This paper shows experimentally effect of gravel beds to reduce erosion of soil downstream of submerged hydraulic jumps by using a physical model, gravel beds are employed downstream of radial gate to dissipate the energy and to control the erodibility of cohesionless soils. Two different types of gravel were considered, natural particle with graded grain sizes, and non-uniform big grain sizes, a state of smooth bed was included to estimate the influence of gravel beds on the scour hole dimensions. A preliminary comparison of the incipient motion values shows that granular soils downstream gravel bed have a smaller free surface flow erosion than the granular soils downstream smooth bed. Additional comparison of the experimental data incipient motion criteria also suggests that decrease void ratio for gravel bed leads to minimize erosion the soil. The gravel beds reduce the maximum scour hole by rate from 47% to 66% in comparing with the smooth bed.