Warragamba Dam spill update

At 11am today, the spill rate from Warragamba Dam was 19 Gigalitres (GL)/day, and continues to decrease, down from a peak of around 225 GL/day late Saturday morning.

The total volume of the spill from Warragamba Dam has been 260 GL, as at 7am today, which is equivalent to approximately half the volume of Sydney Harbour.

Other Sydney dams spilling as at 11am today are Tallowa, Nepean and Woronora dams and the Blue Mountains storages, except Upper and Middle Cascades.

• Woronora Dam spilling at a rate of 0.2 GL/day.
• Nepean Dam spilling at 1.5 GL/day and decreasing.
• Tallowa Dam spilling at 22 GL/day and decreasing.

Warragamba Dam Visitor Centre and grounds reopened to the public today, following a public safety review. Some areas of the grounds remain closed to public access for operational purposes, please follow signage and staff instructions.

WaterNSW continues to work with the Bureau of Meteorology and SES to monitor the weather event.

Follow the Bureau of Meteorology for flood advice and warnings (http://www.bom.gov.au/), and the NSW State Emergency Service as the lead agency for emergency response (https://www.ses.nsw.gov.au/)

Background

Warragamba Dam reached full capacity and started spilling at 5.45am Saturday 6 April following heavy rainfall overnight Friday at the upper end of Bureau forecasts.

The Warragamba catchment received an average of 100 mm over 6 hours from midnight Friday to 6am Saturday, and up to 200mm over 24 hours in some areas. Rainfall overnight Friday in the sub-catchment, close to the dam wall, was about 130mm.

The Warragamba Dam spill peaked at around 225 GL/day late Saturday morning.

The Warragamba Dam catchment area covers 9000 sq/km and stretches across much of the Blue Mountains to Goulburn in the south, and to Lithgow in the north-west.

As manager of the state’s major supply dams, WaterNSW operates Warragamba Dam in line with NSW Government operating rules and protocols.

These rules do not permit water being released to reduce the storage level ahead of predicted rainfall for flood mitigation purposes. This reflects the dam’s critical role in supplying 80% of Sydney’s drinking water.

Background – dam operations

During times of flood, the gates on Warragamba Dam automatically open and close based on water levels.

After rainfall has occurred and when the water rises above full supply level, the gates progressively open in sequence. As water levels begin to drop, the gates will progressively close in reverse sequence.

The gates can be manually operated to reduce the level of water in the lake for operational or maintenance reasons only outside of flood operations.

The dam gates are designed to safely pass extreme floods, much larger than the worst flood on record for the Hawkesbury-Nepean Valley.