چکیده
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Soil water infiltration can be described with the quasi-analytical Haverkamp et al. (1994) equation, defined by
the hydraulic conductivity (Ks), sorptivity (S) and the β parameter. Ks and S are commonly estimated from the
transient cumulative infiltration curve, using a constant β value. The objective of this work was to study the
influence of β on the estimation of Ks and S. The study was first performed on synthetic 1-D infiltration curves
generated at different infiltration times for loam sandy, loamy and silty soils, and next extrapolated to a 3-D loam
synthetic soil and on 10 infiltrations curves measured on the field with a disc infiltrometer on different types of
soils. The infiltration measurements lasted between 600 and 900 s. The results showed that, while early infiltration
times (i.e. 100 s) promoted good estimations for S, longer infiltrations (i.e. 1.000 s) were required to
estimate accurately Ks. Only very long infiltration (i.e. 10.000 s) allowed defining the actual β value. A similar
behaviour was observed for the 3-D infiltration measurements. Except for β, significant relationships (R2=0.99)
were obtained between the Ks and S of the three theoretical soils and the corresponding values calculated by
optimizing the three hydraulic parameters on 2.000 s 1-D infiltration curves. The large confidence interval
observed in β (between 0.3 and 2.0) resulted from the fact that β had a small effect on the infiltration curve. A
significant relationship (R2=0.99) was also obtained between the Ks and S optimized from the experimental
curves using a β=1.1 and the corresponding values obtained by simultaneous optimization of the three hydraulic
parameters. These results demonstrated that S and Ks can be accurately estimated using a constant β and
that downward infiltration is not an appropriate procedure to estimate β.
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