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1.
Previous studies have shown that water retention curve (WRC) and the hydraulic conductivity vary because of changes of the void ratio or porosity of soil. However, limited documents pointed out the change of hydraulic properties of soil when compacted to different porosities while considering both of the drying and wetting processes of the WRC. This information is sometimes necessary for research like finger flow analysis or the occurrence of wetting and drying cycles as what would be seen in the field. Therefore, this study aims to examine the change of WRC characteristics with varied porosity considering both of the drying and wetting path in WRC by conducting a sand box experiment. Results show that the same type of sand compacted to various porosities have different hydraulic parameters. Hydraulic conductivities generally decrease with reduced porosities; shape parameter α of the van Genuchten equation (1980) linearly decreases with declining porosity and shape parameter n in a reversal manner for the sands of interest whether in the drying process or wetting process. The unsaturated properties of sand are further characterized by inspecting the variations of moisture content, matric suction and vertical displacement of soil body subject to periodic changes of the water level by another sand box experiment. The outcomes suggest that the saturated water content and residual water content are changing during the wetting–drying process, which can be an implication of the changed properties of WRC. The characteristics of volumetric deformation might be varied as well because of the observation of the dissimilar patterns of the changing vertical displacements among each wetting–drying process. Infiltration patterns of the sands also are identified through numerical modelling by introducing a constant infiltration flux from the surface followed by a no‐influx condition. Results indicate that less water accumulates in the sand near the surface for the sand compacted to higher porosity, but water can move deeper. Hydraulic conductivity is found as the prime factor dominating the evolvement of wetting fronts. However, shape parameters of water retention curves also affect the infiltration pattern to some extent. In addition, different sands with similar porosities can have quite different infiltrating characteristics. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

2.
In this paper, the feasibility of using magnetic resonance imaging (MRI) to study water infiltration into a heterogeneous soil is examined, together with its difficulties and limitations. MRI studies of ponded water infiltration into an undisturbed soil core show that the combination of one- and two-dimensional imaging techniques provides a visual and non-destructive means of monitoring the temporal changes of soil water content and the moisture profile, and the movement of the wetting front. Two-dimensional images show air entrapment in repetitive ponded infiltration experiments. During the early stages of infiltration, one-dimensional images of soil moisture profiles clearly indicate preferential flow phenomena. The observed advance of wetting fronts can be described by a linear relationship between the square root of infiltration time (√t) and the distance of the wetting front from the soil surface. Similarly, the cumulative infiltration is also directly proportional to √t. Furthermore, from the MRI infiltration moisture profiles, it is possible to estimate the parameters that feature in infiltration equations. © 1997 by John Wiley & Sons, Ltd.  相似文献   

3.
The Beerkan method based on in situ single‐ring water infiltration experiments along with the relevant specific Beerkan estimation of soil transfer parameters (BEST) algorithm is attractive for simple soil hydraulic characterization. However, the BEST algorithm may lead to erroneous or null values for the saturated hydraulic conductivity and sorptivity especially when there are only few infiltration data points under the transient flow state, either for sandy soil or soils in wet conditions. This study developed an alternative algorithm for analysis of the Beerkan infiltration experiment referred to as BEST‐generalized likelihood uncertainty estimation (GLUE). The proposed method estimates the scale parameters of van Genuchten water retention and Brooks–Corey hydraulic conductivity functions through the GLUE methodology. The GLUE method is a Bayesian Monte Carlo parameter estimation technique that makes use of a likelihood function to measure the goodness‐of‐fit between modelled and observed data. The results showed that using a combination of three different likelihood measurements based on observed transient flow, steady‐state flow and experimental steady‐state infiltration rate made the BEST‐GLUE procedure capable of performing an efficient inverse analysis of Beerkan infiltration experiments. Therefore, it is more applicable for a wider range of soils with contrasting texture, structure, and initial and saturated water content. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

4.
Infiltration experiments have been performed at three sites along a well-known catena under virgin tropical rain forest using a portable sprinkling infiltrometer. Experimentally determined infiltration curves are presented. Infiltration curves are also simulated on the basis of the Mein-Larson equation. The parameters for this model have been obtained from the infiltration curves (saturated conductivity) and simple soil moisture determinations (fillable porosity). The agreement between experimentally determined and modelled infiltration is reasonable, provided (a) saturated conductivity as derived from the experimental data is corrected, (b) a storage parameter, also derived from the experimental data, is added to the Mein-Larson model, and (c) the decline in soil porosity with depth is either small or occurs abruptly at shallow depth. Comparison of observed infiltration rates with rainfall intensity shows that Horton Overland Flow has to occur naturally at least on the middle and lower section of the catena. Despite the fact that most parameters can be estimated in principle from basic soil data, it remains advisable to obtain sprinkling infiltrometer field measurements, because of soil variability due to dynamic surface conditions, macroporosity, air entrapment, and irregularity of the wetting front.  相似文献   

5.
Few methods exist for measuring rapidly changing fluid contents at the pore scale that simultaneously allow whole flow field visualization. We present a method for using real-time neutron radiography to measure rapidly changing moisture profiles in porous media. The imaging technique monitors the attenuation of a thermal neutron beam as it traverses a flow field and provides measurements every 30 ms with an image area >410 cm2 and a spatial resolution 0.05 cm. The technique is illustrated by measuring the variation in moisture content across a wetting front moving at constant velocity through SiO2 sand. The relative contributions of the hydraulic conductivity and diffusivity terms in Richards' equation to the total fluid flux within the wetting front region were also measured. The diffusivity was found to rise from zero to a peak value within the wetting front region before falling off while the conductivity was found to rise monotonically. The reliability of the technique was checked via mass balance.  相似文献   

6.
Infiltration into frozen soil is a key hydrological process in cold regions. Although the mechanisms behind point‐scale infiltration into frozen soil are relatively well understood, questions remain about upscaling point‐scale results to estimate hillslope‐scale run‐off generation. Here, we tackle this question by combining laboratory, field, and modelling experiments. Six large (0.30‐m diameter by 0.35‐m deep) soil cores were extracted from an experimental hillslope on the Canadian Prairies. In the laboratory, we measured run‐off and infiltration rates of the cores for two antecedent moisture conditions under snowmelt rates and diurnal freeze–thaw conditions observed on the same hillslope. We combined the infiltration data with spatially variable data from the hillslope, to parameterise a surface run‐off redistribution model. We used the model to determine how spatial patterns of soil water content, snowpack water equivalent (SWE), and snowmelt rates affect the spatial variability of infiltration and hydrological connectivity over frozen soil. Our experiments showed that antecedent moisture conditions of the frozen soil affected infiltration rates by limiting the initial soil storage capacity and infiltration front penetration depth. However, shallow depths of infiltration and refreezing created saturated conditions at the surface for dry and wet antecedent conditions, resulting in similar final infiltration rates (0.3 mm hr?1). On the hillslope‐scale, the spatial variability of snowmelt rates controlled the development of hydrological connectivity during the 2014 spring melt, whereas SWE and antecedent soil moisture were unimportant. Geostatistical analysis showed that this was because SWE variability and antecedent moisture variability occurred at distances shorter than that of topographic variability, whereas melt variability occurred at distances longer than that of topographic variability. The importance of spatial controls will shift for differing locations and winter conditions. Overall, our results suggest that run‐off connectivity is determined by (a) a pre‐fill phase, during which a thin surface soil layer wets up, refreezes, and saturates, before infiltration excess run‐off is generated and (b) a subsequent fill‐and‐spill phase on the surface that drives hillslope‐scale run‐off.  相似文献   

7.
Hysteresis is a common feature exhibited in hydraulic properties of an unsaturated soil. The movement of wetting front and the hysteresis effect are important factors which impact the shear strength of the unsaturated soil and the mechanics of shallow landslides. These failures are mainly triggered by the deepening of the wetting front accompanied by a decrease in matric suction induced by infiltration. This research establishes a method for determining a stability analysis of unsaturated infinite soil slopes, integrating the influence of infiltration and the water retention curve hysteresis. Furthermore, the present stability analysis method including the infiltration model and the advanced Mohr–Coulomb failure criterion calculates the variations of the safety factor (FS) in accordance with different slope angle, depth and hydrological processes. The experimentally measured data on the effect of hysteresis are also carried out for comparison. Numerical analyses, employing both wetting and drying hydraulic behaviour of unsaturated soil, are performed to study the difference in soil‐water content as observed in the experiments. The simulating approximations also fully responded to the experimental data of sand box. The results suggest that the hysteresis behaviour affect the distribution of soil‐water content within the slope indeed. The hysteresis made the FS values a remarkable recovery during the period of non‐rainfall in a rainfall event. The appropriate hydraulic properties of soil (i.e. wetting or drying) should be used in accordance with the processes that unsaturated soil actually experience. This method will enable us to acquire more accurate matric suction head and the unsaturated soil‐shear strength as it changes with the hysteretic flow, in order to calculate into the stability analysis of shallow landslides. An advanced understanding of the process mechanism afforded by this method is critical to realizing a reliable and appropriate design for slope stabilization. It also offers some immediate reference information to the disaster reduction department of the government. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

8.
The hydraulic properties of the topsoil control the partition of rainfall into infiltration and runoff at the soil surface. They must be characterized for distributed hydrological modelling. This study presents the results of a field campaign documenting topsoil hydraulic properties in a small French suburban catchment (7 km2) located near Lyon, France. Two types of infiltration tests were performed: single ring infiltration tests under positive head and tension‐disk infiltration using a mini‐disk. Both categories were processed using the BEST—Beerkan Estimation of Soil Transfer parameters—method to derive parameters describing the retention and hydraulic conductivity curves. Dry bulk density and particle size data were also sampled. Almost all the topsoils were found to belong to the sandy loam soil class. No significant differences in hydraulic properties were found in terms of pedologic units, but the results showed a high impact of land use on these properties. The lowest dry bulk density values were obtained in forested soils with the highest organic matter content. Permanent pasture soils showed intermediate values, whereas the highest values were encountered in cultivated lands. For saturated hydraulic conductivity, the highest values were found in broad‐leaved forests and small woods. The complementary use of tension‐disk and positive head infiltration tests highlighted a sharp increase of hydraulic conductivity between near saturation and saturated conditions, attributed to macroporosity effect. The ratio of median saturated hydraulic conductivity to median hydraulic conductivity at a pressure of − 20 mm of water was about 50. The study suggests that soil texture, such as used in most pedo‐transfer functions, might not be sufficient to properly map the variability of soil hydraulic properties. Land use information should be considered in the parameterizations of topsoil within hydrological models to better represent in situ conditions, as illustrated in the paper. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
Stormwater infiltration systems are a popular method for urban stormwater control. They are often designed using an assumption of one‐dimensional saturated outflow, although this is not very accurate for many typical designs where two‐dimensional (2D) flows into unsaturated soils occur. Available 2D variably saturated flow models are not commonly used for design because of their complexity and difficulties with the required boundary conditions. A purpose‐built stormwater infiltration system model was thus developed for the simulation of 2D flow from a porous storage. The model combines a soil moisture–based model for unsaturated soils with a ponded storage model and uses a wetting front‐tracking approach for saturated flows. The model represents the main physical processes while minimizing input data requirements. The model was calibrated and validated using data from laboratory 2D stormwater infiltration trench experiments. Calibrations were undertaken using five different combinations of calibration data to examine calibration data requirements. It was found that storage water levels could be satisfactorily predicted using parameters calibrated with either data from laboratory soils tests or observed water level data, whereas the prediction of soil moistures was improved through the addition of observed soil moisture data to the calibration data set. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

10.
Antecedent soil moisture significantly influenced the hydraulic conductivity of the A1, A2e and B21 horizons in a series of strong texture‐contrast soils. Tension infiltration at six supply potentials demonstrated that in the A1 horizon, hydraulic conductivity was significantly lower in the ‘wet’ treatment than in the ‘dry’ treatment. However in the A2e horizon, micropore and mesopore hydraulic conductivity was lower in the ‘dry’ treatment than the ‘wet’ treatment, which was attributed to the precipitation of soluble amorphous silica. In the B21 horizon, desiccation of vertic clays resulted in the formation of shrinkage cracks which significantly increased near‐saturated hydraulic conductivity and prevented the development of subsurface lateral flow in the ‘dry’ treatment. In the ‘wet’ treatment, the difference between the hydraulic conductivity of the A1 and B21 horizons was reduced; however, lateral flow still occurred in the A1 horizon due to difficulty displacing existing soil water further down the soil profile. Results demonstrate the need to account for temporal variation in soil porosity and hydraulic conductivity in soil‐water model conceptualisation and parameterisation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
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12.
Stochastic and deterministic upscaling techniques are developed that upscale saturated conductivity at the support of 0.04 m2 to representative actual infiltration (Ib) for support units (blocks) of 101–104 m2, as a function of steady state rainfall and runon to the block, under Hortonian runoff (infiltration excess overland flow). Parameters in the upscaling techniques represent the surface runoff flow pattern and the spatial probability distribution of saturated conductivity within the 101–104 m2 block. The stochastic upscaling technique represents the spatial process of infiltration and runoff using a simple process-imitating model, estimating Ib using Monte Carlo simulation. The deterministic upscaling technique aggregates these processes by a deterministic function relating rainfall and runon to Ib. The stochastic upscaling technique is shown to be capable to upscale saturated conductivity derived from ring infiltrometers to Ib values of plots (1 m2) corresponding to measured Ib values using rainfall simulators. It is shown that both upscaling techniques can be used to estimate Ib for each time step and each block in transient rainfall–runoff models, giving better estimates of cumulative runoff from a hillslope and a small catchment than model runs that do not use upscaling techniques.  相似文献   

13.
Preferred infiltration is mainly perceived as vertically down whereas subsurface storm flow is thought to occur parallel to slopes. The transition from vertical to lateral flow in a layered hillslope soil is the focus of the contribution. Transient flow is assumed to move as a wetting front. Three time‐domain reflectometry (TDR) wave‐guides, each 0·15 m long, were mounted in the shape of a truncated tetrahedron with its peak pointing down. Each wave‐guide focuses the front velocity along its axis. The three front‐velocity vectors are decomposed into their x, y and z components, which are then assembled to the resultant velocity vector. The volume density flux of preferred flow is the product of the front velocity and the mobile water content. The latter is the amplitude of transient soil moisture measured with each wave‐guide. The resultant vector of the volume flux density is computed similarly to the velocity vector. The experimental approach allows for the rapid assessment of transient flows without relying on the variation of water potentials. The experiments indicate that the directions of the resultant vectors of velocity and volume flux density can be estimated if the moisture variations of the three TDR wave‐guides are strongly correlated during the passing of the wetting front. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

14.
Abstract

Using the Monte Carlo (MC) method, this paper derives arithmetic and geometric means and associated variances of the net capillary drive parameter, G, that appears in the Parlange infiltration model, as a function of soil texture and antecedent soil moisture content. Approximate expressions for the arithmetic and geometric statistics of G are also obtained, which compare favourably with MC generated ones. This paper also applies the MC method to evaluate parameter sensitivity and predictive uncertainty of the distributed runoff and erosion model KINEROS2 in a small experimental watershed. The MC simulations of flow and sediment related variables show that those parameters which impart the greatest uncertainty to KINEROS2 model outputs are not necessarily the most sensitive ones. Soil hydraulic conductivity and wetting front net capillary drive, followed by initial effective relative saturation, dominated uncertainties of flow and sediment discharge model outputs at the watershed outlet. Model predictive uncertainty measured by the coefficient of variation decreased with rainfall intensity, thus implying improved model reliability for larger rainfall events. The antecedent relative saturation was the most sensitive parameter in all but the peak arrival times, followed by the overland plane roughness coefficient. Among the sediment related parameters, the median particle size and hydraulic erosion parameters dominated sediment model output uncertainty and sensitivity. Effect of rain splash erosion coefficient was negligible. Comparison of medians from MC simulations and simulations by direct substitution of average parameters with observed flow rates and sediment discharges indicates that KINEROS2 can be applied to ungauged watersheds and still produce runoff and sediment yield predictions within order of magnitude of accuracy.  相似文献   

15.
Post‐wildfire runoff was investigated by combining field measurements and modelling of infiltration into fire‐affected soils to predict time‐to‐start of runoff and peak runoff rate at the plot scale (1 m2). Time series of soil‐water content, rainfall and runoff were measured on a hillslope burned by the 2010 Fourmile Canyon Fire west of Boulder, Colorado during cyclonic and convective rainstorms in the spring and summer of 2011. Some of the field measurements and measured soil physical properties were used to calibrate a one‐dimensional post‐wildfire numerical model, which was then used as a ‘virtual instrument’ to provide estimates of the saturated hydraulic conductivity and high‐resolution (1 mm) estimates of the soil‐water profile and water fluxes within the unsaturated zone. Field and model estimates of the wetting‐front depth indicated that post‐wildfire infiltration was on average confined to shallow depths less than 30 mm. Model estimates of the effective saturated hydraulic conductivity, Ks, near the soil surface ranged from 0.1 to 5.2 mm h?1. Because of the relatively small values of Ks, the time‐to‐start of runoff (measured from the start of rainfall), tp, was found to depend only on the initial soil‐water saturation deficit (predicted by the model) and a measured characteristic of the rainfall profile (referred to as the average rainfall acceleration, equal to the initial rate of change in rainfall intensity). An analytical model was developed from the combined results and explained 92–97% of the variance of tp, and the numerical infiltration model explained 74–91% of the variance of the peak runoff rates. These results are from one burned site, but they strongly suggest that tp in fire‐affected soils (which often have low values of Ks) is probably controlled more by the storm profile and the initial soil‐water saturation deficit than by soil hydraulic properties. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

16.
《Advances in water resources》2005,28(10):1133-1141
We study the motion of wetting fronts for vertical infiltration problems as modeled by Richards’ equation. Parlange and others have shown that wetting fronts in infiltration flows can be described by traveling wave solutions. If the soil layer is not initially dry, but has an initial distribution of water content then the motion of the wetting front will change due to the interaction of the infiltrating flow with the pre-existing soil conditions. Using traveling wave profiles, we construct simple approximate solutions of initial-boundary value problems for Richards’ equation that accurately describe the position and moisture distribution of the wetting front. We show that the influences of surface boundary conditions and initial conditions produce shifts to the position of the wetting front. The shifts can be calculated by examining the cumulative infiltration, and are validated numerically for several problems for Richards’ equation and the linear advection–diffusion equation.  相似文献   

17.
The mining industry has grown strongly in China in recent decades, resulting in large amounts of coal gangues, which cause water and soil pollution, soil erosion, and various other environmental problems. They are often used in reclamation projects in attempts to restore land damaged by mining, hence they are frequently present (in widely varying proportions) in the topsoil in areas around mines. Their presence can strongly affect key soil variables, including its bulk density, structure, water retention, water movement, and solute transport rates. In the study presented here, the effects of gangue contents on infiltration, saturated hydraulic conductivity, and solute transport parameters of a Chinese Loess plateau soil were examined. The results show that infiltration rates and saturated hydraulic conductivity decreased with increasing gangue content. The Peck–Watson equation modeled these relationships well, but Bouwer–Rice equations provided poorer matches with the acquired data. Cumulative infiltration over time was described well by both the Philip equation and Kostiakov equation. Both the simplified convection–dispersion equation and a two‐region model described the solute transport processes well. In addition, the dispersion increased, while both the Peclet number and mobile water fraction decreased, with increases in gangue contents.  相似文献   

18.
Research shows that water repellency is a key hydraulic property that results in reduced infiltration rates in burned soils. However, more work is required in order to link the hydrological behaviour of water repellent soils to observed runoff responses at the plot and hillslope scale. This study used 5 M ethanol and water in disc infiltrometers to quantify the role of macropore flow and water repellency on spatial and temporal infiltration patterns in a burned soil at plot (<10 m2) scale in a wet eucalypt forest in south‐east Australia. In the first summer and winter after wildfire, an average of 70% and 60%, respectively, of the plot area was water repellent and did not contribute to infiltration. Macropores (r > 0·5 mm), comprising just 5·5% of the soil volume, contributed to 70% and 95%, respectively, of the field‐saturated and ponded hydraulic conductivity (Kp). Because flow occurred almost entirely via macropores in non‐repellent areas, this meant that less than 2·5% of the soil surface effectively contributed to infiltration. The hydraulic conductivity increased by a factor of up to 2·5 as the hydraulic head increased from 0 to 5 mm. Due to the synergistic effect of macropore flow and water repellency, the coefficient of variation (CV) in Kp was three times higher in the water‐repellent soil (CV = 175%) than under the simulated non‐repellent conditions (CV = 66%). The high spatial variability in Kp would act to reduce the effective infiltration rate during runoff generation at plot scale. Ponding, which tend to increase with increasing scale, activates flow through macropores and would raise the effective infiltration rates at larger scales. Field experiments designed to provide representative measurements of infiltration after fire in these systems must therefore consider both the inherent variability in hydraulic conductivity and the variability in infiltration caused by interactions between surface runoff and hydraulic conductivity. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
A new probe was designed to quantify groundwater-surface water exchange in the hyporheic zone under dynamic stage condition. Current methods focus on either vertical pore water velocity or Darcy flux measurements. Both parameters must be understood to evaluate residence time and mass flux of constituents. Furthermore, most instruments are not well suited for monitoring instantaneous velocity or flux under dynamic exchange conditions. For this reason, the flux detection probe (FDP) was designed that employs electrogeophysical measurements to estimate in situ sediment porosity, which can be used to convert pore water velocity to Darcy flux. Dynamic pore water velocity is obtained by monitoring fluid conductivity and temperature along the FDP probe. Pressure sensors deployed at the top and bottom of the probe provide the additional information necessary to estimate vertical permeability. This study focuses on the use of a geophysical method to estimate pore water velocity, porosity, and permeability within a controlled soil column where simulated river water displaces simulated groundwater. The difference between probe derived and theoretical pore water velocity using natural tracers such as electrical conductivity and temperature was −4.9 and 3.9% for downward flow and 1.1 and 12.8% for upward flow, respectively. The difference in porosity calculated from mass and volume packed in the soil column and probe measure porosity ranged between −3.2% and 1.5%. Also, the calculated hydraulic conductivity differed from probe derived values by −8.9%.  相似文献   

20.
Determination of saturated hydraulic conductivity, Ks, and the van Genuchten water retention curve θ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimate Ks, α and n from numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces, Ks–n, α–n and Ks–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h + Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils.  相似文献   

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