In Situ Estimation of Breach Outflow Hydrographs from Fluvial Dike Failures: A Methodology Integrating Real-Time Monitoring and Physical Modelling^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present a methodology to calculate the outflow of a dike breach by measuring the surface flow field and the breach geometry. The topic is innovative and of interest for the community. However, the presentation of the study and its results should be improved and I recommend major revision of the paper.

The following, mainly minor, comments and questions should be considered.

 

line 35: I suggest to put a comma: “...carry the risk of failure, a phenomenon that...”

I was struggling with the aim of the study (line 50-83). The text switches between the relevance of understanding the failure mechanisms, investigating the breach evolution, calculating the outflow hydrograph, and developing an integrated monitoring system. These aspects are of course connected, but this is not elaborated. Please rephrase the text so that the red line and in that way the aim of this study becomes clear.

The Froude number was varied between 0.1 and 0.4, i.e. the approach flow was well in the subcritical flow range. Why is it important to take Fr as key factor?

line 107: Either put a comma or make a new sentence: “Both ... are located on an elevated platform, and ...”.

line 110, 111: I suggest to already introduce the parameters of the different discharges, i.e. Q_flood and Q_out. Moreover, it sounds strange, if a discharge “...is measured by comparing water levels above the ... crest with its flow rating curve”. Please rephrase this sentence.

The resolution of all figures is quite bad, in printed and digital version. Please improve.

line 134: The position of the dike is given to 4.97 m while in Fig. 1a it is 4.96 m. Please correct.

line 136: A slope of 1:1.5 is very steep. Please explain why such steep side slopes were chosen.

Fig. 2: I suggest to use different symbols for the two curves. That would easily improve readability of a printed (black and white) version.

Tab. 1: Delta Q_in is used as parameter for the inflow discharge. Delta is usually used for a difference. Why do you use it here? Please introduce the parameters h_MChannel and CD.

line 170: Do you mean “continuous” hydraulic erosion instead of “constant” erosion?

line 175-176: What do you mean by “characteristics of fluvial behaviour”? Which flow does it refer to, the inflow, the one through the breach or the outflow?

line 188: I guess that the spillway is positioned at the outlet of the sediment basin and not “downstream” of it. Please correct, if I am correct.

line 195: How did you determine Q_v?

Eq. (1) and (2): Why do you use dV/dt instead of Q_v?

Eq. (1) and (2): In sec. 3.1.1 you explain that Q_breach was determined via Q_flood, i.e. Q_breach = Q_flood. Then Eq. (1) is wrong. Please explain.

line 201: typo “advanced” instead of “advances”

line 203: It is mentioned later, but the question arises already here: Which tracer was used for PTV?

line 207: Usually the term “flow transition” refers to the change between laminar and turbulent flow. Is it the same meaning here? What is the difference between the flow transition line and the water surface?

line 226: There is an incomplete sentence. Please correct.

line 236: “per points” should be deleted.

Fig. 3d: The water surface flow transition line in green is almost not visible. Can you improve the figure?

Tab. 2: What do you mean by “Event”? Is “Time” the continuing time of the test?

line 337-345: The description of how to determine Q_in and Q_out should already be described in sec. 2.

Fig. 8 and Fig. 9: Please quantify the differences between the methods of determining the breach outflow.

line 362: A full stop is missing at the end of the sentence.

line 378-390: This part needs to be phrased properly.

line 393: Figure 10b instead of Figure 10a

line 395: Figure 10a instead of Figure 10b

line 401-403: The sentence needs to be corrected.

line 414-415 and 420-421: The format needs to be corrected and here and there a minus is missing. In line 421 there is another typo.

In sec. 1 it is mentioned that soil characteristics (grain-size distribution, dry unit weight, water content) are key factors. How do these factors influence the results?

line 448-450: It is stated that the ISBOH method produces less discrepancies than determining the breach outflow at the sediment basin outlet. First: Where did you discuss this? Second: How can this be stated if the hydrograph determined at the sediment basin outlet is taken as a “benchmark”?

line 451: The concept of a flow transition line was not introduced (see questions regarding the flow transition line).

sec. 6.2: The potential of the method for field measurements is addressed. The breach geometry above and below the water surface can be measured by LiDAR. My question is, which degree of turbidity of the water is acceptable to use LiDAR?

Author Response

The attached pdf file is a point-by-point reply to the Reviewer#1 reviews.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper addresses the significant hydraulic engineering disaster of dike breaching by proposing a novel in-situ estimation method for breach outflow hydrographs (ISBOH), which integrates non-intrusive real-time monitoring technologies with physical modeling. The study was conducted on a medium-scale experimental platform, systematically evaluating the evolution of breach morphology and hydrodynamic characteristics by combining multiple techniques such as LiDAR, PTV, and mass balance, and validating the accuracy of the proposed method. Overall, the paper demonstrates strong innovation and significant application value. The topic closely aligns with practical needs for flood prevention and disaster mitigation, with a clear technical approach, reasonable experimental design, comprehensive data, in-depth analysis, and generally clear and concise writing, as well as a complete structure.

(1) Add a figure in Section 6 to compare the breach outflow hydrographs obtained from the ISBOH method with those from the spillway method and the mass balance method, and provide statistical metrics such as correlation analysis, root mean square error (RMSE), and Nash-Sutcliffe efficiency coefficient (NSE) to enhance the credibility of the conclusions.

(2) Add a paragraph in Section 3.2.1 or the discussion section to explain the limitations of LiDAR data acquisition at the water-air interface, the methods used for refraction correction, and the potential error range introduced to the calculation of the cone area.

(3) Although the study is based on a medium-scale experimental facility, it does not systematically discuss the influence of experimental scale (e.g., model scale) on breach evolution dynamics, flow structures, and the measurement accuracy of LiDAR/PTV.

(4) While LiDAR can obtain point clouds below the water surface, its underwater resolution and accuracy are significantly reduced due to light refraction and scattering in water. The paper mentions "post-processing corrected for the refraction indices," but does not specify the correction methods, error ranges, or validation through other means (e.g., contact measurements).

(5) The experiment uses polystyrene (Styrofoam) particles as tracers, but does not specify their density, particle size, or whether they settle or aggregate with the flow, nor does it assess their potential interference with surface tension or local flow patterns, especially in high-velocity or breaking wave regions.

Author Response

The attached pdf file is a point-by-point reply to the Reviewer#2 reviews.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

This paper can be accepted.