prevention and control of mountainous rivers. Is this system the only suitable engineering measure for disaster prevention and control in mountainous rivers in Japan? Is it in line with the basic theories of river dynamics and disaster prevention and reduction? Is there a more advanced or reasonable disaster prevention and control measure?

Author Response

Dear reviewer, 

We thank you for your comments.

1. We wanted to answer to your three questions here. Our explanations have been added to the discussion part of the manuscript alongside previously presented ideas (exact lines are mentionned here).
   • Is this system the only appropriate engineering measure for preventing and controlling disasters in mountain rivers in Japan? Yes, it is the system best suited to high-energy, torrential rivers. The Sabo system is generally effective when several dams are set up in the valley, attenuating slopes and hydraulic energy, promoting sediment storage upstream of each of the structures, and limiting erosion at the foot of the slopes. The field work we have carried out leads us to believe that Japanese engineers design very sophisticated and extremely effective Sabo systems. Each structure is adapted to the specific features and physical constraints of the field. (Lines 687 - 701)
   • Does the Sabo system comply with the fundamental theories of river dynamics and disaster prevention and reduction? Yes, in mountain catchments subject to extremely powerful rivers and flash floods, there is no alternative to heavy engineering works. It's a question of survival for people living downstream of mountain catchments. However, the paper repeatedly stresses the need to take into account the impact of this type of structure on the landscape. Clearly, Japan is tending to install heavy structures across the board, including in large floodplains that are quite far from mountain catchment areas. Admittedly, demographic pressure (population density) is at its highest there, but perhaps the search for areas without too many issues could make it possible to combine engineering structures and flood expansion zones. (Lines 702 - 712)
   •  Is there a more advanced or reasonable disaster prevention and control measure? More advanced, no. Japan has mastered the art of building flood control structures. More reasonable, from a financial point of view, Japan spends millions of yen on flood and landslide prevention, and money is not a constraint in a country where the state promotes full employment and supports national businesses. But no matter how good a hydraulic structure is, even a very good one, none is immune to damage and destruction from floods and landslides. So, beware of the constant bidding to outdo each other and the attempt to tame everything with engineering techniques. Technological mastery is reassuring, but uncertainty persists because there is no such thing as 0 risk. (Lines 713 - 745)
2. We added a quick description of Japanese catchment areas in the introduction (Lines 57 - 62)
3. We did some minor modifications during the proofreading work in the entire manuscript.