The infiltration envelope: Results from a theoretical infiltrometer
Abstract
The theoretical partial differential equation for unsaturated soil moisture flow is solved by a versatile numerical scheme designed for accurate simulation of infiltration from various patterns of rainfall. This model is used to study the independent effects of soil type, initial soil moisture, rainfall rate and rainfall pattern.
The results of the investigation are expressable as a simple parametric model for vertical infiltration. Infiltration from a suddenly ponded surface is shown to be an asymptotic limit to increasing rainfall rates. A single dimensionless formula is found to accurately describe the infiltration decay curves for all soils, initial conditions, and rainfall rates tested, and another dimensionless relation predicts time to ponding under arbitrary rainfall patterns as a function of infiltrated rainfall depth. The effect of initial soil moisture is shown to be well described by a simple linear effect on the normalizing time in the dimensionless system. Uses and implications of these results are discussed.
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Cited by (136)
Focus on the nonlinear infiltration process in deep vadose zone
2024, Earth-Science ReviewsThe 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.
Soil micro-penetration resistance as an index of its infiltration processes during rainfall
2022, Journal of Rock Mechanics and Geotechnical EngineeringRainfall infiltration is one of the most important driving factors of geological hazards, ecological environment problems, and engineering accidents. Understanding the principle of soil wetting during rainfall infiltration and its influence on soil mechanical properties is crucial for preventing geological hazards. In this study, micro-penetration tests coupled with moisture monitoring were performed to investigate the infiltration process during wetting through the measured change in mechanical characteristics. Results show that penetration resistance increases in the deep layer gradually. With increasing infiltration time, the wetting front keeps moving downward, and its range becomes wider. A slight increase of the penetration resistance in the shallow layer (d ≤ 17.5 mm) is observed. However, the penetration resistance in the middle layer (22.5 mm ≤ d ≤ 32.5 mm) decreases firstly before a slight increase. In the deep layer (d ≥ 37.5 mm), the penetration resistance decreases continuously during infiltration. Based on the measured water content profile during infiltration, it is found that the evolution of soil mechanical characteristics is fully responsible by the infiltration-induced re-distribution of water content along depth. Generally, the penetration resistance decreases exponentially with increasing water content in the soil. When the water content is low, wetting can weaken soil strength significantly, whereas this effect diminishes when the moisture surpasses a certain threshold. The results highlight that the penetration curves and water content profile show close inter-dependency and consistency, which verifies the feasibility of using micro-penetration to investigate rainfall infiltration and wetting process in surface soil layer or laboratory small-scale soil samples. This method enables fast, versatile and high-resolution measurements of infiltration process and moisture distribution in soil.
On shapes of cumulative infiltration curves
2022, GeodermaCitation Excerpt :Datasets with B to L CICs constitute 35.6% of the total number of datasets. These CICs cannot be accurately approximated with commonly used equations available from literature, such as Horton (1941), Mezencev (1948), Green and Ampt (1911), Holtan (1961) equations, and their modifications, such as Collis-George (1977), Swartzendruber (1987), Smith and Parlange (1978), Smith (1972), Huggins and Monke (1966) equations. These equations still can be applied, but the fitted CIC will have shapes different from the measured, resulting in erroneous estimates of the soil hydraulic properties (Moret-Fernández et al., 2021).
Water infiltration into soil is the key process in the water cycle, and understanding and predicting infiltration is essential for water management. Measurements of cumulative infiltration are a common part of soil hydrological characterization. Such measurements provide the cumulative infiltration curve (CIC), i.e. dependence of the amount of infiltrated water on time. The classic, usually anticipated CIC shape is the concave increase section transitioning to the linear section. However, other shapes were also observed. The objectives of this work were (a) to use the unique large international infiltration database SWIG to define distinctly different types of CIC shapes, and (b) to see if basic soil properties, land use, and infiltration measurement method can indicate what type of non-classic CIC shapes can be expected in site-specific conditions. Examination of 5023 CIC led to the definition of 12 types of CIC shapes. About 1/3 of SWIG datasets had non-classic CIC shapes. The shape types were visually discernible in most cases. A technique was suggested to distinguish the shape types if needed. The classification tree divided all datasets with non-classic CIC shapes into most similar inside and most different from each other groups. The infiltration measurement method, the clay content, and the organic carbon content were the most influential predictors of the shape type in this classification. Several non-classic shapes were previously related to soil structure and hydrophobicity. The relatively large fraction of non-classic CIC indicates the need to design infiltration experiments accounting for possible non-classic CIC, and the need for the cautious application of common infiltration equations, most of which were developed to simulate classic CIC shapes.
Rainfall and infiltration
2022, Rainfall: Modeling, Measurement and ApplicationsA quantitative representation of the rainfall infiltration process at different spatial scales is needed for understanding and modeling hydrologic processes. Some point infiltration models and their extensions to incorporate complex mechanisms, such as temporal variation of applied water, are presented. At larger scales, spatial heterogeneity becomes important, and various upscaling methods are discussed with a focus on the estimation of field-averaged responses using physical models with probability distribution functions to represent the spatial variation in saturated hydraulic conductivity and/or spatio-temporal variation in rainfall. Challenges facing modeling of field-scale infiltration and runoff are illustrated through a case study. Recent advances made in the field and current challenges are also noted.
Spotting strategic storm drain inlets in flat urban catchments
2021, Journal of HydrologyStorm drain inlet blockage causes more flooding incidents than does storm sewer overloading in flat urban catchments. Although inlet clearance has proved to be cost-effective in mitigating pluvial flooding, clearing all inlets in the wet season is unfeasible. No study has sought to partition the role of storm drain inlets because the dynamic flow exchange at every inlet is impossible to monitor at a catchment scale and even hard to calculate. This study presents a proactive approach to identifying strategic (i.e., most influential) inlets to save considerable labor costs in grate inlet maintenance. Our findings show that the tapered Pareto distribution can describe the distribution of inlet interception rates almost invariant to rainfall types. A modified Pareto principle called the 70–25 rule is derived, suggesting that 70% surface runoff is drained by the top 25% inlets. A nested hydrodynamic model, which solves full shallow water equations and captures detailed physical processes, was built to compute surface runoff intercepted by grate inlets in the built environment. The model is composed of a subcatchment scale, 2D-1D dual drainage model embedded in a catchment scale 1D model. The 2D-1D interaction was described by a piecewise function of piezometric head at the grate inlet; the parameters in each subfunction were statistically derived from a series of 3D numerical experiments involving full processes from free-surface flow to pressurized flow. The 2D model was built on a sensitivity-tested, unstructured mesh with allowable triangle areas ranging from 0.15 to 6 m2. The simulations showed a mild (ca.5%) versus radical (40–50%) reduction in runoff interception with the removal of the non-strategic versus strategic inlets under non-extreme rainfalls. The application to the low-lying, ultra-urban test case confirmed the robustness and effectiveness of the method for strategic inlets identification.
The effect of hillslope geometry on Hortonian rainfall-infiltration-runoff processes
2021, Journal of HydrologyTopography is one of the main factors in hillslope rainfall-runoff processes. The effect of hillslope geometry, representing an important aspect of topography, on Hortonian rainfall-runoff has not been fully understood. In order to investigate this effect, hillslope geometry was abstracted as the combination of longitudinal profile curvature and plan shape, and a set of representative hillslope surfaces were generated using a variety of values of the profile curvature and plan shape factor. The infiltration and Hortonian runoff processes, mainly characterized by ponding time, infiltration rate, and runoff rate and depth, were computed using Richards’ equation for variably-saturated flow with given initial soil moisture, rainfall, and soil texture. The results show that different profile curvature and plan shape can cause more than 10% difference in cumulative runoff and runoff rate and more than 20% difference in ponding time. The curvature of hillslope longitudinal profile affects infiltration and runoff nonmonotonically and plays a more important role than the plan shape, whose effect is monotonic. The profile curvature and plan shape can complicate each other’s effect, but the effect of profile curvature also varies with rainfall duration. For a fixed plan shape, the longest time to ponding occurs on the straight profile hillslope. Hillslopes with opposite values of the plan shape factor and curvature have similar infiltration and runoff processes because of the similar slope gradient distributions. The widely used time compression approximation (TCA) for rainfall infiltration prediction after ponding can lead to an error of more than 37% when applied to hillslopes with a curved profile and variable width. This is because of the inaccurate estimation of the ponding time, especially for low intensity rainfalls, suggesting the presence of partial area runoff on these hillslopes. In addition, the results show that the effect of subsurface lateral flow near surface is generally negligible, and the run-on effect causes more infiltration on convex hillslope topography. The soil property and rainfall temporal variability do not change the trends but can alter the magnitudes of the hillslope geometry effect. The study provides insights into the rainfall runoff processes on natural hillslopes that could benefit studies related to hillslope hydrology and geomorphology.