Anglesea River Estuary Flow Assessment Summary
Victorian estuaries are dynamic, resilient systems that are continually subject to change. Whether it is natural change or human induced changes, estuaries are systems that are ever evolving. The Anglesea River estuary is no exception.
The Anglesea River estuary supports a wide range of environmental, social and economic values. Like many other
Victorian estuaries its catchment, the estuary and its entrance have been subject to many changes over the decades. They include changes to catchment runoff in terms of water quality, quantity and timing, modifications to riparian vegetation, the landscape and changes to the estuary opening. In this instance, the catchment was the site for a now closed coalmine and power station, that contributed water flows to Anglesea River since its establishment in 1963.
Figure 1. Anglesea River estuary and catchment.
Historically river flows to the estuary were intermittent. Discharge of 4.5 ML/day from the mine and power station has resulted in a consistent year round discharge to the estuary. The discharge consists of 2.0 ML/day from groundwater extraction and 2.5 ML/day from the mine pit sump. Both of these water sources are treated to www.delwp.vic.gov.au

Anglesea River Estuary Flow Assessment Summary a generally neutral to alkaline pH and are within EPA licence limits. Discharge from the mine and power station will cease on 31 March 2016.
Salt and Marshy Creek catchments are upstream of the Anglesea River estuary. Compared to Marshy Creek, Salt
Creek has a generally higher sulphate and metal concentration and displays stronger signs of acid drainage from sulfate rich sediments (Maher 2011).
Both Salt and Marshy Creek catchments contribute a significant volume of water during periods of high rainfall to the Anglesea River estuary. During high flows and subsequent flushing of these two Creeks, the estuary surface water pH has rapidly decreased and fish deaths have occurred.
A series of scenarios were modelled to understand the changes expected to the Anglesea River estuary, when the current treated discharge from the mine and power station site ceases.
The modelling showed that:
• The cessation of discharge from the mine and power station is likely to reduce the water level by up to
1m in the summer period. During the winter period, catchment inputs are sufficient to maintain water levels in the estuary.
• The decrease in water level may expose the mudflats at Coogoorah Park. Drying out of the mudflats is likely to result in generation of coastal acid sulphate soils and poses a risk to environmental, social and economic values.
• The magnitude of the risk posed by the presence of acid sulphate soils is not understood as the reaction rate and acid generation potential of these soils is unknown.

The cessation of discharge from the mine and power station will no longer dilute flow contributions from
Marshy Creek. The concentration of flow may amplify a strong ongoing trend of increasing metals including aluminium, iron and zinc.

An estimated minimum flow to the river of 0.75-1.0 ML/day is required to maintain water levels at approximately 1.5 m AHD during the summer period.
As a result of the change in physical conditions it was found that:
• Changes in water levels are likely to result in changes to the composition of vegetation communities. It is likely that there will be a reduction in water dependent and salt sensitive vegetation communities and an increase in vegetation communities that are less water dependent or salt sensitive.
• Reduced water levels may impact frog breeding events and habitat availability with changes to vegetation reducing cover, habitat and foraging areas for waterbird herbivores, ducks, small grebes, and reduced habitat for prey species of fish eating birds.
• The physical and chemical changes to the Anglesea River estuary are likely to result in: o A reduction in the average area of seagrass in the lower estuary and associated indirect effects on aquatic food webs. o Increased risk of algal blooms in the estuary. o Potential benefits to marine and estuarine fish species from increased salinity. www.delwp.vic.gov.au

Anglesea River Estuary Flow Assessment Summary
As a result of the change in physical conditions it was found that:

Reduced water levels over the summer period are likely to impact on water activities such as boating, swimming, recreational fishing, amenity, bird watching, activities on the water frontage, licenced tour operators, estuary education activities and infrastructure.
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Activation of acid sulphate soils and lowering of pH in the estuary has the potential to impact infrastructure such as bridges, boardwalks and jetties increasing deterioration of the asset and a reduction in the design life.
The primary driver for potential management options is to manage the oxidation of acid sulphate soils to reduce risk of acid drainage into the estuary.
Options proposed for further assessment were:
1.
Discharge at a reduced rate to that currently from mine and power station site– modified management of discharge continues to the Anglesea River estuary to maintain condition and values.
2.
Discharge treated mine pit water - This may be implemented in the short and long term and would use water from mine pit during the decommissioning process and continue to access groundwater as it recovers.
3.
Introduce alternative freshwater inflows to Anglesea River estuary –stormwater harvesting and recycled water discharge.
4.
Pump seawater into lower Anglesea River estuary – Seawater has the potential to be pumped into the lower estuary to maintain water levels. This assumes there would need to be construction of temporary or permanent pumping infrastructure
5.
Discharge mine pit water buffered with a mix of water sources from the catchment as well as seawater to buffer acidity and reduce metal concentrations. www.delwp.vic.gov.au

Anglesea River Estuary Flow Assessment Summary
Planning for the future of the Anglesea River estuary must consider the quantity and timing of water from the catchment along with its quality. Active community input and extensive technical information on the estuary and its catchment provides a foundation for planning for the decades to come.
Important considerations:

The water level, that supports the estuary’s current values, can be managed through various means and that quantity and timing of catchment water inflows can be substantially changed without these values being affected.

The upper catchment naturally generates acid events after a prolonged dry period under moderate to high rainfall events.
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The long term management of Coogoorah Park is a key consideration as coastal acid sulphate soils pose a risk to the estuary environment should they be activated.

Management options recommended for further assessment have been identified in this report and will be the subject of another study to look in more detail at their feasibility to reduce changes to values and activation of acid sulphate soils.
In response to the report findings DELWP will now:
1.
Determine the reaction rate and acid generation potential of the soils at Coogoorah Park. The current intent is to complete this investigation by early April 2016. Its findings will help inform future management strategies (and their urgency) for the Anglesea River; and
2.
Assess in detail the feasibility of the management options recommended for further assessment. This will include an expert panel workshop and a community workshop as part of the study. Those options deemed viable will then be taken to the concept stage and fully costed.
For more information about Anglesea Futures visit www.delwp.vic.gov.au/anglesea-futures or contact the DELWP
Customer Service Centre on 136 186 or email anglesea.futures@delwp.vic.gov.au
Source: Corangamite CMA Anglesea River Estuary Flow Assessment Final Report January 2016. Prepared by GHD for Corangamite
Catchment Management Authority, Colac, Victoria.
© The State of Victoria Department of Environment, Land, Water and
Planning 2016
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This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. www.delwp.vic.gov.au