Ed MacMullan on Tsunami Resilience Strategies

Fifty-Year Resilience Strategies for Coastal Communities at Risk for Tsunamis

Presenters: Jay Raskin, FAIA; Ed MacMullan; Josh Bruce

Oregon’s coastal communities face a high risk from inevitable future Cascadia Subduction Zone. Seaside Oregon, chosen as the case study since it has the highest tsunami risk in Oregon, could improve resiliency in the face of this risk by adopting 50-year resilience master plans. This case study looks at strategies and policies to help Seaside implement this approach. The characteristics of other coastal communities with respect to their risk, economies, population, land use, and resident and business populations, may vary in percentage, but not in kind.  The proposed strategies are site specific, but are adaptable for use in the other communities. In addition, these strategies will be useful in developing comparative benefit-cost models for different resilience scenario.  Tsunami mitigation projects in high-risk areas have been shown to have very high benefit-cost ratios.

Seaside is situated in an estuary located at the confluence of two small rivers that run parallel to the coast. It is surrounded by hills to the south and east.  Most of its developed land and population are in the tsunami inundation zone. Few design and safety provisions for either earthquakes or tsunamis were incorporated as the community developed. The city’s economic livelihood is based on its proximity to the ocean. Most of the city’s critical infrastructure, schools, governmental buildings, and essential facilities are in the tsunami inundation zone.  Few of them meet current seismic standards and none are built to resist tsunamis.

To help Seaside become resilient from this tsunami hazard, the case study addressed the steps the city must take, such as moving critical and essential facilities and vulnerable populations to high ground, improve and create evacuation options, improve emergency operations plans, develop redundant and/or alternative critical infrastructure, and create a post-disaster recovery Plan.  It also must address land use planning that looks at balancing tsunami risk versus need to be in tsunami inundation zone and include relevant economic factors that will help local public and private interests think through tradeoffs and decisions regarding improving economic resilience in cases where a significant portion of a local economy’s “engine” resides in the tsunami zone.

The shift in land use and relocation of critical facilities is based on a phased approach over a 50-year period.  The most critical facilities would be moved within a ten-year period and other important facilities would move in two other phases. Relocation of non-critical facilities would be part of post-disaster recovery.

Three scenarios are explored: (1) Emergency response plus, which focuses on evacuation and limited infrastructure improvement; (2) high resilience, which looks at creating a new local town center protected from earthquakes and tsunamis limited resilience; and (3) middle ground resilience, which takes the goals of high resilience and tries match them to the resources and capacity of the community.