The Pressure Head Regime in the Induction Zone During Unstable Nonponding Infiltration: Theory and Experiments

Abstract

Fingered flow rapidly moves water and pollutants from the root tensiometers in Hele-Shaw cells to observe pressure zone to the groundwater through a limited fraction of the unsaturated heads in the induction zone. Of those, only the latter zone, limiting the possibilities for decay and adsorption. The onset had enough observation points in the induction zone to of wetting front instability and the characteristics of the flow pattern under nonponding infiltration have received limited attention. We study lateral flow toward the fingers in an induction aim to theoretically and experimentally advance our understanding zone below a fine-over-coarse interface. Geiger and of pre-fingered flow, and contrast fingered flow under ponding and Durnford (2000) performed similar measurements in nonponding conditions. We developed a Green-Ampt based expres-12.7-mm diameter columns. sion for the pressure head in a developing induction zone (from which As indicated above, detailed lateral pressure head disfingers protrude) for the time before fingers developed. A uniform, tributions in the induction zone have only been observed nonponding water flux was applied to the surface of two-dimensional in ponded fine-over-coarse profiles. We therefore perglass bead porous media with a dry region above a capillary fringe. formed nonponding infiltration experiments with two-Microtensiometers recorded pressure heads in the induction zone. dimensional glass bead porous media. We studied all The pressure head data confirmed both the theoretical early-time stages of finger development and compared finger bepre-finger model, and a model developed earlier for late-time lateral flow toward fully developed fingers. The physically more realistic havior with earlier ponded infiltration experiments (Cho constant flux boundary condition of our experiments gave larger finger and de Rooij, 2002). Flow inside the fingers was theoretispacings and travel times, compared to the frequently used set-up cally treated by Selker et al. (1992b), while de Rooij with ponding infiltration into a fine-over-coarse porous medium.

Water Migration in Covered Waste Rock, Investigations Using Deuterium as a Tracer

“…Preferential flow is also observed in materials that are devoid of obvious structural or physical heterogeneity (Parlange and Hill, 1976, Ghodrati and Jury, 1992, Cho et al, 2005. Preferential flow that is not directly related to the material properties or texture can occur at the redistribution wetting front as the hydraulic gradient reverses following an infiltration event into a drier medium (Diment andWatson, 1985, Wang and.…”

An Assessment of Lime Filter Drainage Systems

“…As in the clay soil the largest part of runoff discharges through more permeable drainage trenches, backfilled trench above drain tiles can be considered as a pathway for preferential transport of biogenic substances (Dekker et al, 2001;Cho et al, 2005). Preferential flow has always been conceived to have a detrimental impact on water quality because it moves solutes beyond the soil zone where both biotic and abiotic chemical reactions are usually at their highest potentials (Ryan 1998;Ekholm et al, 1999;Van den Eertwegh, 2006).…”