New South Wales rain could cause more problems than it solves

Rain is falling across bushfire stricken New South Wales, bringing relief to fire crews battling the catastrophic blazes - but there are fears the weather could cause more problems than it solves.

Landslides, flash flooding, tree fall and water contamination are potential consequences from the 30 to 80 millimetres of rain forecast to hit some areas over the weekend. 

Thunderstorms are also forecast for areas of NSW.

"Heavy rainfall and gusty thunderstorms bring the potential for flash flooding, particularly in the burnt-out areas of NSW and Victoria which are now vulnerable to landslips and trees coming down," Bureau of Meteorology meteorologist Sarah Scully told

The fire damaged landscape could cause flash flooding if hit by heavy rain. 

"In areas impacted by fires where vegetation has been destroyed, water from heavy rainfall can flow into riverbeds and we could see run off in areas we wouldn't normally, resulting in flash flooding," State Emergency Service assistant commissioner Paul Bailey told 

The rain also brings fears of water contamination.  

Almost the entire perimeter of the Warragamba Dam is surrounded by bushfires - the dam supplies more than five million people in Sydney with water. 

"Once you have a fire go through a drinking-water catchment, the ash that's left on the ground and the ground itself becomes more repelling of water," said university of NSW water expert Stuart Kahn.

 "So even small rainfall events, instead of soaking in, do tend to run off after a fire."

The run-off could then contaminate the water in the dam and with heavy drought causing the water levels to be their lowest since 2004, there is less chance for debris like ash and soil to be diluted.