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.

Frequently asked questions (FAQs)

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.
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.
Partially upgrading the Beaconsfield Reservoir 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 of failure is significant. The Beaconsfield Dam Safety Upgrade 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 Reservoir has known deficiencies associated with the stability of the embankment and lack of safety features to prevent internal erosion (piping) failure. 
With our knowledge of these shortcomings in terms of 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. Reducing the overall height of the dam wall and dropping the overall water level will reduce the risk of dam failure.
We understand that the Reservoir water body offers amenity value to the community as well as environmental benefits to the Beaconsfield Nature Conservation Reserve. 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 which will reduce the risk of dam failure.
• 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.

Will lowering of the water level limit firefighting capability?

The community has 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 sought clarification from the CFA and Forest Fire Management Services Victoria.
The advice received is that 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.

• Cardinia Reservoir, Aura Vale or Lysterfield Lake are the approved collection points and listed in the pilot handbook. CFA has 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.
• 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.

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 should be referred to the landowner, the Department of Energy, Environment and Climate Change (DEECA).

What are the project details?

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 3 years.
  
• Removal of redundant infrastructure.
• Construction of a secondary spillway with a rock-lined channel.
• Decommission the high-level outlet function.

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. You can read the full Environmental Impact Assessment on the project webpage.
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 cost of the partial reduction upgrade, and what are the costs of the other options?

In 2019, the estimated cost for the partial reduction upgrade was approx. $8.9M. As part of the detailed design phase, we will revise the costs and communicate 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.

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

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.

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.

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.

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.
 

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 commenced in January 2024. 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.

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
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.
Lowering the water level should occur over a minimum of three years	To commence early 2023
Monitor impacts to biodiversity	Monitoring program to be included as part of the Environmental Management Plan
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)
Undertake spring targeted surveys for threatened species prior to any ancillary works (access tracks etc.)	Spring surveys have been completed and recommendations provided
Control all woody weeds	Melbourne Water to work with the CEC
Repair perimeter fence and undertake intensive deer control throughout the lowering of the water level	Melbourne Water to work with the CEC

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

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.

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 fewer truck movements and traffic impacts to nearby residents on O’Neill Road and surrounds.
Investigation is underway for the old infrastructure to be reused for other projects.

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.

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

Over the past two years, Melbourne Water has also engaged with the Save Beaconsfield Action Group (SBRAG), providing opportunities to hear their concerns and share relevant project details and rationale.
 

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. 
• Notification of reservoir drawdown commencement to 15,000 residents within the direct vicinity of the reservoir in January 2024.

Will there be any further community engagement opportunities?

• Community engagement on the project scope has now concluded. The partial reduction upgrade has been confirmed and Melbourne Water are currently moving forward with planning the logistics of the project in more detail. 
• There will be 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.

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.

How do I find out more detail about the project?

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 via the project web page or you can contact the project team at [email protected].

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 within the Beaconsfield Nature Conservation Reserve (BNCR) which is Crown land, managed by the Department of Energy, Environment and Climate Action (DEECA). 

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.