Evaluation and Sensitivity Analysis of Head-Loss Equations of Free Surface Flow through Rockfill Porous Media

This research was aimed to evaluate the available equations provided for non-Darcy flow in rockfill porous media, when there is a free surface flow, and when vertical pressure distribution is non-hydrostatic. Most of previous investigation about non-Darcy flow performed in permeameter that simulate one dimensional flow in porous media. Because of severe energy loss and considerable difference between upstream and downstream water surface elevations in rockfill porous media, a non-hydrostatic pressure distribution was expected. To carry out the research, a series of laboratory experiments have been conducted on rockfill materials with three differet diameters (1.68, 2.27 and 4.84 cm) and in a medium of 100cm in length, where water temperature varied between 10 and 29 °C. Results indicated that difference between water depth and piezometric pressure increased as water surface and water discharge increased.  Based on statistical analysis of existing experimental data, the most suitable model for energy loss in free surface flow in rockfill materials was introduced. Moreover, it was found that the introduced model had the lowest sensitivity to the variation of the input parameters, and the porosity, apparent velocity, median rockfill diameter and kinematic viscosity, respectively, had highest influence on head-loss results.