Metrics to support integrated coastal flood risk management and resilient ecosystem restoration across the floodplain-estuary-nearshore gradient

Restoring stream and tidal connectivity to floodplains and estuaries through levee breach, setback and removal is crucial to the recovery of salmon populations and ecosystem functioning across the Pacific Northwest (PNW). Barriers to implementation of connectivity-restoration projects include concerns about the perceived potential for increased flood risks and reduced drainage, as well as uncertainty in restoration outcomes. Important concerns in planning for levee modifications are the projections for significantly higher future winter peak flows and greater sediment loads due to climate change that are expected to increase flood risk. In addition, flood conveyance is expected to decrease as sea-level rise traps more sediment in the lower rivers and estuaries. In the coming decades, integrated coastal flood risk management and ecosystem recovery planning will require new approaches to safeguard lowland communities from flood risks while restoring and maintaining coastal habitats and ecosystem functioning. We will present several metrics that we are developing to support integrated PNW coastal flooding/ecosystem recovery planning and management that will: (1) inform current conditions and establish baseline data to detect and track future climate and land-use change; (2) evaluate restoration and flood control performance amid the combined cumulative effects of recovery implementation and future climate/land-use change; and (3) validate process-based models to help predict ecosystem changes/recovery and flood control performance for planners and decision-makers. We use examples building on the extreme hydrologic conditions of the last few years, arguably a window into future conditions in the PNW, to help illustrate how such metrics and models can be used strategically to plan for coastal resilience within and across Puget Sound watersheds