HomeMy WebLinkAboutPN_Floodwall Repair Narrative_170619_v1Project Narrative
The Cedar River levees and floodwalls are part of the Cedar River Section 205 Flood Hazard Reduction
Project (Cedar River 205 Project) constructed in cooperation with the United States Army Corps of
Engineers (USACE) with the City as the local sponsor. The levees are located on the lower 1.25 miles of
the Cedar River and extend from Williams Avenue North to the mouth of the Cedar River at Lake
Washington. The Cedar River 205 Project protects portions of downtown Renton, the Boeing 737 plant,
and the Renton Airport from the 100-year flood. The City is required to maintain the Cedar River 205
Project per the project cooperation agreement with the USACE that both parties entered into prior to
construction.
The joint sealants on the Cedar River floodwalls have significantly deteriorated since they were
constructed between 1999 and 2000. Recent inspection reports by the USACE have raised concern about
the deterioration of the joint sealants and requested that the City address this issue. The joint sealants
properly protect the waterstops that interlock with adjacent wall sections. The waterstops insure that
floodwater from the river cannot seep through the wall. As such, replacing the joint sealants on the
floodwalls is critical to preserve the structural integrity of the floodwall and ensure that it performs its
function of flood protection. Thus, primarily, this repair would enable to the City to remain compliant with
the terms of its agreement with the USACE which obligates the City to perform such periodic maintenance.
Maintenance is also needed to maintain eligibility to receive Federal Disaster Funds to repair the levees if
damaged in a flood under the USACE PL84-99 program.
Secondarily, proper maintenance is also a prerequisite for certifying the levees with FEMA. On July 10,
2012 USACE sent a letter to the City indicating that the levee certification letter would expire on August
31, 2013 because they would no longer be certifying levees and would not be providing the National Flood
Insurance Program levee system evaluation to FEMA. The Cedar River 205 Project levee system
certification to FEMA levee standards allows for FEMA accreditation of the levee system as providing 100-
year level of flood protection. Accreditation enables the properties protected by the levee system to
remain mapped as protected areas instead of being mapped in the FEMA 100-year floodplain, ensuring
that the protected properties would not need to conform to floodplain insurance and development
regulations. Tetra Tech, Inc. was contracted by the City in December 2015, to provide all necessary
engineering consultant services required to recertify the Cedar River 205 Project levees and floodwalls. A
levee certification report is expected to be completed and submitted to FEMA in Fall 2017. Replacing the
joint sealants is needed so that Tetra Tech would certify to FEMA based on their engineering computations
and judgement that the Cedar River Levees and Floodwalls provide a 100-year level of protection
Therefore, a shoreline exemption permit is requested for this project under the category of “normal
maintenance and repair of existing structure or development”.
The following is additional information about the proposed work:
Anticipated Dates of work: July-September 2017. Sealant will need to be replaced on top of the
wall and both the land and the river side.
The work will consist of hand tools. No construction equipment will be needed.
The contractor will need to remove some vegetation around the joints on the riverside in order
to perform the repair work in some locations
There will be no major excavation or filling activities except some minor digging to expose the
joint as needed. The digging would be performed with hand tools and would range from a few
inches to a foot maximum.
The contractor will be restoring the landscape and hand seeding the topsoil where affected
There are no other permits required
There are no hazardous areas, steep slopes or wetlands on the project site
The project area is a medium and heavy industrial employment area and the proposed work will
not alter the use of the area
Soil type in the area varies. Below the top surface (grass, concrete or asphalt), the soil consists
of a mix of sand and silt.
The total estimated cost of the vegetation clearing work is $140,000.
No trees will be removed or impacted
The nature of the existing shoreline is rip rap along the airport clear zone (downstream portion
of left bank) and a vegetation mix of grass, blackberries, and knotweeds elsewhere
The distance between the water surface and the work zone (i.e. the floodwall) will be
approximately 12 to 25 feet.
See Figure 1 for a photo of a joint along the floodwall.
Figure 1