Residents are sandbagging and authorities are considering evacuation orders as floodwaters slowly rise in the New South Wales Central West.
The Bureau of Meteorology (BOM) said floodwaters in the Lachlan River were travelling slower than anticipated.
The river is now expected to peak at about 10.65 metres in Forbes on Wednesday, bringing major flooding similar to that in September 2016.
Major flooding is occurring upstream at Nanami where the river was higher than during the 2016 flood.
The peak is expected there on Tuesday morning.
"We are now very concerned about how that will impact Forbes," the BOM's Justin Robinson said.
The State Emergency Service (SES) has received 100 calls for assistance in Forbes, mainly relating to sandbags.
An evacuation warning for Forbes was issued last night to give residents the heads-up on the potential decision.
Initially, 30 to 35 residents could be asked to evacuate.
SES Chief Superintendent Greg Swindells said that could be upgraded to an evacuation order for as many as 800 properties as soon as this afternoon.
Dozens of roads, including important transport links like most of the Lachlan Valley Way between Forbes and Cowra, are closed.
Properties anticipated to be in danger are those south of Bathurst street, east of Ooma and Ferry streets, between Lake Forbes and Ooma Street, in parts of North Forbes and the CBD, north-east of the Forbes Railway, north of the Newell Highway and in West Forbes, west of Wambat Street.
The SES has doorknocked residents expected to be affected by the initial peak and will expand that to other homes if the river continues to rise.
Forbes, with its normally picturesque riverside views, is no stranger to floods.
The SES has warned the water could reach the height of the devastating September 2016 flood, which caused millions of dollars of damage to farmland and crops around the shire.
Forbes Mayor Phyllis Miller said she did not expect to to be as bad as 2016 because the region had not experienced overland flooding at the same time.
"I think we will be a little bit better this time," she said.
"The biggest problem is the damage it is doing to the farming crops and the isolation that happens west of Forbes once the water gets through."
Impact hard to predict
Resident Leo Pietsch thought it was nothing to be overly worried about.
His son was helping him sandbag his property, which overlooks Lake Forbes, the lagoon in the town.
He said he expected the garden would "be getting a good watering".
Mr Pietsch, 92, recalled large floods in the 1950s, which saw cattle and furniture floating down the swollen river.
"I just hope it's not a major flood," he said.
Mr Griffiths said it was hard to predict how the water would impact the town.
"Historically, Forbes has always had different levels of flooding and different phenomena when it comes to floodwater," Mr Griffiths said.
"In 2012 floodwater moved through the town, in 2016 it didn't move through the town ? so exactly what the water does is kind of like, flip a coin."
Dam influencing flooding
The flood is being intensified by the release of thousands of megalitres from the Wyangala Dam upstream and the swollen Lachlan tributary, the Belubula River.
Overnight, releases from the Wyangala Dam, which was at 105 per cent full, were scaled back from 80 to 50 gigalitres a day.
While the flooding has been exacerbated by the dam, Mr Griffiths said the landscape was now a bigger factor.
"The variables that will change the behaviour of the water is the height of crops, grasses and the saturated soil conditions around the plains," he said.
"They will be influencing what we've got coming through today."
Water NSW spokesman Tony Webber said inflows to the dam had been significant and made a tough situation harder.
"What made this more challenging was the dam was already full ? we pulled it down where we could," Mr Webber said.
"But nothing was going to capture the inflows that we had peaking at something like 10 per cent of the dam's entire volume in one day at one point."
Mr Webber said the authority would now work to lower the dam back to 100 per cent capacity by mid-week to provide some space for the next round of rainfall.
"The challenge is now ? and speaking to the [BOM] ? there's a possibility of a rain event next weekend," he said.
The SES said the Lachlan peaked at Cowra overnight at 12.64 metres.
Preparation for the water is in full swing, with the local football club helping the sandbagging efforts.
© ABC 2021
13:12 AEDT Goondiwindi's 65-year-old levee has once again saved homes from major flooding, but the town is now surrounded by water and there are fears some rural communities could cut off for days, if not weeks.