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Tsunami Most environmental and ecological impacts from tsunamis derive from direct damage from the waves, which can physically remove vegetation and wildlife, increase sediment load, and smother vegetation that is not physically carried away. Other environmental impacts from tsunamis include chemical changes from saltwater intruding into freshwater sources; eutrophication (enrichment) of water from increased runoff; and decomposition of vegetation, wildlife, rotting property (boats or buildings) and unrecovered remains. Non-biodegradable waste, such as plastics, can lead to a buildup in marine debris, and toxic wastes, if inadequately stored, may be released into the environment. Lastly, exotic wildlife may be introduced or may escape into the local ecosystem. 15.5 FUTURE TRENDS IN DEVELOPMENT The County and its planning partners are equipped to handle future growth within tsunami inundation areas. The inundation maps provided by the California Department of Conservation offer jurisdictions a way to guide development away from tsunami-prone areas. Additionally, all partners have committed to integrating their general plans to this hazard mitigation plan. By coordinating their general plans, municipalities and the County will be better able to make wise land use decisions as future growth impacts tsunami hazard areas. New standards for building designs in Alaska, Washington, Oregon, California, and Hawaii that account for tsunami loads and effects have recently been adopted by the American Society of Civil Engineers (ASCE 7-16, Chapter 6), referenced in the 2018 International Building Code (IBC), and included California’s state building code (2019 State of California Building Code Appendix M). This will help to promote structures more resilient to the impacts from tsunami as new development occurs within identified tsunami risk areas. 15.6 SCENARIO The tsunami scenario with the greatest potential impact on the planning area is a tsunami triggered by a major seismic event along the Cascadia subduction zone. Historical records suggest that tsunami wave heights on the order of 15 to 60 feet could be generated by a Cascadia subduction event (see Figure 15-8). The most destructive tsunami will be associated with a local source Cascadia event and will be preceded by strong ground shaking. Significant damage will result from the ground shaking, tsunami wave forces, and impacts associated with debris. A major tsunami event in the region would have devastating impacts on the people, property, and economy of the planning area. A tsunami from a more local earthquake, such along the San Andreas fault, might be less severe than a Cascadia subduction event. Tsunamis are less commonly associated with strike-slip faults such as the San Andreas system. However, a local source tsunami presents a high risk to people, as there would not be time to initiate evacuation; the first surge could arrive in as little as 10 minutes. Strong ground shaking preceding the tsunami could damage buildings, communications and electric utility infrastructure, roads, and bridges, further impairing the community’s ability to evacuate safely. 15.7 ISSUES The planning team has identified the following issues related to the tsunami hazard for the planning area:  To truly measure and evaluate the probable impacts of tsunamis on planning, hazard mapping based on probabilistic scenarios must continue to be updated regularly. The science and technology in this field are emerging. Accurate probabilistic tsunami mapping will need to be a key component for tsunami hazard mitigation programs to be effective. 15-13