The master’s thesis is addressed to the area of the physical hydraulic modeling. Physical hydraulic models, or scale models, are inevitably influenced by the so called scale effects due to disturbed ratios of forces acting on the prototype and the model. These ratios are expressed by the nondimensional numbers. General laws of mechanical similarity are presented. Theoretical bases of the weir flow are also presented. Scale effects were analyzed in the case of the three geometrical similar weirs, made in 1:26, 1:50 and 1:100 scales. The measurements of pressures on the weir surfaces and longitudinal water surface courses have shown the measurement uncertainty is greater than their differences. The discharge coefficient was evaluated by the means of measurements and the equation, which takes into account the essential parameters of the scale effects. It has been shown that a higher relative impact of the scale effects is due to viscosity while surface tension is mostly negligible as it was detected only in the smallest model in the 1:100 scale.