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 along a 26 mile long
tunnel. The function of these dropshafts is to transport the water from
one elevation and energy level to a lower elevation and energy level. At
several locations along the tunnel it is proposed to construct surge shafts
to attenuate surge pressures in the system. To minimize construction
disturbances at the surface, reduce the amount of boring and excavation,
and consequently reduce the construction costs, the surge shafts have been
combined with conventional dropshafts. These combined surge and dropshaft
structures would have dual functions of conveying water from the ground
surface to the underground tunnels and relieving surge pressures in the
Conduits at the ground surface collect the water and convey it to a
quarter cylinder elbow which deflects the water 90 degrees into a verticalrectangular
shaft. The vertical shaft is located inside and at the
upstream side of the surge shaft. One wall of the vertical shaft is
slotted to provide for air re-entrainment and also pressure relief in the
dropshaft. The surge shaft is a large excavated and lined cylinder which
extends from the tunnel level to the ground surface. A boot is attached to
the surge shaft just below the dropshaft. Attached to the downstream side
of the surge shaft is a deaeration chamber containing a slotted weir, false
crown with air slots, and a bellmouth entrance to the exit conduit. An air
vent is provided along the downstream side of the surge shaft.
The water falling through the elbow and vertical shaft entrains considerable
air while gaining kinetic energy. The falling water-air mixture
impinges on the floor of the surge shaft. The boot, surge shaft, and
deaeration chamber dissipate some of the energy, remove and collect the
entrained air, and direct the water at a reduced velocity into the exit
conduit. Some of the entrained air is released in the surge shaft and
rises directly to the surface. The remaining air rises to the false crown
in the deaeration chamber, passes through the air slots into the chamber
above, and returns to the upper part of the surge tank through a vent
shaft. Part of this return air is then recirculated via the dropshaft air
slots and air ramps. A definition sketch (Chart 1) indicates the various
Dahlin, Warren Q.; Wetzel, Joseph M..
Rochester Combined Surge And Dropshaft Model Studies.
St. Anthony Falls Laboratory.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.