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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

Some of the seafloor of Mamala Bay has bedforms visible on the sonar mosaic (figure 4 and plate 1). Bedforms also appear on bottom photographs collected during the site designation studies (Chave and Miller 1977a, 1977b, 1978a; Neighbor Island Consultants, 1977; Tertra Tech, 1977; Goeggel; U.S. Environmental Protection Agency, 1980). The variety of bedforms common throughout the study area document active sediment movement, with the implied potential for the redistribution of dredged material beyond the original disposal site. Therefore, in addition to understanding local and regional ocean circulation patterns, it is critical that any study evaluate the nature and characteristics dredged materials at their source (the harbors) and at the disposal sites.

Environmental studies conducted to date show that the native seafloor sediment is primarily a muddy carbonate sand, with areas of outcrop, and carbonate rubble that includes shell, coral and limestone (Chave and Miller, 1977a, 1977b, 1978a, 1978b; Tetra Tech, 1977; and U.S. Environmental Protection Agency, 1980). Sediment sampling and bottom photography conducted during each phase of the 1977­1978 studies show that there is considerable variation in the composition of the seafloor in and around the disposal sites. Surficial sediment varies from primarily sand to sediment with substantial carbonate rubble (shell, coral and limestone), and the native seafloor sediment consists primarily of carbonate and basalt fragments that constitute about 90% and 10% of the sediment, respectively (Chave and Miller, 1977a, 1977b, 1978a; Neighbor Island Consultants, 1977; Tetra Tech, 1977; Goeggel, 1978; U.S. Environmental Protection Agency, 1980). The 1977­1978 site designation studies show that grain size distributions of sediment collected from the disposal sites during each phase of the study vary considerably from sample to sample, and range from sandy gravel to muddy sand. For example, Tetra Tech (1977) reports that pre­disposal sediment (Phase I) is poorly sorted, averaging 85% sand and 15% mud (silt and clay). Similarly, dredged material (Phase II) is also poorly sorted, but is substantially coarser, containing 49.3% pebbles, 13.8% granules and 36.9% sand (Tetra Tech, 1977). Tetra Tech (1977) reported that the grain size distributions of sediment collected after a disposal action varied considerably from sample to sample, and post­disposal (Phase III) studies samples lack mud, are poorly sorted, and vary from predominantly sand (about 80%) to predominantly gravel (about 75%).

Bottom photography conducted during the 1977­1978 dredging cycle also shows that anthropogenic debris litters the seafloor of Mamala Bay (Chave and Miller, 1977a, 1977b. 1978a, and 1978b; Tetra Tech 1977). Video and still photography collected during a USGS survey conducted in May 1994 (Torresan and others, 1994b) documents the debris to include military ordnance, barrels, a variety of canisters, tires, and lengths of wire rope.


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URL: https://pubs.usgs.gov/of/1995/of95-017/05seafloor.html
Maintained by: Michael Diggles
Author: Florence L. Wong
Last modified: May 27, 2005 (mfd)

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