Abstract
Introduction
Data
GIS Analysis
Results and Conclusions
Acknowledgments
References
External Links

TABLES
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FIGURES
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INTRODUCTION

Pearl and Honolulu Harbors, on the south coast of the island of Oahu, Hawaii, are dredged intermittently to maintain navigability for commercial and strategic purposes. These dredged materials have been disposed of just offshore in Mamala Bay for more than a hundred years. Since 1993, the U.S. Geological Survey (USGS), U.S. Army Corps of Engineers (USACE), and the U.S. Environmental Protection Agency have studied the dredged materials and any associated contaminants for their impact on the marine environment (Hampton and others, 1995; Torresan and others, 1995, Torresan and others, 1996).

Mamala Bay consists of a narrow insular shelf bounded by a steep escarpment that drops from 50 to 250 m water depth on the seaward edge of the shelf. This escarpment borders a broad southwest-trending trough that gently deepens from 250 to 650 m depth in the study area (Figure 1). USACE has designated three areas within Mamala Bay for the disposal of dredged material. The South Oahu site (SO in Figure 1) is the only currently active area. The examples in this report, however, focus on one of the previously active sites, Old Honolulu (OH in Figure 1). The distribution of the dredged material is easily identifiable in sidescan-sonar images (collected by the USGS) because of its high-backscatter signal (Figure 2). Deposits of the dredged material range from coalesced masses in the target disposal sites to solitary blobs on the fringes of the disposal areas where individual unloadings are evident as circular patches 25-150 m in diameter (Torresan and others, 1995).

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U.S. Department of the Interior, U.S. Geological Survey, Western Coastal and Marine Geology