Corangamite CMA Anglesea River Estuary Flow Assessment Final Approved Report January 2016
Table of contents
Executive Summary ...... v 1. Introduction...... 1 1.1 Anglesea River estuary ...... 1 1.2 Purpose of this report...... 3 1.3 Scope and limitations ...... 4 Part 1: Physical, ecological and social changes to the Anglesea River estuary ...... 5 2. Predicted physical changes to Anglesea River estuary ...... 5 2.1 Objective ...... 5 2.2 Approach ...... 5 2.3 Review of Relevant Literature and Data ...... 6 2.4 Conceptual Models and Modelling Framework ...... 12 2.5 Multi-Annual Water Balance Model ...... 16 2.6 June 2012 Winter Hydrodynamic Modelling ...... 20 2.7 Geochemical Modelling - Winter 2012 ...... 23 2.8 Marshy Creek Observations ...... 26 2.9 Summary of predicted physical changes ...... 28 3. Predicted ecological changes ...... 29 3.1 Objective ...... 29 3.2 Approach ...... 29 3.3 Floodplain and aquatic vegetation communities ...... 29 3.4 Floodplain Fauna ...... 33 3.5 Aquatic ecology ...... 36 4. Social (and Economic) Impacts ...... 42 4.1 Objective ...... 42 4.2 Approach ...... 42 4.3 Summary of impacts to social and economic value ...... 46 5. Key Findings Part 1 ...... 47 5.1 Summary of predicted physical changes ...... 47 5.2 Summary of predicted ecological changes ...... 47 Part 2: Assessment of options to manage changes to the Anglesea River estuary ...... 49 6. Options Assessment ...... 49 6.1 Objectives ...... 49 6.2 Approach ...... 49 6.3 Summary of options assessment ...... 54 6.4 Key Findings Options Assessment ...... 57 7. Conclusions ...... 58 8. References ...... 61
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Table index
Table 1 Sum of major water balance terms over the water balance model application period (volumes in m3) ...... 17 Table 2 Geochemical concentration inputs for geochemical modelling. Colour coding re data sources is outlined in Table 3 ...... 23 Table 3 Colour legend for description of data source ...... 24 Table 4 Mixing ratio inputs for geochemical modelling ...... 24 Table 5 PHREEQC geochemical modelling results ...... 25 Table 6 Anglesea Estuary: Ecological Vegetation Classes and their relative estuarine water dependency ...... 30 Table 7 Anglesea Estuary: Estuarine Dependant EVC’s and Habitats ...... 31 Table 8 Summary of current (status quo) estuarine conditions influencing vegetation communities ...... 31 Table 9 Summary of changes to vegetation communities should groundwater pumping cease...... 32 Table 10 Summary of likely changes to terrestrial fauna resulting from mine and power station discharge (status quo) to in the Anglesea River estuary ...... 34 Table 11 Summary of likely changes to terrestrial fauna of changing mine and power station discharge to the Anglesea River estuary ...... 35 Table 12 Summary of expected response of aquatic organisms in the Anglesea River estuary to the increase in summer flows and water height following the commencement of the mine and power station discharge ...... 39 Table 13 Summary of the expected response of aquatic organisms to the removal of the mine and power station discharge to the Anglesea River estuary ...... 40 Table 14 Social and economic values impacted by physical and ecological changes resulting from reduced water levels and ecological changes as a result of ceasing the mine and power station discharge ...... 44 Table 15 Feasibility impact and benefit screening process ...... 50 Table 16 Summary assessment of mitigation opportunities to reduce the impact of changes to water levels and water quality as a result of ceasing the mine and power station discharge. The assessment defines the relative benefit of each mitigation option to key values ...... 52 Table 17 Relation between estuarine levels, volumes and areas ...... 64 Table 18 Monthly evaporation estimates for Anglesea from BoM...... 64
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Figure index
Figure 1 View of Anglesea catchment highlighting major tributaries, mine and power station’s operations and the Anglesea River estuary ...... 2 Figure 2 Mid-estuary pH of surface waters (source mine and power station from Pope (2006) in Maher (2011))...... 6 Figure 3 Inflow pH from June 2010 to May 2011 (from Maher (2011))...... 7 Figure 4 Rainfall and pH of Salt Creek, Marshy Creek and Anglesea River estuary at mine monitring site from November 2010 to January 2011 (Parsons 2011)...... 7 Figure 5 Salt Creek discharge and Al concentrations (data from mine and power station and Barwon Water in Pope (2010))...... 8 Figure 6 Temperature and salinity for top and bottom waters at Coogarah Park site (Pope 2006)...... 9 Figure 7 Temperature, salinity and pH of top and bottom waters at five estuarine sites from May 2010 to October 2015 (source: EstuaryWatch Online Database at www.estuarywatch.com.au). Red arrow demarcates modelled acidic event...... 10 Figure 8 Surface level, temperature, salinity and pH at mid-estaurine site at Great Ocean Road Bridge (site 235278) from October 2011 to August 2015 (source: Victorian Department of Environment, Land, Water and Planning). Red arrow denotes 2010 acidic event...... 11 Figure 9 Water balance and salinity conceptual model...... 13 Figure 10 Geochemical model node configuration to predict geochemistry shortly after the acidic catchment inputs for existing and potential (i.e. no discharge) cases...... 13 Figure 11 Monthly discharge of mine and power station discharge and catchment sources...... 14 Figure 12 (1) Winter 2012 inflows, (2)continuous estuarine water level (m AHD) with predicted ocean tides, (3) continuous salinity with spot measurements from Salt Creek and Marshy Creek and (4) pH with spot measurements from Salt Creek and Marshy Creek). Red arrow denotes focus of hydrodynamic and geochemical modelling investigations...... 15 Figure 13 EstuaryWatch data at surface and bottom at 5 estuarine stations of salinity and pH...... 16 Figure 14 Water balance results for ‘forced’ water balance with past observations (top) and ‘forecast’ water balance with (middle) and without (bottom) Mine and power station discharge. Full (left) and partial (right) ranges of the water balance volumes illustrated to emphasise large (e.g. inflows, outflows) and small (e.g. evaporation, groundwater losses), respectively...... 18 Figure 15 Predicted water levels with and without mine and power station discharge...... 19 Figure 16 Predicted water levels with mine and power station discharge and 0.75 ML/day continuous discharge ...... 20 Figure 17 Simulation of June 2012 inflow event with (left) and without (right) mine and power station discharge ...... 22
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Figure 18 Water volumes contributed by Salt and Marshy Creeks, and mine and power station between 2011 and 2015 ...... 26 Figure 19 Water quality results collected for Marshy Creek, Salt Creek, the mine and power station discharge and mixing zone between January 2010 and January 2015 (Alcoa data)...... 27 Figure 20 Seagrass coverage at times of high (green, Nov 1999) and low (orange, Sep 1993) extent. Data from Pope (2006)...... 37 Figure 21 Simulated leakage from the estuary to groundwater by GHD (2013). Red arrow demarcates modelled acidic event...... 65 Figure 22 Daily rainfall at Aireys Inlet from 1 November 2011 to 1 June 2015 ...... 65 Figure 23 Daily inflows into the estuary from 1 November 2011 to 1 June 2015 ...... 65 Figure 24 Estuarine bathymetry and mesh used by Water Technololgy (2010) (left) and this study (right) ...... 75 Figure 25 Inflow inputs for hydrodynamic modelling of winter 2012 event with (left) and without (right) the mine and power station discharge ...... 76 Figure 26 Half hour wind speeds and directions for hydrodynamic simulations ...... 77 Figure 27 Relation between Salt Creek (SV2) and Marshy Creek (AV2) conductivity and TDS measurement ...... 77
Appendices
Appendix A – Water Balance Inputs
Appendix B – Anglesea River Contour Maps
Appendix C – Hydrodynamic Model Inputs
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Executive 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 Wathaurong people have had a relationship with, and seen a great deal of change over 1,000s of years of utilising its resources. The early European settlers that first mapped the Anglesea River as ‘Swampy Creek’ in 1803 have been changing the catchment ever since. Arguably one of the biggest changes for Anglesea River estuary was in 1963 with the establishment of an open cut coal mine and power station. While mining and power generation have now ceased, their historic operation resulted in river flows to the estuary that have altered from historically intermittent to a consistent year round discharge to the river. In recent times, the operation has consistently contributed 4.5 ML/day into the estuary. This Anglesea River Estuary Flow Report Assessment provides an assessment of the changes to the physical character and ecological, social and economic values resulting from changes to the mine and power station discharge and a high level scoping of options to manage the predicted changes. 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. This report is an important step in this planning. The key points to consider in this planning are: • 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 • The long term management of Coogoorah Park is a consideration as coastal acid sulphate soils pose a risk to the estuary environment should they be activated and • Management options have been identified and screened for feasibility to reduce changes to values and activation of acid sulphate soils.
Physical changes to Anglesea River estuary Under natural conditions without the mine and power station discharge water levels in the Anglesea River estuary would vary between seasons with significantly lower levels during the summer months. Key findings include: • The cessation of discharges from the mine and power station is likely to reduce the water level by up to 1 m in the summer period. During the winter period, catchment inputs are sufficient to maintain water levels in the estuary • The decrease in water level with exposure and drying of mudflats at Coogoorah Park 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 result in an increased proportion of flow contributions from Marshy Creek to the estuary with monitoring indicating there is a strong ongoing trend of increasing metal concentrations (aluminium, iron and zinc) and • 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.
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Ecological changes Ecological communities in the estuary are dynamic and resilient and will adapt and respond to a drier floodplain and to increases in salinity levels through changes to the mosaic of vegetation communities across the floodplain. Key findings include: • Changes in water levels are likely to result in reduced extent and composition of some water dependent and salt sensitive vegetation communities and increased extent to those 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 and • The physical and chemical changes to the Anglesea River estuary are likely to result in: – A reduction in the average area of seagrass in the lower estuary and associated indirect effects on aquatic food webs. – Increased risk of algal blooms in the estuary. – Potential benefits to marine and estuarine fish species from increased salinity.
Social and economic impacts The social values of the Anglesea River estuary are rated highly by the wider community. These values are also of direct and indirect economic importance. The key findings of impacts to both social and economic values include: Reduced water levels over the summer period are likely to impact on water activities (motor and non-motor boating) , swimming, recreational fishing, amenity, bird watching, beside water activities, boat hire business, markets, estuary education activities and infrastructure and Activation of acid sulphate soils and lowering of pH in the estuary has the potential to impact infrastructure increasing deterioration of the asset and a reduction in the design life.
Mitigation options The primary driver for options assessment is to identify options that reduce or halt oxidation of acid sulphate soils to reduce risk to the receiving environment. Options that are recommended for further assessment are: 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 and 5. Mine pit buffering – utilise a mix of water sources, including seawater to buffer acidity and reduce metal concentrations. As a longer term option mine pit water can be used to maintain flows.
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1. Introduction
1.1 Anglesea River estuary
The Anglesea River estuary is the dominant feature of Anglesea. It 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 and surrounding landscape and changes to the estuary opening to Bass Strait. In this instance the catchment has been the location for a coalmine and power station, operated by Alcoa Australia that contributed water flows to Anglesea River during its operational life.
1.1.1 Mine and power station
In recent time, the discharge from the mine and power station has contributed an average flow of 4.5 ML /day via the mixing zone to the Angelsea River. This flow is a contribution of 2.0 ML/day generated by groundwater extraction and an additional 2.5 ML/day as a contribution from the mine pit sump. Both these water sources are treated by a water treatment facility, located adjacent to power station infrastructure. Following treatment of the majority of the source water to remove excess iron and neutralise low pH, the effluent has historically been used in the cooling towers prior to discharge via Ash Pond 2 into the mixing zone. During low flows, usually summer periods, the treated discharge constitutes a major portion, if not 100%, of the Anglesea River estuary flow inputs (Maher, 2011).
The pH of the treated discharge is generally neutral to alkaline and is maintained within EPA licence discharge limits.
1.1.2 Salt and Marshy Creeks
Salt and Marshy Creek are two tributaries that are located upstream of the Anglesea River estuary. These creeks are encompassed within a low lying catchment area of 885 hectares (CCMA 2013). The geological profile of the Anglesea region including Salt and Marshy Creeks is dominated by a coal lithological unit compromising pyritic siltstone, a form of iron sulphide. Coal seams have been reported to contain a high sulphur content are at a relatively shallow depth, and appear to be in contact with the water table (Maher 2011, in Cheng Yau, 2014).
When compared to Marshy Creek, Salt Creek has generally exhibited higher sulphate and metal concentrations, displaying stronger signs of acid drainage from sulfate rich sediments (Maher 2011). Flows from Salt Creek are usually intermittent and result in drying of the marsh sediments.
Low pH stream waters are a feature of the two tributaries. The geological profile of Marshy Creek appears to have a lower acid generating capacity compared to Salt Creek. Marshy Creek contributes higher flows to the estuary due to the larger catchment area. Historic coal mining during the late 1950’s and 1960’s in the lower reaches of Salt Creek west appear to contribute low pH surface waters flows, and trace metals into the estuary. Trace metals measured in catchment surface waters have historically been low.
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Figure 1 View of Anglesea catchment highlighting major tributaries, mine and power station’s operations and the Anglesea River estuary
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1.1.3 Convergence of Water Sources
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 Anglesea River estuary has experienced periods where surface water pH has rapidly decreased and fish deaths have occurred. Targeted monitoring since 2010 has indicated that fish deaths of varying degrees have been noted every year. Fish deaths have been directly related to low pH surface waters entering the estuary following high rainfall events. These inflows have also resulted in elevated trace metals measured in the estuary.
The decreased pH and elevated trace metal concentrations within the Anglesea River following significant inflows (periods of high rainfall) from the upper catchment do not appear to be influenced, i.e. diluted, by the continual discharge from the mine and power station. During periods of low rainfall this contribution can represent as much as 100% of river volume. Alluvium (2014) reported that there is general consensus from scientists, regulatory agencies and the community that the acid events in the Anglesea River system are largely natural. In a workshop convened with an expert panel, participants heard that, in general, the acid events in Anglesea River estuary are associated with rainfall events (freshes) that followed periods of dry conditions. It has been confirmed that Salt and Marshy Creek are the source of the low pH events that have resulted in fish deaths in the Anglesea River estuary.
1.2 Purpose of this report
In recent years the condition of the Anglesea River estuary has been the subject of much community concern, due to acid events and related fish deaths. This has led to a number of investigations and reports on the issues associated with, and the options to address, water quality in the Anglesea River estuary.
In 2015, the mine closed and planning for the decommissioning of the power station and rehabilitation of the mine site commenced. Consequently the discharge of treated process water from the power plant and mine pit would cease.
As a consequence of the forecast change in the hydrology of the Anglesea River estuary, GHD Pty Ltd (GHD) was commissioned to conduct this study with the objective to:
Identify changes to the physical character and potential environmental, social and economic impacts as a result of the mine and power station ceasing the discharge to the Anglesea River estuary and
Scope options that may be available to reduce the predicted impacts.
The outcomes of this project will help inform the decision making and planning process for the Anglesea river estuary.
1.2.1 Approach
The approaches that GHD has applied to complete this project are as follows:
Chapter 1 – Background and objectives A background review of documentation to understand current catchment flows, water quality, and ecological condition.
Chapter 2 – Physical Change to the Anglesea River estuary A series of scenarios were numerically modelled to understand the physical change expected to the Anglesea River estuary, when the current treated discharge from the mine and power station site cease. This includes describing the
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water balance, and defining the hydrodynamics and the geochemical parameters associated with the predicted change.
Chapter 3 – Environmental Change The impacts of the expected physical change (Chapter 2) to the ecology of the system were assessed. This includes a summary of a potentially new ecological baseline likely to emerge including fish, macrophytes, aquatic and terrestrial vegetation.
Chapter 4 – Social (and Economic) Impacts The social impacts (and related economic aspects) that could result from the expected physical change (Chapter 2) have been identified and documented.
Chapter 5 – Options Assessment The potential options for the future management of the Anglesea River estuary have been identified. These options are strongly linked to the expected physical change (Chapter 2), environmental impact (Chapter 3) and social impact (Chapter 4).
Chapter 6 – Conclusion and Recommendations The conclusions and subsequent recommendations surrounding the change in water flows into the Anglesea River estuary have been discussed.
1.3 Scope and limitations
This report: has been prepared by GHD for Corangamite CMA and may only be used and relied on by Corangamite CMA for the purpose agreed between GHD and the Corangamite CMA as set out in section 1.2 of this report.
GHD otherwise disclaims responsibility to any person other than Corangamite CMA arising in connection with this report. GHD also excludes implied warranties and conditions, to the extent legally permissible.
The services undertaken by GHD in connection with preparing this report were limited to those specifically detailed in the report and are subject to the scope limitations set out in the report.
The opinions, conclusions and any recommendations in this report are based on conditions encountered and information reviewed at the date of preparation of the report. GHD has no responsibility or obligation to update this report to account for events or changes occurring subsequent to the date that the report was prepared.
The opinions, conclusions and any recommendations in this report are based on assumptions made by GHD described in this report. GHD disclaims liability arising from any of the assumptions being incorrect.
GHD has prepared this report on the basis of information provided by Corangamite CMA and others who provided information to GHD (including Government authorities)], which GHD has not independently verified or checked beyond the agreed scope of work. GHD does not accept liability in connection with such unverified information, including errors and omissions in the report which were caused by errors or omissions in that information.
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Part 1: Physical, ecological and social changes to the Anglesea River estuary
2. Predicted physical changes to Anglesea River estuary
2.1 Objective
The objective of this chapter is to provide a description of the expected physical change to the Anglesea River estuary when the mine and power station discharge of ~4.5 ML/day ceases on 31 March 2016. The outcomes associated with this chapter will inform the assessment of the environmental, social and economic aspects of the estuary.
2.2 Approach
The assessment of predicted physical and chemical changes to the river once the mine and power station discharge has ceased was undertaken by three different modelling approaches including:
A water balance model to assess the changes in water height across the estuary under different seasonal (summer and winter) conditions. The model defines how water levels change in response to catchment inputs, rainfall, evaporation, mine and power station discharge, seawater and tidal movement and groundwater gains or losses to the system.
A hydrodynamic model to assess the physical movement of water in the estuary and how it mixes with mine and power station water and other inputs including those from Salt Creek and Marshy Creek and groundwater (it is a key linkage to the geochemical model) and
A geochemical model that predicts changes to water quality in the river including pH, salinity, metals as a result of catchment inputs and with and without the mine and power station discharge. The geochemical model will also assess the ability of the mine and power station discharge to neutralise the impact of acidic catchment discharges following moderate to high rainfall events.
The use of these models will provide an assessment of the likely physical changes to the Anglesea River estuary following changes to the mine and power station discharge. The approach to this section is to utilise numerical modelling formulated by Water Technology (2010) as a basis to assess the change to the Anglesea River estuary under current conditions (status quo) and without the mine and power station discharge of ~4.5 ML/day.
2.2.1 Simulation Periods
In order to assess the changes to the physical conditions in the river the following three scenarios have been modelled with and without the mine and power station discharge of ~4.5 ML/day:
1. Scenario 1: A ~5 month simulation during a period of no catchment inputs (i.e. low flow period of spring-summer-autumn) where the objective is to evaluate the effect of ceasing the mine and power station discharge on water levels (which presumably decrease) and hence increase drying of fringing area (including floodplain, swamp/peatlands), increasing risk of activation of acid sulphate soils during the subsequent winter’s inundation.
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2. Scenario 2: A two to four week simulation of relatively small catchment inputs (via mixing ratios/dilution worked out from hydrodynamic modelling that serve as inputs into geochemical modelling) to estimate changes in pH with and without the mine and power station discharge.
3. Scenario 3: As Scenario 2, but for a large catchment rainfall event.
2.3 Review of Relevant Literature and Data
2.3.1 Review of Low Estuarine pH Events
Regular monitoring of the estuary since 1972 has indicated regular periods of low pH (Figure 2). Major fish death events have been documented in 2000, 2007, 2010 and 2013. EPA investigation into the 2010 event found fish deaths most likely resulted from a combination of pH stress (acidic water), aluminium toxicity and suffocation through smothering of gills by precipitated aluminium compounds (Pope 2010).
Figure 2 Mid-estuary pH of surface waters (source mine and power station from Pope (2006) in Maher (2011)).
Surface runoff from both Marshy Creek and Salt Creek is acidic (pH<4) and the discharge from Ashpond 2 located adjacent to the power station is neutral (pH 7-8). The flows associated with the 2010 fish death event led to a prolonged period of several months of low pH in the Anglesea estuary as a result of the acidic inputs form the upper catchment of Marshy and Salt Creeks (Figure 3).
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Figure 3 Inflow pH from June 2010 to May 2011 (from Maher (2011)).
Independent measurements by Parsons (2011) have confirmed that both Marshy Creek and Salt Creek are acidic (pH<4) and the discharge from Ashpond 2 marginally increases the pH at mine monitoring site upstream of Coalmine Rd Anglesea, prior to discharge into the estuary (Figure 4).
Figure 4 Rainfall and pH of Salt Creek, Marshy Creek and Anglesea River estuary at mine monitring site from November 2010 to January 2011 (Parsons 2011).
In short, measurements consistently indicate low pH in both creeks and fluctuating pH at SP3 due to the proportional volumes of creek-derived waters versus the mine and power station discharge (Maher 2011). The sources of acidity are likely to primarily be from the swamps and geology (mineral coal deposits and pyritic strata including marcasite bands) in the catchment
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(Maher 2011). Airborne emissions from the power plant when operating and organic humid acids are also potential contributors (Maher 2011).
During a reported fish death event in 2000, most of the measured aluminium originated from Salt Creek along with elevated levels of sulphate, manganese and zinc (Gower 2000). A similar pattern of elevated acidity, aluminium, sulphate, manganese and zinc was recorded in Distillery Creek, a tributary to Painkalac Creek to the south west of the Anglesea catchment during the same storm event (Gower 2000) indicating these are naturally occurring events. Wet winters after dry years with fish death events have been associated with elevated aluminium levels in Salt Creek. This is illustrated in Figure 5 for the 2010 fish death event.
Figure 5 Salt Creek discharge and Al concentrations (data from mine and power station and Barwon Water in Pope (2010)).
Stratification Stratification is when water within the same water body is separated by stable horizontal or vertical layers that do not mix. Stratification in Anglesea River estuary may be caused by temperature and salinity. It appears that the dominant contributor to stratification in the Anglesea River estuary is salinity rather than temperature. Pope (2006) reported vertical and horizontal variations in temperature and salinity occur in response to seasonal meteorology, freshwater inflows at the head of the estuary and sand bar openings with the concomitant intrusion events of marine water. An example of the vertical temperature and salinity stratification in the estuary is illustrated in Figure 6.
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Figure 6 Temperature and salinity for top and bottom waters at Coogarah Park site (Pope 2006).
2.3.2 EstuaryWatch Data
Temperature, Salinity and pH of Surface and Bottom Waters EstuaryWatch measurements of surface and bottom temperature, salinity and pH are collected monthly at five estuarine sites. Data collected from 2010-2015 is illustrated in Figure 7. The general patterns of temperature and salinity were similar to those measured by Pope (2006) with persistent periods of higher temperatures and salinities in the bottom waters relative to those in the summer at site A3 (Coogoorah Park). Notably, pH generally did not exhibit strong differences between the surface and bottom waters.
Four of the six recent winter-spring periods (2010, 2012, 2013 and 2014) had persistent low pH from catchment-induced acidification events. This frequency seems to be greater than the previous decade (2000, 2007, 2010) (Pope 2010). This may be due to the greater frequency and continuity of recent estuarine monitoring, and/or greater frequency of wet years that generate substantive catchment inflows with low pH.
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Figure 7 Temperature, salinity and pH of top and bottom waters at five estuarine sites1 from May 2010 to October 2015 (source: EstuaryWatch Online Database at www.estuarywatch.com.au). Red arrow demarcates modelled acidic event.
Continuous Surface Estuarine Measurements at Great Ocean Road Bridge Continuous estuarine physico-chemical measurements by Corangamite CMA and Surf Coast Shire from October 2011 to August 2015 at the Great Ocean Road Bridge are shown in Figure 8. Water levels generally ranged between 1.3 and 1.7 m AHD. Over the nearly 4 year record of water levels the estuary was predominately in either a ‘closed2’ or ‘perched3’ state with no ‘tidal4’ influence.
Water temperatures during this period in 2011 and 2015 ranged from 25-30°C in summer and 5- 10°C in winter. Salinity concentrations peaked from 20-30 ppt in October-December 2011, April- June 2012 and July-August 2014. At other times salinity generally ranged from 5-15 ppt.
Continuous measurements since 2011 identified pH was generally greater than 7 except for low pH events that occurred during late June 2012, winter 2013 and August 2014. These reductions were associated with substantive acidic catchment inflows.
1 Sites: A1 – Jetty opposite Angahook Corner Store, A2 – Fishing platform upstream of Great Ocean Bridge, A3 – Footbridge near Bingley Parade, A4 – Footbridge adjacent to Coogarah Park, A5 – Culvert on Coalmine Road. 2 No tidal influence, sand bar well above maximum coastal marine surface elevations, no exchange or overflows of estuarine water 3 Small tidal influence, sand bar below elevated/high tide coastal marine surface elevations with marine waters entering only during elevated surface levels 4 Strong tidal flows, sand bar generally below mean coastal marine surface elevations with nearly constant exchange with estuary
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The lowest water levels in the estuary (1.2-1.3 m AHD) did not decrease below the highest predicted tide levels (1.2 m AHD) (Figure 12). Observations of sand bar openings from the EstuaryWatch website indicate multiple natural and artificial openings over this period, with the majority of observations indicating flows out of the estuary. The combination of storm surges and energetic wave climate may lead to the elevated marine surface water levels. This is unlikely to result in significant saltwater intrusion during the winter period without substantial artificial deepening of the estuary channel through the sand bar. The continuous salinity data does suggest that over the winter period there are numerous events where estuarine salinity increases (Figure 12), presumably from the entry of marine waters via artificial openings. Modelling of the sand bar dynamics is not considered here due to its complexity and need for more detailed sand bar morphometric data.
Figure 8 Surface level, temperature, salinity and pH at mid-estaurine site at Great Ocean Road Bridge (site 235278) from October 2011 to August 2015 (source: Victorian Department of Environment, Land, Water and Planning). Red arrow denotes 2010 acidic event.
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2.4 Conceptual Models and Modelling Framework
2.4.1 Conceptual Models
Water Balance and Estuarine Mixing To predict physical changes associated with changes to the mine and power station discharge to Anglesea River estuary, water balance and mixing models (Figure 9) were developed in the following manner:
A multi-annual water balance model to predict the effect the loss of the change in mine and power station discharge on estuarine water levels comprised of: – Evaporation and rainfall – Leakage to the underlying groundwater – Inflows from the two major catchments (Salt and Marshy creeks) – The existing discharge (status quo) and no discharge and – A constant sand bar elevation is assumed as a simplifying assumption with only over- topping of excess estuarine flows into the adjacent coastal ocean. A mixing model to predict the relative proportions of source waters with and without the mine and power station discharge for the June-July 2012 acidic catchment inputs that considers the following processes:
– Water balance components including evaporation, rainfall, and catchment discharge (no bar openings5) and – Dynamic simulation of vertical and horizontal stratification of salinity in response to catchment inputs and meteorology.
Salt Creek
Marshy Creek
Mine and power station Rainfall treated discharge
No Sand Bar Opening
GW Leakage
5 Simulation of bar openings is beyond the scope of this modelling. Further, a measure of conservativeness results without simulation of bar openings as seawater has a strong buffering effect on the acidic catchment inputs. As the objective is to ascertain the benefit from the mine discharge, no bar openings are used to assess this benefit.
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Figure 9 Water balance and salinity conceptual model.
Geochemistry Figure 10 illustrates the node configuration for geochemical modelling of the onset of the 2012 winter conditions (June-July) of acidic winter catchment inputs whereby: At Node 1, the geochemistry of the mix of the two primary catchment inputs Marshy Creek and acidic Salt Creek is predicted
At Node 2, the geochemistry of the combined acidic Marshy Creek and Salt Creek with the alkaline catchment discharge is predicted for status quo. Note that this node is not modelled for the no discharge case and
At Node 3, the geochemistry of the combined catchment inputs with the estuarine waters is predicted. Mine and power station discharge Marshy Creek Estuary
1 2 3 Salt Creek Existing discharge (status quo) Marshy Creek Estuary
1 3 Salt Creek No discharge Figure 10 Geochemical model node configuration to predict geochemistry shortly after the acidic catchment inputs for existing and potential (i.e. no discharge) cases.
2.4.2 Numerical Models
Hydrodynamic Model The Danish Hydraulic Institute’s three-dimensional hydrodynamic model, Mike 3, was used to simulate the proportion of the various water types within the estuary. These included estuarine prior to catchment inflows, Marshy Creek, Salt Creek, and status quo discharge during the June-July 2012 acidic catchment inflow event. Hydrodynamic modelling was used to predict the estuarine mix of waters from Salt Creek, Marshy Creek, the status quo discharge and marine waters. ‘Mixing ratios’ of these various water types are then derived from the hydrodynamic simulations to serve as inputs into the PHREEQCI modelling package.
Geochemical Model PHREEQCI is a low temperature aqueous geochemical modelling package that simulates chemical reactions in natural or contaminated waters. PHREEQCI simulates aqueous speciation, mineral saturation indices and ion exchange reactions through the provision of mixing ratios of source and receiving waters (i.e. dilution calculations) through the simultaneous solution of inverse equations that maintain mass balance of water quality constituents. Further details of PHREEQCI capabilities, limitations and execution are provided by Parkhurst (1995) and Parkhurst & Appelo (1999).
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2.4.3 Investigation Periods
Figure 11 summarises daily discharges of the three primary sources (Salt Creek, Marshy Creek and 4.5 ML/day discharge) into the estuary from November 2009 to June 2015. The following is noted:
A moderate acidic winter flow occurred in 2010 that followed several dry years and led to a fish death event A relatively dry 2011 led to no winter flows from Salt Creek and low flows from Marshy Creek, and the estuarine pH remained in the range of 7-8 (see Figure 8)
Following the dry winter of 2011, the moderate 2012 winter flows resulted in a moderate pH decrease in the estuary (EstuaryWatch data <5 see Figure 7; continuous data of 5-5.5 see Figure 8) that yielded several dead fish and other aquatic organisms (source: Weekly Times article in 2012) Following the moderate winter of 2012, the large 2013 winter flow event with similar volumetric discharges from both catchments yielded low estuarine pH levels of ~4 that resulted in fish deaths (27 August 2013 EPA Victoria media release) Following the wet winter of 2013, the relatively modest winter of 2014 led to a period of marked decreases in estuarine pH (continuous data of 5-6 see Figure 8, EstuaryWatch data <5 see Figure 7) and
The mine and power station site discharge contributes a major component of the water inputs into the estuary, and generally is the only source during the summer-autumn period. This discharge has a substantive impact on summer estuarine water levels.
Figure 11 Monthly discharge of mine and power station discharge and catchment sources.
Representative Period for Assessment of Acidic Catchment Inputs In order to predict effect of the cessation of mine and power station inputs on estuarine pH (i.e. loss of beneficial dilution and acid neutralising capacity by the mine and power station discharge on acidic catchment winter inflows), the onset of the 2012 moderate winter event has been selected as the investigation period because:
It is likely the mine and power station discharge will be insufficient to mitigate (or buffer) acidic catchment inputs from large winter discharge events (2013)
For moderate flow events such as 2012, 2013 and 2014, the mitigating effect of the mine and power station discharge may be substantive
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The onset of winter 2012 inflows clearly show that Marshy Creek discharge was approximately 2-3 fold greater than Salt Creek with the mine and power station discharge contributing an intermediate volume (Figure 12 top panel). Perhaps more importantly, the initial chemistry of the estuary prior to the 2012 winter can be more readily estimated under these conditions
The continuous measurements show a gradual decline in pH during mid-June followed by a marked estuarine decrease over the period of 26-28 June 2012 (Figure 12 bottom panel), which provides an ideal event to gauge the relative effect of the mine and power station discharge on buffering this event and Estuarine water levels over the winter of 2012 were greater than predicted maximum tides, hence the effect of intrusion of marine waters from the adjacent coastal waters was minimal during the winter, and thereby the simplified assumption of a relatively constant sand bar elevation is justified (Figure 12 upper middle panel).
Figure 12 (1) Winter 2012 inflows, (2)continuous estuarine water level (m AHD) with predicted ocean tides, (3) continuous salinity with spot measurements from Salt Creek and Marshy Creek and (4) pH with spot measurements from Salt Creek and Marshy Creek). Red arrow denotes focus of hydrodynamic and geochemical modelling investigations.
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The EstuaryWatch data provides an indication of the variability in salinity and pH during the 2012 event (Figure 13), namely:
Salinity stratification persists in the bottom waters of sites A3 (~25 ppt) and A5 (~20 ppt), and to a lesser extent at A1 (5-15 ppt)
The salinity of the surface waters tends to be ~4-5 ppt throughout 2012
The pH of the entire estuary decreases to 5-5.5 and remains so throughout the winter and The pH of the bottom waters at site A1 decreases more slowly over the winter period.
Figure 13 EstuaryWatch data at surface and bottom at 5 estuarine stations of salinity and pH.
2.5 Multi-Annual Water Balance Model
2.5.1 Water Balance Description
A multi-annual water balance model was developed using information between 1 November 2011 and 30 June 2015 to predict the effect of the loss of the mine and power station discharge on estuarine water levels. Two types of water balance models were developed, namely:
A ‘forced’ water balance model that calculates the outflow to the ocean as the difference between the predicted volume and the estimated volume on the basis of measured water levels. The primary purpose of the ‘forced’ model was to ‘verify’ the applicability of the ‘forecast’ model (see next) and
A ‘forecast’ water balance model with a user-defined maximum water level (i.e. sand bar elevation), in which excess water above this maximum level discharges into the adjacent coastal waters. This model predicts the water levels explicitly below the maximum sand bar level during periods of a negative water balance when there are no outflows to the adjacent coastal waters.
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The water balance period from 1 November 2011 to 30 June 2015 coincides with the record of continuous water level measurements for the ‘forced’ model.
The ‘forced’ water balance model calculates the estuarine outflows to the adjacent coastal waters as: =
𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 where 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 − 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 = + + 𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌+ 𝑉𝑉𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑉𝑉𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 − 𝐺𝐺𝐺𝐺 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 and 𝐶𝐶ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑖𝑖𝑖𝑖 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 = + 𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 The ‘forecast’ water balance𝐶𝐶ℎ model𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑖𝑖𝑖𝑖 calculates𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 the𝑉𝑉 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀predicted volume𝑉𝑉𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 as: = + + 𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌 The 𝑉𝑉daily𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑃𝑃𝑃𝑃𝑃𝑃estuarine𝑃𝑃𝑃𝑃 𝑉𝑉𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 outflow to𝐼𝐼𝐼𝐼 the𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 adjacent𝐼𝐼 𝑅𝑅𝑅𝑅𝑅𝑅 𝑅𝑅𝑅𝑅coastal𝑅𝑅𝑅𝑅𝑅𝑅 − waters𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 is𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 comprised− 𝐺𝐺𝐺𝐺 𝐿𝐿 due𝐿𝐿𝐿𝐿𝐿𝐿 𝐿𝐿to𝐿𝐿 𝐿𝐿the− 𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂water level𝑂𝑂 above the (user-defined height) of the sand bar. The predicted surface level is derived from the relation between the adopted relation between volume and water level (see Appendix A). Refer to Appendix A for the water balance inputs.
2.5.2 Water Balance Model Results
The ‘forecast’ water balance model outputs shown here with and without the mine and power station discharge are for a sand bar elevation of 1.5 m AHD. Water levels above this elevation are predicted to simply overflow into the ocean. No allowance has been made in the water balance model for inputs of marine water into the estuary.
Volumetric Fluxes The daily volumetric fluxes of each of the water balance components are illustrated in Figure 14 and summarised in Table 17 (Appendix A). A comparison of the ‘forced’ (upper panels) and ‘forecast’ (middle panels) water balance terms with the mine and power station discharge indicate that the two dominant components of inflows (0% difference) and outflows (0.5% difference) are very similar, which suggests the ‘forecast’ water balance approach with a simple maximum water level is a reasonable approximation. Clearly the ‘forecast’ water balance with (middle panels) and without (bottom panels) the mine and power station discharge have a marked impact on greatly decreased summer inflows and outflows. Table 1 Sum of major water balance terms over the water balance model application period (volumes in m3)
Forecast Mine Forced Mine and and power Forecast No Mine Water Balance power station station and power station Inflow 8,740,091 8,740,091 3,551,317 Rainfall 419,570 405,921 279,687 Evaporation -863,976 -844,423 -634,467 Groundwater -267,400 -267,400 -267,400 Change in Storage 37,875 0 -1,122 Outflow -8,024,398 -7,985,927 -2,999,481
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Figure 14 Water balance results for ‘forced’ water balance with past observations (top) and ‘forecast’ water balance with (middle) and without (bottom) Mine and power station discharge. Full (left) and partial (right) ranges of the water balance volumes illustrated to emphasise large (e.g. inflows, outflows) and small (e.g. evaporation, groundwater losses), respectively.
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Water Levels The measured (i.e. inputs to ‘forced’ model) and predicted (from the ‘forecast’ model) water levels are illustrated in Figure 15.
The predicted water levels of the forecast model with the mine and power station discharge were consistently 1.5 m AHD, which corresponds to the constant sand bar height that was configured for the ‘forecast’ water balance. This water level essentially corresponds to the middle of the measured water level range of 1.3-1.7 m AHD that occurred from 1 November 2011 to 30 June 2015.
The predicted water level without the mine and power station discharge by the ‘forecast’ model markedly decreased each summer with the cessation of catchment inflows. The decrease in the estuarine surface is dependent on how late in the spring the catchment inflows ceased. For example, Marshy Creek flowed until mid-January 2014 after which estuarine levels began to decrease, but only after attaining a minimum level of ~0.9 m AHD in June-July 2014 with the onset of winter wet weather. Alternatively the dry winter of 2014 only yielded catchment inflows until the start of November and had attained a low water level of 0.4 m AHD by the end of June 2015.
Figure 15 Predicted water levels with and without mine and power station discharge
To understand the minimum volume of water required to maintain estuary water levels over the summer low flow period in the estuary, a number of alternative discharge volumes were entered into the forecast model to determine changes to the water levels over the summer period.
The water level with a continuous discharge of 0.75 ML/day rather than the mine and power station discharge (4.5 by the ‘forecast’ model) predicts only relatively small decreases in summer water levels from 1.5 m AHD to 1.3-1.5 m AHD. However, there are uncertainties associated with the assumptions of the water balance model, namely:
Estuarine losses to groundwater were assumed to be 0.2 ML/day, but could be greater (Figure 21 in Appendix A) and
Evaporation was from Bureau of Meteorology monthly averages, but could be greater in certain years with elevated summer temperatures for longer time periods (Table 18 in Appendix A).
For example, estuarine groundwater losses of 0.4 ML/day (twice the assumed rate) and an increase in the assumed monthly evaporation rate estimates by 50% would require a 1.5 ML/day continuous discharge to maintain a summer water levels in the range of 1.3-1.5 m AHD.
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For the purpose of defining a minimum volume of water required to maintain the estuary water levels in the range of 1.3 to 1.5 AHD we recommend a range of 0.75 to 1.0 ML/day.
Figure 16 Predicted water levels with mine and power station discharge and 0.75 ML/day continuous discharge
2.5.3 Contour mapping of predicted water level change
To further illustrate the change in water levels with the reduced mine and power station discharge into Anglesea River estuary, a series of contours maps are presented in Appendix B. The contour maps provide an indication of water levels at 1.5 m AHD average river level, 1.0 m AHD and 0.5 m AHD.
For much of the length of the river the contour maps indicate the bed profile is relatively steep and as water levels drop there is minimal reduction in the channel width. At 1.0 m and 0.5 m AHD there is a significant reduction in channel width through Coogoorah Park and the estuary below McMillan St. The bed profile in these locations is shallower and the reduced water levels significantly reduce the channel width. The exposure of channel margins at Coogoorah Park is likely to lead to oxidation of acid sulphate soils.
2.6 June 2012 Winter Hydrodynamic Modelling
To assess the effect of the cessation of the mine and power station discharge in ameliorating the acidification of the estuary, the proportion of estuarine, Salt Creek, Marshy Creek and the mine and power station discharge were simulated for the onset of winter inflows during June 2012. Refer to Appendix C for a description of the hydrodynamic model inputs.
2.6.1 Hydrodynamic Model Results
A comparison of the hydrodynamic simulations during the onset of the 2012 winter (June-July) indicates the following: In both cases with and without the mine and power station discharge the outflows are essentially balanced by the inflows. There is a decrease of approximately 4 ML/Day for both the outflow and inflows from the loss of the mine and power station discharge (top panels of Figure 17)
The simulated static sand bar height yielded a constant water level of 1.45 m AHD with excess water above this height discharged into the adjacent coastal waters (upper middle panels of Figure 17)
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The measured continuous salinity of the bottom waters near the Great Ocean Road Bridge was simulated reasonably well over the first several weeks of the simulation (lower left panel of Figure 17). However, simulated salinity stratification was eroded into a homogenised state by the peak discharge on June 22-23 and
The mine and power station discharge water is simulated to account for approximately 25% of the estuarine volume for 3 weeks following June 28 (bottom lower panel of Figure 17). The simulation without the mine and power station discharge yielded an increase in the proportion of Marshy Creek waters in the estuary on June 28 from 35% to 40% and Salt Creek from 15% to 19%. The proportion of estuarine waters prior to the winter inflows on June 28 increased from 25% to 40%.
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Figure 17 Simulation of June 2012 inflow event with (left) and without (right) mine and power station discharge
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2.7 Geochemical Modelling - Winter 2012
Winter geochemical modelling focused on ascertaining whether the discharge has a material effect on buffering the rapid decrease in pH of the estuary from acidic winter catchment inflows. As discussed in Section 2.4.3 the onset of the 2012 winter was selected because it was a moderate event that was comprised of both Marshy Creek and Salt Creek inflows. The geochemical modelling was performed using weekly data from 7-28 June 2012. As identified in previous investigations (Maher 2011, Pope 2010), elevated levels of dissolved aluminium (particularly in Salt Creek) likely cause aluminium hydroxide precipitation that can greatly increase pH depression of the receiving estuarine waters. To investigate the potential effect geochemical simulations were carried out with and without aluminium hydroxide precipitation.
2.7.1 Geochemical Analyte Inputs
Representative analyte concentrations for the geochemical modelling with PHREEQCI are summarised in Table 2. Limited analyte data sources were available for the geochemical modelling exercise. Table 3 provides a summary of sources to define colour coding in table 2. Table 2 Geochemical concentration inputs for geochemical modelling. Colour coding re data sources is outlined in Table 3
PREEQCI Inflow Inputs Mine and Initial Estuary Analyte Salt Marshy Seawater power (Week 0) station T (°C) 10 10 10 10 10 pH 3.7 3.4 7.5 7.9 8.2 Salinity 1,200 1,900 4335 20,012 34,483 Fe 0.56 1.71 0.23 0 0 Mn 4 0.5 0.09 0 0 Zn 1.7 0.09 0.06 0 0 SO4 755 325 1,300 2,001 2,649
Cl 105 695 600 10,158 18,980
mg/L B 0.09 0.10 8.25 38 65 Al 77 20 0.19 0 0 Ca 26 37 78.8 246 400 K 8.05 14 27.56 211 380 Mg 58 62.5 150.6 729 1,262 Na 87.5 390 596.9 5,776 10,556 Alkalinity (mg 20 CaCO3/L) 0 0 70 117
Acidity (mg CaCO3/L) 500 25 0 0 0
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Table 3 Colour legend for description of data source
Colour Description of Data Source Legend Major ion composition of seawater in mg/L (http://www.lenntech.com/composition-seawater.htm). No cation analysis is available for mine and power station discharge. Values have been estimated as average catchment concentrations based on data from the upper catchment GHD (2014) and increased by a multiplicative factor of 2.5 to reflect geochemical processes in the estuary. Initial estuary concentrations estimated from proportion of seawater and Mine and power station discharge (i.e. no catchment inputs as prior to Salt and Marshy creeks had any runoff). Data from continuous monitoring instrumentation Data from grab sample measurements 'around' the 2012 event sampled by GHD (2014) on 12 June and 7 August 2012 (Salt and Marshy creeks) and from the mine and power station on 19 June and 17 July 2012. Manual adjustments for charge and/or TDS balance Mine and power station compliance monitoring average of July-November 2001 from Hermon (2002) Gower (2000) sampling on one date (27 September 2000) Guestimate on 1990-1997 Alkalinity of site source waters from Gower (2000) reported in Hermon (2002) where Mine and power station discharge has alkalinity of 1.3 mg CaCO3/L at ~2.5 MLD and bore field had 26.2 mg CaCO3/L at ~7.5 MLD to cooling tower, so rough guestimate of (1.3*2.5+26.2*7.5)/(7.5+2.5)= 20 mg CaCO3/L Informed estimate, based on the best available information Nordstram et al. (1979)
2.7.2 Mixing Ratio Inputs
Mixing ratios at each of the nodes (as displayed in Table 4 .) for the geochemical modelling with PHREEQCI are summarised in Table 4. The mixing ratios at Nodes 1 and 2 are simply based on volumetric discharge ratios of the catchment inputs and mine and power station discharge, respectively (refer to Section 2.4.1). The mixing ratio at Node 3 was based on the proportion of the estuarine volume that a particular week of inflows contributed, which was estimated from the conservative inflow tracers from the hydrodynamic simulations. Table 4 Mixing ratio inputs for geochemical modelling
Existing End of Mixing Ratio with Node discharge Week NO discharge (status quo) 1 0.15 0.15 1 (Salt Creek mixing ratio with Marsh Creek) 2 0.42 0.42
3 0.21 0.21 1 0.54 - 2 (Mine and power station Discharge mixing ratio 2 0.33 - with Catchment Inflows) 3 0.31 - 3 (Total Inflows mixing ratio with Estuary Week 0 1 0.10 0.04 concentrations) 2 0.35 0.26 3 0.25 0.28
2.7.3 Geochemical Modelling Results
The preliminary PHREEQCI geochemical modelling results for the two cases (with and without the mine and power station discharge) and with and without the key geochemical process of aluminium hydroxide precipitation are shown in Table 5. The only data available to verify the predictions are pH measurements from the Great Ocean Road Bridge continuous monitoring (Section 2.3.1) and the EstuaryWatch pH measurements (Section 2.3.2).
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A comparison of the geochemical model predictions of pH with measurements indicates that:
The end of week 1 is simulated appropriately at approximately a pH of 8
The end of week 2 is simulated within the observed pH range without aluminium hydroxide precipitation, but simulated too low of a pH with precipitation and
The pH at the end of week 3 is simulated too high without precipitation, but too low with precipitation. Table 5 PHREEQC geochemical modelling results
Mixing Ratio existing discharge Mixing Ratio with NO discharge (status quo) Diss Al Diss Al Diss Al Diss Al End of Observed pH pH pH pH Node (mg/L) (mg/L) (mg/L) (mg/L) Week pH Without Al With Al Without Al With Al Hydroxide Hydroxide Hydroxide Hydroxide Precipitation Precipitation Precipitation Precipitation 1 - 3.4 28.6 3.4 28.6 3.4 28.6 3.4 28.6 1 2 - 3.5 44.0 3.5 44.0 3.5 44.0 3.5 44.0
3 - 3.5 32.0 3.5 32.0 3.5 32.0 3.5 32.0 1 - 4.9 13.3 4.5 12.9 2 2 - 4.0 29.5 4.0 29.5
3 - 3.9 22.1 3.9 22.1 1 1 7.8 8.0 1.3 8.0 0.0 8.0 1.1 8.0 0.0 7.1 1 3 2 2 6.4 11.2 4.7 3.9 6.4 12.3 4.7 4.0 6.3-6.7
5.4 1 3 2 6.1 13.9 4.3 8.5 6.0 17.8 4.0 11.9 5-5.5
(1) Great Ocean Road Bridge on day,
(2) EstuaryWatch on 18-June for Week 2 and 5-July for Week 3) Results presented by Parsons (2011) (see Figure 4) indicate that pH levels below the mine and power station discharge after rainfall range from 3.5-4.9, similar to the simulated range. Hence, this suggests that the modelling reproduces the geochemistry of the mix of source waters to the estuary during inflow events.
There is considerable uncertainty in analyte concentration values used during the assessment, particularly the cations and alkalinity of the mine and power station discharge, and the estuarine chemical composition at the onset of the 2012 winter inflows (Table 2). The effect of aluminium hydroxide precipitation is a key process, whereby the relatively large pH depression is associated with stripping out hydroxide ions from the waters by the precipitate. Further, the PHREEQCI simulations calculate equilibrium concentrations from the resultant mix of different water types in the estuary over a weekly time scale. As such, it may be that the rate kinetics (i.e. the time to reach equilibrium) for the simulated precipitation is not instantaneous (as modelled here). Instead the rate kinetics are potentially slower, over-predicting pH depression of the estuary.
Supposing that the geochemical modelling provides an indication of the ‘relative’ effect of the mine and power station discharge on ameliorating the effect of acidic catchment discharges on estuarine pH levels (and potentially aluminium) of the estuary, the following is noted:
The loss of the mine and power station discharge is predicted to cause a slight pH decrease (0.1-0.3 units) in the simulations with and without aluminium hydroxide precipitation and
The loss of the mine and power station discharge is predicted to cause a 30-40% increase in the dissolved aluminium levels, which though material, will cause a toxic effect. ANZECC & ARMCANZ (2000) trigger values for aluminium at an 80% level of
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species protection is 0.15 mg/L, two to three orders of magnitude less that the aluminium concentrations simulated in the estuary at the end of week 3 (8.5-17.8 mg/L).
2.8 Marshy Creek Observations
During the course of the numerical modelling and analysis of the suite of results available for the Anglesea River catchment, some critical observations were apparent for Marshy Creek from the monitoring results. Marshy Creek has historically contributed the majority of water volumes during catchment inflows from Salt and Marshy Creeks (Figure 18). Both inflows introduce low pH waters into the Anglesea River estuary. The risks from Marshy Creek have usually been viewed as less severe than Salt Creek as Marshy Creek has been reported with less acid generation potential and therefore, less opportunity for metal liberation from the catchment. Figure 18 Water volumes contributed by Salt and Marshy Creeks, and mine and power station between 2011 and 2015
The analysis of the data for Marshy Creek catchment between 2010 and 2015 indicates that Marshy Creek is experiencing a strong trend of increasing metals (aluminium, iron and zinc) (Figure 19). The graphs also depict
The measured pH is consistently low in the catchment, neutral in the mine and power station discharge and some neutralising/dilution of catchment levels in the regulatory mixing zone and
Slight trend of decreasing aluminium, iron and zinc in mine and power station’s discharge and also Salt Creek flows.
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Figure 19 Water quality results collected for Marshy Creek, Salt Creek, the mine and power station discharge and mixing zone between January 2010 and January 2015 (Alcoa data).
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2.9 Summary of predicted physical changes
The numerical modelling presented in this chapter indicates the following: Ceasing the mine and power station discharge is likely to reduce the water level by approximately 1 m in peak summer periods. The contour maps (Appendix B) illustrate that water levels will substantially reduce across more shallow areas of the estuary. The mudflats and channel in the lower estuary and also Coogoorah Park will be exposed during summer periods. Sediments in these areas are coastal acid sulphate soils. Exposure of these sediments has the potential to result in acid generation which can lead to environmental, social and economic impacts. The reactivity and potential rate of oxidation of these soils (and hence risk to the receiving environment) is currently unknown. A predicted continuous discharge of a minimum volume of 0.75 – 1.0 ML/day rather than the 4.5 ML/day of mine and power station discharge will maintain water levels albeit with relatively small decreases in levels. These estimates are conservative and would require more detailed modelling to confirm the volumes required to maintain river levels.
The mine and power station discharge has a neutral to alkaline pH, and is within EPA licence limits. This discharge does not buffer the low pH waters entering the mixing zone, nor mitigate the acidic catchment inputs from large winter discharge events. Moderate winter events are mitigated to an extent by the mine and power station discharge, and it dilutes the high rainfall event catchment inflows.
Stratification of the Anglesea River estuary is a common occurrence, with salt water overlain by freshwater inflows. The reduced mine and power station discharge will increase stratification of the estuary. Stratification will only be reduced with increasing frequency and intensity of freshwater upper catchment inputs.
Though there is considerable uncertainty in analyte concentration values used during the assessment, the geochemical modelling indicates that the concentration of aluminium entering the Anglesea River estuary without discharges is expected to increase by 30 – 40%. Concentrations of aluminium currently entering the River are well above water quality criteria for protection of aquatic species.
The cessation of the mine and power station discharge will result in an increased proportion of flow contributions from Marshy Creek. The analysis of data for Marshy Creek catchment between 2010 and 2015 indicates that Marshy Creek is experiencing a strong trend of increasing metals (aluminium, iron and zinc). This trend does not appear to be plateauing.
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3. Predicted ecological changes
3.1 Objective
The objective to this section is to provide an overview of the impact of the expected physical change arising from changes to the mine and power station discharge on the terrestrial and aquatic ecology of the Anglesea River estuary.
3.2 Approach
The hydrodynamic, water balance and geochemical modelling provides the basis for predicting impacts to the ecological values of the Anglesea River estuary.
The Anglesea River estuary and floodplain contains dynamic and resilient vegetation communities and populations of terrestrial and aquatic fauna. Over the decades these communities have responded to a range of changing environmental conditions and urbanisation of parts of the catchment. The continuous discharge of mine and power station water will have influenced vegetation community composition and distribution providing favourable conditions over a greater area of the floodplain from the higher water levels over the summer period.
The assessment process recognises the current terrestrial and aquatic community structure and diversity will have changed in response to the increased flows. The assessment process was undertaken in two steps
Defined the current terrestrial and aquatic community status under the 4.5 ML/day discharge (status quo) and considered the benefits and impacts created by the mine and power station discharge to these communities
Identified the likely changes to the terrestrial and aquatic communities arising from no mine or power station discharge and defined the plausible benefits and impacts to the ecology of the Anglesea River estuary and floodplain.
An expert panel of highly qualified and experienced ecologists with extensive experience in the ecology of the Anglesea River estuary and floodplain have assessed the impacts of the physical changes to define the plausible direct and indirect impacts to the ecology of the system. Expert Panel included:
Andrew McMahon Ecology Australia - Terrestrial flora
Jonathon Ricciardello Ecology Australia -Terrestrial fauna
Dr Adam Pope Deakin University - Aquatic ecology
Where the modelling of a scenario has identified a significant change to physical parameters, the expert panel has identified and assessed the consequences of these changes to ecological values including wetland / swampland vegetation, fish, macrophytes, amphibians, terrestrial fauna, waterbirds and aquatic mammals.
3.3 Floodplain and aquatic vegetation communities
3.3.1 Vegetation communities
The vegetation of the estuary has been previously mapped by Australian Ecosystems, and incorporated in Investigation of Anglesea River Estuary Mouth Dynamics - Water Technology (2010). They describe 14 Ecological Vegetation Classes (EVCs) ranging in extent from <1 ha to 18 ha over a mapped area of 52 ha.
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Water levels within the Anglesea River estuary are likely to be playing a major role in influencing vegetation composition, distribution and their availability as habitat for fauna. Inflows from the mine and power station discharge, the state of the estuary mouth and seasonal rainfall are all likely to influence the current composition of vegetation communities and its availability as habitat within the system.
For the present study we have assigned an estuarine dependency factor for vegetation (none, low, moderate or high) to each of the EVCs based on the following broad parameters:
Hydrology – seasonal water regime including period and depth of inundation.
Water chemistry – particularly the relationship with freshwater, brackish or saline conditions and;
Topography – including relationship to high tide mark and various landforms, e.g. slopes and terraces. A summary of the geomorphological and water dependency of vegetation communities is provided in Table 6. Table 6 Anglesea Estuary: Ecological Vegetation Classes and their relative estuarine water dependency
Geology/Geomorphology EVCs Estuarine dependency Beach and dune Scrub Coastal Dune Scrub Low Fore-dune Grassland Low River alluvium and Swamp Estuarine Reedbed High deposits Estuarine Wetland High Estuarine Flats Grassland High Coastal Tussock Saltmarsh High Wet Saltmarsh Herbland High Submerged Herbfield High Brackish Sedgland High Saline Aquatic Meadow Low High Level Alluvium Swamp Scrub Moderate Swampy Riparian Woodland Moderate Eastern View Formation Heathy Woodland None
Demons Bluff Formation Coast Alkaline Scrub/Moonah Low/Moderate Woodland (FFG)
Vegetation communities with a moderate to high estuarine water dependency are those most likely to respond and transition to changes to estuarine conditions that could occur as a result of changes to the water regime in the estuary. Estuarine dependent vegetation communities and their key drivers is described in Table 7 along with key environmental attributes (drivers) that mostly likely influence vegetation community distribution and abundance across the estuary. Potential changes to these drivers are then considered in a risk and benefit context in relation to changes to mine and power station discharge or maintaining the status quo.
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Table 7 Anglesea Estuary: Estuarine Dependant EVC’s and Habitats
EVC’s/Habitats Key Drivers
Estuarine Reedbeds, Sedgelands and Fresh-Saline (glyophytes and halophytes) Grasslands Shallow (≤1 m) inundation/or waterlogged conditions Submerged Herbfield Brackish conditions, Near permanent inundation Saltmarsh communities Salinity (halophytes) Frequent or occasional tidal inundation Swampy Riparian Woodlands Freshwater Swamp Scrub Infrequent inundation Seasonally wet soils Moonah Woodlands Calcareous soils Freshwater to brackish conditions Open Water habitat Depth Water Quality
3.3.2 Factors influencing vegetation communities
Table 8 provides a broad assessment of benefits and risk to EVCs under continued flows, and changes to groundwater pumping.
Existing river and estuary conditions and their influence on vegetation communities The current water regime for the river is maintaining relatively high water levels year round. A summary of the benefits and impacts to vegetation communities is provided in Table 8. Maintenance of water levels will maintain current condition and extent of vegetation. One identified impact of the long term maintenance of elevated water levels has been the likely reduction of Swampy Riparian Woodland and Swamp Scrub. Table 8 Summary of current (status quo) estuarine conditions influencing vegetation communities
Values Benefits Impact
Estuarine sedgelands, Maintain condition and extent None foreseeable reedbeds and grassland Submerged Herbfield Maintain condition and extent None foreseeable
Saltmarsh communities Maintain condition and extent None foreseeable
Swampy Riparian Maintain condition and extent Possible historic reduction of Woodland, Swamp Scrub these EVCs with commencement of the mine and power station discharge, and expansion of estuary water levels over a greater area of the floodplain Moonah Woodland Maintain condition and extent None foreseeable
Open water habitats Maintain condition and extent None foreseeable
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Factors likely to influence vegetation communities distribution and composition from changes to mine and power station discharge to the river Notable physical changes to the Anglesea River estuary that may influence changes to vegetation communities include:
Significant decrease in water levels across the river and estuary during the low flow period (summer-autumn) Potential generation of acid sulphate soils within the estuary particularly the Coogoorah Park area, and
Changes in salinity concentrations. Key changes resulting from lower water levels over the summer period include:
Reduced extent and development of more ephemeral vegetation in the summer autumn drawdown zone, and Increased seasonal water stress for swampy riparian woodland and swamp scrub communities.
Reduced water levels may also result in increased salinity within the river Anglesea estuary. Increased salinity is likely to reduce the extent of submerged herbfields which are likely to be replaced by saline aquatic meadow. Impacts to open water habitat are also likely to occur.
Generation of acid sulphate soils due to lower water levels enabling oxidation processes may impact vegetation communities across the floodplain. The type and nature of the impact is difficult to quantify as there is a high degree of uncertainty in the oxidation potential of possible acid sulphate soils and limited knowledge on how vegetation communities may respond. A summary of changes to vegetation communities as a result from changes to the mine and power station discharge are provided in Table 9. Table 9 Summary of changes to vegetation communities should groundwater pumping cease
Values Benefit Impact
Estuarine Sedgelands, None foreseeable Reduced extent, development of a Reedbeds and Grassland more ephemeral vegetation in drawdown zone.
Submerged Herbfield None foreseeable Reduced extent and possibly replaced by Saline Aquatic Meadow if salinity increases during drawdown. Potential aluminium toxicity Saltmarsh communities Possible expansion of some Expansion limited by seasonal species in drawdown zone, inundation and potential acid e.g. Sarcocornia, Selliera and sulphate generation Samolus Swampy Riparian None foreseeable Potential for increased seasonal Woodland, Swamp Scrub water stress where estuary influencing groundwater levels Moonah Woodland None foreseeable None expected
Open water habitats None foreseeable Reduced extent, and change in composition if salinity increases during drawdown. Potential for toxic levels of dissolved aluminium
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3.3.3 Conclusions - Changes to vegetation communities
Ecological communities in the estuary are dynamic and resilient to changes to their environment. They will adapt and respond to a drier floodplain and to increases in salinity levels by changing their distribution. The communities will transition to a different composition and distribution in response to lower water levels and increases in salinity
The changes in water levels are likely to result in reduced extent of ephemeral vegetation during the low flow summer period. There is also likely to be increased seasonal water stress for Swampy Riparian Woodland and Swamp Scrub and
Reduced water levels may also result in increased salinity within the river and estuary. Increased salinity is likely to reduce the extent of Submerged Herbfields which are likely to be replaced by Saline Aquatic Meadow.
3.4 Floodplain Fauna
3.4.1 Faunal communities
The Anglesea River estuary provides habitat for a diversity of terrestrial faunal species and communities including frogs, reptiles, mammals and birds. However, two main groups have been identified that have an obligate dependence on water dependant vegetation types and/or aquatic environments for aspects of their biology. These are as follows:
Frogs Four species of frogs have been recoded within the Anglesea River system (Ecology Australia 2013). This includes three spring/summer breeding species (Common Froglet, Southern Brown Tree Frog and Southern Bull Frog) and one autumn breeding species (Victorian Smooth Froglet).
Waterbirds A diversity of water birds is known to occur in the Anglesea River (VBA 2015). These species fall within a number of functional groups based on their feeding/foraging ecology as defined in Kingsford et al. (2012). These are:
Ducks/small grebes (e.g. Musk Duck, Chestnut Teal, Pacific Black Duck, Hoary-Headed Grebe);
Herbivores (e.g. Eurasian Coot, Purple Swamphen, Dusky Moorhen);
Shorebirds (e.g. Buff banded Rail, Latham’s Snipe, Red-necked stint); Piscivores (Pied Cormorant, Little Pied Cormorant); and
Large Wading Birds (Eastern Great Egret, White-necked Heron).
3.4.2 Factors influencing terrestrial faunal communities
Faunal communities within the Anglesea River estuary are predominantly influenced by the type of habitat that occurs within the system. This includes the structural composition of the habitat (e.g. availability of cover as refuge for a variety of species), availability of feeding foraging substrates (e.g. open mudflats for wader foraging), and water availability for breeding (e.g. frogs).
Water levels within the Anglesea River estuary likely to be playing a major role in influencing habitat characteristics and availability. Inflows from the mine and power station, the state of the estuary mouth and seasonal rainfall are all likely to influence the composition/availability of habitat within the system over the immediate past decades.
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For example, high inflows (natural and pumped) combined with a closed river mouth can result in the inundation of large areas of shallow estuarine wetlands and reed beds. Resulting habitat can be highly suited to frog breeding. These sites provide sheltered locations for egg deposition, and a degree of protection from likely predatory fish found in the deeper more open water areas of the estuary.
Conversely, reduced inflows will reduce the overall water level throughout the estuary over the summer-autumn period and is likely to provide greater areas of exposed sediments available for shorebirds and waders to forage.
An assessment of the benefits and impact to each of the faunal groups is presented in the following section.
3.4.3 Response of terrestrial fauna to physical and chemical changes
A change to the watering regime of the Anglesea River estuary is likely to have a direct influence on habitat availability across the site. These changes are likely to occur in the short and long term, with immediate seasonal changes in habitat availability occurring with the ceasing of mine and power station discharge and long-term gradual changes to vegetation associated with regular decreases in water levels over the summer/autumn period.
Current river and estuary conditions Current conditions maintaining vegetation communities and habitats are in relative equilibrium. Table 10 provides a broad assessment of benefits and risk to fauna and habitats under the current conditions of a mine and power station discharge to the river. Table 10 Summary of likely changes to terrestrial fauna resulting from mine and power station discharge (status quo) to in the Anglesea River estuary
Value Benefit Impact
Frogs Viable breeding habitat available None foreseeable for a longer period of time including during both Spring/Summer and Autumn/Winter breeding species. Waterbirds - Larger areas of open water for None foreseeable Ducks /Small feeding on aquatic plant, Grebes crustaceans, molluscs and insects. Waterbirds - Large areas of cover available Continued high water levels may Herbivores from predators due to shallow reduce available terrestrial flooding of surrounding plains foraging habitat (e.g. extensive areas of estuarine reed bed and wetland). Waterbirds - None expected None foreseeable Shorebirds Waterbirds - Greater availability of aquatic None foreseeable providing fish Piscivores habitat for foraging and available death events are infrequent prey species Waterbirds-Large Increased availability of foraging None foreseeable Wading Birds habitat due to inundation of mudflats, estuarine margin and associated shallow wetland systems.
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Predicted changes to faunal communities from changes to mine and power station discharge to the river Notable physical changes that may impact fauna include: Decrease in water levels across the river and estuary during the low flow period (summer- autumn)
Potential generation of acid sulphate soils within the estuary particularly the Coogoorah Park area, and
Changes to vegetation communities as available habitat.
Table 11 provides a summary of anticipated changes to fauna as a result of changes in the mine and power station discharge.
Lower water levels are likely to influence frog populations by reducing the breeding season (Table 11). The physical changes in the water level will change the distribution of vegetation communities as habitat for different classes of fauna. In particular waterbirds guilds will have varying degrees of benefit and impact as changes to vegetation communities will impact some waterbird guilds and benefit others (e.g. increased foraging habitat for shorebirds and waders) (Table 11).
Impacts to waterbirds are likely to result from changes to vegetation communities reducing foraging habitat where vegetation communities are water dependant. Estuarine Reed Bed and wetland communities cover large areas of the river. A reduction in these vegetation communities could result in a reduction in refuge and cover impacting herbivore waterbirds possibly leading to a reduction in carrying capacity of the vegetation. Table 11 Summary of likely changes to terrestrial fauna of changing mine and power station discharge to the Anglesea River estuary
Value Benefit Impact
Frogs None foreseeable Reduced duration of breeding season for both spring/summer and autumn breeding frogs. Increased risk of aluminium toxicity.
Waterbirds -Ducks None foreseeable Reduction in foraging habitat due to /Small Grebes lower water levels. Increased risk of aluminium toxicity, including impacts to prey species. Waterbirds - Increased availability of Potential reduction in cover/refuge Herbivores terrestrial foraging habitats provided by large areas of inundated due to lower water levels estuarine reed bed and wetland. Waterbirds - Increase in availability of Potential generation of acid sulphate Shorebirds foraging habitat due to soils. increased levels of mudflat exposure Waterbirds - None foreseeable Reduced aquatic habitat for prey Piscivores species. Increased potential for fish death events due to an increase in aluminium levels. Waterbirds-Large None foreseeable Potential generation of acid sulphate Wading Birds soils impacting benthic fauna as a food source.
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3.4.4 Conclusions - Impacts to fauna
While there are potential benefits for a number of values at the site (e.g. increased foraging habitat for shorebirds and waders) there is likely to be a number of changes to habitat associated with lower water levels. The impacts associated with changes will likely lead to reduced water levels that may impact frog breeding events and habitat availability. Changes to vegetation may also lead to reduced cover, habitat and foraging areas for waterbird herbivores, ducks, small grebes, and reduced habitat for prey species for piscivores (fish eating birds).
Generation of acid sulphate soils due to lower water levels may also impact some aquatic vegetation communities. The consequences of these changes are difficult to quantify as there is a high degree of uncertainty in the reaction rate of coastal acid sulphate soils in the river. Acid sulphate soils may also impact benthic fauna as food source for waterbirds and cause increased bioavailability of metals from sediment may also compromise the survival of amphibians.
3.5 Aquatic ecology
3.5.1 Aquatic communities
Anglesea River estuary is home to seagrass beds, benthic microalgae and phytoplankton, benthic and pelagic invertebrates and fish. Related groups - submerged aquatic meadows and wading birds - have been addressed in sections 3.3 and 3.4.
Seagrasses Two genera of seagrass have been recorded in the Anglesea River estuary, Zostera and Ruppia (Pope 2006). These occur in the lower estuary, below the Great Ocean Road bridge (Figure 20) although there are records of plants occurring almost upstream to Coal Mine road prior to the construction of Coogoorah Park (Atkins & Bourne 1983). Within the lower estuary seagrasses typically are found along the edges of the central channel and can extend across the mudflats as far as the seawalls.
The extent of seagrass has varied considerably though time, both seasonally and between years (eg Figure 20). These changes can be related to changes in water level, which affects the amount of habitat available, and salinity, which favours Zostera as it increases.
Algae The algal community of Anglesea River estuary is dominated by phytoplankton in the water column and microphytobenthos on the sediment surface, with macroalgae occurring occasionally, notably as epiphytes on seagrasses. There is little information on species composition or dynamics of these groups in the Anglesea River Estuary specifically however, like many estuaries, algal blooms are experienced occasionally.
An effect of this that has been measured in Anglesea River estuary is dissolved oxygen concentration increased by photosynthesis to well above 100% of the concentration that could otherwise be carried. For example, in the four years between 2006 and 2010 concentrations greater than 120% of were recorded in two years in the lower estuary and one year in the upper estuary (EstuaryWatch data). The likelihood of algal blooms is related to the availability of nutrients and water residence time of an estuary (Suthers & Rissik 2008).
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Figure 20 Seagrass coverage at times of high (green, Nov 1999) and low (orange, Sep 1993) extent. Data from Pope (2006).
Invertebrates No specific studies of the invertebrate community of Anglesea River estuary are known although a typical group of benthic species that have been observed include the crab, Amarinus lacustris and various species of polychaete worms, gastropods and molluscs (Pope pers ob., Atkins & Bourne 1983).
Fish Recent surveys of fish in the Anglesea River estuary have been reported in ARI (2011) and Tonkin et al. (2014). The fish assemblage of the Anglesea River estuary has a group of species typical of estuaries in the region with a combination of estuarine residents, marine species that also live in estuaries and species that migrate through the estuary: Estuarine residents include the black bream (Acanthopagrus butcheri) and several smaller species, the most common of which are the eastern blue-spot goby (Pseudogobius sp.) and the flathead gudgeon (Philypnodon grandiceps), which is also found in freshwater; Marine species that use the estuary include the yellow-eyed mullet (Aldrichetta forsteri) and western Australian salmon (Arripis truttaceus);
Migratory species include the short-finned eel (Anguilla australis) which breeds in the ocean and migrates to freshwater habitats as a juvenile and but can spend months in estuaries before returning to the sea. Galaxiids (Galaxias maculatus, G. truttaceus) also pass through the estuary as part of their breeding cycles.
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3.5.2 Factors influencing aquatic ecology
Physical and chemical changes identified in section 2 have the potential to influence all components of the estuarine ecosystem. Water levels have a direct influence on the extent and nature of habitat available for benthic organisms and seagrass extent has been shown to be strongly influenced by the periods of exposure (Pope 2006). In contrast to the steep-sided upper Anglesea River estuary, the lower estuary has a large area of mudflat that has been exposed following deep openings and which would be exposed most summers should water levels be reduced during the summer period.
The mine and power station discharge has provided continual connectivity between estuarine waters and upstream freshwater environments. Without the discharge movement of fauna between these environments would be restricted on a seasonal basis. The rate of discharge has also led to a relatively short residence time of waters within the estuary, in the order of weeks even with limited tidal exchange. A decrease in the flushing of the estuary would be likely to increase nutrient concentrations and the potential for algal blooms.
Salinity structure is one of the most important drivers of estuarine ecology. Like many Victorian estuaries Anglesea River estuary is regularly stratified, with a surface layer of fresher water overlying denser and saltier marine waters. The spatial distribution of salinity within the estuary is complex, and relates to sequences of freshwater flow and the degree of marine exchange. A dry summer with continual discharge and a closed mouth the Anglesea River estuary has been observed to gradually destratify so that by the end of summer almost all the water in the estuary is close to fresh. In contrast, Painkalac creek estuary, without a continual input has mixed vertically but at moderate to high salinities. Maintenance of a halocline can also lead to deoxygenation of bottom waters, increasing the risk of fish deaths with mouth openings.
The low pH and high metal concentrations that flow from the Anglesea River catchment are toxic to most aquatic organisms (reviewed in Sharley et al. 2014). The inflow of these waters to the estuary during low to medium flows without the mine and power station discharge or from exposure of acid sulphate soils adjacent to the estuary could have impacts for aquatic organisms. Given the history of acid/metal inputs to the estuary, the extent of these changes and the degree of associated impact is unclear. In a stratified system buffering effects would be minimal due to limited mixing, as seen in the first two weeks of the modelled moderate winter flow scenario. In this circumstance there may be an increased frequency or duration where surface waters are unsuitable for most aquatic organisms. There is evidence of substantial resilience to past acid/metal inputs, specifically for seagrasses (Pope 2006) and fish (ARI 2011) but little information to determine where any thresholds may be for these groups.
3.5.3 Response of aquatic communities to physical and chemical changes
Summaries of likely benefits and impacts of the current (with mine and power station discharge status quo) are provided in Table 12 and without mine and power station discharge for all factors are shown in Table 13.
Seagrasses are likely to be the most affected by changes in water levels, with similar effects for other benthic species that live on and in the mudflats in the lower estuary. Losses and gains of seagrass may have effects across trophic levels, affecting abundances of invertebrates and fish as modelled by Sharley et al. (2014).
Increased salinity over summer months is likely to benefit marine and estuarine resident species of fish, particularly in dry years when the mouth remains closed. In these circumstances the majority of estuarine waters have been observed to be derived from the mine and power station discharge at relatively low salinities and
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There is substantial uncertainty about the timing and extent of increased pH/metal exposure and in the capacity of the aquatic organisms to cope with this. In the case of fish there is some evidence that larger bodied species are able to avoid such events (ARI, 2014). Table 12 Summary of expected response of aquatic organisms in the Anglesea River estuary to the increase in summer flows and water height following the commencement of the mine and power station discharge
Value Benefit Impact
Seagrasses In years with no major entrance Reduction in salinity of openings mudflat habitat would be estuary in dry years available for a longer period of time potentially favouring Ruppia including summer growth period. Reduction in frequency and duration of pH/metal exposure during low/moderate flows Microalgae Decreased residence time in low/zero None foreseeable flow reduces risk of algal blooms Invertebrates In years with no major entrance None foreseeable openings higher water level makes mudflat habitat available for benthic invertebrates in lower estuary Reduction in frequency and duration of pH/metal exposure during low/moderate flows Fish – Estuarine Reduction in frequency and duration of Reduction in salinity of Resident pH/metal exposure during estuary in dry years low/moderate flows Reduced incidence/severity of fish deaths due to reduced aluminium levels Increased availability of habitat due to inundation of mudflats, estuarine margin and associated shallow wetland systems. Maintenance of halocline in some years – benefits for black bream recruitment Fish – Marine Reduced incidence/severity of fish Increase in salinity of species deaths due to reduced aluminium estuary in dry years levels. Greater availability of aquatic habitat. Fish - Migratory Continuous passage available between estuarine and freshwater habitats. Inundation of fringing macrophytes – common galaxiid egg laying sites
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Table 13 Summary of the expected response of aquatic organisms to the removal of the mine and power station discharge to the Anglesea River estuary
Value Benefit Impact
Seagrasses Increase in salinity of estuary Exposure of mudflats in lower over summer favouring estuary reducing available Zostera seagrass habitat Increase in frequency and duration of pH/metal exposure during low/moderate flows – reduced growth Microalgae None foreseeable Increased residence time in low/zero flow increases risk of algal blooms Invertebrates In years with no major Exposure of mudflats in lower entrance openings mudflat estuary reducing available habitat habitat available for benthic Increase in frequency and invertebrates in lower estuary duration of pH/metal exposure during low/moderate flows Fish – Estuarine Increase in salinity of estuary Increase in frequency and Resident in dry years duration of pH/metal exposure during low/moderate flows Increased incidence/severity of fish deaths due to reduced aluminium levels Increased availability of habitat due to inundation of mudflats, estuarine margin and associated shallow wetland systems. Fish – Marine Increase in salinity of estuary Increased incidence/severity of species in dry years fish deaths due to elevated aluminium concentrations. Lesser availability of aquatic habitat Fish - Migratory None foreseeable No passage available between estuarine and freshwater habitats at times of zero natural flow.
3.5.4 Conclusions
The commencement of the mine and power station discharge would have increased flows and water levels over the summer low flow period. Aquatic organisms would have responded to this change by increasing seagrass habitat, reducing the risk of algal blooms, increased aquatic habitat for fish and other species, reduction in fish deaths arising from lower residence time of low pH waters in the estuary and increased freshwater habitat in the upper estuary. This aquatic community is one that reflects the duration of mine and power station discharge and shows signs of resilience to physic-chemical challenges.
Ceasing the mine and power station discharge is likely to affect aquatic organisms via several mechanisms including reduced water levels, exposure of mudflats, and increases in salinity levels.
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Major changes to aquatic organisms from cessation of mine and power station discharge would be:
A reduction in the average area of seagrass in the lower estuary over time and associated indirect effects on the aquatic food web
Increased risk of algal blooms
Potential benefits to marine and estuarine fish from increased salinity and Possible but hard to define impacts on all estuarine organisms from increases in acidic inflows and metals due to the longer residence time of estuary waters.
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4. Social (and Economic) Impacts
4.1 Objective
To identify and document potential social impacts (and related economic aspects) that could result from the expected physical change to the Anglesea River estuary.
4.2 Approach
The approach to this section involved a review of studies around the Anglesea River estuary and identifying and cataloguing values described in the reports. Social and economic values have also been discussed and communicated at the Anglesea Futures Forum, a working group that involves Surf Coast Council, DELWP, CCMA and community members. Numerous surveys have been completed that help shape the values and priorities of the range of stakeholders.
4.2.1 Social and Economic Values
Anglesea is a seaside holiday resort and supports permanent residents, holiday makers, day visitors and those on weekends away (CCMA, 2013). Tourism is the primary driver of the town and the seasonal use of the estuary reflects this, with peak use periods in the summer months (CCMA, 2014).
The natural environment of the Anglesea River estuary is commonly emphasised as a core value that requires protection. The natural environment of this system is intrinsically linked to the social and economic values that exist.
In the recently published Anglesea River Estuary Management Plan (EMP CCMA 2013), a spatial tool known as Asset Value Identification and Risk Assessment (AVIRA) has been used to collect data on the values, threats and risk to the Anglesea River estuary. AVIRA was developed by the Victorian State government to support the development of the regional waterway strategies.
The social and economic categories identified in AVIRA have assisted with identifying and categorising this current assessment of the social impacts associated with mine and power station ceasing its licenced discharge, the results of AVIRA have been used as a reference to confirm our understanding of the values that may be compromised. Of 26 values collated within AVIRA, some of the key ones for Anglesea include (in no specific order):
Recreational fishing
Non-motor boating
Motor boating Camping
Swimming
Beside water activities (tracks) Beside water activities (sightseeing)
Beside water activities (picnics and BBQs)
Landscape
Community groups
Boat hire
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Eco tours and
Various recreational camps.
The EMP (CCMA 2104) identified the most common threats to values within the Anglesea River estuary maintained with existing flows relate to visual impact of the consequence of that threat.
The highest risk identified by AVIRA was:
1. Acid sulphate soils Other high risks:
2. Altered water regimes
3. Invasive flora and fauna, and 4. Reduced connectivity.
Additional significant risks identified:
5. Altered physical form 6. Poor water quality and
7. Degraded habitats.
It is important to note that these risks are benchmarked against an intact estuary system and the score reflect changes such as the rock wall on the right hand side of the estuary, urban development, increased flow from the mine discharge, etc. In setting objectives for the River these changes due to urban development etc. would be taken into account and shape the objectives accordingly.
The predicted impact arising from the physical and ecological changes associated with ceasing flows into the Anglesea River estuary are outlined in more detail in Table 14.
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Table 14 Social and economic values impacted by physical and ecological changes resulting from reduced water levels and ecological changes as a result of ceasing the mine and power station discharge
Physical and Environmental Change
Values Description Reduced Decreased Increased Terrestrial Aquatic Terrestrial Aquatic water pH CASS vegetation vegetation fauna ie. fauna ie. levels incidence i.e. EVC ie, Frogs Fish larvae seagrass waterbirds Social
Recreational Fishing from the bank of the river Fishing Fishing in the water Fishing on a motor boat Non-Motor Canoeing/Kayaking
Boating Rowing/Paddleboards Motor Boating Recreational Fishing
Estuary sight seeing Camping Bush camping areas along the river
Campgrounds with facilities Swimming Designated and undesignated
swimming areas Cultural The Wadawurrung Aboriginal Heritage community have stone artefacts and
shell middens located along the entire Anglesea River Estuary Estuary environmental education Education activities Beside Water Walking/Running/Cycling on paths. Activities Extensive network of paths that run along the bank
Picnics and Barbeques Markets Birdwatching Amenity Landscape amenity
Economic Tourism Retail and hospitality industries highly dependent on visitation (incl.
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Physical and Environmental Change
Values Description Reduced Decreased Increased Terrestrial Aquatic Terrestrial Aquatic water pH CASS vegetation vegetation fauna ie. fauna ie. levels incidence i.e. EVC ie, Frogs Fish larvae seagrass waterbirds markets) All social activities listed above in social values Boat hire At least two listed businesses that business hire out watercraft on the river Tour buses Common tourist location and stop
along the Great Ocean Road Markets Regular markets by the riverside Infrastructure Many varied types of infrastructure both private and public run alongside the river. Such as playgrounds, skate park, fishing platforms, public open
space, toilet facilities, trails, weather shelters, jetties, car parks and roads, retail premises, community buildings and boat sheds/ramps
Note: denotes that identified change to the Anglesea River estuary will impact the listed social, environmental and economic values. NA denotes that identified change will not impact values.
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4.3 Summary of impacts to social and economic value
The projected physical changes to the estuary that impact social and economic values would occur during the low flow summer period. During the winter and high flows periods catchment inputs would be sufficient to maintain water levels in the estuary.
Physical changes impacting social and economic values are reduction in water level inhibiting access to the river, exposure of mudflats in the upper and lower estuary. The activation of acid sulphate soils has the potential to lead to a range of impacts through lowering of pH and impacts to the natural environment. Reduced water levels over the summer period are likely to impact on water activities (motor and non-motor boating), swimming, recreational fishing, amenity, bird watching, beside water activities, boat hire business, markets, estuary education activities and infrastructure. The lower water levels will be most noticeable in the lower estuary below McMillan St and Coogoorah Park due to exposure of mudflats.
Reduced water levels in the lower estuary will reduce the availability of shallow water across the berm and area upstream which is heavily utilised by the community and visitors with young children.
Impacts to terrestrial vegetation and fauna are likely to have some impact to educational activities, birdwatching and landscape amenity.
Activation of acid sulphate soils and lowering of pH in the estuary has the potential to impact infrastructure increasing deterioration of the asset and a reduction in the design life.
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5. Key Findings Part 1
5.1 Summary of predicted physical changes
The numerical modelling associated with ceasing the mine and power station discharge presented in this chapter indicates the following:
Ceasing the discharge is likely to reduce the water level by approximately 1 m in peak summer periods. The contour maps (Appendix B) illustrate that water levels will substantially reduce across more shallow areas of the Anglesea River estuary.
The mudflats and channel in the lower estuary and also Coogoorah Park will be exposed during summer periods. Sediments in these areas are coastal acid sulphate soils. Exposure of these sediments has the potential to result in acid generation which can lead to environmental, social and economic impacts. The reactivity and potential rate of oxidation of these soils (and hence risk to the receiving environment) is currently unknown.
A predicted continuous discharge of a minimum volume of 0.75-1.0 ML/day rather than the 4.5 ML/day of mine and power station discharge will maintain water levels albeit with relatively small decreases in levels. These estimates are conservative and would require more detailed modelling to confirm the volumes required to maintain river levels.
The mine and power station discharge has a neutral to alkaline pH, and is within EPA licence limits. This discharge does not buffer the low pH waters entering the mixing zone, nor mitigate the acidic catchment inputs from large winter discharge events. Moderate winter events are mitigated to an extent by the mine and power station discharge, and it dilutes the high rainfall event catchment inflows.
Stratification of the Anglesea River estuary is a common occurrence, with salt water overlain by freshwater inflows. The reduced mine and power station discharge will increase stratification of the estuary. Stratification will only be reduced with increasing frequency and intensity of freshwater upper catchment inputs.
Though there is considerable uncertainty in analyte concentration values used during the assessment, the geochemical modelling indicates that the concentration of aluminium entering the Anglesea River estuary without the mine and power station discharges is expected to increase by 30 – 40%. Concentrations of aluminium currently entering the River are well above water quality criteria for protection of aquatic species.
The cessation of the mine and power station discharge will result in an increased proportion of flow contributions from Marshy Creek. The analysis of data for Marshy Creek catchment between 2010 and 2015 indicates that Marshy Creek is experiencing a strong trend of increasing metals (aluminium, iron and zinc). This trend does not appear to be plateauing.
5.2 Summary of predicted ecological changes
The long term nature of the mine and power station discharge to the Anglesea River estuary has resulted in adaptation by terrestrial and aquatic organisms to the changed conditions in the river and across the floodplain. Ceasing the mine and power station discharge will result in these ecological communities responding and adapting to the altered conditions.
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Terrestrial ecology Ecological communities in the estuary are dynamic and resilient to changes to their environment. They will adapt and respond to a drier floodplain and to increases in salinity levels by changing their distribution. The communities will to transition to a different composition and distribution in response to lower water levels and increases in salinity. The changes in water levels are likely to result in reduced extent and survivability of ephemeral vegetation species in Estuarine Sedgelands, Reed Beds and Estuarine Flat Grass Land communities. There is also likely to be increased seasonal water stress for Swampy Riparian Woodland and Swamp Scrub. Reduced water levels may also result in increased salinity within the river and estuary. Increased salinity is likely to reduce the extent of Submerged Herbfields which are likely to be replaced by Saline Aquatic Meadow. While there are potential benefits for a number of values at the site (e.g. increased foraging habitat for shorebirds and waders) there is likely to be a number of changes to habitat associated with lower water levels. The impacts associated with changes will likely lead to reduced water levels that may impact frog breeding events and habitat availability. Changes to vegetation may also lead to reduced cover, habitat and foraging areas for waterbird herbivores, ducks, small grebes, and reduced habitat for prey species of fish eating birds. Generation of acid sulphate soils due to lower water levels may also impact some aquatic vegetation communities. The consequences of these changes are difficult to quantify as there is a high degree of uncertainty in the reaction rate of coastal acid sulphate soils in the Anglesea River estuary. Acid sulphate soils may also impact benthic fauna as food source for waterbirds and cause increased bioavailability of metals from sediment may also compromise the survival of amphibians.
Aquatic ecology The commencement of the mine and power station discharge would have increased flows and water levels over the summer low flow period. Aquatic organisms would have responded to this change by increasing seagrass habitat, reducing the risk of algal blooms, increased aquatic habitat for fish and other species, reduction in fish deaths arising from lower residence time of low pH waters in the estuary and increased freshwater habitat in the upper estuary. This aquatic community is one that reflects the duration of mine and power station discharge and shows signs of resilience to physico- chemical challenges. Ceasing the mine and power station discharge is likely to affect aquatic organisms via several mechanisms including reduced water levels, exposure of mudflats, and increases in salinity levels. The current aquatic community reflects the duration of the mine and power station discharge and shows signs of resilience to physico-chemical challenges. Major changes to aquatic organisms from changes to the discharge include: – A reduction in the average area of seagrass in the lower estuary over time and associated indirect effects on aquatic food webs – Increased risk of algal blooms in the estuary – Potential benefits to marine and estuarine fish species from increased salinity and – Acute or chronic impacts to estuarine organisms from increases in acidic inflows and elevated metals.
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Part 2: Assessment of options to manage changes to the Anglesea River estuary
6. Options Assessment
6.1 Objectives
To investigate options for the future management of the Anglesea River estuary and assessment to identify mechanisms or opportunities to reduce changes to physical, ecological, social and economic aspects of the estuary. Identification of these opportunities are strongly linked to the impacts arising from the expected physical change, environmental, social and economic impact.
6.2 Approach
The assessment of physical change has identified the proposed alterations to the current discharge of 4.5 ML/day can give rise to a range of impacts. The consequence is dependent on the extent of alteration, time of year and the status of the entrance sandbar.
A large reduction in water levels over the summer period will lead to changes in water chemistry, stratification, vegetation communities, algal blooms and generation of acid sulphate soils. To identify options to manage adverse impacts arising from changes to the status quo a two-step process was conducted to identify and short- list mechanisms or opportunities to reduce the impact of changes to the environmental and social values of the river. The process consisted of:
Identifying actions to mitigate or reduce the physical changes that impact environmental and social values and
Conducting a high level screening assessment (short list) to assess the effectiveness of these actions to reduce impacts.
Actions that were considered effective in reducing impacts to environmental and social values were used to identify and develop potential options to reduce impacts associated with ceasing the discharge.
6.2.1 Hierarchy of impacts
The changes to physical and ecological processes and social and economic values of the estuary will have differing implications and potentially levels of acceptability for the Anglesea community and users of the river and estuary. The reduced water level has the potential to trigger oxidation of acid sulphate soils in the estuary and is likely to lead to significant environmental, social and economic impacts. Should this occur, the oxidation process could last decades and be a source of continuous acid generation in the system which has until now has only been generated in the upper catchments of Marshy and Salt Creek. An asset at risk from continued low pH in the estuary is the Great Ocean Road Bridge. It is a concrete pylon structure and low pH water has the potential to increase deterioration of the concrete and reduce its design life.
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The primary driver for option development is to identify options that reduce or halt oxidation of these soils to reduce risk to the receiving environment.
6.2.2 Action identification and screening process
A screening process has been used to identify options that are likely to reduce or halt oxidation of acid sulphate soils and provide a measurable benefit to multiple values.
The process ranks effectiveness of options in providing benefit to values and identifies where they may result in negative impacts to other values.
Options have been assessed based on a qualitative scoring process defined in Table 15. The options screening process is provided in Table 16. Efficiency of each option has also been qualitatively assessed to define the quantum of effectiveness of the solution.
Table 15 Feasibility impact and benefit screening process
Impact Score Description High Benefit 3 Option to reduce the impact of physical change to the value is considered to provide a significant reduction in impact and limits its change in state Moderate Benefit 2 Option to reduce the impact of physical change to the value is considered to provide a measurable reduction in impact Low Benefit 1 Option to reduce the impact of physical change is considered to be of limited value Neutral impact/benefit 0 Has no impact or benefit on the value Low Impact -1 Option has a small but measurable impact on values Moderate Impact -2 Option has measurable and significant impact on the values resulting in a change in conditions High Impact -3 Option likely to drive significant and long term impacts to value and its condition or distribution
6.2.3 Identification of options
The description of options in the following sections identifies the perceived benefits of the options and their ability to mitigate changes to physical and chemical parameters as well as ecological and social values. The options assessment is weighted towards those options that are capable of reducing potential oxidation of acid sulphate soils in the Anglesea River estuary, as influenced by reduced water levels.
The water balance modelling has also identified that a minimum volume of approximately 0.75 ML/day may be sufficient to significantly reduce a drop in water level in the estuary. For the options that provide a water source they are assessed against the ability to meet the minimum input of 0.75 ML/day.
A range of mitigation options considered in this assessment and their rationale are provided below.
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
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3. Infill Coogoorah Park channels – to reduce the oxidation of acid sulphate soils by infilling with clean fill in Coogoorah Park to reduce or halt the long term discharge of acidic surface water to the river 4. Hydrologically disconnect Coogoorah Park from the Anglesea River estuary - to reduce the oxidation of acid sulphate soils in Coogoorah Park reduce the potential for long term discharge of acidic surface water to the river 5. Introduce alternative freshwater inflows to Anglesea River estuary –Stormwater harvesting, recycled water discharge, potable water. Modelling indicates a threshold value of 0.75 – 1.0 ML/day will significantly reduce the evaporative loss 6. 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 7. Lime dosing – Infrastructure is created to lime dose the river areas particularly in the Coogoorah Park area to adjust pH generated from acid seepage from Anglesea River acid sulphate soils 8. Deep estuary opening – Estuary entrance is deepened to allow increased tidal movement into the estuary and buffering of acidic surface waters
9. Allow the groundwater to naturally recover and provide base flow to Marshy Creek swamplands following cessation of groundwater pumping
10. Salt Creek/Marshy Creek - diversion of water for storage and treatment and then used to supplement river flows
11. Capture and storage of Anglesea River flows- during high flow events where excess river water (higher than environmental flow requirements of the estuary) could be diverted to an off stream storage to supplement summer flows
12. Mine pit buffering – utilise a mix of water sources, including seawater to buffer acidity and metals so for future management, pit mine water can be used to maintain flows and
13. Do nothing – no action is taken to manage changes in the river system.
The screening assessment of options is provided in Table 16.
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Table 16 Summary assessment of mitigation opportunities to reduce the impact of changes to water levels and water quality as a result of ceasing the mine and power station discharge. The assessment defines the relative benefit of each mitigation option to key values
Effectiveness in reducing impact of threats
Maintain Maintain Reduce Maintain Protect Maintain Maintain Maintain Neutralise Reduce existing existing Maintain Further Mitigation option oxidation water fauna fish recreational on water Efficiency Comment pH stratification vegetation estuarine amenity assessment of CASS quality habitat passage land access access communities ecology
1 3 2 2 3 3 3 3 3 3 3 L Yes Anglesea River estuary will be maintained in its current Discharge at a state. reduced rate to that The estuary, including Coogoorah Park would be maintained in a saturated state, and would not likely be oxidised and 1 currently from mine trigger an acid generating event and power station Anglesea community are aware of the acid events and have site accepted their occurrence.
L Yes Mine pit water can contribute 2.5 ML/day of flows into Anglesea River estuary Mine pit water could sufficiently provide the necessary ≥0.75 ML/day required to maintain desired water levels in Anglesea River estuary during summer Coogoorah Park 2 Discharge treated 1 2 2 1 3 3 2 2 3 3 3 would be maintained in its saturated wet state, and would mine pit water only not likely oxidise and trigger an acid generating event. May be seen as a short and long term option and could be altered as groundwater recovers in the mine pit. Examples from oversees indicate option has been implemented with some success. 1 1 0 -3 -2 -3 0 0 -3 -3 -3 L No Unlikely to halt oxidation of acid sulphate soils as lowered 3 In fill Coogoorah water level will allow oxidation and continued acid leaching Park channels to the river over decades. Unlikely to halt oxidation of acid sulphate soils as lowered Hydrologically 1 1 0 -3 -2 -3 0 0 -2 -3 -3 L No water level will allow oxidation and continued acid leaching 4 disconnect to the river over decades. Without input of water level will Coogoorah Park continue to be lowered channels Maintain existing water level over the low flow summer Introduce 1 3 2 -2 3 3 2 3 3 3 3 M Yes period. Volume of water required may vary. Indicative alternative volume of approx. 0.75 ML/day required to maintain levels 5 freshwater inflows with minimal reduction in level in estuary. This approach (recycled water maintains current condition of ecological and social values and/or stormwater harvesting) 2 3 2 -1 -1 -1 2 2 -1 -1 3 L Yes Maintain existing water level over the low flow summer period. Indicative volume of approx. 0.75 ML/day required to maintain levels with minimal reduction in level in estuary. Seawater can buffer acidified catchment inputs entering the Pumping seawater estuary and will reduce the toxicity of elevated metals liberated as a consequence of low pH. 6 into lower Anglesea River estuary Dredging will assist the high acid and metal-contaminated catchment waters flush out of the system. The system is robust and can recover following acid events. Fish may migrate out of the estuary and seek refuge in marine waters away from acid rich waters. Requires infrastructure to provide continued dosing of lime 2 0 0 1 0 0 0 0 0 0 0 L No to increase pH to mitigate ASS oxidation. Does not provide 7 Lime dosing much benefit to other values Options been extensively assessed by Water Technology Deep estuary 8 1 1 2 2 -2 -2 3 1 -1 -2 2 M No (2010) opening
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Effectiveness in reducing impact of threats
Maintain Maintain Reduce Maintain Protect Maintain Maintain Maintain Neutralise Reduce existing existing Maintain Further Mitigation option oxidation water fauna fish recreational on water Efficiency Comment pH stratification vegetation estuarine amenity assessment of CASS quality habitat passage land access access communities ecology Deep openings require continual dredging to keep the mouth open. They are likely to lead to a significant drop in water levels and may expose acid sulphate soils. Leads to prolonged exposure of seagrass beds in lower estuary. Unlikely to maintain water levels in the estuary and reduce activation of acid sulphate soils Expert panel report on management of acid events in the estuary concluded the risks of deep estuary openings outweigh the benefits The expected recovery time of groundwater to contribute 2 -3 -3 0 0 0 0 0 0 0 0 H No Allow natural baseflows to Marshy Creek is decades. Natural recovery will not limit oxidation of acid sulphate soils as they will be 9 groundwater activated once water levels are reduced. Option feasible in recovery the long term but not short term. This option has an impact on environmental flows of the 1 1 2 2 2 2 2 2 L No Anglesea River unless only high flow events are captured. Significant risks of capturing low pH water from catchment under this option which is expected to become worse under Salt Creek/Marshy climate change. 10 Creek - diversion of Requires an offstream storage of sufficient capacity to water for storage maintain flows for extended period due to high evaporative and treatment loss over the summer period. Long lead times to deliver project and secure site. Potential limited security of supply during El Nino events and climate change projections. Requires an offstream storage in the lower catchment of -3 2 2 2 2 2 2 1 3 3 3 L No Capture and sufficient capacity to maintain flows for extended period due storage of to high evaporative loss over the summer period. Limited space available for the siting of the structure on the lower 11 Anglesea River - river environs due to urbanisation. Security of supply is during high flow uncertain due to El Nino events and climate change events projections. Large pump infrastructure requirements to pump seawater 3 3 2 2 3 3 3 3 3 3 3 L Yes and other sources of water from sea level and other locations to mine site. On site treatment is required. Mine pit buffering – Requires pumping infrastructure to pump out of mine site to utilise a mix of river. water sources, Long term design and feasibility requirements. including seawater The future management of the mine decommissioning 12 to buffer acidity and process and time line is unclear and will impact the feasibility metals. As a future of the option as it cannot compromise the site rehabilitation. source, pit mine The timeframe for access to sufficient water to maintain water can be used estuary water levels is unclear and would not prevent to maintain flows. oxidation of acid sulphate soils in the estuary in the short term. Examples from oversees indicate option has been implemented with some success Impacts similar to ceasing groundwater pumping. No -2 -3 -2 -2 -2 -2 -3 -2 -2 -2 -2 H No mitigation of impacts arising from the reduced mine and 13 Do nothing power station discharge.
Note: Effectiveness is a measure of the ability for the potential mitigation options to ameliorate the potential impact of threats. Efficiency refers to the ease to implement the mitigation option, including cost.
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6.3 Summary of options assessment
This assessment has identified a number of options that should be carried forward for further investigation. When assessing the overall impact of a reduction in water levels the most significant threat to the ecology and social values of the river is the oxidation of acid sulphate soils. Other changes also posing a threat to the ecology of the system include drying of wetlands impacting amphibian fauna and altered vegetation community distribution.
Options that are not recommended to be assessed further are:
Infill Coogoorah Park channels – This option has limited effectiveness in mitigating the oxidation of acid sulphate soils as the soils will continue to oxidise due to the lowered water level and exposure to air. The option will also have significant negative impacts on Coogoorah Park as a recreational area for on and off water activities and the overall amenity of the site.
Hydrologically disconnect Coogoorah Park from the Anglesea River estuary - This option has limited effectiveness as the lowered water level will continue to allow oxidation of acid sulphate soils and they are expected to be able to enter the river through groundwater leachate.
Lime dosing is unlikely to be effective and would only be implemented if acid sulphate soils are activated. As an option it is effectively a last resort as preventative actions will not have been implemented.
Deep estuary opening – Estuary entrance is deepened to allow acid water to be flushed. This option is likely to lead to a significant drop in water levels and will not reduce activation of acid sulphate soils. Deep openings lead to prolonged exposure of seagrass beds in lower estuary. Expert panel assessment identified the impacts outweighed the benefits of the option.
Allow natural groundwater recovery. The expected recovery time of groundwater to contribute baseflows to Marshy Creek is decades. Natural recovery will not limit oxidation of acid sulphate soils as they will be activated once water levels are reduced. Option feasible in the long term but not short term.
Salt Creek / Marshy Creek diversion for water storage and treatment requires a large off stream storage of sufficient capacity to maintain water levels during the low flow summer months and reduce activation of acid sulphate soils. Treatment may also be required as the option may capture low pH catchment water. Probable security of supply issues due to drought and climate change may limit ability to maintain water levels.
Capture and storage of Anglesea River flows - during high flow events requires a significant storage on the floodplain in the urbanised area of Anglesea. The security of supply under drought and climate change conditions may reduce the capacity to maintain water levels and reduce activation of acid sulphate soils.
Do nothing – Is not listed as an option as it will not prevent the activation and oxidation of acid sulphate soils in the floodplain.
Options that are recommended for further assessment are:
Discharge at a reduced rate to that currently from mine and power station site– modified management of discharge is an option for future but is dependent on groundwater pumping and treatment infrastructure being in place or purchased and commissioning of new infrastructure following the decommissioning of the site. There are a number of water source options to continue the discharge from the mine site. This includes groundwater sourced through direct groundwater pumping and pumping of mine pit sump water.
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Discharge treated mine pit water only – current mine pit water contributes over 2 ML/day to the current mine and power station discharge. This provides an alternative source to groundwater pumping. The option would maintain water levels in the Anglesea River estuary and reduce likelihood of activation of acid sulphate soils.
Introduce alternative freshwater inflows to Anglesea River estuary – this approach is an amalgam of options to capture recycled water and/or stormwater harvesting as a means to supplement river volumes and reduce reaction of acid sulphate soils. There is high security of both stormwater and recycled water as a source, as the continued increase in urban water demand is in excess of the daily water requirement to maintain water levels in the estuary.
Pumping seawater into the Anglesea River estuary - requires construction of temporary or permanent pumping infrastructure for seawater to be pumped into the lower estuary. Infrastructure would need to be in sufficiently deep water to maintain pumps efficiency and not affect performance at low tides. This option will maintain water levels, reduce acid sulphate soil generation and provide greater buffering capacity for acid catchment events. Mine pit buffering – utilise a mix of water sources, including seawater to buffer acidity and metals. This approach is a future source and builds on continuing the mine and power station discharge. Mine pit water over the longer term can continue to reduce in pH and treatment options may provide an opportunity to access a larger volume of water with good security of supply.
A framework for each option has considered implementation infrastructure requirements.
6.3.1 Discharge at a reduced rate to that currently from mine and power station site
Discharge at a reduced rate to that currently from mine and power station site– modified management of the discharge is possible in the short term using some of the existing mine treatment and pumping equipment. Two sources of water are available at the site groundwater and pit sump water (groundwater and stormwater).
Pit sump water may continue to be discharged depending on stability of rehabilitated mine pit slopes. If they are stable sump water would remain within the pit. The recharge capacity of the mine pit is not currently known.
During the rehabilitation of the site infrastructure will be decommissioned and removed as part of the clean-up process. Due to the groundwater quality (high temperature, sulphides, low pH and iron) treatment is required prior to it being discharged to the river. If treatment facilities are decommissioned new facilities would need to be designed and commissioned. Pumping costs and management of a treatment facility add additional operational constraints. As the current discharge occurs under an EPA licence, a new licence may also be required. Implementation of this option requires
Assessment of pumping treatment and storage assets requirements
Implications of mine rehabilitation and decommissioning of pumping and treatment assets and
Future pumping, treatment and discharge management requirement.
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6.3.2 Introduce alternative freshwater inflows to river
Implementation of an integrated water management regime has the potential to provide additional water supply to the river to maintain water levels and provide an overall benefit. Water would be sourced from rainwater harvesting scheme in Anglesea that captures rainwater during storm events and provides source during the low flow period. For sufficient water to be available this option would need to be coupled with use of recycled water from the Anglesea recycled water plant. This approach may provide the quantity but there are considerations of water quality from a human and estuarine health perspective. A discharge of recycled water is also likely to require an EPA licence. Implementation of this option would require:
Design and construction of a stormwater harvesting and interception scheme requiring storages and some treatment Construction of a water pipeline to deliver harvested stormwater to the river and associated outlet structures and diffuser etc
Upgraded treatment at Anglesea recycled water treatment plant to meet human health and environmental criteria
Construction of a water pipeline to deliver recycled water to the river and associated outlet structures and diffuser etc and
Water quality monitoring program.
6.3.3 Seawater pumping to estuary
Seawater pumping to the Anglesea River estuary is likely to require significant infrastructure requirements to enable a temporary or permanent pumping solution. The high energy coastline of the Anglesea area will mean infrastructure will be required to enable operation and maintenance in a high energy environment
Implementation of this option would require:
Design and construction of a seawater pumping process
Pump system need to be robust / durable, potentially in conjunction with intake screens to address foreign object risk etc. pumps located in a pump house
Assessment of saline water mixing and stratification within the estuary and designs to minimise risks
Pumps, pipeline, diffuser, and other associated infrastructure and
Water quality monitoring program.
6.3.4 Mine pit buffering – utilise a mix of water sources
Mine pit water is a large source of water that is likely to be available to maintain water levels and reduce activation of acid sulphate soils. It differs from the immediate mine and power station discharge as a long term option that integrates with the decommissioned mine site and its long term pit water management.
Implementation of this option requires:
Understanding groundwater recovery and projected water levels and quality
Assessment of pumping and treatment requirements
Integration with mine rehabilitation and decommissioning, and management of water sources including flows from Marshy and Salt Creeks
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Inclusion of alternative sources of water including seawater as a buffer to low pH and
Water quality monitoring program.
6.4 Key Findings Options Assessment
Mitigation options Activation of acid sulphate soils under low water levels over the summer period presents a significant risk to ecological, social and economic assets. The primary driver for option development is to identify options that reduce or halt oxidation of these soils to reduce risk to the receiving environment.
Options that are recommended for further assessment are: 1. Discharge at a reduced rate to that currently from mine and power station site– modified management of the 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 – Alternative freshwater sources that may be relevant include stormwater harvesting, recycled water discharge, and potable water. Modelling indicates a threshold value of 0.75 – 1.0 ML\day will significantly reduce the evaporative loss
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 and
5. Mine pit buffering – utilise a mix of water sources, including seawater to buffer acidity and metals so for future management, pit mine water can be used to maintain flows.
The shortlisted options require further assessment. This will help to determine a preferred option or combination of options to reduce the oxidation of acid sulphate soils in the floodplain of the river and reduce impacts to ecological, social and economic values.
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7. Conclusions
Physical changes to Anglesea River estuary Under natural conditions without the mine and power station discharge the water levels in the Anglesea River estuary would vary between seasons. Significantly lower water levels would occur during the summer months due to low or ceased flow from the catchment. Ceasing the mine and power station discharge is likely to reduce the water level by up to 1 m in the summer period.
The mine and power station discharge during the summer period contributes as much as 100% of the inflows into the Anglesea River estuary.
During the winter period, catchment inputs (most years) upstream of the mine and power station is sufficient to maintain water levels in the estuary. The decrease in water level and exposure and drying of mudflats at Coogoorah Park is likely to result in generation of coastal acid sulphate soils in these areas and poses a risk to environmental, social and economic values. The significance of the risk posed by the presence of acid sulphate soils is not well understood as the reaction rate and acid generation potential of these soils is unknown.
Geochemical modelling indicates mine and power station discharge dilutes the aluminium concentration from catchment sources. Without the discharge aluminium is expected to increase by 30 – 40%. Existing aluminium concentrations are above water quality criteria for protection of aquatic species.
Ceasing the mine and power station discharge will result in an increased proportion of flow contributions from Marshy Creek to the estuary. Analysis of water quality data between 2010 and 2015 indicates there is a strong continuing trend of increasing metals aluminium, iron and zinc.
To maintain water levels at approximately 1.5 m AHD in the Anglesea River estuary during the summer low flow period an estimated a minimum flow to the river of 0.75-1.0 ML/day is required.
The continued upward trend in aluminium and reduction in pH in waters from Marshy Creek pose a risk to the ecological and social values of the lower estuary. The processes in the catchment leading to this continued increase is not understood.
Ecological impacts Ecological communities in the estuary are dynamic and resilient and will adapt and respond to a drier floodplain and to increases in salinity levels. Changes in water levels are likely to result in reduced extent and survival of ephemeral vegetation species in Estuarine Sedgelands, Reed Beds and Estuarine Flat Grass Lands communities and increased seasonal water stress for Swampy Riparian Woodland and Swamp Scrub.
Increased salinity is likely to reduce the extent of Submerged Herbfields and increase the extent of Saline Aquatic Meadow.
Reduced water levels may impact frog breeding events and habitat availability. Changes to vegetation may also lead to reduced cover, habitat and foraging areas for waterbird herbivores, ducks, small grebes, and reduced habitat for prey species for piscivores (fish eating birds).
58 | GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459
Acid sulphate soils may also impact some aquatic vegetation communities, benthic fauna as food source for waterbirds and amphibians.
The physical and chemical changes to the Anglesea River estuary are likely to result in – A reduction in the average area of seagrass in the lower estuary and associated indirect effects on aquatic food webs. – Increased risk of algal blooms in the estuary. – Potential benefits to marine and estuarine fish species from increased salinity. – Acute or chronic impacts to estuarine organisms from increases in acidic inflows and elevated metals.
Social and economic impacts Reduced water levels over the summer period are likely to impact on water activities (motor and non-motor boating) , swimming, recreational fishing, amenity, bird watching, beside water activities, boat hire business, markets, estuary education activities and infrastructure.
The lower water levels will be most noticeable in the lower estuary below McMillan St and Coogoorah Park due to exposure of mudflats.
Impacts to terrestrial vegetation and fauna are likely to have some impact to educational activities, birdwatching and landscape amenity.
Activation of acid sulphate soils and lowering of pH in the estuary has the potential to impact infrastructure increasing deterioration of the asset and a reduction in the design life.
Mitigation options Activation of acid sulphate soils under low water levels over the summer period presents a significant risk to ecological, social and economic assets. The primary driver for option development is to identify options that reduce or halt oxidation of these soils to reduce risk to the receiving environment.
Options that are recommended for further assessment are:
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 – Alternative sources of water that could be identified as freshwater include stormwater harvesting, recycled water discharge, potable water. Modelling indicates a threshold value of 0.75 – 1.0 ML/day will significantly reduce the evaporative loss.
4. Pump seawater into 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. Pit mine buffering – utilise a mix of water sources, including seawater to buffer acidity and metals so for future, pit mine water can be used to maintain flows.
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 59
The shortlisted options require further assessment to determine a preferred option or combination of options to reduce the oxidation of acid sulphate soils in the floodplain of the river and reduce impacts to ecological, social and economic values.
60 | GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459
8. References
ANZECC & ARMCANZ (2000) National Water Quality Management Strategy: Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Atkins, L. & A.R. Bourne (1983) Mine and power station of Australia Limited Anglesea (Vic) Mining Lease Environmental Study – Environmental Survey of metals in the Anglesea River (1981-1982). Volume 2. Deakin University, Geelong, Victoria.
Corangamite Catchment Management Authority (2013) Anglesea River 2012-2020 Estuary Management Plan GHD (2013) Anglesea Borefield Bulk Entitlement Review. Report for Barwon Water. July 2013. Doc No 31\2798008\WP\222020.
GHD (2014) Anglesea Borefield Project: Surface Water Quality Results 2013 – MAP Task 4.1. Report for Barwon Water. July 2014. Doc No 31\2798002\WP\231946.
Gower, F. (2000) Anglesea River report. Report for Mine and power station World Alumina Australia. Hermon, K. (2002) The Cause/s of the Acidification of the Anglesea River, Victoria. Honours Thesis, School of Ecology and Environment at Deakin University. May 2002.
Maher, W. (2011) Anglesea River water quality review. Independent review by Professor William Maher. October 2011.
Nordstrom, D.K., Plummer, L.N.,Wigley, T.M.L.,Wolery, T.J., Ball, J.W., Jenne, E.A., Bassett, R.L., Crerar, D.A., Florence, T.M., Fritz, B., Hoffman, M., Holdren, G.R., Jr., Lafon, G.M., Mattigod, S.V., McDuff, R.E., Morel, F., Reddy, M.M., Sposito, G., and Thraildeath, J. (1979), A comparison of computerized chemical models for equilibrium calculations in aqueous systems, in Jenne, E.A., ed., Chemical modeling in aqueous systems--Speciation, sorption, solubility, and kinetics: Series 93, American Chemical Society, p. 857-892
Parkhurst, D.L. (1995) User's guide to PHREEQC--A computer program for speciation, reaction- path, advective-transport, and inverse geochemical calculations: U.S. Geological Survey Water- Resources Investigations Report 95-4227, 143 p.
Parkhurst, D.L. & C.A.J. Appelo (1999) User's guide to PHREEQC (version 2)--A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Water-Resources Investigations Report 99-4259, 312 p.
Parsons, F. (2011). Submission to the Anglesea River acid and trace metals review.
Pope, A. (2010) Anglesea fish death: causes and recent investigations. Deakin University Report for EPA Victoria. November 2010.
Pope, A. (2006) Freshwater Influences on Hydrology and Seagrass Dynamics of Intermittent Estuaries. Deakin University PhD Dissertation. August 2006. Sharley D, Amos C & Pettigrove, V (2014) Factors affecting the ecology of the Anglesea River - Final report for the Corangamite Catchment Management Authority. Centre for Aquatic Pollution Identification and Management
Suthers, IM, & Rissik, D 2008, Plankton : a guide to their ecology and monitoring for water quality, Collingwood, Vic. : CSIRO Publishing, 2008.
Tonkin, Z., Pickworth, A., O’Mahony, J. and Kitchingman, A. (2014) Assessing the benefits of instream habitat works for fish populations in the Anglesea River. Arthur Rylah Institute for
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 61
Environmental Research Unpublished Client Report for Corangamite Catchment Management Authority, Department of Environment and Primary Industries, Heidelberg, Victoria
Water Technology (2010) Investigation of Anglesea River Estuary Mouth Dynamics. Report for Conrangamite CMA. December 2010. Doc No J1756-01R01v02b.
62 | GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459
Appendices
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 63
Appendix A – Water Balance Inputs
Relations between Water Level, Area and Volume The relation between estuarine water levels, volume and area are provided in the first three (3) columns of Table 17. The Water Technology (2010) volumes were adjusted to allow sensible estimates of the horizontal area at each water level6. Differences between the adjusted and Water Technology (2010) volumes were less than 0.5% at each 0.1 m interval. Further, the adjusted volumes are in reasonable agreement with the Pope (2006) volume estimates at several water levels (Table 17). The relations between water level, area and volume were interpolated to 0.01 m increments to allow finer vertical resolution of the ‘forecast’ daily water levels from the daily predicted water balance volume. Table 17 Relation between estuarine levels, volumes and areas
Adjusted Volume Estimated Area Water Technology Pope (2006) Level (m AHD) 3 2 3 3 (m ) (m ) (2010) Volume (m ) Volume (m ) 0 22,000 30,000 22,000 0.1 26,000 35,000 26,000 0.2 30,000 47,000 30,000 31,900 0.3 34,850 50,000 35,000 0.4 40,150 53,000 40,000 0.5 45,900 65,000 46,000 0.6 52,750 70,000 53,000 0.7 60,200 74,000 60,000 0.8 67,850 83,000 68,000 0.9 77,300 103,000 77,000 1 87,650 110,000 88,000 96,400 @ 1.05 1.1 99,250 115,000 99,000 m AHD 1.2 111,000 125,000 111,000 1.3 124,750 150,000 125,000 1.4 140,500 160,000 140,000 157,000 @ 1.49 1.5 156,750 175,000 156,000 m AHD 1.6 175,250 210,000 176,000 184,000 @ 1.65 1.7 199,000 250,000 199,000 m AHD 1.8 228,150 333,000 228,000 210,000 1.9 263,150 370,000 262,000 2 303,000 450,000 302,000
Water Levels Measured daily water levels served as inputs for the ‘forced’ water balance model to calculate the volume and area of the estuary (Figure 8).
Evaporative Daily volumetric evaporative losses from the estuarine surface were estimated as the surface area on a particular day multiplied by the daily evaporation rate. The daily evaporation rate was derived from the BoM monthly climatic evaporation rates at Anglesea as shown in Table 18. Table 18 Monthly evaporation estimates for Anglesea from BoM.
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Evaporation 180 155 130 85 55 40 45 60 100 110 160 165 (mm/month)
6 Presumably the Water Technology (2010) volumes were based on their DEM.
64 | GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459
Groundwater Losses A groundwater model of the basin simulated leakage of estuarine water to groundwater as 0.2 MLD (GHD 2013) (Figure 21).
Figure 21 Simulated leakage from the estuary to groundwater by GHD (2013). Red arrow demarcates modelled acidic event.
Rainfall Daily rainfall from the Aireys Inlet (BoM Station 90180) is provided in Figure 22. The BoM rainfall station at Anglesea officially ceased operation in 2005.
Figure 22 Daily rainfall at Aireys Inlet from 1 November 2011 to 1 June 2015
Inflows Daily inflows were derived from catchment and Mine and power station sub-daily gauged discharge are illustrated in Figure 23. Stormwater flows (~1,700 MLY) from town of Anglesea into the estuary (Aitkens & Bourne (1983) in Pope (2006)) were not considered.
Figure 23 Daily inflows into the estuary from 1 November 2011 to 1 June 2015
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 65
Appendix B – Anglesea River Contour Maps
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 66 2 2 2.5 2
2
2
2
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-0.5 ANGLESEA2 2
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2 -0.5 2 2
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JobNum b er 31-33459 PaperSize A3 Coran ga m iteCatchm en t A 0 10 20 40 60 80 100 AngleseaRiver Flow Impact Assessmen t Revision Date Dec07 2015 Metres MaProjection: p Tran sverseMerca tor HorizontalDatum GDA 1994 : Appendix B Figure 1 Anglesea River surface water contours without groundwater discharge Grid:GDA 1994MGA Zone 55 o G:\31\33459\GIS\Ma ps\Working\3133459_003_AerialContours_MBA3P.mxd Lonsda180 leStreet Melbourne VIC3000 868780003T 61 868781113 F 61 Emelm a [email protected] Wwww.ghd.com .au ©Whilst2015. every ca ha re sbeen taken prepareto this ma GHD p, (an dDATA CU STODIAN)ma kenorepresen tationswa or rran tiesab outits accuracy, reliab ility,com pleten esssuitab or ilityanfor yparticular purpose an dca n n otaccept liab ilityan dresponsibility anof ykind (whetherincontract, otherwise) or tort anfor yexpen ses,losses, da m a gesan costs d/or (including indirect consequen or tialda m a ge)which maare or ybe incurred by an yparty as aresult theof ma being p ina ccurate,incom pleteun or suitab leinan ywa yan an dfor yrea son. Datasource:Nea rMa–Ima p gery(Date extracted: Ima 07/12/2015, geda Baseda te:02/03/2015, ta(DELWP, Eleva 2015); tionda ta(clien . t) M c ro rie St
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JobNum b er 31-33459 PaperSize A3 Coran ga m iteCatchm en t A 0 10 20 40 60 80 100 AngleseaRiver Flow Impac Assessmen t t Revision Date Dec07 2015 M etres M aProjec p tionTran : sverseMerca tor Appendix B Figure 1 Anglesea River surface water contours without groundwater discharge Horizo n talDatum GDA 1994 : Grid:GDA 1994MGA Zon e55 o Pageof34 G:\31\33459\GIS\Ma ps\Wo rking\3133459_003_AerialCo n tours_M BA3P.mxd Lon180 sda leStreet Melbo urneVIC3000 868780003T 61 868781113 F 61 Emelma [email protected] m Wwww.ghd.co m .au ©Whilst2015. every ca ha re been s taken to prepare this ma GHD p, (an dDATA CUSTODIAN) ma keno represen tationwaor s rran tiesab o utitsac c uracreliab y, ility,co m pletensuitab essor ilityforan yparticular purpose an dca n n oac t c eptliab ilityan drespon sibilityof an ykind (whetherinco n tractortotherwise)or t, foran yexpen losses, ses, da m a gesan co d/or (inc sts ludingindirec coor t n sequen tialda m a ge)which aremaor ybe inc urredby an yparty asaresult of the ma being p ina c c urate,inc o m pleteunor suitab leinan ywa yan dfoan r yrea son . Datasource:Nea rMa–Ima p gery(Date extrac Ima ted: 07/12/2015, geda Baseda te:02/03/2015, ta(DELW Eleva 2015); P, tionda ta(clien . t) -0.5
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1.5 Strea m 13 Bra c kish Sedgela n d 953 Estua rin e Sc rub
Arteria l 48 Hea thy W o o dla n d 999 No n Na tive V egeta tio n
Jo b Num b er 31-33459 Pa per Size A3 Co ra n ga m ite Ca tc hm en t: An glesea River Flo w Im pa c t Assessm en t 0 10 20 40 60 80 100 Revisio n A Da te 16 Dec 2015 M etres Appen dix B M a p Pro jec tio n : Tra n sverse M erc a to r An glesea River V egeta tio n Co m m un ities a n d Surfa c e W a ter Ho rizo n ta l Da tum : GDA 1994 Grid: GDA 1994 M GA Zo n e 55 o Co n to urs W itho ut M in e a n d Po wer Sta tio n Disc ha rge Figure 2 G:\31\33459\GIS\M a ps\W o rkin g\3133459_ 001_ EV C_ M BA3P.m xd 180 Lo n sda le Street M elb o urn e V IC 3000 T 61 3 8687 8000 F 61 3 8687 8111 E m elm a [email protected] o m W www.ghd.c o m .a u © 2015. W hilst every c a re ha s b een ta ken to prepa re this m a p, GHD (a n d DATA CUSTODIAN) m a ke n o represen ta tio n s o r wa rra n ties a b o ut its a c c ura c y, relia b ility, c o m pleten ess o r suita b ility fo r a n y pa rtic ula r purpo se a n d c a n n o t a c c ept lia b ility a n d respo n sib ility o f a n y kin d (whether in c o n tra c t, to rt o r o therwise) fo r a n y expen ses, lo sses, da m a ges a n d/o r c o sts (in c ludin g in direc t o r c o n sequen tia l da m a ge) whic h a re o r m a y b e in c urred b y a n y pa rty a s a result o f the m a p b ein g in a c c ura te, in c o m plete o r un suita b le in a n y wa y a n d fo r a n y rea so n . Da ta so urc e: Nea rM a p – Im a gery (Da te extra c ted: 07/12/2015, Im a ge da te: 02/03/2015, Ba seda ta (DELW P, 2015); Eleva tio n da ta (c lien t) . 7 9 9.5 6.5 937 8.5 8 6.5 2 999 7.5 7 937 5.5 6 6 5 4.5 2.5 5.5 .5 2 3 2 . 4 999 999 4 5 .5 5 3 937 .5 2.5 -1 3.5 4
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0.5 Tra c ks 2 Co a st Ba n ksia W o o dla n d 914 Estua rin e Fla ts Gra ssla n d 1111 Alka lin e b a sa ltic wetla n d a ggrega te
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1.5 Strea m 48 Hea thy W o o dla n d 952 Estua rin e Reedb ed 1119 W et Sa ltm a rsh Herb la n d
Arteria l 53 Swa m p Sc rub 953 Estua rin e Sc rub
Jo b Num b er 31-33459 Pa per Size A3 Co ra n ga m ite Ca tc hm en t: An glesea River Flo w Im pa c t Assessm en t 0 10 20 40 60 80 100 Revisio n A Da te 16 Dec 2015 M etres Appen dix B M a p Pro jec tio n : Tra n sverse M erc a to r An glesea River V egeta tio n Co m m un ities a n d Surfa c e W a ter Ho rizo n ta l Da tum : GDA 1994 Grid: GDA 1994 M GA Zo n e 55 o Co n to urs W itho ut M in e a n d Po wer Sta tio n Disc ha rge Figure 2 G:\31\33459\GIS\M a ps\W o rkin g\3133459_ 001_ EV C_ M BA3P.m xd 180 Lo n sda le Street M elb o urn e V IC 3000 T 61 3 8687 8000 F 61 3 8687 8111 E m elm a [email protected] o m W www.ghd.c o m .a u © 2015. W hilst every c a re ha s b een ta ken to prepa re this m a p, GHD (a n d DATA CUSTODIAN) m a ke n o represen ta tio n s o r wa rra n ties a b o ut its a c c ura c y, relia b ility, c o m pleten ess o r suita b ility fo r a n y pa rtic ula r purpo se a n d c a n n o t a c c ept lia b ility a n d respo n sib ility o f a n y kin d (whether in c o n tra c t, to rt o r o therwise) fo r a n y expen ses, lo sses, da m a ges a n d/o r c o sts (in c ludin g in direc t o r c o n sequen tia l da m a ge) whic h a re o r m a y b e in c urred b y a n y pa rty a s a result o f the m a p b ein g in a c c ura te, in c o m plete o r un suita b le in a n y wa y a n d fo r a n y rea so n . Da ta so urc e: Nea rM a p – Im a gery (Da te extra c ted: 07/12/2015, Im a ge da te: 02/03/2015, Ba seda ta (DELW P, 2015); Eleva tio n da ta (c lien t) . 10 953
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1 River 10 Estua rin e W etla n d 1111 Alka lin e b a sa ltic wetla n d a ggrega te
1.5 Strea m 160 Co a sta l Dun e Sc rub 1119 W et Sa ltm a rsh Herb la n d
Arteria l 858 Co a sta l Alka lin e Sc rub
Jo b Num b er 31-33459 Pa per Size A3 Co ra n ga m ite Ca tc hm en t: An glesea River Flo w Im pa c t Assessm en t 0 10 20 40 60 80 100 Revisio n A Da te 16 Dec 2015 M etres Appen dix B M a p Pro jec tio n : Tra n sverse M erc a to r An glesea River V egeta tio n Co m m un ities a n d Surfa c e W a ter Ho rizo n ta l Da tum : GDA 1994 Grid: GDA 1994 M GA Zo n e 55 o Co n to urs W itho ut M in e a n d Po wer Sta tio n Disc ha rge Figure 2 G:\31\33459\GIS\M a ps\W o rkin g\3133459_ 001_ EV C_ M BA3P.m xd 180 Lo n sda le Street M elb o urn e V IC 3000 T 61 3 8687 8000 F 61 3 8687 8111 E m elm a [email protected] o m W www.ghd.c o m .a u © 2015. W hilst every c a re ha s b een ta ken to prepa re this m a p, GHD (a n d DATA CUSTODIAN) m a ke n o represen ta tio n s o r wa rra n ties a b o ut its a c c ura c y, relia b ility, c o m pleten ess o r suita b ility fo r a n y pa rtic ula r purpo se a n d c a n n o t a c c ept lia b ility a n d respo n sib ility o f a n y kin d (whether in c o n tra c t, to rt o r o therwise) fo r a n y expen ses, lo sses, da m a ges a n d/o r c o sts (in c ludin g in direc t o r c o n sequen tia l da m a ge) whic h a re o r m a y b e in c urred b y a n y pa rty a s a result o f the m a p b ein g in a c c ura te, in c o m plete o r un suita b le in a n y wa y a n d fo r a n y rea so n . Da ta so urc e: Nea rM a p – Im a gery (Da te extra c ted: 07/12/2015, Im a ge da te: 02/03/2015, Ba seda ta (DELW P, 2015); Eleva tio n da ta (c lien t) .
Appendix C – Hydrodynamic Model Inputs
Estuarine Bathymetry A digital elevation model (DEM) of the estuary was developed by Water Technology (2010). However, the resolution of the mesh was too fine to carry out the ~1 month duration simulations within this project’s timeframe (i.e. simulations take too long). Hence, the horizontal model grid size was increased to yield faster simulation run times (Figure 24). As the sand bar dynamics are too complicated to model explicitly and not needed for the June 2012 onset of winter simulations, the highest point in the sandbar was fixed to approximately 1.4 m AHD, which is at the lower range of the water levels measured by the continuous water level monitoring at Great Ocean Bridge (Figure 8). Once the water level increased above the sand bar height it was allowed to overflow into the adjacent coastal waters. Recognising the importance of vertical variations through the water column (particularly for salinity and its influence on vertical density stratification), the model was configured with two (2) sigma layers of equivalent vertical spatial resolution for the upper waters of the estuary (i.e. sigma layers that vertically expand and contract as a function of water level and local water depth) and nine (9) vertically fixed depth layers of 0.25 m below the sigma layers.
Figure 24 Estuarine bathymetry and mesh used by Water Technololgy (2010) (left) and this study (right)
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 75
Inflows Model inputs for discharge, water temperature and salinity of the inflows (i.e. Salt Creek, Marsh Creek, Mine and power station discharge) are shown in Figure 25. Further, conservative tracers to track the proportion of each of the inflows (Salt Creek, Marshy Creek, mine and power station discharge) were also included as model inputs to allow tracking of the source water types in the estuary over time.
Figure 25 Inflow inputs for hydrodynamic modelling of winter 2012 event with (left) and without (right) the mine and power station discharge
Meteorology Half hourly wind speeds and wind directions from the Bureau of Meteorology (BoM) Aireys Inlet meteorological station (Station Number 90180) are shown in Figure 26. Simulations with these wind speeds and directions yielded much greater mixing than observed, which suggests substantive sheltering in the estuary. Hence, for the purposes of the simulation a constant wind speed of 2 m s-1 was applied.
76 | GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459
Figure 26 Half hour wind speeds and directions for hydrodynamic simulations
Daily rainfall from the BoM station at Aireys Inlet was used (Appendix AError! Reference source not found.). Evaporation rates were based on long-term monthly estimates from BoM (Appendix A).
Conversion of Stream Conductivity to Salinity Salinity (or TDS) serves as a key simulation parameter for the hydrodynamic model as it controls most affects vertical (i.e. stratification) and horizontal density variations. Specific conductance measurements in the two catchment streams were converted to TDS on the basis of the relation in Figure 27, which was developed with data from the ambient catchment monitoring program (GHD 2014). TDS in units of mg/L was converted to salinity in ppt by dividing by 1000.
Figure 27 Relation between Salt Creek (SV2) and Marshy Creek (AV2) conductivity and TDS measurement
GHD | Report for Corangamite CMA - Anglesea River Estuary Flow Assessment 31/33459 | 77
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© GHD 2015 This document is and shall remain the property of GHD. The document may only be used for the purpose for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited. N:\AU\Geelong\Projects\31\33459\WP\10857.docx Document Status Rev Author Reviewer Approved for Issue No. Name Signature Name Signature Date J Romero J Gorski Draft D May D May 8/12/2015 A McMahon J Ricaridello J Romero J Gorski 0 D May D May 23/12/2015 A McMahon J Ricaridello Final J Romero J Gorski D May D May 15/01/2016 A McMahon J Ricaridello
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