UNSATURATED HYDRAULIC-PROPERTIES FROM UPWARD FLOW INTO SOIL CORES

Common methods for determining unsaturated hydraulic properties of soi ls are time consuming and measurements are restricted to relatively mo ist soil conditions. This study developed a transient upward infiltrat ion procedure for estimating soil hydraulic properties. The procedure involves pumping a carefully controlled water flux into the bottom of an initially dry soil core. As the unsaturated core slowly absorbs wat er, soil water potentials are measured with tensiometers, and, optiona lly, soil water contents are measured with time domain reflectometry. No porous plates are required for this unsaturated Bow procedure becau se a Bur boundary is used, Applied fluxes of approximately 0.76 cm d(- 1) for 60 h to 7.6 cm diam, by 7.6 cm high cores increased the water c ontent from an initial dry state (approximately - 7500 kPa) to almost saturation. A Levenberg-Marquardt inverse parameter estimation procedu re was combined with a one-dimensional numerical model of the experime ntal Bow system to estimate the soil hydraulic properties from the col lected water potential data using Eve different methods. Parameters in the van Genuchten water retention relationship and the van Genuchten- Mualem or the Campbell hydraulic conductivity relationships were simul taneously estimated, The optional water content data was combined with the water potential data to provide initial estimates of water retent ion parameters. The best method (lowest RMSE) that estimated all param eters in the water retention relationship [phi(m)(theta)] and the hydr aulic conductivity relationship [K(theta)] produced similar hydraulic property relationships for four identically packed cores of a loamy fi ne sand.