Estimation of Brooks‐Corey Parameters from water retention data

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Abstract
The parameters of the Brooks‐Corey soil moisture characteristic may be determined by either graphical or automatic numerical procedures. A popular log‐log procedure for automatic estimation leads to a linear least squares optimization problem. Apparently, it has been applied incorrectly in the past when all measurements were used for parameter estimation, and this realization explains the inconsistencies in some published data. Its proper application generally requires the solution of more than one linear problem for each data set. Alternatively, a nonlinear procedure will yield parameter estimates directly. In either case there may exist multiple local minima in the sum of squared deviations between model and measurements, and the parameter estimates so derived are demonstrably unreliable; this appears to be a result of the distinct air‐entry suction implicit in the Brooks‐Corey model and usually absent in field‐measured characteristic curves. A new procedure based on an integral objective function overcomes the problems cited.