Estimating the saturated soil hydraulic conductivity in a farm constructed wetland by the borehole permeameter infiltration method

The borehole permeameter infiltration method was used to determine the soil hydrodynamic properties at different depths in a farm constructed wetland (CW) in which the saturated soil hydraulic conductivity, $K_{s}$, was already investigated for the uppermost surface layer. With the aim to estimate $K_{s}$ and the sorptive number $\alpha^*$, a non-linear curve fitting approach was used to fit both the Philip (1993) and the Reynolds (2011) models to the experimental infiltration data. The estimated parameters were compared with those obtained with the graphical approach by Philip (1993) and the empirical approach by Regalado et al., (2008). Both $K_{s}$ and $\alpha^*$ varied along the soil profile but also between the inlet and outlet zone of the CW. The graphical approach was not applicable whereas the empirical approach overestimated both $\boldsymbol{K}_{s}$ and $\alpha^*$ compared with the non-linear fitting approach. Despite the differences among the considered approaches, the borehole permeameter technique confirmed that the subsurface $\boldsymbol{K}_{\mathrm{s}}$ was at least two orders of magnitude lower than that obtained by the ring infiltrometer at the CW surface thus confirming the importance of conducting these experiments for the study of the groundwater recharge processes.