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Portland Water Bureau

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Water Levels in Reservoir 1 to Rise and Fall this Spring

By Teresa Black

Water levels in Reservoir 1 at Mt. Tabor Park will fluctuate this spring and early summer as the Portland Water Bureau conducts maintenance and repair work to the water distribution system.

Park users will see Reservoir 1 empty for almost all of March while it undergoes its semi-annual cleaning, maintenance, and repair work. Draining of Reservoir 1 began Friday February 27.

Additionally, the bureau is also conducting scheduled maintenance work in East Portland over the next few months that will impact water levels in Reservoir 1 in Mt. Tabor Park.

That work consists of installing new valves and controls in three vaults. These vaults house the pipes, valves, and controls that make up the ‘intertie’—a system which permits the passage of water from each of the three large conduits to the water distribution system itself. Work can only be performed on one vault at a time, as the water conduit must be shut down to conduct the work. As water from the conduits flow directly to Mt. Tabor Reservoir 1, it will be impacted by the vault work.

When the water conduit is shut down, the water from the large conduits must be drained. Reservoir 1 will serve as the ‘holding tank’ for this water, where it will then be drained to the combined sewer system. Once the repair work is done for each conduit, they will then be disinfected and that water will be flushed once again to Reservoir 1, before it is drained into the combined sewer system.

For almost all of March, the last two weeks of April, and the last two weeks of May, the reservoir will be emptied and filled in order to flush each of the three conduits after the valve and control work is done. Each conduit flushing cycle will take about two weeks. Water quality or service to local residents will not be affected by the maintenance work.

Flow schematic

Work can only be performed on one conduit at a time. Once the shut-off valve is engaged, the water in the isolated part of the pipe (purple pipe) must be drained into the reservoir, where it will be drained into the sewer system. The amount of water drained can be approximately 2-3 million gallons.

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