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Comprehensive Levee Setback Feasibility Study
About the Study
The 2021 Comprehensive Levee Setback Feasibility Study Update (Study) continues Pierce County’s efforts over the last two decades to remove or modify levee structures that have been linked to floods and habitat impacts. The Study helps the County identify, design and implement projects that benefit both human and aquatic communities.
Environmental Science Associates (ESA) has prepared the 2021 Study to support the ongoing development of the 2023 Pierce County Comprehensive Flood Hazard Management Plan (CFHMP) and associated Capital Improvement Plan by providing a complete catalog of potential levee setback sites.
This Study provides an updated assessment of a larger suite of project locations — both including and in addition to — for the 32 project locations evaluated in the 2008 and 2014 studies.
Pierce County identified additional sites to be considered for this study with consultation from stakeholders, including the Puyallup Tribe of Indians, the Muckleshoot Indian Tribe, salmon enhancement groups, and local municipalities.
Since the 2014 update, 27 new sites, spanning a wide range of locations within the watershed, have been added to the potential catalog of levee setback locations.
Three of the original 32 sites are not considered in this study because they have already been completed. As such, the total number of sites evaluated in this 2021 study is 56. Table 2 on page 3 identifies the status of each site, both new and old, dating back to the 2008 study.
Background
To date, nine levee setback projects have been completed in the Puyallup, Carbon, and White River watersheds.
Previous studies in 2008 and 2014 evaluated and prioritized levee setback project sites within the Puyallup, Carbon, and White River watersheds, with the objective of identifying opportunities to set back existing levees to recover lost floodplain storage, channel process, and aquatic habitat.
The 2008 Levee Setback Feasibility Analysis developed a strategy for prioritizing 32 sites in the greater Puyallup River watershed.
In 2014, the County completed the Flood Plain Reconnection Feasibility Study as a follow-up to the original site evaluations.
Whereas the 2008 study evaluated the feasibility and benefits of levee setbacks primarily as a flood hazard mitigation strategy, the 2014 update incorporated criteria related to fish habitat and also to value the benefit of “clustered” projects.
The 2014 study modified the site rankings based on the updated criteria. It also recommended future revisions to project boundaries and identified new setback sites with the intent of restoring a more continuous river corridor to the maximum extent possible.