Effect of stepped spillways on increasing dissolved oxygen in water, an experimental study.

In this study, different physical models of stepped spillways are constructed and the effect of intense water mixing on increasing the dissolved oxygen concentration in water is investigated. The minimum oxygen transfer efficiency ranged from 28% to 56%, which indicates the positive effects of stepped spillways. The results showed that with a stepped spillway, the oxygen transfer efficiency decreases with increasing discharge. As the discharge increases and all steps become submerged, the effect of the spillway steps on the turbulence and aeration of the flow decreases. At high unit discharges (more than 0.15 m/s), aeration efficiency increases with increasing spillway slope. However, for discharges less than 0.15 m/s, the effect of slope on aeration efficiency is negligible. This stepped spillway performance indicates that in the nappe regime, the effect of slope on the aeration efficiency is less than for the skimming regime. A number of nonlinear regression equations are presented to estimate aeration efficiency.