MODIFIED SOIL-WATER RETENTION FUNCTIONS FOR ALL MATRIC SUCTIONS

The Brooks-Corey and van Genuchten functions were modified to adequate ly; represent retention at all matric suctions. The modification consi sted of replacing the residual water content with an adsorption equati on (Campbell and Shiozawa, 1992). The modified functions retain the fo rm of the original functions in the wet range and the form of an adsor ption equation in the dry range. The modified functions provided excel lent fits to data from six soils with textures ranging from sand to si lty clay. The modified van Genuchten function can use previously deter mined parameters to obtain a reasonable representation of the high mat ric suction range, thus allowing for the use of existing parameter set s. The modified functions, as well as the function proposed by Rossi a nd Nimmo (1994), were combined with the Mualem conductivity model to g enerate closed-form analytical expressions for the calculation of hydr aulic conductivity.