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Torresan, M.E., Hampton, M.A., Gowen, M.H., Barber, Jr., J.H., Zink, L.L., Chase, T.E., Wong, F.L., Gann, J.T., and Dartnell, P., 1995, Final report: acoustic mapping of dredged material disposal sites and deposits in Mamala Bay, Honolulu, Hawaii: U.S. Geological Survey Open-file Report 95-17.


Introduction 1, 2
  Study Area
  Previous Studies
  Seafloor Materials

K1-93 Survey
  Scope of Work
  Sidescan Sonar

  Sonar, 3.5kHz 1, 2, 3


  1   2   3   4   5
  6   7   8   9 10
11 12 13 14 15
16 17 18 19 20

Plate 1

Apx 1: Statistics 1
Apx 1: Statistics 2
Apx 2: Equipment 1
Apx 2: Equipment 2

References 1, 2, 3

Estuaries and continental shelves adjacent to metropolitan centers are a focus of increasing public concern owing to contamination from dredged material, pesticides, waste water, and other forms of pollution. Geological studies of a locally impacted marine environment can provide key information on the distribution, transport, and long-term fate of contaminants, because contaminants often accumulate with fine-grained sedimentary particles (Bothner, 1981; Anderson and others, 1988). Geological studies of the seafloor off major population centers allow investigators to understand the effects of anthropogenic stress on the environmental quality and biological health and productivity of these critical nearshore areas, thereby enabling marine policy makers to formulate sound decisions as to the use of the urban ocean (Bothner, 1981; Anderson and others, 1988; Butman and others, 1989; Karl, 1992; Karl and others, 1992; Schwab and Rodriguez, 1992; Hostettler and others, 1993; Hurst, 1993; Parmenter and Bothner, 1993; Shea and Kelley, 1993; Anderson, 1994; Bothner and others, 1994). Specifically, acoustic mapping of the seafloor is a proven geological technique for mapping and assessing the distribution of anthropogenic inputs, including dredged material and hazardous waste disposal in urban ocean settings (Carey and Fredette, 1993; Murray and others, 1993; Schwab and Rodriguez, 1993; Torresan and others, 1993a 1993b; Karl and others, 1994; Chavez and Karl, in press).

Mamala Bay is the embayment located between Diamond Head on the east and Barbers Point on the west, along the south coast of Oahu, and is adjacent to the city of Honolulu, Hawaii (figures 1-6). The geological characteristics of the seafloor and near-surface substrate play a fundamental role in determining the exposure of fauna in Mamala Bay to pollution and other forms of anthropogenic stress. Dredged material disposal, run off, and waste water outfalls can disperse contaminants in Mamala Bay, and many of these contaminants can adhere to fine sedimentary particles that concentrate in depositional sites (Bothner, 1981). The infaunal and epifaunal communities can then be exposed to the contaminants, and since the benthic communities are near the base of the food chain they can transfer a pathogenic load to indigenous aquatic species (Long and Morgan, 1990; Roesijadi and others, 1992).

The Hawaiian Islands have five offshore disposal sites that receive dredged material; Port Allen and Nawiliwili off of southern Kauai, South Oahu offshore of Honolulu, Kahului off of northeast Maui, and Hilo off the southeast coast of Hawaii (figure 1). All Hawaiian deep-draft harbors are dredged in 5- to 10-year maintenance cycles, or on an as-needed basis, and factors including high runoff may necessitate changes in dredging frequency. Dredging and disposal schedules for Mamala Bay show that Pearl Harbor is dredged on an as-needed basis while Honolulu Harbor is dredged at five-year intervals.


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Author: Florence L. Wong
Last modified: May 27, 2005 (mfd)

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