Probabilistic Tsunami Design Zone Maps for Oʻahu
The Office of Planning Coastal Zone Management Program (OP-CZM) in partnership with Hawaiʻi Emergency Management Agency (HI-EMA) seeks to mitigate tsunami hazards in Hawaiʻi through the development of comprehensive high resolution probabilistic Tsunami Design Zone maps compatible with American Society of Civil Engineers 7-16 for the Island of Oʻahu, State of Hawaiʻi.
The probabilistic Tsunami Design Zone mapping for Oʻahu will provide a probability distribution, incorporating variables, for tsunami events or phenomena, leading to more accurate mapping and modeling for a more resilient Oʻahu. Probabilistic mapping is different from deterministic modeling, which predicts exactly the occurrence of future events without the added complication of randomness existing in nature.
The Hawaiʻi Multi-Hazard Mitigation Plan identified tsunamis as a significant hazard, posing a high coastal hazard risk across the State.
There were, however, no national standards for designing critical facilities against the effects of a tsunami. As a result, in 2016, the American Society of Civil Engineers (ASCE) developed ASCE 7-16, Chapter 6 – Tsunami Loads and Effects – the first national, consensus-based standard for tsunami resilience in Alaska, Washington, Oregon, California, and Hawaiʻi. The new ASCE 7-16 tsunami design provisions will be referenced in the 2018 International Building Code (IBC 2018) and will apply to a limited class of Risk Category III and IV buildings and structures, as well as taller Risk Category II buildings.
Risk Category III includes, but is not limited to, structures such as theaters, lecture halls, elementary schools, prisons and small healthcare facilities. Risk Category IV facilities include, but are not limited to, buildings and structures such as hospitals, emergency communication centers and similar emergency facilities, as well as ancillary structures required for the operation of these facilities during an emergency. Risk Category II includes, but is not limited to, residential and commercial buildings such as condominiums, office towers, etc. Tsunami design will only be required for Risk Category II buildings that are tall enough to provide safe refuge above the maximum considered tsunami flow level. This threshold height will be established by each county as they adopt the new building code, based on the tsunami hazard and building inventory for that county.
Risk Category IV (Queens Medical Center)
Risk Category III (Halawa Correctional Facility)
Risk Category II potentially (Downtown Honolulu, Hawaiʻi Condominiums and Office Towers)
The development of comprehensive high resolution probabilistic Tsunami Design Zone maps for Oʻahu is anticipated to be completed in 2019, unless otherwise noted. The development of comprehensive high resolution probabilistic Tsunami Design Zone maps is part of OP-CZM’s coastal hazards strategy, which was approved and funded by the NOAA Office for Coastal Management (OCM).
It is anticipated that once the probabilistic Tsunami Design Zone maps for Oʻahu are completed, mapping and modeling will be initiated for Hawaiʻi, Maui, and Kauaʻi counties.
Additionally, the Project will propose draft language for each of the county councils to consider amending their building codes to adopt the probabilistic Tsunami Design Zone maps and model data developed along with styles of maps appropriate for use in their respective county building codes and the ASCE Tsunami Design Geodatabase.
The development of probabilistic Tsunami Design Zone maps is envisioned to be a multi-year process covering the major Hawaiian Islands and culminating in changes to county building codes for the safety and future resiliency of Hawaiʻi.
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