Morphological Characteristics of Constrained Meandering Rivers in the Loess Plateau
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview of “Morphological Characteristics of Constrained Meandering Rivers in the Loess Plateau”
By Li et al.
The manuscript is of importance for the Water Journal. The comparison between constrained and non-constrained river characteristics is important for the scientific community. I have found interesting results and discussions along the manuscript. Lots of references that tackle several parts of the manuscript are not updated, and I am mentioning some of them. What is needed is a description of the setting of each river used in the analysis, thus to go beyond to merely geometric comparison.
Main issues:
· The idea of comparing river planform configurations of the Shanxi-Shaanxi gorge with data from Guo et al. (2019) and Zolezz and Guneralp (2016) is appealing, but even in a single river, there are several external drivers such as vegetation, man-made structures, hydrological differences among rivers, soil composition along the floodplain, and of course geological constrain. Without the proper analysis, this comparison presented in this study is merely geometrical one, we need more process-based of the rivers used in the analysis.
· Row 41: the authors have mentioned “The main difference between constrained meandering rivers and freely-developed alluvial rivers is reflected in their plane shapes and migration characteristics (Nicoll and Hickin, 2010)”, however, constrained meandering rivers are located upstream in the watershed while lowland meandering rivers in the middle or lower portion of the watershed, thus, slope is also playing an important role.
· Figure 1: Since we have several rivers listed in Figure1, I recommend to show (in zoom windows) the planform configuration of specific reaches (the most interesting ones) so we can appreciate the diverse in planform configuration between constrained and non-constrained valleys.
· Rows 140 and 292: The authors should cite Gutierrez and Abad (2014) and Gutierrez et al. (2014) first introduced wavelet analysis into the study of meandering rivers. Additionally, important contributions by Vermeulem et al. (2016).
· Row 172: Additional articles are suggested to be cited: Ruben-Dominguez et al (2021) that also discusses the morphodynamic signals and the application of wavelet techniques.
Detailed issues:
· Figure 1: The resolution of the image should be higher. I can barely read the coordinates and text, and appreciate the colors.
References:
1. Ruben-Dominguez, L., Naito, K., Gutierrez, R. R., Szupiany, R., Abad, J. D. (2021). “Meander Statistics Toolbox (MStaT): a toolbox for geometry characterization of bends in large meandering channels”. SoftwareX, 14, 100674, https://doi.org/10.1016/j.softx.2021.100674.
2. Vermeulen, B., Holtink, T., Zolezzi, G., Abad, J. D., Aalto, R. (2016) “Multi-scale structure of meanders”, Geophysical Review Letters, 43: 3288–3297
3. Gutierrez, R. R., Abad, J. D., Choi, M, Montoro, H. (2014) “On the morphodynamics of free meanders confluences at the Upper Amazon Basin”, Geomorphology, 220: 1-14.
4. Gutierrez, R. R., Abad, J. D., (2014) “On the analysis of the medium-term planform dynamics of meandering rivers”, Water Resources Research, AGU, 50, doi:10.1002/2012WR013358.
Author Response
Comment 1: The idea of comparing river planform configurations of the Shanxi-Shaanxi gorge with data from Guo et al. (2019) and Zolezz and Guneralp (2016) is appealing, but even in a single river, there are several external drivers such as vegetation, man-made structures, hydrological differences among rivers, soil composition along the floodplain, and of course geological constrain. Without the proper analysis, this comparison presented in this study is merely geometrical one, we need more process-based of the rivers used in the analysis.
Response 1: Thank you for your suggestion. Vegetation, human activities, hydrological differences, and geological factors significantly influence river planform morphology. It is important to note that the rivers in this study are located on the Loess Plateau, incising into bedrock composed mainly of quartz sandstone and shale, which slows vertical incision and lateral erosion. Remote sensing images show that the planforms of these constrained rivers have changed very little over the past 40 years. The planform morphology at different scales can influence each other and may correspond with local geological constraints, vegetation, or other factors affecting meander formation. For rivers incising into bedrock, their planform shape is tied to the bedrock type. We have added a description of the geological distribution in the discussion section.
Comment 2: Row 41: the authors have mentioned “The main difference between constrained meandering rivers and freely-developed alluvial rivers is reflected in their plane shapes and migration characteristics (Nicoll and Hickin, 2010)”, however, constrained meandering rivers are located upstream in the watershed while lowland meandering rivers in the middle or lower portion of the watershed, thus, slope is also playing an important role.
Response 2: Thank you for your suggestion. The role of slope is indeed significant according to the erosion mechanisms of bedrock rivers. We have added an explanation of the importance of slope.
Comment 3: Figure 1: Since we have several rivers listed in Figure1, I recommend to show (in zoom windows) the planform configuration of specific reaches (the most interesting ones) so we can appreciate the diverse in planform configuration between constrained and non-constrained valleys.
Response 3: Thank you for your suggestion. Following your advice, we have revised Figure 1, increasing the resolution and adding planform configurations of three constrained river segments.
Comment 4: Rows 140 and 292: The authors should cite Gutierrez and Abad (2014) and Gutierrez et al. (2014) first introduced wavelet analysis into the study of meandering rivers. Additionally, important contributions by Vermeulem et al. (2016).
Response 4: Thank you for your suggestion. We have cited the works of Gutierrez and Abad (2014) and Gutierrez et al. (2014) in both locations, as they first introduced wavelet analysis into the study of meandering rivers. We have also integrated the methods and findings from Vermeulen et al. (2016).
Revised sections: "Wavelet transformation of curvature series is used to describe meandering behavior, detect changes in meandering characteristics, analyze changes in different supersinuosity scales, and characterize meander wavelength (Gutierrez et al., 2015; 2014; Gutierrez and Abad, 2014; Vermeulen et al., 2016). Gutierrez and Abad (2014) employed wavelet transformation to quantify meandering morphology metrics, such as the planform curvature signal of meandering rivers. Vermeulen et al. (2016) proposed a quantitative approach using continuous wavelet transformation to study the planform shape of meandering features."
"Gutierrez and Abad (2014) and Gutierrez et al. (2014) were the first to introduce wavelet analysis into the study of meandering rivers. Gutierrez and Abad (2014) used Morlet wavelet functions to perform wavelet analysis on the local transverse coordinates of dimensionless curvature in natural meanders."
Comment 5: Row 172: Additional articles are suggested to be cited: Ruben-Dominguez et al (2021) that also discusses the morphodynamic signals and the application of wavelet techniques.
Response 5: Thank you for your suggestion. We have added the work of Ruben-Dominguez et al. (2021), revising the section as follows: "Ruben-Dominguez et al. (2021) proposed the Meander Statistics Toolbox to compute sinuosity, meander length, chord length, meander amplitude, and meander direction from river centerline data plotted from upstream to downstream."
Comment 6: Figure 1: The resolution of the image should be higher. I can barely read the coordinates and text, and appreciate the colors.
Response 6: We have revised Figure 1 and added images of three river segments, increasing the resolution.
Reviewer 2 Report
Comments and Suggestions for AuthorsYour paper on meandering rivers in the Loess Plateau is insightful, but I suggest few suggestions to improve the current manuscript:
1. Your introduction needs significant improvement; it currently lacks key references and a thorough review of recent advancements in geospatial technologies and soft computing (AI/ML based study). Additionally, for the morphometric analysis, please ensure you address relevant advancements and clearly outline research gaps and objectives, rather than just focusing on changes.
2. The manuscript lacks a discussion on how erosion is influenced by rainfall, including the erodibility rate. Please include an analysis of this relationship and specify the erodibility rate to provide a comprehensive understanding of the erosion dynamics.
3. The research motivation is unclear and needs to be better articulated. Please provide a more detailed explanation of the underlying reasons for your study and its significance in addressing the identified research gaps.
4. Abstract has to be written in such a way that it reflects the motivation, research gap, data used, methodology, and application of the research findings.
5. The study should address how various factors, including rainfall, influence river course changes. Please include details on the spatial distribution of the study area, the intensity of rainfall leading to erosion, and a description of soil types. This information is crucial for understanding the erosion dynamics in your study area.
6. The analysis of river meandering parameters such as sinuosity lacks a clear connection to river hydraulics and geomorphology. The significance of each parameter in relation to river flow and deposition rates is not adequately discussed, making it challenging to understand their implications. Please provide a detailed explanation of how each parameter affects river dynamics and deposition processes, linking them explicitly to hydraulic and geomorphological concepts to enhance the technical rigor of your analysis.
7. The significance of "Cartesian wave number" and skewness characteristics is unclear. Please provide a more detailed explanation of how these metrics are relevant to your study and their implications for understanding river dynamics or geomorphological processes.
8. The manuscript lacks a discussion on how the results of different parameters compare with similar properties observed in other regions. Please include an analysis of these comparisons and their impacts to provide broader context and relevance for your findings.
9. The manuscript does not address how the findings can assist policymakers and river engineers in designing hydraulic structures. Please add a section discussing the practical implications of your results for these stakeholders. Additionally, include an analysis of how future climate changes might affect river course dynamics and floodplain impacts. This will enhance the relevance and applicability of your research for real-world applications.
10. Please revise the Abstract and Conclusion sections in accordance with the above suggestions and additional suggestions provided in the attached file. Ensure that you incorporate the suggested changes and make any necessary minor English corrections to improve clarity and coherence.
Comments for author File: 
Comments.pdf
Minor English corrections is required
Author Response
Comments 1: Your introduction needs significant improvement; it currently lacks key references and a thorough review of recent advancements in geospatial technologies and soft computing (AI/ML based study). Additionally, for the morphometric analysis, please ensure you address relevant advancements and clearly outline research gaps and objectives, rather than just focusing on changes.
Response 1：Thank you for the reviewer’s suggestions. We have revised the introduction and added recent references on methods for analyzing river planform morphology.
” In terms of the elucidate the morphological characteristics of meandering bends, Ruben-Dominguez et al. (2021) proposed meander statistics toolbox to calculate the river centerline’s sinuosity, meander length, chord length, meander amplitude, and meander orientation, while the data of the river centerline was drawn from upstream to downstream. Numerous efforts have been made to characterize large planforms dynamics using satellite images on GIS planforms (Fisher et al., 2013), as well as on MATLAB and Python platforms (Monegaglia et al., 2018; Schwenk et al., 2016). Recently, He Y et al. (2024) based on GEE (Google Earth Engine) platform, they used multi-source remote sensing images (Landsat 5/7/8 and Sentinel-2) for water segmentation of braided rivers and calculated the morphological characteristics parameters.” However, it should be noted that on the Loess Plateau, the difficulty in river extraction lies in its high sediment concentration. During the extraction process, the turbid river water is easily extracted along with mountains, shadows, and other features, which increases the complexity of the extraction.
Comments 2： The manuscript lacks a discussion on how erosion is influenced by rainfall, including the erodibility rate. Please include an analysis of this relationship and specify the erodibility rate to provide a comprehensive understanding of the erosion dynamics.
Response 2：Thank you for the reviewer’s suggestions. We indeed did not discuss the impact of rainfall on erosion. It is important to note that the rivers we are discussing are incised into bedrock, also referred to as constrained rivers in the paper. Both lateral and vertical erosion rates in such rivers are relatively slow, typically measured on a geological timescale. Therefore, from the perspective of the past 40 years, their erosion can be considered negligible. In response, we have added a brief analysis of the geology of the rivers in the study area in the discussion section to clarify the scale and magnitude of the erosion occurring there.
Comments 3：The research motivation is unclear and needs to be better articulated. Please provide a more detailed explanation of the underlying reasons for your study and its significance in addressing the identified research gaps.
Response 3：Thank you for the reviewer’s suggestions. We have added the motivation and fundamental reasons for the study in the introduction. Currently, with the construction of China's national water network, key hydraulic nodes such as the Dongzhuang Reservoir on the Jing River, the Malian River Reservoir on the Malian River, and the Guxian Reservoir in the Jin-Shaanxi Canyon are crucial. The rivers analyzed in this study are mostly within the impact areas of these important reservoirs. Therefore, analyzing the planform characteristics of these rivers is highly significant for understanding sediment deposition along the river and changes in hydrodynamic conditions after the reservoirs are built. Additionally Gutierrez and Abad (2014) thought that the quantification of the variability of meandering rivers morphometrics is necessary for scientific, such as analyzing the interrelationship between meanders and riparian vegetation, the influence of sinuosity on surface and groundwater interrelationship, distinguishing natural from modeled channels, and among others, and practical purposes, such as the design of civil infrastructure projection, impact of reservoir on meandering planforms, river restoration, and among others.
Comments 4：Abstract has to be written in such a way that it reflects the motivation, research gap, data used, methodology, and application of the research findings.
Response 4：hank you for the reviewer’s suggestions. We have revised the abstract to highlight the significance and motivation of this study.
“In the Loess Plateau of China, loess is widely distributed and forms a unique geomorphic feature of the world. Meanwhile, the Yellow River water and sediment regulation system is under construction. Nontheless, the morphological characteristics of constrained meandering rivers in the Loess Plateau are still unknown due to the difficulty of extracting the sediment-laden water body. An improved method is proposed based on Landsat 8 imagery, which automatically extracts the multi-band spectral relationship of high sediment concentration rivers in valleys. This study analyzes the morphological characteristics of constrained meandering rivers in the middle reaches of the Yellow River Basin, including their sinuosity, periodicity, curvature, and skewness. These characteristics are then comparing them with those of other constrained meandering rivers and alluvial meandering rivers. The results show that the sinuosity of the constrained river bends is mainly low (<1.50) due to the limitations imposed by the riverbanks, preventing full development. Regarding skewness, the skewing angle of the constrained river bends is similar to that of alluvial bends, generally inclining upstream. In constrained river bends, as the sinuosity increases, the proportion of bends skewing upstream initially increases and then gradually decreases. This indicates that constrained river bends can develop similarly to alluvial bends at lower sinuosity but are limited by the mountains on both sides at medium sinuosity. The analysis of river characteristics in regions with different geological structures reveals the effect of geological structures on the formation of constrained rivers in the Loess Plateau. These findings can provide a reference for selecting reservoir dam sites and are important for the dredging engineering layout in the middle reaches of the Loess Plateau. They also offer quantitative explanations for the meandering characteristics of these rivers.”
Comments 5: The study should address how various factors, including rainfall, influence river course changes. Please include details on the spatial distribution of the study area, the intensity of rainfall leading to erosion, and a description of soil types. This information is crucial for understanding the erosion dynamics in your study area.
Response 5：Thank you for the reviewer’s suggestions. We have added a new section in the discussion, analyzing the erosion characteristics in different regions. However, it is important to note that the scale of these erosion characteristics is relatively long-term, with minimal changes over the past 40 years. Since the substrate is primarily bedrock, the rates of downcutting and lateral erosion are very slow.
窗体底端
Comments 6: The analysis of river meandering parameters such as sinuosity lacks a clear connection to river hydraulics and geomorphology. The significance of each parameter in relation to river flow and deposition rates is not adequately discussed, making it challenging to understand their implications. Please provide a detailed explanation of how each parameter affects river dynamics and deposition processes, linking them explicitly to hydraulic and geomorphological concepts to enhance the technical rigor of your analysis.
Response 6：Thank you for the reviewer’s suggestions. We need to clarify that the rivers discussed in this paper are constrained meandering rivers. As mentioned in the paper, “the constrained meandering rivers in the Shanxi-Shaanxi gorge section of the Loess Plateau belong to the second type of Lewin’s classification (Lewin and Brindle, 1977). This classification indicates that the width of the valley is less than the amplitude of the meandering river, the distribution of alluvial sediment is discontinuous, and the outer bank of the meandering river is close to the constrained gorge.” According to field observations, the bedrock is exposed, and there are essentially no continuous sediment deposits. This is primarily related to the specific hydrological environment: concentrated flow during the flood season and low flow during the dry season. Additionally, the riverbed has a steep gradient, leading to high flow velocities during floods, with the sediment transport capacity often exceeding the sediment concentration, resulting in minimal sediment deposition on the riverbed. However, the sedimentation in the reservoir areas of the Guo Xian, Dongzhuang, and Mianhe Reservoirs in the studied river section will have a certain relationship with the planform characteristics of the river channel. This study aims to provide references for future sedimentation patterns.
Comments 7: The significance of "Cartesian wave number" and skewness characteristics is unclear. Please provide a more detailed explanation of how these metrics are relevant to your study and their implications for understanding river dynamics or geomorphological processes.
Response 7：According to Zolezzi & Günera (2016), the Cartesian meander wavelength (Lx) is the Cartesian distance between the upstream and downstream endpoints of the considered meander, and the Cartesian wavelength ,λx =π/(Lx/W), W is the width of river. And the intrinsic meander wave number λ=λx/μH，μH为半河湾弯曲度。The dominant meander wavelength is the wavelength associated with the highest oscillation energy. Therefore, the Cartesian wave number indicated the intrinsic meander characteristics. For bankfull hydraulic conditions, the instability mechanism has been found to invariably operate such that the straight channel becomes unstable only for ‘long enough’ planform perturbations, which commonly characterized by the Cartesian wave number below 0.1~0.2. And the bend growth rate increases nonlinearly with decreases value of Cartesian wave number
In meandering rivers, a frequently used shape of river planfroms is generated with the Kinoshita curve, and the Kinoshita curve gives an angle of the planform as a function of the s-coordinate.
Where cf and cs account for flatting and skewing of meanders, respectively.
Meander bends are rarely symmetric in the streamwise direction. Instead, they tend to show a preferred skewing, with the apex either pointing upstream (upstream-skewed) or downstream (downstream-skewed). The skewness of bends in meandering rivers reveals the future development trends of the river bends and the potential for shortcutting，which means that rivers often carry an imprint of the direction of the flow that created them.
Zolezzi G, Güneralp I. Continuous wavelet characterization of the wavelengths and regularity of meandering rivers[J]. Geomorphology, 2016,252:98-111.
Comments 8: The manuscript lacks a discussion on how the results of different parameters compare with similar properties observed in other regions. Please include an analysis of these comparisons and their impacts to provide broader context and relevance for your finding
Response 8：Thank you for the reviewer’s suggestions. Firstly, it should be noted that the Loess Plateau in China has its unique characteristics. It features a thick loess cover, but the rivers that develop there cut deeply into the bedrock. During periods of intense rainfall, the erosion intensity of the mountain slopes increases, and finer sediment particles become suspended in the river, though coarse sediments are less prevalent. To address the unique planar morphology of constrained rivers on the Loess Plateau, we have added an analysis of different geological structures on the Loess Plateau in the discussion section. We analyzed the development process of constrained rivers from a geological perspective and compared their morphological characteristics with those of other constrained rivers.
Comments 9: The manuscript does not address how the findings can assist policymakers and river engineers in designing hydraulic structures. Please add a section discussing the practical implications of your results for these stakeholders. Additionally, include an analysis of how future climate changes might affect river course dynamics and floodplain impacts. This will enhance the relevance and applicability of your research for real-world applications.
Response 9：Thank you for the reviewer’s suggestions. We have added a section in the discussion on the implications of our research results for river engineers in designing hydraulic structures. Due to the lack of analysis on the process of river planform evolution and the relatively minor changes in river planform over recent decades, we will include an analysis of the potential impacts of future changes in water and sediment conditions in the Yellow River Basin. Additionally, we will discuss possible future changes in river sedimentation and planform morphology in relation to the ongoing construction of hydraulic engineering.
Comments 10: Please revise the Abstract and Conclusion sections in accordance with the above suggestions and additional suggestions provided in the attached file. Ensure that you incorporate the suggested changes and make any necessary minor English corrections to improve clarity and coherence.
Response 10：Thank you for the reviewer’s suggestions. We will make detailed and careful revisions to the manuscript based on the recommendations and improve its clarity and coherence.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have revised the manuscript and I agree with the current version
Author Response
Comments 1:The authors have revised the manuscript and I agree with the current version
Response1 :Thank you very much for your thorough review and positive feedback on our revised manuscript. We greatly appreciate your time and valuable suggestions, which have helped improve the quality of our work.
Reviewer 2 Report
Comments and Suggestions for Authors1. Improve the abstract by clear wring the methodology adopted and key results (quantitative) values.
2. Many figures are not clearly discussed and co-relate it with the reasons.
3. Make out the future scope of this study with respect to the regional development and overall management/mitigation of Meandering in the Loess Plateau.
4 Rewrite conclusions in summary form.
Comments on the Quality of English LanguageCheck for the Typo errors and minor english editing.
Author Response
Comments 1: Improve the abstract by clear wring the methodology adopted and key results (quantitative) values.
Response 1: Thank you for your valuable comments. We have added a description of the methodology used and included quantitative results in the abstract, as per your suggestion. The second-round revisions have been highlighted in red in the revised manuscript.
Comments 2: Many figures are not clearly discussed and co-relate it with the reasons.
Response 2: Thank you for your valuable feedback. We acknowledge that the analysis of some figures was not sufficiently detailed. In response, we have provided more thorough discussions and analyses of each figure in relation to the corresponding research content. The second-round revisions have been highlighted in red in the revised manuscript.
Comments 3: Make out the future scope of this study with respect to the regional development and overall management/mitigation of Meandering in the Loess Plateau.
Response 3: Thank you for your valuable suggestion. We have added a section at the end of the manuscript discussing the future scope of this study. For example: "As the water and sediment regulation system in the Yellow River Basin continues to improve, along with the construction of key reservoirs, future research should focus on exploring the sedimentation processes in constrained river bends and selecting appropriate dredging sites based on the findings of this study. This would help extend the service life and preserve the effective storage capacity of the reservoirs in the Yellow River Basin, thereby promoting the high-quality development of the region." These revisions have been highlighted in red in the revised manuscript.
Comments 4: Rewrite conclusions in summary form.
Response 4: Thank you for your suggestion. We have revised the conclusions to provide a more concise summary, highlighting the key findings of the study and outlining future research directions. The revisions have been highlighted in red in the updated manuscript.
