Reversing Direction of Flow in Water Main
Reversing Direction of Flow in Water Main
(OP)
We are planning a water project in an urban setting. We will be taking a section of a large water main out of service. The temporary water service will result in the direction of flow in some streets being reversed. What are the risks? How can this be assessed in advance? What can be done to reduce the risk?





RE: Reversing Direction of Flow in Water Main
RE: Reversing Direction of Flow in Water Main
Assuming a strongly looped and well sized distribution system with relatively low head losses, it is very possible that the flow in the pipes you are concerned about already reverses during emergency conditions (i.e. fire flows) and maybe even during normal operation.
Water systems are typically modeled for extreme conditions to establish an envelope of operation. But, what happens in the middle of the envelope? It is likely that flows sometimes reverse in the loops as demands continuously vary.
For modeling purposes, demands are usually assumed to be consistent by type, location, and time, but in reality demands continuously vary. While assumed consistency suffices for global modeling, it is not actually the case on a connection by connection basis or a neighborhood by neighborhood basis. For example, I can guarantee that your water use pattern and rate is as unique as your next-door neighbor's, and this applies system-wide. A neighborhood with lots of school-age children and working adults will probably show a much stronger morning peak than a neighborhood full of retired people. These little nuances can add up to temporary reversal of flow in a looped pipe from the normal direction. Only the dead ends are guaranteed to have one direction of flow.
Fred
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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill
RE: Reversing Direction of Flow in Water Main
Check the pipe velocities of the current layout and compare the velocities to the proposed layout. If the velocities are similar, you don't have much to worry about. You will typically flush out the water mains after you make the connections and chlorinate.