Eurobodalla Integrated Water Cycle Management Strategy

Eurobodalla Integrated Water Cycle Management Strategy
pumping effectively reduces the security of supply resulting in more frequent restrictions
than predicted (3 times in the past 15 years compared with modelling parameters of 10
restrictions every 100 years). A filtration plant would eliminate the need for turbidity limit on
run-of-river pumping and would restore the original secure yield under the current licence
conditions. The current licence condition allows all the water available at the intakes to be
extracted to meet the urban demands. As a result there is no explicit protection of the
downstream environment and water users particularly during low flow periods. However, in
recognition of the social and environmental values, Council generally tends to cease
pumping when flows in the rivers are low. This has also contributed to lower supply security
and more frequent restrictions than the model suggests, which is based only on the licence
condition.
Current Security of Supply Status
Figure 6-17 shows that the secure yield of the existing scheme based on the current licence
conditions is about 8 200 ML/a. Based on population projections, the existing system of
source infrastructure is adequate to supply demand for the next 40+ years. However, due to
Council’s operating strategy, which limits extraction when the river water is turbid and
protects low flows by ceasing to pump, the actual secure yield is likely to be substantially
less. Due to the lack of operational turbidity data the secure yield based on the current
operational strategy cannot be accurately quantified at this stage.
Whilst the above observations are based on system modelling outcomes, in the
development of the model care has been taken to ensure that it represents the actual
situation as far as practical. There are still areas of uncertainty, and in developing the model
the following assumptions have been made:
Extraction is not constrained by water quality of the supply sources (e.g. turbidity)
The accuracy of the system modelling outcome is limited by the extent and
accuracy of the last 104 years of historic stream flow and rainfall data used
Any changes to catchment land use and irrigation practices will not significantly
alter the stream flow sequence
Future climate will be statistically similar to the observed historic climate
Future urban water use pattern will be statistically similar to observed historic usage
patterns and that the current legislation and community ‘consciousness and
awareness’ on conservation will continue
The population of Eurobodalla will continue to increase albeit at a slower rate than
in the past and that it will remain a popular tourist and holiday destination.
Environmental Flow and Access Sharing
As discussed in section 6.1.1, the Water Management Act will affect how much water is
available for harvesting during low flow periods. Leaving water for the river environment will
improve the environmental health and the long term sustainability of the river, however it
also reduces the secure yield of the water supply system. The quantity of water required for
the environmental flows has yet to be decided by the water management committees. At
the inter-agency meeting (October 2002) it was agreed that the future planning should
consider the following cease to pump and flow access conditions as the base level cases
for the three supply sources:
Within the first 10 year cycle of the water sharing plan, cease to pump when
Moruya, Tuross and Buckenboura Rivers flow drops below 12 ML/d, 17 ML/d and
1 ML/d respectively at the water supply intake (95 th percentile).
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