Reversal of the matric potential gradient during redistribution of soil water following infiltrat... more Reversal of the matric potential gradient during redistribution of soil water following infiltration has been hypothesized as a cause of preferential flow by inducing a fluid instability at the leading edge of the wetting front. In this paper, we present results of 17 field experiments carried out to quantify the effects of redistribution on preferential flow in nonstructured soils. The experiments were performed in three field soils (Superstition sand, Delhi sand, and Hanford sandy loam) under saturating and nonsaturating water application rates. Water flow patterns were monitored at various times during redistribution with photography using anionic dyes and by intensive core sampling of bromide added during infiltration. The soil surface was either tilled or undisturbed, exposed or covered with a plastic membrane, and the top 20‐cm fine layer was either left in place or removed in various treatments. The infiltration water containing tracers was applied continuously and uniformly ...
Unstable flow causes major uncertainties in the characterization of drainage in the vadose zone b... more 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, ...
Reversal of the matric potential gradient during redistribution of soil water following infiltrat... more Reversal of the matric potential gradient during redistribution of soil water following infiltration has been hypothesized as a cause of preferential flow by inducing a fluid instability at the leading edge of the wetting front. In this paper, we present results of 17 field experiments carried out to quantify the effects of redistribution on preferential flow in nonstructured soils. The experiments were performed in three field soils (Superstition sand, Delhi sand, and Hanford sandy loam) under saturating and nonsaturating water application rates. Water flow patterns were monitored at various times during redistribution with photography using anionic dyes and by intensive core sampling of bromide added during infiltration. The soil surface was either tilled or undisturbed, exposed or covered with a plastic membrane, and the top 20‐cm fine layer was either left in place or removed in various treatments. The infiltration water containing tracers was applied continuously and uniformly ...
Unstable flow causes major uncertainties in the characterization of drainage in the vadose zone b... more 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, ...
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Papers by William Jury