Seqwater reduced the Full Supply Level for North Pine Dam following further assessments of the potential safety risks associated with rare and extreme flood events.

Lowering the full supply level for the dam until an upgrade is completed is a precautionary measure, which will help reduce the safety risks associated with 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 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 water that was stored in the dam.

Lowering the Full Supply Level of dams is an accepted and long-established way of reducing the safety risks associated with rare and extreme flood events. The reduced Full Supply Level assists to reduce the peak lake level in the dam for potential flood events in the future.

Dams which have previously been lowered as part of our Dam Improvement Program include Sideling Creek, Cooloolabin and Leslie Harrison dams.

North Pine Dam is in good structural condition and continues to safely operate. The existing dam can withstand rare and extreme floods including possible inflows much greater than the January 2011 flood. However, the largest possible flood we can estimate would exceed the capacity of the dam.

With a large population living downstream of North Pine Dam, the risk to downstream communities means the dam needs greater capacity to withstand the Probable Maximum Flood (PMF).

The planned upgrade will enable the dam to continue to operate safely and improve the capacity of the dam to withstand rare and extreme floods in the future.

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

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

With a large population living downstream of North Pine Dam, the risk to downstream communities means the dam needs greater capacity to withstand the Probable Maximum Flood (PMF). 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 strengthening. 

We are in the early planning stages and no options have been finalised or decided at this time. Seqwater will continue to conduct assessments and investigations to develop and review feasible options.

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

The reduced Full Supply Level (FSL) for North Pine Dam is 36.0 metres Australian Height Datum (AHD). This level is equivalent to about 68% of the dam's original water storage capacity or Full Supply Volume (FSV). The dam was below 60% in December 2019 when the reduced FSL was enacted so there was no need to release water at the time.

The reduced Full Supply Level for North Pine Dam is not expected to impact the long-term water supply security for South East Queensland. This will be reviewed periodically until the dam is upgraded to make sure there are no negative impacts to water supply and long-term water security.

Reducing the Full Supply Level for the dam until an upgrade is completed will help reduce the 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 flood houses. It is possible releases may occur more frequently in minor flow events (much smaller than those that flood houses), which may result in temporary closures to roads in low-lying areas downstream.

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

Planning for the North Pine Dam upgrade is underway. Seqwater will provide further information about the timing and impacts as planning progresses.