Portland Metro Levee System, Oregon, FONSI
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FINDING OF NO SIGNIFICANT IMPACT
Portland Metro Levee System Feasibility Study, Integrated Feasibility Report and
Environmental Assessment
Portland Oregon
The U.S. Army Corps of Engineers, Portland District (Corps) has conducted an environmental
analysis in accordance with the National Environmental Policy Act of 1969, as amended. The
Final Integrated Feasibility Report and Environmental Assessment (IFR/EA) dated June 2021
for the Portland Metro Levee System (PMLS) Feasibility Study (Study) addresses flood risk
reduction opportunities and feasibility in Multnomah County, Oregon, including areas within the
cities of Portland, Fairview, Gresham, and Troutdale. The final recommendation is contained in
the report of the Chief of Engineers, dated August 20, 2021.
The Final IFR/EA, incorporated herein by reference, evaluated various alternatives that would
improve levee performance, incorporate resilience and reduce flood risk in the study area. The
Recommended Plan (RP) is the National Economic Development (NED) Plan.
The RP seeks to address inconsistencies within the PMLS, which is comprised of four
integrated and contiguous levee systems: Peninsula Drainage District No. 1 (PEN 1), Peninsula
Drainage District No. 2 (PEN 2), Multnomah County Drainage District No. 1 (MCDD), and Sandy
Drainage Improvement Company (SDIC), in order to provide more uniform flood risk throughout
the study area. The RP focuses on both internal and external sources of flooding. Measures in
the RP include the following structural and non-structural measures. The measures in the RP
would:
• Widen the PEN 1 Columbia Slough levee and add seepage controls (toe drains). In
MCDD West, replace portions of the landward toe of the Peninsula Canal cross levee
and Columbia Slough levee with gravel to enhance stability. In SDIC, install a stability
berm for the Columbia River levee from the pump station to Sundial Road.
• Prepare information content that can be incorporated into existing local planning
framework to boost effectiveness of flood warnings and evacuation. Includes flood risk
information resulting from this feasibility study.
• Increase levee heights for portions of PEN 1 and PEN 2 levees along Columbia
mainstem and Columbia Slough. In MCDD West, fill isolated low spots in the Peninsula
Canal cross levee and Station 511+00 of the Columbia River levee (near Broughton
Beach Park). Raise low spots near the Troutdale outlet mall and the Columbia River
segment of SDIC.
• Add capacity at PEN 2 13th Avenue and MCDD Pump Station 2. Replace pumps,
associated intakes, discharge lines, and trash racks.
• Develop 4-season gravel maintenance road on railroad parallel levee and Peninsula
Canal cross levee between MCDD and PEN 2.
• Replace SDIC Sandy Pump Station at a higher elevation and install redundant power
sources within the system of pump stations.
• Replace Trash Rakes at MCDD Pump Station 4.
• Construct a parallel levee at the PEN 1 railroad embankment and new floodwall to
connect to existing PEN 1 floodwall.
• Develop flood risk education materials for the population at risk and visitors within the
study area.Portland Metro Levee System, Oregon, FONSI
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• Design and install flood hazard and evacuation route signage throughout the study area.
• Develop designated safe zones at high points within the PMLS for those that cannot
evacuate from the floodplain. Would be implemented in conjunction with Measure 6.
In addition to a “no action” plan, a total of four action alternatives were considered, and three
were evaluated in detail. Each alternative included both structural and non-structural flood risk
reduction measures. The alternatives included Alternatives 3, 4, and 5, each including
components of levee widening, seepage controls, increasing the I-5 floodwall, and addressing
pump station deficiencies, along with non-structural measures such as creating safe zones,
improving evacuation routes, and increasing education of flood risks. Alternative formulation is
discussed in Section 3 of the Final IFR/EA, and alternative evaluation and selection is
discussed in Sections 4 and 5 of the Final IFR/EA. Alternative 5 is the RP.
For all alternatives, the potential effects were evaluated, as appropriate. A summary
assessment of the potential effects of the RP are listed in Table 1: