Day 5: Dredging Engineering

Guidelines for dredging and environmental studies in Australia

Sediment transport

Wave boundary layer =Waves flow are not uni-directional (oscillatory) Wave breaking will mobilise sediments

Cross-shore sediment transport and beach profile, generally grain size varies between 0.1 and 2mm.

Sediment transport in open channels

Steady uniform flow in open channels

Longshore sediment transport

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

Sediment properties

Grain size distribution found via sieve analysis

Settling velocity = omega_s

Density

Threshold of sediment movement

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

  1. 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

Development of coastal profile

Berms

Longshore bars

Coastal profile

Coarser = steeper beach slope

fine = shallow beach slope

Slope varies between 1-10%

Longshore transport calculation - use CERC

click to edit

Coastal structures

Erosion

Accretion =growth or increase by the gradual accumulation of additional layers or matter.

Groins used to stabilise beach.

Energy flux = how quickly waves and energy are moving

Permitting process

Assessment framework

Legislative framework

Guidelines objective - based on NAGD (2009)

Sediment quality assessment

Site assessment

Alternatives to ocean disposal

Management and monitoring

Subsurface investigations case study

Prevent marine pollution

Provide guidance on assessment and permitting process

Help preserve marine ecosystems

There's international agreements like London Protocol.

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

State Government

Sea dumping act does not apply where dumping is to occur entirely in internal waters (3Nm) such as rivers, port phillip bay.

Sea Dumping Permit Process

Refer to lecture slides

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.

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