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TECHNICAL NOTES

Alternative Unsaturated Flow Analyses for the Falling-Head Ring Infiltrometer

Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, 2585 County Rd. 20, Harrow, ON, Canada N0R 1G0
^* Corresponding author (reynoldsd{at}agr.gc.ca).

Received 2 March 2007.

The Green–Ampt expression for determining field-saturated hydraulic conductivity (K_fs) and matric flux potential (_m) from falling-head ring infiltrometer measurements produces a singularity when the standpipe cross-section divided by the ring cross-section (R) equals the change in porous medium water content (). As R = is clearly possible in wet, low-permeability materials, the objective of this study was to develop an alternative falling-head ring infiltrometer analysis that applies for 0 < R < +, including R = . This was accomplished by replacing the natural logarithm in the Green–Ampt analysis with a Taylor series expansion, which removes the (R – ) divisor from the analysis. The Taylor series form of the Green–Ampt expression collapses to a simple algebraic expression when R = . Combining this algebraic expression with a similar analysis developed for gravitationless infiltration provides an improved approximate relationship for estimating K_fs when standpipe drawdown is small and R < .