Experimental studies on air entrainment and oxygen content downstream of sharp-crested weirs

The concentration of dissolved oxygen (DO) is an important indicator of water quality because aquatic life survives on the DO in water. A free overfall jet from a weir plunging into downstream water causes entrainment of air bubbles if the free overfall jet velocity exceeds a certain critical value and hence aeration occurs. This paper investigates the free overfall jets from sharp‐crested weirs and their effect on air entrainment and aeration efficiency. The results indicate that the air entrainment and aeration efficiency of triangular sharp‐crested weirs are significantly better than those for the other sharp‐crested weir types. Therefore, the triangular sharp‐crested weirs can be used as highly effective aerators in streams, rivers, constructed channels, fish hatcheries, water treatment plants, etc. Regression equations were obtained for the triangular sharp‐crested weirs relating air entrainment rate and aeration efficiency to drop height, discharge and angle in the triangular sharp‐crested weir. There was good agreement between the measured values and the values computed from the predictive equations.