Floodplain Impacts
In May 2018, Pierce County completed a Final Supplemental Environmental Impact Statement (EIS) for the New Rhodes Lake Road East Project. The EIS identified unavoidable impacts to floodplains in the project area and conditions the project to comply with Pierce County floodplain development regulations. Since the completion of the EIS, the project design has advanced to comply with these regulations.
The EIS requires the project to cause no additional flood impacts (in flood elevation or area) to private properties. Fill placed in the floodplain to build the new road would act as a dam during major floods causing water up-river to rise (see figures above showing project without culverts and the number of properties impacted upstream). Many of these up-river properties currently flood during heavy rains; however, the project cannot make the flooding worse than it already is. To reduce the number of properties potentially impacted by additional flooding caused by the project, two large culverts would be installed under the roadway (see figure).
These culverts would allow floodwater to pass under the new roadway which would eliminate most flood impacts up-river. During floods, water would pass through these culverts and cause additional flooding on down-river properties. Due to the sheer size and severity of flooding along this reach of the Puyallup River, it is not possible to build the project and not cause additional flooding to private properties. The design team examined multiple alternatives to minimize flooding, including an option that does not place fill in the floodplain. They have determined that acquisition of properties down-river is the best alternative because it minimizes impacts to private properties and project cost.