<p>Nonlinear weirs at low water loads have a relatively high discharge capacity. Since the weir performance is reduced in terms of the interference of the flow blades at high water loads; therefore, in the present study, the study was based on piano keys and labyrinth weirs with and without stepped sidewalls. This study investigates the effect of stepped sidewalls (with 3 heights) on weir inlet immersion. For this purpose, 6 models of stepped side walls were employed on two models of labyrinth and piano key weirs with trapezoidal cross-sections. The results suggested that raising the height of the stepped sidewall reduces the discharge coefficient in the labyrinth weirs and piano key weirs (P.K.W) up to 50% and 39% of the control model (tested step-free weirs). The performance of stepped sidewalls in labyrinth weir is up to 22% higher than their performance in piano key weirs. In control models, the flow discharge coefficient (Cd) of the piano switch weir is 30% lower than the labyrinth weir. The highest discharge coefficient occurred in the labyrinth weir at Fr = 0.94 and in piano key weir at Fr = 0.83. Finally, the statistical relationships to estimate the discharge coefficient in the two weir models were presented.</p>