On April 13, 2022, the commander of Portland District Corps of Engineers signed a Finding of No Significant Impact for Portland Metro Levee System Feasibility Study, Integrated Feasibility Report and Environmental Assessment. The Corps 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.
The reporting officers recommend authorization of the NED plan that reduces flood risks to the Portland, Ore., metro area. Based on the Fiscal Year (FY) 2021 price levels, a 2.5% discount rate and a 50-year period of analysis, the estimated cost of the plan is $110,490,000 with average annual benefits of $15,371,000; an average annual maintenance cost of $4,126,00; net benefits of $11,245,00 and a benefit-to-cost ratio of 3.7.
“We appreciate the work the Corps did to avoid and minimize potential environmental impacts while formulating strategies to make our eighty-year-old levee system more reliable, resilient, and ready to meet the demands of climate change,” -- Multnomah County Drainage District, (non-federal project sponsor).
The principal features of the plan include:
- A levee raise and other improvements to the levees in PEN 1 and PEN 2 to address both fragility and overtopping risks. The levee raises in PEN 2 along the Columbia River and Columbia Slough are embankment raises, with small stretches of new floodwall.
- A new floodwall along the Columbia River segment of PEN 1, including under the I-5 bridge.
- A new levee parallel to the existing railroad embankment on the western edge of PEN `1.
- Scour protection for the existing floodwall in PEN 1.
- Increased levee heights at locations with low spots in MCDD and SDIC.
- Improvements to pump stations including capacity increases at three locations, improved debris control at one location, and elevating/replacing the Sandy pump station.
- Compensatory mitigation for impacts to approximately 0.4 acres of freshwater wetlands.