Built to Last: A Resilient Water System

With recent studies predicting a major earthquake occurring in the Pacific Northwest sometime within the next 50 years, the Partnership took steps to ensure the survivability of its drinking water system. By requiring each of the new water supply facilities to be designed and constructed to remain functional after a 9.0 magnitude earthquake, we have improved our odds of bouncing back quickly from a significant seismic event. Here are several design features that will help keep water flowing soon after an earthquake:

• All facilities are designed to seismic standards above current codes.
• The reinforced concrete river intake pump station on the Clackamas River is anchored to basalt bedrock with 14 ground anchors. It also features retractable fish screens to protect against river debris, as well as a fully redundant electrical supply from Portland General Electric (PGE), which keeps power flowing if the primary supply is out.
• Critical treatment facilities and pipelines at the water treatment plant are supported by 1,110 deep reinforced concrete piles to keep them in place during shaking (shown in featured image). This facility also features a fully redundant electrical supply from PGE.
• The large-diameter water pipelines are made from steel with each joint double welded for added strength (shown below). This design is based on the performance of similar large pipelines that survived earthquakes in Japan.
• The 3.5 million gallon Waluga Reservoir 2 utilizes seismic cable connections between tank walls as well as a foundation specially designed to move without cracking or leaking. Pre-stressed concrete was also used to increase resiliency as well as seismically-activated closure valves on inlet and outlet pipes, which protect against tank emptying should connecting pipes be damaged.
• The Bonita pump station is also designed to be resilient against large seismic events, featuring discharge pumps with their own foundations and flexible couplings. These design features allow the pumps to move independently from the building during an earthquake. In addition, the building utilizes reinforced masonry shear walls that prevent crumbling.

After an earthquake, Lake Oswego and Tigard’s water supply system will be in much better shape than most in the region because of the newer, robust ‘backbone’ infrastructure that supplies and distributes water. With these new features, businesses and residents in Lake Oswego and Tigard are protected by one of the most resilient water supply systems in Oregon.