Portland, OR

Willamette Water Supply Program

Tualatin Valley Water District & The City of Hillsboro


The Willamette Water Supply Program (WWSP) is a drinking water infrastructure program that provides the Tualatin Valley Water District, the City of Hillsboro, and the City of Beaverton with a seismically resilient water supply to meet future demands and will provide redundancy in case of an emergency event. The WWSP includes more than 30 miles (48 km) of transmission pipelines ranging from 48 to 66 inches (1,220 – 1,675 mm) in diameter from the Willamette River Water Treatment Plant in Wilsonville, north to Hillsboro and Beaverton, Oregon. 

The WWSP also includes construction of finished water storage tanks (terminal storage) and seismically improving the existing raw water intake, including fish screen replacements at the existing intake facility and a new water treatment plant.

Fast Facts
  • Over 30 miles (48 km) of transmission pipelines
  • Transmission pipeline diameters ranging from 48 to 66 inches (1,220–1,675 mm)
  • Large conveyance pipeline assessment
  • Seismic resilient pipeline design

Scope of Work

Delve Underground developed a seismic mitigation strategy and led the development of the seismic design guidelines. During the design phase, we continue to provide geotechnical services, trenchless design services, and seismic engineering services involving geotechnical explorations, trenchless crossing tunnel and shaft designs, seismic hazards evaluation and modeling, seismic soil-pipe interaction modeling, and seismic resilient pipe designs. 

Overall, Delve Underground performed hundreds of geotechnical explorations (including borings, cone penetration tests, geo-probes, and rock coring), conducted FLAC and ABUQUS numerical modeling, and designed more than 20 trenchless crossings, including a 2,000-foot-long (610 m), 84-inch-diameter (2,135 mm) microtunnel crossing under the Tualatin River. 

Challenges & Innovations

During the development of the seismic analysis, Delve Underground engineers worked with nationwide seismic experts and coauthored the technical content to define guidelines for the WWSP. The purpose of the guidelines was to consolidate the current state of practice in seismic design into a design framework used by multiple design teams to apply a consistent and defensible seismic design approach that ensures the WWSP’s seismic resiliency goals are achieved across the entire system. 

Delve Underground also streamlined the numerical analysis process for seismic ground deformation and soil-pipe interaction modeling. The results are a more effective and efficient seismic resilience design.