The hydraulic performance of rectangular labyrinth weirs has been investigated by many researchers, however, the effects of the corner shape on the hydraulic performance of rectangular labyrinth weirs have not been addressed in the current literature. Accordingly, this experimental study aims to explore the effect of the corner shape of on discharge efficiency of rectangular labyrinth weirs. Five flat-crested rectangular labyrinth weirs, with five different corner shapes, were made of High-Density Polyethylene Plastic (HDPE) and tested in a rectangular flume. Under different overflow discharges, the discharge coefficients for the rectangular labyrinth weirs were determined. The results showed that the shape of corners for rectangular labyrinth weirs was an effective factor. For example, rounding or beveling the corners can significantly increase the discharge capacity of the rectangular labyrinth weirs. However, the rounded corner shape was slightly better than the beveled corner shape. Among all labyrinth weir models tested in this study, the rectangular labyrinth weir with a semi-circular apex showed the highest hydraulic efficiency, while the one with an acute-angle corner shape showed the lowest hydraulic efficiency. For the rectangular labyrinth weir having a semi-circular shape, although the original effective length reduced by about 14%, the discharge coefficient, CL, increased by 16.7% on average. For the rectangular labyrinth weir that has an acute-angle corner shape, although the effective length (LC) of the weir increased by 23%, its discharge capacity decreased by 35.2% on average. Accordingly, improper folding of the side-walls of the rectangular labyrinth weir led to a significant reduction in the weir’s hydraulic performance.

The top and downstream face of the embankment dams must be protected from overtopping damages happen due to extreme floods. This can be achieved by providing one of the overtopping protection systems. The most common overtopping protection systems are those which have stepped fashion. This type of protection systems consists of a series of continues steps mostly made of concrete. In this study, the effects of the transverse slope of steps on flow properties over the overtopping protection systems were explored experimentally. Steps with transverse slopes are those which have inclinations from one spillway wall towards the other spillway wall in a zigzag way. To achieve the goals of the study, three physical models, stepped spillways, were made of wood and tested in a prismatic flume. The width, depth, and length of the wooden models were 0.6 m, 0.96 m and 1.92 m respectively. Sixteen steps (with three different transverse slopes ranging from zero to 5.7°) were cut into the surface of the models from the crest to the toe. The models were then tested under various flow rates ranging from 0.003 to 0.05 m³/s. The results showed that the models with steps having transverse slope had higher energy dissipation capability compared to the model with steps having zero transverse slopes (flat steps); up to 14% higher. In addition, for the models with steps having the transverse slope, the onset of the skimming flow occurred at higher ratios of critical depth (y_c) to step height (h); greater than 1.37. However, the distances of the inception points from the first step brink (inception point locations) were reduced by half, on average, for the model with steps having a transverse slope of 5.7°.

The hydraulic performance of round-cornered rectangular labyrinth weirs with varying weir heights and effective lengths has not been explored in the existing literature to the authors’ knowledge. The purpose of this experimental study was to see how the height and effective length of round-cornered rectangular labyrinth weirs affect their discharge efficiency. Nine flat-crested rectangular labyrinth weirs made of high-density polyethylene (HDPE) were tested in a rectangular flume under various discharges to fulfill the goals of this study. The discharge coefficients for the weirs were then calculated. The hydraulic efficiency of weirs with round corners increases as the weir height (P) increases, according to the findings; however, with effective length of the weir to channel width ratios (L_C/B) ≤ 1.78, the effect of the weir height diminishes. For the H_T/P ranges used in this study, 0.1 ≤ H_T/P ≤ 0.65, the round-cornered rectangular labyrinth weirs with higher L_C/B ratios (greater M values) showed improved hydraulic efficiency. Furthermore, the effects of the round-cornered rectangular labyrinth weirs’ headwater inflation can be mitigated by increasing the effective length of the weirs;by increasing M values (L_C/B ratios). Using multiple linear regression analysis, a satisfactory correlation equation was found between discharge coefficients of round-cornered rectangular labyrinth weirs, C_B, and the other parameters, L_C, P, and h.