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ORIGINAL RESEARCH

Uncertainty of Hydraulic Conductivity under Field Conditions and at Fixed Pressure Heads and Water Contents

Department of Exact Sciences, University of São Paulo, Piracicaba, SP, Brazil
^* Corresponding author (qdjvlier{at}esalq.usp.br)

Received 21 January 2004.

Unsaturated hydraulic conductivity (K) can be expressed as a function of soil water content () or pressure head (h). Methods to determine K often give highly variable results, thus making it difficult to report values for K in a reliable manner. Due to the sensitivity of pore conductivity to pore radius, it can be expected that K expressed as a function of h shows less variability than expressed as a function of . To test this hypothesis, K was determined at several values of and h using the instantaneous profile method at 48 locations in the surface and a subsurface layer of a Typic Hapludox in Brazil. Results were analyzed considering the field values of K at the time of observation (K_t), at fixed values of (K), and at fixed values of h (K_h). Results show that the coefficient of variation of K is higher than that of K_h, especially in the surface layer, which suggests that, if one has the choice, it would be preferable to estimate soil water movement using measured h values, and using K(h), instead of measuring and using K(). We also show that the variability in K_t increases as the soil gets drier, while K and K_h show more variability for wetter soil.

Abbreviations: ZFP, zero flux plane