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Reconnaissance investigation characterizes the surficial
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morphology of the bay floor as revealed by side-scan sonar imaging
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and high-resolution bathymetry and deduces the general nature of
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sedimentation, bedload sediment transport directions, and areas of
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depostion versus erosion. Results should apply to current issues
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involving sedimentation, dredging, pollution, and the disposal of
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dredge spoils in the San Francisco Bay system and the highly
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developed urban areas that border it.
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Field work for this study was conducted using the USGS Water
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Resources Divsion Research Vessel Polaris. Side-scan sonar profiles
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were collected using a Klein system operated at a frequency of
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either 100 kHz (South Bay or 500 kHz (North Bay). This system is
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comprised of a graphic recorder and towfish that can be operated at
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varying frequencies and slant ranges. In general, slant ranges of
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100 m (200-m swath) or 150 m (300-m swath) were used for optimum
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resolution of bottom features on the bay floor. Towing speed
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averaged 7.4 km/hour, although this varied greatly with tidal current
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speed and direction as well as local wind regime. No attempt was
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made to acqurie overlapping side-scan sonar images.
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An Innerspace fathometer was used to acquire high resolution
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bathymetry. This system operated at a frequency of 200 kHz with a
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hull-mounted transducer. The bathymetry was not corrected for tidal
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elevation. Navigation was obatined with a shipboard Raytheon precision
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radar. Fixes were plotted every 5 min. and correspond to the event
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marks on the side-scan sonar and fathometer records.
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The floor of South and North San Francisco Bay is characterized by
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five surficial bottom types based on a reconnaissance survey using
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side-scan sonar and a fathometer. The five bottom types are
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1) furrows,
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2) lineations,
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3) sand waves,
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4) tonal patches,
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5) featureless.
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