The Territory of Guam is principally an island located in the western Pacific
Ocean at approximately 144.5 east longitude and 13.5 north latitude. Guam
lies north of Australia and northwest of New Zealand (Figure 1). Guam is one of
the Mariana Islands, an island group at the southern end of a volcanic ridge
stretching south from the Japanese island of Honshu. The Mariana Trench, a
deep rift in the ocean floor, wraps around Guam to the east and south.
The island of Guam is approximately 50 km (30 miles) long and 6 to 14 km
(4 to 8.5 miles) wide. It covers an area of 540 sq km (209 square miles). Most
coastal shelf and beach areas are narrow, with steep, rugged terrain inland of the
coast, as is typical for volcanic islands. Fringing coral reefs are common around
the island. Water depth over the reefs is very shallow and some reef areas are
exposed at low tide. Thus, the reefs provide a measure of natural protection from
damaging waves to coastal areas.
Guam's low-latitude location is favorable for tropical storm and typhoon
formation and passage. The island often experiences typhoon impacts and
occasionally a typhoon passes directly over the island. Typical typhoon impacts
include wind and rainfall damage to buildings, roads, and crops and coastal
damage due to high waves and water levels.
Apra Harbor, Guam's commercial port, is located on the west side of the
island. The harbor is well protected by a combination of natural features and
Glass Breakwater, a long man-made breakwater connecting into Cabras Island on
the shoreward end (Figure 2). Cabras Island is a narrow, east-west oriented
island which not only affords protection to the harbor, but also accommodates
many of the commercial port facilities.
Route 11, the port access road, runs along the north side of Cabras Island.
The container yard occupies most of the west-central part of Cabras Island
(Figure 3). In this area, the road is protected from the sea by a relatively low,
recurved concrete seawall fronted by a rubble-strewn beach. During storms,
waves can run up the beach, overtop the seawall, and cause disruption and
damage to the road and port facilities beyond the road. Potential damage during
intense storms is significant.