Transient flow from tension infiltrometers: II. Four methods to determine sorptivity and conductivity

In Vandervaere et al. (2000) it was shown that the transient regime of axis ymmetric infiltration can be described by a two-term equation with one term proportional to the square root of time and the other term proportional to time. The two corresponding coefficients, C-1 and C-2, are functions of th e hydraulic conductivity, K, and the sorptivity, S. In this paper we propos e four different methods to achieve the determination of S and K. The four methods differ by the number of disk radii and the number of supply pressur e head values which are utilized. We show that the accuracy of a given meth od is highly dependent on the combination of S and K values obtained. Three situations can be distinguished, depending on the disk radius: (i) the now is dominated by the lateral capillary term; (ii) the now is dominated by t he gravity term; (iii) lateral capillary and gravity terms have equivalent weights. The seven model soils tested here all correspond to the first situ ation with usual disk radius values. This tends to show that a precise esti mation of K is unlikely from disk infiltrometer data. We introduce a new ti me scale, t(stab), which generalizes the concepts corresponding to the two well known time scales t(grav) and t(geom). We propose a guideline for the investigator to choose between all existing methods of analysis that use st eady or transient now. Finally, the four new methods are tested against num erically simulated tests with Grenoble sand and Yolo light clay.