Abstract In this paper, the empirical equations that estimate hydraulic parameters for non-linear flow through coarse porous media are evaluated using a series of independent data collected in the laboratory. In this regard, three different relatively uniform soils ranging in size from 8.5 to 27.6 mm have been selected and three random samples drawn from each material. The physical characteristics such as size distribution, porosity, and shape factor have been measured for the 9 samples. In total, 9 permeameter tests have been conducted on the samples to create a set of reliable hydraulic gradient vs. bulk velocity data. Statistical measures have been used to compare the permeameter data with those predicted by the empirical equations. The study shows that McCorquodale et al. and Stephenson equations, which some subjective parameters related to the surface characters of the material, have been incorporated in their structures, can give good results. Also, equation developed by Adel who considers d15 as characteristic size of the media, shows acceptable performance. Other equations either underestimate or overestimate hydraulic gradient based on experimental work and analysis conducted in this study.

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