Open AccessThe Pressure Head Regime in the Induction Zone During Unstable Nonponding Infiltration: Theory and Experiments
Author(s) -
Cho H.,
Rooij G. H.,
Inoue M.
Publication year - 2005
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2004.0158
Subject(s) - ponding , infiltration (hvac) , pressure head , porous medium , mechanics , geotechnical engineering , vadose zone , geology , capillary pressure , head (geology) , capillary action , instability , limiting , hydraulic head , groundwater , porosity , materials science , geomorphology , composite material , thermodynamics , physics , engineering , mechanical engineering , ecology , drainage , biology
Fingered flow rapidly moves water and pollutants from the root zone to the groundwater through a limited fraction of the unsaturated zone, limiting the possibilities for decay and adsorption. The onset of wetting front instability and the characteristics of the flow pattern under nonponding infiltration have received limited attention. We aim to theoretically and experimentally advance our understanding of pre‐fingered flow, and contrast fingered flow under ponding and nonponding conditions. We developed a Green‐Ampt based expression for the pressure head in a developing induction zone (from which fingers protrude) for the time before fingers developed. A uniform, nonponding water flux was applied to the surface of two‐dimensional glass bead porous media with a dry region above a capillary fringe. Microtensiometers recorded pressure heads in the induction zone. The pressure head data confirmed both the theoretical early‐time pre‐finger model, and a model developed earlier for late‐time lateral flow toward fully developed fingers. The physically more realistic constant flux boundary condition of our experiments gave larger finger spacings and travel times, compared to the frequently used set‐up with ponding infiltration into a fine‐over‐coarse porous medium.