Why was this section of the river selected for these modifications/improvements?
This area is being studied further because the County’s Comprehensive Flood Hazard Management Plan identified problems at the 128th Street Bridge on the west and east sides of river (SW and SE quadrants). This is being addressed at multiple areas along the river.
What stage is the study in now?
We are currently drafting the report and plan to share the draft alternatives and seek community feedback summer 2022.
Why can’t the river be dredged?
Pierce County recently completed a 10-year study looking at the feasibility of removing sediment from the Puyallup River with the intent to reduce flooding. The results can be found in a summary report. Because of the results of that study, dredging or removing sediment from the river channel will not be considered in this study.
What is the new engineering or technology in the design of levees?
New technology for flood reduction and floodplain reconnection projects include newer and more advanced practices for hydraulic modeling. This includes one- and two-dimensional modeling that analyzes flow depth, velocity, depth, and hydraulic forces that are highly dynamic and variable.
Geomorphic or land changing processes are also important to analyze and understand in riverine systems to understand the movement, formation, and interaction of sediment transport. No existing model can actually replicate natural riverine processes and dynamics, however new modeling technologies and methods have greatly helped to increase understanding of highly dynamic riverine systems like the ones we see in the Puyallup River.
What kind of levees would be considered for the Puyallup River? Will new ones be different, if so, what is that difference?
It is essential to design flood reduction measures and features that are ‘fish friendly’ and most beneficial for fish and their habitat, especially for the threatened species listed in the Endangered Species Act. Listed species include chinook salmon and steelhead. This is especially important in order to obtain permits from the resource permitting agencies at the federal, state and local levels. Adverse impacts to fish and their habitat from proposed flood reduction measures and features must be mitigated accordingly, which is part of the permitting review and approval process.
New levees typically incorporate wood and other natural elements which is often required by permitting agencies. When these new levee design elements are incorporated properly, levees are quite resistant to riverine forces and help to address and mitigate for fish habitat impacts. Levees that are mostly comprised of rock rip-rap (face/ toe rock) and gravel without other fish friendly and natural features are typically not supported. Integrating wood and other natural elements has advanced design methods and techniques which result in effective and more favorable function and performance benefits.
How are the current levees evaluated and assessed to be effective?
Latest hydraulic analysis methods, techniques and capabilities results in improved design of levees and revetments that are more resistant to riverine forces thereby reducing the risk of failure. However, it is not realistic to eliminate the risk of failure from riverine impacts entirely.
Flooding & Erosion
If you build these setback levees in these four quadrants, what happens when they fill up? Will flooding continue to the north or south?
The goal of any setback levee is to give the river access and connectivity to floodplain areas beyond the existing levees to provide for more room for the river to ebb and flow throughout the channel. While these can fill with sediment if the levees are not set back far enough from the current river channel, it is unlikely there will be much visible change in water surface elevations downstream.
Are you looking at the erosion factor? And how will that be included as you anticipate bank erosion and continued accumulation of sediment in the river?
Regarding bank erosion, the general concept of setting back levees provides more area for a given flood to flow and store water, which typically reduces forces that cause bank erosion. Computer models provide a tool to assess pre- and post- project changes for hydraulic characteristics and features. Geomorphologists on the team have been doing research looking back and forward to assess how trends will influence this area.
Will the new habitat areas be like a retention pond for river flooding – a place for flood water to go instead of into homes and croplands?
Connecting the floodplain area with the active river channel would not look like a retention pond. Instead, it would not even be noticeable because the newly reconnected habitat would simply be a part of the river channel and more natural floodplain. These same areas provide a place for flood water to go instead of into homes and croplands and help reduce peak flows.
Connecting the floodplain also helps to restore, enhance, and create additional habitat and wetland areas which helps with retention and detention storage benefits to an extent. In general, the greater the floodplain connection area that is provided, then the greater the floodplain storage (including reduced peak flow water levels), habitat and wetland complexes that result.
Do we know how many homes and properties are typically affected by river flooding in this study area?
Around a few dozen homes and other improvements. As flooding trends continue to worsen, there will likely be more direct impacts to the structures in this area. Access is already impacted and will become more heavily impacted (i.e., the project team has heard already that some properties cannot be accessed when there is a flooding event).
If you’re reconnecting the flood areas in these four quadrants, what will happen to the homes in those area?
This will depend on what alternatives are identified. In the SE quadrant, some of the alternatives could be a partial setback or another flood reduction measures. Or it could go beyond the homes, so the extent of effects will be determined as more specific alternatives are identified. At that time, the County will come back to the community for further comment and input.
Will the County will be buying property?
Pierce County currently owns several parcels within the study area. If a property owner is interested in selling their flood-prone property, the County will purchase from willing sellers as funds are available. Once the alternatives are identified, the County will have a better idea of any need for additional property. The feasibility study will make recommendations for specific measures and features to be implemented, including property acquisition.
Will there be impacts to properties and shorelines downstream from the study area?
There should not be increased impacts downstream because the main objective of the project is to give the river more room to flood. Potential adverse impacts will need to be properly addressed and mitigated. There will be beneficial effects, but these haven’t been identified yet. The current hydraulic modeling shows flood inundation.
When this work is finished, built, and done, will our flood insurance go down?
The act of building a new levee does not always directly correlate to a reduction in flood insurance rates. When new levees are constructed, they need to be accredited by the Flood Emergency Management Agency (FEMA) in order have any effect on flood insurance rates. The accreditation process is arduous and to date, FEMA has not accredited any Pierce County Levees within its system.
Currently FEMA is reviewing their policies related to levee accreditation. Part of this review may provide more substantial changes in how insurance policies are rated based on multiple risk factors. Pierce County will know more once the revised FEMA program is formally rolled out. Pierce County participates in the FEMA Community Rating System (CRS) program. CRS is a voluntary incentive program that recognizes and encourages community floodplain management activities that exceed the minimum National Flood Insurance Program requirements.
Pierce County’s participation in the CRS program requires an annual recertification of the activities that presently result in a 40% reduction in flood insurance policy premiums for properties in unincorporated Pierce County. When projects are built that reduce flood impacts to nearby residents, such as levee setbacks, Pierce County gets “credit” under the CRS program. You can find more information on the CRS program webpage.
How is the work on the new highway from Tehaleh and the new alignment of McCutcheon Road connected to this project?
The proposed Rhodes Lake Road Corridor project runs through the project area as it connects State Route 162 to the Tehaleh community. The Rhodes Lake Road Corridor project is being designed to avoid flooding impacts; however, the project is not being designed to resolve current flooding impacts in the area. Instead, the Levee Setback Feasibility Study is intended to resolve current flooding issues.
Find out more information and connect with staff designing the Rhodes Lake Corridor project.
The proposed Rhodes Lake Road Corridor project is actively acquiring property necessary to construct the new road that will run through the study area. Properties will also necessary for acquisition to offset a rise in flood levels, resulting from the proposed project. These acquisitions are currently underway and are unrelated to the feasibility study.
Canyonfalls Creek often floods the stretch of
McCutcheon Road it parallels, is this going to
be critically examined as we move forward with
This will be considered as the study continues. The stream is above a roadway and the County would like to put in a bridge that is fish passable, though currently it is still being determined what elevation to set the bridge at. The information that the bridge project is waiting for will depend on what comes out of this study for long-term planning. Learn more information about the bridge project and connect with staff here.