Parts of Sydney’s north and west could face flooding with the latest big rain event predicted to cause the city’s main dam to spill.
WaterNSW is forecasting Warragamba dam will reach full capacity and begin overflowing into the Hawkesbury-Nepean River downstream from Friday evening.
At the upper end of predictions, the dam’s catchment area will receive as much as 100mm of rain from the current event. If the forecasts are correct, Warragamba’s spill could reach a peak rate of as much as 100 gigalitres a day by Saturday morning, WaterNSW’s modelling shows.
Such a flow, though, would only be one-fifth of the rate during March’s extensive flooding in the region, a WaterNSW spokesperson said.
“Downstream impacts are likely and will be determined by the spill volume combined with downstream tributary flows,” the official said.
Waragamba was at about 99% full on Thursday with the city’s overall reservoir network sitting at 95.5% full.
On Friday morning, the Bureau of Meteorology issued a weather alert, advising motorist to “take extreme care”.
“Flooded roads and reduced visibility in heavy rain will make driving conditions dangerous during Friday in all suburbs,” the warning said.
The Bureau earlier this week declared a La Nina event is under way in the Pacific. The weather pattern, combined with other influences, typically means eastern Australia will have above average rainfall for the coming summer. Insurers are among those gearing up increased damage bills from floods and a more active cyclone season than usual.
The bureau’s latest seasonal forecast, issued on Thursday, also pointed to a cooler than average summer for eastern parts of the summer at least for daytime temperatures.