environmental geophysics for coastal management€¦ · environmental geophysics for coastal...

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

Paul.Donaldson@bmt.global.com

Tel: (02) 4940 8882

Brisbane, Sydney, Newcastle,

Melbourne, Perth

www.bmt.org