Introduction
The safety of dams is directly related to the sufficiency of weir capacity. Most of the failures of dams occur due to water passing over their crests, the most important factor of which is insufficient weir capacity. Non-linear weirs can increase the discharge coefficient for a certain width without increasing the water head compared to the traditional linear weirs (such as a Ogee weirs). The hydraulics of labyrinth weirs has been investigated for the first time by Gentling (1940). Dabbling et al. (2013) investigated Labyrinth weirs with different crest height (Stage). Majediasl, et al. (2024) compared the performance of laboratory and meta-model methods to predict the discharge coefficient of labyrinth weirs. Due to the fact that in most of the previous studies, the geometric parameters have been examined separately, therefore, the purpose of this research is to investigate the simultaneous change of the geometric parameters such as the angle of the weir wall (α), the height of the weir (P), the shape of the apex, and the shape of the crest. The weir, the slope of the entrance openings and the change of the shape of the apex into a semi-circle are on the hydraulic performance of Labyrinth weirs.
Methodology
The experiments of this research were carried out in a channel with a length of 13 meters, a width of 1.2 meters and a depth of 0.8 meters with a free flow system. Weirs were installed at a distance of 5 meters from the upstream of the canal, and by establishing a steady flow, hydraulic parameters were measured. In order to check the hydraulic efficiency of Labyrinth weirs, 9 physical models have been built and a total of (196) tests have been performed on them, in which three wall angles (α = 12, 20, and 35) degrees, the height of the weirs are 10 and 11.5 centimeters (15% increase), the number of cycles in all experiments is equal to four cycles, the width of the channel is W =120 cm, the width of each cycle is w = 30 cm, the length and diameter of the apex (in the form of half circle) 2 cm and the presence or absence of slope in their entrance and exit openings (the slope of the openings 1:1:5) was investigated.

Results and Discussion
The discharge coefficient of the Labyrinth weirs with the wall angle (α=12 o) is lower than the wall angle (α=20 o) and the discharge coefficient of this wall angle is also lower than the wall angle (α=35 o). The reason for this can be stated that by increasing the angle of the wall of the cycles, the angle of approach of the flow with the wall of the cycles becomes closer to the vertical state and these weirs act like linear weirs and as a result the flow rate coefficient It becomes more. In the Labyrinth weir (α=12 o) the slope of the entrance the inlet openings of the cycles (1:1.5), the discharge coefficient has increased due to the reduction of the drop in the input flow to the Labyrinth weirs. The discharge coefficient of the Labyrinth weir (α=12 o) in the water head ratio (Ht/p=0.2) has increased by about 7.5% and with the increase of the water head ratio, the efficiency of sloping the openings decreases. In these weirs, the change of the upstream apex to a semi-circular shape has not caused a change in the discharge coefficient, which can be explained by the small length of the apex (A=2cm). Also, increasing the height by 10% and changing the shape of the crest of this weir to a quarter-circle shape has slightly increased the discharge coefficient.
In the Labyrinth weir (α =35 o) the slope of the entrance of the cycles (1:1.5) and changing the upstream apex to a semi-circular shape, the discharge coefficient of the Labyrinth weirs (LW35) in all the water head ratio (Ht/p) has increased (about 8-10%). Also, increasing the height by 10% and changing the shape of the crest of this weir to a quarter-circle shape has significantly increased the discharge coefficient in the range (0.6>Ht/p>0.1).

Conclusion
The purpose of this research is to investigate the change of geometrical parameters such as the angle of the weir wall (α), the height of the weir (P), the shape of the apex, the form of the weir crest and the slope of the inlet openings on the hydraulic performance of the Labyrinth weirs. By reducing the angle of the wall, the efficiency of the cycle or the efficiency of the weirs increases, and the reason for this can be stated that by reducing the angle of the walls, the length of the weir increases, and on the other hand, the discharge of the weirs has a direct relationship with the length of the weir. As a result, the flow and efficiency of the weir increases, that is, the effect of increasing the length of the weir crest is greater than the discharge coefficient.