In this paper, the relation between the brink and critical depth is studied experimentally and theoretically to predicted theoretical discharge equation using in rough free overfall. Three different; bed rough materials, sizes and distributions were used and tested experimentally to developed the discharge relationship. An equation is proposed to determine the flow rate using brink depth for a channel of known roughness, Froude number and normal depth. The equation shows that (95) % of the estimated discharge within (4) % error of the experimental data. The magnitude of the ratio (yb/yc) dependent of both the free overfall roughness materials and its distribution, the maximum values of this relation were happened at smooth free overfall and reduced gradually at rough one for wood material, then more decreases for 6mm and 2mm stone material

In this paper, the relation between the brink and critical depth is studied experimentally and theoretically to predicted theoretical discharge equation using in rough free overfall. Three different; bed rough materials, sizes and distributions were used and tested experimentally to developed the discharge relationship. An equation is proposed to determine the flow rate using brink depth for a channel of known roughness, Froude number and normal depth. The equation shows that (95) % of the estimated discharge within (4) % error of the experimental data. The magnitude of the ratio (yb/yc) dependent of both the free overfall roughness materials and its distribution, the maximum values of this relation were happened at smooth free overfall and reduced gradually at rough one for wood material, then more decreases for 6mm and 2mm stone material.