Bushfires trigger fears ash, debris will wash into Sydney’s water supply in downpour

Sydney’s main water reservoir Warragamba Dam has been forced to install nets to stop bushfire debris flowing into the city’s drinking supply.

Warragamba Dam, supplies five million Sydneysiders with water. Source: AAP

While rain expected to hit eastern New South Wales this week will provide some reprieve to firefighters, there are concerns it could wash ash and bushfire debris into Sydney’s main water supply, which more than five million people rely on. 

Authorities have raised concerns about the more than 300,000 hectares of burnt land that surround Warragamba Dam, fearing debris could be washed into Sydney’s main reservoir. 

Warragamba Dam is surrounded by about 300,000 hectares of burnt land. Source: SBS News

Water NSW system operations manager Adrian Langdon said nets have been installed to catch fallen trees and protect the city’s drinking water.

“We have a number of Water Quality experts that are consistently monitoring where water comes into the storage and at what depth,” he said. 

The Bureau of Meteorology is predicting up to 50mm of rain for NSW later this week. 

“It is great to see any rainfall on these fire grounds but unfortunately it does make it a bit more hazardous in those areas, because of all the burnt area there is a risk of localized flash flooding just due to the fact there is not much vegetation around those areas,” forecaster Grace Legge said. 

Firefighters battle bushfires in northern NSW. There's fears ash from the fires will contaminate drinking water. Source: AAP

There are fears torrents of water will sweep ash and debris into the catchment, but hydrologists, such as Professor Ashish Sharma believe the water should still be drinkable. 

Water is much needed at Warragamba dam - levels are down to 43 per cent, which is the lowest level since 2004, during the millennium drought. 

Damn water levels are down to 43 per cent, which is the lowest level since 2004, during the millennium drought. Source: AAP

The smaller pool of water means the effect of the contaminants is much greater. 

Authorities are worried algal blooms could form in the next few months if the fire ground receives the type of downpours needed to put out the blazes.  

“A lot of what we are concerned about after these bushfires, especially if we get heavy downpours, a lot of that sediment material from the areas, will be washed into the storage and with that will come nutrients,” Mr Langdon said.