Multi-Hazard Mitigation Plan: 19. Mitigation Strategy

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Chapter 19:Mitigation Strategy tsunami and hurricane surge inundation limits and base flood elevations require verification with modeling and historical data. The zoning and flood control code use the FIRM as the basis to avoid exposure or apply special flood-proofing standards. Repetitive loss programs need to be incorporated into the flood control and land use systems to buyout and prevent future construction in such areas. Current drainage standards, which are based on 10-year storms,need to be reevaluated to better account for cumulative upslope development. • Warning and public education systems. The National Weather Service has installed tele- metered rain gages to aid in flood prediction and wave buoys for high waves. Two Doppler radars on this island provide rainfall intensity in quantitative graphic form. NWS's system needs to be supplemented with an improved field reporting system and stream gauging sys- tem related to rainfall gages to better predict flash flooding and to extend flood warnings to areas that NWS's system cannot monitor. Warnings for specific areas are broadcast via nor- mal and special radio/TV forecasts and by special County Civil Defense announcements, as well as over the NOAA Weather Radio (for airplanes and boats). Public education needs to be improved to address the problem of vehicles being driven across flooding streams-- road hazard signs need to be quickly erected along highways, and hunters and residences in re- mote areas should be educated. For high waves, the most effective action is the closure of beaches and coastal roads. • Flood control structural and nonstructural projects. Flood control channels have long been established on this island; however, with increased urbanization some channels have been overloaded and need or have received enlargement or rerouting. The recent upgrade of Alenaio Stream in Hilo is a good example. As part of the cost-benefit for such projects, nonstructural alternatives need to be examined such as better watershed management. To reduce coastal damage to high waves, improvements to the seawall system in Hilo and Kailua-Kona have been discussed, but there are no firm plans. There is a tradeoff between the cost of expensive structural improvements and the cost of more frequent and extensive cleanup. 19.2.5 Lava Flows Mitigation actions include preventive measures such as zoning, emergency services improve- ments such as warning systems based on improved predictive mapping, and limited structural protection measures. • Identification of hazard areas. The Hawaiian Volcanoes Observatory(HVO),part of the U.S. Geological Survey, has developed very capable methodology and systems for predicting eruptions in a timely manner, and evaluating the probable lava flow hazard areas. All historical lava flows have been well mapped, and zonation depicted showing the chances of more lava flow for all parts of the island. In recent years, improved mapping programs have moved away from the discrete zonation boundaries to indicate more realistic probabilities for hazard areas and transition regions. Lava shed programs, analogous to water flooding maps, are under development. Planning, zoning, and insurance factors now mitigate against unwarranted development in high hazard areas. • Warning systems. HVO, in conjunction with Civil Defense and other County agencies, is on standby to provide warning and evacuation when an eruption occurs. Though most lava flows have been slow enough to allow easy evacuation and even removal of some structures, 19-7 Hawaii County Multi-Hazard Mitigation Plan