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3 Summary 
Ofu Harbor is subjected to severe storm conditions in the South Pacific, 
including tropical storms, hurricanes, and cyclones. The original revetment and 
mole used for harbor protection was damaged several times, and in 1991, was 
almost completely destroyed. As a result, a new breakwater was constructed in 
1994 which included the use of 4,080-kg (4.5-ton) concrete tribar armor units. 
Various concrete underlayer units were also used in the structure, since local 
stone was not available. No sound, quantifiable data relative to the movement or 
positions of the concrete armor units had been obtained for the structure prior to 
this study. 
Under the current Periodic Inspections work unit of the Monitoring Com- 
pleted Navigation Projects Program, data from limited ground-based surveys, 
aerial photography, and photogrammetric analysis were obtained to establish 
base level conditions for the Ofu Harbor breakwater. Logistical problems were 
encountered attempting to obtain low-altitude aerial photography in this remote 
location. The planned low-altitude photography was not obtained; however, 
oblique images taken from a fixed-wing aircraft were analyzed using convergent 
photogrammetric techniques, which proved to be acceptable. Accuracy of the 
photogrammetric analysis was validated and defined through comparison of 
ground and aerial survey data on control points and targets established on the 
structure. The procedure utilized the oblique images, a stereoplotter, and 
Intergraph-based software to analyze the entire above-water armor field and 
quantify armor positions. A detailed walking survey of the structure conducted 
during the effort resulted in a well-documented data set that can be compared to 
subsequent surveys. 
Now that base (control) conditions have been defined at a point in time and a 
methodology has been developed to closely compare subsequent years of data 
for the Ofu Harbor breakwater, the site will be revisited in the future under the 
Periodic Inspections work unit to gather data by which assessments can be made 
on the long-term response of the structure to its environment. The insight 
gathered from these efforts will allow engineers to decide, based on sound data, 
whether or not closer surveillance and/or repair of the structure might be 
required to reduce its chances of failing catastrophically. Also, the periodic 
inspection methods developed and validated for this structure may be used to 
gain insight into other Corps structures. 
Chapter 3 Summary 
