Investigation of flow characteristics in gabion stepped weirs

Abstract

Weirs are widely used to control and regulate the flow in open channels. In gabion structures, the flow conditions are more complex due to the complexity of flow through the porous body of a gabion. The present study aims to investigate the water surface profile, the overflow velocity profile, and both the through-flow and overflow ratios. Six physical models of the three downstream slopes (V:H 1:1, 1:2, and 1:3) and two types of rockfill (crushed stone and rounded gravel) were investigated. Results show that for the same discharge, the milder slope model (1:3) shows higher water surface and higher velocity than the steeper slope (1:1) with about 9 and 8% on average respectively. The water surface was 60% higher on the lower steps than on the upper steps at the nappe flow regime. Moreover, the low porosity models show a slightly higher velocity and flow depth than higher porosity models for all sections. Furthermore, increasing the porosity from 0.38 to 0.42 led to about a 27% increment in the through-flow ratio. Finally, four relationships were developed to estimate the through-flow and overflow ratios at the upstream and inner sections of the gabion weir. The suggested relationships can be considered novel relationships.

Investigation of the Effect of Downstream Slope and Rockfill Materials on Flow Regimes over Gabion Stepped Weirs

“…The determination of the onset of regimes usually depends on visual interpretation. Table 3 shows the criteria utilized in this study to determine the flow regimes [11].…”

“…In a gabion weir, the flow can pass through its body in addition to the overflow of the weir [6]. Therefore, there is an additional flow regime, which is known as a through-flow regime [11]. The throughflow has a high impact on the energy dissipation over the gabion weirs.…”

“…This change occurs gradually and continuously. In the transition flow, the regime can begin as a nappe regime on the upper steps, becoming a skimming regime on the lower steps [11]. The nappe flow regime can be classified into three types: the nappe flow with a complete hydraulic jump at a small discharge, the nappe flow with a partial hydraulic jump, and the nappe flow without a hydraulic jump.…”