The proposed channel would be subject to sufficiently high velocities
during flooding to scour its banks. Therefore, it is assumed that the
banks will be protected with rock and be sloped.
Sweeneys and Saltwater Creek floodgate levees are raised Based on
experience elsewhere, the environmental impacts of the excavation on a
wide range of environmental, social and cultural issues would need to be
carefully assessed prior to approval being granted. The benefits of the
channel would also need to be fully justified.
The analysis indicates that an acceptable return on the initial outlay
would be achieved if the channel scoured within 20 to 30 years and no rock
protection is required. Without having undertaken specific geotechnical or
hydraulic investigations into the likelihood of a similar channel forming
naturally, it is difficult to make a definitive statement on the viability
of such a proposal. However, based on anecdotal evidence of scouring both
prior to and after the construction of Carello's levee, it is considered
unlikely that a channel of this size would form naturally over a 20 to 30
The raising of the levees is not expected to have any environmental
impacts given that the floodgates are already in place. The increase in
floodgate levee height would bring a positive social benefit by increasing
the warning time to residents and business protected by the levees.
However, it is likely that the fall of the floodwaters in the town area
will be slightly retarded by the increased height on the levees.
It was assumed that the levee would be concrete in front of waterfront
properties and earth in other areas.
1. dredge to stockpile and sell in Cairns;
2. dredge to stockpile and sell locally;
3. dredge to spoil
However, anecdotal evidence obtained during discussions with long-term
observers of the river would suggest that the sediment load in the river
is relatively high. If this is the case, then there may be significant
costs in maintaining the dredged river profile. It is possible that in a
larger flood, the dredged channel may be filled which would then require
that the full dredging be undertaken to maintain the flood benefits.
Removal of Carello's
Removing Carello's levee would give the river a wider channel through
By removing rubbish and fill that has accumulate in ther /town /swamp over
the years river flow should be improved and there is a greater low lying
area in which to hold surplus water during flooding events.
The Bruce Highway is the major and only coastal main north south highway
in the region.In order to prevent road transport from being stopped by
minor flooding across the highway, it was raised sometime in the past.
During major flooding the highwayacts as a giant low dam , backing up huge
volumes of water and making it harder for the area to quicklydrain of
flood waters. In backing up ther is potential for the waters to flood
numerous home and businesses.
Modifying the Shape of Carello's Levee
This levee protects a residentail suburb but also reduces the flow of the
main river channel
Dredging the River Channel
By removing accumulated river silt from the main channel, river flow is
increased. But dredging lasts only a short time and is expensive. Flooding
rivers carry huge volumes of sediment..Sediment load can only be reduced
by revegitating river banks upstream.
Impact of Carello's Levee on Once in Two Year Flood
The levee protects those on the left bank but puts those on the right bank
at greater risk.
Impact of Carello's levee on Once in Ten Year Flood
In a once in ten year flood a considerable area od the right bank is
innundated to protect a small but populated area on the left bank.