Multi-Hazard Mitigation Plan: Executive Summary

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Executive Summafv EXECUTIVE SUMMARY The Island and County of Hawaii has experienced 42 natural disaster events since 1977 and five tsunamis (1946, 1952, 1957, 1960, and 1964) since 1940. This island is uniquely exposed to all the major natural hazards due to its active volcanoes (lava flow and earthquake hazards), young geological age (sheetflow flooding due to undefined drainage-ways), vast land area larger than all the other islands combined(expansive areas vulnerable to wildfires), varied topography dominated by five mountains (complex hurricane wind acceleration patterns), and easternmost location in the Hawaiian islands chain (hurricane exposure). Of lesser concern is sandy beach erosion due to the geologically youthful age of this island resulting in few sandy beaches; instead, sea cliff erosion is of greater concern to control building too closely to the cliff edge. The purpose of this multi-hazard mitigation plan is to provide a strategy to reduce or eliminate loss of life or property caused by natural hazard events. A multi-hazard strategy addresses the relationship among various types of hazards, leverages resources to benefit multiple hazards, and allocates limited resources to areas susceptible to the most severe or frequent hazards. Risk and Vulnerability Assessment Hazard Anal The state of knowledge and hazard mapping are summarized below: • High Wind Storms. For high wind risks, the areas exposed to wind acceleration due to topography have been mapped. • Hurricanes. Similar to high winds, the areas exposed to wind acceleration due to to- pography have been mapped. For storm surge risks, the Flood Insurance Rate Maps (VE zone)will be updated based on hurricane surge modeling. • Landslides and Rock Falls. GTS mapping has been developed to identify areas susceptible to landslide or rock falls based upon the slope of the terrain, soil type, and ground moisture level. • Earthquake. The County should adopt the 2006 International Building Code as the official building code; this better classifies the probabilistic acceleration parameters of the Island than previous versions of the obsolete 1991 Uniform Building Code currently enforced by the County. Maps have also been developed to distinguish areas where ground motion could be significantly increased by softer soil conditions. • Lava Flows and Volcano Gases (VOG). Although mapping exists that zones the entire island into nine lava hazard zones, the Hawaii Volcano Observatory is presently working to replace this map with a probabilistic hazard map. UH Manoa Center for the Study of Active Volcanoes (CSAV) is developing a modeling system to predict direction and speed of flow for a given eruption. ix Hawaii Countv Multi-Hazard Mitigation Plan