The Territory of American Samoa typically experiences a deepwater wave
climate with significant heights ranging from 1 to 3 m (3 to 10 ft) and peak wave
periods of 5 to 9 sec. Peak periods of up to 25 sec can occur, but available
information indicates that the longer peak periods appear infrequently. The wave
climate varies little with season and is relatively consistent from year to year.
The low-latitude location of the Territory of American Samoa is favorable
for tropical storm and hurricane formation and passage. Historically, the area has
experienced infrequent, but devastating, major hurricanes. During the atypical
period 1987 through 1991, three intense hurricanes severely impacted the area.
Storm damage included: village damage and destruction, road washout, harbor
destruction, and crop damage (Sea Engineering, Inc. and Belt Collins Hawaii
1994). A coastal inundation study was initiated to calculate hurricane stage-
frequency hydrographs for five of the seven islands (Militello, Scheffner, and
Thompson 2002).
Extreme wave conditions for Western Samoa were estimated by Kinhill,
Riedel & Byrne (1992) in relation to coastal revetment design. Although the
study was not aimed at south-facing coasts, these estimates have some relevance
for the Territory of American Samoa. Hurricanes and other tropical storms were
considered separately from the general wave climate. For the general wave
climate, significant height with 5-year return period was 3.1 m (10.2 ft), increase-
ing to 3.5 m (11.5 ft) for 50-year return period. When hurricanes and other
tropical storms were included in the design wave estimate, the 5-year significant
height was 3.75 m (12.3 ft) and the 50-year height was 7.3 m (23.9 ft). The study
results suggest that hurricanes and tropical storms are a minor concern over a
typical period of several years, but a major concern over long return periods.
The astronomical tide range at Pago Pago Harbor between mean high water
and mean low water is 0.8 m (2.5 ft). Extreme low water extends 0.8 m (2.5 ft)
below mean low water.
The present harbor facilities on Tutuila are expected to be insufficient to
meet future needs of the Territory of American Samoa. The U.S. Army Engineer
District, Honolulu (HED), is investigating possible new sites for dock facilities
on Tutuila. The present study objective, in support of HED's effort, is to analyze
wave response at alternative sites under preliminary consideration. All sites
included in this study are within the Pago Pago Harbor embayment.
Study Approach
The study described in this report was performed by the U.S. Army Engineer
Research and Development Center (ERDC), Coastal and Hydraulics Laboratory
(CHL), in support of HED planning for harbor needs on Tutuila. The approach
consisted of the following components:
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Chapter 1 Introduction
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