System Wide Sediment Impacts of Crso Snake River Dam Removal Alternative

A 2019 Environmental Impact Statement (EIS) was completed to review and update management of the Columbia River System comprised of fourteen federal water regulation projects in Idaho, Montana, Oregon, and Washington. One multiple objective alternative included structural measures for breaching of the four Lower Snake River dams (Ice Harbor, Lower Monumental, Little Goose, and Lower Granite). This alternative explored potential impacts of breaching the earthen embankments for these four dams. The analysis included a sediment impact assessment of a two-stage dam removal. This talk will describe the overall dam removal sediment analysis framework and provide Columbia system context for sedimentation results. A suite of models and analysis were developed to understand system-wide sedimentation processes in the portion of the Columbia River System covered under the Columbia River System Operations EIS with particular focus on the ability to analyze an alternative that included breaching of the Lower Snake River dams. The framework includes 1D mobile bed HEC-RAS, 2D AdH and particle tracking modeling, system-wide 1D HEC-RAS stochastic data analysis for sediment suspension potential and a literature review of sedimentation processes in the affected reaches and notable historic events. This talk will describe how the pieces of the framework work together to inform on system wide sedimentation, major sedimentation findings of the dam removal alternative and provide system context for those findings.