ÔEHUKAI AREA DESCRIPTION
The ÔEhukai shoreline study area (transects 0 -117) is on
the north shore of Oʻahu and is the site of world-famous big wave surf
breaks including Rock Piles, Pipeline, and Rocky Point. ÔEhukai is the southern
portion of a continuous (4 mi long) beach composed of carbonate sand and
characterized by occasional outcrops of limestone and basalt. The area is
exposed to swells from the north Pacific in winter months and easterly
tradewind waves year-round.
Large winter swell causes dramatic changes in shoreline position
that largely recover the following season. Because of this, shoreline change
rates at ÔEhukai have high uncertainty due to short-term variations in
shoreline position. Despite wide variations in beach width, the vegetation line
has remained approximately stable since 1928. The high rate uncertainty and
stable vegetation line suggest that the shoreline has remained approximately
stable over the long-term or that seasonal variations are masking the true
long-term change. These characteristics may also reflect shoreline
stabilization by armoring that holds the vegetation line in place.
Much of the beach typically loses two-thirds of its
summer-time width in winter (see Jan 1971 and Feb 1988 shorelines), especially
from Rock Piles to Pipeline and at Rocky Point. Short-term erosion is a
significant hazard to beach-front homes, especially in
winter with run-up from large waves. A number of beach-front
homes were destroyed during a massive winter 1969 swell.
Previous studies by Hwang (1981) and Sea Engineering (1988)
found little net change in the vegetation line at
Pūpūkea-Paumalū 1949 -1988. Hwang found the water line varied by
over 100 feet in several locations.
For more information see: http://www.soest.hawaii.edu/asp/coasts/oahu/index.asp
1 Hwang, D. (1981) "Beach changes on Oʻahu as
revealed by aerial photographs", State of Hawaii, Department of Planning
and Economic Development.
2 Sea Engineering, Inc. (1988) ÒOʻahu shoreline studyÓ,
City and County of Honolulu, Department of Land Utilization.
Keywords:
Oʻahu; ÔEhukai Beach Park; Rock Piles; Pipeline; Rocky
Point