Aeration performance of triangular-notch weirs

Hydraulic structures have an impact on the concentration of dissolved oxyge n in a river system, even though the water is in contact with the structure for only a short period of time. The same oxygen transfer that would norma lly occur over several kilometres in a river can occur at a single hydrauli c structure, because the flow over a structure is typically highly turbulen t, resulting in increased interfacial renewal. Plunging overfall jets from weirs are a good example of this fact, and the aeration properties of such structures have been studied widely in the laboratory and field over a numb er of years. This technical note (a) describes triangular-notch weirs havin g a different weir angle a and how they affect aeration performance, and (b ) demonstrates that aeration efficiency decreases with increasing weir angl e.