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What
are my risks?
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 Hawaii 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 Hawaii County?
 Click
to enlarge
According
to the data from the last 50 years, on average a damaging
flood event occurs on the Big Island every 2 years. During
this past 50 years, however, the threat due to stream
flooding has increased dramatically because of the risk
taken to develop extensively in flood prone areas. Flooding
along the wet, windward side of the island is expected
due to high annual rainfall (300 inches on the slopes
of Mauna Kea above Hilo). 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. The latest
severe flooding occurred in November
2000. The Kohala Coast has had a long and active history
of flooding largely due to flash flooding and intense
storms. During the last 3 years, the South Kohala and
Waikaloa areas have experienced intense flash flooding
that has caused considerable damage. Kilauea and Hualalai
volcanoes are located in more arid regions but occasionally
do receive intense rainfall that causes flash floods downslope.
Annual rainfall ranges between to below 10 and 20 inches
in the arid regions of Kawaihae and South Point. The young
lavas that comprise the coastal terraces of Mauna Loa,
Kilauea, and portions of Hualalai, are very porous. Often
heavy precipitation simply infiltrates into the rock and
flows toward the sea in underground streams. As a result,
stream flooding is generally less of a hazard on the younger
coastlines. Flash floods, however, do happen on the slopes
of Kilauea, Hualalai, and Mauna Loa. During these times
of intense rainfall, overland runoff will occur.
Where
have high waves been recorded in Hawaii County?
 Click
to enlarge
On the big island, high waves (10-20 feet) arrive from
north swell each winter. Occasional extreme wave events
do occur. The enormous north swells of February 1993 and
January 1998 brought 20-30 foot waves to the north facing
shores. Overwash of the Hilo breakwater and flooding of
the coastal roads near Hilo, caused damage in November
1996 and January 1998. The summer south swell generally
ranges 4-6 feet. Significant south swells also occur,
such as in July 1986 and June 1995, producing 8-12 foot
surf along southern shores. Alii Drive in Kailua town,
for example, is located particularly close to the ocean
in many places and suffers periodic overwash. High waves
of 6-8 feet can be produced by well-developed trade wind
swell, but usually trade wind waves are 2-4 feet. Tropical
storms and hurricanes bring damaging high waves of 10-30
feet to any and all shorelines.
November
200 Floods on the Big Island
Homes
were flooded, roads closed, and emergency shelters filled
as families flocked to find help during the floods that
affected the Big Island from October 28-November 3, 2000.
According to the National Weather Service, 26.22 inches
fell at Hilo airport in 24-hours on November 1,200. The
previous record was 22.3 inches on February. 19-20 in
1979. Damage on the Big Island was estimated to be $20
million. Civil Defense Deputy Bruce Butts said 77 businesses
and as many as 300 homes were damaged. At Pahala in the
Kau District, two bridges on the Hawaii Belt Road were
severely damaged.
On
November 3, Governor Cayetano declared the islands of
Hawaii and Maui a disaster area, which authorizes use
of major disaster fund, relocation and rehabilitation,
housing relief, commercial and personal loan program,
and relief to farmers.
On November 9, President Clinton declared Hawaii County
a federal disaster area, which authorized federal assistance.
More
than 1,131 Big Island flood victims have registered for
assistance through FEMA's toll-free Teleregistration number
as of November 30, 2000. The US Small Business Administration
(SBA) has approved $2,210,000.00 in low interest disaster
loans. For more information on Federal disaster recovery
on the Big Island, click
here.
Source:
Fletcher, Charles, Eric Grossman, Bruce Richmond. Atlas
of Natural Hazards in the Hawaiian Coastal Zone. 2000. |
