No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Characterizing scale-dependent heterogeneity of soil water movement through dying infiltration experiments
Abstract
To address the flow heterogeneity issue, the objective of this study are to investigate heterogeneity of soil water flow at different measurement scales using dying infiltration experiments and characterize the heterogeneity information included in different scales with the random cascade model. The random cascade model with a lognormal distribution is used to simulate the infiltration process in soils, and the different methods are applied to estimate the model parameters. Results based on the experimental data and the model simulations show that the measurement scale is important factors affecting the flow patterns in soils. To accurately describe flow transport processes at different scales, it is necessary to consider heterogeneities in the vertical and horizontal directions. As the measurement scale increases, the effect of multi-dimensional heterogeneities on the flow processes in soils becomes more significant.
The vadose zone serves as a crucial link for the mutual transformation of atmospheric, surface, ecological, and groundwater systems. Infiltration recharge in the vadose zone is a key step in the Earth's water cycle and plays an extremely important role in the sustainable development of groundwater resources, particularly in arid and semi-arid regions. However, under the influence of extreme climatic conditions and intense human activity, the vadose zone has thickened in many places globally. Changes in the vadose zone structure lead to alterations in the infiltration process. Researchers have attempted to quantify this process using various methods. However, it has been found that conventional monitoring methods are inadequate to effectively describe the complex infiltration recharge process under the multifactorial influence of a deep vadose zone. Through an analysis of relevant literature published from 2000 to 2023 regarding deep vadose zone infiltration recharge, this paper identifies four contentious bottlenecks: (1) effective monitoring and simulation of deep vadose zone infiltration recharge, (2) modes of deep infiltration recharge, (3) issues related to the quantity and recharge period of precipitation and irrigation infiltration recharge, and (4) quantification of spatial variations and scale effects of infiltration recharge. After reviewing the latest developments in infiltration recharge monitoring and simulation and systematically analyzing the influencing factors and mechanisms of deep vadose zone infiltration recharge, this study provides answers to the aforementioned issues. The combined use of monitoring and numerical simulation methods, taking into account infiltration recharge scenarios and scales, can enhance the reliability and accuracy of the calculation results. Additionally, piston flow may not be the primary mode of water movement in the deep vadose zones. Understanding the modes and characteristics of water movement, as well as the differences in suction and desorption processes, is fundamental for accurately describing nonlinear infiltration recharge processes. Furthermore, the measured average vertical infiltration rates of the deep vadose zone vary widely from 0.14 to 500 mm/d globally. In the North China Plain, vertical infiltration recharge rates range from 133 to 300 mm/a. These significant differences are related to the research scale, external conditions, and internal soil structure within the vadose zone. Finally, a systematic analysis of the driving factors of nonlinear infiltration recharge in the deep vadose zone is a prerequisite for quantifying spatial variations and scale effects. Only by fully considering the interactions and contributions of various driving factors can the spatiotemporal variations in soil infiltration be effectively quantified. Therefore, our research team suggests that future studies on deep vadose zone infiltration recharge should focus on establishing a unified layout for large-scale, multi-point, synchronous, in situ, and long-term monitoring; constructing relationships between the vadose zone structure and hydraulic characteristics; and conducting comprehensive studies on the overall water cycle in the Earth's surface layers, with the deep vadose zone as the core. These will help build a research system for the spatiotemporal infiltration recharge of water in the deep vadose zone at multiple layers and scales, achieving the closest approximation to a realistic description of the deep vadose zone infiltration recharge.
The water movement in landfill cover soils is studied using the information theory measures. The volumetric soil water contents beneath landfill obtained from the field experiments, and the simulations using the Active Region Model (ARM) and the continuum soil model are used in this study. ARM performs better than the continuum soil model compared to the observations. The time series of simulated soil moisture contents is encoded into a binary form with 'zero' and 'one' respectively representing the situations of below and above the mean soil moisture content. The information content is evaluated using the information entropy and the mean information gain. The complexity of flow patterns is quantified using the effective complexity value and the fluctuating complexity value. The result shows that the information theory measure appears to be a versatile tool of discriminating the soil moisture models. The time series of soil moisture contents simulated by ARM retains more information contents and complexities compared to those simulated by the continuum soil model.
Heterogeneous soil water flow was investigated by using the iodine-starch staining patterns. The field experiments were conducted at four plots with ponding water depths of 20, 40, 60, and 80 mm, respectively. The stained patterns of soil profiles show that soil water flow changes from the preferential flow with a few flows path and low stained coverage to the homogeneous infiltration of the decreased unstained areas with the increase of ponding water depths. The redistribution of infiltration water is mainly influenced by the stained patterns. Flow patters are characterized by using the distributions of the maximum and actual depths. The heterogeneous soil water flow patterns from the four experiments show the multifractal nature. The flow heterogeneity is closely correlated to the multifractal spectrum. The constitutive properties of the fractal spectrum function are determined by the soil texture, whereas the range and shape of the function are affected by the nonlinearity of the heterogeneous flow.
The objectives of this study are to develop a quantitative method to describe heterogeneous flow patterns and identify the heterogeneous information characteristics based on flow patterns. Dye tracer experiments were performed on plots with different conditions. The flow patterns were separated into similarly stained horizontal layers based on the width distributions of the stained areas. Then the layers identified in the flow patterns were partitioned into groups with similar patterns by hierarchical clustering. The results show that the dye coverage and width of stained structures are the most indicative factors for the different clusters. The number of clusters affects the degree of layer discrimination. Three and eight clusters seem to be sufficient to capture the main characteristics of the heterogeneous flow patterns. For the experimental plots where the vertical flow is dominated, the clusters contain the layers with the homogeneous flow, preferential flow, and those with flow changes from homogeneous infiltration to preferential flow. For the experimental plots where the horizontal heterogeneous is significant, the soil horizons has a strong influence on the water flow patterns.
The major objective of this study is to investigate the heterogeneity of soil water flow. Field experiments were performed in loam and clay soil and an iodine-starch staining method was applied to visualize flow paths in the soil. Heterogeneous flow patterns were described by using information entropy and multifractal theory. Results show that information entropy increases with decreasingly characteristic length, which is a scale used to characterize flow stained patterns. The soil flow heterogeneity is similar at different measurement scales. However, the variance of flow distributions change with scales. In the loam soil, scaling invariance of water flow distributions is in a larger range than that in the clay soil.
Preferential flow is a main type of soil water movement in the structured soil. Although previous researches have made a great progress in preferential flow, how to compare the level of preferential flow based on the dyed pattern of soil profile by dyeing tracers is not reported yet. Therefore, in this paper, the Brilliant Blue FCF (C.I. 42090) dye tracer experiment was designed to investigate and quantify the preferential flow in five intact and five disturbed soil columns sampled at the depth of 0-100 cm from the Experimental Station of the Institute of Hydrogeology and Environmental Engineer, Chinese Academy of Geological Science (Hebei, China) and from Luancheng Experimental Station of Chinese Academy of Science (Hebei, China). Soil water movement patterns of the intact and disturbed soil columns were compared. The results showed that the preferential flow was developed in the intact soil columns, while the piston flow in the disturbed soil columns. The characters of preferential flow in the soil profiles varied along both horizontal and vertical directions. The coefficients of variation (C.V) of the dyed area percentages in the whole profiles of soil columns were proposed to quantify preferential flow in the undisturbed columns and the capacity of soil water movement in the disturbed columns as long as 1) the irrigation conditions were same for all columns; 2) the area of preferential flow was larger than that of uniform flow in intact columns; and 3) the mass-transfer coefficients of soil water flowing horizontally from the preferential path to the matrix were same. Small C.V value represented the high levels of preferential flow in the intact columns. The C.V≥0.5% indicated the low levels of preferential flow, while C.V of >0.25%~<0.5% and ≤0.25% suggested the medium and high levels, respectively. However, the estimated principle may be not suitable for intact soil columns with different kinds of preferential path, i.e., soil cracks and plants' root and earthworm burrows. The preferential levels of the soil columns assessed by the C.V of the dyed area percentages were verified successfully by the irrigation test of undistributed and distributed columns designed to quantify the percentage of preferential flow. However, the results of preferential flow levels estimated by the C.V may be affected by size of columns, because the characters of preferential flow varied with study scales. Therefore, more studies were needed to verify the feasibility of C.V in estimating the preferential flow level. The study here proposed a quantitative method to assess the preferential flow level directly from the dyed pattern of the soil profile, and to evaluate the groundwater recharge, saving water and soil polluting in agriculture.
With a soil field infiltration test in the Yangling area as the basis, Philip's infiltration equation was calibrated by using the calibration theory. The calibration coefficient and the spatial variability of soil physical properties were analyzed using the multifractal method, and based on the joint multifractal theory, a pedo-transfer function of calibration factors was constructed. The research has shown that the calibration results of arithmetic calibration factors are the most optimum. Calibration factors and soil physical properties within the research area possess multifractal characteristics, and on single and multiple scales, the spatial variability of calibration factors, sand content and organic matter content are relatively strong. The spatial variability of calibration factors and sand content is composed of high values in different scale intervals, and the spatial variability of coarse dust content is composed of low values in different scale intervals. On a single scale, there is relatively significant correlation between calibration factors and the content of organic matter as well as clay particles, and on a multiple scale, there is a significant correlation between calibration factors and soil bulk density, clay particle content and organic matter content. The soil transformation function of calibration factors from joint multifractal theory has relatively small calculation errors, and the pedo-transfer function from joint multifractal analysis can possesses a strong theoretical basis and value.
Based on the experimental data collected from the first terrace in Yangling station, we perform both multifractal analysis and joint multifractal analysis to investigate the spatial variability and relationship between the stable infiltration rate and soil infiltration characteristics, and establish the pedo-transfer functions (PTFs) of soil infiltration characteristics. The results show that the infiltration characteristics are multifractal. The observed spatial variability of stable infiltration rate and the beginning 30-min cumulative infiltration are mainly caused by the different sand and clay contents in the soil samples. The multi-scale analysis results show that the spatial variations of soil sand content and organic matter content have significant influences on the spatial variability of steady infiltration rates. The beginning 30-min cumulative infiltration is mainly affected by the distributions of slit and clay content which are the same factors in multi-scale as the observation scale. Two pedo-transfer functions of infiltration characteristics are established with the joint multifractal analysis and the beginning 30-min cumulative infiltration, respectively. The computational error of the former is less, the later is relatively larger.
The preferential flow is common in the soil with preferential paths, which affects soil water infiltration greatly. Although previous studies have made a great progress in preferential flow, the effect of preferential paths on preferential flow has not been reported, and a great effort is necessary to understand how precipitation intensities affect preferential flow. Therefore, in this paper, five undisturbed soil columns were sampled at the depth of 0-100 cm with different distribution of preferential paths from the Experimental Station of the Institute of Hydrogeology and Environmental Engineer, Chinese Academy of Geological Science (Hebei, China) and from Luancheng Experimental Station of Chinese Academy of Science (Hebei, China). Tests of different precipitation intensities, i.e., 0.23-0.24, 0.07-0.11, and 0.008-0.042 cm/min, were done to investigate preferential flow of the five soil columns. And the Hydrus-1D software coupling a dual-permeability model was applied to simulate the preferential flow of the soil columns under differential rainfall intensities. The results showed that the preferential paths played a vital role in development of the preferential flow since the levels of preferential flow were higher with more preferential paths in the soils. The relative transport abilities of preferential paths, which were defined by the ratio of velocity of preferential flow to rainfall intensity, increased with heavier rainfall. When the rainfall intensities were larger than the maximal coefficients of hydraulic conductivity of the intact soil columns, the velocities of preferential flow increased remarkably with increase of rainfall intensities. However, when the rainfall intensities were smaller than the maximal coefficients of hydraulic conductivity, the velocities of preferential flow increased little or no change. The effect of rainfall intensities on the ν and increased ranges of ν was related to the development of preferential paths in the intact soil columns, i.e., the effect can be stronger with the higher degree of preferential paths. In the soil columns with better development of preferential paths, the initial times of soil water flowing out at the bottom of the soil columns were shorter when rainfall intensities were larger, while in the soil columns with well developed preferential paths, the initial times of soil water flowing out at the bottom of the soil columns decreased firstly with a higher rainfall intensity, and then increased. The dual-permeability model described preferential flow well but couldn't simulate the process that soil water in the soil matrix flowed out horizontally to preferential paths after the rainfalls. As such the model was not suitable for the soils with plenty of soil fissures. The percentage of preferential flow obtained from the results of modeling was 93.6%-99.9%, which was in agreement with the tested results in undisturbed to disturbed soil. It suggested the model could simulate the preferential flow well. However, the results may be affected by size of columns since the characteristics of preferential flow varied with study scales. Therefore, further studies were needed to improve the understanding of preferential flow in larger scales. The results here will be useful to evaluate the groundwater recharge, water saving methods and movement of soil pollutants in arable land. ©, 2014, Chinese Society of Agricultural Engineering. All right reserved.
In order to analyze the horizontal distribution characteristics of different influence radius preferential flow paths and the spatial associations of biological activity in purple sandstone regions of farmland (vertical soil depths of 10~50 cm) in Three Gorges Reservoir Area, the spatial point pattern analysis method (g(r) function) of quantitative ecology was used. After the Monte-Carlo stochastic simulation test, the results showed that the number of preferential flow paths with the same influence radius decreased with the soil depth's decreasing, while the number of preferential flow paths with different influence radii decreased in the same soil layer. The preferential flow paths with lower influence radii only displayed an aggregated distribution at a small scale (0~20 mm). But the aggregated distribution was obviously as the increase of influence radius and scales. The preferential flow paths with different influence radii also displayed an aggregated distribution in deeper soil layer. The preferential flow paths with higher influence radius were more significantly aggregated distribution than those with lower influence radius. The distribution and formation of preferential flow paths were not only influenced by the soil swelling and shrinkage, but also exhibited a positive correlation with animal activity in spatial associations, especially the preferential flow paths with larger influence radius (R≥1.0 mm). The spatial point pattern analysis method is simpler than CT and soil water breakthrough curves methods to estimate the preferential flow paths. This proposed method can quantitatively analyze horizontal distribution characteristics of the preferential flow paths with morphology and it is better to reveal the underlying formation process. ©, 2015, Chinese Society of Agricultural Machinery. All right reserved.
With the purpose of evaluating the development degree of preferential flow under dry and wet farmland in Three Gorges Reservoir Area, the statistical sample variability analysis method and morphological image processing technology were used to analyze variability of the preferential flow areas in the field scale soil profile dyed images. The results showed that soil wetting front infiltration rate and soil dyeing image parameters, including wetting front infiltration rate, dye coverage, uniform infiltration depth, preferential flow fraction and length index, changed in the characterization development degree of preferential flow wet farmlands were higher than those of dry farmlands. The preferential flow evaluation method was proposed according to the comparison with soil dyeing image parameters. The same result showed the accuracy of preferential flow area dyed image variability analysis method to analyze the development degree of preferential flow. The new method is simpler than the others, and can improve the accuracy of the visual evaluation dyed images. It is also better to combine statistics and morphology to quantitatively analyze the development degree of soil preferential flow. ©, 2015, Chinese Society of Agricultural Machinery. All right reserved.
The preferential flow plays a vital role on the infiltration of irrigation or rainfall. The objective of this study was to quantify preferential flow in the processing of irrigation infiltration in the field scale. Tests of different initial soil water contents and irrigation intensities were conducted using Brilliant Blue FCF (C.I.42090) dye tracer in Luancheng County of the North China Plain. The results showed that the percentages of infiltration by the preferential flow for irrigation depth of 25, 50, and 75 mm were 16.67%, 43.67%, and 34.17%, with 19.72%, 61.42%, 66.64% of dyed areas in the soil profile, respectively, which indicated that preferential flow was enhanced with increasing irrigation intensity, but reduced when the irrigation intensity was over 50 mm. The percentages of preferential flow for 75 and 180 mm previous irrigation producing different initial soil water contents were 23.26% and 18.97%, with 53.23% and 39.94% of dyed areas in the soil profile, respectively. Compared with the 75 mm without previous irrigation, the results indicated that higher initial soil water contents restrained the preferential flow in the field. Therefore, intermittent irrigation and low irrigation intensity patterns, and larger depth of plowing would be suggested to reduce the preferential flow which would increase the soil water utilization efficiency and reduce pollution risk of pesticide and fertilizer to groundwater.
ResearchGate has not been able to resolve any references for this publication.