Parameter Equivalence for the Brooks‐Corey and Van Genuchten Soil Characteristics: Preserving the Effective Capillary Drive

Abstract

This paper provides a simple way to convert Brooks‐Corey (BC) parameters 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 of the maximum value of a physical characteristic, the “effective capillary drive” H cM [ Morel‐Seytoux and Khanji , 1974], defined with a good approximation for a soil water and air system as H cM = ∫ 0 ∞ k rw dh c , where k rw is relative permeability (or conductivity) to water and h c is capillary pressure (head), a positive quantity. With this conversion, 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‐runoff modeling or for low‐level radioactive waste disposal design is a serious matter.