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The City of Portland, Oregon

Portland Water Bureau

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Reservoir Management

Mt Tabor Reservoir Management sign

Reservoir 5 in June 2018. Reservoir 5 was not drained, cleaned and refilled this spring. The bright blue color is from naturally occurring, non-toxic algae. Water quality and quantity are being monitored over the summer and the reservoir will undergo annual maintenance this fall.

There have been many changes to the Portland Water Bureau operations at Mt Tabor in the past couple of years, particularly with the disconnection of the open reservoirs from the water system. 

When the reservoirs were in service as part of the potable water system, they were typically drained and cleaned twice per year – once in spring and once in Fall.  Before cleaning, most of the water in the reservoirs was delivered to customers and to other lower-elevation reservoirs to limit the volume drained to the Bureau of Environmental Services collection system. Now that the reservoirs are no longer in service, new protocols for maintaining water in the reservoirs must be devised.

In July 2015 the Portland City Council directed the Water Bureau to work with the Mt Tabor Neighborhood Association (MTNA) in managing the quantity and quality of water in the Mt Tabor open reservoirs.

Together the Water Bureau and MTNA are developing a maintenance plan for the reservoirs that ensures their cleaning and draining has negligible impact on water quality; provides annual water use monitoring at each feature; and minimizes water use, in accord with City Council requirements for managing water features.

Reservoir Cleaning Schedule

The reservoirs at Mt. Tabor are drained and cleaned to protect the quality of this non-potable water and conduct reservoir condition inspections. The cycle of draining, cleaning, and refilling takes several weeks. This work is weather dependent; if heavy rainfall is expected, the work will be postponed so as not to over burden the sewer system. If the work cannot be performed for other reasons, the water quality will be monitored and the maintenance plan will reflect needed modifications.



Reservoir 1

12 million gallons

Reservoir 1 is currently empty while   extensive preservation work is conducted on the walls, sidewalks and gutters.   A separate contract for basin repairs is under development and anticipated to   be bid in summer 2018.

Reservoir 5

50 million gallons

This reservoir was unable to be cleaned this spring due to   several factors including lack of the ability to drain it into the sewer   system on schedule, and a drier than usual spring.  If projected weather conditions change, the   Portland Water Bureau will assess whether rescheduling this work prior to the   fall is a viable option.

In the meantime, the appearance of the reservoir is not   the same as the fresh water in Reservoir 6. The color is caused by a   naturally occurring non-toxic algae. The bureau is adding water as the summer   moves on to protect the liner from sun damage and to mitigate the algae   growth.

Water quality and quantity monitoring is on-going until   the reservoir can be drained, cleaned and filled.

Reservoir 6

75 million gallons

Both cells of Reservoir 6 were   drained, cleaned, and underwent concrete wall and basin repairs between April and June.   They were filled by mid-June 2018.