July progress update
On 7 June 2023, a workshop was held in Bendigo with the following agencies and local councils:
- Department of Energy, Environment and Climate Action - Water and Catchments Group
- Goulburn-Murray Water
- Coliban Water
- North Central Catchment Management Authority
- Campaspe Shire Council
- City of Greater Bendigo Council
- Central Highlands Water (apology but briefed separately)
Hydrology and Risk Consulting (HARC), the independent consultants engaged to undertake the technical assessment of Lake Eppalock, facilitated the workshop.
The group discussed the 2 most recent floods at Lake Eppalock in 2011 and 2022 to help shape the options for assessment.
Workshop participants agreed to move forward with the assessment and modelling of the following 5 options to see if they would provide opportunities to mitigate flooding further downstream:
Option 1: Reduction of target storage levels (for example, holding the lake at a maximum volume of 70%, 80%, 90% all year round), using existing infrastructure.
Option 2: Reduction of target storage levels (for example, holding the lake at a maximum volume of 70%, 80%, 90% all year round) and increasing the outlet capacity (from 1,600 ML/day to approx. 5,000 – 8,000 ML/day).
Option 3: Reduction of Full Supply Level (for example, lake level held at less than 100%) using a passive spillway slot. Example storages that utilise a passive spillway slot include Hinze Dam, Queensland and South Para Dam, South Australia.
Option 4: Maintenance of Full Supply Level and the addition of spillway gates.
Option 5: Maintenance of Full Supply Level, and the reconfiguration of spillways (not including gates) and embankments to make them higher.
There was also a discussion around if a filling curve option, similar to that applied at Lake Eildon, targeting the current Full Supply Level, without changes to infrastructure, would be beneficial.
It was agreed that due to the variable nature of the inflows into catchment above Lake Eppalock, a target filling curve would have little impact on flood mitigation, as the filling curve would not create enough airspace alone to provide additional mitigation of large flood events.
However, elements of filling curves could be used to help refine the options listed above.
In delivering this assessment, it was acknowledged that the rights of existing entitlement holders are a key consideration in any potential changes to infrastructure or operating arrangements and any impacts need to be documented.
The 5 options will be modelled to identify for each scenario:
- How the flood frequencies at Lake Eppalock change, including using the 2011 and 2022 floods as reference points.
- How any change in flood frequencies at Lake Eppalock would be anticipated to change flood frequencies at Rochester.
- The water security impacts to existing entitlement holders.
Following the modelling, an impact assessment will be undertaken which identifies:
- How for different peak outflow scenarios from Lake Eppalock – each option will reduce the extent of property and infrastructure inundation downstream from Lake Eppalock to Rochester (including using the 2011 and 2022 floods as reference points).
- High-level concept design and estimated cost for the infrastructure required.
- How the options impact upstream landholders and the recreational values provided by the storage.
- How the modelled reliability of entitlements held by existing entitlement holders changes.
- How the downstream daily flow regime is expected to change, with particular focus on environmental implications.
- Findings about how each option may impact Traditional Owner values.
- Commentary on how potential future climate change is expected to influence the options.
A final report is due to be released publicly by November 2023 and the details will provide valuable input to the review of the Rochester Flood Management Plan that is being undertaken by Campaspe Shire with support from North Central Catchment Management Authority.
The Rochester Flood Management Plan will update and review flood mapping and modelling with October 2022 data, revisit mitigation options previously considered and investigate any new options, including the findings from this assessment. Community members’ input will be sought in the review of the Rochester Flood Management Plan.
In October 2022, the Goulburn River and the Campaspe River experienced major flooding with flood waters causing significant damage to farms, townships, roads, water supply infrastructure and communities.
Following these floods, we are undertaking a technical assessment on the operating and infrastructure options for Lake Eppalock. This is to determine if changing the operating arrangements or infrastructure could have any material opportunities to mitigate flooding downstream and any associated financial and non-financial implications of such changes.
In delivering this assessment, the rights of existing entitlement holders are a key consideration in any potential changes to operating arrangements. This assessment will clearly document the impact any changes to operations would have on existing entitlement holders, landholders and other users.
The outputs from this assessment will be a valuable resource to the community and will be available when Campaspe Shire Council, with support from North Central Catchment Management Authority (North Central CMA), review the Rochester Flood Management Plan.
The assessment will:
- Review and consider what updates are required to previous modelling work and investigations into Lake Eppalock operating arrangements.
- Develop and assess operating arrangement options and operating rules (taking into consideration current operating rules) for Lake Eppalock for the purpose of flood mitigation.
- Investigate, at a conceptual level, possible infrastructure options, such as installation of gates on the dam wall or bigger release valves, that could potentially support the operation of Lake Eppalock prior to, and during flood events.
- Design a methodology and deliver a flood impact investigation to identify how effective each operating arrangement option for Lake Eppalock would be at reducing peak flows downstream and mitigating the flood risk (for example inundation of public and private land and infrastructure) when compared to current operating arrangements.
- For each operating arrangement option that has a material opportunity to mitigate flooding downstream, undertake an impact assessment that identifies any costs, risks and benefits (including modelled changes to reliability) on how the changes would affect existing entitlement holders, landholders and other users.
An independent consultant will be engaged to undertake the modelling and develop a report.
The assessment is technical, and therefore there will not be a formal round of community consultation. The assessment is being conducted in consultation with local councils, water corporations and CMAs. Community members can speak to their local council or CMA about any comments or questions relating to the assessment.
The community will have a chance to have a say and input into potential changes to storage management operations when Campaspe Shire Council, with support from North Central CMA, review their Rochester Flood Management Plan. The outputs from this assessment work will feed into this review and look at a range of mitigation options.
The department is leading this work to allow all agencies to provide input in line with their functions and responsibilities. The time to deliver the final report reflects the detailed modelling and assessment which needs to be undertaken. The final report will be made publicly available once complete.
Deliverables and timeline
Scoping document developed and reviewed by key stakeholders
Independent consultant engaged to undertake assessment and prepare report
Final report released
Lake Eppalock is designed and operated to provide a secure and safe water supply. Whilst Lake Eppalock does provide flood mitigation benefits, the ability to mitigate downstream flows so they remain below flood thresholds reduces as the storage becomes fuller and floods become larger.
Lake Eppalock’s full supply level is 193.91 m AHD, at which it holds 304,650 ML. The dam is constructed of earth and rockfill and has 3 fixed crest spillways, each of which begins to spill water at different reservoir levels and has limited pre-release capability (max. approx. 1,800 ML/d).
Prior to January 2011, there had only ever been flows through the primary spillway.
On 14 October 2022, flows over the spillways peaked at 103,000 ML/day; a new historical high.
The Goulburn-Murray Water website provides more information on the flood event in October 2022.
Page last updated: 08/09/23