Seqwater enacted a Reduced Full Supply Level for North Pine Dam following further assessment of potential safety risks for very extreme flood events.

Lowering the full supply level for the dam until an upgrade is completed is a precautionary measure which will help reduce safety risks associated for rare and extreme flood events, beyond which the dam has experienced to date.

North Pine Dam is in good structural condition and continues to safely operate.

Due to the current dry conditions and low lake level at the time the reduced full supply level was enacted in December 2019 there was no requirement to release any of the stored water that is conserved for drinking water supply.

Lowering the storage level (full supply level) of dams is an accepted and long-established way of reducing safety risks associated with rare and extreme flood events. The lower full supply level assists to reduce the peak lake level in the dam for potential future flood events. 

Several other dams have previously been lowered as part of our Dam Improvement Program including Sideling Creek, Cooloolabin and Leslie Harrison dams, all of which have now been upgraded.

North Pine Dam is in good structural condition and continues to safely operate. The dam is currently able to manage large and extreme floods including events greater than the 2011 flood. 

The planned upgrade is to enable the dam to continue to operate safely in the future and improve the capacity of the dam to manage rare and very extreme flood events into the future.

North Pine Dam is one of a number of dams across South East Queensland identified as requiring an upgrade as part of Seqwater’s Dam Improvement Program.  Other dams across South East Queensland currently scheduled for future upgrades include Lake Macdonald and Ewen Maddock dams on the Sunshine Coast as well as Wivenhoe and Somerset dams.

The upgrade of the dam will increase the dam's capacity to withstand very extreme floods.

With a large population living downstream of the dam, the risk to downstream communities means North Pine Dam needs greater capacity to withstand the most extreme floods. The potential options to increase the capacity of the dam for extreme floods may require a selection, or combination of, spillway modification, dam raising, and dam strengthening. 

No options have been finalised or decided at this time and further work is required. Seqwater is undertaking assessments and investigations to develop and review feasible options for further consideration. 

North Pine Dam is in good structural condition and continues to safely operate. With the reduced full supply level, it is estimated that North Pine Dam can withstand a flood approximately two times larger than the rare extreme flood that occurred in January 2011.

Data collected from significant rainfall and flood events since the dam was designed and constructed, and the developments in flood estimation methods, have improved the ability to estimate the magnitude of potential rare and extreme flood events.

The probability of a flood sufficient to cause dam failure is low. Based on National and State guidelines for dams, Seqwater considers the very low probability of dam failure to be an unacceptable risk due to the potential consequences for a large population downstream of the dam.

The planned upgrade will aim to provide capacity for very extreme floods up to three times larger than the January 2011 flood. 

The Reduced Full Supply Level for North Pine Dam is 36 metres AHD which is a storage volume of approximately 145,500 ML and represents 68 per cent of the original water supply storage capacity. The lake level in January 2020 was below 60 per cent capacity and as such there was no immediate requirement to release water.

The reduced dam level is not expected to impact on the long-term water supply security for SEQ. 

Planning for the North Pine Dam upgrade is underway. Seqwater will provide further advice to the community on the timing and details of improvement work as the project progresses.

Lowering the full supply level for the dam until an upgrade is completed will help reduce safety risks associated with rare and extreme flood events, beyond which the dam has experienced to date (i.e. floods considerably larger than the 2011 flood).

The flood operations for North Pine Dam with the reduced full supply level are not expected to impact downstream flood levels for large and rare floods that can impact houses. 

Any future flood releases will be managed in accordance with the 2019 Flood Mitigation Manual for North Pine Dam.