AERATION PERFORMANCE OF TRIANGULAR PLANFORM LABYRINTH WEIRS

A high level of dissolved oxygen is vital for the maintenance of healt hy streams and rivers. Structures in rivers can increase dissolved oxy gen levels by creating turbulent conditions where small air bubbles ar e carried into the bulk of the flow. Plunging overfall jets from weirs are a particular instance of this, and the aeration properties of suc h structures have been studied widely in the laboratory and field over a number of years. On the other hand, labyrinth weirs, where the weir sill is cranked in planform thus increasing their length, have receiv ed little or no attention in this context. They have a proven hydrauli c advantage over straight weirs of increased discharge at the same hea d for design conditions. However, they also serve to modify the combin ed overfall jet as individual jets from adjacent sections of the weir collide. This paper describes an experimental investigation into the n ature of these jets and how they affect the aeration performance of a triangular plan labyrinth weir. It is demonstrated that the aeration e fficiency of these labyrinth weirs generally is better than their equi valent-length linear weir and that this advantage becomes more pronoun ced as the weir included angle becomes smaller and also at lower overf all drop heights and higher discharges. These results point to the pos sible advantage of these type of weir in situations where both hydraul ic and aeration performance needs to be optimized.