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The Environmental Management Plan
(EMP) acts as the "rule book" for the Channel
Deepening Project. It sets out the environmental
safeguards required to protect bay assets during dredging,
including the management and monitoring of turbidity from
dredging works.
Turbidity is cloudiness caused by the suspension of
sediments in the water, through movement of material on the
sea floor.
Turbidity rises and falls naturally in Port Phillip Bay and
is an important part of its functions. Turbidity can be caused
by naturally occurring phenomena such as tide and weather
conditions. For instance following storm events the bay will
experience turbidity as water runs off from stormwater drains
and the Yarra River. Turbidity also occurs from man made
activities, such as propellers from ships and dredging.
When dredging, this turbidity is often seen as a plume
of cloudy water on the surface. While most of this plume is
contained close to the dredge vessel and can be discerned from
the water surrounding it, at times it can increase
in intensity and extent depending on factors such as
weather conditions and length of dredging operations in an
area.
Another source of turbidity, in the southern parts of the
bay, is created by tidal flow of water out of the bay, known
as ebb flows. The ebb flows are often swift and can
pick up loose silt, sand and weed from the seabed, during
certain times of the tidal cycle. The cloudiness caused by
this material are often seen in turbidity measurements.
To ensure turbidity remains within
defined limits set out in the EMP, and that key
bay assets, i.e. fish and seagrass, are protected, sophisticated
technology, such as an "environmental green
valve
", is used to keep the turbid plumes to a minimum and
continuous monitoring is undertaken.
These defined limits, or environmental limits, have
been set for turbidity at various locations around the bay.
The environmental limits have been established following
detailed scientific investigation into various assets in the
bay and potential impacts from turbidity. These limits
have then been set in accordance with the environmental
tolerances of the most sensitive assets in that particular
location. These include:
To ensure early detection, and importantly, to avoid
exceeding the environmental limits identified, a number of
"response levels" have also been established. If a response
level is reached an action will be taken to prevent
limit exceedences, for instance, the instigation of
additional monitoring, or taking management action to reduce
the intensity and/or extent of the plume.
In order to detect increases in turbidity continuous
monitoring is undertaken at fixed monitoring locations around
the bay. Turbidity measurements are taken every 12
seconds, then relayed to a computer server which can send
automatic notifications to the dredge vessel when turbidity
limits are approaching response levels and limits.
The results of turbidity monitoring (at conformance
locations and support sites) will be made
available on this page each week for the duration of
the project. The results cover the period from
the previous week (Sunday to Monday).
Further information on the turbidity monitoring program, including
environmental limits, can be found in the EMP and
turbidity detailed design available at this link.
For further information on the technology used to reduce
turbidity please follow this link.
To view archived weekly turbidity
monitoring results, please click here. |
