DESCRIPTION
Pierce County performed and completed a Setback Levee Feasibility Study. The study identified numerous potential setback levee site locations along the Puyallup, Carbon and White Rivers. The study also developed criteria to evaluate the feasibility of each of the identified setback levee sites. The feasibility study was identified as a high priority need in the Lead Entity Strategy in that because setback levees result in reconnection of river main stem channels to their associated floodplains. This type of project planning and implementation is deemed a top priority restoration action.
The study identified project site locations based on several criteria and features. These include historic side-channels and hydrology that indicate the likelihood that given the opportunity, natural processes will act to create the desired habitat. Engineering concerns, land-use, hydrology and flood protection, cost, and landowner willingness was evaluated along with habitat restoration for project priortization.
The study developed a comprehensive catalog of potential levee setback projects on the mainstems of the Puyallup, White, and Carbon rivers. Conceptual designs were evaluated and prioritized, and two high priority projects proceed through preliminary design; including levee alignment and profile. This is basically at the 30% design level for the two identified highest priority sites. A Flyby animations was developed and created as a representative river segment with and without setback levee conditions, under normal flow and flood conditions to provide the community with a compelling picture of effective flood control and growth opportunities coexisting with major salmon recovery actions.
The study builds on an earlier oxbow catalog produced by the Puyallup Tribe, a georeferenced Channel Migration Zone study (2003), and a new FEMA floodplain mapping for the entire study area. Other county GIS info, including orthophotographs, land use and tax parcel data was also used in this analysis.