Three-dimensional Infiltration Research Articles

Study on the influence of design parameters of porous asphalt pavement on drainage performance

To investigate the design factors influencing the drainage performance of porous asphalt pavement and its performance degradation, a three-dimensional infiltration model of porous asphalt pavement was established. The influence of permeability coefficient, drainage layer thickness, drainage path length, and pavement cross slope for drainage performance was analyzed. The drainage performance was evaluated with the multiple influence factors, and the drainage performance degradation was explored with the porosity decay. The results showed that the design parameters including permeability coefficient, drainage layer thickness, drainage path length, and pavement cross slope exhibit strong correlations with pavement drainage performance, with correlations greater than 0.6. The increase in the permeability coefficient, drainage layer thickness, pavement cross slope, and the reduction in drainage path length are all benefits to improved drainage performance. It is effective to enhance drainage performance by increasing the permeability coefficient combined with a higher pavement cross slope in high drainage requirement areas. The porosity decay caused by road load and porosity reduction leads to a 20%-45% degradation in drainage performance. Therefore, during the road surface design process, it is necessary to comprehensively consider the synergistic effects of design parameters, while also evaluating both the initial and residual drainage performance with the combined influence of load and dust.

Estimation of soil hydraulic and solute transport properties from field infiltration experiments

To model water flow and solute transport in soils, hydrodynamic and hydrodispersive parameters are required as input data in the mathematical models. This work aims to estimate the soil hydraulic and solute transport properties using a ponded axisymmetric infiltration experiment using a single-ring infiltrometer along with a conservative tracer (Cl-) in the field. Single ring infiltration experiments were accomplished on an Oxisol in Areia in the state of Paraíba, Brazil (6o 58' S, 35o 41' W, and 645 m), in a 50 x 50 m grid (16 points). The unsaturated hydraulic conductivity (K) and the sorptivity (S) were estimated for short or long time analysis of cumulative three-dimensional infiltration. The single tracer technique was used to calculate mobile water fraction (Ф) by measuring the solute concentration underneath the ring infiltrometer at the end of the infiltration. Two solute transfer numerical models based on the mobile-immobile water concept were used. The mobile water fraction (Ф), the dispersion coefficient (D), and the mass transfer coefficient (a) between mobile and immobile were estimated from both the measured infiltration depth and the Cl- concentration profile underneath the infiltrometer. The classical convection-dispersion (CD) and the mobile-immobile (MIM) models showed a good agreement between calculated and experimental values. However, the lowest standard errors to the fitted parameters were obtained by the CD model.

Experimental Study and Calculation of a Three-Dimensional Finite Element Model of Infiltration in Drainage Asphalt Pavement.

Drainage asphalt pavement provides excellent drainage performance and driving safety, where the permeability of the pavement is the critical performance. When analyzing the permeability of drainage asphalt pavements, the previously used two-dimensional infiltration calculation model with boundary conditions deviates from the real situation. In this article, a three-dimensional infiltration finite element method was proposed to evaluate the permeability of pavement, and the feasibility of the three-dimensional infiltration finite element method to evaluate the drainage capacity of drainage asphalt pavement was verified by using the single-sided permeability test of indoor rutted slabs of drainage asphalt mixtures as an example. Finally, the effects of the longitudinal slope of the pavement on the drainage performance of the drained asphalt pavement was investigated by calculations based on the three-dimensional infiltration finite element method. The results indicated that: when the longitudinal slope was less than 6%, the influence of longitudinal slope size on the drainage capacity of drainage asphalt pavement was very small. When the gradient of the longitudinal slope from 0 to 6%, the critical drainage capacity of the pavement corresponding to each cross slope was maintained at a relatively stable value.

Mathematical modeling of the infiltration in a permeable pavement on the field scale

ABSTRACT Permeable pavement (PP) is an alternative for the management of urban rainwater that allows the reduction of effective precipitation through the infiltration process. In this study was evaluated the infiltration capacity of a PP of hollow concrete blocks in a parking lot of the Federal University of Pernambuco. The hydraulic characterization and the infiltration capacity were analyzed in real scale, using a simple ring infiltrometer of 100 cm in diameter through the Beerkan method. Infiltration tests were carried out at twelve points of the PP. The BEST algorithm was applied in it Best-Intercept and Best-Slope version, to estimate the hydraulic parameters of the van Genutchen and Brooks and Corey equations for the retention and hydraulic conductivity of the PP surface. The values of saturated hydraulic conductivity determined by the BEST Intercept method were higher than those obtained by BEST Slope. The sorptivity values estimated by BEST Slope and Intercept were similar, with BEST Slope values slightly higher. Moderate infiltration variability was observed on the PP surface, as well as within the same type of texture. The Beerkan method proved to be adaptable to measure, in field scale, the three-dimensional infiltration in the PP covering layer.

A Note on One- and Three-Dimensional Infiltration Analysis from a Mini Disc Infiltrometer

Disc infiltrometers are used to characterize soil hydraulic properties. The purpose of this study was to determine the difference between three- and one-dimensional infiltration and to calculate the infiltration shape parameter γ from a proposed analytical infiltration equation. One- and three-dimensional infiltration tests were done on three repacked soils (loam, sandy loam, and silty clay loam) for two negative pressure heads. A mini disc infiltrometer of a radius of 22.5 mm with suction that ranged from −5 mm to −70 mm was used. The difference between experimental three- and one-dimensional cumulative infiltration was linear with time, which confirmed the proposed equation. In this study, the shape parameter γ seems not to be seriously affected by the soil type and acquires values from 0.561 to 0.615, i.e., smaller than the value γ = 0.75, which is widely used. With these values, the criteria proposed for calculating hydraulic conductivity using three-dimensional infiltration data may be fulfilled in most soils.

A 2D curvilinear coupled surface–subsurface flow model for simulation of basin/border irrigation: theory, validation and application

Despite the development of pressurized irrigation systems in the second half of the twentieth century, surface irrigation continues to be the most used system in the world. Computer tools are required to support performance improvements leading to its sustainability. A simulation model of basin/border irrigation is presented in this paper combining two-dimensional overland hydraulics based on Saint–Venant equations with three-dimensional infiltration based on the mixed form of Richards’ equation. The coupling of these equations is attained by enforcing continuity of pressure at the soil surface. The model applies a finite-volume approach using the diffusion-wave approximation form of the shallow water equations. Water flow on undulated topographies is simulated using a non-orthogonal curvilinear coordinate system. An underrelaxed-modified Picard iteration algorithm is used for Richards’ equation, and an underrelaxed Picard iteration algorithm is used for Saint–Venant equations. The model was validated using experiments from the literature. Model performance was robust and accurate, even in complex theoretical cases with strong soil-surface undulations. Mass conservation was judged satisfactory in all cases, with the long-term ratio of mass balance error in the order of 10−2 in the most complex simulations. Soil type, mesh non-orthogonality, and the interaction of these variables had a strong effect on CPU time. Additional research will be required to transform this simulation model into an operational tool for surface irrigation. Attention will need to be paid to additional surface irrigation systems, soil types, and the optimization of computational speed.

A thermo-poroelasticity theory for infiltration processing of interpenetrating phase composites

This work describes a thermo-poroelasticity theory to investigate the effects of temperature gradients on infiltration kinetics, pore pressure distribution of the liquid phase, and liquid content variation due to preform deformation for infiltration processing of interpenetrating phase composites. Governing equations for three-dimensional infiltration processing are presented. A similarity solution is derived for one-dimensional infiltration assuming no solidification of the liquid phase. The solution indicates that besides the liquid viscosity, the infiltration front also depends on the poroelastic properties of the preform. A numerical example for a polymer–ceramic IPC shows that the temperature gradients may produce significant liquid content increment beyond the amount that can be accommodated by the initial pore volume of the preform. This liquid content increment may compensate some solidification shrinkage of the liquid phase, thereby suppressing occurrence of microdefects in the composite.

Cartilage invasion patterns in laryngeal cancer.

The cartilaginous invasion determines the T and is one of the most common sources of mistake in tumor staging. Also it is of great importance when planning any therapeutic alternative. In the latest revision of the TNM classification a clear distinction is made between infiltration of cartilage without going through it, considered a T3 recently and that would be a T4 according to the previous classification, and those going through the cartilage, classified as T4a. While this classification makes the difference in depth of infiltration, it does not emphasize the extent of invasion. This paper provides a detailed description of the laryngeal cartilage tumor infiltration by whole organ serial section in which the invasion is considered both horizontal (transcartilaginous) and vertical (extent of invasion) and establishing patterns of three-dimensional infiltration of the cartilage. This is a cross-sectional study of prevalence. 275 records of patients treated for laryngeal squamous cell carcinoma between 1995 and 2000 were reviewed. The pathological processing of laryngectomy surgical specimens was performed following the method of whole organ serial section described by G. F. Tucker. The following patterns of cartilaginous infiltration were defined: (1) transcartilaginous infiltration; (2a) partial focal infiltration of the cartilage: infiltration not going through the cartilage but occupying one third or less of its extent; (2b) partial extensive infiltration of the cartilage: infiltration occupying two thirds or more of its length and (3) no cartilage infiltration: tumor in contact with the cartilage (paraglottic space) but without affecting it. 161 patients met the inclusion criteria. The most frequent tumor location was supraglottic (58 cases) followed by glottic (47). 109 patients (67.7%) were treated with total laryngectomy. Partial surgical techniques were performed in the remaining cases. TNM tumor staging was performed according to the results of pathological study (pTNM). 72.06% (116) were classified as advanced laryngeal tumors (pT3 and pT4). 46% of patients showed some extent of laryngeal cartilage infiltration (thyroid, cricoid, arytenoids, epiglottis). The cartilage most frequently infiltrated was the thyroid in 48 patients (29.8%) and when it is affected, in most cases (66.7%), the infiltration is transcartilaginous. The next most common pattern is partial focal infiltration (27%). In the cricoid cartilage, the most common pattern of infiltration is focal partial infiltration (52.6%). Of the 19 cases with infiltration of the cricoid, there are 12 cases with extra laryngeal invasion through a cricothyroid membrane perforation. The study of laryngeal cancer by laryngeal whole serial section has been proved to be very useful in offering a high precision pTNM staging and a detailed description of the infiltration of cartilage. We have seen that when the thyroid cartilage is infiltrated the tumor often passes through the cartilage. However, there are cases where the tumor is extremely aggressive, being very widespread in cartilage thickness without actually crossing it. The isolated infiltration of the cricoid cartilage is exceptional.

Unsteady Infiltration from Point and Line Sources in Laterally Confined Domains

In this study, a linearized form of Richards’ equation is used to derive analytical solutions for the problems of unsteady three-dimensional infiltration from (surface or subsurface) point sources into rectangular, strip-shaped, and cylindrical domains and for two-dimensional infiltration from a line source into a strip. All solutions are given for an inhomogeneous Philip’s soil whose hydraulic conductivity is an exponential function of the pressure head and the depth and for evaporative water loss at the surface. Numerical examples serve to illustrate the effects of lateral confinement, water loss at the soil surface, and change in the hydraulic conductivity with depth on the time-dependent response to constant or cyclic inputs of water from irrigation sources that arise at different depths. Lateral confinement (i) damps the fluctuations in the soil water potential caused by cyclic water inputs, (ii) increases the value of the quasi-steady periodic water potentials, especially at greater soil depths, and (iii) spreads the response to the inputs across longer times. The effect of lateral confinement on the response curves decreases in soils with higher hydraulic conductivity or when the conductivity increases with depth. On the contrary, if the hydraulic conductivity decreases with increasing depth, the effect of lateral confinement increases and the response curves stretch out in time, even for a single, short daily irrigation input. Surface losses reduce the water potential at all depths but do not appreciably affect its temporal evolution. Although the results presented are for surface sources, the analysis may easily be extended to subsurface sources.

Estimate of Soil Hydraulic Properties from Disc Infiltrometer Three-dimensional Infiltration Curve: Theoretical Analysis and Field Applicability

This paper describes a new method (NSQE) to estimate soil hydraulic properties (sorptivity, S, and hydraulic conductivity, K) from full-time cumulative infiltration curves. The technique relies on an inverse procedure involving the quasi-exact equation of Haverkamp et al. (1994). The numerical resolution is described and the sensitivity of the method is theoretically evaluated, showing that the accuracy of the estimates depends on the measured infiltration time. A new procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve is also given. The method was subsequently compared to the differentiated linearization procedure (DL), which calculate K and S from the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. A total of 264 infiltration measurements performed with a 10cm diameter disc under different soil conditions were used. Compared to the DL procedure, field measurements showed that the NSQE method allowed better estimates of soil hydraulic properties, independently on the infiltration noise and the presence of contact sand layer. Overall, although comparable S values were estimated with both methods, the longer infiltration times allowed by the proposed method made this procedure more accurate estimations of K. In conclusion, the NSQE method have shown to be a significant advance to accurate estimate of the soil hydraulic properties form the transient water flow.

A field assessment of the Simplified Falling Head technique to measure the saturated soil hydraulic conductivity

The Simplified Falling Head (SFH) technique to measure field saturated soil hydraulic conductivity, Kfs, has received little testing or comparison with other techniques. Different experiments were carried out to i) determine the effect of ring size on the measured conductivity; ii) compare the SFH and Pressure Infiltrometer (PI) techniques in a clay loam soil; and iii) evaluate the approach used in the SFH methodology to estimate the α* parameter. Sampling a relatively large number of sites allowed to detect statistically significant relationships between the Kfs values obtained with rings differing in diameter (0.15 and 0.30m, respectively). The ring size effect was substantial (factor of discrepancy between Kfs results of more than an order of magnitude) for low Kfs values (~2mmh−1) but it was practically negligible (factor≤1.7) for high conductivities (Kfs≥350mmh−1). Data supporting the hypothesis that the detected ring size effect was an effect of the different total area sampled with the two rings were obtained. A test carried out with a small ring contained enough information to approximately predict the Kfs value that would be obtained with a larger ring. The SFH and PI techniques yielded statistically similar means of Kfs but substantially different coefficients of variation, that was particularly high for the SFH technique. The duration of the infiltration run, appreciably shorter for the SFH than the PI technique with the Two‐Ponding Depth approach, probably influenced swelling phenomena of the field soil during the run and this circumstance determined the detected discrepancies. The two techniques should be considered complementary, being usable to determine Kfs at the beginning (SFH) and at a later stage (PI) of a ponding infiltration process. Using α* values directly measured by the tension infiltrometer or estimated on the basis of a general description of soil characteristics did not affect significantly the results of the SFH technique. Therefore, the approximate criterion to estimate α* was appropriate. In conclusion, this investigation gave support to the use of the SFH technique for a rapid and reasonably simple approximate determination of Kfs. Developments should consider a transient, three-dimensional infiltration process established by a ring inserted a short distance into the soil.

Caracterização Hidrodinâmica dos Solos da Bacia Experimental do Riacho Guaraíra Utilizando o Método Beerkan

Knowledge of hydraulic properties of soil, such as the water retention and hydraulic conductivity curves, is indispensable for water and sediment transport modeling. Thus, in this work, a methodology used to obtain hydrodynamic soil properties, known as Beerkan, is presented to spatially characterize the main soil hydrodynamic characteristics, i.e., saturated hydraulic conductivity, porosity, and water retention in the soil, for the Guaraira River Experimental Basin, located in the coastal zone of northeastern Brazil. Disturbed soil samples were collected and infiltration tests were accomplished in a regular grid of 196 cells in the basin with 200 m spacing. This method was applied to two soil types (Argisols and Spodosols) with different textural classification (sand, loamy sand, sandy loam). For the hydrodynamic characterization, the shape and the normalization parameters of the θ(h) and of K(θ) curves were determined. The shape parameters depend upon the soil texture and they were obtained from the cumulative particle size distribution curve; the normalization parameters depend on soil structure and they were obtained from the infiltration experiments using the simple ring infiltrometer. The obtained results showed that the values of sorptivity (S) and saturated hydraulic conductivity (Ks) are slightly higher for soils with a lower sand percentage. It was also verified that S and Ks values are higher for the Spodosols, showing that Spodosols are more permeable than Argisols, for any textural class analyzed. Finally, the Beerkan method showed to be a promising method and easily applied to modeling three-dimensional infiltration in the field, as

Adhesion, migration and mechanics of human adipose-tissue-derived stem cells on silk fibroin–chitosan matrix

Silk fibroin–chitosan (SFCS) scaffold is a naturally derived biocompatible matrix with potential reconstructive surgical applications. In this study, human adipose-derived mesenchymal stem cells (ASCs) were seeded on SFCS scaffolds and cell attachment was characterized by fluorescence, confocal, time-lapse, atomic force, and scanning electron microscopy (SEM) studies. Adhesion of ASCs on SFCS was 39.4 ± 4.8% at 15 min, increasing to 92.8 ± 1.5% at 120 min. ASC adhered at regions of architectural complexity and infiltrate into three-dimensional scaffold. Time-lapse confocal studies indicated a mean ASC speed on SFCS of 18.47 ± 2.7 μm h −1 and a mean persistence time of 41.4 ± 9.3 min over a 2.75 h study period. Cytokinetic and SEM studies demonstrated ASC–ASC interaction via microvillus extensions. The apparent elastic modulus was significantly higher ( p < 0.0001) for ASCs seeded on SFCS (69.0 ± 9.0 kPa) than on glass (6.1 ± 0.4 kPa). Also, cytoskeleton F-actin fiber density was higher ( p < 0.05) for ASC seeded on SFCS (0.42 ± 0.02 fibers μm −1) than on glass-seeded controls (0.24 ± 0.03 fibers μm −1). Hence, SFCS scaffold facilitates mesenchymal stem cell attachment, migration, three-dimensional infiltration, and cell–cell interaction. This study showed the potential use of SFCS as a local carrier for autologous stem cells for reconstructive surgery application.

Caracterização hidrodinâmica de solos: aplicação do método Beerkan

O conhecimento das propriedades hidráulicas do solo, tais como as curvas de retenção da água no solo teta(h) e da condutividade hidráulica K(teta), é indispensável para a modelagem do transporte de água e de poluentes em sistemas agrícolas. Várias técnicas experimentais têm sido propostas para determinar essas características do solo diretamente no campo, porém a complexidade, os custos elevados e o tempo de execução dessas medidas, são fatores que limitam bastante a obtenção dessas informações em grande escala. Apresenta-se, no presente trabalho, uma metodologia conhecida como "Beerkan", com a qual se busca minimizar esses fatores utilizando-se dados experimentais de infiltração, da distribuição granulométrica e da massa específica do solo, para então se estimar os parâmetros das curvas de teta(h) e K(teta). O método foi aplicado em dois solos com diferentes classes texturais (três de um Latossolo Amarelo e três de um Neossolo Flúvico). Determinaram-se, com vistas à caracterização hidrodinâmica, os parâmetros de forma das curvas de teta(h) de van Genuchten e de K(teta) de Brooks e Corey, dependentes majoritariamente da textura do solo e obtidos a partir da curva de distribuição dos tamanhos das partículas, além dos parâmetros de normalização dependentes, essencialmente, da estrutura do solo e obtidos a partir dos ensaios de infiltração utilizando-se o infiltrômetro de anel simples. O método Beerkan provou ser robusto e adaptado à caracterização hidrodinâmica dos dois solos.

Calibration of a Vadose Zone Model Using Water Injection Monitored by GPR and Electrical Resistance Tomography

The noninvasive characterization of the vadose zone has been the objective of intense research aiming at collecting data for the calibration of flow and transport models. This interest is motivated by the difficulty of accessing the vadose zone with direct methods without causing disturbance to the natural conditions. On the other hand, characterizing the vadose zone requires detailed knowledge of space and time variations of water distribution. Geophysical methods capable of imaging the moisture content, such as ground penetrating radar (GPR) and electrical resistance tomography (ERT), provide data with high resolution in space and time: natural infiltration and artificial injection (tracer) tests can be imaged, by repeating measurements over time (time‐lapse mode). We conducted a forced‐injection experiment at a test site in Gorgonzola, east of Milan (Italy). The site is characterized by Quaternary sand and gravel sediments that house an extensive unconfined aquifer. We used ERT and GPR in two‐dimensional cross‐hole configuration and time‐lapse mode during a period of several days preceding and following a tracer experiment with the injection of about 20 m3 of fresh water in a purposely excavated trench. The calibration of a three‐dimensional infiltration model on the basis of the geophysical data provides useful estimates of vertical saturated hydraulic conductivity; however, we observed a discrepancy in mass balance between calibrated simulations and measurements. This fact cannot be explained using a simple isotropic model for hydraulic properties; therefore, the method requires further investigation before being fully established.

Wetting front instabilities: a three-dimensional experimental investigation

Wetting front instability or fingering experiments were conducted in three-dimensional infiltration columns, featuring stratified fine-over-coarse texture porous media, to investigate the influences of various soil and wetting phase properties on finger diameter and propagation velocity. The system parameter varied in this study included permeability, system flux rate, media size and gradation uniformity, initial moisture content, viscosity, density, and surface tension. The influence of each parameter is discussed and compared, where applicable, to the finding of previous studies. Finger diameter and velocity data were acquired using a neutron radioscopy based, real-time imaging system. Through the use of the imaging system, a very accurate and reliable experimental data set was produced for three-dimensional fingering events.

Measurement of Hydraulic Properties and Mobile Water Content of a Field Soil

The last years have seen the development of field methods that are capable of being applied to the direct measurement of simultaneous water and solute transport properties of soils. A tension disk infiltrometer was used to determine the ratio (f = θm/θ) between mobile water content (θm) and the total volumetric water content (θ) of a soil and to characterize the hydraulic properties. The soil is a heterogeneous stony soil of a cultivated plot, recently plowed. The hydraulic conductivity and the sorptivity were obtained using a new approach that considers the transient three-dimensional infiltration from a disk. The measurement of the mobile water content was performed by adding KCl tracer after prewetting the soil with water. Results show an important nonlinearity in both conductivity and sorptivity of the soil with applied pressure heads. The mobile water content ratio changes with the applied water pressure, and it was found to be a function of the effective mean pore size, λm. Results show a transition from a capillary-dominated to a gravity-dominated flow. The soil water flow changes to a macroporosity flow when the water pressure head increases from −100 to 0 mm, resulting in an abrupt increase in the mobile water content ratio from 0.11 to 0.37. The proposed f(λm) relationship is an S-shaped analytical equation. It appears that for a given porous network topology, the mobile water content depends both on the dynamics of the water movement and on the connectivity of the porous network.

Soil physical properties of three geomorphic zones in a semiarid mulga woodland

Soil physical properties were measured in three contiguous geomorphic zones of a patterned sequence of alternating groves and intergroves in a semi-arid mulga (Acacia aneura) woodland : (1) a runoff zone of stony, severely sealed, surface soil, (2) an interception zone at the bottom of the runoff zone, and adjoining (3) a runon zone of mulga groves. Infiltration was measured in the field under unsaturated and saturated conditions using a disc permeameter at water supply potentials of -40 and +10 mm respectively. Under unsaturated flow conditions, there were no significant differences in the sorptivity, three-dimensional infiltration rate and hydraulic conductivity between the three zones. However, under saturated flow conditions, the soils in the mulga groves had infiltration rates 5-10 times higher than the soils in the runoff and interception zones. This difference was explained by the presence of stable macropores &gt;0.75 mm diameter in the mulga grove soils. Surface soil (0-10 mm) aggregates from mulga groves were also particularly stable to rapid wetting, measured by wet-sieving. Volumetric water contents (measured over a range of matric potentials from 0 to -5.0 kPa) of the 0-50 mm layer of soil from the mulga grove and interception zone were significantly (P = 0.05) higher than the 0-50 mm layer from the runoff zone. Micromorphological and scanning electron microscope (SEM) examination indicated that the total porosity of the soil surface from the mulga groves and interception zones was greater than that of the runoff zones. Measurement of soil-water content following a major rainfall event indicated that water had flowed off the runoff zones and accumulated in the mulga groves. These findings are consistent with the higher herbage production and biotic activity that is found to occur in the mulga grove and interception zone compared with the runoff zone following adequate rainfall. They also reveal part of the delicate balance of runoff redistribution in grove/intergrove areas and the potential for management to alter this balance.

1‐D, 2‐D, and 3‐D Infiltration for Irrigation

Models for one-, two-, and three-dimensional infiltration for irrigation are derived using an energy equation and Darcy’s law. The models were verified with previously published experimental data. A good agreement is found between the model-computed and observed values of infiltration. Average relative error of cumulative infiltration values is less than 5%.

Three-Dimensional Infiltration and Trickle Irrigation

ABSTRACT SHORT and long time theories of water movement during three-dimensional infiltration are tested both in the laboratory and the field. The utility of Wooding's (1968) theory of infiltration from a shallow, surface pond is demonstrated. Inefficiencies in trickle irrigation can in some cases result from surface free water accessing vented macropores and rapidly by-passing the root zone.