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Gabion weirs have been widely used in rivers restoration and diversion water projects because of their hydro-environmental aspects and eco-friendly features. In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. For gabion weirs, three different filling materials were tested. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. The results show that decreasing upstream slopes, from 90º to 26.5º, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios passing through all faces of the gabion weirs decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.

Flow over stepped weirs are characterized by their strong turbulent mixing which enhances the oxygen transfer and dissolved oxygen (DO). This paper investigates the aeration performance of stepped weirs, and in particular, the effects of installation of the labyrinths on the steps, various weir slopes, upstream DO concentrations and tailwater depths. 19 physical models of flat, stepped-labyrinth and pooled-stepped weirs with three different slopes (1:1, 1:2 and 1:3 V: H) were tested. For each configuration, the downstream concentration of DO was measured utilizing a wide range of upstream concentrations of DO. The results indicated that the DO ratio with the best configurations were the stepped-labyrinth weirs with slopes of 1:1 and 1:2; approximately 62% higher than that of the flat stepped weirs. However, the dissolved oxygen efficiency showed a 15% decrease in models with a slope of 1:3 compared to those with a slope of 1:1. In all cases, the results demonstrated that the dissolved oxygen efficiency decreased either by increasing the upstream DO concentration or by increasing the flow discharge. The results yielded new design criteria for flat and stepped-labyrinth weirs to attain maximum aeration performance. Finally, empirical correlations were proposed for predicting the DO over stepped-labyrinth weirs.