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During pressure flushing of deposited sediments over large dam intakes, a funnel-shaped crater is formed due to considerable shear flow around the opening. Experiments with variable flow depth and discharge were conducted to determine the geometry of the flushing cone for fine, medium and coarse non-cohesive sediments. These sediments increase with increasing discharge and decrease with increasing reservoir depth and sediment particle size. Using the test results, two equations are proposed to estimate scour cone length and volume. While the water depth over the sediments is the most significant parameter in the collapse of sediments above the intake and initial development of the cone, the sensitivity analysis indicated that the intake flow velocity is the most significant parameter in determining the final equilibrium size of the scour cone. The results were compared with a previous study made with a small-scale model to confirm the proposal.