Ces 5.1 Crew Evaluation System.rarl
Celena Holtzberg
The Draft Integrated Feasibility Report and Environmental Assessment is posted below in the Related Documents and Resources section. *This document is large and may take a moment to fully load.*
The U.S. Army Corps of Engineers has initiated a Feasibility Study focusing on Flood Risk Management of the Portland Metro Levee System in partnership with the Columbia Corridor Drainage Districts (CCDD) Joint Contracting Authority. CCDD consists of four drainage districts: Peninsula Drainage District #1, Peninsula Drainage District #2, Multnomah County Drainage District and the Sandy Drainage Improvement Company. The study area includes 27 miles of levees along the lower Columbia River within the Portland Metropolitan Area, running from Sauvie Island to the Sandy River.
The levee system is experiencing significant signs of structural vulnerabilities during high water, including sloughing, boils, and seepage. The three-year federal feasibility study process will lead to a recommendation to Congress for federal investment in addressing the problem areas in the Portland metropolitan area levee and drainage system.
The study will focus on developing an integrated plan to address potential system failures, meeting current levee safety standards, and identifying potential impacts from future changes including system consolidation, changing water flow conditions and potential operational changes to the Columbia River System.
The Non-Federal Sponsor on the project is the Multnomah County Drainage District (MCDD), which has been granted decision authority to act on behalf of the four drainage districts. The feasibility study is authorized in Section 216 of the Flood Control Act of 1970.
The U.S. Army Corps of Engineers, in partnership with Levee Ready Columbia, has been hosting ongoing informational meetings on the Portland Metro Levee System feasibility study. The events are open to the public and provide updates on the feasibility study including refinement of alternatives, technical information and analysis conducted to date, and the next steps in the feasibility study process. Past public meetings occurred in August, October and December of 2019. The presentations shown at those meetings are posted below in the Related Documents and Resources section.
Public input is critical to the development of this feasibility plan. The Corps wants to hear the concerns and ideas of community members regarding the Columbia River corridor levee system and managed floodplain. The draft report is posted below in the Related Documents and Resources section.
Past public engagement: The Corps and MCDD held two scoping meetings in December 2018 to engage community members in discussing the study process, study milestones, and the development of preliminary alternative strategies for the reduction of flood risk in the Portland metropolitan area. Discussion also focused on modernization of the levees, flows and flood risk, geotechnical studies of the levees, and the economic risk and consequences posed by various flooding scenarios, as well as the effects on natural and cultural resources of alternatives considered.
Flood risk is made up of a variety of factors, beyond exclusively the condition of the levees themselves. These factors include: the hazard, system performance, exposure, vulnerability, and consequences.
Q: How much community support do you need to move forward?
A: Community involvement and input is critical in helping to identify areas of concern related to various proposals and to evaluate tradeoffs. Overall, reducing flood risk in the region is important to the community, local landowners, and the private and public sector. With this support, the study has progressed to the final phase of completion and making a recommendation for Congressional Authorization. The opinions and support of the community are very important to your Drainage District Board Members. The Drainage District Board Members will need to make the decisions about endorsing the preferred plan in the Feasibility Study and ultimately committing to the cost sharing requirements.
Q: What level of protection (e.g., 500-yr) is currently and planned to be provided?
A: The final estimates of flooding probability will be included in the feasibility report. After improvements are made, the probability of flooding is projected to be about five times less likely than the existing condition. Currently, the system has greater than a 1% (1 in 100) chance of failing in any given year. The proposed improvements reduce the chance of flooding to less than 1 in 500.
Q: What role did the recent Amazon warehouse construction have on this process?
A: The increased impervious area resulting from the Amazon warehouse development was included in the pump station assessment. The addition of paved areas increases demand on the pump station, since less rainwater is able to infiltrate into the ground and instead moves downstream to the pump station. The Amazon warehouse is also accounted for in the inventory of buildings and structures in the system, which affects the economic benefits of the project.
Q: Can you specify details regarding the remaining HTRW site? location? type of contamination?
A: Details on the remaining hazardous, toxic, and radioactive waste (HTRW) site will be included in the final feasibility study report. A more detailed investigation, including soil samples, will be conducted in a later phase, subject to federal authorization. This information will be given to the local sponsors for their use. As stated during the presentation, the alignment has been refined to avoid known or potential areas of contamination and this sampling will reduce uncertainty at this site.
Q: How about green infrastructure approaches?
A: The focus of this study is on the existing flood risk system and infrastructure already in place to reduce risks to lives and properties protected by the levee system. Non-structural measures were considered throughout the alternatives development process and are included in the preferred Alternative 5.
Local sponsor perspective:
The drainage districts recognize that interior drainage and stormwater attenuation can greatly benefit from green infrastructure, including on-site swales, meandering stream channels, and similar designs. This infrastructure improvements may be incorporated as a part of the capital program of the Urban Flood Safety & Water Quality District (UFSWQD). Improvements to return the watershed to a more natural hydrology (slowing the speed at which water reaches our pumps) is important to the function of the internal conveyance system, but such changes require a comprehensive watershed plan and are out of the scope of the Feasibility Study.
Q: Remind us how does the 38 feet height compare to Vanport flood? 1996 flood?
A: At the I-5 bridge, the 1996 flood reached an elevation of approximately 32.5 feet NAVD88*, and the 1948 Vanport flood reached an elevation of approximately 36.3 feet NAVD88*. While it would take a large flood to generate river levels higher than 38 feet, the consequences of levee failure are very high and justify the levee improvement. For context, the 1894 flood crested at 39.7 feet NAVD88, though this was before upstream reservoirs had been constructed. *NAVD88 is a vertical datum that provides a common reference point for height measurements. Elevations in NAVD88 are 5.3 ft higher than elevations in the Vancouver Gauge datum, which is the datum that the average river user commonly references.
Q: We have a longitudinal section of elevations along Bridgeton Road but no idea of the current height on the unpaved levee west of the road - in the NW corner of Pen2 in front of condos and apartments. What is current height along that section?
A: Existing top of levee elevations in the northwest corner of PEN 2 near the condos, apartments, and hotels range from around 37 feet NAVD88 to 38.5 feet NAVD88. As noted in the PowerPoint presentation, the levee would be raised up to a foot in this area. The elevations in this area do not reflect the elevation of the levee for the remainder of PEN 2. In order to provide a consistent height, the levee will need to be raised by different amounts in other locations.
Q: How many trees are scheduled for removal at the railroad embankment?
A: The exact tree count has not yet been surveyed but the impact will be considerably less than previously anticipated based on the concept in the Draft Feasibility Report (Jan 2020) due to reduction in the levee footprint. Vegetation, including trees, removed during construction will be replaced. Additional information on vegetation will be included in the Final Report.
Q: Is the Pen 1 railroad embankment where the Vanport flood breached?
A: Yes, the PEN 1 railroad embankment is where the 1948 Vanport floodwaters first breached. The railroad embankment was never designed to perform as a levee, and there is low confidence it would withstand another flood as large as Vanport. During the Vanport flood, subsequent breaches occurred at the southern section of the Denver Avenue cross-levee between PEN 1 and PEN 2 and the MCDD levee near the MCDD Headquarters.
Q: Are the closure structures hydraulic or manual?
A: The closure structures in the Portland Metro Levee System are manual, and no automated equipment is proposed. High water conditions can be forecasted well in advance of a flood, so there is adequate time to dispatch crews to erect the closure structures.
Q: Will you be working with property owners on size of closure structures to access their property?
A: Yes, the Corps and the Drainage Districts will reach out to property owners affected by new closure structures when more detailed designs of the closure structures are available, which will occur in a later phase of design.