Tamar Estuary
River Health Action Plan
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Table 1. Investment in Land uses by major subcatchments under balanced options
Some of the benefits that can be expected from these investments include:
Immediately after actions are undertaken
Reduced stock trampling of the river and consequent turbidity and stream health impacts.
Reduced pathogens in the rivers and estuary from direct manure inputs to streams and effluent runoff from
dairy farms.
Pathogens are very rapidly reduced by fixing intrusion of sewage into Launceston’s separated stormwater
system.
Medium term
Riparian vegetation grows providing streambank stability and reduced streambank erosion.
Riparian vegetation increases river shading and reduces stream temperatures, improving instream habitat.
Riparian vegetation provides corridors for the movement of flora and fauna increasing the connectivity of
populations and their resilience to change.
Further improvements in water quality are experienced as riparian vegetation provides a filter for runoff
from grazing properties and improved effluent management reduces overloading of nutrients in soils on
dairy farms and reduces losses through runoff and infiltration.
Long term
The landscape becomes more resilient to change. Fencing and off-stream water ensures increasing numbers
of stock (through intensification and/or conversion of grazing into dairy) are unable to access the stream.
Riparian buffers filter increased pollutant exports off paddocks caused by intensification of land use.
Flora and fauna corridors provided by riparian vegetation allow for species retreat under climate change
and variability, increasing the resilience of flora and fauna populations to these changes.
Impact of investments on greater Estuary pollutant loads
Figure 7 shows the relative cost-benefit of the balanced investment options in terms of reduced Greater TEER
catchment loads. The balanced investment options are very cost effective for reducing all pollutant loads, but
particularly effective for reducing enterococci loads.
The low end $2 million investment option can be expected to achieve roughly a 9 per cent decrease in
enterococci loads for the Greater TEER catchment, equivalent to 25 per cent of the potential decrease in
enterococci from fully funding all actions considered ($117 million), but for only 1.7 per cent of the budget.
Relative benefits for other pollutants are smaller but still represent a greater relative benefit than cost, with
roughly 9 per cent of the potential benefit for nutrient and sediment loads achieved for only 1.7 per cent of the
fully funded budget.
Tamar Estuary
River Health Action Plan
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While the marginal benefit of further investment decreases with subsequent investment, investment of $10 million
is still shown to be very cost effective with 25 to 30 per cent of the potential decrease in nutrients and sediment
and over 60 per cent of the potential decrease in enterococci loads achieved for only 8.5 per cent of the cost of
fully funding potential actions. This represents a very good return on investment. It should be noted that benefits
in terms of reduced sediment loads are likely to be significantly underestimated. This is because the benefits for
increased streambank stability and reduced streambank erosion through exclusion of stock and riparian
revegetation are not included in the modelling. Using very conservative estimates of the benefits of these actions
for streambank erosion the reduction in tonnes of sediment is likely to be at least twice what is estimated using
the CAPER DSS model
4
, and potentially a lot higher.
Figure 7. Decrease in pollutant loads in Greater TEER catchment from balanced investment option
On the basis of this analysis, the Taskforce recommends a $10 million investment in catchment actions. While
significant benefit is expected to be realised from the first $2 million investment, an almost 20 per cent reduction
in enterococci loads in the catchment is thought possible if the upper budget is allocated. This is almost two-
thirds of the benefit thought possible if the full $117 million of actions initially considered were implemented.
4
For example – for a $10 million investment in the balanced option, the CAPER DSS estimates a decrease of 1560 tonnes of
sediment as a result of the management actions. This action includes roughly 390km of streams with stock excluded,
including 50km on dairy properties with a single wire fence and 340km on grazing properties with both stock exclusion and a
5m vegetated riparian buffer. If this reduces streambank erosion by 1cm per year on the affected streambanks, assuming a
uniform streambank height of 1m then 6650 tonnes of sediment export through streambank erosion is avoided. This is over
4 times more than the reduction in sediment load estimated by the CAPER DSS. Similar calculations for the $2 million and $5
million investment find reduced sediment exports through avoided streambank erosion of 2.5 and 3.4 times respectively.
Tamar Estuary
River Health Action Plan
28
5.
Combined
System Overflows Working
Group
5.1
Membership and specialist advice
The Combined System Overflows Working Group included Launceston City Council (Shane Eberhardt, Kathryn
Pugh, Michael Newby and Randall Langdon), TasWater (Andrew Truscott, Cameron Jessup), Infrastructure
Tasmania (Stewart Sharples), independent consulting expertise from local engineering firms JMG (Geoff Brayford)
and GHD (Ray Dodson), international experience in combined systems management provided by GHD
(particularly Richard Roll from Buffalo, New York State) and integrated catchment assessment by isNRM (Dr
Rebecca Kelly).
5.2
Previous work available
While there is a history of reports and studies relating to the issues of the in Tamar’s river health, the Work
Group’s investigations extends the detail looking at the combined system impacts and possible mitigations.
In 2015, through funding provided by the Australian Department of Energy and Environment, TasWater (who is
the asset owner of the Launceston combined system) engaged consultant Beca to prepare a long term strategy
for the combined system based on an understanding of the frequency, extent and environmental impact of the
overflow events on the receiving environment. In April 2016, Beca delivered a report entitled Launceston
Combined Drainage System Investigation Interim Options and Strategy Report.
The Beca report set out a number of potential options for dealing with combined system overflows, but
importantly noted that “the results and potential solutions are predicated on the results of an out-dated hydraulic
model that requires calibration and refinement” and further, that this model be improved “as a matter of
urgency”. While Beca’s report made progress in understanding how the combined system functions, the Working
Group has built on the work undertaken and extended it.
5.3
Hydraulic modelling and scenarios considered
Prior to the commencement of the Taskforce’s efforts, the Launceston City Council (as the authority required to
provide stormwater drainage in the City) had commenced progressing the recommendations of Beca in relation
to improving the hydraulic modelling relating to the combined system.
When the Taskforce was formed and the Combined System Overflows Working Group set up, it made sense to
build upon Council’s work and help to expedite the completion and validation of the model. Crucial to the
validation was information provided to the working group by TasWater, which allowed validation against actual
pump run data in rainfall events. This gave sufficient confidence to the working group that the model was ready to
run the mitigation scenarios.