Progress at Skagit PUD – Moving Towards Seismic Resiliency

Construction of Murraysmith’s largest reservoir in Washington, a 6.0 million-gallon (MG) AWWA D110, Type I, prestressed concrete tank is well underway!

Skagit PUD’s new reservoir replaces an existing 1.0 MG steel reservoir that lacked the storage capacity to serve the 10,000 customers within the PUD’s 322 Pressure Zone.  The larger volume of the new reservoir provides for current needs and has the capacity to serve the future build-out population.

This type of concrete reservoir is designed to survive a large earthquake, as anticipated in the Pacific Northwest. The reservoir structure allows for flexibility, while always maintaining compression of the concrete walls to prevent cracking during a seismic event.  Flexible wall-to-footing and wall-to-roof joints allow movement during ground shaking. Seismic cables between the wall and footing provide the needed restraint to keep the reservoir in place. The walls are prestressed with 154, 1-1/4-inch diameter vertical tendons and wrapped with 46 miles of 3/8-inch diameter galvanized strand pulled at 15,000 pounds to keep the concrete in constant compression.

Murraysmith has designed 20 prestressed concrete reservoirs in the Pacific Northwest since 1996, which includes 16 in the last 10 years. Murraysmith is proud to serve our public agency clients by designing resilient and reliable water systems for our local communities.