Effect of Air Flow Ahead of the Wetting Front on Infiltration

Wilson, L. G.; Luthin, James N.

doi:10.1097/00010694-196308000-00010

Cited by 44 publications

(23 citation statements)

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“…Ponding at the surface of both soil columns was apparent from before 18 min into each experiment. Even in large fields, rainwater can prevent the escape of air from the soil surface (Wilson and Luthin, 1963;Youngs and Peck, 1964;Grismer et al, 1994;Wang et al, 1998). After the water table rose past the column access holes for the 7Ð9 cm deep TDR probes (which were not airtight initially), no air escape was possible between this depth and the surface, until air was released through holes bored from the surface (Figures 10 and 11).…”

Section: Unsaturated Pore-water Pressures and Soil Shear Strengthmentioning

confidence: 99%

The influence of groundwater on surface flow erosion processes during a rainstorm

Rockwell¹

2002

Earth Surf Processes Landf

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Surface erosion rates on a disturbed natural soil in a 10 m indoor flume increased by an order of magnitude when a water table developed at a 10 cm depth during simulated rainstorms. Erosion rate increases did not correlate well with surface hydraulic flow conditions, and all significant erosion increases began before the full soil depth was saturated, before the water table reached the soil surface, and before seepage was possible. Groundwater influenced erosion processes primarily by increasing unsaturated pore-water pressures and decreasing soil shear strength in surface rainflow, rather than through the direct entrainment of soil particles by seepage flow.There was no unique morphologic expression of the influence of groundwater during a rainstorm. Subsurface processes influencing surface erosion were detected only by appropriate subsurface instrumentation, which included micropiezometers, tensiometers and time domain reflectometry. Erosion rate increases occurred all along the slope, and were not concentrated at the base of slope due to a seepage zone. Soil depth was crucial to determining surface erosion increase. It is likely that confusing trends in surface flow erosion rates in past studies have occurred due to unrecorded groundwater development or an emphasis on seepage effects. Groundwater must be monitored along hillslopes under all moisture and soil conditions in order to avoid misleading and inconsistent conclusions derived solely from surface flow or seepage data.

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Section: Unsaturated Pore-water Pressures and Soil Shear Strengthmentioning

confidence: 99%

The influence of groundwater on surface flow erosion processes during a rainstorm

Rockwell¹

2002

Earth Surf Processes Landf

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“…As water infiltrates into the vadose zone, soil air is being displaced and may become compressed ahead of the wetting front. Existing laboratory studies [Wilson and Luthin, 1963;Peck, 1965 the hydraulic conductivity and on the onset and extent of unstable flow (fingering) are also assessed.…”

Section: Introductionmentioning

confidence: 99%

Air entrapment effects on infiltration rate and flow instability

Wang¹,

Feyen²,

Genuchten³

et al. 1998

Water Resources Research

165

123

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Abstract. Experiments were conducted to quantify the effects of entrapped air on water infiltration into a loamy sand. Transparent three-dimensional (3-D) and 2-D columns were used for experiments carried out for two infiltration conditions: (1) when air was free to move ahead of the wetting front and leave the bottom of the column (air draining) and (2) when air was confined ahead of the wetting front and hence could escape only through the soil surface (air confining). The measurement setup was composed of a tensionpressure infiltrometer, an air flowmeter, water manometers, and video-picture cameras. We applied both positive and negative water pressures at the soil surface and measured the simultaneous changes in the rates of water inflow and air outflow, the air pressure ahead of the wetting front, and the dynamic behavior and advance of the wetting front. The air pressure ahead of the wetting front for the air-confining condition was generally found to increase with time rather than reaching a constant level, as observed in other studies by other researchers. The air pressure fluctuated locally because of air escaping from the soil surface. On the basis of an analysis of the results we present two empirical equations to predict the maximum air pressure at which air begins to erupt from the soil surface and to predict the minimum air pressure at which air eruption stops. We found that the infiltration rate was always equal to, and controlled by, the rate of air outflow. The infiltration rate varied inversely with the air pressure ahead of the wetting front and with the ponding depth at the soil surface. The infiltration rate fluctuated with time rather than undergoing changes in a three-stage process, as is often characterized in the literature. The volume of residual entrapped air in the air-confining condition increased 7% on average, and the infiltration rate decreased threefold to tenfold as compared to the air-draining condition. Finally, it was shown that the air-confining infiltration flow is fingered and unstable, consistent with the predictions of an existing theory.

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“…However, it is well known that during transient infiltration events, the pressurization of air ahead of a wetting front can produce significant flow effects, especially in low-permeability systems [Wilson and Luthin, 1963;Youngs and Peck, 1964;Bianchi and Haskell, 1966;Green et aI., 1970J. One may envision a situation in which a matrix block is suddenly surrounded by liquid water on all sides.…”

Section: Additional Issuesmentioning

confidence: 99%