MANAGING OUR LEVEES IN A POST KATRINA WORLD
After Hurricane Katrina in 2005, the Federal Emergency Management Agency (FEMA) and US Army Corps of Engineers (USACE) completely overhauled the federal safety standards for levees, including significantly increasing what’s required of local levee managers.
To prove that the local levee system meets federal standards, the Levee Ready Columbia partners funded the completion of the first ever comprehensive geotechnical assessment of the levee system. The full investigation took about five years and cost about $5 million to complete.
Although the investigation showed that the levees are in fairly good shape, the following problem areas were identified where the levee system does not currently meet minimum federal safety standards.
The railroad embankment, which is a railroad trestle that has been filled with non-compacted earth, makes up the western edge of the PEN 1 system. Although it functions as a part of the levee system, the embankment was not engineered to function perform as a levee. During the 1948 Vanport Flood, it was unable to hold back the floodwaters and ultimately collapsed under the pressure, flooding the City of Vanport and leading to breaches in three out of four of the adjacent districts. Seventy years later, this is still the area of most uncertainty within the system.
Although the embankment was originally constructed in 1907 for rail transport, it later came to be considered a part of the levee system. The embankment was rebuilt after the 1948 flood but was not constructed to the same standards as other sections of the levee. Instead, the railroad built a temporary trestle to restore service, which was later filled in with dredged material to complete the embankment. In 1972, PEN 1 reached an agreement with BNSF and Union Pacific – the railroad companies that own the embankment – allowing the drainage district to build a maintenance road and add some fill. At the same time, the Army Corps placed a sand blanket on the eastern slope to increase stability. These improvements, however, were not enough to qualify the embankment as a levee.
During the recent technical investigation, Levee Ready Columbia and the drainage districts attempted to reach an agreement with BNSF and Union Pacific to gain access to the site to assess the conditions of the embankment.
Unfortunately, LRC’s engineers were not granted access to the center section and the necessary analysis has not been completed. Historic documents and samples taken near the railroad property suggest that the embankment does not, meet stability and seepage standards and that significant improvements would need to be made to bring the embankment up to levee design standards.
A portion of Interstate 5 sits on an embankment that forms the cross-levee between PEN 1 and PEN 2. Two low spots have been identified under the I-5 interchange at Marine Drive, one that is too low by four inches and another that is low by 16 inches short of certification standards. Certification standards require levees to have three feet of freeboard above the 1% annual-chance-flood. -ACE Freeboard is the vertical distance between the expected elevation of a 100-year flood and the top of the levee. FEMA requires at least 3 feet between the flood elevation and the top of the levee to Freeboard provides a “factor of safety” to accommodate additional flood heights and wave wash. These low spots will need to be elevated to reach certification standards.
A note on cross levees:
Although some of the cross-levees align with the boundaries of the drainage districts, the cross-levees were never intended to be political boundaries. Instead, they were originally designed and constructed to create additional flood protection within the system. If one section of the system were to flood, the cross-levees create a barrier to reduce the risk of flooding in other sections of the system. While the cross-levees provide additional protection, no levee can ever completely eliminate the risk of flooding in historic floodplains. East-to-west, cross levees are found between SDIC and MCDD near NE 223rd Avenue; at NE 142nd Ave. dividing MCDD into two sections; near NE 33rd Ave. dividing MCDD and PEN 2; and along Denver Ave. and I-5 dividing PEN 2 and PEN 1.
A stretch of approximately 1,800 feet of the interchange on to the I-5 at Marine Drive is below the levee certification standards for FEMA. This area is highly constrained as it along an Interstate highway. Resolving this issue will likely require some combination of a levee raise and floodwall to address the low spot.
About 300 feet of the levee along Marine Drive in the northeast corner of PEN 2 – just to the west of NE 33rd Avenue and to the north of the Columbia Edgewater Country Club – ranges from 1 to 6 inches short of the required elevation.
Following a structure fire in this location, the site was cleared and graded to remove the foundation of the building, which caused these low spots that will need to be elevated to meet certification standards.
The Peninsula Drainage Canal levee between PEN 2 and MCDD is too narrow and the levee walls on the eastern bank are too steep. The level of water in the canal is too low, which can cause stability issues resulting in large amounts of erosion, which can ultimately cause failure. Additionally, the original PEN 2 levee on the western bank of the canal is unofficially decommissioned, which needs to be addressed.
This canal is designated as a Special Habitat Area by the Oregon Department of Fish & Wildlife as home to multiple protected species of turtles.
Previous high-water events have caused erosion and other sloughing on the waterward side of the Columbia Slough levee in MCDD. As a result, the levee no longer meets structural requirements for certification and may need to be repaired. The interior elevations may allow for minimal remediation to adequately reduce the risk of failure in this section.
A section of the primary levee along the Columbia River in MCDD has suffered erosion and damages caused by extensive animal burrowing, over-steepened slopes, and excessive vegetation that will need to be remediated to meet certification standards.
This location meets certification minimums as the landward side of the levee is robust, but the waterward side requires remediation to keep sections near Marine Drive from sloughing.
The “Gate Tower” structure along NE 223rd Avenue on the west side of the MCDD and SDIC cross levee is no longer functional. This facility operates a tide gate closure structure on dual 42-inch pipes that connects the two districts through the cross levee. In 2015, divers inspected the tide gate and found that it is partially blocked and inoperable. Additionally, the physical conditions of the tower structure is so unsafe, it can no longer be accessed by operations staff, meaning the valve structure cannot be operated.
Flow control and closure structures, like this one, are used throughout the system to provide interior drainage and control the flow of water inside the levee system. These structures can be used to both stop interior flooding from moving to other areas of the system or to relieve pressure building up in one section of the system by allowing some of the water to flow into the adjacent section. One reason the SDIC Pump Station wasn’t further inundated during the 2015 internal rain event was because the tide-gate controlled by the Gate Tower structure was already stuck open, allowing water to flow westward into MCDD.
About 500 linear feet of the levee along the east-bound I-84 on-ramp at Graham Road needs to be raised to meet standards for certification.
The projects listed above will need to be addressed to meet FEMA’s requirements for levee certification. Through our investigation, however, we also identified other parts of the system that will require modernization over time, including reshaping levee sections to meet current design guidelines. In addition to the structural issues with the levees, there are a number of issues related to the age, use, and conditions of many of the pumps, pump stations, pipes, and drains that convey water as a part of the overall system. The conveyance infrastructure plays a critical role in moving significant amounts of water out of the system during the winter, spring, and early summer months to help reduce the risk of flooding in the managed floodplain behind the levees.
Levee Ready Columbia is pursing both short- and long-term approached to recertify and modernize the levee system, including agreeing to continue to work together as a partnership through 2024. On top of this, the partners have pursued the designation of a US Army Corps New Start Feasibility Study, which is the only pathway we have been able to identify to secure federal investment in the levee system. More information about the US Army Corps of Engineers’ Feasibility Study is available here.
The partners are also working on reforming the way the levee system is managed to help modernize and maintain the system to higher standards and to be able to leverage opportunities to contribute to the environmental and recreational value in the managed floodplain. Get more information about LRC’s efforts to modernize the funding and management structures of the drainage districts responsible for operating and maintaining the levees here.