Tamar Estuary
River Health Action Plan
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In the dairying and grazing spaces, large benefits were determined available from limiting stock access to streams
to minimise input of faecal matter into tributaries, while improved effluent management practices in dairies and
the implementation of riparian zones on grazing properties were also assessed to have good potential for
pathogen load reduction. The Macquarie and North Esk catchments are the focus of these actions and build on
the significant success NRM North have had in addressing these challenges in the Meander catchment.
With respect to the urban catchment actions, the WQIP 2015 had focused on water sensitive urban design
(WSUD), but it was found that these actions don’t provide great benefit for cost when looking at pathogen load
reduction. Instead action options in the urban area turned to focussing on removing cross connections from
separated sewerage and stormwater systems, where recent programs by Launceston City Council had been
shown to deliver good reductions in sewage load during overflow events.
Three different investment budgets, $2 million, $5 million and $10 million, were considered and a series of
actions allocated for each budget amount. The chart below shows the expected reductions in pathogen, nutrient
and solids concentrations in the Launceston to Legana zone (Zone 1) at the various investment levels. The far
right of the chart includes the benefits possible from a full investment of all the programs initially considered by
the Working Group ($117 million).
The findings show that there are significant benefits in reducing Zone 1 pathogens that cause a threat to public
health (i.e. enterococci) for relatively small investments. It is the Taskforce’s view that a $10 million investment in
catchment actions would be preferable and deliver around 80 per cent of what is possible for the full $117 million
of initially considered actions.
Tamar Estuary
River Health Action Plan
3
Combined System Overflow Working Group
The Combined System Overflow Working Group leveraged off work already commenced by the Launceston City
Council to build a detailed hydraulic model of the combined system. The model allowed a better understanding of
how the network functions in various levels of rainfall event and through this greater detail became known about
where the majority of overflows from the system occur. The Group then shortlisted a number of possible
mitigation treatments (captured in the table below).
Treatment option
High level description
7.
Legislation, regulation
and policy improvement
Changes to the legislative and regulatory environment to
incentivise continuous improvement of the combined system
8.
Community information
and education
Ongoing monitoring of river health to facilitate continuous
system improvement, education streams and warnings in the
event of an overflow
9.
Operational
improvements and
system optimisation
Review existing operational environment of the combined
system to ensure existing infrastructure is operating efficiently
and effectively (i.e. Margaret Street Detention Basin and weir
levels at CSO locations)
10.
Green infrastructure
(primarily WSUD
treatments)
Develop the framework required to transition from
"traditional" drainage systems to WSUD drainage systems
including detention, wetlands, ponds, bio-filtration systems and
infiltration systems to decrease runoff frequency, volume and
peak flow. Green infrastructure would also be considered for
the immediate mitigation
options
11.
Screening, preliminary
treatment and/or
Installation of screening and chemical treatment facilities at the
3 key CSO locations
Tamar Estuary
River Health Action Plan
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Treatment option
High level description
disinfection at CSO
locations
12.
Offline storage
Underground storage tanks located at the key CSO locations
13.
Live storage
Storage within the existing system, requiring baffles, weirs,
actuators at the 3 key CSO locations
14.
Separation
Full separation of the combined system and construction of a
separated sewer and stormwater network
15.
Diversion of separated
sewage catchments
Diversion of the West Launceston and South Launceston trunk
sewerage mains directly to the Ti Tree Bend STP
16.
Diversion of separated
stormwater catchments
Construction of required stormwater drainage components to
enable direct discharge to the Estuary at Margaret Street
17.
System upgrade i.e.
additional combined
rising main to Ti Tree
Bend and reconfiguration
of network components
Increase the pump rate to Ti Tree Bend for the key CSO
locations
18.
Consolidation and
movement of discharges
further downstream.
Pump combined discharge further downstream to where the
Estuary widens and dilution is increased
A multi-criteria analysis and preliminary examination of these treatments led to a shortlisting of six “hard”
infrastructure projects as being the most feasible in terms of their practical delivery and expected return on
investment as measured by reduction of sewage loading to the Estuary.
These projects were:
1.
The West Launceston Diversion – a diversion of the separated sewerage catchment that currently joins the
combined system at the Margaret Street pump station (and therefore which can then be overflowed to the
Estuary in higher rainfall events) and instead extend the trunk main directly to Ti Tree Bend sewerage
treatment plant;
2.
New Combined Rising Main – a project to upgrade the Margaret Street pump station to allow for greater
pumping rates and adding a new combined rising main to Ti Tree Bend to accommodate the increased
flows;
3.
An offline storage located at New Margaret Street Pump Station – a project to provide a storage to
capture the “first flush” sewage that would otherwise spill straight to the Estuary in higher rainfall events,
that can then be bled back into the system and receive treatment at Ti Tree Bend;
4.
An offline storage located at Forster Street Pump Station – as with project 3;
5.
The South Launceston Diversion – similar to project 1, this project would see the separated sewerage
catchment that joins the combined system at Shields, Tamar and Willis Streets being redirected to a new
pump station and sent straight to Ti Tree Bend; and
6.
The offline storage proposed to service the Esplanade – as with projects 3 and 4.