Average Soil Water Retention Curves Measured by Neutron Radiography

Area of Science:

• Environmental science
• Geophysics
• Hydrology

Background:

• Water retention curves are vital for modeling hydrologic behavior in partially saturated porous media.
• Understanding flow and transport processes in the vadose zone requires accurate water retention data.

Purpose of the Study:

• To directly measure the drying and wetting branches of average water retention functions using 2D neutron radiography.
• To assess the effectiveness of neutron imaging as a tool for quantifying water retention curves.

Main Methods:

• Flint sand columns were drained and rewetted under quasi-equilibrium conditions using a hanging water column setup.
• 2D neutron radiography was used to acquire images of transmitted neutron flux at various matric potentials.
• Volumetric water contents were calculated using Beer-Lambert's law, with corrections for beam hardening and scattering, and normalized to relative saturations.

Main Results:

• Average relative saturations from neutron radiography closely matched volumetric measurements from the hanging water column setup.
• Parameters of the van Genuchten equation fitted to neutron radiography data showed no significant differences compared to hanging water column data.
• Neutron imaging proved to be a highly effective tool for quantifying average water retention curves.

Conclusions:

• Neutron imaging provides a reliable and effective method for determining average water retention curves.
• The findings validate the use of neutron imaging in hydrological studies of partially saturated porous media.
• This technique enhances the understanding of water movement and storage in the vadose zone.