Geophysical Quantification of a Moisture Content Profile in the Near Surface

Paula Hahesy; Graham Heinson; Anthony L. Endres

doi:10.1071/EG01070

ISSN: 0812-3985
E-ISSN: 1834-7533

Geophysical Quantification of a Moisture Content Profile in the Near Surface
Authors Paula Hahesy^a, Graham Heinson^b and Anthony L. Endres^c
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^a School of Chemistry, Physics and Earth Sciences Flinders University of South Australia, GPO Box 2100 Adelaide, , South Australia, , 5001, Phone: +61 8 8201 3601, Facsimile: +61 8 8201 2676, E-mail: [email protected] ^b Department of Geology and GeophysicsUniversity of Adelaide Adelaide, , South Australia, , 5005, Phone: + 61 8 8303 5377, Facsimile: +61 8 8303 4347, E-mail: [email protected] ^c Department of Earth SciencesUniversity of Waterloo Waterloo, , Ontario, Canada, , N2L 3G1, Phone: (519) 888 4567, Facsimile: (519) 746 7484, E-mail: [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: Exploration Geophysics, Volume 32, Issue 1, Mar 2001, p. 70 - 74
DOI: https://doi.org/10.1071/EG01070
- Published online: 01 Mar 2001

Abstract

Geophysicists commonly have a simplistic view of the water table as a sharp interface between the vadose zone (unsaturated region) and the phreatic zone (saturated region). In reality, this boundary is a transition zone where moisture content varies continuously with depth. Since geophysical methods respond to depth-related variations in water content, the use of this simplistic model could lead to significant errors in the interpretation of surface geophysical data. An improved model for the moisture content profile that incorporates different soil structures, soil type and water qualities would allow better interpretation of nearsurface geophysical surveys. In this study, an analysis of the relationship between time-varying moisture content and the response of commonly used near-surface geophysical methods has been performed using the soil-moisture simulation program LEACHM.

Model studies reveal that the interpreted depth to water table will be less than the true depth to 100% saturation, and that the non-uniqueness of interpretation generates a wide range of possible vadose models that fit data to within 5%. Heavy summer rainfall events significantly change surface geophysical responses over a two-week period; lighter winter rain will introduce smaller changes, but with greater frequency. Additionally, temperature variations in the top one metre are also important for pore-water electrical conductivity. Such variability has important consequences for the repeatability of measurements over time, and in comparing data from different areas.

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Article Type: Research Article

Keyword(s): acoustic velocity; dielectric permittivity; electrical conductivity; Soil moisture; soil structure; water table

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Geophysical Quantification of a Moisture Content Profile in the Near Surface

Abstract

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