In the present research, an experimental set up was arranged to investigate the scale effects in the free efflux below the sluice gate of variable openings and also to study the turbulence structure in the generated submerged hydraulic jump below the silled gate. The objective of the present study research was is to analyze the collected experimental data on the effect of constructing a sill under a sluice gate on the free and submerged flow bellow it. Also, this paper presents the results of a laser Doppler Anemometry (LDA) study of submerged hydraulic jumps in a horizontal rectangular channel with the different submergence factor S and different inlet Froude number Fr1. Measurements include surface profiles , mean velocity components of ū andV– ;turbulence intensities ú and v' and turbulence shear stress, ú vꞌ Major flow characteristics of submerged hydraulic jumps were discussed and analyzed , The flow in the fully developed region is found to have some degree of similarity . It was also found that a submerged jump was three dimensional in nature. The maximum vertical velocity in the recirculating zone for all submerged jumps is about 7% of U1. Also, the results show that the maximum streamwise velocity near the center plane was smaller than that near the side wall . The turbulence shear stress near the center is about 46% higher than that near the side wall. After the jump the flow will recover into a two dimensional flow. The coefficient of discharge becames smaller at constant opening ratio Y1/h1. The results showed that there was a close relationship between the scale effects in the contraction coefficients and in the discharge coefficients. The energy dissipation in effluxes was also related to the scale effect in the discharge coefficients closely. The scale effects in the contraction coefficient and in the coefficients of energy loss which are the main factors composing the discharge coefficients showed the same trend as in the discharge coefficient.