Thank you for your kind responses. As the reviewers suggested, I will give you a major revision.

I have a question regarding your responses to reviewer #2. The main novelty of the work is the use of a third-order numerical method in model structure. It is not clear in the manuscript.

Besides the questions and suggestions from the reviewers, there are still some questions need to be clarified:
1. Some tables can be merged
2. Page 11969: Line 13: “Dal = 0.8” cannot guarantee that the parameters are correct. The meaning of Table 4 is not clear, which need to be clarified. Also On page 11971 line 24.
3. The case study doesn’t consider the processes of absorption and dissolution, which need to the clarified.
4. Rewrite this sentence “In the following, for showing the higher accuracy of numerical method that used in the presented model, the results of three models, CTQS, CTCS and BTCS in compare with 2-D model ones, are presented.” On Page 11972. For me, it is not clear. What is the difference between the three models and the 2-D model?
5. A figure indicating your study area is suggested. And it is also suggested to add a figure showing the advection movement and the grid (Fig. 9) compared to the movement of 2-D model. If the experiments with different parameters, data and structure can be shown as figures or tables, it could be easier to understand. The experiment design is not clear through the whole manuscript. For example, how many dataset, models, setup are used?
6. Why no merge Fig. 7a and Fig. 7b? It is obscure.
7. The usage of “real data” and ”correct parameter values” are not rigorous.
8. About the sensitivity analysis, I don’t think it is reasonable: 1) “Input parameter” is not good, consider input variable or model parameter; 2) It is obvious that with changes in model parameter, the model performance will change; 3) Consider using the sensitivity analysis method in (Max D Morris, 'Factorial Sampling Plans for Preliminary Computational Experiments', Technometrics, 33 (1991), 161-74.)
9. Conclusions need to be more concise and should give the scientific contribution of this manuscript.

Dear Authors,

First of all, I have to tell you that another referee was anominated to review your manuscript. The most critical comments are listed below and I hope to recieve your reply soon.
1) The results show that the numerical schemes (including, in particular, OTIS, MIKE11) produce minor improvements in accuracy compared to the finite-difference scheme implemented in the software OTIS.

2) Contrary to the Authors' claim that the "paper proposes a one-dimensional model to simulate pollutant transport in rivers", the work is just an application of a standard numerical scheme to the solution of a well-established model for solute transport in rivers.

Best regards,
Y. Chen

1. Again, writers are suggested to ask the help from an English-speaking reviewer.
2. According to your responses, this study improved the one-dimensional model OTIS instead of “propose” a new model. The corresponding sentences should be corrected in the revised version. Maybe a name should be given for your model. What is the main contribution of this manuscript? This should be clearly addressed in the introduction part. The performances of several models were compared and better results were obtained using OTIS for advection flows. Therefore, some corrections are needed to better address the objective of this study.
3. It is not clear about the “two hypothetical examples and four sets of observed data”. The overall design of the six examples should be clarified. And their results should also be summarized.
4. All the tables and figures should be consistent and self-explaining. For example, CTQS in Table 2 is discretization scheme, but in Table 6 and Table 9 is one kind of models.
5. All the tables and figures should be concise. This manuscript is not interesting with the tables and figures that are often confusing in the current status. I have to look up for the meaning of the models or schemes or experiments. In addition, I don’t see any necessity to separately display the results of CTCS and BTCS in Figure 7.

First of all, I cannot find the exact correction in this version compared to the last version. In the response, the authors committed that the revisions have been done, which are suggested to be included in the response together with the line number.

About the figures and tables, I think some comparison is not well designed! Figure 7 can be merged in one to compare the results even if they are quite close. It does not make sense if you separate them.

Figure 9: What are the differences among figure 9 (a, b, c)?

Figure 15: “observes” should be corrected “observed”

The presentation of Figure 16 is not proper. Concentration at different times of different spot should be shown, that is to say, the time series of station 281 should be compared instead of comparison of different stations.

Figure 17 and figure 22: why does MIKE11 behave so badly?

Figure 19: why not add the simulation results?

Figure 20: it can be merged into one figure.

Figure 23: it is not clear. Is it observed data or simulated data?