How gated dams work.
Stay informed this wet season.
Dams collect and store water primarily to provide South East Queensland with the drinking water that comes out of our taps. Seqwater manages 25 referable dams across the region, three of which are operated by gates (North Pine, Wivenhoe and Somerset).
Our two largest dams, Wivenhoe and Somerset, also provide flood mitigation benefits for the region. Wivenhoe and Somerset Dams are located upstream on the Brisbane River (approximately 80 and 100 kilometres north of Brisbane respectively) in the Somerset Region.
These dams cannot prevent flooding from occurring but can temporarily store flood waters for a period of time and release these waters at a controlled rate to mitigate impacts downstream.
Did you know?
- Wivenhoe Dam can store over 1 million megalitres (ML) for water supply and hold nearly 2 million ML of extra flood water, with a total capacity of about 3.2 million ML.
- Somerset Dam can store about 380,000 ML for water supply and hold an additional 705,000 ML of extra flood water, with a total capacity of 1.08 million ML.
How gates dams work
Hear from our teams at Wivenhoe Dam and our Flood Operations Centre about how South East Queensland’s largest dam works, including in times of flooding.
History of Brisbane River flooding with Dr Margaret Cook
Dr Margaret Cook, and the author of ‘River with a City Problem’, takes us on a journey back in time looking at the history of Brisbane River flooding, starting with the first flood on record in 1841.
Climate patterns affecting South East Queensland
Climate Specialist Professor Roger Stone and Flood Specialist Ella Harrison discuss the weather patterns of La Nina and El Nino and what these mean for South East Queensland.
Behind the scenes at gated dams in South East Queensland
Up to 100 Seqwater staff are monitoring our network at any one time. Take a look behind the scenes at Seqwater’s gated dams and meet some of our team.
Living downstream of a dam? Be informed and prepared.
During major weather events, areas of South East Queensland near waterways may be impacted by flooding. Because weather can be unpredictable, it’s important for those living downstream of a dam to understand their flood risk and know how to stay informed during an emergency.
Seqwater provides regular updates to local communities and authorities on dam levels and spilling and release, although dam releases and spilling does not necessarily mean flooding will occur in your area.
While Seqwater dams continue to operate safely under normal conditions, it’s important to be prepared in the event of an emergency. Your local council offers a range of tools and information to help you understand your individual flood risk.
Gated dams and flood operations manual
During a flood event, Seqwater monitors the safety of its dams. Gated dams cannot prevent flooding from occurring altogether and in an extreme flood, there are risks that the safety of a dam can become compromised.
The Flood Operations Manual contains procedures to be used for releasing water from the gated dams during flood events, or to achieve a temporary or reduced full supply level of water. Any releases made outside of these reasons are considered operational (for example, releases through a cone valve to assist with downstream flows for the environment).
The objectives of the Flood Operations Manual are to protect the structural integrity of the dam during flood events, mitigate downstream flooding, reduce environmental impacts, minimising disruption to transport and maintaining a full drinking water supply at the end of the event.
The procedures are designed to minimise the risk to human life and safety by prioritising the structural safety of the dam. An appropriate balance is needed to manage the different objectives, and care must be taken not to hold back too much water and risk the structural integrity of the dam.
Visit the Understanding the flood operations manual page for more information.
Ungated dams and spilling
An ungated dam is built in a way that means Seqwater has no control over water spilling from the dam once the dam water level surpasses the Full Supply Level (FSL) i.e. the dam is full.
The dam spillway crest is set lower than the top of the dam embankment so that water can flow over the spillway and safely out of the dam into the creek or river system the dam is built on. This allows releases to be made through engineered structures and prevents the dam embankment from being overtopped.
All ungated dams help mitigate flooding to some extent. The peak outflow from an ungated dam during a flood event is less than the peak outflow that would have occurred had the dam not been built, because some water is temporarily held in the dam while it is spilling and released out of the dam at a slower rate. The presence of the dam in the river attenuates floods as they pass through the dam. Dams such as Hinze Dam use this attenuation to provide significant flood mitigation benefits to the downstream communities.
This means that if you are downstream of the dam, avoid potential hazards such as fast flowing or deep water near waterways and floodplains. These hazards potentially threaten the safety of you and your property.
Emergency Action Plans
During a flood event, Seqwater monitors the safety of all its dams.
Seqwater has an Emergency Action Plan (EAP) for each of its 25 referable dams—those that could pose a risk to two or more people if they were to fail. These plans help identify potential hazards, such as floods or earthquakes, and outline how Seqwater will respond to reduce risks to downstream communities.
Under the Water Supply (Safety and Reliability) Act 2008, all referable dams must have an Emergency Action Plan (EAP) in place, and this standard industry practice and regulatory requirement will assist to support a quick and coordinated approach in the event of an emergency.
EAPs are approved by the Queensland Government and support coordinated emergency responses between Seqwater, local councils and Local and District disaster management groups (LDMGs and DDMGs). These plans help activate disaster management procedures and guide evacuation messaging when needed.
If a dam-related risk or hazard is identified, Seqwater notifies the relevant disaster management groups. While Seqwater is responsible for issuing emergency notifications to potentially affected residents, the disaster management groups lead the broader emergency response, including evacuations, resource deployment, and recovery efforts.
By working together, Seqwater and its emergency partners ensure community safety remains the top priority during dam or flood emergencies.
Types of messages that could be used
WARNING LEVEL – Watch and Act
Prepare to leave and/or move to higher ground
What you should do:
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Prepare to leave so you can go quickly if water levels start to rise. Get ready now.
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Decide where you and the people you live with will go if the situation worsens. Find a safe and high place away from flooding such as an Evacuation Centre.
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Stay where you are and get up as high as you safely can. This could be upstairs or the roof.
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Warn friends, family and neighbours in the area of the possibility of flooding.
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Tell someone where you are.
- Stay in place until you are rescued, or wait until the water goes down to safely leave.
To view the Emergency Action Plans, visit the Queensland Government page for referable dams.
Dam release notification service
To receive updates on gated releases and un-gated dams spilling, subscribe below. The notifications will tell you when the dam is spilling, when there may be potential downstream hazards, and when the dam has stopped spilling. We do not provide information on the expected timing of water spilling from ungated dams as flows will automatically start once the dam is full. We will notify you if the outflows have increased to a level that may cause potential hazards to the safety of people and property downstream.
Sign up for email notifications >
Summer preparedness
Summer is the peak season for bushfires, storms, floods and cyclones in Queensland. Ahead of the summer season, Seqwater undertakes a range of activities to ensure its teams are well prepared to respond to extreme weather and emergency events that may impact the Seqwater network.
Seqwater’s Flood Operations Centre continually monitors catchment and weather conditions throughout South East Queensland.
Every flood event is different, and there can be multiple sources of flooding. It’s important to stay informed ahead of the wet season.
Frequently Asked Questions (FAQs)
No FAQs match your query
Seqwater manages 25 referable dams across the South East Queensland (SEQ) region – 22 of which are un-gated (such as Baroon Pocket, Borumba, Moogerah and Hinze) and three of which are operated via gates as required (North Pine, Somerset and Wivenhoe).
A map of the Seqwater network can be found here.
At our un-gated dams, excess water naturally flows over the spillway and safely out of the dam into the creek or river system the dam is built on.
A gated dam is built to enable Seqwater to have some control over the release of water. Seqwater operates three gated dams–Wivenhoe Dam and Somerset Dam in the Somerset Region and North Pine in the Moreton Bay Region.
Once a gated dam reaches its Full Supply Level, Seqwater controls the release of water over the spillway using specially designed gates. The operation of the gates is determined by operating rules in the approved Manual of Operational Procedures for Flood Mitigation for Wivenhoe, Somerset and North Pine dams. These manuals are publicly available on the Seqwater website.
A controlled release of water from a gated dam will not necessarily result in downstream flooding.
The Full Supply Level (FSL) of a dam refers to the approved level that water can be stored in the dam for drinking water or irrigation.
When un-gated dams fill, they are designed to pass excess water into the creek or river system they are built on. This is called ‘spilling’ and is not controlled by gates or valves.
For gated dams (Wivenhoe, Somerset and North Pine), if the water level rises above the Full Supply Level, Seqwater will use valves or gates to make controlled releases for flood mitigation and to protect the safety of the dam.
Flood mitigation is the process of capturing water in a dam and then releasing it downstream at a slower rate. The water is released in a controlled manner through a spillway, with the aim of minimising river levels downstream of the dam.
Dams cannot always stop flooding occurring downstream. This may be because the size of the flood is larger than the dam’s storage capability or the rain has fallen downstream of the dam’s catchment. Dams also do not have an infinite storage capacity and during a flood our teams work to balance the provision of flood mitigation benefits with protecting the integrity and safety of the dam.
You can check where Seqwater’s 25 dams are located here.
It’s important to know that there can be multiple sources of flooding such as from local creeks, stormwater drains or overland flows. Your local council has a variety of flood information tools to help you understand your individual flood risk.
Each dam has a full supply level (FSL), which is the approved water storage level of the dam for drinking or irrigation. This FSL is equivalent to 100 per cent supply volume.
The storage level of a dam can rise above 100 per cent when there is water being held in the ‘freeboard’ as well as going over the spillway. The freeboard is a space between the full supply level (how much is held in the dam for drinking water and irrigation) and the level of the dam crest.
The size of a freeboard depends on the dam type, size, spillway and spillway dimension.
Once the full supply level is reached, water can flow out of the dam in multiple ways, depending on the dam design.
South East Queensland’s gated dams – Wivenhoe, Somerset and North Pine – have the ability to store extra water for a period of time before controlled releases of this water commence through gates or valves.
When we say Wivenhoe Dam is 100 per cent full, this means the amount of storage allocated for drinking water and irrigation is full, but additional water (up to 2 million megalitres) can be temporarily stored above this during a flood event.
So when you hear a dam is more than 100 per cent full, it simply means it’s doing what it’s designed to do – releasing excess flood water to keep the dam safe and provide flood mitigation downstream.
When levels go above the Operational Full Supply Level, the Seqwater Flood Operations Centre directs the operation of the dam gates to release water in accordance with the Flood Operations Manual.
The objectives of the Flood Operations Manual are to protect the structural integrity of the dam during flood events, mitigate downstream flooding, reduce environmental impacts and maintain a full drinking water supply at the end of the event.
Somerset Dam is upstream of Wivenhoe Dam. All releases from Somerset Dam end up in Wivenhoe Dam, which is about three times larger than Somerset.
Wivenhoe Dam has a floodwater storage compartment, which enables the dam to temporarily hold back water on top of the drinking water stored in the dam. Wivenhoe Dam can hold 1.165 million megalitres of drinking water, but also has a flood storage compartment of another 1.967 million megalitres. Therefore, the dam has a total storage capacity of 3.132 million megalitres.
When levels go above the Full Supply Level, the Seqwater Flood Operations Centre directs the operation of the dam gates to release water in accordance with the Flood Operations Manual. The objectives of the Flood Operations Manual are to prevent structural failure of the dam during floods, mitigate downstream flooding, reduce environmental impacts and maintain a full drinking water full supply at the end of the event.
North Pine Dam provides some downstream flood mitigation benefit by capturing rainfall and runoff entering the dam from upstream (inflows) and then releasing excess water (outflows) at a slower rate. This process typically helps to reduce flooding impacts downstream.
Care must be taken not to hold back too much water and risk the structural integrity of the dam.
The flood storage compartment is designed to temporarily store floodwater and release it at a controlled rate with the aim of minimising downstream impacts and not exacerbating peak river levels and flows downstream.
Dams do not have an infinite amount of storage space and flood water unfortunately cannot be stored in the dam indefinitely. This excess water must be allowed to pass through the dam during the flood in preparation for any further rain.
Seqwater aims to empty the dam of floodwater after the flood has peaked, so that the flood storage compartment remains available to manage inflows if another rain event occurs. This has to be done relatively quickly, usually within seven days, in case we receive another burst of heavy rain as has happened in previous flood events. This means we generally cannot wait until the flood event has completely passed before releasing water from the dam.
The Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam (or Flood Operations Manual) explains how the flood storage compartments of these dams are used during flood events and is available on the Seqwater website.
There can be many sources of flooding in South East Queensland, and every flood is different. Water released from a gated dam is only one source of water contributing to flows in rivers or watercourses downstream.
Half of the Brisbane River catchment is located below Somerset and Wivenhoe Dams – this includes the Bremer River and Lockyer Creek. As these river systems enter the Brisbane River below Somerset and Wivenhoe Dams, the dams cannot help mitigate flooding from these rivers, and if heavy rain is received downstream of the dams they cannot play a role in mitigating these floodwaters.
Other sources of flooding can include heavy rainfall in downstream areas, flooding from local creeks and tributaries, stormwater drains and overland flows.
Your local council has a variety of flood information tools to help you understand your individual flood risk.
Details of releases from gated dams are provided by Seqwater to the Bureau of Meteorology, which is responsible for calculating river heights and issuing flood warnings. Please follow updates from www.bom.gov.au including severe weather warnings and river levels.
Seqwater works with emergency services, as well as state and local government, to inform and update the community about flood events. During a flood event, Seqwater activates its Flood Operations Centre where dam engineers and staff monitor conditions 24/7.
The best source of information during a flood event is your local council.
You can stay aware of any releases from Seqwater dams by signing up to our free dam notification service or downloading the Seqwater app.
Flood mitigation in the urban areas downstream of North Pine Dam can be affected by other flood water entering the catchment from places such as Sideling Creek (Lake Kurwongbah), the South Pine River, other smaller creeks and surrounding urban areas.
Moreton Bay Regional Council provides information about potential flood risks in the Moreton Bay Region including mapping and tips on how to be prepared. To find out about the impacts of localised flooding or flash flooding in your area, you should contact Moreton Bay Regional Council or visit moretonbay.qld.gov.au.
Moreton Bay Regional Council have a Flood Check Property Report available to all residents. You can access this service here.
Flood mitigation in the areas downstream of Somerset and Wivenhoe dams can also be affected by other flood water entering the catchment from places such as the Bremer River, Lockyer Creek and other smaller creeks and tributaries in surrounding urban areas.
Ipswich City Council, Brisbane City Council and Somerset Regional Council provide information about potential flood risks including mapping and tips on how to be prepared. To find out about the impacts of localised flooding or flash flooding in your area, you should contact your local council.