the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Feb 2025
Quantification of capillary rise dynamics in snow using neutron radiography
Abstract. Liquid water flow in snow is important for snow hydrology, remote sensing, and avalanche formation. Water flow in snow is often dominated by capillary effects, which are responsible for the formation of capillary barriers, capillary flow paths, and capillary rise. Unfortunately, there is little quantitative data on the capillary forces of snow, particularly with respect to capillary rise dynamics. Here, we present the results of 4 capillary rise experiments using neutron radiography. The experiments were performed in 13 x 13 x 1 cm3 glass columns with sand-snow and sand-gravel-snow layering mimicking the capillary forces at the soil-snow interface. Images were taken at 10 s to 15 s intervals with a pixel size of 92 μm. The experiments provided quantitative results of high resolution liquid water profiles, wetting front progression, flow rates, and parameterization of snow hydraulic properties. The experiments showed that the snow properties influenced the capillary rise height while the hydraulic properties of the transitional layer below the snow influenced the flow rates. Flow rates in all three layers were significantly below the expected saturated hydraulic conductivity values.
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-304', Anonymous Referee #1, 19 Mar 2025
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In this paper, the authors report on the results of measurements of capillary rise in snow, which is important not only for understanding the hydrological characteristics of snow but also for considering the interaction between snow and soil, using neutron radiography with high spatial and temporal resolution. In addition, based on the measurement results, they calculated the water retention curve and saturated hydraulic conductivity, which are important for understanding the characteristics of water movement in snow, and compared them with previous research.
The structure of the paper is very well organized and easy to understand. In particular, the experimental methods and analysis methods are described in detail, and this will be very useful when conducting additional experiments in the future. The results and discussion are highly reliable, as the study not only compares with previous research, but also takes into account the limitations of the measurement methods used in this study. The results of this research will undoubtedly contribute to the development of wet snow research, and are of sufficient scientific value to be published in academic journals.
The paper is of a high standard and there are no major points that need to be revised, but I will list some points that I noticed.
Mejor comments:
- When determining the water retention curve and saturated hydraulic conductivity, the measured data is fitted using the least squares method. I understand that you have chosen the best method for determining the parameters, but in some cases, the fitting seems to be unreasonable depending on the experimental conditions. This is particularly true for the fitting used to determine the saturated hydraulic conductivity. I recommend that you show the regression error so that readers can judge the reliability of each fitting.
- The dry density of the snow sample is required to calculate the liquid water content, and they were calculated from their optical density of the first image. As Table 1 shows, the dry density calculated from the optical density differs even for the same snow quality (ex. FGs, g, FGs) and they also differ from the density obtained from X-ray CT. As the authors point out, it is not necessary for the density obtained from X-ray CT to match the density of the sample in the case. However, when calculating the liquid water content using the density obtained from X-ray CT, how much difference is there compared to when calculating the liquid water content using the density obtained from the optical density? Such information (The impact of density estimation on results) should be important for readers to understand the reliability of the results of this study and the points for improvement of this method. Therefore, I propose adding this kind of discussion to the paper.
Specific comments:
L81: How was the melt form created in an environment with -1 °C?
L263: In the text, it is claimed that “the fine-grained snow led to higher final wetting front positions (7 cm to 8 cm) compared to the coarse-grained snow (4 cm to 5 cm).” Which diagram did you use to make this judgement?
Citation: https://doi.org/10.5194/egusphere-2025-304-RC1 -
RC2: 'Comment on egusphere-2025-304', Anonymous Referee #2, 19 Mar 2025
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This paper presents neutron radiography results of snow/soil interface fitting it with a 1D model. The paper is very well written and clearly structured.
My main concern is heterogeneity: the sample is highly heterogeneous and so is the fluid flow (e.g., Fig. 9), yet the methods adopted essentially neglect this intrinsic heterogeneity. The adoption of radiography (over neutron tomography) for example, could be questioned. Even neglecting the third dimension, the fitting curves appear rather far from the experiments (e.g., Fig. A8/9/10) both in terms of local fluctuations and overall trend (this could also explain some of the convergence issues).
Much of the discussion is focused on the mismatch between the fitted parameters and literature predictions but this discussion could appear a bit stretched once accounting for this simplification.
In the 2D analysis you make the hypotheses that the snow does not move but playing the videos in the supplementary materials they all move by a significant amount downwards with a slight turn.
Specific and minor notes:
= Section 2.4 appears scientifically correct and clear, but it follows mostly a well-established approach and could conceivably be moved to an Appendix.
= The review in the introduction is paraphs a bit broad compared to the actual topic of the work and could conceivably be refocused. Also, it does not mention if a similar experimental approach has been adopted before.
= Why deduce the density from CT and not gravimetric measures?
= “weak capillary forces of a high porosity layer of a vegetation layer” perhaps rephrase to avoid repetition?
Citation: https://doi.org/10.5194/egusphere-2025-304-RC2
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