International Conference on Rain Water Cistern Systems
USA - June 1982
6: Related Topics
Models for Storm Sewer Systems
University of Minnesota, USA
The traditional role of a sewer network has been primarily that of conveyance
of waste water and storm water. A common design criterion was to ensure an adequate
hydraulic capacity to convey a maximum design flow at a steady rate without surcharging
the sewer. The design objective and criterion of a sewer network have undergone
a fundamental change in recent years due to upgraded pollution control rules.
To meet these goals, it has become increasingly clear that a substantial saving
can be achieved by utilizing the in-line storage capacity of a sewer network.
Most existing sewer networks have enough capacity to store the entire runoff due
to a storm equal to or less than the one-year storm. The majority of storm runoffs
can thus be stored for future treatment if there are provisions for a suitable
control mechanism or some precautions against transient pressure.
A sewer network designed to store as well as convey storm water would undergo
changes in flow regimes following a large storm event. Typically, the flow would
initially be free surface flow and then begin to pressurize starting at the downstream
end of the sewer system. At this time there would be a combined flow regime consisting
of free surface flow and pressurized flow separated by one or more moving surge
fronts. The magnitude of such a surge may build up to a significant amount as
it moves upstream, and would generate severe water-hammer pressure upon collision
with an upstream boundary. Clearly, a steady state or a kinematic wave type model,
such as the SWMM model, is not suitable for a sewer network used as a storage-conveyance
system. A complete dynamic model capable of simulating unsteady mixed-flow is
This paper describes some experiences with two dynamic models: (1) the Priessmann-Cunge-Wagner
model and (2) the Song-Cardle-Leung model developed at the St. Anthony Falls Hydraulic
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