Proposed actions at the McCutcheon Road and 128th Site include removal of existing levees and construction
of new levees farther back from the Puyallup River. Approximately 3,657 linear feet of existing levees and
revetments located along the right (east) bank of the Puyallup River between Puyallup RM 16.7 and 17.5
upstream from the McMillin Bridge would be removed and a new armored levee of approximately
4,913 linear feet would be set back from the Puyallup River to the east, encompassing an area of
approximately 1,861,335 square feet (42.7 acres). This project would reconnect the Puyallup River with a
large wetland, side-channel and spring complex located along the right bank of the river. This project would
also improve connectivity to an unnamed tributary flowing to the Puyallup River from the east.
The total probable area of inundation following levee setback was estimated to be 536,410 square feet
(12.3 acres). The project would be expected to add floodplain inundation area of 657,036 square feet
(15.1 acres) during 2-year events and, 1,039,461 square feet (23.9 acres) during 5-year events. This project
would not be expected to contribute significantly to flood storage during low frequency events with projected
storage volumes of only 576 acre-feet and 3,667 acre-feet during 25-year and 100-year events, respectively
(Table E-12).
The sediment transport capacity and storage capacity would be expected to improve both during high
frequency events (e.g. 5-year steady state flows) and during low frequency events (e.g. 25-year steady state
flows) if the levee is set back. The majority of the Site is located within an designated as having severe
channel migration potential (GeoEngineers 2003). The total area of the Site is 1,861,335 square feet
(42.7 acres), of which 1,276,132 square feet (29.3 acres and 69% of the Site) is located within an area
delineated as having severe (high) migration potential. The remaining 585,203 square-feet (13.4 acres and
31% of the Site) is located in an area delineated as having moderate channel migration potential.
The McCutcheon Road and 128th Site is presently used for residential purposes. The Site has significant
areas of open space with intact riparian trees, wetlands and side channels and springs associated with the
historic Puyallup River riparian zone. In addition, levee setbacks at this Site would enhance connectivity
between the Puyallup River and an unnamed tributary. The prevalence of riparian trees, tributary habitat,
remnant side channels wetlands and springs would support the natural recruitment of large woody debris and
formation of pools. These features would also be expected to enhance aquatic habitat diversity and use, but
were predicted to have little biological benefits. Models predicted minimal increases in productivity and
abundance for coho (O. kisutch) and Chinook salmon (O. tshawytscha).
Based on a HEC-RAS Model analysis of boundary shear stress for 5-year and 25-year recurrence intervals,
levee setbacks at the McCutcheon Road and 128th Site appear to pose minimal risk of changes in downstream
deposition of bed material or downstream erosion were predicted.
