MODIFIED SOIL-WATER RETENTION FUNCTIONS FOR ALL MATRIC SUCTIONS

The Brooks-Corey and van Genuchten functions were modified to adequately; represent retention at all matric suctions. The modification consisted of replacing the residual water content with an adsorption equation (Campbell and Shiozawa, 1992). The modified functions retain the form of the original functions in the wet range and the form of an adsorption equation in the dry range. The modified functions provided excellent fits to data from six soils with textures ranging from sand to silty clay. The modified van Genuchten function can use previously determined parameters to obtain a reasonable representation of the high matric suction range, thus allowing for the use of existing parameter sets. The modified functions, as well as the function proposed by Rossi and Nimmo (1994), were combined with the Mualem conductivity model to generate closed-form analytical expressions for the calculation of hydraulic conductivity.