Channel Flow Over Permeable Beds of Graded Spheres

Tests were carried out to determine the velocity distribution and the hydraulic roughness in flows over 20 permeable beds made up of different sizes and gradings of spherical particles. Corresponding tests were carried out to determine the surface rugosity and the permeability of these beds. The investigation showed that the virtual zero of the velocity profile was depressed below the surface of the bed due to flow occurring in the permeable bed material. Despite this the hydraulic roughness of the permeable beds was higher than that for equivalent impermeable beds of the same surface rugosity. There was strong correlation between the hydraulic roughness of permeable beds and a simple parameter which included both a characteristic particle size of the bed material, and the permeability.