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Day 5: Dredging Engineering (Sediment transport (Wave boundary layer…
Day 5: Dredging Engineering
Guidelines for dredging and environmental studies in Australia
Permitting process
Sea Dumping Permit Process
Refer to lecture slides
Assessment framework
Sediment quality assessment
Phase 2: Sampling and analysis of sediments
Phase 3: Elutriate and bioavailability testubg. Examining of the bio availability of contaminants
Phase 1: Evaluate existing information
Phase 4: Toxicity and bioaccumulation testing
Phase 5:
Weight of evidence assessment
Lines of evidence can include sediment chemistry
Lines of evidence can include toxicity
Lines of evidence can include bioaccumulation
Lines of evidence can include ecology
Site assessment
Alternatives to ocean disposal
Once its destroyed, reduced, can the materials have beenficial use?
IF they have no beneficial use, can they be treated to destroy or reduce or remove hazardous constituents?
What are the comparative risks to the environment and human health of the alternatives?
Can the materials be beneficial? or recycled?
Costs and benefits of the alternatives/
NEXT: Waste prevention audit needs to be undertaken to identify opportunities for preventing or minimising pollution and any sediment contamination.
Management and monitoring
Subsurface investigations case study
Legislative framework
NAGD framework
Evaluate alternatives to ocean disposal
Assess loading and disposal sites
Assess potential impacts on marine environment and other users
Determining management and monitoring requirements
3 commonwealth acts to
ocean disposal
EPBC Act
Great Barrier Reef Marine Park Act 1975
Sea Dumping Act
Guidelines objective - based on NAGD (2009)
Prevent marine pollution
Provide guidance on assessment and permitting process
Help preserve marine ecosystems
There's international agreements like London Protocol.
State Government
Sea dumping act does not apply where dumping is to occur entirely in internal waters (3Nm) such as rivers, port phillip bay.
Sediment transport
Wave boundary layer =Waves flow are not uni-directional (oscillatory) Wave breaking will mobilise sediments
Shear stress and boundary layer thickness
Concept of wave boundary layer
Boundary layer in turbulent flow
Wave friction coefficient
Mechanisms of sediment transport
Coastal processes
Sea floor eroded nearshore by action of waves and wave breaking which generates alot of turbulence
Sediment is transported away by reflected long waves = infra gravity waves
Sediment reaches the port facilities eventually due to tidal currents
Cross-shore sediment transport and beach profile, generally grain size varies between 0.1 and 2mm.
Development of coastal profile
Berms
Longshore bars
Coastal profile
Coarser = steeper beach slope
fine = shallow beach slope
Slope varies between 1-10%
Sediment transport in open channels
Sediment properties
Grain size distribution found via sieve analysis
Settling velocity = omega_s
Density
Threshold of sediment movement
Steady uniform flow in open channels
Types of flow
Laminar (low velocity) - usually at the bed
Turbulent (high velocity)
Expect turbulent boundary layer >>> laminar boundary layer
Eddy viscosity = Measure of magnitude shear stress
Classification of flow layer
Velocity distribution
Chezy coefficient = proposed an empirical formula for average velocity of steady uniform channel flow
D90 = 90% of the size of the particles would be smaller than the value of 0.15mm
Drag and lift
Longshore sediment transport
Longshore transport calculation - use CERC
Energy flux = how quickly waves and energy are moving
Coastal structures
Erosion
Accretion =growth or increase by the gradual accumulation of additional layers or matter.
Groins used to stabilise beach.