Investigation of flow regimes and energy dissipation in gabion stepped weirs

Weirs are hydraulic structures generally used in open channels to regulate and control flow. Gabion weirs are considered an economical alternative to use in areas where rock-fill materials are available Energy dissipation in weirs and spillways is critical as uncontrolled dissipation can cause damage to hydraulic structures and the downstream channel. The investigation of the flow regime is an important aspect in the design of stepped weir due to its effect on the rate of energy dissipation. The aim of this study was to investigate the effect of downstream slope (of the stepped weir) and rock fill materials on flow regimes and energy dissipation in gabion stepped weirs. For this purpose, eight physical models of gabion weirs with slopes of 1:0.5,1:1,1:2, and 1:3(V:H) and two types of rock fill materials were tested over a range of discharges. The number of steps used was four for all experiments with step height of 100 mm (scale 1:10). The rock fill material was crushed stone of nominal size (37.5 mm-13.2 mm) D 50 = 23 mm, and rounded gravel of nominal size (26.5 mm-13.2 mm) D 50 = 16 mm. Results showed that the effect of downstream slope on flow regime is significant at medium discharge, and less at low and high discharges. Moreover, it was found that the downstream slope has a significant effect on energy dissipation, increasing as the downstream slope decreased especially at the transition and skimming flow regimes.