Beaconsfield Dam Safety Upgrade project

Beaconsfield Dam is an asset owned and maintained by Melbourne Water, with the land surrounding the reservoir managed by the Department of Energy, Environment and Climate Action (DEECA). The priority for the Beaconsfield Dam Safety Upgrade project is to protect properties and communities located downstream of the reservoir.

Why is this project important?

Beaconsfield Dam was built over 100 years ago and needs to be upgraded in order to meet current guidelines set by the Australian National Committee on Large Dams (ANCOLD). These dam safety management principles help Melbourne Water to make decisions about the reservoirs/dams it is responsible for. These guidelines apply to all dams that could present a risk to communities downstream and assist Melbourne Water to manage the risk of dam failure.

Why was the partial upgrade chosen? 

The partial upgrade is the preferred and agreed option. This is based on the assessments conducted and it would successfully reduce potential consequences whilst still maintaining a permanent water body. This has been assessed as the best option which balances risk reduction while taking into consideration environmental and community concerns about the reservoir. 

What does this option involve?

A partial upgrade of the reservoir will involve:

• Reduction of the dam wall height 
• Slow drawdown of the water level over three years from 98.85 m AHD to 94.0m AHD
• Removal of infrastructure that will no longer be needed
• Constructing a secondary spillway with a rock-lined channel
• Decommissioning the high-level outlet function

Protecting the environment

In June 2021, Arthur Rylah Institute (ARI) for Environmental Research conducted a desktop assessment of environmental values and potential impacts. This report focused on the lowering of the water level and how that would impact the surrounding environment.

The ecological report recommends a slow draw-down of the water level over a minimum three-year period to allow the vegetation around the edge of the reservoir to migrate with the changing waterline. This will minimise the impact on the environment. Melbourne Water commenced lowering the water level in early 2024.

When was the dam wall built? 

Beaconsfield Reservoir and its dam wall was constructed by the State Rivers and Water Supply Commission in 1918 as part of the water supply scheme for the Mornington Peninsula. Water was harvested from the Bunyip River and conveyed to Beaconsfield Reservoir by the Bunyip Main Race which was later supplemented by the construction of the Tarago Main Race.

Is there a historical value of the dam wall and reservoir? How will Melbourne Water capture the history of the dam wall with the local community?

The dam wall and associated infrastructure is not listed on the Victorian Heritage Register. Melbourne Water understands the strong community historical connection with the dam and its place in history. The project commits to working with the local community to capture and preserve the history of the Beaconsfield Reservoir.

Melbourne Water acknowledges the value of heritage assets, and what they mean to local communities. While this reserve has been closed off to the public, we understand that there is a strong community sentiment to preserve and record history from old assets like the dam wall that can help illustrate the importance of past feats of engineering, sense of community and events.

Have Traditional Owners been consulted on this project?

We’re committed to working with Traditional Owners and recognise their deep connection to Melbourne’s land and waterways. Melbourne Water has held an initial project briefing with the Bunurong Land Council Aboriginal Corporation (BLCAC). We are currently developing a Cultural Heritage Management Plan and will continue to engage with BLCAC for their feedback.

What is the project scope?

A partial upgrade offers the benefit of retaining the body of water while minimising community risk. This scope significantly reduces the ANCOLD Consequence Category from high A to low.

The current scope includes:
• reduction in the dam wall height
• slow drawdown of the water level over three years
• removal of redundant infrastructure
• construction of a secondary spillway with a rock-lined channel
• decommission the high-level outlet function, and
• installation of interpretative heritage signage and works

I would like more detail of the project scope. Can you please provide further technical detail?

During the detailed design phase, further studies will be undertaken to define and further develop the project scope. Melbourne Water is committed to providing ongoing project information. There are several avenues available to access this information such as via the project web page or contacting the project team at [email protected].

What is the rationale for undertaking this upgrade?

The dam was built over 100 years ago to the standards at that time, and no longer meets current safety standards and risk guidelines in terms of stability, internal erosion (piping) protection and general design deficiencies.

Melbourne Water manages its dams portfolio in accordance with Australian National Committee on Large Dams (ANCOLD) Guidelines which is required under our Statement of Obligations and in line with general duty of care expectations.

Australia has a strong emphasis on dam safety management principles set out by these Guidelines.

As a minimum, dam managers are required to achieve a level of dam safety which is as low as reasonably practicable and where this is not the case, undertake further measures to reduce the risk.

Upgrading the Beaconsfield dam will:
• satisfy Melbourne Water’s Statement of Obligations
• demonstrate an appropriate duty of care to downstream communities.

While the likelihood of dam failure is low, the consequence is significant. The Beaconsfield Reservoir Dam Safety project will reduce the risk of Beaconsfield Reservoir failing, protecting life, properties, and community located downstream of the dam.

Why does the height of the dam wall need to be reduced?

The dam was built over 100 years ago and does not meet current industry standards for the design of a dam of its size.

Melbourne Water is required to manage the risk associated with our dams to be As Low As Reasonably Practicable (ALARP) due to the hazard posed by the storage of the water.

Beaconsfield Dam has known deficiencies associated with the stability of the embankment and lack of safety features to prevent internal erosion (piping) failure. Considering our knowledge of the shortcomings in the design, construction, and performance of the dam, as well as the consequences of the dam failing, Melbourne Water has a duty of care and a regulatory obligation to reduce the risk of the structure. We understand that the reservoir water body offers amenity value to the community, and this has been carefully considered throughout the decision-making and engagement process.

What other options were considered and why did they not progress?

Melbourne Water assessed a range of options for Beaconsfield Reservoir Dam, including:
• Do nothing – this was not considered as a feasible option, because the risk to the downstream community was too high – i.e. not ALARP.
• Partial reduction upgrade (partial decommissioning) – this would see a reduction in water level and height of crest
• Full decommissioning – this would see the removal of all dam infrastructure and a return to previous state before dam was built
• Full upgrade (Safety Upgrade) – this would involve buttressing the dam wall and drawing down the water level for the duration of works. There would be a high volume of external materials brought on site, preliminary estimates suggest over 2,000 additional truck movements moving approximately 20,000 m^3 of fill on local roads in a 6-month period. This also had the highest cost and require removal of vegetation.

A full copy of the GHD report is available on the website.

Melbourne Water initially presented an option to ‘do nothing’. Why is that option now off the table?

When planning for major projects such as the Beaconsfield Dam Upgrade Project, Melbourne Water considers all options, including ‘do nothing’. This allows us to fully assess the full consequences of all possible options. In the case of the Beaconsfield Dam Safety Upgrade Project the ‘do nothing’ option is not feasible as it does not resolve the important safety issues which the project will address.

What are the benefits of the partial reduction upgrade?

Melbourne Water chose the partial upgrade after considering a range of factors, including: risk management and public safety; community impacts; cost and environment and ecological impacts. The technical experts have advised this is the best option to reduce risk and adhere to our legal and moral obligations while taking into consideration commercial responsibility and community concerns.

There are several benefits that flow on from the partial reduction upgrade.
• Safety: The reduced dam crest level reduces the volume of stored water therefore reducing the consequences of failure. The upgrade also results in an effective widening of the embankment which further reduces the likelihood of failure.
• Community: Landscaping the rock lined channel and decommissioning broad crested spillway will improve public space. Investigation underway for old infrastructure to be reused for similar projects.
• Environmental: Possible to re-introduce species to the area; Reduced potential for weed invasion.

What is the relevance of ANCOLD Guidelines to this project?

Under the Water Act 1989, Melbourne Water is responsible for the safety of our dams, including Beaconsfield Reservoir Dam.

We reduce risks by conducting routine dam surveillance, inspections, and detailed risk assessments, as part of our proactive approach to managing dams.

The management of all our dams is in line with the ANCOLD guidelines, which represent the best Australian and international engineering practice in the safe design, management, and operation of dams. They provide a consistent framework for assessing risk and allow Melbourne Water to prioritise safety upgrade works across our portfolio of dams.

The Beaconsfield Reservoir Dam was built over 100 years ago and therefore is not built to modern safety standards.

Proposed upgrade works will ensure it meets requirements in line with current industry standards and ensure protection of the local community who live downstream of the dam.

The Beaconsfield Dam Safety Upgrade project is part of our ongoing Dam Upgrade Program to ensure continued compliance with the ANCOLD Guidelines. Under this program, we have completed upgrades to the Frankston, Tarago, Toorourrong, Greenvale and Upper Yarra Reservoirs and soon to commence, Cardinia Reservoir.

What is the cost of the partial reduction upgrade, and what are the costs of the other options?

In 2019, the estimated cost for the partial decommissioning was approx. $8.9M. As part of the detailed design phase, we will be revising the costing in due course and communicating this to the community.

Melbourne Water undertook a multi-criteria analysis (MCA) in choosing a preferred option. Costs are just one component of the assessment – Melbourne Water look to maximise safety and community benefit from our investment and selected the option that does that.

Detailed cost estimates were only developed for the partial reduction upgrade, as the preferred option. Initial cost estimates utilised in the MCA indicated the full safety upgrade option to be approximately 50% more expensive than the partial decommissioning option, without taking into consideration ongoing lower maintenance costs.

What did the Multi-Criteria Analysis (MCA) consider for Melbourne Water to select the partial reduction over other options?

An MCA was used to compare each option (partial upgrade, full decommissioning, full upgrade or no action) objectively. MCA provides a robust evaluation of key aspects of the options by rating measurable criteria (e.g. compliance and cost) and those that are harder to quantify (e.g. social benefit). In the case of Beaconsfield Reservoir, the primary objective was to reduce the risk posed by the dam.

Criteria and weighting	Sub-criteria
Risk management 30%	Life safety risk Compliance with good practice
Community Impacts 20%	Provision of public amenities and safe access Visual appearance of landscape Visual appearance of lake/retained water Retention/incorporation of heritage and ‘past infrastructure’ element Impact on community by construction activity, vehicle movements etc. Fire Flood mitigation
Cost 30%	Construction Cost Ongoing maintenance cost Cost of public amenity operations and maintenance Approvals, public engagement costs Design, engineering costs Fire Flood mitigation
Environmental and conservation impacts 20%	Construction and rehabilitation period Long term impacts on flora and fauna communities

 

Why was the partial reduction scope chosen over the full upgrade scope?

Partial upgrade: Confirmed scope	Full upgrade: Not in scope
Lower community risk • Low consequence category dam • Less cost • Improved environmental qualities that make water suitable for supporting aquatic ecosystems • Less truck movements therefore less impacted residents • Low volume of external material required to be brought onto site • Less removal of vegetation • Partial water body retained for amenity • Smaller construction footprint	No improvement in community risk - does not reduce the consequence level if the dam were to fail • Higher cost • More truck movements and substantial number of residents impacted • High volume of external materials to be brought on site, including over 2000 additional truck movements on local roads in a 6 month period • More removal of vegetation to make way for construction lay down area

Where will the excess soil and materials from the reduced dam wall go? What will happen to the redundant infrastructure that is removed?

As Melbourne Water progresses through the detailed design phase, we will have more information and will communicate this information to the community. Where appropriate, we endeavour to reuse materials as much as possible for other projects happening across our city.

The excess soil and materials will remain on-site and will be used to reshape the existing dam wall.

This means less truck movements and traffic impacts to nearby residents on O’Neill Road and surrounds.

How was the maximum water level of 94.0m AHD decided?

Initially, the proposed water level was 92.0m AHD. Following community consultation and hearing how important the water level is, we undertook further investigations and were able to refine the initial engineering assessments and determined that the project could achieve its objective of a low consequence category dam with the maximum water level raised to 94.0m AHD.

Why do dams have spillways?

When a rainfall event occurs, a dam will fill, and if it fills to the level of the spillway, flows can exit the dam safely down a designated flow path without overtopping the dam and causing damage and possible dam failure.

What modelling did Melbourne Water undertake to determine that the town of Officer would be impacted by flooding if a 1 in 10,000 year storm event occurred?

The dam currently stores a large volume of water which could pose a high hazard to the downstream population. Risk associated with the current dam is not considered to be As Low As Reasonably Practicable (ALARP).

Melbourne Water’s chosen project scope is to lower the water level to reduce the hazard posed to the downstream population. The aim of the works is to ensure that, if the dam were to fail in the future under any circumstance, there would be no loss of life and minimal damage to property.

Melbourne Water have previously indicated that the current total likelihood of failure is 1 in 10,000 AEP (Annual Exceedance Probability). AEP is a detailed technical measure used in flood management. The likelihood was calculated as the sum of all the probability of all the different failure modes considered by Melbourne Water.

While the likelihood of dam failure is low, the consequence could be significant.

What is the water in the reservoir currently used for?

The reservoir was decommissioned from the State’s water supply in 1988. This was due to water quality not meeting improving standards and the commissioning of Cardinia Reservoir.

This reserve harbours flora and fauna that are, to varying degrees, reliant on the habitat provided by the waterbody. As such, Melbourne Water engaged the Arthur Rylah Institute for Environmental Research and Dellbotany to assess potential environmental impacts of the proposed activities on these communities.

You can read the full Environmental Impact Assessment on the project webpage.

Is there a need to remove any vegetation? What is the plan to revegetate the affected area?

There is a requirement to remove some vegetation to create a safe and stable access track to the dam wall. The project will work to minimise tree removal as much as possible. As we move into the detailed design phase, further information will be communicated.

In line with the Victorian Government’s Biodiversity Offset scheme, we will procure vegetation removal offsets for the vegetation loss and where appropriate work with the local community to facilitate additional planting in the local area and enhance biodiversity.

Why is the reservoir deemed unsuitable to provide potable water to the South Eastern suburbs?

Beaconsfield Dam has not been connected to the water distribution network since 1988, following the connection of Cardinia Reservoir and upgrades to the water transfer network allowing water supply to the Mornington Peninsula.

This site is not required as part of Melbourne Water’s plans for future water supply.

Why do we need to drawdown or lower the water in the reservoir?

The project driver is to ensure that, if the dam were to fail in the future under any circumstance, the risk of loss of life or damage to property would be minimised.

The water level needs to be lower to reduce risk to the downstream population.

We will be lowering the water level over 3 years for environmental reasons in line with the Arthur Rylah study.

The ecological report recommends a slow draw-down of the water level over a minimum three-year period to allow the vegetation around the edge of the reservoir to migrate with the changing waterline. This will minimise the impact on the environment. This water from Beaconsfield Reservoir over a three year period will flow into Haunted Gully Creek, a nearby waterway.

In 2019, 40 properties directly adjacent to the Reservoir and downstream from the reservoir were contacted directly by the project team. Residents are aware of the scope and will be updated regularly as the project progresses.

What is the volume of water that will be drawn down?

Approximately 245 ML of water will be drawn down slowly over a three-year period flowing into Haunted Gully Creek. The draw down level will be continually monitored and can be adjusted in line with weather conditions. I.e. heavy rain events.

What will happen once the drawdown commences? Won’t it flood the properties downstream?

The slow drawdown of water from Beaconsfield Reservoir into Haunted Gully Creek will have a flow rate of 3 litres per second. If there is a large rain event, Melbourne Water can control the flow of water by opening the channel further to increase the flow rate. The draw down will be continually monitored.

What are the environmental impacts of this upgrade?

Following an Environmental Impact Assessment conducted by Arthur Rylah Institute in 2021, there were several recommendations outlined to minimise the risk to flora and fauna, which Melbourne Water has committed to, including:

Project item	Project action	Project status
Before commencing work, a detailed ecological assessment of flora and fauna to be undertaken	Targeted seasonal field surveys have been completed. Both reports are available on the website.	Surveys completed Environmental Management Plan to be developed as part of the next phase
Lowering the water level should occur over a minimum of three years	To commence early 2023	Commencement Autumn 2023
Monitor impacts to biodiversity	Monitoring program to be included as part of the Environmental Management Plan	This will be developed during the detailed design stage of the project
Collect seed from Swamp Gum and Green Scentbark in the first year of lowering the water level	Melbourne Water to discuss further with the Cardinia Environmental Coalition (CEC)	Commencement early 2023
Undertake spring targeted surveys for threatened species prior to any ancillary works (access tracks etc.)	Spring surveys have been completed and recommendations provided	Completed – ongoing monitoring as part of the Environmental Management Plan
Control all woody weeds	Melbourne Water to work with the CEC	Ongoing
Repair perimeter fence and undertake intensive deer control throughout the lowering of the water level	Melbourne Water to work with the CEC	In progress

Melbourne Water take any environmental impacts very seriously and will monitor the reservoir pre, during and post construction.

When will work on the dam begin?

Melbourne Water will be following the advice from ARI and lower the water level down slowly to allow the environment the best chance to establish. The drawdown will commence in Autumn 2023. We will continue to regularly monitor the embankment and manage vegetation regrowth with a view to commencing the works in the summer of 2026/27.

Which community groups have Melbourne Water engaged with during the consultation and project notification process?

Melbourne Water undertook engagement with the following groups:
• Cardinia Environment Coalition (CEC) –made up of 25 local environmental groups
• Friends of Beaconsfield Nature Conservation Reserve (BNCR)
• Upper Beaconsfield Association (UBA)
• Beaconsfield Progress Association
• Hughendon Rd Community Fireguard Group
• Officer Community Association

Who was notified of the proposed redevelopment and when?

Melbourne Water doorknocked the residents immediately downstream and adjacent to the dam to discuss the project and the proposed plans
• Melbourne Water provided these residents and key community groups with information bulletins.
• Melbourne Water attended a meeting of the Upper Beaconsfield Association to discuss plans in mid-2018.
• Melbourne Water attended an open day at Beaconsfield Reservoir in July 2018 to talk to the wider community about the dam and plans for risk reduction activities
• Melbourne Water put notices in the local newspaper (Pakenham Gazette) regarding the community information sessions.
• Melbourne Water held six small community sessions in Upper Beaconsfield and Officer to discuss project and preferred option. These were open to the public and were held in April 2019.

What consultation has been done to date on this upgrade project by Melbourne Water?

Melbourne Water has been engaging with the Department of Environment, Land, Water and Planning (DELWP), Cardinia Shire Council, CEC and Friends of Beaconsfield Nature Conservation Reserve about the project since 2016.

Jacobs were appointed by Melbourne Water to undertake the Community consultation for the project and prepared an extensive Communications and engagement plan.

Melbourne Water decided that consultation should be with those with an active interest and responsibility for managing the site.

Will lowering of the water level limit firefighting capability?

The community raised concerns in relation to the fire risk for the area, especially after the devastation of Black Friday. With this in mind, the project team has sought clarification from the CFA and Forest Fire Management Services Victoria.

The advice received is that Beaconsfield Reservoir Beaconsfield Reservoir is an approved water pick up point with 2 avoidance areas.

The below information has been prepared by Forest Fire Management Victoria who work in conjunction with the CFA’s Aviation team and is current as of October 2023.

• There is no single specified depth for the variety of helicopter we use as it varies between the bombing systems - buck or tank.
• Some of the buckets are nearly 2 metres in height so depths need to cater for this.
  Pilots will determine what is safe and appropriate as the amount of weed, obstructions in the water, mud etc. all need to be taken into consideration.
• The size of the site will also be determined by the prevailing wind and clear exit and entry points. A dam that may be suitable with a northerly wind may not be suitable once the wind swings.
  Additionally, it depends if the helicopter is using a bucket or tank. As above, the pilots will make a determination as to the safety and suitability of any site based on the wind, surrounding canopy etc.
  Tanked helicopters may also make a decision on the height of the dam wall they may have to lift up and over.
• The pilots will determine the number of helicopters using a site – they set up a rotation and it will be determined by the all the factors above. Pilots will also determine flight paths based on minimising flights over houses etc.
• Depending on tank or bucket and the size of the helicopter – fill times generally vary between 30 and 60 secs.

• Cardinia Reservoir, Aura Vale or Lysterfield Lake are the approved collection points and listed in the pilot handbook. CFA have informed Melbourne Water that they have used several large farm dams in the area for pick up and Beaconsfield Reservoir could still be used if required in extreme circumstances at the reduced level.

I think the reserve should be open to the public for recreational use. Who do I advocate to about this?

We recognise there is a strong community voice to open the Beaconsfield Nature Conservation Reserve and Beaconsfield Reservoir for public use, however this project is to specifically address dam safety only. Public access issues can be referred to the landowner, the Department of Energy, Environment and Climate Change (DEECA).

The planned work is necessary to allow safe community access for all to enjoy the area as a recreation space. The only way the site can be potentially opened to the public is if the risk profile is reduced, which these works will achieve.

Will there be any further community engagement opportunities?

Community engagement on the project scope has now concluded. The partial upgrade has been confirmed and Melbourne Water are currently moving forward with planning the logistics of the project in more detail. There will be a number of opportunities for further community engagement on elements of the detailed design phase, one being how to capture the heritage value of the dam and natural surrounds. These opportunities will be communicated via the project website in due course.

About Beaconsfield Reservoir

The Beaconsfield Dam sits within the Beaconsfield Nature Conservation Reserve (BNCR) on the Haunted Gully Creek, located within Cardinia Shire, approximately 45km south-east of Melbourne. The reservoir is on-stream storage, with a local catchment area of around 334ha.

It was constructed by the State Rivers and Water Supply Commission in 1918 as part of the water supply scheme for the Mornington Peninsula. Water was harvested from the Bunyip River and conveyed to Beaconsfield Reservoir by the Bunyip Main Race which was later supplemented by the construction of the Tarago Main Race.

The reservoir was permanently disconnected from Melbourne's water supply and distribution network in 1988, following the connection of Cardinia Reservoir.

Beaconsfield Reservoir is owned by Melbourne Water, but is located on Crown Land managed by the Department of Energy, Environment and Climate Action (DEECA). The Cardinia Environmental Coalition (CEC) manage the surrounding Beaconsfield Nature Conservation Reserve (BNCR) under an agreement with the Minister for Water.

About Beaconsfield Nature Conservation Reserve (BNCR)

In 2005, the state government gazetted the 172-hectares surrounding the reservoir be set aside as the BNCR to help conserve species of plants and animals that may be rare or endangered, contain critical habitat, or hold conservation significance. The BNCR includes a variety of vegetation listed as endangered, vulnerable, and depleted in Victoria's east.