HomeMy WebLinkAboutC_ConcreteWallClarification_200724_v1.pdf
July 24, 2020
Matt Herrera, AICP
City of Renton
Community & Economic Development
1055 South Grady Road
Renton, WA 98057
Re: Cedar River Apartments (LUA19-000161): Concrete Wall Clarification
The Watershed Company Reference Number: 170314
Dear Matt:
This letter relates to portions of your December 4, 2019 “On-Hold” Notice letter (City
Letter) for the Cedar River Apartments project (LUA19-000161) and is intended to clarify
and supplement information submitted thus far regarding the on-site concrete wall that
parallels the Cedar River. It will also provide additional detail related to project
compliance with applicable City of Renton regulations.
City Comments
The City Letter included multiple comments related to aspects of the on-site concrete
wall. Comment #5 reads as follows:
Disconnected Migration Area - In part, for consideration for a Disconnected Migration
Area for the area identified as a Channel Migration Zone on the subject property
requires “legally existing artificial channel constraints that limit channel movement.”
According to the technical memorandum prepared by Golder Associates (pgs. 8 and
9), the shoreline stabilization on the subject property was constructed sometime
between 1985 and 2002. Please provide documentation the shoreline stabilization is
legally existing by providing local, state, and federal approval for its construction.
Additionally, Comment #13 reads as follows:
Third Party Geotechnical Review – Please provide responses, corrections, and
requested analysis from the enclosed GeoEngineers third party review of the
project’s documents related to the bulkhead along the Cedar River.
Cedar River Apartments
Concrete Wall Clarification
July 24, 2020
Page 2
The cross-referenced GeoEngineers review letter (GE Letter) spelled out the protocol for
designating the project site as a Disconnected Migration Area (DMA), including
demonstration that the existing concrete wall was constructed consistent with current
design standards and that a prepared hydraulic analysis determines that scour potential
at the site won’t destabilize the wall.
Prior Submitted Documentation
In addition to multiple geotechnical and engineering documents prepared for the project
(by Terracon Consultants, Inc. and DCI Engineers), Golder Associates, Inc. previously
prepared a technical memorandum related to the on-site concrete wall (Review of
Shoreline Stabilization Alternatives for the Cedar River Apartments Project, in Renton, WA,
October 30, 2018) (Golder Report). The Golder Report was submitted to the City as part
of the initial application package and was intended to address project compliance with
Renton Municipal Code (RMC) 4-3-090.F.4.a.iii. This specific regulatory provision
requires a demonstration that shoreline stabilization can only be utilized when more
natural or nonstructural methods are not feasible. In addition to addressing compliance
with this provision, the Golder Report also included cursory information regarding the
history of the on-site wall as well as information related to the mapped channel
migration zone. This letter will further clarify the historical status of the wall and will
provide additional context regarding the presence of a channel migration zone at the
site.
Clarifications
Proposed Project
No new shoreline stabilization measures are proposed for the Cedar River Apartments.
The project includes retention of the existing concrete wall adjacent to the Cedar River.
The upper portion of one area of the wall will be removed; otherwise the wall will be
retained in its existing condition. Further, aside from partial removal in the one area, no
repairs, modifications, or expansions of the wall are proposed.
Site History
As described within the Golder Report, the project site has included shoreline
stabilization along the Cedar River for many decades. However, additional analysis and
research has been conducted to further clarify the origin and history of stabilization at
the site. The Golder Report included several aerial photos of the site. The 1961 oblique
photo (see Figure 1 of this letter) shows a linear and hardened shoreline along the river’s
edge. The photo pre-dates the State’s Shoreline Management Act (1971) and documents
the presence of legally established stabilization at the site. A second photo, , from 1977
and taken at more of an overhead angle (see Figure 2 of this letter), shows a similar
hardened shoreline.
Cedar River Apartments
Concrete Wall Clarification
July 24, 2020
Page 3
Two separate permits from 1976, one from the City of Renton and one from the WA
Dept. of Fisheries, authorized repairs to the hardened shoreline. Both permits are
attached to this letter. These permits further demonstrate that the wall was legally
established.
Figure 1. 1961 aerial view of the subject site.
Cedar River Apartments
Concrete Wall Clarification
July 24, 2020
Page 4
Figure 2. 1977 aerial view of the subject site.
Channel Migration Zone
The project site is located within a mapped channel migration zone (CMZ). City review
Comments #5 and #13, as shown above, both presume a request for a conversion from
CMZ to DMA. Accordingly, the City has requested a demonstration that the existing
wall was legally established and that it was constructed consistent with current design
and construction standards. These requests appear to stem from King County guidance
pertaining to CMZ to DMA conversions.
To clarify, the applicant has not requested that the project site be removed from the
CMZ through a conversion to DMA. The reason that no such request has been made
relates to City of Renton code requirements. Specifically, no portion of the code requires
a conversion from CMZ to DMA; nor does the code specifically prohibit development
within a CMZ. As such, the current proposal includes development within the CMZ,
subject to the protection provided by the existing wall.
Rather than prohibiting development within a CMZ, the City’s code strives to protect
development within a CMZ by ensuring that adequate stabilization measures are
present (and otherwise prohibiting new stabilization). As required under RMC 4-3-
090(F)4.c.iii., (“Changes in Land Use”), the applicant initially submitted reports from
Terracon and Golder establishing a demonstrated need to protect principal uses and
structures from erosion, as required under F.4.c.iii.(a), as well as an evaluation of the
existing shoreline stabilization structure on the site (the wall) in relation to the hierarchy
Cedar River Apartments
Concrete Wall Clarification
July 24, 2020
Page 5
of alternatives established in subsection RMC 4-3-090(F)4.a.iii, as required under RMC 4-
3-090(F)4.c.iii.(b). Under that hierarchy of alternatives, stabilization measures are to
ensure that, where feasible, the softest measures are undertaken. Additionally, RMC 4-3-
090(E)9.d stipulates that an analysis be undertaken to demonstrate that new stabilization
will not be necessary to support the project during the life of the development. The
Terracon and Golder reports establish the need to protect the proposed development
from erosion and that the existing wall is the most appropriate shoreline stabilization
measure under the hierarchy of alternatives.
The City subsequently requested in a letter dated April 2, 2019 an analysis of the
integrity of the wall and whether it can withstand the river’s flow “over the life of the
project.” Accordingly, additional reports from Terracon and DCI Engineers were
submitted to address this request and the standard set forth in RMC 4-3-090(E)9.d.
In light of the above clarifications, the portion of Comment #13 (GE Letter) referencing
King County guidance (from the Cedar River Channel Migration Study) and WAC
regulations for developing shoreline master programs, related to legally established
artificial structures and DMAs is not applicable to continuation of the existing wall. That
is, the King County and WAC guidance is not binding, as the City of Renton code does
not include similar language, nor does it stipulate compliance with such guidance. Thus,
the entire purpose of the third party geotechnical review – stated on Page 2 of the GE
Letter as “…to determine if the analyses required to establish if the existing concrete
bulkhead is likely to restrain channel migration have been performed with current
relevant design standards” – is not applicable. As described above, the applicant is
required to demonstrate that new shoreline stabilization is unlikely to be necessary to
support intended development during the life of the development.
Supplemental Studies
The applicant has commissioned several additional studies to further demonstrate that
new shoreline stabilization is unlikely to be necessary during the life of the
development, including the following:
• Cedar River Apartments Scour Analysis Technical Report. March 31, 2020; Revised
July 10, 2020. The Watershed Company. (Scour Report)
• Bulkhead Wall Stability Addendum No. 2, Cedar River Apartments. May 21, 2020.
Terracon Consultants, Inc. (Stability Addendum No. 2)
• Bulkhead Wall Stability – Response Letter Addendum No. 3, Cedar River Apartments.
July 24, 2020. Terracon Consultants, Inc. (Stability Addendum No. 3)
• Channel Migration Risk Assessment Memo. April 8, 2020. The Watershed Company.
(CMZ Memo)
Cedar River Apartments
Concrete Wall Clarification
July 24, 2020
Page 6
The Scour Report concluded that the on-site wall has remained structurally sound and
stable during its life, withstanding the effects of river scour and erosion for a wide range
of river conditions and flooding events. If a potential wall failure were to occur,
Terracon (within Stability Addendum No. 3) concludes that the extent of a potential
failure would not extend beyond the 100 ft setback of the development. Therefore, the
proposed development, which would be situated a minimum distance of 100 feet from
the wall, would not be at risk of impact from any type of wall failure. Further, the CMZ
Memo concluded that there is no channel migration hazard present on the site. Thus, in
compliance with RMC 4-3-909(E)9.d, the applicant has demonstrated that new shoreline
stabilization is unlikely to be necessary at the site to support intended development for
the life of the development.
Thank you for your attention to this matter. Please call if you have any questions or if
we can provide you with any additional information.
Sincerely,
Kenny Booth, AICP
Senior Planner / Principal