Determination the Constant Parameters of Van Genuchten-Mualem and Gardner's Equations Using a Statistical Model to Estimate the Permeability in Unsaturated Soil

Availability of accurate information regarding permeability of soil is needed in planning for the development projects, especially hydraulic structures. Laboratory determination of unsaturated permeability of soil involves high costs and is very time taking. Therefore, it is preferred to determine it using such indirect methods as making use of soil-water characteristic curve. These indirect methods are of constant parameters the determination of which needs such special information of soil water characteristic curve as residual and saturated water contents. Through initially examining a statistical model ( not a function of residual and saturated water contents) the permeability coefficients of unsaturated soil that were in acceptable correlation with famous models were determined. The constant parameters of some of the equations for estimation of the permeability of unsaturated soil were then estimated. The results finally show a high accuracy of the proposed model for a determination of the constant parameters.