128th Street Comprehensive Setback Levee Feasibility Study
Pierce County Planning and Public Works is conducting a feasibility study to reduce the flooding risk and impacts along both the right and left banks of the Puyallup River, near the 128th Street East bridge crossing. Though levees are present along both banks of the Puyallup River, this area experiences widespread flooding due to insufficient channel capacity and existing levee protection. Setback levee features can help to reduce risk from flooding to nearby property, infrastructure, and also improve fish and wildlife habitat.
The objective of this study is to learn how levee setbacks or other flood risk reduction measures would benefit the public, residents, and natural environment.
Throughout this study, Pierce County is committed to working with the community and nearby property owners to develop alternatives and prioritize potential future projects. To hear more about the project background and what we are working on, please watch the video below.
This project is funded through a combination of SWM funds, Flood Control District funds, and grants.
The 128th Street Comprehensive Levee Setback Feasibility Study will prioritize up to four setback levee projects to reduce flood risks to areas that have experienced repeated flooding. Of the four proposed levee setbacks, any one setback will likely influence all three of the others. Therefore, all the setbacks need to be evaluated concurrently.
Field crews have completed the data collection portion of the study. The technical team is now working on developing several hydraulic modeling scenarios which will be shared in the draft report anticipated in 2022.
Pierce County is consulting with Environmental Science Associates (ESA) for conducting research for this study. Findings will consider stakeholder feedback and community safety as well as potential benefits to agricultural operations and salmon habitat.
The project area is east of State Route 162, west of McCutcheon Road East, south of 112th Street East and north of 144th Street East and along both the right and left banks of the Puyallup River between river miles 15.7 and 17.5, bisected by the 128th Street East bridge crossing (and north of the City of Orting limits).
(Click the Image to Enlarge)
This area is divided into four quadrants: NE, NW, SE, and SW to help assess the unique existing conditions, flood risk reduction opportunities and problems in each. A proposed levee setback in one quadrant may influence flood risk reduction in all three of the others. Therefore, all the quadrants are being evaluated concurrently.
The Puyallup River is Evolving
Over time, rivers erode rocks, dirt, and other sediments and deposit them downstream. This is one of several factors that can cause rivers to change course and flow into new areas over time. The maps below show how the Puyallup River near the 128th Street East bridge crossing has changed its course over time. The Height Above Water Surface Map (shown to the right) shares more information about this. For example, the purple areas on the mapping indicate locations on the floodplains that are relatively lower than other areas, and the darker the purple color the lower the floodplain surface. The patterns that are evident in the mapping show old river meander locations and other depressions that can provide increased flood storage and more frequent seasonal habitat benefits if re-connected to the river.
The Historic Channel Occupation Tract Map (shown to the right) reflects how the dynamic Puyallup River has shifted its active channel over time. Starting in 1880, the US General Land Office did a survey to start tracking river meanders. Incorporating this with the historical aerial photos taken between 1931 and 1998, we start to see a picture of how much the Puyallup river systems has changed in the last 140 years.
This Historical Channel Occupation Tract map is produced using a compilation of active historical Puyallup River channel occupation location areas changing over time. With this ever evolving channel, it’s important to understand the changes in history so we can help protect for the future.
Puyallup River (and 128th ST E Bridge Crossing) 1931 Historical Aerial Photograph
As the river moves and changes, flooding can become more pronounced during times of heavy rainfall. This flooding can damage property and public infrastructure, impact travel and evacuation routes, and cause a loss of fish habitat. Moving existing levees back from the river’s edge and reconnecting floodplains provide increased storage for flood waters. This additional capacity helps to reduce flood risks to the public, residents and property, create more reliable access to roads, reduce flooding of structures and risk of damage to the levees, fields and farmland, and create more fish habitat and spawning areas.
From our work to date, we have analyzed existing flood conditions in the study area, identified opportunities to reduce flood risk, and are starting to develop conceptual alternatives.
The video below shows a flood event passing through the study area. This animation was generated from a hydraulic model simulation of the November 2006 flood event on the Puyallup River. The animation shows the pattern, timing, and the spatial extent of flooding for existing conditions during a major flood. The peak discharge in the Puyallup River for the simulated flood event is 40,300 cubic feet per second.
Please see the maps and details below to learn more about what we expect to see if no changes are made, as well as some opportunities that we would expect to see if setback levees or other project opportunities are implemented into the area. Each quadrant has Existing Conditions and Opportunities, and Maps. Click on each Map to review in detail.
Our next step in this work is to identify and develop several different conceptual alternatives or how we can manage levees in this area to best meet project goals and fully realize identified opportunities in this area. This work will likely involve balancing different needs for the project and it may involve some tradeoffs.
As we look ahead to developing alternatives, we want to make sure that we’re keeping important needs, and benefits, in mind. Part of our analysis of the alternatives we develop will be to evaluate and score each one using a set of benefit measures (which are general benefit categories at this point), and then determine whether or not the alternative strikes the appropriate balance between tradeoffs and opportunities.
We need your help with providing initial input about what benefit categories you value the most. The high-level elements that we have in mind as we start to examine feasibility study alternatives include:
- Flood risk reduction
- Habitat creation