PARAMETER EQUIVALENCE FOR THE BROOKS-COREY AND VANGENUCHTEN SOIL CHARACTERISTICS - PRESERVING THE EFFECTIVE CAPILLARY DRIVE

This paper provides a simple way to convert Brooks-Corey (BC) paramete rs to van Genuchten (vG) parameters and vice versa, for use primarily in situations where saturated conditions are likely to be encountered. Essential in this conversion is the preservation df the maximum value of a physical characteristic, the ''effective capillary drive'' H-cM [Morel-Seytoux and Khanji, 1974], defined with a good approximation fo r a soil water and air system as H-cM = integral(0)(infinity)k(rw)dh(c ), where k(rw) is relative permkability (or conductivity) to water and h(c) is capillary pressure (head), a positive quantity. With this con version, infiltration calculations are essentially insensitive to the model used to represent the soil hydraulic properties. It is strictly a matter of convenience for the user which expression is used. On the other hand, the paper shows that other equivalences may lead to great variations in predictions of infiltration capacity. Consequently, the choice of the proper equivalence to use in calculations for rainfall-r unoff modeling or for low-level radioactive waste disposal design is a serious matter.