Land and Water Link
November 2003
The Science behind the Western
Port Bay Sediment Study
How did CSIRO scientists detect where the mud originated, how much there
is, why it ended up in the bay and how it is redistributed?
The first phase of the team’s investigation involved understanding
the dynamics of sediment transport and accumulation within the bay itself.
This required some novel research to determine:
- particle residence times in the water column
- sediment accumulation rates in different parts of the bay
- particle size distribution throughout the bay (conducted with the
Victorian EPA)
- radionuclide sediment-tracing – to link the sediment in different
parts of the bay to the erosion source and the different rivers in the
catchment.
The second phase involved moving up into the Western Port Bay catchment
to use a sophisticated landscape erosion model (SedNet)
that was initially developed for the National
Land and Water Resources Audit. This model used Western Port soils,
land use, rainfall, landcover, stream network and topographic data to
calculate how much mud and sand was eroding from the surrounding catchments
of the bay. It also showed where the sediments were coming from and whether
it was from hillslopes, gullies or channels. This powerful tool ranks
the catchments in terms of their mud inputs to the bay.
The third phase entailed a forensic exercise to match the ‘fingerprints’
of the mud from the different rivers flowing into the bay with those of
the muds in the bay. This was done by the CSIRO team with significant
on-ground assistance from the Melbourne
Water Corporation. This also showed the amount of mixing between bay
muds from the different rivers.
CSIRO contact:
Dr Peter Wallbrink
Ph: +61-2-6246 5823
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