Funneled flow mechanisms in layered soil: field investigations

Abstract

The movement of water and potential pollutants in the vadose zone of fluvial deposits is often difficult to predict because fineover-coarse layers may behave as capillary barriers, funneling water and dissolved solutes into concentrated preferential flow paths. Capillary barriers have been studied in laboratory experiments and by mathematical analysis with well-defined boundaries but little is known about water and solute movement in naturally layered soils. This paper demonstrates how naturally occurring capillary barriers affect water and solute movement. Experiments were carried-out in a river valley near Amherst, MA and on a prehistoric beach near Cornell University in Ithaca, NY. Dye tracer and chloride were initially applied near the soil surface, followed by intermittent rainfall over several weeks. After 2-6 weeks the blue dye, soil water content, and chloride concentration distributions in the soil profile were examined by excavating a trench and photographing and sampling the exposed soil face. At both sites, the infiltrating water was diverted and flowed laterally over a relatively coarse layer. At the Cornell site, flow broke through the fine -coarse interface into the coarse layer at a few points along the barrier. The primary breakthrough at the Cornell site occurred at a horizontal section of the interface, 2 m down-slope from the point of dye application. The capillary diversions generally agreed with current theory, however, the flow patterns were difficult to predict accurately without more detailed information about the soil layering characteristics. q

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

“…8). 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).…”

“…However, few studies focused on the soil water in dam farmland where the heterogeneous layered soil existed on the Loess Plateau of China as far as we know. Moreover, the studies focusing on water distribution and movement in layered soils were mainly conducted in laboratory (Stauffer and Dracos 1986;Miyazaki 1988;Samani et al 1989;Antonopoulos 1993;Sakellariou-Makrantonaki 1997) and very few studies have conducted in field for complex field condition under tougher operations (Heilig et al 2003;Gish et al 2003).…”

Water percolation through the deep vadose zone and groundwater recharge: Preliminary results based on a new vadose zone monitoring system

“…Non vertical flow may occur at the interface between two layers with contrasting hydraulic conductivities, even when the mean hydraulic gradient is vertical [Hendrickx and Walker, 1997;McCord et al, 1997;Hielig et al, 2003].…”

Impacts of a capillary barrier on infiltration and subsurface stormflow in layered slope deposits monitored with 3-D ERT and hydrometric measurements

“…As a result to the supply from the entire surface, the breakdown of a capillary barrier would be more extensive. For a continuous capillary barrier, different flow regimes may occur and alternate along the interface: "capillary diversion", "partial" or "complete breakthrough" and "toe diversion" (Walter et al, 2000;Heilig et al, 2003). The length of the diversion strongly depends on hydraulic conductivity of the fine material, the slope of the interface as well as the infiltration rate (Ross, 1990).…”