Rochester Dropshafts Model Studies

The City of Rochester, New York, is developing the combined sewer overflow and abatement plan (CSOAP) to handle sanitary sewage and storm water. The West Side System contains 40 dropshafts with drop heights varying from 50 ft to 150 ft which are required to handle design discharges from about 150 to 900 cfs. The function of these dropshafts is to trans~ port the water from one elevation and energy level to a lower elevation and energy level. Conduits near the ground surface collect the water and convey it to an elbow which deflects the water 90 degrees into the vertical shaft. The vertical shaft which has a slotted divider wall separating the falling water-air mixture and the released air returning to the surface, terminates in a sump. The sump is a large excavated and lined chamber. The water falling through the elbow and vertical shaft entrains considerable air and gains kinetic energy. The purpose of the sump and deaeration chamber is to dissipate some of the energy, to remove and collect the entrained air, and to direct the water at a reduced velocity into the exit conduit.