Analysis and testing of a concentric-disk tension infiltrometer

Tension infiltrometers are widely used to measure soil hydraulic properties at soil potentials near saturation in the held. Current methods of hydraul ic property analysis using tension infiltrometers rely on secondary measure ments of soil water content and/or use of a specific hydraulic conductivity (K(h)) form. in this paper, design criteria and method of application for a concentric disk (CD) infiltrometer are proposed, which can be used to mea sure saturated and nearly saturated hydraulic conductivities (K(h(o))) and matric flux potential (Phi(h(o))) in the field without secondary measuremen ts or explicit reliance on a specific conductivity form. Using measured pai rs of K(h(o)) and Phi(h(o)), a parameter estimation method is suggested to allow extrapolation of K(h) to lower than measured soil water potentials. T he design of the infiltrometer and the accuracy of parameter estimation wer e tested against results of numerical simulations. We found that an outer-d isk radius of 150 mm was sufficient to establish a 50-mm-radius inner-disk of one-dimensional (1-D) infiltration under a wide range of simulated condi tions. Identification of input K(h) functions using the suggested: method o f analysis was excellent, although errors were introduced by nonsteady-stat e infiltration data. A field test of a CD infiltrometer yielded a promising comparison with K(h) data generated by the instantaneous profile method, a n alternative approach but one that is, more labor intensive. The advantage of the CD infiltrometer is that, in addition to providing a rapid, direct estimate of K(h(o)), the results are not conditional upon an assumed form o f K(h) and they may be used to estimate the parameters of a K(h) form of ch oice.