Steve Watt - Sea Engineering, Inc.

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Monitoring harbor dredging and sedimentary
changes in coastal habitats of the Santa Cruz
Bight, California
Steve Watt - Sea Engineering, Inc. H. Gary Greene
Center for Habitat Studies, MLML
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Study Area

• Fine-grained dredging
• 2,300 m3
• 40 sand
• 60 silt clay

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• Two month monitoring program
• Benthic habitat characterizations
• Offshore sediment sampling and analysis
• Ground truth for seafloor imagery
• Grain-size changes over time
• Two geophysical surveys (in conjunction with SFML
  CSUMB)
• Before and after dredging 2 months apart
• Multibeam and backscatter imagery
• Benthic habitat comparisons
• Sediment shifts map
• Limitations - Future Improvements
• Questions?

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Ground truth Offshore sediment sampling (over 200
samples)
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Before dredging multibeam bathymetry
R/V MacGinitie (SFML CSUMB) 240 kHz Reson 8101
SeaBat TEI Isis Sonar data acquisition
Processed w/ CarisHIPS to 1 m cell-size
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Before dredging backscatter
R/V MacGinitie (SFML CSUMB) 240 kHz Reson 8101
SeaBat TEI Isis Sonar data acquisition
Processed w/ TEI Isis Sonar to 0.2 m cell-size
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Four habitat types (classification after Greene
et al., 1999)
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Before dredging habitat characterization
Habitat Characterization
Sediment filled scours and depression
Sediment covered outcrops/subcrops
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After dredging habitat characterization 2
months later
Habitat Characterization
Sediment filled scours and depressions
Sediment covered outcrops/subcrops
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Sediment shift example
Before Dredging rock outcrop
After Dredging rock outcrop at the same
geographic location
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Intersection and identification
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Sediment shifts map
Pt. Santa Cruz
Soquel Point
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Sediment shift area analysis
No habitat change
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• Considerations and limitations
• Same resolution and artificial shading angle
• Same interpreter at identical scales
• Quantifies area (m2) - Not volume (m3)
• No directional sediment transport component
• Changes are taking place in areas of no habitat
  change

• Future improvements
• Gridded cut/fill volume calculations at cm
  vertical scale (RTK positioning)
• Bridge the data gap between the beach and
  offshore (bathymetric LIDAR?)
• Incorporate sediment transport modeling into GIS
  framework (estimate sediment transport
  direction and magnitude)

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Any questions?