11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 15: Progress in Understanding the Hydrodynamics of Coral Reef Systems
15.523
Island-Scale Circulation Patterns Around Moorea, French Polynesia
James LEICHTER* 1
1 Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA
A 2.5 year record of water column temperature and currents was collected at multiple
fore reef sites to study spatial and temporal patterns in physical forcing around the island
of Moorea. Dominant modes of variability were analyzed across a range of frequencies
from seasonal to daily time scales. At low frequencies variability was dominated by
seasonal temperature trends and seasonal patterns in mean and peak velocities among
shores. Daily mean temperatures varied from approximately 26 to 29 °C and peak
velocities ranged from approximately 30 to 50 cm s-1. Mesoscale oceanographic
processes associated with oceanic currents and possibly influenced by an island wake
generated by the neighboring island of Tahiti appear to dominate the observed variability.
Strong variability was also observed at scales of multiple days to weeks. At higher
frequencies, variability included diel patterns associated with daily warming and cooling
as well as fluctuations at scales of hours to minutes associated with thermocline
oscillations indicative of the impact of internal waves especially at deep (depth > 20 m)
sites on the fore reef slope. These processes across the range of studied frequencies have
significant implications for the delivery of nutrients and for larval transport and
recruitment in this system. The high frequency variability associated with internal waves
was itself variable at lower frequencies among seasons, pointing to modulation of forcing
by low frequency, large scale phenomena. The high frequency temperature patterns and
spatial variability among sites and across depths apparent in the in situ records was not
predictable from remotely sensed surface data. Thus, long term physical data collected in
situ, continuously, and at high frequencies are necessary to characterize oceanographic
forcing in this oceanic reef system and to measure effects at annual to climate scales.
15.524
Laboratory And Field Experiments Of Waves And Water Levels Over Fringing
Reefs in Guam And Hawaii
Zeki DEMIRBILEK* 1 , Mark MERRIFIELD 2 , Okey NWOGU 3
1 US Army Corps of Engineers, Engineer R&D Center (ERDC-CHL), Vicksburg, MS,
2 SOEST, University of Hawaii, Honolulu, HI, 3 Naval Arch. and Marine Engineering,
University of Michigan, Ann Arbor, MI
The US Army Corps of Engineers has partnered with the National Data Buoy Center, The
University of Hawaii (UH), and CDIP of the Scripps Institution of Oceanography, to
measure wave and water level, and meteorological conditions on the fringing reefs of
islands of Oahu and Guam. The goal is to determine protective role of fringing coral reefs
on inundation of exposed coastlines for the design of Pacific island coastal infrastructure,
and protection of coastal residents and their property. A CDIP directional wave buoy was
deployed on the SE coast of Guam on the steep shelf break offshore of the fringing reef.
A directional wave buoy was deployed by UH/CDIP seaward of reef on the NE side of
Oahu. The UH deployed a bottom mounted instrumentation packages on the fore and mid
reef of a site on the NE shore of Oahu near Kahuku, and a cross-shore instrument transect
on the SE side of Guam near Ipan. Real time data at these sites are analyzed to calculate
spatial variation in water level and waves over fringing reefs. Data shed light into poorly
understood reef processes such as wave setup, wave-induced ponding, wind-forced wave
uprush, and wave runup. Study plans, logistics, experience with instrumentation, and
different field measurements obtained over reefs are discussed with samples of measured
raw and analyzed data.
Part two of this presentation describes a laboratory study conducted at the University of
Michigan (UM) wind-flume to provide data for waves, winds, wave setup and wave
runup over a scaled (1:64) fringing reef of Guam at Ipan modeled in these experiments.
A large number of tests were performed at four water levels with only waves or winds,
and both. A unique data set for fringing reefs is established for research and engineering
analysis of reefs.
15.525
Reef Rip Current Generated By Tide And Wave During Summer Season: Field Observation
Conducted in Yoshiwara Coast, Ishigakijima, Okinawa, Japan
Mario DE LEON* 1 , Ryuichiro NISHI 2 , Fumio KUMASAKA 3 , Tsuyoshi TAKAESU 4 , Ryosuke
KITAMURA 5
1 Graduate School of Science and Engineering, Kagoshima University, Kagoshima, Japan, 2 Faculty of
Fisheries, Kagoshima University, Kagoshima, Japan, 3 Japan Hydrographic Association, Tokyo, Japan,
4 Japan Coast Guard, Tokyo, Japan, 5 Department of Ocean Civil Engineering, Kagoshima University,
Kagoshima, Japan
In 2004 and 2005, five drowning accidents in Ishigakijima, Okinawa were documented by
Japan Coast Guard and local people and were found out to be caused by a strong offshore
current in coral reef. The strong seaward current is commonly known by the local people in
Okinawa as “reef current”. However, in this paper, the researchers define offshore current in
coral reef as “reef rip current”. Thus, a reef rip current study was conducted to determine the
location and time of strong offshore current. A nearshore hydrodynamic project which consists
of field observation was then carried out in Yoshiwara Coast in two phases; Phase 1 was
conducted during normal (tide dominated) condition and Phase 2 during storm (wave
dominated) condition. The project was implemented during summer season from June 25 to
July 25, 2006, the period during which the drowning accidents occurred. Wave gages, electronic
current meters, ADCP, tide gages, and thermometer were installed in reef lagoon, on reef flat,
edge and gap. In addition, GPS floats and fluorescent dye experiment were performed. An
anemometer was also set up on the dry beach. Water level, wave height, wave period, current
and wind speed and direction were measured for both tide and wave dominated conditions. In
this study, a strong reef rip current was revealed at the reef gap during ebb tide with maximum
average velocity at 1.2 m/s (2.4 knots) during normal condition. This velocity definitely has an
impact on the safety of swimmers, snorkelers, and scuba divers. Therefore, understanding the
mechanism, location and time of occurrence of strong reef rip current will definitely lead to
reduction of drowning accidents which is the ultimate goal of this project.
15.526
Spatial differences of the linear extension of Pocillopora damicornis in Polhena reef of
Southern Sri Lanka
Wickrama Arachchige UPASANTA KUMARA* 1 , Terney PRADEEP KUMARA P.B. 1 ,
Cumaranatunge P.R.T. 1
1 University of Ruhuna, Matara, Sri Lanka
Near shore patchy reefs located at the leeward side of the fringing reef in Polhena at Southern
coastal belt of Sri Lanka were surveyed in 2005. This study was carried out on a patchy reef
considering three slopes of the reef front, side and back and identified as sites. Three locations
were selected in each site as surface, bottom and middle considering the depth. Pocillopora
damicornis colonies were selected for diameter extension studies.
Mean, standard deviation and one–way ANOVA was used during the statistical analysis.
Multiple comparisons were done using least significant different (LSD) for light intensity and
sediment volume. The physico-chemical parameters of water observed were 28.06±1.140C for
temperature, 8.78±0.40mgL-1for DO, 1.40±0.32 mgL-1for BOD, 31.91±3.49ppt for salinity,
8.12±0.40for pH, and 1.01±0.61mgL-1for reactive phosphate, 5.78±2.37NTU for turbidity,
49.17±1.89Lux for light intensity and 90.08±39.65mL for sediment volume respectively. It was
observed that the mean difference of light intensity and sediment volume between each location
were significantly different. The highest sediment volume and the lowest diameter extensions
(0.055±0.01mm day-1) of coral colonies were observed at back bottom location. The highest
value for diameter extension (0.22±0.01mm day-1) was observed at front surface location.
ANOVA showed a significant difference of the diameter extension of P. damicornis between
locations and sites. Diameter extension was significantly low at the back bottom location
showing a significant negative correlation with increased sedimentation rate (7897.26gm-2 day-
1).
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