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Unidirectional Flushing Program
For decades, Portsmouth has used a
conventional citywide flushing program to maintain water
quality. Conducted every spring, conventional flushing consists
of opening hydrants in a specified neighborhood to flush out
accumulated rust and sediment. While effective, this type of
flushing does not increase the speed of water flow through the
pipes enough to dislodge stubborn deposits.
Using new computer mapping technology, the Department of Public
Utilities is developing a new unidirectional flushing program.
Unidirectional flushing consists of closing approximate water
system valves to create one way flow in a neighborhood water
pipe loop and then opening hydrants in a set sequential manner.
This increases the speed of the water flow in the pipes to six
feet per second or higher. These high velocities produce a
scouring action in the pipes, removing even the most stubborn
deposits. This program is a good tool for use in Portsmouth,
with its large inventory of older rusty pipes.
Unidirectional flushing uses up to 40% less water than
conventional flushing, and allows for a better response to
localized water quality complaints. Because of better sediment
removal, the effects of unidirectional flushing last much
longer. Additionally, unidirectional flushing will test almost
all of the water system valves and hydrants, identifying those
in need of repair or replacement.