Dam safety

Protecting our dams and communities

We manage 16 declared dams (including reservoirs) to ensure they remain safe and the environment around them is protected. 

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About this project

We work in partnership with WaterNSW, who manages 11 major dams and reservoirs that supply us with untreated raw water from river and dams. We then treat and supply this as drinking water to the Greater Sydney region.

Dams Safety NSW declares dams that can:

  • potentially endanger life downstream
  • cause major damage or loss to infrastructure or the environment
  • have major health and social impacts.

Each declared dam has a consequence category reflecting its potential risk. Any risks concerning our dams must follow safety requirements from the Dams Safety Act 2015 and the Dams Safety Regulation 2019. These provide the framework and activities to ensure dams don't put people's safety, property or the environment at risk.

In accordance with the Dams Safety Act 2015 and associated regulations and guidelines, we will complete dam maintenance at some of our dams. This work includes removing vegetation, predominantly trees and shrubs, from dam embankments and, where required, from within 5 metres of the embankment base. This allows us to effectively assess ground, below ground and the structural condition of our dam and minimise safety and operational risk.

What is a dam?

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

  • has a wall that's higher than 15 metres
  • could endanger life or result in a 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. Ten of our reservoirs are declared dams because they're supported by earthen embankments, which would endanger life and result in catastrophic consequences if they fail. Our other 6 dams include one large concrete structure at Manly, and 5 are stormwater retarding basins used for flood mitigation.

Dams we manage

These are our declared dams:

  • Centennial Park Reservoir 1, 2
  • Dover Heights Reservoir
  • Killara Reservoir
  • Manly Dam
  • Maroubra Reservoir
  • Oak Flats Reservoir
  • Potts Hill Reservoir 2
  • Rouse Hill Retarding Basin 5, 9
  • Rouse Hill Retarding Basin 13, 9B, 16AB
  • Thornleigh Reservoir
  • Warringah Reservoir
  • Waverley Reservoir

Benefits

We need to comply to standard regulations so we can continue to provide world class services to our customers. This includes ensuring that our dams are safe and we can continue to protect communities living around the dams that we manage.

Regular maintenance of dam embankments ensures slope stability, and permits observation of any cracking, sliding or seepage. For example:

  • 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 increased leakage.
  • Roots can disguise, absorb and transpire substantial amounts of water, which could prevent early detection of water leaking through cracks and joints in the wall or foundation.
  • Trees falling down during windstorms may cause damage to the embankment, wall or foundation if substantial material is dislodged with the root system.
  • Trees and large shrubs limit access and visibility, and prevent effective inspection for early identification of structural issues
  • Vegetation can also provide habitat and cover for ground-burrowing or digging animals (foxes and rabbits) that may also impact and threaten the safety of the embankment.

Project updates

09 December 2024
Update on vegetation removal at Maroubra Reservoir

Earlier in 2024, we let you know about plans to remove vegetation at Maroubra Reservoir as part of our dam safety work. This work is required to ensure that we meet our statutory obligations under the Dams Safety Act.

Read more
25 June 2024
Maroubra Reservoir Review of Environmental Factors (REF) now on display

We've prepared the REF document guided by the Environmental Planning and Assessment Regulation 2021. The REF looks at all the potential benefits and impacts of this project, including environmental impacts.

Read more

More information 

FAQs

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

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 systems
  • 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'.

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 specify that embankments must be clear of vegetation, including trees and shrubs, from within 5 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, and damage to properties and community infrastructure.

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

In NSW, development is regulated under the Environmental Planning & Assessment Act 1979 (EP&A Act), the Environmental Planning & Assessment Regulation 2021, state environmental planning policies (SEPPs) and local environmental plans (LEPs).

This work can be approved by Sydney Water in accordance with the EP&A Act. We have a stringent process for environmental and project management, and are certified to ISO14001, ISO9001 and ISO55001. We must consider environmental impacts of any proposed work before proceeding. We prepare a Review of Environmental Factors (REF) using assessments made by independent ecologists.

We aim to retain and minimise vegetation impacts as much as possible. This involves doing additional technical investigations, including an arborist assessment, along with consultation with dam safety engineers and Dam Safety NSW.

We have been looking at ways to minimise our impact at Maroubra Reservoir. We'll be removing all trees on the embankment, regardless of tree type or condition, as this is a strict dam safety regulation. Where possible, we'll assess the ability to maintain trees within 5 metres of the embankment toe, based on the dam structure and risk profile.

For example, at Maroubra Reservoir there's a retaining wall on the southeast section of the dam, which is supporting the embankment. Healthy trees in this location will be retained.

No trees on the downward side of the stormwater drainage are being removed as they've been assessed as not impacting the drainage or structure of the dam.

Vegetation on the eastern embankment is below telecommunication structures that have been structurally reinforced, so have also been assessed as lower risk. There are some weeds on this embankment that will be removed.

Maroubra Reservoir is a critical asset that 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 2 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.

The reservoir receives water from Warragamba Dam via Randwick Reservoir. If there's an incident with water supply, water can also be directed to Maroubra Reservoir from Waverley Reservoir.

We have implemented a Property Environmental Management Program (PEMP) that aims to rehabilitate areas within our landholdings, 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.

There will be no replanting of trees on the dam embankments. We're committed to replanting on-site away from the embankments where possible, and removing dead and dying vegetation and weeds.

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

At Maroubra Reservoir, we will:

  • where possible, relocate suitable and viable native plants 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 Council to ensure the preservation and enhancement of green spaces and habitat corridors in the area.

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.

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.
  • There are safety hazards at this site, including disinfection chemicals.
  • There is other critical infrastructure on-site, including telecommunication towers.
  • The reservoir roof area must remain secure to ensure we don't lose water supply to 27,000 properties. We must ensure safety and mitigate security risk as much as possible.