Embed Size (px)
Citation preview
Environmental Geophysics for Coastal Management
Paul Donaldson1, Dr Douglas Bergersen2, Dr Matthew Barnes3, Conor Jones3
Coast To Coast, Hobart
April 2018
Image: Google Earth
1BMT Newcastle, Australia, 2Acoustic Imaging, Cooroy, Australia, 3BMT Brisbane, Australia
Outline
Overview
• What is environmental geophysics?
• Geophysical methods for coastal
management
• Coastal management applications
• Case study examples
Aim
• Provide a practical intro to the uses,
advantages and limitations of
environmental geophysics
[image to go here]
What is Environmental Geophysics?
Image: NOAA
Geophysical Methods for Coastal Management
Image: USGS
Marine Acoustics MethodsMagnetometryResistivity
Seismic (various onshore methods)Electro-Magnetics (EM)Ground Penetrating Radar (GPR)
Image: GBG MAPS Image: GBG MAPS
Image: Edge Tech
Image: USGS
Image: BMT
Image: BMT
Geophysical Outputs for Coastal Management
Image: GBG MAPS
Image: USGS
Marine Acoustics MethodsMagnetometryResistivity
Seismic (various onshore methods)Electro-Magnetics (EM)Ground Penetrating Radar (GPR)
Image: GSC
Image: USGS Image: USGS
Image: Acoustic Imaging
Image: GBG MAPS
Image: Donaldson (2010)
Applications
Coastal Management Applications
• Geomorphology
• Geotechnical
• Environmental
• Asset Management
Workflow
Physical
Investigation
Geophysics
Method #1
Geophysics
Method #2
Problem /
Knowledge Gap
Geophysics
Method #4
Geophysics
Method #3
Scope Survey
Field
Investigation
Investigation
OutcomeDo Management!
?
?
?
?
?
?
?
Scenario #1a
Physical
Investigation
Ground
Penetrating
Radar
Geophysics
Method #2
Problem /
Knowledge Gap
Scope Survey
Field
Investigation
Investigation
Outcome
Do Management!
(Hazards, Risk,
Options, Action)Geophysics
Method #4
Geophysics
Method #3
Coastal Erosion Risk
• Geological / geotechnical
unknowns
1
Scenario #1b
Problem /
Knowledge Gap
Geophysics
Method #3
Scope Survey
Field
Investigation
Investigation
Outcome
Do Management!
(Hazards, Risk,
Options, Action)Geophysics
Method #4
Physical
Investigation
Ground
Penetrating
Radar
Seismic
(MASW)
Coastal Erosion Risk
• Geological / geotechnical
unknowns
1
2
Scenario #2
Geophysics
Method #1
Geophysics
Method #2
Problem /
Knowledge Gap
Scope Survey
Field
Investigation
Investigation
Outcome
Do Management!
(EIA, Approvals,
Action) Multibeam
Bathymetry
Backscatter
Acoustic
Sub Bottom
Profiling
Marine
Sediment
Coring
Beach Nourishment
Feasibility
• Sand source opportunities?
• Sand source constraints?
2
1
1
• Original hazard study: applied simple
engineering methods; did not consider
varying geological conditions
• Community did not accept report / maps
BMT Study
• GPR survey presence & depth of bedrock
• GPR correlated with existing boreholes
• Coastal geomorphology interpretation
• Map sand/rock interface (bedrock control)
• Geotechnical adjustment of hazard lines
GPR Study of Coastal Geology and Erosion Hazards
Blueys and Boomerang Beaches
GPR Coastal Geology Results
Bedrock Control MapOriginal Hazard Lines
Bedrock Revised Lines
• SEMP: Beach nourishment preferred
option
• Limited options: environmental and
legislative constraints
BMT Study
• Offshore sand source one of four options
• Bathymetry and sub-bottom profiling
• ‘Basement’ reflection used to infer sand
layer thickness (>9m in areas)
• Results mapped – significant deposits in S
Sub-Bottom Profile Survey of Offshore Sediments
Sunshine Coast Sand Sourcing Study
GPR Survey of Buried Historic Seawalls
Gold Coast Beaches
• 1960/70’s seawalls (A-line) buried below
the ground – location & condition unknown
• Council seeking engineering certification
BMT Study
• Many GPR profiles collected - detailed
processing and interpretation
• Engineering parameters imaged
(crest location & height, slope, width)
• Results enabled certification of some walls
and guided maintenance elsewhereHistoric Seawall Design (1967)
GPR Seawall Profiles
GPR Analysis and Results
Key Messages
Environmental Geophysics for Coastal Management
• Variety of non-destructive methods, each with a suite
of possibilities, advantages and limitations
• Can help resolve critical knowledge gaps regarding:
• subsurface conditions
• buried infrastructure
• Can provide alternative to (or complement) intrusive
investigation (e.g. boreholes, excavation)
• Can provide considerable cost saving
• Many coastal management applications!
Thank you
Paul Donaldson
Senior Coastal Scientist
Tel: (02) 4940 8882
Brisbane, Sydney, Newcastle,
Melbourne, Perth
www.bmt.org
