Rainfall simulation is a commonly used approach for studying runoff and erosion from forest roads, and a method is needed to estimate infiltration parameters from these experiments. We used two algorithms, the Simplex and Shuffled Complex Evolution, to estimate parameters for a physically based infiltration and overland flow model. Each algorithm was tested by estimating parameters for 92 field-measured hydrographs from forest roads. Nine of the field-measured hydrographs allowed us to further test whether estimated parameters could be extended to other antecedent conditions and plot sizes. The results demonstrate (1) the physically based model is able to estimate hydrographs from forest roads, (2) the two algorithms find unique parameter sets in spite of an error surface that suggests identifiability problems between the hydraulic conductivity and pressure parameters, (3) the two algorithms converged to the same parameter values, and (4) that parameters estimated for one antecedent condition and plot size can be extended to others with reasonably small error.