Ungated dams 

An un-gated 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 un-gated dams help mitigate flooding to some extent. The peak outflow from an un-gated 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. 

To receive updates on un-gated dams, subscribe here. 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 un-gated 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. 

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.

Gated dams 

Wivenhoe and Somerset dams have floodwater storage compartments, which enable the dams to temporarily hold back water on top of the drinking water supplies stored in these dams. For example, Wivenhoe dam utilises approximately 1/3 of storage for water supply, and the remaining 2/3 is set aside for the flood storage compartment to provide flood mitigation and protect the safety of the dam during extreme floods. 

Once a gated dam reaches its FSL, Seqwater controls the release of water using specially designed gates, which enables targeted mitigation of flood impacts. Seqwater also operate the dams with the aim that released water does not combine with downstream floodwaters to worsen flooding. This can be difficult as water released from gated dams can take more than 24 hours to reach urban areas, which receive flood water from a variety of sources in a catchment (not just the gated dam). 

The operation of the gates is determined by operating rules in the approved Manual of Operational Procedures for Flood Mitigation at Wivenhoe, Somerset and North Pine dams. These manuals are publicly available on the Seqwater website. 

Seqwater empty the dam of floodwater after the flood has peaked to return it the normal full supply level, so that the flood storage compartment remains available to manage inflows if another flood occurs within a short time period. 

A controlled release of water from a gated dam will not necessarily result in downstream flooding. 

Seqwater has a specialised Flood Operations Centre team, who manage FSL releases on gated dams.  

You can subscribe to notifications for gated dam updates here. You will then receive a notification to your preferred channel (email, SMS, recorded message to landline or the Seqwater mobile app). 

If you choose to receive information about gated dams, the notifications will tell you about the potential and likelihood of gated dam operations, the timing of water releases from each selected dam and the impacts on selected bridges and crossings downstream of the dams. You will also receive notifications when gated dam releases cease.