Tualatin Basin Water Supply Location Map



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Sustaining our economy, watershed, and community.

Project Description
A coalition of local governments formed the Tualatin Basin Water Supply Project Partnership over a decade ago to develop a basin-wide, integrated water resource management project to diversify the region’s water supply; help ensure we are able to respond to anticipated climate change; and meet the 50-year water supply needs for:


  • Water quality and critical habitat improvements in the Tualatin River and its tributaries
  • Cities, industry and economic development
  • Agriculture

The Water Supply Partners have been working closely with the Bureau of Reclamation, which owns Scoggins Dam, to study the expansion of Hagg Lake to meet future needs for water. Nearly a decade of analysis has produced a wealth of technical information about Hagg Lake and Scoggins Dam, as well as options for moving forward.

Major Milestones

  • 2002 – 2004 Water Supply Feasibility Study identifies a range of water supply options and recommends alternatives for further study
  • 2005 – 2008 Alternatives for Draft Planning Report/Environmental Impact Statement (PR/EIS) include 40-foot raise of Scoggins Dame and multiple source option including a 25-foot dam raise and expansion of the Willamette River water treatment plant for municipal uses
  • 2008 – 2009 New science about the Cascadia Subduction Zone off Oregon’s coast showed that a major earthquake could occur in the region of a magnitude 9 or greater for several minutes. Reclamation initiates a Safety of Dams study of Scoggins Dam (SOD) to assess its risks and determines that the dam would need to be strengthened to withstand such an earthquake. Water Supply partners commission a Dam Raise Appraisal Study to identify options for addressing the seisimic issues including a new downstream dam
  • 2010 – 2012 Reclamation proceeds with a Corrective Action Study of Scoggins Dam to identify options for repairing the dam and costs for the repairs. The Partners are working closely with Reclamation to integrate the Water Supply Project with federal government's SOD assessment to ensure safe, secure and reliable water for the region.
  • 2012 - 2013 Some water providers explore other options for meeting long-term water needs in the basin due to the uncertainty about Scoggins Dam.