What are my risks?

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

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.

Even so, updates to these maps have not kept up with development in Maui County. Each year, numerous properties not officially mapped as “flood prone” are flooded.

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.

Where have stream floods been recorded in Kauai County?

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Click to enlarge Stream flooding on Kauai is characterized by numerous flash floods as well as prolonged flooding associated with slowly passing rainstorms that saturate the soils. Kauai, famous as one of the wettest places on Earth, receives between 20 and 80 inches of annual rainfall along the coast and more than 400 inches at the higher elevations of Mt. Waialeale Flash floods resulting from a storm on December 14, 1991 that dropped over 20 inches of rain in 12 hours over Anahola, caused five deaths, intense flooding, bank failures, erosion, and slides, totaling more than $5 million in property damages. During recent recorded history, such events are not uncommon. On January 24-25 1956, 42 inches of rain fell in 30 hours on the northeast side of Kauai leading to 10 ft of floodwaters in the streams between Kilauea and Anahola. The Hanalei River, which most directly drains the wettest region of Mt. Waialeale, overflows its banks at the coast nearly every year. Some years are considerably more damaging than others, for example, November 1955, January 1956, April 1994, and September 1996. In September of 1996 for instance, 9 inches of rain were recorded in 12 hours along the coast, and an uncertain amount fell in the uplands. This event led to flooding of Hanalei town and temporary closure of the Hanalei Bridge, the residents' sole access to the rest of the island. In the western portion of Kauai, the flooding hazard is primarily due to overland flows, especially after storms. Waimea River, for example, has a long record of flooding dating back to 1916 and includes numerous occasions where its channels overflowed after storm-fed precipitation in Waimea Canyon above. The challenge to mitigating the hazard due to stream flooding is in large part one of obtaining adequate warning in the case of flash floods and in improved planning of developments in areas of known flood history.

Where have high waves been recorded on Maui?

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High waves can damage life and property, even inundate far inland. Because of Hawaii's isolation, and the lack of inhabited islands north of Kauai, the magnitude and threat of high waves from north swell is often only recognized as the waves crash upon Kauai's shores. New technologies, including offshore wave sensors, are helping to provide adequate warning to approaching high waves with damaging potential. The largest wave events occurred on the north shore due to strong storms in the north Pacific (e.g., December 1985, February 1993, November 1996, and January 1998). They were associated with beach erosion and overwash of coastal property and, in the case of the November 1996 event, 20-25 foot waves and a high tide swept a rental home off of its foundation. The west shore on average sees waves of 15-20 feet each year, but occasionally there are waves as large as 40 feet (e.g., February 1986). Wave heights of 8-12 feet occasionally reach the south and southwest shore. Hurricanes have generated the highest wave heights along the south and east-facing shores. Waves ranging 20-30 feet were associated with Hurricanes Nina (1957), Iwa (1982), and Iniki (1992) along the south coast near Poipu. Run up of ~29 feet above sea level was recorded during Hurricane Iniki, which left a debris line more than 800 feet inland of the shoreline. Waves as high as 15-20 feet were reported along Kauai's east shores during Hurricanes Iwa and Iniki.