CHAPTER 3 APPENDIX C: Hazard Summary Maps for the State of Hawai‘i Hazard Map Explanation The following maps were copied directly from the Coastal Hazard Atlas (Source: Fletcher III, Charles, Eric Grossman, and Bruce Richmond. Atlas of Natural Hazards in the Hawaiian Coastal Zone. 2000. Funded by State of Hawaii Office of Planning, Coastal Zone Management Program and Coastal and Marine Geology Program U.S. Geological Survey) for use in thinking about hazard mitigation activities that should occur in these areas. The summary maps show four general types of hazards that may be linked with stronger hazard events. These maps show tsunami inundation, stream flooding, high winds, and damaging high waves, and provide a general history of these event occurrences collected through extensive research from various sources. Although the histories only go back to the 1800s and are not exhaustive, they do show that certain areas have an increased likelihood of certain types of hazard occurrences. (Given the small size of Hawaii State, an area that does not have a prerecorded history of a natural hazard occurrence does not preclude it from being affected in the future). In the atlas, a second set of maps (not reprinted in this document because these maps appear in each of the county mitigation plans and are accessible online and in the atlas) shows the communities in sections approximately 5 to 7 miles in length, with colored bands that rank the relative intensity of each hazard at the adjacent shoreline. Darker sections of the band indicate higher intensity. These bands have been labeled as follows, from the inner coastal band to the outer band: G: Geology - B=Beach; S=Stream; R=Rocky; H=Headland; D=Developed; fr=fringing reef; br=barrier reef; e=embayed coast; w=wetland. CS: Coastal Slope T: Tsunami SF: Stream Flooding W: High Waves S: Storms E: Erosion SL: Sea Level V/S: Volcanic/Seismic The intensity readings are APPROXIMATIONS, based on the best available scientific evidence. In many cases, data is limited or not available, which is the reason that the authors of the hazard atlas did not pinpoint the exact location of the hazards, but used the intensity bars to show likelihood. Table 2 explains the intensity rankings. Again, the lack of evidence or data does not mean that a specific hazard will never occur in the area. Therefore, it is important to prepare inclusive hazard mitigation plans that will deal with a variety of contingencies. Hawaii State Hazard Mitigation Plan APPENDIX: Hazard Risk ◊ A3-13 Table 2. Hazard Intensity Rank Definitions Low (1) Moderately Low Moderately High High (4) (2) (3) Tsunami No history of History of Minor History of major History of major Inundation tsunami activity flooding (<10 ft. flooding (>10 ft. flooding (>10 ft. and no reasonable elev.); future elev.) but elev.) with basis for expected flooding hazard is historical damage, significant activity. low because of a and expected damage because steep coastal zone future damage is of a moderate (>45%) or some slight because the slope. other mitigating steep coastal zone factor (tsunami slope (>45%) barrier). makes development unlikely. Coastal No history of History of Abundance of Historically high Stream coastal stream nondamaging streams and high flood damage on Flooding flooding and no flooding where seasonal rainfall gentle slope, reasonable basis streams or in watershed watershed rainfall for expected highlands (monthly max. >8 monthly max. >8 flooding due to w/seasonal high in) and history of in, no mitigation low seasonal rainfall are present damaging floods efforts or rainfall in (monthly max. >8 with partial improvements watershed in) and coastal mitigation; or no since last (monthly max. <5 slope >20%; or mitigation where damaging flood. in); or steep history of flood slope >20% and coastal slope damage with full <45%. (>45%). mitigation since last major flood. High No reasonable Seasonal high Seasonal high Seasonal high Waves basis to expect waves 4-6 ft. waves 6-8 ft. waves > 12 ft., high waves. characterized by rapid onset. Storm No history of Minor historical Historical Historical Overwash overwash or high overwash (<10 ft), overwash >10 ft overwash >10 ft and/ or winds, and no and/or high winds on steep slope, on moderate to High reason to expect (-40 mph gust). and/or high winds gentle slope, Winds them. with localized and/or high winds (isolated cases) with widespread structural damage structural damage (-40 mph (-75 mph gust). sustained). Hawaii State Hazard Mitigation Plan APPENDIX: Hazard Risk ◊ A3-14 Coastal Long-term Long-term stable, Long-term erosion Chronic long-term Erosion accretion (>10 yr) or minor erosion/ rate <1 ft/yr; or erosion >1 ft/yr, with no history of accretion cycles highly dynamic or beach is lost, or erosion, or with erosion fully erosion/ accretion seawall at water- dynamic cycles recovered by cycles with line for portions with consistent accretion; low significant lateral of the tidal cycle. annual accretion. rocky coasts; shifts in the perched beaches. shoreline. Sea-Level Steep coastal Gentle or Gentle or Gentle or Rise slope where rise moderate slope moderate slope, moderate slope >0.04 in/yr or where rise >0.04 where rise >0.08 where rise >0.12 gentle slope where in/yr or steep in/yr or steep in/yr. rise <0.04 in/yr. slope where rise slope where rise >0.08 in/yr. >0.12 in/yr. Volcanism No history of No volcanic Limited history of Frequent and/or volcanic or activity in recent volcanism, volcanism, Seismicity seismic activity; recorded history; seismic seismic seismic seismic probability zones probability zones probability zone probability zone 2 or 3 2 or 3 (frequent 0. 1, minor historic recommended historic damage). seismic damage. (historic seismic damage). Hawaii State Hazard Mitigation Plan APPENDIX: Hazard Risk ◊ A3-15 Hamakua Coast 1890 Dec 9 Flash floods @ Hamakua & Honoka‘a 1902 Mar 6 Flash floods @ Hamakua 1965 Aug 4–5 Sheet flows 1982 Jul 16–17 Flash flooding @ Hamakua Hawaii 1982 Aug 1 TD Gilma, flash flooding 1982 Aug 9–10 TS John, flash flooding @ Honoka‘a 1983 Oct 26 Hamakua Coast Stream flooding Upolu Waipio Valley 1984 Feb 8 Flooding Point 1902 Mar 6 Flash flooding 1985 Mar 11 Flash flooding 1972 Aug 18–Sep 3 Flash flooding 1986 Mar 16 Flash flooding 1978 Dec 6 Flooding 1986 Apr 3 Flash flooding Islandwide stream flooding 1979 Dec 14–18 Severe flooding 1986 Apr 8 Flooding because of heavy rains Kohala 1989 Apr 4–9 Flooding 1986 Sep 26 Flash floods, 6–10" rain 1918 Apr 9–10 Flash flooding 150 1991 Aug 5–7 Flooding 1987 May 5–6 Extensive flash flooding, over 10" rain 1959 Aug 4–7 H Dot 1936 Jan 17 Flash flooding @ N. Hi 1987 Oct 1 Flooding, 10–15" rain 1979 Feb 19–20 Flooding 175 1966 Nov 20 Flash flooding @ S. Kohala 75 1987 Nov 21 Flash flooding 1979 Dec 14–18 Flooding 1967 Jan 11 Flooding 1988 Mar 14–18 Flooding, 5–10" rain 1980 Mar 6–25 Episodes of flooding 1982 Aug 9–10 Flash flooding 1989 Apr 28–29 Flooding @ Honoka‘a 1981 Oct 27–28 Flash flooding 1983 Dec 24–26 Flooding Kawaihae 75 1989 Aug 20–21 Minor flash floods 1982 Jul 21–22 TD Daniel, flash flooding 1986 Feb 16 Localized flooding 50 1990 Dec 18–20 Flooding 1984 Dec 24–25 Kona storm, flooding 1986 Apr 8 Flooding @ Waimea & Kohala Waimea 40 30 1991 Aug 5–7 Flooding 1986 Apr 8 Flooding 1889 Feb 3–5 Flash flooding @ Pahala 20 1994 Apr 11–12 Floods, landslides 1986 Nov 10–11 Flooding 1989 Apr 28–29 Flash flooding @ Waimea 1987 Jul 21–23 Flooding 1991 Aug 5–7 Flash flooding 10 1987 Dec 11–19 Flooding 1996 Sep 8–9 Flash flood 20 1988 Mar 14–18 Flooding S. Kohala and Waikaloa 1988 Aug 4–8 H Fabio, flooding 1997 Jan 5 Widespread floods 1989 Feb 3–5 Flooding Waikaloa Village 30 1989 Mar 1–4 Flooding 20 Hilo / Puna 40 15 1989 Jul 18–20 TS Dalilia, flooding Keahole 15 Hilo 1928 Oct 1 Flash flood of Wailuku R. 1990 Jan 14–22 Flooding 250 300 1966 Jul 25 Sheet flow 1992 Sep 14 TS Orlene, flooding Point 50 1967 Aug 2–11 Flash flood, 12" rain 1992 Nov 29 widespread flooding 1971 Apr 23 Flash floods, 9.66" in 24 hrs 1993 Jul 21–22 TS Dora, flooding 60 1979 Feb 19–20 Flooding @ Hilo, Ke‘eau, Kailua–Kona Pahoa, Kurtistown 1918 Apr 18 Flash flood @ Kona sugar mill 200 1980 Mar 18 Flooding 1922 Oct 22 Flash floods @ South Kona 1980 Sep 20–22 Flooding 1930 Jan 25 Holualua reservoir burst, flash floods 100 150 1982 Mar 30–31 Flooding, 10" rain 1961 Oct 30 Flash floods @ South Kona 1982 Jul 16–17 TS Emilia, flash flooding 1963 Apr 29 Flash floods @ Kaimaliu 75 125 1982 Jul 23 Flash flooding, 29" rain in July 1965 Sep 25 Capt. Cook, Kaimaliu 15 1982 Aug 1 TD Gilma, flash flooding 1966 Oct 3–5 Flash floods @ Capt. Cook & Holualua 100 1984 Nov 3–4 Flooding, 4–6" rain 1967 Oct 12 Overland flow @ Ho‘okena 1985 Sep 25 Flash floods 1967 Oct 24 N. Kona 75 1986 Apr 3 Flash floods 40 1986 Sep 26 Flash flooding, 6–10" rain 1968 Jul 17 Local flash flooding @ Kealakekua 50 0 20mi 1968 Oct 3 Flash floods @ N. Kona 1986 Nov 8 Flash flooding, 10" rain 1974 Oct 15 Flooding Kaloloa to Honaunau, 4.5" in 7 hrs 1987 Oct 1 Flooding, 10–15" rain 1976 Apr 26 Flash flooding Honaunau 1988 Aug 4–8 H Fabio, flooding in Hilo 1982 Mar 17 Minor flooding @ Kona 75 40 and Kurtistown 020km 1985 Sep 29 Flash flooding Capt.