Unstable Flow during Redistribution in Homogeneous Soil

Wang, Zhi; Tuli, Ataç; Jury, William A.

doi:10.2136/vzj2003.0052

Cited by 22 publications

(32 citation statements)

References 4 publications

(7 reference statements)

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“…The field observations of funnel flow in the dam farmland proved the existence of this phenomenon which was reported by prior researchers (Miyazaki 1988;Kung 1990;Walter et al 2000;Heilig et al 2003;Gish et al 2003), but not "fingers" reported by Hill and Parlange (1972), Samani et al (1989), and Wang et al (2003). This can be explained that the "fingers" are very small with the diameter of only several centimeters, about 4 cm by Hill and Parlange (1972), about 6.8 ± 2.2 cm in mean size by Wang et al (2003). They could not be easily observed in the dam farmland for the relative large scale.…”

Section: Funnel Flow Observationssupporting

confidence: 62%

Soil Water Distribution and Movement in Layered Soils of a Dam Farmland

Zhao

Shao

Melegy

2010

Water Resour Manage

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In soil profiles, special emphasis has been placed on the migration of agricultural chemicals spread intentionally or accidentally into deep soils or groundwater body. To prevent soil water pollution and estimate the magnitude of the hazard caused by these chemicals, it is necessary to know the processes controlling their movement from the soil surface, through the root zone and eventually to the water table. This paper deals with two-dimensional soil water distribution and movement in sloping layered soils of a dam farmland on the Loess Plateau of China. In the dam farmland, soil water content showed horizontal distribution corresponding to spatial patterns of the particle sizes. The soil water content of deeper soil was relatively stable compared with topsoil. Generally, rainfall infiltration was limited to 0.8 m in the study period. Funnel flows were found in the layered soils of the dam farmland after rainfall proving the existence of this phenomenon which was observed in simulation experiments and field observation by previous researches. In the study area, the wetting front was unstable due to the layered soils. The spatial correlation analysis of the soil water content showed water movement along the layers in the wetting process with 7 m day −1 only on the first day after rainfall. On the vertical direction, the velocity of water movement was 0.3 m day −1 on the first day after P. Zhao State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, P. Zhao et al.rainfall. The results indicated that the quantity of funnel flow increases with distance along the inclined interfaces in the dam farmland which can cause contamination of groundwater. Consequently, future studies should consider the funnel flow and the management of agriculture chemicals in dam farmlands.

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Section: Funnel Flow Observationssupporting

confidence: 62%

Soil Water Distribution and Movement in Layered Soils of a Dam Farmland

Zhao

Shao

Melegy

2010

Water Resour Manage

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“…However, Diment and Watson's (1985) experiments in a small slab box showed that redistribution “stabilized” when the initial water content was increased to only a few percent of saturation. In contrast, recent experiments of Wang et al (2003a)(2003b) in the field and with a large slab box showed that redistribution is unstable even in a very wet uniform sand. Nicholl et al (1994) observed fingering during redistribution in initially dry fractures.…”

mentioning

confidence: 71%

“…The length of this zone is equal to the capillary suspension length ( S ). Since the water‐entry value ( h we ) decreases as initial water content θ i increases (Smith, 1967; Liu et al, 1994; Wang et al, 2003a), the blob is longer in relatively moist soils than in dry soils.…”

Section: Theorymentioning

confidence: 99%

Unstable Flow during Redistribution: Controlling Factors and Practical Implications

Zhi

Jury

Tuli

et al. 2004

Vadose Zone Journal

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Unstable flow causes major uncertainties in the characterization of drainage in the vadose zone by inducing finger‐like flow paths in soils with or without macropores. Recent studies have identified the major factors governing fingered flow to be the combined effects of capillary hysteresis, the existence of a threshold water‐entry value in a porous medium, and a positive matric potential gradient behind the wetting front. This situation typically occurs during redistribution following high‐rate infiltration, a common occurrence in hydrology. The conditions favoring instability can also develop during infiltration into a fine‐over‐coarse layered soil, into hydrophobic or air‐entrapped soils, or even in a homogeneous coarse‐textured soil if the infiltration rate is low. An analysis of the conditions necessary for the onset of unstable flow in a uniform soil is provided in this paper. We demonstrate that if the matric potential gradient (dh/dz) becomes positive during redistribution, a perturbation at the wetting front will cause finger flow. However, if dh/dz remains negative, the perturbation will be dissipated. The analysis is used to predict a critical depth of irrigation (Ic) beyond which the flow should become unstable. A series of point‐source and line‐source infiltration experiments were conducted using a slab‐box filled with uniform sands. The results confirmed that as soon as Ic is exceeded, a finger was formed at the bottom of the wetting front, channeling the flow and stopping water movement in the surrounding areas. We discuss this phenomenon's implications for practical irrigation and leaching designs.

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“…Raats (1973) explained that an increase of soil water pressure with depth above the wetting front in general leads to instabilities of the wetting front. Entrapment of air, the presence of layers with higher water‐entry values, water repellency, but also the reversal of pressure gradients during redistribution just after infiltration at the soil surface has ceased can cause such an increase in pressure above the wetting front that leads to unstable wetting fronts (Wang et al, 1998, 2003a, 2003b). Another process, which originates at the pore scale and which can explain the persistence of individual fingers due to pressure increase or pressure overshoot above the wetting front of a single finger, is the dynamic pressure–water content relation that results from a rapid filling of larger pores and a subsequent redistribution (DiCarlo, 2013).…”

Section: Improving the Infiltration Process In Land Surface Modelsmentioning

confidence: 99%

Infiltration from the Pedon to Global Grid Scales: An Overview and Outlook for Land Surface Modeling

Vereecken

Weihermüller

Assouline

et al. 2019

Vadose Zone Journal

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Core Ideas Land surface models (LSMs) show a large variety in describing and upscaling infiltration. Soil structural effects on infiltration in LSMs are mostly neglected. New soil databases may help to parameterize infiltration processes in LSMs. Infiltration in soils is a key process that partitions precipitation at the land surface into surface runoff and water that enters the soil profile. We reviewed the basic principles of water infiltration in soils and we analyzed approaches commonly used in land surface models (LSMs) to quantify infiltration as well as its numerical implementation and sensitivity to model parameters. We reviewed methods to upscale infiltration from the point to the field, hillslope, and grid cell scales of LSMs. Despite the progress that has been made, upscaling of local‐scale infiltration processes to the grid scale used in LSMs is still far from being treated rigorously. We still lack a consistent theoretical framework to predict effective fluxes and parameters that control infiltration in LSMs. Our analysis shows that there is a large variety of approaches used to estimate soil hydraulic properties. Novel, highly resolved soil information at higher resolutions than the grid scale of LSMs may help in better quantifying subgrid variability of key infiltration parameters. Currently, only a few LSMs consider the impact of soil structure on soil hydraulic properties. Finally, we identified several processes not yet considered in LSMs that are known to strongly influence infiltration. Especially, the impact of soil structure on infiltration requires further research. To tackle these challenges and integrate current knowledge on soil processes affecting infiltration processes into LSMs, we advocate a stronger exchange and scientific interaction between the soil and the land surface modeling communities.

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Unstable Flow during Redistribution in Homogeneous Soil

Cited by 22 publications

References 4 publications

Soil Water Distribution and Movement in Layered Soils of a Dam Farmland

Soil Water Distribution and Movement in Layered Soils of a Dam Farmland

Unstable Flow during Redistribution: Controlling Factors and Practical Implications

Infiltration from the Pedon to Global Grid Scales: An Overview and Outlook for Land Surface Modeling

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