the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Feb 2024
Comprehensive Factors Influencing Lateral Soil Water Flow Patterns on Hillslopes: Insights from Experimental and Simulation Studies
Abstract. This study conducted a rainfall tracer experiment on the slope to investigate water flow patterns. Three distinct water flow patterns were observed within the slope, including lateral upslope and vertical flow during rainfall, followed by lateral downslope flow after rainfall. A series of scenario simulations were conducted to enhance understanding of the comprehensive factors influencing lateral water flow on the slope. These simulations considered various factors, including two rainfall patterns (RP), three soil types (ST), three slope angles (SA), three anisotropy ratios (AR), and two layered slope systems (LS). The Hydrus-2D model was applied based on the two-dimensional Richards equation under given initial soil water and boundary conditions. Spatiotemporal variations in horizontal flux (qx), vertical flux (qz), and deviation of the water flow direction from vertical (DWFFV) in the central slope profile were calculated. The simulations of water flow on slopes under different conditions also confirmed three distinct water flow patterns manifesting within slopes during rainfall. The results indicated complete consistency between the direction of lateral water flow (lateral unsaturated upslope or downslope flow) and soil water potential horizontal gradients (∂φ/∂x). This suggests that the direction of lateral water flow is regulated by ∂φ/∂x rather than the change in water content over time (∂θ/∂t). The rate of movement of the wetting front differed among soil types, with the highest in sand. DWFFV and the corresponding qx value showed positive correlations with SA and AR.
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RC1: 'Comment on hess-2024-19', Ying Zhao, 22 Mar 2024
This study implemented a rainfall tracer experiment on a slope to analyze water flow patterns. Simultaneously, the HYDRUS-2D model was employed for scenario simulations, encompassing two rainfall patterns (RP), three soil types (ST), three slope angles (SA), three anisotropy ratios (AR), and two layered slope systems (LS), aiming to deepen comprehension of the those factors affecting lateral water flow on slopes. It has a potential contribution to the community as this topic is not well covered in the previous research, e.g., simulating of subsurface lateral flow based on the observation data. However, the current paper has some deficiencies:
I. A significant concern arises from the lack of connection between the experimental data and the model's approach or outputs. Essentially, the model remains unvalidated or untested against experimental data. Furthermore, even for tracer experiments, there was no data provided apart from a picture.
II. The paper contains an excessive amount of abbreviations, leading to poor readability. The introduction lacks significance, and the contents is not good enough to clearly specify the research's contributions. Furthermore, the literature review is outdated and fails to reflect the recent progress in related research.
III. The term "deviation of water flow direction from vertical (DWFFV)" could potentially be effectively assessed in HYDRUS by considering the velocity vector. The concept of a layered slope system appears challenging to interpret or assess. It appears to be described as altering the depth of the model domain from 200 cm to 100 cm and incorporating two layers of soil, each 50 cm thick, to represent layered soil, with the interfaces between layers aligned parallel to the slope surface. However, this description lacks clarity for me.
IV. The finding lacks novelty. I observed that the outcomes demonstrated "complete consistency between the direction of lateral water flow (lateral unsaturated upslope or downslope flow) and soil water potential horizontal gradients (∂φ/∂x)." Nevertheless, what sets this finding apart as novel?
V. To sum up, the paper lacks a clear purpose. I'm unsure about the problem it aimed to address.
More details:
Fig 5., the legend did not indicate the difference of slope angle.
Fig 11., Anisotropy ration should be anisotropy ratio.
It is unclear why “At the beginning of rainfall, the direction of water flow near the slope surface was towards the upslope.”Citation: https://doi.org/10.5194/hess-2024-19-RC1 -
RC2: 'Comment on hess-2024-19', Anonymous Referee #2, 25 Mar 2024
Review for “Comprehensive Factors Influencing Lateral Soil Water Flow Patterns on Hillslopes: Insights from Experimental and Simulation Studies”
This paper investigates the factors influencing lateral soil water flow on hillslope by both experimental and simulation methods. It is an interesting topic and is widely concerned. However, there are several problems that needs to be revised.
The main conclusion “The direction of lateral water flow is regulated by δψ/δx rather than the change in water content over time on hillslope” is easy to obtain according to basic soil physics and is not new to me. I suggest the authors to express this more explicit.
Lines 27-28. The factors influencing lateral flow could be more specific.
In the manuscript, both field experimental and numerical simulation are conducted to study the factors influencing lateral soil water flow patterns. What’s the relationship between the filed experimental and numerical simulation is not clear. The manuscript seems mainly focus on the numerical simulation.
Lines 85-100. The rainfall dye tracer was conducted with much heavy rainfall with an average rate of 0.3125 cm/min which is about 50 times the value for numerical simulation. The rainfall is too large to the real rainfall and may make saturated flow. Meanwhile, the soil water content is needed to show the unsaturated soil water condition during the experiment. Besides, the soil texture and hydraulic properties should also be presented.
Fig 1. It’s better to mark the direction of slope foot in fig (a) and (b).
Fig 3 (a) is normal to surface, (b) is vertical?
In line 175 DWFFV=-arctan(qx/qz), when qz<0 and qx>0, DWFFV>0. The signs seem reversed in Fig 5, where positive qx and negative qz corresponds to negative DWFFV.
Lines 200. What is duration of the rainfall, when rainfall ceases.
Fig 10. What does the blue color mean? The sub-figure number (d-e) should be consistent with (a-c).
Line 360. (b) “Conatant” should be “Constant”.
Citation: https://doi.org/10.5194/hess-2024-19-RC2
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