Transient flow from tension infiltrometers. I. The two-parameter equation
2000
Vandervaere, J.P. | Vauclin, M. | Elrick, D.E.
Tension disk infiltrometer experiments are generally conducted until apparent steady state is reached because most of the methods of analysis are based on Wooding's solution for steady state flux. However, the time necessary to reach steady state may be a penalizing aspect for soils with low permeability and the information contained in the transient stages is not utilized. Moreover, these methods assume homogeneous soil and a uniform initial water content, which may be unrealistic when a large volume of soil is sampled. In this series, we propose and compare several new methods of analysis that are based on the transient stage of axisymmetric infiltration. In the first part, we show that a two-parameter equation-one term linear in square root of time and one term linear in time-adequately describes the transient flow from the disk infiltrometer for both simulated and laboratory tests. The technique used for the determination of the two coefficients must meet two criteria; it must verify the validity of the two-term equation throughout the duration of the experiment, and it must account for the early-time perturbation that is induced by the sand-contact layer placed between the disk and the soil. We show that the best technique consists in linearizing the data by differentiating cumulative infiltration with respect to the square root of time. Direct nonlinear fitting on cumulative infiltration or infiltration flux is likely to lead to unacceptable errors, either because of the undetected invalidity of the two-parameter equation or arising from the influence of the contact layer.
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