A quick update for our community, given the weather and flood risk:

While the Hawkesbury Post is closed, we felt it was important to share this update from WaterNSW tonight. With more than 100mm of rain falling across the region in the past 24 hours and localised flooding already affecting low-lying areas, the situation is one to watch closely - especially with the ground already saturated across the floodplain.

Here is the update from WaterNSW at 7pm tonight (22nd May 2025).

WaterNSW is advising the public that based on current rainfall forecasts by the Bureau of Meteorology, there is a possibility Warragamba Dam may fill and spill in coming days.

The Warragamba Dam storage level is currently at 96% of capacity.

The timing and peak rates of a possible spill will depend on the exact timing and location of the rainfall received. The catchment area upstream of Warragamba Dam is over 9,000 square kilometres in area and inflows can be received from a number of different rivers.

The Bureau is forecasting periods of intense rain overnight in the catchment, which could see the dam fill and begin spilling as early as tomorrow (Friday) morning under the Bureau's less likely (25%) scenario.

Under the more likely forecast (50% chance) scenario, the dam would begin to spill later Friday or into Saturday morning.

It is likely that a number of other smaller Greater Sydney dams may experience minor spills in coming days, including Nepean, Cataract and Woronora.

The community should continue to monitor advice on river levels and any flood warnings from the Bureau of Meteorology.

For the latest weather and flood information, check the Bureau website – http://www.bom.gov.au/

For emergency information, contact the NSW SES – 132 500 or ses.nsw.gov.au (https://www.waternsw.com.au/community-news/media-releases/2025/www.ses.nsw.gov.au)

Background

Spills from Warragamba Dam are not uncommon, occurring more than 50 times since 1960. In 2024 the dam has spilled on 5 April (peak spill rate 220GL/day), 6 May (peak spill rate 30GL/day), and 7 June (peak spill rate 240GL/day),

The Warragamba Dam  (https://www.waternsw.com.au/nsw-dams/greater-sydney-dams/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.

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

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, (https://www.waternsw.com.au/documents/publications/general-publications/strategies,-plans-and-policies/WaterNSW_WarragambaDamFloodFactSheet_Nov-2023.pdf) 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