Multi-Hazard Mitigation Plan: 10. Floods

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Chapter 10:Hazard Analysis—Floods 10.3.1 Regional Hazards Annual rainfall on the island of Hawaii ranges between 300 inches on the slopes of Mauna Kea above Hilo, to below 10 and 20 inches in the and regions around Kawaihae and South Point. As expected, flooding is rather common on the wet, windward side of the island where high annual rainfall is the norm. Most of the flooding that has caused damage has been flash flooding during extreme rainfall events that bring about sheet flow between stream channels. In addition, the soils along the Hamakua Coast readily absorb precipitation - thereby facilitating mudslides and landslides. The Hilo and Puna areas are probably the most frequently flooded and hardest hit by flash floods on the Big island and perhaps in the State.51 Perhaps more surprising is the degree of flooding experienced by the more and regions of the Big Island. The Kohala and Kona districts have a long and active history of flooding largely due to flash flooding and intense storms. More recently, the South Kohala and Waikoloa areas have experienced intense flash flooding that has caused considerable damage.'` 51 Fletcher,C,B.Richmond,E.Grossman,A.Gibbs,Atlas of Natural Hazards in the Hawaiian Coastal Zone, Prepared in cooperation with University of Hawaii,State of Hawaii Office of Planning,and National Oceanic and Atmospheric Administration,U.S.Geological Service Geologic Investigations Series 1-2761, 2002. 52 Ibid. 10-8 Hawaii County Multi-Hazard Mitigation Plan