What are my risks?

• Do I live in a flood prone area?
• Where have stream floods been recorded on Oahu?
• Where have high waves been recorded on Oahu?

Do I live in a flood prone area?

For information on flooding in your neighborhood, refer to a Flood Insurance Rate Map (FIRM). These maps are computed water surface elevations that are combined with topographic mapping data to develop flood hazard maps. They provide information on areas subject to flooding. They are used to guide future development away from flood-prone areas and to regulate development that is proposed to occur within such areas.

Call your Flood Coordinator (587-0248) for information about flooding. Or, ask your regional librarian to see the Flood Insurance Rate Map for your community.

Click here for a general map of the flood zones on Oahu.

Where have stream floods been recorded on Oahu?

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The most frequent and severe flooding occurs where steep sloping hillsides abruptly meet flat or low-lying coastal plains, such as those found in Waimanalo, Kailua, Kaneohe (November 1992), and Laie (April 1994). The heaviest rainfall during the last decade in Kaneohe occurred in October 1991, when 15 inches fell in 48 hrs leading to intense flash flooding. Stream mouths are also commonly susceptible to flooding, especially during marine storm or high wave events, as runoff from streams reach a sea that is partly elevated by the combination of high waves, winds, and storm surges. Some of the largest rainfall counts and most severe flooding events have occurred in the last several years. During the first 15 days of November 1996, record-breaking rainfall occurred along the Waianae Coast, where 21 inches fell in an area where the average annual rainfall is 2 inches. In Ewa, 12.5 inches fell in 7 hours on the 5th of that month, inducing flooding of the low coastal plain. A series of slow moving storms with prolonged rains that saturated the soils of south-central Oahu culminated on New Years Day of 1988 in severe runoff and hillside erosion, resulting in catastrophic damage to stream flood mitigation channels, homes, and roads in Aina Haina and Niu Valleys. Other recent severe events on Oahu include October 1981 flooding of Waiawa Stream after heavy rains that lead to $786,000 damage and January 1968 flooding in Pearl City, which caused $1.2 million damage.

Where have high waves been recorded on Oahu?

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The largest waves reach Oahu in winter. Along the north shore, it is common to see wave heights between 15-20 feet annually from winter swell. Wave heights of 50 feet have been reported (December 1969 and January 1998). Often, winter north and northeast swells wrap around Makapuu Point and generate waves at Sandy Beach that are as high as the largest summer surf found there. Trade wind waves can be high, but because of their shorter wavelengths, they have less energy than north and south swell. Trade wind swell has a greater easterly directional component, which enables them to refract around to south and southwest-facing shorelines producing wave heights of 1-4 feet. In the summer, south-facing shorelines receive 4-6 foot swell. South swells tend to have less energy and longer wave periods than winter swells. Hurricane generated waves have exceeded 15 feet along east Oahu and 10 feet on Oahu's southern shores. Combined with storm surge and high tides, hurricane waves can overwash coastal roads and properties, as they did along the Kaaawa and Kaneohe coasts during Hurricane Fernanda in 1993 and along the Honolulu and Waianae coasts during Hurricane Iniki in 1992.