AERATION PERFORMANCE OF SHARP CRESTED WEIR

Abstract

The level of dissolved oxygen (DO) in water is crucial for assessing its quality, as it directly impacts the survival of aquatic organisms. When water flows over a weir and plunges downstream, it can trap air bubbles if the velocity of the flow surpasses a critical threshold, leading to aeration. This study examines how this phenomenon, known as free overfall jets, occurs with sharp-crested weirs and its impact on air entrainment and aeration effectiveness. The findings reveal that triangular sharp-crested weirs outperform other types significantly in terms of air entrainment and aeration efficiency. Consequently, they can serve as highly efficient aerators in various water bodies like streams, rivers, man-made channels, fish farms, and water treatment facilities. The study also establishes regression equations for triangular sharp-crested weirs, connecting air entrainment rate and aeration efficiency to factors such as drop height, discharge, and weir angle. The measured values align well with those predicted by the equations, indicating their reliability. Dimensionless correlation equations have been developed and some success has been achieved in determining the modelling laws governing the oxygen transfer in an air entrainment situation. Modelling according to the Froude law of similarity has shown that the oxygen transfer expressed as a deficit ratio varied as a simplified function of the scale. For the first time, the laboratory measurements of oxygen transfer due to a free falling jet entering a free water recipient have been successfully correlated with data received for a • number of prototype dam and weir structures.