Water authorities are preparing for the potential of a polluted Katherine water supply as a result of the forecast return of a better wet season.
Even harsher water restrictions may be needed if a big flush hits the river so guaranteed safe drinking water can be supplied to residents.
Each year, after heavy rainfall, the river can be inundated with sediment and organic matter that has accumulated within the catchment during the dry season.
Most Katherine residents would have seen this over the years with the frothing, highly turbid, muddy water rushing downstream.
Senior manager Operations and Maintenance, Peter Hopkins says this water can be extremely murky and sometimes isn't able to be treated adequately to the required drinking water standards.
"Often, this water passes through the Donkey Camp weir pool very quickly thanks to follow up rain.
"Power and Water is able to manage this appropriately by monitoring the weather and taking the main surface water treatment plant offline for a brief time, checking the water and restoring operations as soon as the dirty water has passed," Mr Hopkins said.
Katherine's water supply is predominantly sourced from the Katherine River - 90 per cent, the other 10 per cent is taking from two bores and treated for PFAS contamination.
This year, after subsequent wet seasons without good rain and the prediction of La Nina conditions, there is a greater likelihood of organic matter that has built up in the catchment being washed into the river, Power and Water believe.
This run-off has the potential to result in poor river water, which would impact the water supply.
If there is a prolonged period between rain events, the water could be compromised for a longer than usual period of time, which most years is just a few hours.
Historically, the duration of these events have been relatively short, however some were quite severe.
In 1987, the river experienced an initial rainfall and run-off event on October 31 with 65.2 mm recorded at Tindal Airport.
It wasn't until November 17 that subsequent rains, some 100 mm, flushed the weir pool of poor quality water.
In this instance, Katherine's water supply was uninterrupted thanks to the groundwater that supplied the town for the duration of the event.
Today we know the bores are contaminated with PFAS as a result of the use of fire fighting foams at the Tindal RAAF Base, much higher than the recommended Australian safety standards.
Only a limited amount of the bore water can be treated by an emergency treatment plant provided by the Department of Defence which means Katherine could be forced onto even harsher water restrictions than it is today.
The larger treatment plant is being built now but is unable to help this year.
Power and Water is planning for such an event through its emergency management and business continuity function.
"The provision of safe drinking water to our customers is our number one priority and as part of this, we factor in many water supply and environmental risks every day, and we plan accordingly.
"In this case, the small pilot treatment plant can continue to produce the maximum 1 million litres per day of treated groundwater, which supplements the main river water supply, and our tanks hold some stored water that would only last a short period of time.
"In these circumstances, our ability to adequately supply sufficient potable water for the town will be constrained and will mean that short term higher level water restrictions would be necessary to preserve the water supply for as long as possible.
"While we hope this situation doesn't occur, we do need to be prepared and we need Katherine residents and businesses to be prepared as well for this potential risk to the water supply.
Power and Water will be closely monitoring the Bureau of Meteorology weather forecasts and will advise residents very quickly if there is an emergency situation.
"It is important that everyone is ready to respond if the need arises.
"We welcome the much needed rain, however we need to be prepared for everything it may bring with it."
More information about Katherine's water supply is available at: https://www.powerwater.com.au/about/what-we-do/water-supply/katherine-water-supply
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