Dam safety management
Dam safety is about managing dams at a level of safety to minimise any risk to life, property, essential services and the environment.
Victoria's dam safety record is very good but it is important to maintain effective oversight. Catastrophic dam failures regularly occur internationally.
Victoria faces many risks including bushfires, floods, severe storms, climate change and drought. Compared to these, the risk to the public from dam failure is relatively low.
Dam owners and managers can implement engineering controls and safety management systems to reduce the risk.
Australia has a good dam safety record and the likelihood of a major dam failure is very low. Nevertheless, the history of serious dam failures internationally is testimony to the importance of maintaining comprehensive dam safety management programs.
How owners manage their dams
The greater the damage a dam could cause if it were to fail, the more effort a dam owner needs to put into monitoring it.
Larger dams have safety plans which include regular inspections by experienced and qualified people and monitoring of instruments installed at dam sites. Information from such instruments is collected regularly and dam safety managers are continually looking for signs of change in their dams.
Dam owners also prepare operations and maintenance manuals with instructions on how to operate the dam under many different conditions, such as during a big flood.
Victoria has a good dam safety record but some old dams were built as far back as the 1860s. Although these dams were constructed to the best standards of the day, design standards have improved over time as we gain better knowledge on storms, earthquakes and construction techniques.
As standards improve, dam owners assess their dams for risks and identify work that can be done to improve safety. A list of dam safety upgrades can be found at Victorian Dam Sfatey Improvement Program.
All large dams or dams which may cause significant damage if they fail, need to have a Dam Safety Emergency Plan. This plan guides the dam owner's response to an unwanted situation at the dam. Testing the plan with emergency service organisations builds trust and an understanding of everyone's responsibilities in the unlikely event of a dam safety emergency.
The Emergency Management Manual of Victoria assigns roles to emergency service organisations and other agencies for types of incidents. For more information go to the website of the Emergency Services Commissioner.
In a dam safety emergency, the dam owner along with DEPI, manages response activities to minimise the impact on the community and the environment from the incident.
If warning or evacuation is needed, the State Emergency Service (VICSES) and Victoria Police are involved. Local councils provide emergency relief to the community.
How dams can fail
It is very unlikely that a well-constructed and maintained dam would fail. A failure that causes serious damage to the structure is called a dam break. This extremely rare event can occur by:
Overtopping – During a flood, water that cannot be stored or controllably released, overtops the dam. Dams made of earth or rock can erode and fail quickly if overtopping continues to occur.
Structural failure - causes of structural failure include:
- Internal erosion – water flowing through, or beneath, the dam that 'washes out' material from the dam wall can lead to the collapse of the wall.
- Earthquake – shaking during strong earthquakes may make an earth wall settle and become lower (like shaking a sand castle on a tray) potentially causing overtopping. Strong earthquakes may cause a concrete wall to crack.
- Mechanical failure of the gates or outlet works may prevent the dam operator from releasing water and lead to overtopping failure.
The chance of a dam break happening is very low. If a break were to happen the flooding associated with such a situation would depend on the height of the dam wall, the amount of water in the dam and the shape of the valley below the dam.
Flood engineers make predictions of the flow paths and levels of the released water and plot them on maps known as 'inundation maps'. These maps are useful in planning for the impacts of a potential dam break scenario since the inundation maps give some indication of the flow path. However, the actual flood can be different as these maps are based on assumptions of how the dam will fail, which is difficult to predict.
The path of water during the flood can also be difficult to predict as erosion or blockages by debris can change the course of the flood.
Find out more about dams in your area
Satellite images available on the internet are a good place to locate dams that are close to you.
Visit the interactive map of Victorian dam sites for information on some of the states major dams.
If you live close to a large dam, it is likely that your local water corporation will know who owns it and can let you know who to speak to for more information.
If you live near a private dam, the local water corporation who issues licences can provide some information about it.
The information in this section is available to print and download on the dam safety fact sheet .