Coastal Forests as a Tsunami Mitigation Measure in Pacific Northwest Coastal Communities

Abstract

The Pacific Northwest coast has tsunami risk in both non-local and local forms. Most significant is the tsunami risk that comes from the Cascadia subduction zone, and scientists predict that more major seismic events along this zone are due to occur in the future. These events may generate tsunami waves in excess of 30 feet for PNW coasts, leaving coastline areas with as little as 15 minutes advance warning to prepare and seek high ground shelter. Given this significant risk of non-local and local tsunamis, multiple tsunami mitigation measures and emergency preparedness strategies have been implemented in Washington’s coastal communities. It was learned from the 2011 Great East Japan Tsunami that coastal forests were not negligible in mitigation of the tsunami. In this design research thesis, I explore the applications of coastal forests as a natural tsunami mitigation measure in PNW coastal communities. Specifically, there are two research questions I investigate: 1) What elements of a coastal forest contribute to effective tsunami mitigation? and 2) How can these elements be translated into a coastal forest design to function as a tsunami mitigation measure? Coastal forests have clear potential for tsunami mitigation. When designed with the five Performance Factors in mind (forest area, gap layering, tree crown height, tree distribution, landform), they can have direct effects on a tsunami’s wave energy, flow speed, inundation depth, and inundation extent. This mitigation potential can result in positive changes to tsunami risk by slowing wave inundation rates and increasing evacuation warning times. This site-specific design investigation in Westport, WA could influence future site developments to include coastal forests for tsunami mitigation purposes. Further research on the properties of coastal forests that can contribute to tsunami mitigation need to be carried out in the fields of soils and geoengineering, forest restoration, park and campground site design, and ecotourism and economic development.