Rochester Control Structure 46 Siphon Riser Structure Model Studies

Abstract

The City of Rochester, New York, is developing the Combined Sewer Overflow Abatement Program (CSOAP) to handle sanitary sewage and storm water. The system includes many conventional dropshafts which transport the water collected in surface conduits to the storage and conveyance tunnels at a lower elevation beneath the ground surface. At several locations where surge shafts are near conventional dropshafts the two structures are combined. These combined surge and dropshaft structures have a dual purpose of conveying water from the ground level to the underground tunnels and relieving surge pressures in the system. Located throughout the system are control structures to regulate and divert the flow as required. One of these structures is designated as control structure 46 (CS46). The structure is to be located near the Van Lare treatment plant at the end of the three-mile long siphon tunnel. This is also the downstream terminus of the 22 mile tunnel system. The. primary purpose of the structure is to raise flows coming in through the siphon tunnel and direct them to. a distribution structure at the head of the Van Lare treatment plant. The configuration of the structure in this siphon mode is intended to maximize the transport of sediment entering through the siphon tunnel, up the siphon riser, and through the bifurcation structure. Since it will be difficult to remove all the sediment in the siphon mode, the structure will be operated in the flushing mode. In this mode, supercritical flows will pass straight through the structure and enter a tunnel to the Cross:Irondequoit pumping station. The effectiveness of the structure in transporting sediment is one of the major concerns in the operation of CS46.