Development of a compact air-regulated siphon for use in storm sewage overflows.

An air regulated siphon has been developed to operate as a storm water overflow. One of the main requirements has been that a siphon of compact design can accommodate high discharges for relatively small increases in upstream level thereby preventing the possibility of surcharges in the sewer upstream of the overflow.The s-shaped siphon was chosen for development as it has, by virtue of its natural shape, an efficient priming system. The downstream leg of the s-shaped siphon is returned beneath the crest so that a vertical wall of water formed shortly after first spill thereby effecting a seal which ensures priming.A sectional perspex model was used to determine the effects of inlet lip length, inlet lip elevation, tailwater level, siphon width, upstream channel width, vortices at inlet and revised outlet configurations.Results were compared using a dimensionless plot of the ratio of priming head and throat depth (hi/d) against co-efficient of discharge (CD). The curves obtained for all the differenct configurations are useful as design aids for the design of a compact air regulated siphon for use in storm sewage overflows.