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Why is Mount Tabor Reservoir 6 Under Construction?

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Crews excavating Reservoir 6 at Mount Tabor
Mount Tabor Reservoir 6 is under construction to repair structural issues.

Construction update: 

Reservoir six is undergoing repairs 

The Portland Water Bureau started construction on Reservoir 6 in winter 2023–2024.

  • Construction is scheduled to be completed in spring 2024. 
  • Planned repairs include removing small sections of the concrete liner in three locations, removing loose material around the voids, repairing a drain line, filling the voids, and pouring concrete to seal the liner. 
  • Once the concrete work is complete, and allowed to cure, the reservoir will be refilled. 
  • This timeline is subject to change based on weather conditions and construction logistics. 

Community impacts 

If you visit the area during construction, you may see and hear crews and equipment working. The Portland Water Bureau crews are doing everything they can to minimize the impact to park visitors while they work to repair the reservoir.  

Page last updated April 16, 2024.

Project Timeline 

2021 

The Water Bureau Dam Safety Group’s investigation showed that there were voids underneath portions of the reservoir. 

Initial photo of a void underneath Reservoir 6 

Underneath the reservoir is a small space with rocks and dirt.
​​​​​​This photo, taken in October 2021, shows one of the larger voids underneath Reservoir 6. Ideally, there would not be any space between the concrete underside of the reservoir and the ground beneath it. The concrete of the reservoir is visible at the top of each photo. The earth below the concrete has been washed away, leaving a gap and nothing to support the concrete.

2022 

A consultant completed a GPR scan of the floor and sloping walls of Reservoir 6. Analysis determined that none of the detected voids would contribute to the failure of the reservoir, but they will require ongoing monitoring and maintenance to avoid cracking and leaking of the liner. Three voids need to be repaired before Reservoir 6 can be refilled and will require ongoing monitoring and maintenance. 

2023–24 

We are currently working to complete the necessary repairs. Planned repairs include removing small sections of the concrete liner in three locations, two in the south cell and one in the north cell. Loose material around the voids will be removed, one drain line will be repaired, the voids will be filled, and concrete will be poured to seal the liner. Once the concrete is cured, the reservoir can be refilled. 

Frequently asked questions 

When will Reservoir 6 be filled? 

The Water Bureau started construction on Reservoir 6 in winter 2023–2024. Construction is expected to conclude in spring 2024. Once the concrete rests the appropriate amount of time, the reservoir will be refilled. 

Who pays for maintenance and repairs?  

Unlike the reservoirs at Washington Park, the Mount Tabor reservoirs are no longer connected to the water system. Therefore, the cost for maintenance and repairs must come out of the City’s budget rather than the funds the Water Bureau collects from ratepayers. 

Is the dam impacted by the voids?   

The hill that can be seen on the western edge of Reservoir 6 along SE 60th Avenue is an earthen dam. This dam supports the sides of the reservoir and helps hold the water in place. Before the extent of the voids were known, there was concern that water leaking from the reservoir could potentially cause more soil erosion and destabilize the dam. 

Updated analysis in the winter of 2022–23 found that none of the detected voids would contribute to failure of the dam. Ongoing additional monitoring and maintenance of the voids will be needed to prevent cracking and leaking of the reservoir's liner. 

Were Reservoir 1 and 5 inspected too?  

Yes. In 2018, Reservoir 1 was surveyed using the same GPR technology and repairs were made to the voids as necessary. The repairs at Reservoir 1 were much less extensive than those needed at Reservoir 6 because Reservoir 1 is smaller. 

Reservoir 5 has a liner that prevents water from seeping through the concrete and eroding the ground underneath, so the likelihood of voids beneath it is significantly lower. 

How does the city manage Mount Tabor reservoirs? 

City Council passed Resolution 37146 in 2015, establishing City’s responsibility for preservation activities at the Mount Tabor Reservoirs and setting aside funding for that work. Since then, the Water Bureau and a committee of partners have completed several preservation tasks and planned for more, all of which are outlined on our Reservoir Construction Projects page. The Water Bureau also conducts regular maintenance and cleaning of the reservoirs, which is outlined on our Reservoirs Management page. 

Where can I learn more? 

Water Bureau staff meets with representatives from the Mount Tabor Neighborhood Association and Friends of Mount Tabor for periodic check-ins related to reservoir management and restoration. Updates will be communicated through those organizations and will also be posted to this webpage.