Average Soil Water Retention Curves Measured by Neutron Radiography

Published

April 21, 2021

Author(s)

Daniel S. Hussey, David L. Jacobson, Chu-lin Cheng, Misun Kang, Juske Horita, sophie voisin, Hassina Bilheux, Warren Jeffery, Edward Perfect

Abstract

Water retention curves are essential for understanding the hydrologic behavior of partially- saturated porous media and modeling flow transport processes within the vadose zone. In this paper we report direct measurements of the main drying and wetting branches of the average water retention function obtained using 2-dimensional neutron radiography. Flint sand columns were saturated with water and then drained under quasi-equilibrium conditions using a hanging water column setup. Digital images (2048 x 2048 pixels) of the transmitted flux of neutrons were acquired at each imposed matric potential (10-15 matric potential values per experiment) at the NCNR BT-2 neutron imaging beam line. Volumetric water contents were calculated on a pixel by pixel basis using Beer- Lambert's law after taking into account beam hardening and geometric corrections. To remove scattering effects at high water contents the volumetric water contents were normalized (to give relative saturations) by dividing the drying and wetting sequences of images by the images obtained at saturation and satiation, respectively. The resulting pixel values were then averaged and combined with information on the imposed basal matric potentials to give average water retention curves. The average relative saturations obtained by neutron radiography showed an approximate one- to-one relationship with the average values measured gravimetrically. There were no significant differences between the parameters of the van Genuchten equation fitted to the average neutron radiography data and those extracted from replicated hanging water column data. Our results indicate that neutron imaging is a very effective tool for quantifying the water retention curve.

Citation

Soil Science Society of America Journal

Pub Type

Journals

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Keywords

capillary pressure, neutron imaging, non-destructive testing, relative saturation, soil water

Citation

, D. , Duewer, D. , Cheng, C. , Kang, M. , Horita, J. , voisin, S. , Bilheux, H. , Jeffery, W. and Perfect, E. (2021), Average Soil Water Retention Curves Measured by Neutron Radiography, Soil Science Society of America Journal, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=909425 (Accessed May 10, 2024)