FAQs

A dam is a barrier or structure built across a waterway to obstruct and control the flow. Dams vary in size from small earth embankments, often for farm use, to large concrete structures. Dams Safety NSW regards the following structures as dams:

• dams
• weirs
• off-river storages
• retarding basins
• reservoirs
• tailings dams.

Dams Safety NSW assesses all dams in NSW and determines dams that can potentially endanger life downstream, cause major damage or loss to infrastructure or the environment, or have major health and social impacts. These are referred to as declared dams. 

Each declared dam has a consequence category that reflects its potential risks. Sydney Water is required to address any risk concerning our the safety of our dams in accordance with the Dams Safety Act 2015 and the Dams Safety Regulation 2019. 

These provide the framework and activities that ensure dams don't put the safety of persons, property or the environment at risk. 

Each year we produce a Dams safety standards report for each of our declared dams – see the latest summary (201 KB). For more information or complete reports, email damsafety@sydneywater.com.au.

We work in partnership with Water NSW, which supplies much of the untreated raw water from rivers and dams. Water NSW manages eleven major dams and reservoirs (21 declared storage dams) that provide drinking water to Greater Sydney.

Our 16 declared dams

A dam is a structure that stores or holds back water that meets the following criteria:

• with a wall that is more than 15 metres high or;
• it would endanger life or result in major or catastrophic level of damage if it fails.

Dams vary in size from small earth embankments, often for farm use, to large concrete structures. Sydney Water manages 16 declared dams. Ten of Sydney Water’s reservoirs are declared dams because they are supported by earthen embankments, which would endanger life and result in catastrophic consequences if they fail. Of the six other dams owned by Sydney Water, one is a large concrete structure at Manly, and five are stormwater retarding basins used for flood mitigation.

Maroubra Reservoir is classified as a High A consequence dam. It is primarily built into the ground with earth embankments, which provide support to the structure. The embankment is a structural part of the dam which if compromised could result in a dam break impacting a large part of the local community. Whilst the top of the dam is visible to the community, most of the dam is located below ground and extends deeper and wider than what is visible.

This Dams Safety Regulation 2019 sets out operational details and safety standards that declared dam owners must comply with to satisfy the provisions of the Dam Safety Act 2015.

1. The owner of a declared dam must establish and implement a dam safety management system for the dam in accordance with the act.
2. The dam safety management system must be designed to be used by the owner of the dam as the primary means of ensuring, as far as is reasonably practicable, the safety of persons, property and the environment is not put at risk from the dam.
3. The dam safety management system must provide a comprehensive and integrated system for the management of all aspects of foreseeable risks in relation to the failure of the dam that addresses all aspects of the life cycle of the dam, including the design, construction, operation, maintenance and decommissioning of the dam.

In 2013 the NSW government initiated a review of the Dams Safety Act 1978 and its associated regulatory framework. This resulted in new legislation in the form of the Dams Safety Act 2015 and the regulation which commenced on 1 November 2019.

The key principles guiding the new regulation and standards are that:

• the responsibility of declared dam owners for dam safety is reinforced.
• regulation is principle-based to the greatest extent possible
• declared dam owners must implement a safety management system based on an internationally recognised asset management system.
• declared dam owners must make safety risk decisions about their dams.
• declared dam owners must mitigate dam safety risks ‘so far as is reasonably practicable’.

Our dams must be safe, so we can protect people, property and the environment around the dams we manage. We rely on the dams to store water for our customers so we need to comply to this regulation to ensure we continue to provide world class services for our customers. 

Our dams also provide community infrastructure and recreational space, so we need to ensure that these are safe and reliable and do not cause any disruption to neighbouring communities.

The regulation ensures the best standards to maintain our Dams. We have internal/ audits and inspections that identify what  actions we need to take to meet the requirements of the legislation.

Dams Safety NSW is responsible for monitoring our compliance with dam safety legislation. 

Dams Safety NSW exercises a range of proactive, planned compliance activities with declared dam owners, including:

• running a risk-based audit program with compliance priorities determined by dam consequence category and other risk factors
• risk-based inspections.

This work is necessary for us to comply with the Dams Safety Act (2015), associated regulations (2019) and Australian National Committee on Large Dams (ANCOLD) guidelines which specifies that embankments must be clear of vegetation, including trees and shrubs. The guidelines specify that vegetation must be cleared from dam embankments and from within five metres of the embankment base, also known as the toe.

These regulations are in place to manage the risk of dam failure and the associated impacts to the community, which include potential loss of life, flooding, damage to properties and community infrastructure.

The embankment is a structural component of the dam and is supporting the dam walls. Managing the vegetation allows Sydney Water to effectively inspect and assess the structural condition of the dam and respond early to mitigate the risk to the community.

Regular maintenance of dam embankments is required to ensure slope stability and to allow observation of any cracking, sliding or seepage, for example:

• Tree roots can dislodge joint fillings and penetrate cracks in concrete walls or foundation rock possibly leading to crack widening and concrete or rock deterioration resulting in leakage and instability.
• Roots can provide a pathway for water movement and cause internal erosion within the dam that can erode the embankment from within and lead to a dam failure.
• Vegetation can absorb and transpire substantial amounts of water and, therefore, could prevent early detection of water leaking through cracks and joints in the wall or foundation.
• Toppling of trees during windstorms can create large voids in the embankment, damage the dam wall or foundation materials if substantial material is dislodged with the root system.

In NSW, development is regulated under the Environmental Planning & Assessment Act 1979 (EP&A Act) and Environmental Planning & Assessment Regulation 2021, State Planning Policies (SEPPs) and Local Environmental Plans (LEPs).

The work (development) proposed at Maroubra reservoir does not require consent and can be approved by the public authority, in this case Sydney Water. This also means Sydney Water do not required approval from Randwick City Council for the work or tree removal.

Sydney Water must however consider the environmental impacts of proposed works before proceeding. A Review of Environmental Factors (REF) has been prepared using the assessment of an independent ecologist, and the works were found to have no significant impact.

The REF will go on public display in late May for three weeks, after which Sydney Water will review the feedback and prepare a Decision Report. A final REF will then be published.

No, this is an operational asset, and the drawings and associated asset information are confidential to ensure security of the water supply.

This work can be approved by Sydney Water in accordance with the Environmental Planning and Assessment Act 1979 . Sydney Water has a very stringent process for environmental and project management, and are certified to ISO14001, ISO9001 and ISO55001. Sydney Water must consider environmental impacts of any proposed work before proceeding. A REF (Review of Environmental Factors) has been prepared for this work using the assessment made by independent ecologists.

Sydney Water has revised and modified this proposal aiming to retain plants and minimise vegetation impacts as much as possible. This has involved undertaking additional technical investigations, including an arborist assessment, along with consultation with Dam Safety Engineers and Dam Safety NSW. The outcome is that a number of plants initially identified as requiring removal have now been identified as able to be retained.  The updated REF, including ecological and arborist assessments, will go on public display in late May for three weeks, after which Sydney Water will review the feedback and prepare a Decision Report. A final REF will then be published.

Sydney Water has commissioned studies with independent ecologists and have engaged qualified experienced arborists. There is a threatened ecological community to the east of the site which is outside the dam embankments and has always been excluded from the work. There are two Magenta Lilli Pilli’s (Syzygium paniculatum) on site, but they are also outside the work zone and are not impacted by our work. The ecologists have determined that there is no significant environmental impact to flora or fauna.

We have been looking at ways to minimise our impact at Maroubra reservoir/dam. We will be removing all trees on the embankment, regardless of tree type or condition, this is a strict dam safety regulation. Where possible, we will assess the ability to maintain trees that are within five metres of the embankment toe, based on the dam structure and risk profile. 

For example, at Maroubra there is a retaining wall on the southeast section of the dam, which is supporting the embankment, and healthy trees in this location will be maintained.

No trees on the downward side of the stormwater drainage are being removed as they have been deemed not to impact the drainage or structure of the dam.

We need to comply with the Dams Safety Regulation so we can continue to provide world class water services to our customers. The regulation is in place to ensure dam owners have sound safety management practices in place and the risk to the community is managed. This includes, ensuring that the likelihood of a dam failure is exceedingly rare.

The Dams Safety Regulation and associated ANCOLD guidelines specify that vegetation, primarily trees and shrubs over a metre in height, must be removed from dam embankments and within five metres of the base or toe of the embankment.

The decision to remove the vegetation at Maroubra was made in accordance with recommendations from competent and independent Dam Safety Engineers who inspect Sydney Water’s dams as per the Dam Safety Regulation 2019. We won’t be removing all vegetation, only those that pose a risk to the dam.

This will enable Sydney Water’s technical and engineering teams to effectively assess the structural condition of the dam and manage the risk to the community.

No. The ANCOLD guidelines do not specify tree species or root structures, all trees and shrubs over a metre in height must be removed from embankments and within five metres of the toe. The risk of trees coming down in a storm, or dying and falling, is as much of a problem as the invasiveness and water carrying properties of roots on the stability of the embankments.

Not all vegetation will be removed, the following is planned to stay:

• All vegetation under a metre in height if it doesn’t inhibit inspection.
• All vegetation beyond the toe drain.
• All vegetation on the southern side, which is built on rock.
• Vegetation on the eastern side below the telecommunications tower and associated infrastructure.
• We will leave vegetation at the toe deemed low risk by our independent Dam Safety Engineers and reassess at a later date.

Maroubra reservoir is a critical asset which receives, and stores treated water for supply to the southern areas of Randwick LGA. The reservoir is a composite concrete/earth fill embankment divided into two equal and independent halves. It has an aluminium roof constructed over the water area, is 11.6 metres above foundation and has a capacity of 128 megalitres. This water is distributed to 27,000 households and businesses in the Maroubra area.

Water is pumped from Warragamba to Randwick Reservoir (WS101) and then on to Maroubra. If there is an incident with water supply, water can also be directed to Maroubra Dam from Waverley Reservoir (WS134).

We will work with individual property owners to understand their concerns, assess the risk to their properties, and manage as required.

Vegetation on the southern embankment has been deemed low risk by our independent Dam Safety Engineers. 

Vegetation on the eastern embankment is below telecommunication structures which have been structurally reinforced, so have also been assessed as lower risk. There are some weeds on this embankment which we will take the opportunity to remove. 

Sydney Water has implemented a Property Environmental Management Program (PEMP) which aims to rehabilitate areas within our land holdings, such as threatened ecological communities and other areas of significance. The PEMP area on site is around the toe of the eastern embankment extending down to the property boundary.

Sydney Water is also committed to replanting on site away from the embankments and removing dead and dying vegetation and weeds. We will also be working with Randwick Council to do offset planting elsewhere in the LGA.

The cleared areas will be recompacted to the required engineering standard and covered by turf, we will maintain it according with the vegetation standard for our dams. This will enable us to carry out regular inspections and maintenance.

There will be no replanting of trees on the dam embankments. There are some limited opportunities for replanting onsite, however we will work with local Councils to provide some offset planting in the local government area.

At Maroubra we will:

• Relocate suitable native plants where possible and viable away from the clearance zone and towards the perimeter of the site.
• Plant non-invasive endemic vegetation outside the clearance zone to provide additional habitat.
• Install habitat boxes to support local bird and bat populations.
• Undertake offset planting in collaboration with Randwick City Council to ensure the preservation and enhancement of green spaces and habitat corridors in the area.

Remediation of the site will be performed in stages:

1. Tree and vegetation removal/ relocation of natives to other areas on site where possible.
2. Immediate remediation of the site , such as backfilling and recompaction of the embankment and laying of turf.
3. Inspection to determine whether any further remediation required.
4. Planting of low growing shrubs onsite in suitable locations.
5. Installation of habitat boxes.
6. Off set planting – working with Randwick Council to find suitable locations and tree species.

We are currently finalising the revegetation plan and aim to begin this work once the site has been cleared, and any remediation work completed.

No, we don’t have enough room on site and can’t replant on the embankments. The base or toe of the embankment is on the fence line for most of the site. We will however be working with Randwick City Council to do offset planting elsewhere in the LGA.

Yes, however impacts of carrying out this work would require us to remove a greater number of trees, than is required now. It would also be very expensive to achieve and would require the reservoir to be taken offline for a considerable period creating a risk to water supply.

We can’t do nothing, the risk to the community is unacceptable. The dam will be assessed as above the safety threshold.

Yes, community members can contact us if they are interested in receiving mulch.

Yes, we will continue to update the community of our work.

No. The purpose of removal is to ensure the likelihood of a dam break is exceedingly rare, removing trees in stages will not ensure the risk is effectively mitigated. Our independent Dam Safety Engineers have determined that the risk of leaving vegetation at the toe of the embankment is low, so we aren’t removing all vegetation. There will still be screening wherever possible for neighbouring properties, and we will provide replanting on site where we can to provide buffering.

No. There are several reasons why we can’t open this site up for public access:

• Having the public walk on the embankments will cause erosion. We see this at sites where the dam is completely underground.
• There are safety hazards at this site, including disinfection chemicals.
• There is other critical infrastructure onsite, including telecommunication towers.
• The reservoir roof area must remain secure to ensure we don’t lose water supply to 27,000 properties. We must mitigate the safety and security risk as much as possible.

For further information on Dams, visit Dams Safety NSW 

For information on Sydney Water visit sydneywater

For  Dams safety standards report download  summary (201 KB).

 For more information or complete reports, email damsafety@sydneywater.com.au.