Channel and Water Quality
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The concept of improving water quality in Lake Macquarie
through increased tidal flushing has been the subject
of numerous investigations over the past decade.
This research has identified a number of reasons that
make increasing the size of the Channel opening problematic.
Increasing the size of the channel opening is not only
unlikely to result in significant water quality improvements,
but there would also be side effects that would have
more serious social and environmental implications than
the ones it intended to fix.
Many people believe incorrectly that by increasing
the tidal flushing of Lake Macquarie, the issue of poor
water quality would be solved automatically. However,
because the Lake contains such a huge volume of water,
increasing the tidal exchange would have little impact
on water quality.
Studies have shown that even if the Lake entrance was
increased by 20% the impact on the tidal exchange would
only be 0.2%.
However, an increased tidal range between high and
low tide within the Lake itself would result and this
would cause significant problems such as flooding of
low-lying areas around the Lake foreshore, increased
channel bank erosion, possible destruction of seagrass
beds and increased exposure of mud flat areas at low
Any significant opening or enlarging of the Channel
will raise flood levels particularly when ocean levels
are high. The frequency of flooding in low-lying areas
such as Marks Point, Swansea Flats and Belmont South
would be increased.
Research has shown that the best way to improve water
quality is to stop sediments and nutrients from entering
the Lake via stormwater. The best way to achieve this
is to restore and mimic natural processes.
Supporting natural filtration systems like wetlands
and vegetated areas (especially around creek banks and
in drainage lines) is important as they remove contaminants
from stormwater to reduce the stress on the Lake.
The Project Management Committee has funded a number
of projects to ensure that stormwater entering the Lake
does not contain excessive sediments, nutrients and
other contaminants. These include the construction of
wetlands, sedimentation traps, vegetated drainage swales
and foreshore vegetation.
We are starting to see some early signs of improvement
in Lake health, although it is a long term task and
we still have a long way to go.