Public Utilities
"High Speed" Flushing
Maintains Water Quality

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. Portsmouth is in the forefront in applying this new program.

Unidirectional flushing consists of closing appropriate 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 6 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.

Because of better sediment removal, the benefits of unidirectional flushing last much longer, use up to 40% less water than conventional flushing and allows a better response to localized water quality complaints. Additionally, unidirectional flushing will test almost all of the water systems valves and hydrants, identifying those in need of repair or replacement.

The unidirectional flushing program has been designed for a third of Portsmouth's water distribution system. The remainder will be designed by the end of 1998. The program will be implemented beginning in 1999.

Flushing is the single most powerful tool available
to maintain quality in a water distribution system!