PEDO-TRANSFER FUNCTIONS FOR ESTIMATING UNSATURATED HYDRAULIC-PROPERTIES OF PORTUGUESE SOILS

The measurement of unsaturated soil hydraulic properties is expensive and time consuming. These properties are hence frequently predicted wi th so-called pedo-transfer functions (PTFs) using basic soil propertie s (e.g. particle-size distribution, organic matter content and bulk de nsity). In this study PTFs are developed by regression between hydraul ic data and basic soil properties. Parameters are quantified for: (i) the retention model of van Genuchten using 80 soil profiles with a tot al of 230 retention curves, and (ii) the conductivity model of Gardner using 20 soil profiles and 129 hydraulic conductivity curves. The pro files represent the main soil families in Portugal, ranging from coars e sands to heavy clays. The PTFs derived from data for all soils provi de a fairly poor description of the hydraulic parameters because of th e heterogeneity of the profiles. The description of several parameters is improved by using PTFs that are developed for more homogeneous soi ls grouped according to their particle-size distribution. A further im provement is achieved by including the water contents at 2.5 cm, 100 c m, and 15 000 cm water suctions in the retention PTFs, or the saturate d hydraulic conductivities in the conductivity PTFs.