By Doug Peters, Watershed Planner, Washington State Department of Commerce
There is growing awareness of the potential risks associated with another Cascadia subduction zone seismic event. We expect large-scale destruction of existing infrastructure, which will not only be very disruptive to human society, it will present new opportunities to reconfigure our current shoreline infrastructure to reduce impacts to habitat forming ecosystem processes. There are numerous habitat problems caused by our current shoreline infrastructure. These include shoreline armoring, which can destroy beach structure and eliminate areas for forage fish spawning and predator evasion; railroads and roads that both block sediment supply from feeder bluffs but that also get blocked from regular landslides; docks and piers that block sunlight and increase predation impacts on smaller fish; and stormwater outfalls delivering pollutants to the nearshore.
Sea level rise (SLR) will affect some shoreline areas even without any seismic impact, and if SLR is coupled with the seismic event impact, it will likely result in significant damage to current shoreline infrastructure. Scenarios can be developed ahead of time that allow for creative consideration of infrastructure redevelopment and abandonment options that work synergistically to support and sustain natural habitat-forming processes. Advance planning for possible alternatives to address both shoreline infrastructure and habitat should significantly reduce the time and effort needed at the time of the seismic event. It also allows for collaborative development of alternatives with potential for multiple benefits, promoting a more sustainable shoreline environment.
To propose options for shoreline infrastructure retrofits and relocations, we could use the motivation of the impending subduction zone seismic event while focusing on desired and possible habitat restoration options. We could also use existing data on known shoreline areas with priority habitat and existing evaluations of at-risk shoreline infrastructure to discover priority geographies for potential future restoration efforts. But to do that, we need criteria to evaluate both current and potential habitat functions and values, and we need different possible future scenarios to include varying scales of potential habitat restoration, as well as options for removal or relocation of damaged infrastructure. The goal is to develop multi-benefit options for consideration in local and regional land use plans.
Using existing information on shoreline area habitats and shoreline infrastructure, an approach to multi-benefit infrastructure relocation and habitat restoration could include these steps:
Evaluating the likely seismic damage scenarios and planning for strategic relocation of damaged shoreline infrastructure offers opportunities to restore degraded shoreline habitat. Advance planning can establish some basic understanding of the potential options available for both minimizing threats to life and property and for restoring degraded habitat.
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