Application of Running Water-Type Retarding Basin to Old Kinu River Floodplain, Japan
Round 1
Reviewer 1 Report
Dear Authors, the manuscript is interesting, well prepared and well written. The only problem is that the problem and the solutions described are not new or innovative. It could be a new approach for Japan, but the type of solution proposed is commonly used in other countries of the world subject to flood risk. this is also reflected in the lack of a more precise literature review on the technical solutions adopted in other countries.
Anyway, I definitely appreciate the fact that you propose 4 inverted siphons, instead of a single one to empty the RWRB, because during floods trees and other objects carried by the flood wave may block a single siphon, while redundancy reduces the risk of a total blockage.
To conclude my review, I invite you to improve the reference list as well as the description of what you consider innovative in this work.
Author Response
Dear Reviewer:
Thank you for your careful review and kind comments on our article.
Flood control projects should be planned based on the natural and social conditions of the target site. In practical treatment of the river overflow to the floodplains due to the rain runoff exceeding the capacity of river channel, not only the topographic and hydrological conditions, social factors such as systems of laws, common sense, history and life style which are peculiar in each nation or region are very important. We think that the novelty or innovation of the technology to be introduced is judged under the above social conditions. Therefore, before the description of RWRB in Chapter 3, we added a new section 3-1 in which the social and topographic conditions as the background for the idea of RWRB was explained (lines 140-223).
As already stated in lines 54-57 of the manuscript, RWRB is a combination of floodway and retarding basin, which was often used in early modern Japan when flood exceeding channel capacity frequently occurred. In addition, the necessity and effectiveness of connecting river channels and floodplains has recently been discussed in terms of green infrastructure for the preservation of natural ecosystems as well as flood control (In lines 141-146). However, since they are from different historical condition and in different basin condition, we have only quoted representative articles.
The parts of RWRB are an overflow dike installed upstream and a drainage facility installed downstream (levee opening in the original idea and inverted siphon in this case study). Since these are general structures that have existed for a long time, no specific references are given. The main body of the RWRB is the elongated closed floodplain itself shown in Figure-3 (line 121) and Figure-7 (line 282). That is why we have elaborated on the description of those topographical and social conditions in sections 2 and 3-1 of this article.
Since this research is for future practical flood control projects under the conditions peculiar to Japan, it differs in composition from ordinary scientific papers. We would appreciate if you evaluate the article based on the above points.
Reviewer 2 Report
The management of inhabited river floodplains is a topic of great interest for engineering practice, especially in the context of uncertainty associated with climate change scenarios. The type of study presented is of limited scientific soundness but provides a useful analysis for river basin managers.
The study is applied to a single case study located in Japan, with the particular characteristics of the site. The concept of target safety level is applied; however, its definition is not explained. As this concept may differ from region to region, it would be useful for potential readers that authors clarify it.
There is a lack of contextualization of the application of this solution and the conclusions obtained with other cases analyzed in other river basins. That is to say, to compare the way in which its implementation is proposed and the results obtained with those obtained in basins located in other countries with different characteristics.
Linked to the above, it is mentioned in the Introduction Section that the return period of 1.5 years is usually considered as a criterion for defining the river channel. In many basins this value is different and is calculated following a statistical analysis of the floods. Considering that river channel delimitation is an essential aspect of river flood management, it would be appropriate to address this issue in more detail.
I consider that it is appropriate to clarify and deepen these issues in order to enrich a research article. I recommend that, after implementing these minor improvements, the article would be ready for publication.
Author Response
Dear Reviewer:
Thank you for your careful review and kind comments on our article.
Flood control projects should be planned based on the natural and social conditions of the target site. In practical treatment of the river overflow to the floodplains due to the rain runoff exceeding the capacity of river channel, not only the topographic and hydrological conditions, social factors such as systems of laws, common sense, history and life style which are peculiar in each nation or region are very important. We think that the novelty or innovation of the technology to be introduced is judged under the above social conditions. Therefore, before the description of RWRB in Chapter 3, we added a new section 3-1 in which the social and topographic conditions as the background for the idea of RWRB was explained (lines 140-223).
As for the target safety level, a brief explanation was added for the current river improvement works (line 84). But it was difficult to describe it in detail because the practical process to determine it (from rainfall data -> runoff analysis -> flood propagation analysis) is very complicated in Japan.
As for the comparison of the result of this study with those in other river basins, I am sorry we could not describe because of the lack of our knowledge. As mentioned at the first part of this reply, flood control strategy must highly depend on the social condition as well as the topographic condition. This is why we elaborated the descriptions in the section 2 and 3-1.
Since this research is for future practical flood control projects under the conditions peculiar to Japan, it differs in composition from ordinary scientific papers. We would appreciate if you evaluate the article based on the above points.
As for the return period of bankfull flow in natural streams (without embankments), we have the same thought as yours that it depends on the definition of river channel. The number in question was not scientifically derived, but was a round number based on the image of the author of the reference paper. The implication of this sentence is that bankfull discharge in natural rivers is much less than the target discharge of modern flood control schemes. In the newly added reference [Ref. 2], the bankfull flow frequency is written as about 1 to 3 years depending the definition of the position of low water channel bank, so I wrote the value in the new manuscript (lines 26-28).
