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Un-Steady Sewer Networks

September 12, 2013

Rainfall is usually a highly dynamic event, with numerous variations,
and various patterns of intensity, timing, and duration.
In order to really understand what happens in the underground pipes
the entire “natural event” from beginning to end needs scrutiny.

Storm water runoff can be grouped as :
a.) Open channel , free surface , gravity flow
b.) Pressurized conduit , surcharged flow , aka backups
c.) A transition between open channel and pressurized conditions

A sewer system is a network of manholes or junctions
connected by sewer pipes and usually considered
a dendritic type network (tree like -stems, branches,trunks)

Flow in a sewer pipe has three regions;
the entrance, the pipe flow, and then the exit.
Sometimes the entrance of a pipe may be wide open,
other times the entrance may be partially submerged,
or even complete submerged, trapping air in the pipe.
Flow can be controlled on the downstream side
or at some upstream point.

Pipe Conditions

Pipe Conditions

There is NOTHING simple about water flow in a pipe.
Turbulence, friction, etc., etc. complicate it immensely.
Efficiently moving large amounts of water
in a short amount of time,
is a true engineering headache,
of monumental proportions.
Fluid mechanics and dynamics are extremely challenging
courses at the university level and simply can’t be
covered with a few diagrams.

Community planning from the 1950’s and 1960’s
simply doesn’t compare to what is being proposed now
to compensate for the inadequacies back then.
It costs BIG BIG MONEY to get something that works well
and provides the infrastructure for the future.

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