Experimental investigation of dissolved oxygen efficiency in stepped-labyrinth 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.