In this paper, we have been used an experimental model to analyze the nonlinear free surface radial flows and to introduce an equation compliant with these flows. This is a semi cylindrical model including a type of coarse grained aggregate which leads the radial flow into the center of a well. Thereafter, the hydraulic gradient was measured on different points of the experimental model by three distinguished methods of difference of successive radii, keeping constant the minimum and maximum radii. An equation, describing the behavior of free surface radial flow, was then proposed by measured data (as regression data) from the laboratory and analysis of the results. Verification of the proposed equation by test data shows that the equation is valid on the established limits of the data.
