Mount Tabor Reservoir 6 Structural Repairs

The Portland Water Bureau completed repairs on Mount Tabor Reservoir 6. Work included 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 was removed, one drain line was repaired, the voids were filled, and concrete was poured to seal the liner. 

The reservoir was refilled one cell at a time to help identify the location of any potential leaks. Reservoir 6 is now refilled and will continue to be monitored. 

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. Once the extent of the voids was determined, we began planning cost-effective repairs. 

In October 2021, an investigation by the Water Bureau Dam Safety Group showed that there were voids underneath portions of the reservoir. Photos showed that earth underneath the reservoir was washed away, leaving a gap and nothing to support the concrete.

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. 

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. 

Yes. Ongoing monitoring of Reservoir 1 water levels identified possible leaks. In 2018, Reservoir 1 was surveyed, and repairs were made to the voids and cracked concrete basin liner as necessary.

Reservoir 5 has a liner that prevents water from seeping through the concrete and eroding the ground underneath. In Fall 2022 after noticing increases in the water loss rates the reservoir was drained to allow inspection of the liner. The liner was inspected, and tears were found in several locations. The reservoir remained empty until the repairs were made, and the reservoir was refilled in April 2023.

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.