Summary and Conclusions
A set of typhoon-induced overtopping-frequency relationships was devel-
oped for a proposed project area along the north shore of Cabras Island, Apra
Harbor, Territory of Guam. Both existing and plan nearshore profiles were
considered. The objective was to assist the Honolulu District in evaluating
vulnerability of the commercial port road, container yard, and other port
facilities to wave overtopping of the existing seawall, which will remain in the
proposed project. Calculation of surge, wind and pressure field, and wave
characteristics were performed for 30 historical storms through application of
numerical models. Wave-induced setup, runup, and overtopping rates were
calculated at 15 profile locations specified by the Honolulu District nearshore
surveys in the project area.
A similar analysis was conducted for the south shore of Cabras Island, along
existing and potential commercial dock areas, to evaluate exposure to storm
events on the harbor side. Stage-frequency relationships were developed.
The circulation model ADCIRC was applied for calculation of storm surge
in the study area. Model calculations compared well to NOS tide and storm surge
data for Apra Harbor. For storm surge calculation, ADCIRC applied wind and
pressure fields calculated by the PBL model as the atmospheric forcing.
The PBL model was applied for simulation of storms whose path brought the
storm center within a 370-km (200-mile) radius of Guam and Rota. Historical
data from the storms were input into the PBL model for calculation of wind and
pressure fields. Atmospheric fields calculated by the PBL model were applied as
forcing for the circulation and wave models.
Deepwater wave heights, periods, and directions for each storm were calcu-
lated by application of the wave model WISWAVE. These deepwater waves
were transformed along the north shore of Cabras Island by application of the
wave-transformation model WAVTRAN.
Storm surge (wind- and atmospheric pressure-induced) was simulated for
30 historical storms and referenced to mean sea level. Guam is a volcanic cone
with steep sides. Shallow shelf areas do not exist around the island, so the storm
surge does not build appreciably near shore, as on the east coast of the United
States. Consequently, the storm surge (without consideration of waves) is
generally small and contributes only a small amount to coastal inundation during
Summary and Conclusions