SCALING WATER CHARACTERISTIC AND HYDRAULIC CONDUCTIVITY BASED ON GREGSON-HECTOR-MCGOWAN APPROACH

Gregson, Hector, and McGowan reported recently that the two constants, a and b, of the Brooks and Corey type log-log model of the soil water characteristic, psi(theta), were highly correlated for a range of diverse soils. The linear relationships between a and b for individual soils were very close to one common relationship. This relationship provides a new method of scaling psi-(theta). We found also a strong a vs. b relationship in experimental psi-(theta - theta-r) data for 10 different soils, where theta-r, the residual water content, was equal to zero or constant within a given soil. These individual relationships were close to each other and to the common relationship for Gregson et al. soils. However, their classification into three textural groups seemed more desirable. Relative efficiency of scaling psi-(theta - theta-r) for different locations within individual soils ranged from 39 to 83%. These efficiencies were generally greater than the efficiencies calculated by the extended similar-media scaling using one measured value for each psi-(theta) curve. We also extend our investigation to unsaturated hydraulic conductivity, K(psi), data for six soils. Here, too, we found a strong relationship between the two constants, A and B, of the log-log equations for K(psi). Furthermore, the individual A vs. B relationships for all soils merged into one unique relationship. This common relationship was used to scale combined K(psi) data for all soils, with a relative efficiency of 94%. Finally, we demonstrate the application of the A vs. B relationship for estimating K(psi) from infiltration data.