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Lower Willamette River Environmental Dredging and Ecosystem Restoration Project, OR, 30 July 2015

Lower Willamette RiverABSTRACT:   The purpose of this project is to restore ecosystem structure and function within a highly urbanized area surrounding the Lower Willamette River.  This project will help to reestablish riparian and wetland plant communities; improve aquatic and riparian complexity and diversity; and restore floodplain function and connectivity.  The non-Federal sponsor is the City of Portland.

The Lower Willamette River is defined as the area downstream, and north, of Willamette Falls, which occurs at River Mile 26 in Oregon City, and continues downstream to its confluence with the Columbia River at River Mile 0.  The study area includes two key tributaries; Tryon Creek and Columbia Slough.  Most of the study area is within the city limits of Portland.

Historically, the Willamette River watershed in the Portland area was an extensive interconnected system of active channels, open slack waters, emergent wetlands, riparian forest, and adjacent upland forest.  The development and industrialization of the study area over the last 150 years has adversely affected natural riverine functions in the mainstem of the river, with altered hydrology, loss of habitat complexity, loss or degradation of off-channel habitats, reduction in nutrients and woody material, degraded water quality, and the creation of barriers to valuable fish rearing habitat within the Willamette River Tributaries.

The Willamette River is one of the largest tributaries to the Columbia River, and is the 10th largest river in the U.S. based on average annual flow.  The Willamette River was awarded the Thiess International River Prize in 2012 as a high profile watershed for restoration and was named an American Heritage River in 1998 (1 of 14).

The overall goal of this project is to improve aquatic habitat structure and function.  A fundamental component of meeting this goal is to reestablish, in measurable terms, the dynamic balance between the physical, chemical, and biological habitat components that formerly existed in the watershed.  Although the watershed has been modified extensively and it is unlikely that the habitat that once existed can be fully restored, the functions that arise from the interplay of the habitat components can be restored.  The objectives and actions that are proposed to achieve this goal are:  1. Reestablish Riparian and Wetland Plant Communities, 2. Increase Aquatic and Riparian Habitat Complexity and Diversity, and 3. Restore Floodplain Function and Connectivity.  The restored aquatic habitat would increase habitat for Endangered Species Act-Listed fish species; Chinook salmon, Coho salmon (Upper Columbia spring-run and Snake River spring/summer-run), steelhead, bull trout (Upper Columbia, Snake and Upper Willamette), North American green sturgeon, Pacific lamprey and coastal cutthroat trout.  Important wildlife linkages provided in this tidally influenced area are unique to the project area, providing wintering and breeding habitat for waterfowl, shorebirds, and neotropical migrants along the Pacific Flyway.

The recommended plan for this project is the National Environmental Restoration (NER) plan, and will restore approximately 74 acres of riparian, wetland, shallow water and backwater habitats, as well as 2.7 stream miles at five locations within the study area.  Based on October 2014 price levels, the total estimated project first cost of the recommended plan is $29.7 million and provides an increase of 1,430 in habitat units from 1,627 HUs under existing conditions to 3,057 HUs over the 50-year period of analysis.  The Federal share of the cost is $19.1 million and the non-Federal sponsors’ share is $10.6 million.  Minimal operations, maintenance, repair, rehabilitation, and replacement (OMRR&R) expenses are estimated to be $3,500 per year, which will be a non-Federal responsibility.

REPORT DOCUMENTATION:  Pertinent documentation on the project, the results of the Civil Works Review Board, and subsequent Washington-Level Review Actions are listed below (items not linked will be provided when available):

  • CWRB Agenda
  • Project Map/Placemat
  • Report Summary
  • CWRB Briefing Slides
  • CWRB Lessons Learned
  • CWRB Meeting Record
  • State & Agency Review Comment Letters
  • Documentation of Review Findings
  • Signed Chief of Engineers Report
  • Advance Copy to Congressional Committees
  • ASA(CW) Memo to OMB
  • OMB Response
  • ASA(CW) Transmittal to Congress
  • Signed Record of Decision
  • Authorization