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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.
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