DESCRIPTION
Proposed actions at the 116th Reconnection Site include removal of existing levees and construction of new
levees farther back from the Puyallup River. Approximately 4,933 linear feet of existing levee and
revetments located along the left (west) bank of the Puyallup River between Puyallup RM 15.7 and 16.7
would be removed and a new armored levee of approximately 6,910 linear feet would be set back from the
Puyallup River to the west, encompassing an area of approximately 4,539,440 square feet (104 acres). The
project would reconnect the Puyallup River with riparian vegetation, wetlands and ponds.
The total probable area of inundation following levee setback was estimated to be 2,111,168 square feet
(48.5 acres). The project would be expected to add floodplain inundation area of approximately 2,678,118
square feet (61.5 acres) during 2-year events and approximately 3,860,546 square feet (88.6 acres) during 5-
year events. This project would contribute modestly to flood storage during low frequency events with
projected storage volumes of 6,809 acre-feet and 21,343 acre-feet during 25-year and 100-year events,
respectively.
The sediment transport capacity and storage capacity would be expected to improve during both high
frequency (e.g. 5-year steady state flows) and low frequency events (e.g. 25-year steady state flows), if this
project is constructed. This is consistent with findings that a majority of the Site would be located within an
area delineated as having severe or high channel migration potential in the Puyallup River watershed
(GeoEngineers 2003). The total area of the Site is 4,539,440 square feet (104 acres), of which 3,569,076
square feet (81.9 acres and 79% of the Site) is located within an area delineated as having severe migration
potential. An additional 874,573 square-feet (20.1 acres and 19 % of the Site) is located within an area
delineated as having moderate channel migration potential (Figure E-10 and Table E-10).
The 116th Reconnection Site is presently used for a combination of residential, agricultural, and open-space
purposes. The Site has significant areas of open space with intact riparian trees and vegetation associated
wetlands and pond habitat. The prevalence of riparian trees 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 only moderate benefits. Models predicted minimal increases in
productivity and abundance for coho salmon (O. kisutch) but greater increases for Chinook salmon (O.
tshawytscha).
Based on a HEC-RAS Model analysis of boundary shear stress during 5-year and 25-year recurrence
intervals, levee setbacks at the 116th Reconnection Site are estimated to pose minimal risks of changes in
downstream deposition of bed material or downstream erosion were predicted.
