Operating Effects of the Three Gorges Reservoir on the Riverbed Stability in the Wuhan Reach of the Yangtze River

Round 1

Reviewer 1 Report

Dear authors.

the work is interesting, but I think that is too much focus on you specific case study. I don't see a general interpretation of your results that can be used in other case studies. 

The English must be improved and also some image quality. 

Author Response

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Reviewer 2 Report

The paper deals with a still current and interesting topic and refers to the influence of water reservoir construction on river morphodynamics especially in riverbed instability. The authors conducted a large-scale field study, based on which they calculated the indexes representing the channel stability. Furthermore, they proposed a method to determine the equilibrium values of cumulative erosion and lateral migration intensity of thalweg  based on flow conditions, sediment concentration and gradation, and water depth. In addition, the authors used a Delayed Response Model to comprehensively analyze changes in the longitudinal and lateral stability of the river channel. In summary, the paper has a logical structure and is well written. It is enriched by numerous analyses and figures. The research experiment was well planned and executed.  However, there are still a few details that need clarification namely: (i) why did not the authors of the paper discuss the results of the grain size distribution of sediment? Such information would certainly increase the cognitive value of the article, (ii) are the correlation coefficients shown in Figure 10 and Table 5 statistically significant?

 

However in my opinion, the article should be published in its present form.

Author Response

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Reviewer 3 Report

General comments:

The authors present the analysis of changes in the Yangtze riverbed shape, and the alteration of the observed trends that appeared after the Three Gorges Dam started to operate. They propose a mathematical model to track the changes  and they compare the observed bed characteristics with the model predictions, reaching a good agreement.

The obtained results seem to be well justified and backed by appropriate data series. There are, however, a few serious concerns, and several places for improvement as listed below in appropriate sections of this review.

As for the language, generally it is understandable, but long and compound sentences appear frequently and make the text hard to comprehend at the first glance. Rewording is welcome particularly for lines (25-26), (32-36), (57-62), (95-99), (180-186), (249-254), (275-278), (346-349), (365-373), (375-383), (465-473), (536-539).

The references are up to date.

 

Specific major issues:

(67) An explanation, describing what kind of “memory” is meant here, is necessary. The word “memory” can have a lot of different meanings in this context. Is this the “river memory effect” mentioned in a few earlier papers by various authors?

(112) Ambiguity: do the Authors mean “the river current” or “the current values”? This changes the meaning substantially.

(165) It would be fine to specify which cross-section it actually is. In what sense is it “typical”, when below, in (168) it is stated that each cross-section is in fact different? Clarification is needed.

(171) In the terms of calculating an average, being “geometric” and being “weighted” are different dimensions. An average can be any of “weighted geometric”, “non-weighted geometric”, “weighted non-geometric”, and even “non-weighted non-geometric”. Thus a brief (but definite) description of the method taken from [33] is needed.

(255) The meaning of the word “limit” in the context of the equilibrium state is not clear.

(384) Vertical axis of fig 6 is ambiguous: Elevation relative to what? What is the zero point?

(384), (410), (412) While these graphs are meant to illustrate the impact of the dam existence, one can have an concern, that between the first and the second observation there was a time span of 5 years while between the second and the third one there was 11 years, so bigger differences may just be the effect of a longer time that passed.  Addressing this by using supplementary data (maybe year 2014?) is necessary.

 

Specific minor issues:

(46) Last “the” is not necessary and in fact misleading.

(92) Inconsequence in the name spelling. In text it’s “Wyzga” in references (627) “Wyżga”.

(104) and (114). Unnecessary repetition. I suggest removing (104), as a reader can clearly see that the next chapter will be devoted to the study area.

(109) This sentence would be better without the words “comprehensive” and “various”.

(114-124) This paragraph can benefit from slight shortening.

(127-133) Is there a specific reason to put a division between upper and middle sub-reaches? (The lower one is clearly different.)

(205) DRM is explained in (210), but it should be done here.

(237) It is not clear what “1 a” means here. I guess “1 year”, but in such a case using the word “year” or even the abbreviation “yr” would spare the doubts.

(256) Variables description for equation 5 is missing.

(291-301) As Coriolis force is well known, substantial shortening of this paragraph is desirable.

(308) “g” is the gravitational acceleration on the Earth, it may also be called “acceleration of free fall”, or less formally abbreviated to “standard gravity”, but definitely it is not “unit of gravity”.

(327-328) It would be better to call a and b by their role in the model in addition to the position in equation, i.e. “exponent parameters”.

(342) It is better to use exponential notation than the word “billion”. In some countries a billion is 10^9, but in some other it is 10^12.

(351) In table 3 and fig 3: 10,000 t = 10^5 t = 10^8 kg. As the runoff is in 10^8 m^3, specifying both of them in the terms of 10^8 would make the table and graph easier to comprehend (note that this would immediately indicate how many kilograms of sediment are present on average in each cubic meter of water).

(359-362) Figures 4 and 5 seem to somewhat duplicate each other. Please consider putting two vertical axes to show both quantities in one graph (like fig 3).

(397) The spline connecting the points seems unnecessary.

(443), (445) “Validated” would be a better description of black dots.

(459) I suggest putting “Discussion” sub-header here.

(476) Possible typo: 16 instead of 36 (otherwise ref 36 is not mentioned in the text).

(517) Here, repeating the year range would be better than using the word “recent”.

Author Response

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Reviewer 4 Report

 

Comments on the manuscript with the title: Operating effects of Three Gorges Reservoir on the riverbed stability in the Wuhan reach of the Yangtze River.

 

The authors of the manuscript present the experimental results on the evolution of the river catchment before, during and after the construction of the Three Gorges Reservoir. They specially focus on the Wuhan reach of the Ynagtze River. They also present a model to predict the evolution of the riverbed stability. I find both the results and the model interesting of being published. However, I would suggest some modifications of the manuscript before being finally accepted for publication.

 

1. The main concern that I have on the manuscript is that authors present equations like they were already familiar to the readers. However, I strongly suggest a more detailed explanation of the model. If it is necessary, they should include more references to be able to understand all the parameters they use. A notation table would also be helpful to readers. Otherwise, the model is too difficult to understand. Furthermore, if in the future readers want to use this model in their studies, a detailed explanation is needed.
2. Figure 2. Where is this measured? I recommend to show its position in Figure 1.
3. Pg 3, lines 147-149: This sentence has some problem….. please revise.
4. Could authors comment whether the model is able or not to predict future scenarios? Future climate change predicts more drought periods…..could this model give us some indications on the impact of such scenarios?

Author Response

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Round 2

Reviewer 3 Report

The authors present the analysis of changes in the Yangtze riverbed shape, and the alteration of the observed trends that appeared after the Three Gorges Dam started to operate. They propose a mathematical model to track the changes  and they compare the observed bed characteristics with the model predictions, reaching a good agreement.

 

The overall language quality has been improved, the paper is now easier to read and comprehend. Previous reviewers' remarks have been well addressed.

 

There are a few minor changes to make:

(109) To save all the doubts I suggest the wording: “between the current values and the equilibrium ones”.

(209) Period instead of coma would be better here. Moreover “which requires a time process” is unclear. Maybe “… a time-dependent approach” suits better here.

(228-232, 242) A few spaces are lacking.

(363) One forgotten “billion” remained.

Author Response

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Reviewer 4 Report

The authors have improved considerably the manuscript. However, I would made a couple of suggestions.

1. in lines 328, 286 and 278 authors define the standard gravity (g, N/Kg). One definition of g is enough. No need to repeat it.
2. The figure legend of Figure 1 is poorly detailed. I strongly suggest a better description of this figure since it has like different pannels. I would include that the codes or names of the stations studied are shown in the figure.

Author Response

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