USACE Typhoon Wave Inundation Pilot Study

Study Description



1. Background

Pacific islands are prone to hazardous wave inundation in low-lying coastal areas during typhoons. Accurate prediction of typhoon waves, and the resulting wave inundation of exposed coastlines, is important for both the design of Pacific island coastal infrastructure and the protection of coastal residents and their property.

The US Congress has authorized the USACE to conduct a study of typhoon wave inundation in the western Pacific. The study goal is improved prediction of inundation events through a better understanding of the underlying physical processes.

The USACE has partnered with the National Data Buoy Center, The University of Hawaii, and Scripps Institution of Oceanography, to measure and model wave, water level, and meteorological conditions during large wave events on the islands of Oahu and Guam.




2. Program Plan

Two major components govern the understanding, prediction and characterization of wave inundation owing to major storm events such as hurricanes, typhoons and other large wave episodes in the Pacific.

The two governing components are:

1) Deep ocean conditions (waves and wind):

To test and improve existing deep ocean models, PILOT will conduct deep ocean measurements of wind and waves at an unsheltered location selected for exposure to the storm-track most important for the South Pacific region in general. This location, selected by the researchers who will be working this aspect of the problem, might be near or far from the island test sites.

2) Island Conditions (waves and water levels):

A) Island conditions, buoy measurements:

Deep ocean waves are transformed by propagation over complex island bathymetry (e.g. fringing reefs). Models for this transformation are initialized with deep ocean conditions just offshore of the island. One nearshore buoy has been deployed on the SE coast of Guam in a water depth of 200m, on the steep shelf break, offshore of the fringing reef. This buoy will establish an observational database of wave conditions near the field site.

B) Island conditions, bottom mounted instruments:

Guam has been chosen as an island test site because of the frequency of typhoon wave and wind driven events. It will be necessary to develop new experimental methods, and to extend existing models, to deal with extremely large waves on coasts with a fringing coral reef. For example, the longevity of armored cable (reliable on sandy bottoms) may be much reduced when deployed across coral table reefs. Deployment of a reliable big-wave system on Guam must be preceded by a serious development effort in a big wave and reef-type beach environment.

The University of Hawaii has considerable expertise with reef-mounted instrumentation, and will deploy and test the effectiveness and survivability of bottom mounted instrumentation packages in extreme wave conditions (waves larger than 3 meters) on the fore and mid reef of a site on the NE shore of Oahu.

Results of this trial will help design instrumentation fixtures and deployment methods for cross-reef transect water pressure and current measurements in the Guam PILOT study.

Logistical considerations dictate that such preliminary studies be conducted in Hawaii where field, technical and other support are readily available. Using Hawaii as an instrumentation test bed will significantly reduce the instrumentation development and deployment methodology costs for this study.




3. PILOT Study Field Measurement Milestones


Deep Water Wave and Wind Observations


+ New CDIP coastal directional wave buoy deployed seaward of reef on the SE side of Guam. [operational]

+ New NDBC offshore 3m directional buoy SE of the island of Guam. [2004]

+ New UH/CDIP coastal directional wave buoy deployed seaward of reef on the NE side of Oahu. [2004]


Nearshore Wave and Wind Observations


+ Cross-shore instrument transect on the NE side of Oahu near Kahuku. [2004]

+ Cross-shore instrument transect on the SE side of Guam near Ipan. [2005]




4. Experimental Products and Data Dissemination


Realtime Data


+ CDIP coastal directional wave buoy deployed seaward of reef on the SE side of Guam. [operational]

+ NDBC offshore moored buoy SE of the island of Guam. [2004]

+ CDIP/UH coastal directional wave buoy deployed seaward of reef on the NE side of Oahu. [2004]


Realtime Experimental Model Nowcasts and Forecasts


+ Nearshore wave nowcast for SE coast of Guam (initialized with CDIP Ipan Buoy). [operational]

+ Wave/Wind forecast for CDIP wave buoy deployed seaward of reef on the SE side of Guam. [operational]

+ Wave/Wind forecast for UH/CDIP wave buoy deployed on the NE side of Oahu. [operational]

+ Nearshore wave forecast for SE coast of Guam (initialized with deep water forecast). [2003]

+ Nearshore wave forecast for NE Oahu coast. [2003]

+ Nearshore wave inundation forecast for the SE coast of Guam. [2005]




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