Design and hydraulics of a combined storm overflow structure

Storm overflow structures in combined sewers are used to separate sewage from storm water. For subcritical approach flow, sideweirs are currently used; however, they often behave hydraulically poor. This study was conducted to explore a combined storm overflow structure able to improve the hydraulic performance of sewer sideweirs. Such a structure consists of a low-crested sideweir and a bottom opening just downstream from the sideweir end. First, the hydraulic design procedure is described, and then, based on laboratory experiments and by using the governing flow equations, the main hydraulic features are highlighted. The results indicate that the proposed device has advantageous characteristics in terms of hydraulic efficiency, reliability, and maintenance.